June 2008
Consultation on Thames Water’s Draft
Strategic Proposals for Sludge Management
Thames Water Utilities Ltd Draft Strategic Proposals for Sludge Management
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EXECUTIVE SUMMARY
Background
Thames Water Utilities Ltd. (Thames Water) has developed high-level strategic proposals for
sludge management/disposal in our region for the 25 years to 2035. The decision to carry out
the strategy development was taken for the following reasons: (1) to provide a broad
framework for our specific investment proposals, particularly in the period 2010-2015 for the
periodic review of our charges in 2009, and (2) to review the appropriateness of our current
strategy (i.e. wherever possible recycle sludge to land) going forward, given the increasing
costs and regulatory/other constraints arising from this outlet.
Thames Water further decided to commission a voluntary, independent Strategic
Environmental Assessment (SEA) of our proposed long-term strategy, carried out by
consultants, Entec. This was to ensure that potential environmental, economic and social
impacts were properly understood and accounted for in all stages of the strategy
development. A key benefit of completing the SEA is that it involves formal stakeholder
consultation and we were keen to ensure that consultation was carried out concurrently with
the development of our proposed strategy. This approach was reviewed and approved by the
Executive Management Team of Thames Water.
In developing our proposals, the following objectives were adopted:
• To manage sludge so as not to endanger human health or harm the environment, by
ensuring that all regulatory and legislative controls are met;
• To establish long term, secure and sustainable outlets;
• To ensure that sludge is managed on behalf of customers in a cost-effective and
efficient manner, minimising the potential for impact from transport and odour;
• To have due regard to non-statutory Codes of Practice and industry guidance;
• To use the latest available information in formulating and implementing the strategy;
and
• To encourage stakeholder participation in the development of the strategy.
The strategic proposals cover all wastewater sludges produced at Thames Water sites and
consider predicted sludge production up to 2035, over a 10 year and 25 year horizon.
Current Strategy
In the Thames Water region the quantities of sludge produced have risen in recent years.
Similar increases are common to all regions in the UK and elsewhere in Europe, arising
mainly as a result of population increases and from more stringent levels of wastewater
treatment. The current sources and quantities of sludge produced are identified in greater
detail in Section 2 of the full strategy document.
Thames Water has always sought to adopt a variety of sustainable, beneficial and cost-
effective solutions to sludge management. The breakdown of outlets in 2006 is summarised in
Figure 1 below.
Thames Water Utilities Ltd Draft Strategic Proposals for Sludge Management
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Figure 1. Thames Water Outlets for Sewage Sludge 2006
1%
1%
Agriculture
36% Thermal destruction
with energy recovery
Compost
62%
Land Restoration
A number of issues are impacting on the land recycling outlet and these have, in part, driven
the need to review and revise the company-wide sludge strategy. The most notable
constraints (legislative and practical), which affect potential outlets, are considered more fully
in Section 3 of the strategy document but include:
• A gradual loss of available landbank in the region due to the reluctance of some parts
of the supply chain to accept products grown on land treated with sludge;
• The impact of the Nitrates Directive (Nitrate Vulnerable Zones Regulations) that has
reduced the volume of sludge able to be applied to most of the land in our region,
with resulting implications on the available land-bank; and
• In addition, in the future, it is expected that there will be increasing competition for the
available landbank from other fertilisers and organic resources such as composted
material from Local Authorities
ADAS/Grieve Strategic consultants were commissioned to complete a detailed review of
landbank availability to inform our proposals, a summary of which is provided in Section 4 of
the strategy document.
Strategic Proposals
General
The main conclusions of our strategic vision are to favour processes that (a) maximise energy
recovery and (b) minimise sludge volumes. Where there is suitable land bank availability,
utilising the recycling to land outlet remains the favoured option. To help protect this outlet we
anticipate investing in sludge treatment to improve product quality e.g. reduced odour and dry
solids. However, in predominately urban areas, the use of thermal destruction processes with
energy recovery may be more appropriate, thus avoiding the increased environmental impact
and costs of transporting the treated sludge to land.
Further, more detailed conclusions include:
• Processes that enable the efficient extraction of energy from sludge should be
adopted e.g. the installation of enhanced digestion or best practice thermal
destruction with energy recovery;
• The minimisation of vehicle movements on and off sites is also an important factor in
identifying our preferred options. Reducing lorry movements will provide benefits in
Thames Water Utilities Ltd Draft Strategic Proposals for Sludge Management
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minimising carbon footprint and environmental impacts through reducing fuel use and
reducing the potential for nuisance to our customers;
• Techniques that minimise sludge volumes will also be adopted and this will provide
benefits through:
a) Reducing vehicle movements if the sludge is being recycled to land;
b) Minimising the need to store sludge hence reducing the potential for odour
nuisance; and
• In addition, should we be required to find alternative disposal routes as recycling to
land becomes more restricted, then volumes for disposal will have to be minimised.
In the longer term, the benefits of carrying out co-digestion with other wastes (e.g. municipal
wastes) are attractive, particularly from the point of view of increasing energy production.
However, the potentially negative impacts of increased traffic movements required to
transport additional material on site and the increased operational complexity involved, would
need to be assessed on a site-by-site basis.
10-year strategic recommendations
• Convert our main sludge treatment centres, where the primary disposal route is
recycling to land, to enhanced digestion to increase energy production and minimise
solids.
• Our preliminary view of sites that are projected for the installation of enhanced
digestion in the next 10 years include Banbury, Basingstoke, Beddington, Bracknell,
Camberley, Crawley, Didcot, East Hyde (Luton), Hogsmill, Little Marlow, Oxford,
Riverside, Swindon and Witney. However, this selection will be reviewed on the basis
of more detailed site-specific assessments.
• Although recycling to land remains our favoured option, we plan to reduce our current
dependence on land bank in view of potential constraints on this outlet. This will be
achieved in the short to medium term through solids reduction as a result of
improvements to digestion. The impact this will have on our outlets is shown in Figure
2.
Figure 2. Predicted Outlets for Sewage Sludge - 10 year recommendations*
1%
1%
Agriculture
42%
Thermal destruction with
energy recovery
Bioenergy crops
56%
Land Restoration
* There is anticipated to be a relative increase in the proportion of sludge being treated by the thermal destruction process
due to increase in sludge production in East London based on population growth including urban regeneration. The reduction
in the proportion of sludge recycled to land is as a result of solids reduction through enhanced digestion
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• Provide additional sludge treatment capacity for our large East London treatment
works at Beckton and Crossness to deal with population growth and refurbishment of
existing assets. This is likely to be additional thermal destruction capacity with energy
recovery.
• Towards the end of the 10-year period (2017-2018) we will undertake a further
strategic review of the current capacity of treatment/outlets employed, location and
number of sludge centres in the Region, in order to inform the next 15-year
investment programme.
25-year strategic recommendations
• Our strategy for the period 2020-2035 will be informed by the outcome of an updated
strategic review and on assessment of landbank availability. However, it is anticipated
that our main proposals will be to:
o Maintain recycling to land where the landbank availability allows
o Introduce thermal destruction units with energy recovery at large urban sites
impacted by land-bank constraints
o Introduce co-digestion with municipal waste where capacity exists or it can be
deployed
Further development of sludge management proposals
It should, however, be stressed that these preferred treatment/outlet options should not be
regarded as site-specific recommendations. For developments at specific sites, the preferred
options would need to be reconsidered in order to check that the assumptions made here are
still valid.
In progressing favoured options, it is recognised that some of these may fall within the scope
of the Environmental Impact Assessment (EIA) Regulations. This high level assessment of
sub-regional areas will contribute to future assessments but further detailed work on a site-
specific basis may be required to take any preferred option forward.
CONTENTS
1. INTRODUCTION 8
1.1 THE ROLE OF THAMES WATER 8
1.2 WHAT IS SLUDGE? 8
1.3 PURPOSE OF THE STRATEGIC PROPOSALS 9
1.4 STRATEGIC OBJECTIVES & SCOPE 10
1.5 BUSINESS PLANNING 2005-2010 11
1.6 METHODOLOGY 11
1.7 INTEGRATION OF THE STRATEGIC PROPOSALS WITH THE SEA 12
2. SLUDGE PRODUCTION, TREATMENT CAPACITY & HEADROOM 14
2.1 SLUDGE LOADINGS 14
2.2 TREATMENT CAPACITIES 15
2.3 SLUDGE PRODUCTION 15
3. REGULATION OVERVIEW 19
3.1 INTRODUCTION 19
3.2 SUMMARY OF KEY LEGISLATION AND NON-STATUTORY GUIDANCE 19
3.3 REVIEW OF PLANS AND PROGRAMMES 22
4. TREATMENT OPTIONS, CURRENT & FUTURE OUTLETS FOR SLUDGE 23
4.1 AGRICULTURE 23
4.2 NON-AGRICULTURAL OUTLETS 28
4.3 ENERGY BASED OUTLETS 30
4.4 LANDFILL 32
5. OPTIONS ASSESSMENT METHODOLOGY 34
5.1 ASSESSMENT OF OPTIONS 34
5.2 SELECTION OF POTENTIAL TREATMENT/OUTLET OPTIONS – PHASE 1 34
5.3 SELECTION OF POTENTIAL TREATMENT/OUTLET OPTIONS – PHASE 2 35
5.4 FURTHER DEVELOPMENT OF SLUDGE MANAGEMENT PROPOSALS 37
6. DETAILED ASSESSMENT OF SUB-REGIONAL AREAS 38
6.1 INTEGRATED IMPLEMENTATION STRATEGY FOR EAST LONDON 38
6.2 EAST LONDON (THERMAL DESTRUCTION WITH ENERGY RECOVERY) 38
6.3 EAST LONDON (DIGESTION) 41
6.4 MOGDEN (WEST LONDON) 43
6.5 MAPLE LODGE 45
6.6 SOUTHERN REGION 47
6.7 WESTERN REGION (DIGESTION) 49
6.8 SOUTH-EAST REGION (LIME) 51
6.9 WESTERN REGION (LIME) 53
6.10 WEST LONDON 55
6.11 NORTH LONDON 57
6.12 NORTH EAST PROVINCES 59
7. MAIN CONCLUSIONS 61
8. GLOSSARY 63
APPENDICES
Thames Water Utilities Ltd Draft Strategic Proposals for Sludge Management
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1. INTRODUCTION
1.1 The Role of Thames Water
Thames Water Utilities Ltd (Thames Water) is the UK’s largest regulated water and
wastewater services company based on number of properties served. We have over 8 million
clean water and over 13.5 million sewerage customers, which is nearly a quarter of the total
population of England and Wales.
The region within which we provide regulated water and sewerage services occupies about
13,750 km2 and encompasses more than 9% of the total area of England and Wales. Thames
Water serves London with the consequent very high concentrations of traffic and economic
activity around the clock and our regulated business area reaches as far as Cirencester in the
west, Dartford in the east, Banbury in the north and Haslemere in the south.
We have a responsibility to supply clean, safe drinking water and to collect, treat and safely
return society’s wastewater to the environment. Thames Water is a privately owned business
with a duty to deliver all of its activities in compliance with relevant regulations and at a cost
that delivers value to our customers.
The supply of water to our customers involves abstracting water, treating it to strict drinking
water quality standards and then distributing it to customers’ premises through our network of
pipes or mains. Water is abstracted from surface sources, such as rivers or via reservoirs, or
from underground sources, via wells and boreholes. We use reservoirs to store untreated raw
water and underground service reservoirs for treated water, in order to maintain supply.
Providing sewerage services involves the collection, treatment and disposal of sewage.
Sewage is collected through our network of sewers and moved, by gravity or pumping, to
sewage treatment works where it is treated. The bulk of Thames region’s sewers are
combined surface water and foul water systems, taking wastewater from domestic, trade and
commercial customers as well as runoff from roads and roofs. Collection and treatment of
these wastewaters is regulated through the Urban Wastewater Treatment Directive and
associated Regulations.
The relevant legislative requirements have driven extensive investment in wastewater
treatment in recent years to ensure that appropriate treatment is delivered for the vast
majority of Thames Water region’s population, with the remainder being largely individual
settlements with private septic tank arrangements. In addition to this, trade inputs to the
wastewater system have been subject to increasingly stringent, rigidly enforced trade effluent
discharge consents in order to protect both the quality of the water discharged from
wastewater treatment works and to maintain the quality of the residual sludge.
1.2 What is sludge?
Sludge is produced as an unavoidable natural by-product of the processes used in both
wastewater treatment works and water treatment works, and comprises the solids removed
during the treatment processes.
1.2.1 Wastewater Treatment Works Sludge
Sludge from wastewater treatment works is primarily the organic by-product of the biological
treatment of wastewater, formed during the settlement of the breakdown products of the
treatment process. Wastewater treatment works operate biologically active processes and
sludge is the natural product of this process. It should be emphasised that sludge is not
untreated faecal matter, nor is it an industrial or hazardous waste. When appropriately treated
and managed it does not present a risk to the environment or human health and it can be
safely recycled to provide a benefit to society and the environment - sewage sludge resulting
from the treatment processes is predominately recycled to land, acting as a fertiliser or
incinerated and used for power generation.
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Thames Water treats around 2,8000 million litres of sewage per day from households,
businesses and industry in the Thames Water region. There are two basic forms of sludge
produced from the treatment of wastewater – raw primary sludge (consisting largely of faecal
material) and secondary sludge (a living ‘culture’ of organisms that help remove contaminants
from wastewater before it is returned to rivers or the sea).
Wastewater is initially collected as a liquid containing typically 0.1% dry solids (DS). It is then
dewatered to typically 3-5% DS for efficiency of treatment and transported to one of 37 sludge
treatment centres. Here the sludge is further treated via mechanical, biological or chemical
processes prior to recycling. Typically Thames Water will manage liquid sludge at between
1% and 5% DS and caked sludge at around 25% DS.
The sewage sludge is transformed into treated products (also known as biosolids) using a
number of treatment processes such as digestion, thickening, dewatering and lime
stabilisation. With respect to the recycling of sludge to agricultural land, two levels of sludge
treatment are defined:
• Conventional treated sludge - Processes that are capable of reducing the
microbiological content of sludge by 99%. The most common form of treatment is
anaerobic digestion, where sludge is digested at a temperature of around 35oC for
several days, followed by a further period of maturation.
• Enhanced treated sludge - Processes that are capable of virtually eliminating
(99.9999% removal) any pathogens that may be present in the sludge. Processes
such as thermal drying the sludge, lime treatment or pasteurisation followed by
digestion are capable of achieving this.
Whilst the drive to improve wastewater treatment standards has led to a significant
improvement in the quality of Thames region’s streams and rivers, this has in turn resulted in
wastewater treatment works producing more sludge. As this drive for water quality
improvement is continuing, in addition to anticipated increases in the population served, we
expect the quantity of sludge produced in the Thames region to continue to increase for the
foreseeable future.
1.2.2 Water Treatment Works Sludge
Water treatment produces much smaller volumes of sludge than wastewater treatment -
around 19,000 tonnes dry solids annually. With respect to water treatment processes,
coagulants are added to the untreated water that assist silt and other fine particles to settle
out. The resulting water treatment sludge is thickened to around 2-3% DS and then
dewatered to a 20-25% DS cake by pressing or centrifuging.
Much of this sludge is discharged to sewer and treated within a wastewater treatment works –
therefore, water treatment works sludge will not be considered separately but as part of the
Sludge Strategy for wastewater treatment sludge. Water treatment sludge is a very different
material to sewage sludge being largely inert, but containing useful trace elements and
carbon that are beneficial to soils, when the product is recycled to land.
1.3 Purpose of the Strategic Proposals
These strategic proposals (the sludge strategy) have been developed to address the current
and future requirements for the management of sludge in the Thames Water region. It will
form a framework within which Thames Water’s investment, operational and planning
decisions will be made and takes into account key contextual factors including:
• Changes in the quantity of sludge produced;
• Regulatory requirements and changes in the way that legislation controlling current
sludge outlets is implemented; and
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• The perception of sludge and the outlets employed by the public, regulatory
authorities and commercial organisations.
The strategy considers the quantities of sludge that will be produced by Thames Water as a
consequence of wastewater treatment processes up to a planning horizon of 2035. Thames
Water has responsibility for the management of the sludge produced in the course of these
wastewater operations. As such Thames Water seek to manage the production, treatment
and recycling of sludge by adopting sustainable, secure and cost effective methods and
outlets.
In developing an appropriate strategy, it must be recognised that sludge production is a direct
consequence of human activity. Equally the outlets selected for the recycling or disposal of
sludge can also have direct or indirect effects on society. It is therefore essential that the
public, regulatory authorities and other stakeholders have an understanding of the issues
affecting sludge management and can contribute to the approach to finding the most
appropriate solutions to the management of sludge in the Thames region.
In order to develop sustainable, secure and cost-effective solutions, this strategy aims to look
beyond immediate operational issues and will inform long-term strategic decisions and
investment plans. However, it must also be recognised that circumstances may continue to
change in future and therefore the strategy will be reviewed at appropriate intervals to ensure
its continued relevance.
1.4 Strategic Objectives & Scope
Thames Water treats large volumes of sludge on a daily, weekly, monthly, annual basis. The
volumes are such that only tried and tested technology can be used as the waste stream
cannot simply be switched off given its origin, or stored for a long periods of time given its
nature and volume.
Thames Water cannot expose itself to the risk of investing in unproven or innovative
technology, particularly in the short term, which may not work. Equally, Thames Water is
subject to financial regulation by Ofwat. The regulator sets the charges Thames Water may
make to its customers. This has regard to the capital investments Thames Water needs to
make but Ofwat will broadly favour proven affordable solutions. The consequence of the
nature and volume of the waste stream, and the financial regulation Thames Water is subject
to, means it can only invest in proven, robust and affordable treatment/outlet options.
In developing and implementing the strategy, Thames Water will adopt the following strategic
objectives:
• To manage sludge so as not to endanger human health or harm the environment, by
ensuring that all regulatory and legislative controls are met;
• To establish long term, secure and sustainable outlets;
• To ensure that sludge is managed on behalf of customers in a cost effective and
efficient manner, minimising the potential for impacts from transport and odour;
• To have due regard to non-statutory Codes of Practice and industry guidance;
• To use the latest available information in formulating and implementing the strategy;
and
• To encourage stakeholder participation in the development of the strategy.
The strategy covers all wastewater sludges produced at Thames Water sites and considers
sludge production up to 2035 over a 10 year and 25 year horizon. We further decided to
commission an independent, voluntary Strategic Environmental Assessment (SEA) of our
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long-term strategy (carried out by the consultants, Entec) which has been completed con-
currently, with the plan to ensure that the environmental, social and economic effects of the
strategy, and its alternatives, are properly evaluated. In addition, ADAS/Grieve Strategic were
commissioned to complete a detailed review of landbank availability (the area of agricultural
land available for recycling treated sewage sludge) to inform our strategic proposals. It is
important to note that this strategy does not attempt to develop site-specific recommendations
but rather to set out our broad preferred approaches at a sub-regional level.
1.5 Business Planning 2005-2010
Our investment programme for 2005-2010, agreed with our economic regulator Ofwat in
2004, includes no specific investment on sludge treatment assets other than that required to
maintain existing asset condition. We did, however, set out a broad strategy for sludge
management and this is set out below. The strategy set out here updates this. The Thames
Water Business Plan for 2005 – 2010 included the following main sludge related elements:
• Our strategy, in line with Government policy, is to focus on recycling to agricultural
land. Currently we recycle around 60% of sludge to agricultural land with the
remainder put to beneficial use through the generation of energy in our two Sludge
Powered Generators. We have put in a great deal of effort over the past 3-4 years
(alongside other companies and Water UK), to try to improve communication with our
stakeholders to ensure that the recycling outlet remains available to us. Indeed, the
focus of our 2000 - 2005 investment was to ensure that the agricultural land outlet
remained viable.
• We do not envisage a major change in our use of the recycling to land option in the
short term. However, it is clear that this outlet remains vulnerable to external
pressures and, in particular, to media scares and individual stakeholder concerns,
regardless of the good science and safety record underpinning the practice.
• Thus, whilst we remain confident in the viability of the agricultural outlet, we are
reviewing alternatives with a long-term aim of reducing our dependence on this outlet.
Few feasible alternatives are currently available. However, the most promising with
respect to the sustainability of the outlet and relative cost, is the thermal destruction
of sludge with energy recovery.
• We have had preliminary discussions on this subject with the major power producers
in the UK and they did express an interest. Whilst it is technically feasible to co-fire
sludge in a coal or oil fired power station, some issues remain to be resolved, notably
in the design of suitable sludge reception facilities and the control of emissions from
the plant.
• Discussions have indicated that it is unlikely to be cost effective to burn sludge in
existing power stations, largely because of the expense of retro-fitting necessary
emissions control equipment. Therefore we do not anticipate making extensive use of
this outlet in the short term (before 2010).
• Investment will be made at existing wastewater treatment works and sludge treatment
facilities to deal with additional quantities of sludge production. Where sludge
treatment already exists, the level of treatment currently installed will be maintained.
1.6 Methodology
The work undertaken to develop this Sludge Strategy has been structured to produce an
analysis of potential outlets for sludge up to the 2035 horizon. A range of outlets have been
identified and considered including:
a) Those that are currently used or have been used in the past;
b) Those that have been previously proposed as realistic outlets; and
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c) Those that are commonly used elsewhere in the UK and Europe.
For the purposes of developing this strategy, the range of potential outlets considered has
been restricted to those that have the potential to form principal outlets. Potential minority,
subsidiary or contingency outlets may then be considered in the context of the agreed overall
strategy. In order to assess the risks associated with the range of outlets considered, options
have been assessed with regard to their likelihood of providing a sustainable, secure, cost
effective outlet over the life of the strategy. The methodology by which this has been carried
out is described in more detail in Section 5.
The strategy has been developed by considering a number of regional areas, due to the
different circumstances across the Thames Water operational areas (e.g. in terms of sludge
production, population distribution, topography, agricultural practices and current operational
facilities). The defined regions and sludge production in each area are described in Section 2.
The strategy development for wastewater sludges comprised the following key activities:
• Data gathering and validation, including analysis of;
a) Existing and future sludge production
b) Sources and existing outlet routes for Thames Water
c) Constraints affecting potential outlets, including legislative, commercial,
environmental and practical constraints;
• Identification of areas to be adopted for strategy development;
• Identification of the range of outlet options to be considered;
• Internal workshops to agree options and the method of assessing
sustainability/security risk;
• Assessment of selected options, based on sustainability/security risk, using the
information regarding potential outlets;
• Presentation of the results of the assessment for each area and production of
strategy recommendations for each area; and
• A sensitivity analysis undertaken to double-check that the accepted methodological
approach is appropriate.
The methodology from the wastewater sludge treatment/outlet options assessment is detailed
in Section 5 and the results from the assessment are summarised in Section 6. Appendix 4
details the sensitivity analysis undertaken.
1.7 Integration of the Strategic Proposals with the SEA
The SEA process envisages early and continual, interaction between the preparation of the
strategy and the SEA, from the generation of objectives through to scoping, assessment of
impacts, consideration of alternatives and through to final reporting.
A technical specialist from Entec was involved in developing and commenting on the
methodological approach attached to the strategy from Summer 2007. Entec validated our
method of assessment and provided supporting specialist advice on the operational
performance of sludge management options not currently present within Thames Water's
operational area such as pyrolysis and gasification. This assisted in providing a comparative
strategic level assessment of the options within each sludge sub-region.
Entec also helped facilitate an external workshop on 30th November 2007 to explain the SEA
objectives, the scope of the study, and the intended approach to the assessment of impacts
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attached to the options within the draft strategy. This allowed the objectives of both
documents to be compared as detailed in section 3.2 of the SEA.
The SEA has benefited the strategic proposals in that the compilation of the SEA assessment
matrices (see Appendix C of the Entec SEA Environmental Report) has allowed the high level
environmental performance of the initial preferred options to be assessed across the eleven
sludge catchment areas. The scope of the SEA's objectives (see Section 3.2 of the SEA
Environmental Report) has achieved consistent consideration of all aspects of environmental
impacts, from biodiversity and landscape issues through to energy use & climate change. The
SEA matrices will also be helpful to Thames Water in assisting future decision making within
the life time of the Strategy and provide a point of reference to the development of specific
proposals at particular locations.
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2. SLUDGE PRODUCTION, TREATMENT CAPACITY & HEADROOM
Not all sludge is treated on the site of origin – a number of sites have been designated as
“sludge centres” which act as regional hubs treating both indigenous as well as imported
sludge from nearby satellite sites. Due to day-to-day operational constraints, it is possible that
sludge from satellite sites may be processed at a secondary location, sometimes through
alternative treatment technologies. However, by calculating sludge loads from a population
equivalent base for all sites, the net effect of this variation is zero. The location of our current
sludge centres is illustrated in Figure 3.
2.1 Sludge Loadings
Sludge loading is calculated using the per capita sludge figure of 80g sludge/head/day for
standard non-chemically assisted treatment. This value is then adjusted depending on
process type (Table 1).
Table 1. Sludge loading design parameters per capita
Type Total Primary SAS
g/head/day g/head/day g/head/day
Current Generic 80
Filters 73 73 0
Crude Sewage Activated Sludge 65 0 65
Settled Sewage Activated Sludge 80 48 32
Biological Nutrient Removal 80 45 35
Pre-Precipitation Filters 96 96 0
Simultaneous Precipitation Activated 92 48 44
Sludge
Simultaneous Crude Activated Sludge 78 0 78
Pre-Precipitation Activated Sludge 100 75 25
Wastewater sludge loading figures in Table 2 are listed per sludge centre and are the sum of
indigenous sludge and sludge imported from satellite sites. They are subdivided into the
following treatment types and display sludge production from 2006 with expected growth until
2035:
• Mesophillic Anaerobic Digestion;
• Lime treatment;
• Thermal destruction with energy recovery; and
• Composting.
The quantities listed in Table 2 are considered to be sufficiently accurate for the development
of the Sludge Strategy, but will be reviewed in more detail when considering future project
feasibility and implementation at specific sludge centres. The quantities detailed in Table 2
are derived from Thames Water’s Strategic Overview of Long-term Assets and Resources
(SOLAR) database of current and projected population equivalents. Data in the SOLAR
database comes from flow and load surveys carried out by Thames and Local Authority
Development Plans, which detail projected population growth per area. It includes population
equivalent data for trade effluent and cess loadings in addition to the residential and
commuter populations.
Future loadings until 2021 are based on Local Authority growth projections, taking into
consideration such variables as new development and housing density. Data beyond 2021
has been linearly extrapolated to provide best future estimates. No specific allowance has
been made for additional sludge arising from currently unknown changes in legislation,
treatment standards, customer behaviour or other factors, such as the impact of Local
Authority waste strategies.
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2.2 Treatment Capacities
Digestion capacities are calculated as ranges, which give a conservative capacity and a
“stressed” maximum available capacity to meet the required standards for the control of
pathogens and provide acceptable product quality. This range is generated from a model that
considers factors such as effective digester volumes; feed dry solids and hydraulic retention
times; volatile solids loading from proportions of primary and surplus activity sludge; amount
and type of secondary storage. It is clear from the figures that our current digestion capacity is
limited and plants are operating at or close to their maximum.
Lime treatment capacities are also expressed as a range. This is calculated on a known
throughput over a normal 8-hour working day and a 24-hour working day. Assumptions are
made on actual working hours based on “down times” associated with start up and shut down
times, to give a range based on 8 hrs to 18 hrs operation per day.
Sludge Powered Generator capacities are expressed as a range from a 24-hour 365-day
operation, to a more achievable level, which incorporates maintenance shutdowns.
2.3 Sludge Production
As a data check, the calculated sludge loading figures for 2006 were compared to the
measured annual sludge mass removed from each site. It is important to remember that
calculated sludge loading is a pre-treated annual mass and sludge hauled to land is a post-
treated annual mass. A total value for 2006 actual digested sludge hauled to farm is expected
to be between 45% and 60% of calculated pre-treated sludge mass. This takes into account
known variables:
• Expected destruction in digesters (35%);
• Consented solids in final effluent (calculated from known data); and
• An estimated +/- 16.6% combined error (+/- 15% sludge hauled to farm, +/- 5% per-
capita sludge loads and +/- 5% in SOLAR figures).
For lime treatment, the mass of sludge recycled should increase by approximately 5%
through lime addition. A total value for 2006 actual limed sludge hauled to farm is expected to
be between 95% and 110% of calculated pre-treated sludge mass. This takes into account
known variables:
• Consented solids loss in final effluent; and
• An estimated +/- 16.6% combined error (+/- 15% sludge hauled to farm and +/- 5%
per-capita sludge loads and +/- 5% in SOLAR figures).
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Table 2. Wastewater sludge loading figures per sludge centre*
Sludge Centre AMP4 Sludge
Conservative Loading
capacity (85% EDV tds/year
& 5% DS) Projected Sludge loads, tonnes dry solids per year Sludge to Land
TDS/year (tds/year) tds/year
2006 2011 2016 2021 2026 2031 2035 2006
Thames Valley
All sites capacities include AMP4 Upgrades
Mesophilic Anaerobic Digestion
Ascot 1,143 1,061 967 964 961 912 881 851 276
Aylesbury 7,804 5,273 5,552 5,866 6,157 6444 6762 7005 2640
Banbury 4,174 4,542 4,713 4,751 4,814 4877 4927 5020 1877
Basingstoke 5,567 5,768 5,957 6,112 6,257 6530 6757 6950 3432
Beddington 7,821 10,786 11,085 11,301 11,440 11549 11657 11882 4988
Bishops Stortford 3,171 2,399 2,844 2,906 2,970 3294 3517 3695 1909
Bracknell 4,158 3,697 3,683 3,820 3,971 4107 4225 4291 1562
Camberley 3,411 4,490 4,553 4,614 4,682 4749 4799 4858 2283
Chertsey (Cambi) 9,472 10,708 10,732 10,796 10,812 10818 10820 10876 4598
Cranleigh 886 505 498 494 493 493 491 487 142
Crawley 2,495 5,634 5,863 6,059 6,116 6534 6832 7070 1647
Deephams 26,515 27,148 27,493 27,730 28,122 28590 28885 29172 9028
Didcot 1,740 1,879 2,007 2,271 2,385 2495 2519 2724 1035
East Hyde (Luton) 3,463 4,711 4,839 5,144 5,364 5443 5506 5820 2428
Haslemere 591 468 467 464 460 459 458 456 109
Hogsmill 9,560 11,787 12,023 12,267 12,464 12586 12698 12929 4226
Maple Lodge 26,705 20,087 20,298 20,541 20,735 20802 20815 21103 9791
Mogden (Pre- 82,733 58,797 60,322 61,474 62,470 64447 66080 67386 22039
pasteurisation)
Oxford 6,335 8,559 8,904 8,999 9,117 9233 9316 9530 4644
Reading (Pre- 13,335 8,702 8,890 9,089 9,258 9422 9566 9738 3262
pasteurisation)
Rye Meads 22,604 16,927 17,843 18,627 19,361 20925 22198 23283 10514
Slough 12,103 11,140 11,360 11,437 11,500 11536 11548 11693 5710
Swindon (Acid 7,825 9,051 9,564 10,098 10,533 11103 11628 12075 6589
Phase Digestion)
Wargrave 4,895 3915 4,166 4,372 4,555 4611 4629 4877 1720
Woking 2,686 2563 2,557 2595 2639 2681 2714 2732 811
Others 3676
Subtotal Digestion 268,509 240597 247180 252792 257635 264641 270226 276501 110936
Lime 8 hr operating
capacity tds/year
Basingstoke 2417
Farnham 4,942 5,942 6,159 6,335 6,481 6768 7003 7201 5077
Guildford 4,530 6,892 6,946 7,006 7,070 7151 7221 7281 9219
Earlswood 3,594 4,207 4,266 4,382 4,482 4578 4610 4713 3847
Fleet 2,471 4,410 4,491 4,495 4,486 4578 4631 4675 1958
Newbury 4,118 3,643 3,771 3,862 3,950 4037 4111 4210 4484
Bicester 1,498 1,652 1,722 1,797 1,856 1914 1965 2029 1093
Wantage Batch 2,548 2,567 2,668 2,755 2824 2865 2960 2003
Witney 1,498 3,439 3,593 3,655 3,686 3717 3813 3881 2223
Subtotal Liming 22,652 32734 33514 34199 34767 35567 36220 36952 32321
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Composting Theoretical max
tds/year
Little Marlow 4,550 5,382 5,429 5,459 5,486 5638 5746 5833 2659
Sub total Composting 5382 5429 5459 5486 5638 5746 5833 2659
Sub Totals (Non-East London) 278712 286123 292449 297888 305845 312193 319286 145916
East London
Mesophilic Anaerobic Digestion
Long Reach 22,044 24,674 24,968 25,509 26,115 26689 27141 27553 9259
Thermal Design capacity if Total sludge
Destruction 100% operational throughput 2006
tds/year (tds/year)
Beckton 71,175 112,096 116,934 121,473 125,546 129146 134162 137710 49398
Crossness 38,325 56,940 57,487 59,382 61,243 62976 64313 65561 31733
Liming
Beckton Batch 3310
Crossness 29,200 16467
Sub total East 160,744 193,710 199,390 206,364 212,904 218,810 225,616 230,825 110,167
London
Waste Water Totals 472422 485512 498814 510792 524656 537808 550111 256083
tds/year
*The quantities listed above are considered to be sufficiently accurate for the development of the Sludge Strategy
and are a snapshot as of mid 2007. These will be reviewed in more detail when considering future project feasibility
and implementation at specific sludge centres.
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Figure 3. Thames Water Sludge Treatment Centres
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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3. REGULATION OVERVIEW
3.1 Introduction
The production, treatment and consequent recycling, reuse or disposal of sewage sludge is
controlled by a substantial amount of legislation. This legislation and non-statutory codes of
practice and guidance are summarised below. This strategy will only consider legislation
relevant for England, as the area of sludge production, consequent treatment and outlet is
only likely to be within areas controlled by English legislation.
It is possible for sewage sludge to be taken beyond the Thames Water region for
treatment/disposal and, in theory, this movement is only limited by the distance involved. The
legislation considered will impact sewage sludge at different stages of the process - the
production/primary treatment, the movement/intermediate treatment and the final
recycling/disposal process. All of these stages will be considered in this section.
3.2 Summary of key legislation and non-statutory guidance
Driver Impact on Sludge
Urban Waste Water Treatment
Due to practical implementation of the Directive, and the cessation
(England and Wales) Regulations 1994
of sea disposal, sewage sludge quantities requiring disposal have
(SI 1994 No. 2841) implementing the
increased due to the increased level of wastewater treatment and
Urban Waste Water Treatment Directive
tighter discharge consents.
(UWWTD) 91/271/EEC
This Directive forms the backbone of most of current legislation and
sets the framework for waste management and most significantly
defines the waste hierarchy as the hierarchy of all waste
Waste Framework Directive
management options. The Directive is currently being revised - the
75/442/EEC (as amended)
effect of this revision will be felt through most of the forthcoming UK
legislation.
These Regulations lay down the requirements for applying sewage
sludge to agricultural land and are supported by a Code of Practice,
which details all aspects of sludge recycling to land. The regulations
Sludge (Use in Agriculture) Regulations
set permissible limits for soil concentrations and rates of annual
1989 implementing the Sewage Sludge
additions of Potentially Toxic Elements (PTEs). The allowable limits
Directive 86/278/EC
for Zn, Cu and Ni in soils vary with the pH of the soil. There are no
restrictions on the concentrations of PTEs in sludge.
This voluntary agreement made between the UK water and sewage
operators and the British Retail Consortium came into force in 1998
(revised in 2001). The matrix requires strict microbiological controls
on the quality of Sludge and the correct procedures to be adopted
for its application to agricultural land used to grow food crops. The
provisions of the Matrix go beyond the requirements of the Sludge
The Safe Sludge Matrix 1998 (3rd
(Use in Agriculture) Regulations as they currently stand. It was
edition 2001)
originally envisaged that the Safe Sludge Matrix would be
incorporated into the Revised Sludge (Use In Agriculture)
Regulations and Code of Practice for Agricultural Use of Sewage
Sludge. These amendments have been delayed and are still not
embedded into the regulations.
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Driver Impact on Sludge
The Nitrates Directive aims to tackle pollution of waters caused by
nitrogen from agricultural sources. This limits application of nitrogen
(and hence the amount of sludge) able to be applied to land in
designated Nitrate Vulnerable Zones (NVZs). The Action
Programme establishes NVZs inside which organic manure and
The Nitrates Directive (91/676/EC) and
sludge applications are limited and also includes soil type and
The Action Programme for Nitrate
application date restrictions to reduce the risk of diffuse nitrate
Vulnerable Zones Regulations 1998
pollution of watercourses. The impact of this is the need to find more
land suitable for recycling sludge and the increased number of sites
designated as NVZ will effectively reduce the amount of land
available to spread sludge. Defra are currently consulting on
revisions to these regulations it is expected that these will come into
force during 2008.
These Regulations state that anyone who proposes to deposit,
recover or dispose of a controlled waste must hold a licence issued
by the Environment Agency. Thames Water has a responsibility,
under the ‘duty of care’, to ensure its wastes are only passed on to
companies that hold an appropriate waste management licence
(WML). There is a range of exemptions for activities with
Waste Management Licensing (WML)
environmental benefits, but certain conditions apply. Most
Regulations 1994 (as amended 2005)
importantly, sewage sludge being applied to land is exempt provided
it can be shown to demonstrate benefit to agricultural land or
ecological improvement. Further exemptions allow sludge to be
stored on site prior to agricultural land application, land reclamation
and forestry.
PPC applies an integrated approach to the regulation of certain
industrial activities. Emissions to air, water and land plus a range of
environmental effects are considered together. The EA set permit
conditions that include a wide range of energy, waste and raw
The Pollution Prevention and Control material efficiency measures. The permit also includes emission
(PPC) (England and Wales) limit values and emission monitoring requirements for pollutants
Regulations 2000 (as amended) likely to be emitted from the installation in significant quantities and
(implementing EU Directive 96/61/EC measures to prevent accidents and limit their environmental
and 2000/76/EC) consequences. Permits are required for facilities from which sludge
goes for disposal, or at which sludge is dried, gasified or burnt.
These regulations put in place permit conditions on such plants and
force onerous controls on these operators.
Impacts on all thermal processes for the thermal destruction of
wastewater sludge. The disposal of sewage sludge by incineration
Waste Incineration Directive (WID) or gasification/pyrolysis is required to meet the standards specified
2000/76/EC implemented by the Waste by the Waste Incineration Directive given in Annex I & V and
Incineration Regulations (S.I. 2002 No. emission limit values for discharges of wastewater from the cleaning
2980) of exhaust gases given in Annex IV. For co-incineration, fuel
substitution in power generating plant or cement manufacture the
emissions limits are given in Annex I & II.
These regulations came into force in April 2008 and introduce a
single environmental permitting and compliance regime to apply in
England and Wales. This regime streamlines and combines Waste
Management Licensing (WML) and Pollution Prevention and Control
(PPC) to create a single environmental permit with a common
Environmental Permitting (England &
approach to permit applications, maintenance, surrender and
Wales) Regulations 2007
enforcement. These regulations will follow the format of PPC
regulations but with a two-tiered approach. The WML permitted
process will be changed into a simplified PPC permit format,
although the PPC permit sites are not expected to change.
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Driver Impact on Sludge
It is an offence to create a statutory nuisance and under section
Part III of the Environment Protection 79(1)(d) of the EPA the definition of statutory nuisance includes: "
Act 1990 (EPA), The Noise and smoke, fumes or gases, dust, steam or smell emitted from premises
Statutory Nuisance Act 1993, and so as to be prejudicial to health or a nuisance”. Local Authority
Section 17 of the Environment Act 1995 Environmental Health Departments have the power to serve an
Abatement Notice on any person causing or likely to cause a
statutory nuisance.
The Code of Practice aims to provide a framework under the
statutory nuisance regime within which the appropriate regulators
and sewerage undertakers can operate, to minimise the likelihood
and impact of nuisance from odours. The code provides practical
advice and a framework for local authority Environmental Health
Code of Practice on Odour Nuisance Practitioners who enforce the statutory nuisance regime and sets
from Sewage Treatment Works 2006 out for the public what they can expect during an investigation of a
complaint of odour nuisance from sewage treatment works.
Sewage treatment works operators have the responsibility and
ability to put in place the measures to control or abate odour
problems from their plant.
Landfills are categorised into one of three groups; inert, non-
hazardous and hazardous. Waste is categorised into these groups
by using the European Waste Catalogue (EWC codes). Hazardous
and inert wastes must meet Waste Acceptance Criteria (WAC)
which specifies a series of leachable, inorganic and organic
parameters (these are maximum limits) in order to be accepted to
The Landfill Directive (99/31/EC) landfill. Each waste stream must undergo periodic checks to ensure
Landfill Regulations 2002 its compliance. As of October 2007, landfill sites are unable to
accept untreated waste with the aim to encourage the recovery of
waste and to reduce the impact of the waste. An increase in gate
fees, reduction in void space available in England, limitations on the
biodegradability of the sludge cake/pellets disposed of and the
prevention of liquid sludge disposal mean that the disposal of
sewage sludge to landfill should only be regarded as the final option.
The term "Hazardous Waste" refers to waste that has toxic or
dangerous properties. Hazardous waste is classified by its entry
found in the European Waste Catalogue 2002 (EWC). These
The Hazardous Waste Regulations regulations should not affect sewage sludge, as it is not classified as
2005 a hazardous waste. Although, this may affect dedicated processing
plants such as incineration or gasification/pyrolysis where the ash
may be classified as a hazardous waste dependent upon its
physical characteristics and composition.
Establishes national emission limits for releases of NOx, SO2, VOC
National Emissions Ceiling Directive
and NH3 from all sources and impacts most forms of sludge
(2001/81/EC)
treatment.
Directive 2001/77/EC on the promotion
of electricity produced from renewable
Promotes the generation and use of electricity from renewable
energy sources in the internal energy
sources.
market.
A Renewables Obligation Order is issued annually detailing the
precise level of the obligation for the coming year-long period of
obligation and the level of the buy-out price. This order provides a
market based system giving increased financial returns from the
The Renewables Obligation Order 2006
generation of electricity from renewable sources when there is less
(Statutory Instrument (SI) 2006 No.
renewable generating capacity than the obligation placed upon
1004)
companies licensed to supply electricity. The order allows for the
power generated from the co-firing of wastewater sludge with fossil
fuels to receive Renewable Obligation Certificates (ROCs) up to
31st March 2009 without the introduction of biomass as energy
crops.
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Driver Impact on Sludge
The climate change levy is a tax on the use of energy in industry,
The Climate Change Levy commerce and the public sector with additional support for energy
(General) Regulations 2001 and efficiency schemes and renewable sources of energy. The aim of
subsequent related legislation. the levy is to encourage users to improve energy efficiency and
reduce emissions of greenhouse gases.
SI 2001 No.1139 The Climate Change
Agreements (Energy-intensive This reduces the levy on electricity used on energy efficient
Installations) installations and which come from renewable sources.
Regulations 2001.
This directive essentially sets greenhouse gas emissions limits for
Directive 2003/87/EC establishing a
installations to meet the Kyoto agreement. Installation may be given
scheme for greenhouse gas emission
credits from performance better than specified limits, these credits
allowance trading within the Community
may be traded against poor performing installation.
There is a requirement to reduce carbon use/emissions through
implementation of the Climate Change Act, with an increasing
The Climate Change Bill (expected to requirement to manage/reduce carbon footprint and an increasing
receive royal assent in summer 2008) focus on GHG emissions other than CO2 i.e. N2O, CH4
The requirements of the Climate Change Act will be statutory.
3.3 Review of plans and programmes
The SEA Scoping Report (October 2007) and Appendix B of the SEA Environmental Report
identifies and reviews other relevant plans, programmes, policies and strategies that are
applicable to the Thames Water region. The review identifies the relationships between the
proposed strategy and these other documents i.e. how the strategy might be affected by the
published plans’ aims, objectives and/or targets or how the strategy could contribute to the
achievement of any environmental protection and sustainability objectives.
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4. TREATMENT OPTIONS, CURRENT & FUTURE OUTLETS FOR SLUDGE
As outlined in Section 1, Thames Water is considering a range of outlets for its wastewater
sludges. In this section, the current and future outlet options are reviewed, with a description
of the route, a summary of the current legislation and operating guidance affecting it and a
discussion of the potential impacts of regulatory changes and other stakeholder impacts. This
review is used in the assessment of the outlets for the wastewater sludges in the following
sections.
The following outlets are currently used for the recycling/disposal of the sludge produced at
Thames Water’s treatment plants.
Figure 4 - Summary of sludge make and outlets 2006
1%
1%
Agriculture
36% Thermal destruction
with energy recovery
Compost
62%
Land Restoration
4.1 Agriculture
Treated sewage sludge (commonly known as biosolids) has been safely utilised on
agricultural land for a substantial number of years and is recognised as the best practicable
environmental option in most circumstances by the EU and UK Government at the current
time, for dealing with this wastewater residual. Application of treated sewage sludge to
agricultural land provides wastewater operators with a flexible solution to sludge
management. Unlike incineration or other thermal destruction technologies, agricultural sites
can be changed or sourced relatively quickly in order to meet changing operational needs.
Liquid sludges are transported to the field recycling site by tanker and discharged into a buffer
tank from where they are pumped to the tractor via a hose (known as an umbilical) and
injected below the surface of the soil; storage at the sewage works is either in tanks or
lagoons. Cake sludges are stockpiled on the works before being transported to a field site by
a tipping vehicle where they are stored prior to application with a self-propelled spreader.
Sludge stored at a field site can remain there for up to 10 months.
Energy recovery from sludge is widely practiced in the water industry through the use of
Combined Heat and Power (CHP) plants in combination with anaerobic digestion. The
ultimate disposal route in this case is recycling to land, but the combination of digestion and
CHP both reduces the mass of sludge to be disposed of, and the subsequent number of
associated vehicle movements, while providing heat and power for the site thus reducing
fossil fuel usage. The high maintenance requirements of the CHP units mean that this
methodology is not feasible for smaller sites.
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4.1.1 Current Legislation
The main legislation applying to the use of wastewater sludge in agriculture is derived from
the Sewage Sludge Directive 86/278/EEC, incorporated into UK law by the Sludge (Use in
Agriculture) Regulations 1989 (SI 1989/1263) (as amended) and supported by the DEFRA
Code of Practice for Agricultural Use of Sewage Sludge. These regulations set certain limits
on the concentration of potentially toxic elements permissible in agricultural land, depending
upon the pH of the land, and on the addition rate of wastewater sludge in any 10-year period.
They also identify requirements for the testing of sludge and soil, and withdrawal periods for
the grazing of animals or harvesting of crops.
Historically there were concerns from some food producers and retailers that using sewage
sludge as a fertiliser may be linked to public health issues, despite there being no proven link.
These concerns were primarily driven by perception and the need to protect the
producers/retailers end markets (the consumer). This led to negotiations involving the UK
water industry, the British Retail Consortium (representing the major retailers), the
Government, the Environment Agency and ADAS, aimed at securing a sustainable route for
recycling sludge to agricultural land that was acceptable to the food industry, water industry,
regulators, farmers and growers. The negotiations resulted in the publication of the ‘Safe
Sludge Matrix’, which came into force on 31st December 1998. This voluntary code identifies
minimum acceptable levels of treatment to microbiological standards for sludge applied to
various crop types and application windows related to harvesting of the crop.
As an additional Quality Assurance measure, the UK water industry also adopted the Hazard
Analysis Critical Control Point (HACCP) methodology in the treatment and management of its
sludges. This approach involves the identification and close monitoring of Critical Control
Points (CCPs) throughout the treatment process to ensure that the required treatment
standard is met, rather than relying solely on the traditional final product testing quality
assurance methods.
Farmers within Nitrate Vulnerable Zones (NVZs) must also comply with the Action
Programme for Nitrate Vulnerable Zones Regulations, maintaining a Fertiliser and Manure
Plan, observing closed periods for fertiliser application and restricting the application of
nitrates. In these NVZs, restrictions are in place to limit the application or organic nitrogen to
250 tonnes/ha on any one field and the whole farm average to 170 tonnes/ha. Prior to
October 2006, Thames Water sludge was applied to land at a rate based on RB209 Fertiliser
recommendations for Agricultural and Horticultural Crops (Defra publication). Since the
auditing that is carried out on each farm examines the actual amount of organic nitrogen that
is applied to land, spread rates had to be changed in order to prevent farmers from
contravening the NVZ regulations and thus ensuring the land would continue to be available
for recycling.
4.1.2 Potential regulatory changes and their impact
Action Programme for Nitrate Vulnerable Zones
In 2007, Defra consulted on a revision to the Nitrate Vulnerable Zone Action Programme,
which implements the requirements of the Nitrates Directive. The changes are being driven
by the European Commission who are not satisfied that UK regulations implement the
requirements of the Directive.
The key change is that the ‘closed periods’ (when no nitrogen can be applied to land) will be
extended. These revisions will restrict the application of organic manures with high available
nitrogen to farmland to specific periods of the year - this includes liquid digested sewage
sludge. Any extension of the closed periods would impact on our liquid sludge (or biosolids)
recycling activities with the need for more storage facilities.
Defra have recently announced in their summary of consultation responses, that the revised
regulations will now come into force in mid-July 2008, with compliance required by mid-July
2010.
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Sewage Sludge Directive 86/278/EEC
Revision of the Sewage Sludge Directive 86/278/EEC has been on the agenda of the EC for
some time but there has been a lot of uncertainty over the timing. The Directive is likely to
introduce tighter metals limits for sludge and soil, and introduce new controls on organic
compounds and pathogens in sludge.
Common Agricultural Policy
The EU have three separate exercises in the pipeline that will effect the Common Agricultural
Policy (CAP), the first is the ‘Simplification Exercise’ which is a minor tidying up of legislation
and should hopefully simplify cross compliance rules. The second part of the exercise is the
‘Health Check’ and the third is the ‘Budget Review’.
The ‘Health Check’ will consider the operation of Pillar 1 of the CAP (Single Payment and
market support mechanisms) up to the end of 2012, with any changes being implemented
from 2009. The two changes that may affect some UK producers are the capping of aid
payments and an increased rate of EU compulsory modulation. Coupled with this is the likely
end of set-aside by 2012. The ‘Budget Review’ that is scheduled for 2008 – 2009, will look at
the whole spending priorities of the EU budget, not just agriculture, with any changes affecting
the 2013 – 2020 budget period. The following are some of the possible outcomes that may
impact the agricultural sector:
• A major shift of agricultural budget funds from Pillar 1 to Rural Development (Pillar 2);
• The single farm payment will still be in existence but at a greatly reduced level by
2020;
• Full decoupling from production will be in place across the whole of the UK; and
• Market support mechanisms are likely to be further reduced to safety net levels
(cereal & dairy).
It is difficult to estimate the net effect that changes to the CAP will have on the sludge strategy
therefore this area will be kept under review.
Waste Management Licensing Regulations
The Waste Management Licensing regulations are likely to be further reviewed in the short to
medium term as Defra are already in the informal consultation stage with respect to the
exemptions process. A formal consultation is planned in summer 2008, the aim of which is to
streamline and standardise the exemptions process; this may result in the Paragraph 8b
exemptions being brought into the charging structure that exists for other exemptions.
4.1.3 Outlet Constraints and Risks
Nutrient Restriction
In addition to the proposed changes to the Nitrate Vulnerable Zones Action Porgramme, the
Single Farm Payment (SFP) system, which was introduced as a replacement to the
production-based subsidy as part of the Common Agricultural Policy (CAP) review, has also
started to impact on phosphate additions to farmland.
In order to qualify for the SFP, the farmer has to enter into a stewardship scheme, which
requires them to adhere to codes of practice and other guidelines. Previously, farmers were
happy to accept sludge on a specific field every year as they valued the nitrogen and organic
matter more than the phosphates; this has led to the development of higher phosphate
indices on some fields. Now that farmers have to comply with all of the guidelines in order to
receive the SFP they are generally only willing to accept sludge onto any particular field in a
one in three year rotation, as each application of sludge will typically provide a three-year
maintenance dressing of phosphate. This has resulted in a requirement for additional land,
which has contributed to an increase in the required haulage distance. A consequence of this
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increase is that the average haulage distance for sludge from the sewage works to suitable
land has increased over the last few years. This has consequences with respect to increasing
cost and greater carbon and environmental impacts.
Safe Sludge Matrix and Producer Concerns
It was originally envisaged that the agreement and the Safe Sludge Matrix would be
incorporated into the Revised Sludge (Use In Agriculture) Regulations and Code of Practice
for Agricultural Use of Sewage Sludge during 2001. These amendments have been delayed
and are still not embedded into the regulations. The UK water industry has voluntarily
complied with the requirements of the revised regulations since January 2002.
Despite the introduction of the agreement and the water industry’s voluntary adoption of the
requirements prior to them becoming law, producer concerns and associated actions still
present the greatest risk to agricultural recycling. Some food producers, retailers and grain
merchants still have sludge exclusion clauses in their purchasing contracts and work
continues via Water UK to resolve these outstanding issues. It is estimated that within the
Thames Water region, the total capacity for accepting biosolids following the restrictions
applied, was estimated to be 446,000 ha. This represents a reduction from the original
capacity of just over 30%.
Odour
Odour complaints generated by sewage sludge vary depending on the source of the sludge,
the treatment method and the recycling location. With the increasing incursion of suburbia
into the countryside, more people are becoming aware that certain agricultural practices can
generate short-term odour problems, one of which is sludge recycling.
Planning stockpile and spreading locations and taking into account proximity to sensitive
receptors and prevalent wind directions can mitigate odour risk. However, with the population
growth in the South East and the other pressures on the farming community (single farm
payment, financial, regulation etc.) finding suitable sites is contributing to a gradual increase
in haulage distances and an associated rise in costs.
Vehicle Movements
During 2006, in excess of 44,000 vehicle movements (journey from STW to field site and
back) took place whilst carrying out recycling operations; this represents approx. 1,500,000
radial kilometres hauled. With increasing sludge volumes and longer haulage distances, the
number of vehicle movements and the carbon footprint of sludge recycling will both increase –
at it’s most extreme, this may have an impact on the viability of this outlet in some sub-
regions. Vehicle movements are also taken into account when planning a recycling operation
in order to avoid impinging on local communities. This can involve avoiding sites during
school run hours, having different in and out routes, or providing additional vehicles to
minimise the amount of time it takes to deliver the sludge to a site.
4.1.4 Agricultural Landbank Assessment
Over 60% of our current sludge production is currently recycled to agricultural land in the form
of treated sludge cake or liquid (also known as biosolids), thus an assessment of the
availability of suitable land going forward 25 years is an essential component of our strategy.
In general farmers are very willing to accept biosolids on their land as it provides a very good
source of nutrients and organic carbon at low cost. However, in recent years finding suitable
land has become more difficult due to restrictions placed on certain products grown on land
treated with biosolids by some sectors of the supply chain.
In addition, tightening regulations, in particular the implementation of the Nitrates Directive
and the establishment of Nitrate Vulnerable Zones (NVZs), has reduced the rate at which
biosolids can be applied to land in most parts of our region. This means that an increasing
area of land is required to manage the outlet.
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Whilst the UK Government, the European Commission, the Environment Agency and a
number of other organisations still regard recycling to land as best practicable environmental
option for treated sewage sludge, it is important that a critical assessment was made of the
viability of the outlet over the next 25 years. Thames Water therefore contracted ADAS and
Grieve Strategic to carry out a detailed assessment of landbank availability over this period. A
summary of their report is provided in Appendix 1. The assessment was made based on the
following methodology and additional factors:
• Analyse agricultural land areas and cropping patterns where biosolids are applied;
• Input data on landbank availability to the “ALOWANCE” (Agricultural Landbank,
Organic Waste A National Capacity Estimator) prototype data management tool and
crop exclusion clause limitations ;
• Determine the current available landbank for biosolids;
• Compare the available landbank against likely future production trends;
• Input scenario data on exclusion clauses, land use restrictions and competitive
materials (e.g. livestock manures);
• Provide an outlook for up to 25 years;
• Comment on the increased production of biofuels (e.g. bioethanol from
wheat/maize/sugar beet, biodiesel from oilseed rape) and likely impact on landbank
availability; and
• Comment on potential agricultural produce market volatilities (e.g. grain prices,
inorganic fertiliser costs) and the influence this may have on the demand for
biosolids.
The main conclusions of the landbank assessment carried out are as follows:
• In principle, there is sufficient land available for recycling biosolids within the Thames
region;
• However suitable land is becoming more difficult to secure as demonstrated by the
increased volume of biosolids migrated into and out of the region;
• There is a significant urban area within the Thames region and, in particular the east
and south east of the region is likely to become more constrained by the end of the
period;
• In general, parts of the west, south and north-east regions appear to be less
constrained and more able to accommodate the biosolids production; and
• The security of the landbank is critically dependant on the continuing support and
confidence of the farming community and product supply chain. Continued access to
arable land growing wheat and oil seed rape is crucial to the continued viability of the
outlet in the Thames region.
4.1.5 Agricultural Outlet – Conclusions
Despite the restrictions limiting application rates and on-farm storage, sludge is still valued by
farmers for the nutrients and the organic matter that it contains. Increasing oil prices and
diminishing phosphate supplies provide greater incentive for farmers to accept alternatives to
the main fertiliser options. There is also a growing need for farmers to put organic matter back
into soils that are becoming poorer due to many years of intense production. This will also
improve the soils water holding capacity and assist with improved yields.
Agricultural recycling of treated sludges will continue to play a key role in the overall disposal
strategy, however it is expected that this route will become more expensive as regulations
tighten and haulage costs increase, thus impacting on the feasibility of the outlet for some
sub-regions.
Reliance on agriculture as the primary disposal route also brings an element of risk to
Thames Water, as other disposal options cannot be implemented quickly if the land recycling
route were to be severely curtailed especially at short notice. Although this scenario is
considered unlikely, having more options available means that any fluctuations in any of the
proposed disposal routes can, to a certain extent, be balanced out by the others.
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In the short to medium term, it is unlikely that the primary legislation governing sludge
recycling to agriculture will change significantly (unless any research identifies a proven link to
an environmental issue), however further revisions to the Common Agricultural Policy (CAP)
and Single Farm Payment schemes are planned.
The biggest risk that still exists for agricultural recycling is public/market perception and
producer concerns. Although there are early signs that some of the producers may be
changing their stance on the use of crops grown on sludge treated land, this risk is one that
could have the most dramatic impact on sludge disposal, with the ability to have a significant
and rapid impact on agricultural recycling.
Whilst having a strong reliance on agricultural recycling complies with the best practicable
environmental option for sludge disposal in most instances, it means that there are no other
options available to Thames Water for the short to medium term disposal of sludge – if the
land recycling route were to be curtailed due to perception issues, Thames Water (and all
other water and sewerage companies) would be facing a severe problem.
Overall, agricultural recycling is expected to remain feasible in the longer term, but it will
become increasingly expensive as transport costs increase and land availability becomes
restricted due to nutrient loading or changes to the agricultural industry. Going forward there
will also be a knock-on effect from transporting the increasing volumes of sludge from our
large urban centers further from their point of origin. This may impact on the available
landbank for the predominately rural sites and hence reinforce the need to develop alternative
sustainable outlets in order to increase business flexibility.
4.2 Non-Agricultural Outlets
There are other uses of land where the sludge can be applied beneficially to complete nutrient
cycles and conserve organic matter. The following section lists the more significant of these.
4.2.1 Forestry & Land Restoration
There are many examples where sludge has been the key to successful restoration of
disturbed and derelict land to agriculture, forestry and green areas. The use of sludge in
forestry can increase the growth of trees and can be very useful for stabilising soil,
establishing vegetation and re-forestation.
Sewage sludge can also be used as a remediation material on brownfield sites or as an input
for the restoration of closed landfill sites. The sludge is generally incorporated with poor
quality soil, or other materials, prior to establishing grass, trees or other ground cover. The
sludge provides structure, organic matter and slow release nutrients which are ideal for use in
land restoration because one initial application can be used to provide enough nutrients for
long-term vegetation growth. Opportunities for the restoration of landfill sites have been
increasing over the last few years as a number of sites have reached capacity and are now
moving into their remediation phase.
4.2.2 Energy Crops
Bioenergy production could change the face of agriculture in the UK as farmers shift from
food production to meeting the needs for alternative energy sources. This change may also
assist sludge recycling, as these crops are not destined for the food chain although they
would be grown as part of a normal agricultural cycle. As with recycling to agriculture, the use
of sludge within Nitrate Vulnerable Zones (NVZs) must also comply with the Action
Programme for Nitrate Vulnerable Zones Regulations.
Bioenergy covers crops grown for:
• Biomass – crops such as short rotational coppicing, miscanthus which are co-fired in
power stations;
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• Bioethanol – wheat or starch based crops that are fermented to produce ethanol; and
• Biodiesel – rape or other oily crops that can be either blended with diesel or used as
a diesel substitute.
Sludge is used to increase yields of bioenergy crops that are harvested as sources of non-
fossil fuel. High yielding perennial members of the grass family of plants (such as Miscanthus)
or trees, such as willow and poplar, that will re-grow after they have been cut to the ground
are harvested, dried and burnt as fuel. The nutrient requirements are similar to any other
crops producing large amounts of biomass. Sludge can provide these nutrients, which would
otherwise be supplied by mineral fertiliser or manure if comparable yields were to be
obtained.
Where crops have been forward sold into energy markets, or farmers have decided to use
bioenergy crops as part of their rotation, an opportunity exists to increase farm profitability by
using sludge as the fertiliser option provided that robust audit schemes are in place to ensure
that the crop is not destined for the food chain.
4.2.3 Current Legislation
Under the Waste Management Licensing (England & Wales) (Amendment and Related
Provisions) Regulations 2005, in order to use sludge in land restoration, bioenergy crops or
forestry there must be a Waste Management Licence exemption for each site, which must be
authorised and registered in advance by the Environment Agency. These regulations control
the maximum amounts of materials that can be applied on land exempt from a Waste
Management Licence.
The Paragraph 8a exemption (for which planning permission is not required) relates to the
use of wastewater sludge for the ecological improvement of non-agricultural land or the
improvement of non-food crops, and includes a cross-reference to the soil PTE limits
identified in the Sludge (Use in Agriculture) Regulations 1989. As with recycling to agriculture,
the use of sludge within Nitrate Vulnerable Zones (NVZs) must also comply with the Action
Programme for Nitrate Vulnerable Zones Regulations.
The Paragraph 9 exemption, which does require planning permission, relates to the treatment
of land with identified wastes for agricultural or ecological improvement for
restoration/reclamation, at a rate of up to 20,000 m3/ha and up to 2m depth. Both these
clauses refer to wastewater sludges, but do not identify treatment requirements. Under the
Waste Management Licensing Regulations 2005 Part 2 in assessing benefit to agriculture, the
application rate for nitrogen is limited to 250 kg/ha/year.
4.2.4 Outlet Constraints and Risks
Site availability
There are no large forestry sites readily available in the South East of England. Forestry sites
also tend to be smaller blocks of land (5 – 10 hectares) than those available for normal
agricultural recycling. The longer haulage distances and exemption application costs are
offset by the higher possible application rates and the use of raw cake - forestry sites provide
alternative outlets for problem products such as untreated or very wet sludges.
Costs of restoration of landfill with sludge are largely dependent on the location and the on-
site activity required to receive and incorporate the sludge. This is currently comparable with
both forestry and brownfield restoration sites, making these sites only suitable for untreated or
problem sludges. As with forestry, there are a limited number of suitable sites in the South
East of England and consequently haulage costs for these outlets may be higher than other
options and in addition the operators of these sites may charge a gate fee.
At present there is insufficient bioenergy crop production in the UK to meet the needs of all of
the sludge producers, but this situation may change over time as more pressure is brought to
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bear on fossil fuels and the UK or European markets acquire greater biofuel processing
capacity. On the 23rd January 2008, The European Commission (EC) presented a mid-term
review of its Biofuels Directive, as part of a package on promoting renewable energies. The
EC has adopted an action plan for the promotion of alternative fuels and biofuels in road
transport concentrates policy efforts on the promotion of biofuels, natural gas and hydrogen.
The action plan outlines a strategy to achieve a 20% substitution of diesel and gasoline fuels
by alternative fuels in the road transport sector by 2020.
Additional Risks
Due to the higher application rates associated with land restoration, there may be an
increased risk of odour from these sites, especially during warmer weather or when
incorporation is slower than application. Each site is monitored on a regular basis to assess
the odour and any potential leaching issues associated with the higher application rates.
Both forestry and restoration are therefore only regarded as tactical opportunities for sludge
disposal as it is difficult to predict where and when these sites will occur and if the
landowner/operator will be willing to accept the use of sludge. Landfill restoration can be
predicted in terms of location and when each site will be closing, but there still remains a risk
associated with planning permissions and acceptability - both of which increase the cost and
the mobilisation time of this type of outlet.
Since some of these sites may be capable of taking many thousands of tonnes of sludge,
planning them in as one of the primary recycling routes would bring significant pressure to the
more established routes should the forestry/restoration site fail.
4.2.5 Non-Agricultural Outlets – Conclusions
There are no major changes expected to the forestry and land restoration recycling routes;
they continue to be viewed largely as tactical opportunities to recycle problematic sludges due
to the relatively small area of land available in the South East. However, it is expected that
some of the drivers that will affect the agricultural route will also begin to influence these
outlets, namely changes to the Waste Management Licensing Regulations (exemption
process), perception issues and nutrient loading, all of which will drive up costs. If costs
associated with other outlets increase at a faster rate than those associated with the
forestry/restoration routes then this route may become more viable as time progresses,
depending on land availability.
4.3 Energy Based Outlets
Recovering energy from sludge is lower down the waste management hierarchy than
recycling to land, but where recycling is less secure or problematic, this route can offer a
sustainable outlet.
4.3.1 Thermal Destruction (dedicated sludge incineration)
The end of sludge disposal at sea in 1998 brought about an increase in large-scale energy
recovery from sludge using incineration. Incineration is the process whereby sludge is burnt
in a furnace, the hot gases produced pass into a boiler, where steam is produced to meet the
heat needs of the process and power a turbine for electricity generation. Several stages of
cleaning of the flue gases are incorporated within the process to ensure they meet EU
emission limits.
Thames Water currently operates two Sludge Powered Generators at Beckton and
Crossness, which use the heat from the incineration of the indigenous sludge to generate
electricity. Liquid sludge from the treatment works is stored in buffer tanks prior to being
pumped into plate presses from which a 32% (target) DS cake is produced. This cake is then
fed into the incinerator where it is burnt, the residual ash (15-20% of the total volume) is
collected and either recycled or disposed.
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Typically, sludge incineration plants (such as Thames Water’s existing operations at Beckton
and Crossness) process undigested sludge. This is because the calorific value of undigested
sludge is higher than digested sludge: more heat energy can therefore be released per tonne
of sludge processed, offering the opportunity to both meet the heat needs of the process and
generate electricity. A lower calorific value also means that the sludge would need to be drier
when burnt for the process to be ‘autothermic,’ i.e. not requiring supplementary fuels such as
natural gas to maintain temperature within the process.
4.3.2 Co-incineration with other wastes
Incineration as applied within the UK water industry is exclusively dedicated to sludge
disposal. In other European Countries (e.g. Germany) co-incineration of sludge and municipal
waste is also practiced. The sludge, either as dewatered cake, but generally as dried pellets,
can be burnt in a specifically built plant with refuse derived fuel. It is possible to burn
wastewater sludge with municipal waste however; the furnace technology used needs to be
capable of handling both fuels because the municipal fraction tends to dominate both the
design and operation.
4.3.3 Gasification & Pyrolysis
Gasification and pyrolysis technologies are potential alternatives to incineration but have yet
to be proven either at large scale, or using sludge as a feedstock. In gasification the sludge is
heated (but not burnt) to produce a synthetic gas (‘syn-gas’) which can be used either as a
fuel source in a gas turbine, or in a boiler to raise steam for a steam turbine. The fuel value of
syngas is not typically as high as that of digester gas, perhaps 60% of digester gas energy
values. Pre-drying of the sludge is necessary, which takes most of the available energy
unless a supplementary fuel is co-gasified with the sludge (such as a secondary recovered
fuel (SRF) from municipal waste operations).
Pyrolysis is similar to gasification with the main difference being that sludge is thermally
treated in an oxygen free atmosphere. The sludge is not actually burnt, but brought to a
temperature of typically 500°C. The process generates three residues: solids containing
mineral matter/carbon, water, and pyrolysis gases (the main constituent is carbon dioxide).
The pyrolysis gases may be condensed to produce oil which, in turn can be used to generate
energy or in an engine. Pyrolysis is not an end disposal route for sludge and it is mainly used
as a pre-treatment step to gasification or combustion.
4.3.4 Co-firing in Cement Kilns & Coal Fired Power Stations
The cement industry is energy intensive and has a commitment to the use of alternative
waste derived fuels. Wastewater sludge, generally as dried pellets, can be co-combusted in
coal-fired power stations and cement kilns. In power stations, sludge can contribute <5% by
weight of the fuel input. Dried sludge has a calorific value similar to a low-grade brown coal.
Sludge cake is “dried” prior to firing using the spare water evaporation capacity of the power
station required to dry the coal. If wet cake is co-combusted it will account for approximately
30% of the water load into the mills. Very little infrastructure is required in the power station
compared with building similar thermal treatment technologies.
4.3.5 Current Legislation
The Waste Incineration Regulations came into force in 2002 and transpose the Waste
Incineration Directive (WID) 2000/76/EC. The Directive applies to incineration and co-
incineration plants and sets out measures such as operating conditions, emission limit values
and emission and monitoring requirements. The WID requires the operators of incineration
and co-incineration plants to apply for a permit to operate under the Pollution Prevention and
Control regime (PPC). PPC permits are required for facilities from which sludge goes for
disposal, or at which sludge is dried, gasified or burnt.
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4.3.6 Outlet Constraints and Risks
The high capital cost for a dedicated sludge powered generator (SPG) and complexity of the
process equipment means this technology is likely to be only viable at large sites. Should the
ash be classed as a hazardous waste this would further escalate operating costs. The poor
perception of municipal waste incineration with the public to date has made promoting
schemes through the planning system more difficult. Indeed, planning policies, such as
policies within the London Plan (2004), do not support the development of more municipal
incineration.
The drying of sludge for use in co-firing in cement kilns and power stations is energy intensive
and is only viable when combined with anaerobic digestion, such that the biogas can be used
to fuel the dryer (as opposed to a CHP unit). The incorporation of sludge into other processes,
such as a power plant, changes the licensing and regulatory framework for those operations.
This, together with the low energy value of the sludge compared with the primary fuel has
discouraged the uptake of this method.
The process of gasification and pyrolysis is commercially unproven on wastewater sludge
applications and has yet to be demonstrated at a large scale and using a mixed feed. Despite
several pilot schemes on gasification of sewage sludge, there is a lack of commercial
schemes that have gone forward.
4.3.7 Energy Based Outlets – Conclusions
Of the energy-based outlets for sludge disposal, thermal destruction remains the accepted
technology. The complexity of this process makes it only applicable to larger sites. Co-
incineration of sludge with municipal waste is practiced in some EU countries, however the
municipal fraction tends to dominate both the design and operation of these facilities.
Moreover, Municipalities (with responsibility for both municipal waste disposal as well as
sewage treatment) purchase most co-incineration plants, avoiding any significant problems
over priority (disposal route security) and accountability, which could pose significant
contractual challenges for separate organisations. This application of co-incineration with
other wastes is therefore unlikely to be widely implemented within the UK without clarification
of the responsibilities for co-management of different waste streams.
Emerging technologies, and in particular gasification, may become attractive alternatives to
thermal destruction in the long term. All the alternatives require the sludge to be much drier
than for standard mass burn sludge incineration, which uses a significant portion of the
available energy within the sludge. The more promising application of gasification is perhaps
in combination with secondary recovered fuels from municipal waste plants, however this is
yet to be proven at a significant scale.
Furthermore, the low calorific value of sludge compared with primary fuels used in power
stations or cement kilns, coupled with the increased complexity of the environmental
monitoring and licensing that the introduction of sludge to these processes would bring,
provides significant barriers to the widespread adoption of co-firing alternatives. In addition,
while mass-burn incineration is a proven technology, the effectiveness of pyrolysis and
gasification has not yet been fully demonstrated.
4.4 Landfill
To date, very low volumes of sludge have been disposed of to landfill. The main advantage of
landfill is that it can generally be used at very short notice, sometimes on the same day as a
requirement is identified. This route is not sustainable in the longer term and the costs
associated with it are increasing as landfill tax levels go up and void space is reduced. In
addition, due to the high water content of sewage sludge only a limited number of sites are
willing to accept it due to any potential impact on the sites leachate management programme.
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4.4.1 Current Legislation
The European Landfill Directive, transposed by the Landfill (England and Wales) Regulations,
includes a ban of the landfilling of liquid wastes and also requires all wastes to be pre-treated.
Under the Landfill Tax Regulations 1996 (as amended), any waste that is sent for disposal to
landfill is subject to a levy according to the nature and weight of the material. Wastewater
sludges fall into the ‘active’ waste category and are subject to the standard rate of tax – the
current (2007/08) standard rate of landfill tax is £24 per tonne. The 2007 budget announced
annual increases in the standard rate of landfill tax of £8 per tonne from 2008/09 until at least
2010/11, by which time it will have reached £48 per tonne.
4.4.2 Outlet Constraints and Risks
As outlined in section 4.4.1, there is an EU policy towards progressive reductions in the
amount of biodegradable waste sent to landfill. As such, the landfilling of sludge is becoming
increasingly restricted and any available landfill will be at a very high cost - the cost for
landfilling sludge now exceeds £50 per tonne including haulage, gate fees and landfill tax. In
addition, other constraints on the landfill of sludges include the landfill operator’s willingness
to accept odourous sludge.
4.4.3 Landfill – Conclusions
Landfill does not present a sustainable option for the disposal of large quantities of sludge
and loses the opportunity to recycle the phosphate and other beneficial constituents sludge
contains. As per the waste hierarchy, the disposal of sludge to landfill should be considered to
be the last solution.
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5. OPTIONS ASSESSMENT METHODOLOGY
A number of factors need to be taken into account when developing a view of the most
appropriate outlets for sludge in different parts of our region. This process was therefore high
level and aimed at generating a set of broad preferred strategic proposals for each region that
would be ‘tested’ by the independent Strategic Environmental Assessment (SEA). Where
individual development proposals at particular locations are brought forward in the future,
these will be the subject of a more detailed assessment.
5.1 Assessment of Options
The high level options assessment process utilized has been derived from approaches used
previously by Thames Water, and by other water companies/utilities, for similar assessments
e.g. for the sludge strategy developed by Scottish Water.
The broad process adopted was as follows:
Phase 1
• Assess suitability of treatment/outlet options based on generic criteria; environmental,
climate change, customer and business impacts
Phase 2
• Divide the region into groups of treatment centres based on location and/or
treatment/outlet, referred to as ‘sub regions;
• For each sub-regional area, assess the preferred options for treatment/outlet against
a set of agreed pre-selected business drivers by assigning a score of 1-5 (1 low and 5
high) according to significance. The list of business drivers, weightings and scores
were derived from meetings with all parts of the business including Thames Water
Senior Managers and Directors, whilst keeping in mind the basic principles of the
Waste Management Hierarchy and taking advice from the consultants completing the
SEA; and
• Rank options based upon the aggregated score each treatment/outlet and develop a
matrix of preferred options for each sub region for (a) a 10-year and (b) a 25-year
horizon.
5.2 Selection of potential treatment/outlet options – Phase 1
A range of treatment/outlet options were considered for potential implementation at sludge
centres. These were assessed against a range of generic criteria to assess their suitability for
implementation and undertaken using the information in Section 4 regarding the constraints
and risks associated with each outlet. This analysis was based on qualitative judgement and
operational experience from a team drawn from experts in the business. This assessment
was supplemented by a more detailed technical review carried out by consultants.
The judgements made in this phase 1 analysis had no geographic focus since the approach
in the first stage was to assess treatment/outlet options solely against the pre-set criteria. The
criteria used in our assessment were as follows:
• Environmental impact – emissions to air, water and land.
• Climate change impact – greenhouse gas emissions, total energy use
• Customer impact – potential nuisance (e.g. odour, vehicle movements), public
perception
• Business impact – supply chain security, market stability, robustness of technology.
As a result of this exercise, those treatment/outlet options that were not considered to be
feasible on the basis of issues such as product demand, proven technology and regional
requirements were removed from further consideration.
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Sludge dryers were not considered further in our assessment following this analysis, although
it is recognised that there are potential advantages in producing a product that would be
suitable for combustion as well as recycling to agricultural land. However, the disadvantages
arising from (a) the high energy requirements for operation and (b) the technical difficulties
experienced with respect to their routine operation for sludge processing, were considered to
outweigh any potential advantages.
The decision not to consider sludge dryers also effectively ruled out the options of co-
incineration and co-firing in a cement kiln or power station, as these outlets require an
essentially ‘dry’ product in order to be viable. In addition, the infrastructure for these outlets
was not available in the Thames region at the time this assessment was carried out. (Note
that powers stations that accept sludge as a fuel would have to meet the requirements of the
Waste Incineration Directive and hence be equipped with flue gas desulphurisation).
The following treatment/outlet options were therefore assessed in our detailed options
appraisal.
1. Mesophilic anaerobic digestion (MAD) – well-established digestion technology
which is the main process currently in use in the UK water industry
2. Acid phase digestion (APD) – pre-treatment process to MAD that allows more
efficient digestion. System works by reducing the pH of sludge for about 2 days at a
temperature of 35oC and then passing onto conventional MAD.
3. Enhanced digestion - e.g. a Thermal hydrolysis process (THP) - a high
pressure/temperature pre-treatment to MAD, allowing more efficient digestion. THP
works on the basis of a pressure cooker, and raises the temperature of the sludge to
approx. 160oC. This is generally more effective than APD
4. Co-digestion – anaerobic digestion with other wastes (e.g. green wastes)
5. Composting – well-established technology used for sludge treatment. Sewage
sludge is usually mixed in with a bulking agent such as woodchip or straw.
6. Co-composting – sludge composted with additional wastes
7. Pyrolysis/gasification – techniques not fully established for this application but
expected to be developed over the next 25 years. Pyrolysis is the thermal
degradation of waste in the absence of air. Gasification is the breakdown of
hydrocarbons into a syngas by carefully controlling the amount of oxygen present.
8. Thermal destruction – Thermal treatments has traditionally been incineration, which
is an established technology and there is potential for the development of alternative
thermal destruction processes. Mass burn incineration is well developed both
commercial and technical respects, with nine major sewage sludge installations in the
England.
9. Enhanced digestion/thermal destruction – combination of enhanced digestion or
co-digestion (involving THP or equivalent), followed by thermal destruction.
Note that treatment options 1 to 6 would normally be followed by recycling the product to land
while, for the remainder, the final product would be ash (or equivalent) that would either be
recycled (e.g. into aggregates) or taken to landfill.
5.3 Selection of potential treatment/outlet options – Phase 2
The following sludge centres were identified as requiring development over the 10 and 25-
year periods, based on projected sludge volumes and available capacity. These centres were
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grouped into the following sub-regional areas based on location and current treatment type
and in some instances are named after the current sludge disposal outlets in operation:
East London (thermal destruction) Crossness, Beckton
East London (digestion) Long Reach, Riverside
Mogden area Mogden
Maple Lodge area Maple Lodge
Southern region Ascot, Bracknell, Chertsey, Camberley, Cranleigh,
Crawley, Haslemere, Woking
Western region (digestion) Aylesbury, Banbury, Basingstoke, Didcot, Oxford,
Wargrave, Reading, Little Marlow, Swindon
South East region (lime) Earlswood (Reigate), Farnham, Fleet, Guildford
Western region (lime) Bicester, Newbury, Wantage, Witney
West London Beddington, Hogsmill, Slough
North East Bishops Stortford, East Hyde (Luton)
North London Deephams, Rye Meads,
An assessment was then made of the suitability of the treatment/outlet options identified in
the first phase against a set of business drivers and a weighting was applied to each business
driver for the reasons detailed below:
Business Driver Rationale for business weighting and scoring
Cost (capex) Scores are relatively high for lower costs per tonne thus providing better value
£M/tonne for money for customers. A weighting of 4 reflects the importance of
demonstrating good value for money to Ofwat and other stakeholders
Regulatory Capital Assumed that all capex will be part of the RCV therefore earning a return for
Value (RCV) impact investors. High capex therefore scores relatively highly. A weighting of 3 reflects
(capex) the need to provide a return on investment to shareholders but is less important
than efficient capital delivery
Cost (Opex) Opex is assumed to be neutral through price limits but broad business objective
is to reduce opex therefore low opex scores better. A relatively low weighting (2)
as opex should be recovered through price limits therefore should be 'neutral' to
the business.
Ease of Promotion We will need to promote the development of new assets with local and regional
stakeholders. The more difficult a scheme is to promote the greater the cost to
the business. A high score indicates the option is perceived to be relatively easy
to promote. Weighed 3 to reflect a desire to avoid the promotion of
controversial/difficult schemes
Minimise customer We want to reduce impact on customers e.g. reduce noise, odour, lorry
impacts movements. A high score implies relatively reduced impact. A maximum
weighting (5) reflects the importance of customers in our business strategy
Maximise energy We want to maximise energy recovery in order to reduce costs and to reduce
production our carbon footprint. A maximum weighting (5) to reflect the need to reduce use
of energy and cost.
Avoid landfill High score for minimal use of landfill thus reducing cost and promoting
sustainable recycling opportunities. Weighted 4 to reflect the importance of
minimising the use of unsustainable outlets and reducing cost. The weighting on
the 25 year assessment was increased to 5 to further reflect that landfill will be
prohibitively expensive
Minimise carbon foot In line with likely business targets arising from the Climate Change Bill
print sustainability criteria. A higher score was awarded for a reduced carbon
footprint. Weighted 4 to reflect importance of reducing carbon impacts. The
weighting on the 25 year assessment was increased to 5 to further reflect the
importance of carbon management
Minimise other Broad business objective consistent with stakeholder expectations. A higher
environmental score was awarded for reduced impacts. Full regulatory compliance is assumed
impacts for any option selected – a weighting of 3 reflects the desire to minimise impacts
beyond regulatory compliance.
The development and operational features of each of the treatment/outlet options were
assessed against each of the business drivers above. An indicative score of 1-5 (1 low and 5
high according to significance) was assigned for each driver. The analysis was based on
qualitative judgement and operational experience using a team drawn from experts across the
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business including engineering, operations, asset strategy, regulation, environment and
finance. The team also included representatives from Entec, the consultants engaged to carry
out the SEA. Professional judgement was applied in each topic area. Preferred options were
then ascertained based upon the aggregated score.
The conclusions from the assessment have been reviewed and endorsed by the Thames
Water Executive Management Team. This exercise provided a broad view of the preferred
hierarchy of treatment/outlet options for each of the groups of treatment centres over the 10
and 25-year periods. The Strategic Environmental Assessment was undertaken on this high
level analysis and the results are presented in the SEA Environmental Report.
The assessments made for each sub-region are explained in Section 6. This describes how
the various options were judged to perform against the business drivers, and summarises
(taking into account the relative weight that was considered to apply) how the options
performed overall, indicating those that performed well. In support of this explanation,
Appendix 2 presents the full business and sustainability assessment graphs. The
accompanying scoring of all options for each sub-region can be found in Appendix 3.
5.4 Further development of sludge management proposals
The preferred options for each area are described in more detail in the following section. The
output from the options assessment is a hierarchy of preferred treatment options for the 10-
year and 25-year horizon for each sub-region. It should, however, be stressed that these
should not be regarded as site-specific recommendations. For developments at specific sites,
the preferred options would need to be reconsidered in order to check that the assumptions
made here are still valid.
In progressing favoured options, it is recognised that some that some of these may fall within
the scope of the Environmental Impact Assessment (EIA) Regulations. This high level
assessment of sub-regional areas will contribute to future assessments but further detailed
work on a site-specific basis may be required to take any preferred option forward.
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6. DETAILED ASSESSMENT OF SUB-REGIONAL AREAS
This section describes the assessments and summarises the recommended strategy for each
sub-region. Appendix 2 presents the full business and sustainability assessment graphs. The
accompanying scoring of all options for each sub-region can be found in Appendix 3.
6.1 Integrated Implementation Strategy for East London
For East London, thermal destruction and digestion sites have been considered in separate
sub-regions, primarily to reflect the principal sludge management streams already in
existence and to achieve consistency with the approach taken within the other sub-regions.
However, the strategy does recognise the geographical proximity and the linkages between
these sets of sites and the large volumes of sludge produced in the region. For East London,
we consider that there is merit in having a strategy involving both digestion with recycling to
agricultural land, taking advantage of the locations where there is reasonable access to the
landbank, and thermal destruction with energy recovery. The dual approach within this region
therefore meets the operational needs of the company by reducing the risk from not relying on
one outlet and also ensures that the benefits that can be derived from digestion and recycling
sludge to land (energy generation and nutrient and organic value of sludge as a fertiliser) are
achieved from a proportion of sludge generated within East London.
6.2 East London (Thermal Destruction with Energy Recovery)
6.2.1 Sludge Treatment Centres in Area
There are two sewage treatment works in this part of our region - Beckton and Crossness.
Beckton Sludge Powered Generator receives indigenous raw sludge from Beckton sewage
treatment works and Riverside sewage treatment works via a dedicated pipeline. Sludge
treatment comprises of dewatering and incineration of the raw cake. Energy is recovered from
the installation, producing 41.5 GWh in 2006/07 which is used to supply the SPG
requirements as well as a proportion of the sewage treatment works electrical supply.
Beckton is the largest sewage works in the UK (3.3 million PE) and it serves a large part of
central and east London. Due to on going long-term operational issues, a small proportion of
the sludge from this site is currently being lime treated and recycled to agricultural land.
Current sludge production (2006) including Riverside is 112,096 tonnes dry solids per year.
Crossness Sludge Powered Generator receives raw sludge from Crossness sewage
treatment works; a very large works (1.9 million PE) serving a large part of south and central
London. Sludge treatment comprises of dewatering and incineration of the raw cake. Due to
on going operational capacity constraints a small proportion of the sludge from this site is
currently being lime treated and recycled to agricultural land. The energy produced from the
installation was 18.7 GWh in 2006/07. Current sludge production (2006) is 56,940 tonnes dry
solids per year.
The Sludge Powered Generators at both sites were brought into commission at the end of
1998. Thus during the period considered by this strategy, it is anticipated that both assets will
require substantial renovation or replacement.
6.2.2 Factors relevant to the assessment
Both sewage works are located in predominately urban areas with little agricultural land in the
immediate vicinity. The current option for sludge disposal (thermal destruction with energy
recovery) was selected in the mid 1990s following an extensive best practicable
environmental option assessment that subsequently informed individual planning applications.
Recycling to agricultural land was not favoured due to the very large volumes of sludge
produced on the two sites and the corresponding high number of lorry movements required to
take the treated sludge off site to land suitable for recycling.
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This factor is just as relevant for the current assessment and a large number of lorries would
be required to take the current sludge product to suitable agricultural land. The application of
techniques requiring more lorry movements (e.g. composting, co-composting and co-
digestion) would therefore be potentially detrimental to local residents due to increased risk of
nuisance, plus the carbon footprint and environmental impact due to the increased use of fuel.
These techniques were therefore not considered further in this assessment. The land bank
analysis carried out as part of the strategy development illustrates that these sites are located
in a part of the region amongst the most constrained with respect to the availability of land for
recycling.
Both sites have some existing digestion capacity but the digesters are currently in a poor
state of repair and in use for the blending and buffering of sludge prior to thermal destruction
and for temporary sludge storage during the annual statutory maintenance shutdown of the
Sludge Powered Generators. Considerable refurbishment of the digesters would therefore be
needed before they could be used for the digestion of sludge (or other wastes) and alternative
storage capacity would be needed for use during annual maintenance and in case of other
operational issues giving rise to loss of treatment capacity.
Part of the assessment process involved consideration of the continued transfer of sludge
between Riverside to Beckton, particularly in view of the long term capacity issues at Beckton
and energy requirements of continued pumping of sludge between the two STWs during the
period considered in the strategy. Riverside STW is considered a large enough site to enable
efficient on-site treatment of indigenous sludge.
6.2.3 Summary of assessment
The preferred options for the 10-year horizon are based on processes that minimise vehicle
movements on and off site and enable efficient extraction of energy from the sludge. The
processes included installation of additional thermal destruction capacity and (if technically
feasible) pyrolysis/gasification techniques and enhanced digestion (e.g. thermal hydrolysis)
followed by thermal destruction. These scored highly in our assessment with respect to
maximising energy production, minimising customer impacts and minimising carbon footprint.
The installation of additional thermal destruction capacity was a favoured option in part,
because this technology produces less residual waste than pyrolysis/gasification and involves
minimal offsite disposal resulting in low traffic generation. The emissions from this installation
would be regulated under Integrated Pollution and Prevention Control (IPPC) and the Waste
Incineration Directive (WID) and, on the basis that permit conditions would be met, the
potential for public nuisance arising from odour or emissions is judged to be low.
Enhanced digestion followed by thermal destruction of the remaining sludge, was amongst
the best performing options, based on the assumption that it is an efficient way of extracting
energy from the sludge and, at the same time, minimising the volume of sludge requiring
further treatment. It should be noted, however, that this solution would need to be verified by
a detailed technical evaluation of site-specific issues such as:
a) The condition of the existing digesters and cost of
refurbishment/replacement
b) The energy balance of utilising digested versus raw sludge and
c) The ability of the existing incinerator streams to burn digested cake
compared with the raw cake it was designed to handle.
The installation of pyrolysis/gasification technologies also scored highly. In our assessment, it
was assumed that more efficient energy production would be possible with
pyrolysis/gasification compared with thermal destruction. The technology review has,
however, indicated that currently neither pyrolysis nor gasification is considered to be a
proven technology, either from the perspective of reliability or a secure supply chain. In the 10
to 25 year period this may change.
The application of techniques that require sludge to be recycled to agricultural land were not
favoured at East London thermal destruction sites due to:
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• The size of the sites and large volumes of sludge, and hence, very high number of
lorry movements required to take the product to land. The potential for public
nuisance caused by the movement of these vehicles was therefore considered to be
high
• Large land bank requirement and competition for available land with other sites in the
area - the land bank assessment supports the conclusion that the sludge should be
treated and disposed of on-site
In the longer term (25 years), our assessment indicated consideration should also be given to
co-digestion followed by a thermal destruction process. However, the feasibility of installing
additional digestion plants at either Beckton or Crossness and the impact of importing
additional material on site, would need to be investigated before this option could be
promoted.
6.2.4 Conclusions
• Processes allowing the efficient extraction of energy and minimising lorry movements
are the most suitable.
• Recycling to land is not a viable option for these sites due to the large volume of
sludge produced.
6.2.5 Recommended strategy
(a) 10 year
• Install additional thermal destruction with energy recovery capacity
• Assess whether more efficient energy recovery can be achieved at these
sites by carrying out digestion in advance of a thermal destruction process
• To help manage short-medium term capacity issues at Beckton, install
treatment capacity at Riverside
(b) 25 year
• In the longer term consideration should also be given to co-digestion followed
by thermal destruction in order to try to maximise the potential for energy
recovery. However this would involve bringing additional material on site and
the impact of this activity would need to be fully assessed.
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6.3 East London (Digestion)
6.3.1 Sludge Treatment Centres in Area
There are two sites in this region; Long Reach and Riverside, serving areas to the east of
London. The sites operate conventional wastewater treatment with sludge treatment at Long
Reach via anaerobic digestion, followed by recycling to agricultural land. The sludge from
Riverside is currently transported by pipeline to Beckton sewage works where it is incinerated,
however, the Riverside site previously provided on-site digestion. The current sludge
production (2006) from these sites is 24674 tds. Long Reach operates a CHP plant producing
15.3 GWh in 2006/07.
6.3.2 Factors relevant to the assessment
Access to both sites is reasonable but with increasing congestion on all roads in the area,
processes that minimise sludge volume and hence lorry movements in and out of the sites
are favoured. These sites are considered potentially large enough to operate a thermal
destruction process; although a more detailed feasibility study would be required for each of
the sites were a thermal destruction process to be considered.
As discussed in Section 6.2.2, it was deemed appropriate to consider the feasibility of
reverting to digestion on the site since, (a) some of the required assets already exist and (b)
to utilise more fully the potential for energy production. In addition, Riverside is considered a
large enough site to enable efficient on-site treatment of indigenous sludge. In the longer
term, this would also have the added benefit of avoiding the need to regularly pump sludge
between Riverside and Beckton. Both Long Reach and Riverside are situated in parts of the
region that are constrained with respect to land availability. However, these sites do offer
reasonable access to the North East part of the region where land availability is better.
6.3.3 Summary of assessment
The preferred options for the 10-year horizon included using enhanced digestion (with thermal
hydrolysis or acid phase digestion) followed by recycling to land; and installation of enhanced
digestion followed by thermal destruction. These scored highly with respect to avoiding landfill
and maximising energy production.
Utilising enhanced digestion (with thermal hydrolysis) followed by recycling to land was a
preferred option largely on the basis that it minimises the sludge volume, resulting in fewer
vehicle movements compared with acid phase digested sludge. This option also maximises
gas (energy) production.
Digestion (with thermal hydrolysis) followed by the application of a thermal process was
amongst the best performing options on the basis that it would result in fewer vehicle
movements and the assumption that this was an efficient method for energy production.
However, as mentioned above, the technical feasibility and energy balance of installing a
thermal destruction plant would need to be assessed further on a site-by-site basis.
Composting and co-composting were not favoured for this sub-region mostly due to the
increased lorry movements associated with having to import additional material into the sites
e.g. straw/woodchips, as well as more product leaving the site for recycling to land. These
options also had no benefits of energy recovery.
With respect to the 25-year period, the additional option of co-digestion followed by thermal
destruction should also be considered. This option, however, would be confined to those sites
with reasonable access and able to accommodate the additional lorry movements. There
would also need to be space on-site to construct more digestion capacity.
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6.3.4 Conclusions
• Processes that maximise extraction of energy and minimise lorry movements are the
most suitable
• Two options appear to be available to meet these criteria - both require
implementation of advanced digestion followed either by recycling to land or thermal
destruction on site.
• Landbank constraints suggest that application of a thermal destruction process may
need to be considered in the longer term but currently there is sufficient land available
to support sludge generated by these sites to be recycled to agricultural land
6.3.5 Recommended strategy
(a) 10 year
• Introduce enhanced digestion on both sites followed by recycling to land
• In the longer term, review land bank availability for the sub-region and, if
necessary, assess the feasibility of carrying out enhanced digestion followed
by thermal destruction.
(b) 25 year
• The installation of enhanced digestion, possibly with co-digestion with
municipal waste followed by thermal destruction, should additionally be
considered over the 25-year period.
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6.4 Mogden (West London)
6.4.1 Sludge Treatment Centres in Area
Mogden sewage treatment works is a large site (approx 1.8 million PE) receiving waste from
West London. The existing sludge treatment process involves a pasteurisation phase followed
by conventional anaerobic digestion, with 33.4 GWh power generated on site in 2006/07. The
liquid sludge is then pumped via a dedicated pipeline to Iver South for dewatering before
being taken to agricultural land for recycling. Current sludge production (2006) is 58797 tds
per year.
6.4.2 Factors relevant to the assessment
Mogden is located in a heavily populated part of west London and, although it is a large site,
there is little opportunity for expansion of the existing treatment processes. Access to the site
is via roads already heavily congested thus the application of processes that would require
additional lorry movements (i.e. either taking material on or off site e.g. composting) is not
favoured, therefore these techniques were not considered further. In addition, the close
proximity of housing is connected to the number of odour complaints, thus the application of
processes with the potential to exacerbate this problem should be avoided.
Large-scale thermal destruction would require the installation of dewatering equipment,
currently located at Iver South. This was not considered feasible at Mogden due to the lack of
space. At Iver South, where the current sludge production is dewatered and stored before
removal to land, more land is available and access is less problematic. It is therefore likely
that any future process development for sludge treatment at Mogden would have to make
greater use of the site at Iver South. There is some agricultural land in the vicinity of Iver
South but most of the sludge taken from the site has to be transported west along the M4
corridor to find suitable land. The land bank assessment shows that Mogden lies in a part of
the region likely to be heavily constrained with respect to future land availability.
6.4.3 Summary of assessment
The preferred options for the 10-year horizon are based on processes that minimise vehicle
movements on and off site and enable efficient extraction of energy from the sludge. The
processes included the application of enhanced digestion (with thermal hydrolysis) followed
by recycling to land and (if necessary and technically feasible) pyrolysis/gasification
techniques and installation of enhanced digestion (e.g. thermal hydrolysis) followed by
thermal destruction. These scored highly with respect to maximising energy production,
minimising customer impacts and minimising carbon footprint.
The continued application of enhanced digestion (with thermal hydrolysis or equivalent)
followed by recycling to land was a preferred option largely on the basis that it minimises the
sludge volume requiring further treatment, thus resulting in fewer vehicle movements
compared with acid phase digested sludge or mesophillic anaerobic digested sludge. In
addition, by minimising the volume of sludge requiring storage, this should reduce the
potential for odour nuisance. This option also utilises the existing digesters on-site and
maximises gas (energy) production thus offsetting grid power use. However, the land bank
assessment illustrates that the land bank is relatively constrained in this part of the region.
Thus, in the longer term, this outlet may not be viable.
The installation of pyrolysis/gasification technologies was also a preferred option. In our
assessment, it was assumed that more efficient energy production would be possible with
pyrolysis/gasification compared with thermal destruction. However, the technology review has
indicated that, currently, neither pyrolysis nor gasification is considered to be a proven
technology, either from the perspective of reliability or a secure supply chain. In the 10 to 25-
year horizon this may change.
Digestion (with thermal hydrolysis) followed by the application of a thermal process was a
preferred option on the basis that it would result in fewer vehicle movements and the
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assumption that this was an efficient method for energy production. However, the technical
feasibility and energy balance of installing a thermal destruction plant, would need to be
assessed on a site-by-site basis.
Composting and co-composting were not favoured for this sub-region mostly due to the
increased lorry movements associated with having to import additional material into the sites
e.g. straw/woodchips, as well as more product leaving the site for recycling to land. These
options also had no benefits of energy recovery. Large-scale thermal destruction was not
considered viable at Mogden due to the space requirements for the installation of dewatering
and other ancillary equipment.
With respect to the 25-year period, the additional option of co-digestion followed by thermal
destruction should also be considered. However, the feasibility of installing additional
digestion plant at Mogden or Iver South, and the impact of importing additional material to
either site, would need to be investigated before this option could be promoted.
6.4.4 Conclusions
• Processes that enable efficient energy extraction and reduced lorry movements have
been identified by this assessment to be the most suitable
• Enhanced digestion followed by either recycling to land, or thermal destruction, meet
these criteria
• Land bank constraints may impact on the feasibility of recycling to land in the longer
term.
6.4.5 Recommended strategy
(a) 10 year
• In the short to medium term continued use of pasteurisation, digestion and
recycling to land is recommended
• In the longer term, review land bank availability and if necessary, assess the
feasibility of carrying out enhanced digestion followed by a thermal
destruction process
(b) 25 year
• Over the 25-year period, the potential constraints on available land bank may
render the recycling outlet less viable. Thus increasing the capacity/efficiency
of the existing enhanced digestion process (possibly with co-digestion with
municipal waste), followed by application of a thermal destruction process,
should additionally be assessed.
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6.5 Maple Lodge
6.5.1 Sludge Treatment Centres in Area
Maple Lodge is a large sewage treatment works (478,000 PE) located in the north west of
London, receiving waste from towns such as Watford, Rickmansworth and the surrounding
area. The existing sludge treatment process is by conventional anaerobic digestion with 16.5
GWh power generated in 2006/07. The liquid digested sludge is dewatered before being
taken to agricultural land for recycling. Current sludge production (2006) is 20087 tds per
year.
6.5.2 Factors relevant to the assessment
Maple Lodge occupies a large site near to the M25 and M40 and currently has reasonably
good access and farmland suitable for recycling at a reasonable distance from the site.
However, the roads are becoming increasingly congested and thus the application of
processes that require additional lorry movements (i.e. either taking material on or off site e.g.
composting) are not favoured due to the impact of potential nuisance, carbon footprint and the
environment. The land bank assessment shows that Maple Lodge is situated in a part of the
region fairly heavily constrained with respect to land availability.
6.5.3 Summary of assessment
The preferred options for the 10-year period included the application of enhanced digestion
(with thermal hydrolysis or acid phase digestion) followed by recycling to land and (if
necessary and technically feasible) installation of enhanced digestion (e.g. thermal hydrolysis)
followed by thermal destruction. These scored highly with respect to maximising energy
production, avoidance of landfill and minimising carbon footprint.
Utilising enhanced digestion (with thermal hydrolysis or acid phase digestion) followed by
recycling to land was a preferred option largely on the basis that there are fewer vehicle
movements associated with this option as the technology minimises the sludge volume
requiring further treatment. This option also utilises the existing digesters on-site and
maximises gas (energy) production thus offsetting grid power use. However, the land bank
assessment again illustrates that the land bank is relatively constrained in this part of the
region.
Digestion (with thermal hydrolysis) followed by the application of a thermal process was a
preferred option on the basis that it would result in fewer vehicle movements and the
assumption that this was an efficient way of extracting energy from the sludge. However, the
technical feasibility and energy balance of installing a thermal destruction plant would need to
be assessed on a site-by-site basis.
Composting and co-composting techniques were not favoured for this sub-region mostly due
to the increased lorry movements associated with having to import additional material into the
sites e.g. straw/woodchips, as well as more product leaving the site for recycling to land.
With respect to the 25-year period, consideration should also be given to co-digestion
followed by thermal destruction (or an equivalent process). However, the impact of importing
additional material on site would need to be investigated before this option could be
promoted.
6.5.4 Conclusions
• Processes that maximise extraction of energy and minimise lorry movements are the
most suitable
• Two options appear to be available to meet these criteria for Maple Lodge. Both
require implementation of advanced digestion followed either by recycling to land or
thermal destruction on site.
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• Land bank constraints may impact on the feasibility of recycling to land in the longer
term.
6.5.5 Recommended strategy
(a) 10 year
• In the short to medium term, introduce enhanced digestion (thermal
hydrolysis or equivalent) and continue recycling to land
• In the longer term, review land bank availability and if necessary, assess the
feasibility of carrying out enhanced digestion followed by a thermal
destruction process
(b) 25 year
• Over the 25-year period, the potential constraints on available land bank may
render the recycling outlet less viable. Thus increasing the capacity/efficiency
of the existing digestion process (possibly with co-digestion with municipal
waste) followed by application of a thermal destruction process should
additionally be assessed.
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6.6 Southern region
6.6.1 Sludge Treatment Centres in Area
There are eight sludge centres in this regional area (Ascot, Bracknell, Camberley, Chertsey,
Cranleigh, Crawley, Haslemere and Woking). These sites are of medium size located in the
southern part of the region. All of the sites operate conventional anaerobic sludge digestion
treatment processes with the products recycled to agricultural land. There are variations in the
process used, notably at Chertsey where the ‘Cambi’ process is employed. This is a thermal
hydrolysis treatment phase designed to help break down the natural organic material present
in sewage and hence obtain a more efficient sludge digestion phase. The total sludge
production from these sites is currently (2006) 29126 tds. Energy recovery is currently in
operation at Camberley, Crawley and Bracknell, producing a total of 3.5 GWh in 2006/07 and
there are plans to install further CHP plant at Chertsey and Woking.
6.6.2 Factors relevant to the assessment
Access to the sites is mostly reasonably good, although there is increasing congestion on all
roads in the area thus processes that minimise lorry movements in and out of the site are
favoured. Techniques that require the movement of additional material on and off site (e.g.
composting, co-composting and co-digestion) are therefore not favoured. Some of the sites
also face increasing pressure from urban encroachment, thus odour issues are likely to
become more important in the future. Thus processes that reduce sludge volume and hence
minimise storage requirements are favoured.
In principle some of the centres are considered large enough to operate a small thermal
destruction process on each site. However, a more detailed feasibility study would be
required for each of the sites should this option be taken forward. The eight sites cover a
large area with variable land bank availability. The land bank analysis indicates that the region
around Crawley, Cranleigh, Woking and Chertsey is particularly constrained.
6.6.3 Summary of assessment
The preferred options for the 10-year horizon included the application of enhanced digestion
(with thermal hydrolysis or acid phase digestion) followed by recycling to land and (if
necessary and technically feasible) installation of enhanced digestion (e.g. thermal hydrolysis)
followed by thermal destruction. These scored highly with respect to maximising energy
production, avoidance of landfill and minimising environmental impact.
Utilising enhanced digestion (with thermal hydrolysis or acid phase digestion) followed by
recycling to land was a preferred option largely on the basis that it minimises the sludge
volume requiring further treatment, thus resulting in fewer vehicle movements and easing the
congestion on the local roads. In addition, by minimising the volume of sludge requiring
storage, this should reduce the potential for odour nuisance on-site. This option also avoids
disposal to landfill and maximises gas (energy) production thus offsetting grid power use etc.
However, the land bank assessment illustrates that the region is relatively constrained with
variable land bank availability.
Digestion (with thermal hydrolysis) followed by the application of a thermal destruction
process was a favoured option on the basis that it would result in fewer vehicle movements
and the assumption that this was an efficient method for energy production. However, as
mentioned above, the feasibility of installing a small thermal destruction process would need
to be assessed on a site-by-site basis.
The implementation of large-scale thermal destruction process by transporting sludge from
several sites to a central location was not favoured due to a range of potential nuisance (e.g.
traffic movements), carbon footprint and environmental impacts. In addition, composting and
co-composting techniques were not favoured for this sub-region mostly due to the increased
lorry movements associated with having to import additional material into the sites e.g.
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straw/woodchips, as well as more product leaving the site for recycling to land and the lack of
opportunity of renewable energy generation.
With respect to the 25-year period, the additional option of co-digestion followed by thermal
destruction should also be considered. However, this option would be confined to those sites
with good access, that have space on-site to construct more digestion capacity and be able to
accommodate the additional lorry movements. The impact of importing additional material to
site would need to be investigated before this option could be promoted.
6.6.4 Conclusions
• Processes that maximise extraction of energy and minimise lorry movements are the
most suitable
• Two options meet these criteria. Both require implementation of advanced digestion
followed either by recycling to land or thermal destruction on site.
• Land bank constraints at some sites suggest that on site treatment and application of
a thermal destruction process may be the favoured option in the longer term.
6.6.5 Recommended strategy
(b) 10 year
• Introduce enhanced digestion on all sites followed by recycling to land
• In the longer term, review land bank availability for the sub-region and, if
necessary assess the feasibility of carrying out enhanced digestion followed
by thermal destruction at those sites with particular land bank constraints.
(b) 25 year
• The installation of enhanced digestion possibly with co-digestion with
municipal waste followed by thermal destruction should additionally be
considered over the 25-year period.
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6.7 Western region (digestion)
6.7.1 Sludge Treatment Centres in Area
There are nine sludge centres in this regional area (Aylesbury, Banbury, Basingstoke, Didcot,
Little Marlow, Oxford, Reading, Swindon and Wargrave). These sites are of small to medium
size located in the western part of the region. All of the sites operate conventional anaerobic
sludge digestion treatment processes with the products recycled to agricultural land. There
are variations in the process used, notably at Reading where pre-pasteurisation is employed
and at Swindon, where acid phase digestion is practised before conventional anaerobic
digestion. The combined current sludge production (2006) from these sites is 53071 tds.
Energy recovery is currently in operation at Aylesbury, Basingstoke, Banbury, Oxford,
Reading, Swindon and Wargrave, producing a total of 14 GWh in 2006/07.
6.7.2 Factors relevant to the assessment
Access to these sites is variable, although there is increasing congestion on all roads in the
area, thus processes that minimise lorry movements in and out of the sites are favoured. The
implementation of processes requiring the movement of additional material on and off site
(e.g. composting, co-composting and co-digestion) is also therefore not favoured. Some of
the sites also face increasing problems from housing encroachment and therefore odour
issues are likely to become more important. Thus processes that minimise sludge volume and
hence minimise storage requirements are favoured.
Some of these sites are considered large enough potentially to operate a small thermal
destruction process, although a more detailed feasibility study would be required for each of
the sites should this option be taken forward. Little Marlow has been included in this group as,
although it currently operates a composting plant, the intention is to close this operation in the
short to medium term due to problems arising from odour associated with the process and
cost. The nine sites cover a large area but, in general, are located in those parts of the region
with reasonably good access to land suitable for recycling.
6.7.3 Summary of assessment
The preferred options for the 10-year period included the application of enhanced digestion
(with thermal hydrolysis or acid phase digestion) followed by recycling to land and (if
necessary and technically feasible) installation of enhanced digestion (e.g. thermal hydrolysis)
followed by thermal destruction. These scored highly with respect to maximising energy
production, avoidance of landfill and minimising environmental impact.
Enhanced digestion (with thermal hydrolysis or acid phase digestion) followed by recycling to
land was favoured, largely because the process minimises the sludge volume requiring
further treatment. This results in fewer vehicle movements thus easing congestion on the
roads and a reduction in the volume of sludge requiring storage, which should help to reduce
the potential for odour nuisance on-site. This option is also the least likely to utilise disposal to
landfill and maximises gas (energy) production thus offsetting grid power use.
Digestion (with thermal hydrolysis hence maximising gas production) followed by the
application of a thermal destruction process was also favoured. This was on the basis that it
would result in fewer vehicle movements and the assumption that this was an efficient method
of energy production. However, the feasibility of installing a small thermal destruction process
would need to be assessed on a site-by-site basis.
The implementation of processes requiring the movement of additional material on and off
site (e.g. composting and co-composting) were not favoured in the 10 year horizon due to the
increased lorry movements associated with having to import additional material into the sites
e.g. straw/woodchips and increasing congestion on all roads. In addition, the implementation
of a large-scale thermal destruction process by transporting sludge from several sites to a
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central location was not favoured due to a range of nuisance, carbon footprint and
environmental impacts.
With respect to the 25-year period, the additional option of co-digestion followed by thermal
destruction, should also be considered due to the opportunity to align with Local Authorities
waste strategies and thus avoiding the use of unsustainable and (anticipated) prohibitively
expensive landfill. This option, however, would be confined to those sites with reasonable
access and those able to accommodate the additional lorry movements and also have to
space on site to construct more digestion capacity. The impact of importing additional material
to site would need to be investigated before this option could be promoted.
6.7.4 Conclusions
• Processes that maximise the generation of energy and minimise lorry movements are
the most suitable
• Two options appear to be available to meet these criteria. Both require
implementation of advanced digestion, followed either by recycling to land, or thermal
destruction on site.
• Land bank availability is generally good, however, local constraints at some sites may
mean that on-site treatment/thermal destruction may be the favoured option in the
longer term.
6.7.5 Recommended strategy
(a) 10 year
• Introduce enhanced digestion on all sites followed by recycling to land
• In the longer term, review land bank availability for the sub-region and, if
necessary, assess the feasibility of carrying out enhanced digestion followed
by thermal destruction at sites with specific land bank constraints.
(b) 25 year
• The installation of enhanced digestion possibly with co-digestion with
municipal waste, followed by thermal destruction, should additionally be
considered over the 25-year period.
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6.8 South-East region (lime)
6.8.1 Sludge Treatment Centres in Area
There are four sludge centres in this area (Earlswood, Farnham, Fleet, Guildford). They are
medium-sized sites largely serving the town in which they are located plus the surrounding
housing. All sites carry out conventional sewage treatment with the raw sludge treated with
lime before recycling to agricultural land. The current sludge production (2006) from these
sites is 21451 tds.
6.8.2 Factors relevant to the assessment
Access is variable but generally poor thus the application of processes that minimise lorry
movements is favoured. Techniques that require the movement of additional material on and
off site (e.g. composting, co-composting and co-digestion) are therefore not favoured. All sites
have experienced encroachment of housing to a certain extent. This is likely to continue and
odour is already an issue at some sites. Due to the nature of the sludge treatment processes
there is currently no energy recovery in operation on any of the sites. The lime treatment
process increases the volume of sludge to be managed and it is our intention to replace this
process in the short to medium term. The land bank assessment indicates that availability is
relatively poor in this part of the region.
6.8.3 Summary of assessment
The preferred options for the 10-year horizon are based on processes that reduce sludge
volumes and maximise gas production potential. These processes include the application of
enhanced digestion (with thermal hydrolysis or acid phase digestion) followed by recycling to
land and (if necessary and technically feasible) installation of enhanced digestion (e.g.
thermal hydrolysis) followed by thermal destruction. These scored highly with respect to
maximising energy production, avoidance of landfill and minimising environmental impact.
Utilising enhanced digestion (with thermal hydrolysis or acid phase digestion) followed by
recycling to land scored highly on the basis that it minimises the sludge volume requiring
further treatment, thus resulting in fewer vehicle movements. In addition, by minimising the
volume of sludge requiring storage, this should reduce the potential for odour production. This
option also avoids disposal to landfill and maximises gas (energy) production thus offsetting
grid power use. However, the land bank assessment illustrates that availability in the region is
relatively poor, thus the viability of continuing to use this outlet will need to be kept under
review.
An alternative is to utilise digestion (with thermal hydrolysis hence maximising gas
production), followed by the application of a thermal destruction process on-site, in place of
recycling. This was also a favoured option on the basis that it would result in fewer vehicle
movements and on the assumption that this was an efficient method for energy production.
However, the feasibility of installing a small thermal destruction process needs to be
assessed on a site-by-site basis to determine the most favoured option for each site.
It should be noted that the implementation of large-scale thermal destruction processes by
transporting sludge from several sites to a central location was not favoured due to a range of
nuisance, carbon footprint and environmental impacts. In addition, composting and co-
composting techniques were not favoured due to the relatively poor access and the increased
lorry movements associated with having to import additional material into the sites e.g.
straw/woodchips. In addition, these options would require more landbank and have no
opportunity for the generation of renewable energy.
Over the long term 25-year period, consideration should be given to the option of co-digestion
followed by a thermal destruction process providing an opportunity to align with Local
Authorities waste strategies. However, site-specific issues, and in particular, the ease of
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access for bringing in the additional material to be digested needs to be taken into account
and investigated before this option could be promoted.
6.8.4 Conclusions
• Processes that maximise extraction of energy and minimise sludge volume and
hence lorry movements are the most suitable
• Two options appear to be available to meet these criteria. Both require
implementation of advanced digestion followed either by recycling to land or thermal
destruction on site.
• Land bank availability is variable and constraints at some sites may mean that on-site
treatment/thermal destruction may be the favoured option in the longer term.
6.8.5 Recommended strategy
(a) 10 year
• Introduce enhanced digestion on all sites followed by recycling to land
• In the longer term, review land bank availability for the sub region and, if
necessary, assess the feasibility of carrying out enhanced digestion followed
by thermal destruction at those sites with particular land bank constraints.
(b) 25 year
• The installation of enhanced digestion with co-digestion with municipal waste,
followed by thermal destruction, should additionally be considered over the
25-year period.
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6.9 Western region (lime)
6.9.1 Sludge Treatment Centres in Area
There are four sludge centres in this area (Bicester, Newbury, Wantage and Witney). They
are relatively small sites largely serving the town in which they are located. All sites carry out
conventional sewage treatment with the raw sludge treated with lime before recycling to
agricultural land. The outlet for sludge from Wantage is currently a land restoration site but
this is a relatively short-term option. The combined current sludge production (2006) from
these sites is 11252 tds.
6.9.2 Factors relevant to the assessment
Access is variable but generally poor thus the application of processes that minimise sludge
volume and hence lorry movements would be favoured. Techniques that require the
movement of additional material on and off site (e.g. composting, co-composting and co-
digestion) are therefore not favoured. All sites suffer from encroachment of housing to a
certain extent and this is likely to get worse; odour is already an issue at some sites. All sites
are reasonably close to agricultural land suitable for recycling.
Due to the nature of the processes on site, there is currently no energy recovery in operation.
These sites are not considered large enough to operate a thermal destruction process
although a more detailed feasibility study would be required to completely eliminate this
option for each site. This is a site-specific issue that would be picked up in considering any
future development for that site. The lime treatment process increases the volume of sludge
to be managed and it is our intention to replace this process in the short to medium term. The
land bank analysis suggests that land is relatively unconstrained in this part of our region.
6.9.3 Summary of assessment
The preferred options for the 10-year horizon included the application of enhanced digestion
(with thermal hydrolysis or acid phase digestion) followed by recycling to land and co-
digestion followed by recycling to land. These scored highly with respect to maximising
energy production and avoidance of landfill.
Utilising enhanced digestion (with thermal hydrolysis or acid phase digestion) followed by
recycling to land was a preferred option, largely because the process minimises the sludge
volume requiring further treatment. This results in fewer vehicle movements thus easing
congestion on the roads in the area and a reduction in the volume of sludge requiring storage,
which should help to reduce the potential for odour nuisance on-site. This option is also the
least likely to utilise disposal to landfill and maximises gas (energy) production thus offsetting
grid power use.
The implementation of a large-scale thermal destruction process by transporting sludge from
several sites to a central location was not favoured due to a range of potential nuisance,
carbon footprint and environmental impacts. Similarly, the application of digestion followed by
a thermal destruction process was also not considered viable given the size of the sites in
question – this option would require the installation of several small thermal destruction units
with associated relatively high costs.
In the longer term (25 years), consideration should also be given to co-digestion followed by
recycling to land, although site-specific issues, and in particular ease of access for bringing in
the additional material to be digested, would need to be taken into account before co-
digestion could be promoted.
6.9.4 Conclusions
• Processes that maximise extraction of energy and minimise lorry movements are the
most suitable.
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• Installation of enhanced digestion followed by recycling to land meets these criteria
• The land bank assessment suggests that sufficient land should be available.
6.9.5 Recommended strategy
(a) 10 year
• Introduce enhanced digestion on all sites followed by recycling to land
(b) 25 year
• The installation of enhanced digestion with co-digestion with municipal waste
followed by recycling to land should additionally be considered over the 25-
year period.
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6.10 West London
6.10.1 Sludge Treatment Centres in Area
There are three sludge centres in this area (Beddington, Hogsmill and Slough). They are
medium to large sized works largely serving areas to the south and west of London. The sites
operate conventional wastewater treatment with sludge processing via anaerobic digestion
with energy recovery, followed by recycling to agricultural land. The total current sludge
production (2006) from these sites is 33713 tds. All sites operate CHP plant producing a total
of 17.2 GWh in 2006/07.
6.10.2 Factors relevant to the assessment
Access to all of the sites is generally poor and, with increasing congestion on all roads in the
area, processes that minimise sludge volume and hence lorry movements in and out of the
sites are favoured. Techniques that require the movement of additional material on and off
site (e.g. composting, co-composting and co-digestion) are therefore not favoured. Some of
the sites also face increasing problems from housing encroachment thus odour issues are
likely to become more important. Thus processes that minimise sludge volume and hence
minimise storage requirements are favoured.
These sites are considered large enough to potentially operate a small thermal destruction
process, although a more detailed feasibility study would be required for each of the sites
should this option be taken forward. These sites lie in a part of the region with relatively heavy
constraints on available land for recycling.
6.10.3 Summary of assessment
The preferred options for the 10-year horizon are based on processes that reduce sludge
volumes and maximise gas production potential. These processes include the application of
enhanced digestion (with thermal hydrolysis or acid phase digestion) followed by recycling to
land and (if necessary and technically feasible) installation of enhanced digestion (e.g.
thermal hydrolysis) followed by thermal destruction. These scored highly with respect to
maximising energy production, avoidance of landfill and minimising environmental impact.
One of the preferred options was utilising enhanced digestion (with thermal hydrolysis or acid
phase digestion) followed by recycling to land, largely because the process minimises the
sludge volume requiring further treatment. This results in fewer vehicle movements thus
easing congestion on the roads in the area and a reduction in the volume of sludge requiring
storage, which should help to reduce the potential for odour nuisance on-site. This option is
also the least likely to utilise disposal to landfill and maximises gas (energy) production thus
offsetting grid power use.
A favoured alternative would be to utilise digestion (with thermal hydrolysis hence maximising
gas production) followed by the application of a thermal destruction process on-site in place of
recycling. This was also scored highly on the basis that it would result in fewer vehicle
movements and on the assumption that this was an efficient method for energy production.
However, as mentioned above, the feasibility of installing a small thermal destruction process
needs to be assessed on a site-by-site basis to determine the most favoured option for each
site.
Composting and co-composting techniques were not favoured for this sub-region, largely due
to the poor access in this sub-region and the increased lorry movements associated with
having to import additional material into the sites e.g. straw/woodchips, as well as more
product leaving the site for recycling to land. This option also has no opportunity for the
generation of energy.
With respect to the 25-year period, the additional option of co-digestion followed by thermal
destruction should also be considered. This option, however, would be confined to those sites
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with reasonable access and able to accommodate the additional lorry movements and also
have to space on site to construct more digestion capacity – this would need to be
investigated before this option could be promoted.
6.10.4 Conclusions
• Processes that maximise extraction of energy and minimise lorry movements are the
most suitable
• Two options appear to be available to meet these criteria - both require
implementation of advanced digestion followed either by recycling to land or thermal
destruction on site.
• Landbank constraints suggest that on site treatment and application of a thermal
destruction process may be the favoured option in the longer term.
6.10.5 Recommended strategy
(a) 10 year
• Introduce enhanced digestion on all sites followed by recycling to land
• In the longer term, review land bank availability for the sub-region and, if
necessary, assess the feasibility of carrying out enhanced digestion followed
by thermal destruction.
(b) 25 year
• The installation of enhanced digestion possibly with co-digestion with
municipal waste followed by thermal destruction should additionally be
considered over the 25-year period.
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6.11 North London
6.11.1 Sludge Treatment Centres in Area
There are two sludge centres in this area; Deephams and Rye Meads. They are both large
works largely serving areas to the north of London. The sites operate conventional
wastewater treatment with sludge processing via anaerobic digestion with energy recovery
followed by recycling to agricultural land. The total current sludge production (2006) from
these sites is 44075 tds. Both sites operate CHP plants recovering 25.5 GWh in 2006/07.
6.11.2 Factors relevant to the assessment
Access to the sites is reasonable but with increasing congestion on all roads in the area,
processes that reduce sludge volume and hence minimise lorry movements in and out of the
sites are favoured. Techniques that require the movement of additional material on and off
site (e.g. composting, co-composting and co-digestion) are not favoured. These sites are
considered large enough to operate a thermal destruction process, if necessary, although a
more detailed feasibility study would be required for each of the sites should this option be
taken forward. Deephams is relatively close to the centre of London and, as expected, the
land bank assessment confirms that availability of agricultural land is constrained in this area.
However, Rye Meads is located in an area with good potential availability.
6.11.3 Summary of assessment
The preferred options for the 10-year horizon are based on processes that reduce sludge
volumes and maximise gas production potential. These processes include the application of
enhanced digestion (with thermal hydrolysis or acid phase digestion) followed by recycling to
land and (if necessary and technically feasible) installation of enhanced digestion (e.g.
thermal hydrolysis) followed by thermal destruction. These scored highly with respect to
maximising energy production, avoidance of landfill and minimising environmental impact.
One of the preferred options was utilising enhanced digestion (with thermal hydrolysis or acid
phase digestion) followed by recycling to land, largely because the process minimises the
sludge volume requiring further treatment. This results in fewer vehicle movements thus
easing congestion on the roads in the area and a reduction in the volume of sludge requiring
storage, which should help to reduce the potential for odour nuisance on-site. This option is
also the least likely to utilise disposal to landfill and maximises gas (energy) production thus
offsetting grid power use.
A favoured alternative would be to utilise digestion (with thermal hydrolysis hence maximising
gas production) followed by the application of a thermal destruction process on-site in place of
recycling. This was also scored highly on the basis that it would result in fewer vehicle
movements and on the assumption that this was an efficient method for energy production.
However, as mentioned above, the feasibility of installing a small thermal destruction process
needs to be assessed on a site-by-site basis to determine the most favoured option for each
site
Composting and co-composting techniques were not favoured for this sub-region, largely due
to the poor access to these sites and the increased lorry movements associated with having
to import additional material into the sites e.g. straw/woodchips, as well as more product
leaving the site for recycling to land. This option also has no opportunity for the generation of
renewable energy.
With respect to the 25-year period, the additional option of co-digestion followed by thermal
destruction should also be considered. This option, however, would be confined to those sites
with reasonable access and able to accommodate the additional lorry movements and also
have to space on site to construct more digestion capacity.
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6.11.4 Conclusions
• Processes that maximise extraction of energy and minimise lorry movements are the
most suitable
• Two options are available to meet these criteria - both require implementation of
advanced digestion followed either by recycling to land or thermal destruction on site.
• Land bank constraints at Deephams suggest that on site treatment and application of
a thermal destruction process may be the favoured option in the longer term.
6.11.6 Recommended strategy
(a) 10 year
• Introduce enhanced digestion on all sites followed by recycling to land
• In the longer term, review land bank availability for the sub-region and, if
necessary, assess the feasibility of carrying out enhanced digestion followed
by thermal destruction.
(b) 25 year
• The installation of enhanced digestion possibly with co-digestion with
municipal waste followed by thermal destruction should additionally be
considered over the 25-year period.
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6.12 North East Provinces
6.12.1 Sludge Treatment Centres in Area
There are two sludge centres in this area; Bishops Stortford and East Hyde (Luton). They are
medium sized works largely serving areas to the north of London. The sites operate
conventional wastewater treatment with sludge processing via anaerobic digestion followed
by recycling to agricultural land. The current sludge production (2006) from these sites is
7110 tds. Luton currently operates a CHP plant producing 1.8 GWh in 2006/07 and equivalent
plant is currently being installed at Bishops Stortford, due for completion during 2008.
6.12.2 Factors relevant to the assessment
Access to the sites is reasonable, although there is increasing congestion on all roads in the
area thus processes that minimise sludge volume and hence lorry movements in and out of
the site are favoured. Some of the sites also face increasing problems from encroachment,
thus odour issues are likely to become more important. Thus processes that minimise sludge
volume and hence minimise storage requirements are favoured. These sites may not be large
enough to operate a small thermal destruction process and a more detailed feasibility study
would be required for each of the sites should this option need to be taken forward. The land
bank assessment shows that availability is relatively good for both of these sites.
6.12.3 Summary of assessment
The preferred options for the 10-year period included the application of enhanced digestion
(with thermal hydrolysis or acid phase digestion) followed by recycling to land and (if
necessary and technically feasible) installation of enhanced digestion (e.g. thermal hydrolysis)
followed by thermal destruction. These scored highly with respect to maximising energy
production, avoidance of landfill and minimising environmental impact.
Enhanced digestion (with thermal hydrolysis or acid phase digestion), followed by recycling to
land, was favoured, largely because the process minimises the sludge volume requiring
further treatment. This results in fewer vehicle movements thus easing congestion on the
roads and a reduction in the volume of sludge requiring storage, which should help to reduce
the potential for odour nuisance on-site. This option is also the least likely to utilise disposal to
landfill and maximises gas (energy) production thus offsetting grid power use.
Digestion (with thermal hydrolysis hence maximising gas production) followed by the
application of a thermal destruction process was also favoured. This was on the basis that it
would result in fewer vehicle movements and the assumption that this was an efficient method
of energy production. However, the feasibility of installing small thermal destruction process
would need to be assessed on a site-by-site basis.
The implementation of processes requiring the movement of additional material on and off
site (e.g. composting and co-composting) were not favoured in the 10 year horizon due to the
increased lorry movements associated with having to import additional material into the sites
e.g. straw/woodchips and increasing congestion on all roads. In addition, the implementation
of a large-scale thermal destruction process by transporting sludge from several sites to a
central location was not favoured due to a range of nuisance, carbon footprint and
environmental impacts.
With respect to the 25-year period, the additional option of co-digestion followed by thermal
destruction should also be considered due to the opportunity to align with Local Authorities
waste strategies and thus avoiding the use of unsustainable and (anticipated) prohibitively
expensive landfill. This option, however, would be confined to those sites with reasonable
access and those able to accommodate the additional lorry movements and also have to
space on site to construct more digestion capacity. The impact of importing additional material
to site would need to be investigated before this option could be promoted.
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6.12.4 Conclusions
• Processes that maximise extraction of energy and minimise lorry movements are the
most suitable
• Two options meet these criteria. Both require implementation of advanced digestion
followed either by recycling to land or thermal destruction on site.
• Land availability is relatively good hence recycling to land is the favoured option.
6.12.5 Recommended strategy
(a) 10 year
• Introduce enhanced digestion on all sites followed by recycling to land
• In the longer term, review land bank availability for the sub-region and, if
necessary, assess the feasibility of carrying out enhanced digestion followed
by thermal destruction.
(b) 25 year
• The installation of enhanced digestion, possibly with co-digestion with
municipal waste, followed by recycling to land or thermal destruction
depending on land availability should additionally be considered over the 25-
year period.
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7. MAIN CONCLUSIONS
Although a detailed analysis has been carried out for each sub region and separate
conclusions have been drawn for each of these areas, a number of common themes and
trends are evident. The approach of carrying out separate assessment analyses for a 10 year
and 25 year horizon has also provided useful information in identifying trends over the longer
term.
The main conclusions are that processes that (a) maximise energy recovery and (b) minimise
sludge volumes are favoured. Where there is suitable land bank availability, utilising the
recycling to land outlet remains the preferred option. To protect this outlet, we anticipate
investing in sludge treatment to improve product quality e.g. reduced odour and dry solids.
However, in predominately urban areas, the use of thermal destruction processes with energy
recovery may be more appropriate, thus avoiding the increased environmental impact and
costs of transporting the treated sludge to land.
Further more detailed conclusions include:
• Processes that enable the efficient extraction of energy from sludge should be
adopted e.g. the installation of enhanced digestion or best practice thermal
destruction
• The minimisation of vehicle movements on and off sites is also an important factor in
identifying our preferred options. Reducing lorry movements will provide benefits in
minimising carbon footprint and environmental impacts through reducing fuel use and
reducing the potential for nuisance to our customers
• Techniques that minimise sludge volumes will also be adopted and this will provide
benefits through:
a. Reducing vehicle movements if the sludge is being recycled to land
b. Minimising the need to store sludge hence reducing the potential for odour
nuisance
• In addition, should we be required to find alternative disposal routes as recycling to
land becomes more restricted, then volumes for disposal will have to be minimised.
In the longer term, the benefits of carrying out co-digestion with other wastes are attractive
from the point of view of increasing energy production. However the potentially negative
impacts of increased traffic movements required to transport additional material on site and
the increased operational complexity would need to be assessed on a site-by-site basis.
10-year strategic recommendations
• Convert our main sludge treatment centres, where the primary disposal route is
recycling to land, to enhanced digestion to increase energy production and minimise
solids.
• Our preliminary view of sites that are projected for the installation of enhanced
digestion in the next 10 years include Banbury, Basingstoke, Beddington, Bracknell,
Camberley, Crawley, Didcot, East Hyde, Hogsmill, Little Marlow, Oxford, Riverside,
Swindon and Witney. However, this selection will be reviewed on the basis of more
detailed site specific assessments
• Although recycling to land remains our favoured option we plan to reduce our current
dependence on landbank in view of the potential constraints on this outlet. This will
be achieved in the short to medium term through solids reduction as a result of
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improvements to digestion and the impact this will have on our outlets is shown in
Figure 5.
Figure 5. Predicted Outlets for Sewage Sludge - 10 year recommendations *
1%
1%
Agriculture
42%
Thermal destruction with
energy recovery
Bioenergy crops
56%
Land Restoration
* There is anticipated to be a relative increase in the proportion of sludge being treated by the thermal destruction process
due to increase in sludge production in East London based on population growth including urban regeneration. The reduction
in the proportion of sludge recycled to land is as a result of solids reduction through enhanced digestion
• Provide additional sludge treatment capacity for our large East London treatment
works at Beckton and Crossness. This is likely to be additional thermal destruction
capacity with energy recovery to deal with population growth, plus refurbishment of
existing assets
• At the end of the 10 year period (2017/2018) we will undertake a further strategic
review of the current capacity of treatment/outlets employed, location and number of
sludge centres in the Region, in order to inform the next 15 year investment
programme
25-year strategic recommendations
• Our strategy for the period 2020-2035 will be informed by the outcome of the updated
strategic review and on assessment of landbank availability. However, it is anticipated
that our main proposal will be to:
o Maintain recycling to land where the landbank availability allows
o Introduce thermal destruction units with energy recovery at large urban sites
impacted by land-bank constraints
o Introduce co-digestion with municipal waste where capacity exists or it can be
deployed
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8. GLOSSARY
APD Acid Phase Digestion
Biosolids Treated sewage sludge. Product of treatment processes such as digestion,
dewatering, lime stabilisation.
BPEO Best Practicable Environmental Option
BRC British Retail Consortium. Trade Association representing a wide range of UK
retailers.
BSI PAS 100 Publicly Available Specification for compost materials.
CAP Common Agricultural Policy
Capex Capital expenditure
CC Climate Change
CCPs Critical Control Points – used in HACCP methodology
CHP Combined Heat and Power
DEFRA Department of the Environment, Food and Rural Affairs
Dewatering The process of reducing the water content within sludges; typically used to
describe the transition from liquid sludge to sludge cake.
DS Dry Solids content. The weight of dry solids per unit weight of sludge, expressed
as a percentage or as mg/kg.
EA The Environment Agency
EC European Commission
EDV Effective Digester Volumes
EEC European Economic Community
EIA Environmental Impact Assessment
EPA Environmental Protection Act
EPP Environmental Permitting Programme
EU European Union
EWC European Waste Catalogue
Gasification Gasification is the breakdown of hydrocarbons into a syngas by carefully
controlling the amount of oxygen present.
GHG Greenhouse Gas
HACCP Hazard Analysis Critical Control Point – identification and close monitoring of
CCPs throughout a treatment process to ensure the required quality standard is
met. Also widely used in food safety management.
IPPC Integrated Pollution Prevention and Control
LA Local Authority
Landbank The area of agricultural land available for recycling treated sewage sludge
MAD Mesophillic Anaerobic Digestion
MSW Municipal Solid Waste
MWh Megawatt hours
NVZ Nitrate Vulnerable Zone
Ofwat Economic regulator for the water industry.
OJEC Official Journal of the European Communities
Opex Operational expenditure
PE Population Equivalent
PPC Pollution Prevention and Control
PTEs Potentially Toxic Elements
Pyrolysis The thermal degradation of waste in the absence of air. Sludge is heated to a
high temperature in an oxygen-free atmosphere. Mainly used as a pre-treatment
step to gasification.
QA Quality Assurance
RCV Regulatory Capital Value
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ROCs Renewables Obligation Certificates
SEA Strategic Environmental Assessment
SFP Single Farm Payment
Sludge Sludge is produced as an unavoidable natural by-product of the processes used
in both wastewater treatment works and water treatment works, and comprises
the solids removed during the treatment processes
SOLAR Strategic Overview of Long-term Assets and Resources
SRC Short Rotation Coppice
SRF Secondary recovered fuel
SSM Safe Sludge Matrix – voluntary code identifying minimum acceptable levels of
treatment to microbiological standards for wastewater sludge products applied to
various agricultural crops, and application windows related to harvesting.
STC Sludge Treatment Centre – the final location at which sludge is prepared for reuse
or recycling.
STW Sewage Treatment Works
Syngas Synthetic gas
TDS Tonnes Dry Solid – the preferred unit of measurement for sludge.
THP Thermal Hydrolysis Process
TTQI Thames Tideway Quality Improvement project.
TWUL Thames Water Utilities Limited
UWWTD Urban Waste Water Treatment Directive
WAC Waste Acceptance Criteria
WID Waste Incineration Directive. Sets specific concentration limits for emissions,
operating conditions and monitoring requirements for facilities which combust
waste.
WML Waste Management Licensing
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APPENDICES
Appendix 1: Biosolids recycling to agriculture - The impact of exclusion clauses and other
restrictions on the agricultural landbank
Appendix 2: Business & Sustainability Assessments - graphs
Appendix 3: Business & Sustainability Assessments - scoring sheets
Appendix 4: Sensitivity Analysis
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Appendix 1
Biosolids recycling to agriculture: The impact of exclusion clauses and other
restrictions on the agricultural landbank
Investigation for Thames Water carried out by ADAS and Grieve Strategic.
October 2007
Summary
• Thames Water produces c.253,000 tonnes of sludge dry solids per year (2006 figure),
with c.61% (c.156,000 tonnes dry solids) recycled to agricultural land within and outside
the Thames region.
• Thames Water require an agricultural landbank of 20,000–25,000ha/annum (within and
outside the Thames Water region) to recycle its biosolids products. Presently Thames
Water uses c.14,000ha of land within the Thames region itself.
• The total agricultural landbank in the Thames Water region is c.670,000ha. The total
capacity for accepting biosolids in the Thames Water region, after accounting for existing
land use/physical constraints and the area already occupied by animal manures was
estimated to be c. 460,000ha.
• Current exclusion clauses for arable crops (malting barley, milling wheat and milling oats)
were estimated to reduce the landbank area by c.131,000ha, leaving an available area of
c.329,000ha. The geographical spread of available agricultural land within the Thames
Water region is illustrated in Figure 1.
• If in the future exclusion clauses were applied to all wheat, barley and oilseed rape crops
(which are the main crops used for biosolids recycling by Thames Water) the estimated
landbank remaining would be c.70,000ha. An illustration of how these potential exclusion
clauses could impact on the size of the agricultural land bank is shown in Figure 2.
Taking into account farmer acceptability and cropping constraints, such exclusion clause
introduction would lead to a total collapse of the agricultural landbank.
• We recommend that Thames Water (in collaboration with other Water Companies who
have participated in detailed landbank assessment work such as this) should form a
‘Biosolids Club’ and lobby government on the landbank impacts of exclusion clauses, and
to develop a positive public relations campaign.
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Figure 6. The available landbank for biosolids within the Thames Water region
under current exclusion clauses
N.B. Each grid square = 10,000 hectares
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Figure 7. Landbank assessments and the impact of current and potential arable
crop exclusion clauses
800000
700000
600000
500000
ha 400000
300000
200000
100000
0
Headline landbank Post ALOWANCE restrictions
Post current exclusions Post milling wheat exclusion
Post oilseed rape exclusion Post feed wheat/barley exclusion
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Appendix 2
Business and Sustainability Assessment Graphs
East London (Thermal Destruction) Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + APD + MAD + Pyrolysis, Thermal Composting Co- Co-digestion Enhanced Enhanced
digestion digestion digestion gasification destruction composting digestion + co-digestion
thermal + thermal
destruction destruction
10 year strategy 25 year strategy
East London (Digestion) Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + APD + MAD + Pyrolysis, Thermal Composting Co- Co-digestion Enhanced Enhanced co-
digestion digestion digestion gasification destruction composting digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Mogden Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + APD + MAD + Pyrolysis, Thermal Composting Co- Co-digestion Enhanced Enhanced co-
digestion digestion digestion gasification destruction composting digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
Maple Lodge Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + digestion APD + digestion MAD + Pyrolysis, Thermal Composting Co-composting Co-digestion Enhanced Enhanced co-
digestion gasification destruction digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Southern Region Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + digestion APD + digestion MAD + Pyrolysis, Thermal Composting Co-composting Co-digestion Enhanced Enhanced co-
digestion gasification destruction digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
Western Region (Digestion) Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + digestion APD + digestion MAD + Pyrolysis, Thermal Composting Co-composting Co-digestion Enhanced Enhanced co-
digestion gasification destruction digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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South-East Region (Lime) Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + digestion APD + digestion MAD + Pyrolysis, Thermal Composting Co-composting Co-digestion Enhanced Enhanced co-
digestion gasification destruction digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
Western Region (Lime) Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + digestion APD + digestion MAD + digestion Pyrolysis, Thermal Composting Co-composting Co-digestion Enhanced Enhanced co-
gasification destruction digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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West London (Digestion) Strategy
160
150
140
130
120
Option score
110
100
90
80
70
60
THP + digestion APD + digestion MAD + digestion Pyrolysis, Thermal Composting Co-composting Co-digestion Enhanced Enhanced co-
gasification destruction digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
North London Strategy
160
150
140
130
120
Option score
110
100
90
80
70
60
THP + digestion APD + digestion MAD + digestion Pyrolysis, Thermal Composting Co-composting Co-digestion Enhanced Enhanced co-
gasification destruction digestion + digestion +
thermal thermal
destruction destruction
10 year strategy 25 year strategy
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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North-East Provinces Strategy
150
140
130
120
Option score
110
100
90
80
70
60
THP + APD + MAD + Pyrolysis, Thermal Composting Co- Co-digestion Enhanced Enhanced
digestion digestion digestion gasification destruction composting digestion + co-digestion
thermal + thermal
destruction destruction
10 year strategy 25 year strategy
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Appendix 3
Business & Sustainability Assessments – 10 year scoring sheets
10 year strategy - E London (Thermal Destruction Sites)
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 5 20 4 16 3 12 2 8 1 4 0 0 0 2 8
RCV 3 3 9 2 6 1 3 4 12 5 15 0 0 0 3 9
Cost (Opex) 2 2 4 1 2 1 2 4 8 4 8 0 0 0 5 10
Ease of Promotion 3 2 6 2 6 1 3 4 12 4 12 0 0 0 5 15
Minimise customer impacts 5 1 5 1 5 1 5 4 20 5 25 0 0 0 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 1 5 0 0 0 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 3 12 0 0 0 3 12
Minimise carbon foot print 4 2 8 2 8 1 4 5 20 4 16 0 0 0 5 20
Minimise environ impacts 3 1 3 1 3 1 3 5 15 5 15 0 0 0 5 15
Overall 100 86 67 119 112 0 0 0 139
10 year strategy - E London digestion
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 4 16 5 20 3 12 3 12 1 4 3 12 2 8 3 12 2 8
RCV 3 2 6 1 3 3 9 4 12 5 15 1 3 3 9 3 9 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 2 4
Ease of Promotion 3 3 9 5 15 3 9 3 9 1 3 4 12 4 12 5 15 3 9
Minimise customer impacts 5 3 15 3 15 3 15 4 20 4 20 2 10 1 5 2 10 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 3 12 5 20 5 20 5 20 4 16
Minimise carbon foot print 4 4 16 3 12 2 8 4 16 3 12 2 8 1 4 3 12 5 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 5 15 1 3 1 3 3 9 5 15
Overall 129 122 103 112 93 75 68 113 137
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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10 year strategy - Mogden (West London)
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 4 16 5 20 3 12 3 12 0 0 0 3 12 1 4
RCV 3 2 6 1 3 3 9 4 12 0 0 0 3 9 5 15
Cost (Opex) 2 5 10 4 8 3 6 1 2 0 0 0 3 6 1 2
Ease of Promotion 3 3 9 4 12 3 9 3 9 0 0 0 1 3 5 15
Minimise customer impacts 5 3 15 3 15 3 15 5 25 0 0 0 1 5 5 25
Maximise energy production 5 5 25 3 15 1 5 4 20 0 0 0 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 0 0 0 5 20 3 12
Minimise carbon foot print 4 4 16 2 8 1 4 4 16 0 0 0 2 8 5 20
Minimise environ impacts 3 4 12 2 6 1 3 5 15 0 0 0 3 9 5 15
Overall 129 107 83 115 0 0 0 92 133
10 year strategy - Maple Lodge
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 4 16 5 20 3 12 3 12 1 4 3 12 2 8 3 12 2 8
RCV 3 2 6 1 3 3 9 4 12 5 15 1 3 3 9 3 9 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 2 4
Ease of Promotion 3 3 9 5 15 3 9 3 9 1 3 4 12 4 12 5 15 3 9
Minimise customer impacts 5 3 15 3 15 3 15 4 20 4 20 2 10 1 5 2 10 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 3 12 5 20 5 20 5 20 4 16
Minimise carbon foot print 4 4 16 3 12 2 8 4 16 3 12 2 8 1 4 3 12 5 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 5 15 1 3 1 3 3 9 5 15
Overall 129 122 103 112 93 75 68 113 137
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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10 year strategy - Southern digestion sites
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 4 16 5 20 3 12 2 8 1 4 2 8 2 8 2 8 2 8
RCV 3 2 6 1 3 3 9 5 15 5 15 3 9 3 9 3 9 4 12
Cost (Opex) 2 5 10 3 6 2 4 2 4 1 2 1 2 1 2 3 6 4 8
Ease of Promotion 3 3 9 4 12 3 9 3 9 1 3 4 12 5 15 4 12 2 6
Minimise customer impacts 5 4 20 3 15 3 15 3 15 1 5 1 5 1 5 2 10 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 3 12 5 20 5 20 5 20 3 12
Minimise carbon foot print 4 4 16 2 8 1 4 4 16 2 8 1 4 1 4 1 4 5 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 1 3 1 3 2 6 5 15
Overall 134 113 97 106 65 68 71 95 131
10 year strategy - Western digestion sites
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 4 16 5 20 3 12 2 8 1 4 2 8 2 8 2 8 2 8
RCV 3 2 6 1 3 3 9 5 15 5 15 3 9 3 9 3 9 4 12
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 3 6
Ease of Promotion 3 3 9 4 12 3 9 3 9 1 3 4 12 5 15 4 12 2 6
Minimise customer impacts 5 4 20 3 15 3 15 3 15 1 5 1 5 1 5 2 10 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 2 8 5 20 5 20 5 20 2 8
Minimise carbon foot print 4 4 16 2 8 1 4 4 16 2 8 1 4 1 4 1 4 5 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 2 6 1 3 3 9 5 15
Overall 134 115 99 106 61 71 71 98 125
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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10 year strategy - South East Region (lime)
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 3 12 4 16 5 20 2 8 1 4 3 12 2 8 3 12 1 4
RCV 3 3 9 2 6 2 6 5 15 5 15 1 3 2 6 3 9 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 3 6
Ease of Promotion 3 4 12 4 12 3 9 3 9 1 3 4 12 4 12 5 15 1 3
Minimise customer impacts 5 4 20 3 15 3 15 3 15 1 5 1 5 1 5 2 10 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 3 12 5 20 5 20 5 20 3 12
Minimise carbon foot print 4 3 12 2 8 1 4 4 16 2 8 1 4 1 4 1 4 5 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 1 3 1 3 3 9 5 15
Overall 132 114 104 106 65 66 65 105 125
10 year strategy - Western Region Lime Sites
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 3 12 4 16 5 20 2 8 1 4 2 8 1 4 4 16 0
RCV 3 3 9 2 6 1 3 5 15 5 15 3 9 3 9 3 9 0
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 0
Ease of Promotion 3 3 9 4 12 3 9 3 9 1 3 4 12 5 15 4 12 0
Minimise customer impacts 5 5 25 4 20 3 15 3 15 1 5 1 5 1 5 2 10 0
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 0
Avoid landfill 4 5 20 5 20 5 20 1 4 3 12 5 20 5 20 5 20 0
Minimise carbon foot print 4 3 12 2 8 1 4 5 20 2 8 1 4 1 4 3 12 0
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 2 6 1 3 3 9 0
Overall 134 119 101 110 65 71 67 114 0
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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10 year strategy - West London Digestion
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 4 16 5 20 3 12 3 12 1 4 3 12 2 8 3 12 2 8
RCV 3 2 6 1 3 3 9 4 12 5 15 1 3 3 9 3 9 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 2 4
Ease of Promotion 3 3 9 5 15 3 9 3 9 1 3 4 12 4 12 5 15 3 9
Minimise customer impacts 5 3 15 3 15 3 15 4 20 4 20 2 10 1 5 2 10 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 3 12 5 20 5 20 5 20 4 16
Minimise carbon foot print 4 4 16 3 12 2 8 4 16 3 12 2 8 1 4 3 12 5 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 5 15 1 3 1 3 3 9 5 15
Overall 129 122 103 112 93 75 68 113 137
10 year strategy - N London digestion
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 4 16 5 20 3 12 3 12 1 4 3 12 2 8 3 12 2 8
RCV 3 2 6 1 3 3 9 4 12 5 15 1 3 3 9 3 9 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 2 4
Ease of Promotion 3 3 9 5 15 3 9 3 9 1 3 4 12 4 12 5 15 3 9
Minimise customer impacts 5 3 15 3 15 3 15 4 20 4 20 2 10 1 5 2 10 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 3 12 5 20 5 20 5 20 4 16
Minimise carbon foot print 4 4 16 3 12 2 8 4 16 3 12 2 8 1 4 3 12 5 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 5 15 1 3 1 3 3 9 5 15
Overall 129 122 103 112 93 75 68 113 137
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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10 year strategy - NE Provinces digestion sites
Business Driver weight THP APD MAD Pyrolysis, Thermal Composting Co-composting Co-digestion Digestion +
gasification destruction thermal
destruction
score total score total score total score total score total score total score total score total score total
Cost £M/ton 4 4 16 5 20 3 12 2 8 1 4 2 8 2 8 2 8 2 8
RCV 3 2 6 1 3 3 9 5 15 5 15 3 9 3 9 3 9 4 12
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 3 6
Ease of Promotion 3 3 9 4 12 3 9 3 9 1 3 4 12 5 15 4 12 2 6
Minimise customer impacts 5 4 20 3 15 3 15 3 15 1 5 1 5 1 5 2 10 5 25
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25
Avoid landfill 4 5 20 5 20 5 20 1 4 2 8 5 20 5 20 5 20 2 8
Minimise carbon foot print 4 4 16 2 8 1 4 4 16 2 8 1 4 1 4 1 4 5 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 2 6 1 3 3 9 5 15
Overall 134 115 99 106 61 71 71 98 125
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Business & Sustainability Assessments – 25 year scoring sheets
25 year strategy - E London incineration
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 5 20 4 16 3 12 2 8 1 4 0 0 0 2 8 2 8
RCV 3 3 9 2 6 1 3 4 12 5 15 0 0 0 3 9 5 15
Cost (Opex) 2 2 4 1 2 1 2 4 8 4 8 0 0 0 5 10 3 6
Ease of Promotion 3 2 6 2 6 1 3 4 12 4 12 0 0 0 5 15 4 12
Minimise customer impacts 5 1 5 1 5 1 5 4 20 5 25 0 0 0 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 1 5 0 0 0 4 20 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 3 15 0 0 0 3 15 4 20
Minimise carbon foot print 5 2 10 2 10 1 5 4 20 3 15 0 0 0 5 25 4 20
Minimise environ impacts 3 1 3 1 3 1 3 5 15 5 15 0 0 0 5 15 4 12
Overall 107 93 73 120 114 0 0 0 142 138
25 year strategy - E London Digestion
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 4 16 5 20 3 12 3 12 1 4 3 12 2 8 3 12 2 8 2 8
RCV 3 2 6 1 3 3 9 4 12 5 15 1 3 3 9 3 9 5 15 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 2 4 3 6
Ease of Promotion 3 3 9 5 15 3 9 3 9 1 3 4 12 4 12 5 15 3 9 4 12
Minimise customer impacts 5 3 15 3 15 3 15 4 20 4 20 2 10 1 5 2 10 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 4 20 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 3 15 5 25 5 25 5 25 4 20 4 20
Minimise carbon foot print 5 4 20 3 15 2 10 4 20 3 15 2 10 1 5 3 15 5 25 4 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 5 15 1 3 1 3 3 9 5 15 4 12
Overall 138 130 110 117 99 82 74 121 141 138
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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25 year strategy - Mogden (West London)
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 4 16 5 20 3 12 3 12 0 0 0 3 12 1 4 2 8
RCV 3 2 6 1 3 3 9 4 12 0 0 0 3 9 5 15 5 15
Cost (Opex) 2 5 10 4 8 3 6 1 2 0 0 0 3 6 1 2 3 6
Ease of Promotion 3 3 9 4 12 3 9 3 9 0 0 0 1 3 5 15 4 12
Minimise customer impacts 5 3 15 3 15 3 15 5 25 0 0 0 1 5 5 25 4 20
Maximise energy production 5 5 25 3 15 1 5 4 20 0 0 0 4 20 5 25 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 0 0 0 5 25 3 15 4 20
Minimise carbon foot print 5 4 20 2 10 1 5 4 20 0 0 0 2 10 5 25 4 20
Minimise environ impacts 3 4 12 2 6 1 3 5 15 0 0 0 3 9 5 15 4 12
Overall 138 114 89 120 0 0 0 99 141 138
25 year strategy - Maple Lodge
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 4 16 5 20 3 12 3 12 1 4 3 12 2 8 3 12 2 8 2 8
RCV 3 2 6 1 3 3 9 4 12 5 15 1 3 3 9 3 9 5 15 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 2 4 3 6
Ease of Promotion 3 3 9 5 15 3 9 3 9 1 3 4 12 4 12 5 15 3 9 4 12
Minimise customer impacts 5 3 15 3 15 3 15 4 20 4 20 2 10 1 5 2 10 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 4 20 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 3 15 5 25 5 25 5 25 4 20 4 20
Minimise carbon foot print 5 4 20 3 15 2 10 4 20 3 15 2 10 1 5 3 15 5 25 4 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 5 15 1 3 1 3 3 9 5 15 4 12
Overall 138 130 110 117 99 82 74 121 141 138
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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25 year strategy - Southern digestion sites
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 4 16 5 20 3 12 2 8 1 4 2 8 2 8 2 8 2 8 2 8
RCV 3 2 6 1 3 3 9 5 15 5 15 3 9 3 9 3 9 4 12 5 15
Cost (Opex) 2 5 10 3 6 2 4 2 4 1 2 1 2 1 2 3 6 4 8 3 6
Ease of Promotion 3 3 9 4 12 3 9 3 9 1 3 4 12 5 15 4 12 2 6 4 12
Minimise customer impacts 5 4 20 3 15 3 15 3 15 1 5 1 5 1 5 2 10 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 3 15 5 25 5 25 5 25 3 15 4 20
Minimise carbon foot print 5 4 20 2 10 1 5 4 20 2 10 1 5 1 5 1 5 5 25 4 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 1 3 1 3 2 6 5 15 4 12
Overall 143 120 103 111 70 74 77 101 139 138
25 year strategy - Western Digestion Sites
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 4 16 5 20 3 12 2 8 1 4 2 8 2 8 2 8 2 8 2 8
RCV 3 2 6 1 3 3 9 5 15 5 15 3 9 3 9 3 9 4 12 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 3 6 3 6
Ease of Promotion 3 3 9 4 12 3 9 3 9 1 3 4 12 5 15 4 12 2 6 4 12
Minimise customer impacts 5 4 20 3 15 3 15 3 15 1 5 1 5 1 5 2 10 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 2 10 5 25 5 25 5 25 2 10 4 20
Minimise carbon foot print 5 4 20 2 10 1 5 4 20 2 10 1 5 1 5 1 5 5 25 4 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 2 6 1 3 3 9 5 15 4 12
Overall 143 122 105 111 65 77 77 104 132 138
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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25 year strategy - South East Region (Lime)
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 3 12 4 16 5 20 2 8 1 4 3 12 2 8 3 12 1 4 2 8
RCV 3 3 9 2 6 2 6 5 15 5 15 1 3 2 6 3 9 5 15 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 3 6 3 6
Ease of Promotion 3 4 12 4 12 3 9 3 9 1 3 4 12 4 12 5 15 1 3 4 12
Minimise customer im pacts 5 4 20 3 15 3 15 3 15 1 5 1 5 1 5 2 10 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 3 15 5 25 5 25 5 25 3 15 4 20
Minimise carbon foot print 5 3 15 2 10 1 5 4 20 2 10 1 5 1 5 1 5 5 25 4 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 1 3 1 3 3 9 5 15 5 15
Overall 140 121 110 111 70 72 71 111 133 141
25 year strategy - Western Region (lime) Sites
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal
gasification destruction Co-digestion +
thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 3 12 4 16 5 20 2 8 1 4 2 8 1 4 4 16 0 0
RCV 3 3 9 2 6 1 3 5 15 5 15 3 9 3 9 3 9 0 0
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 0 0
Ease of Promotion 3 3 9 4 12 3 9 3 9 1 3 4 12 5 15 4 12 0 0
Minimise customer impacts 5 5 25 4 20 3 15 3 15 1 5 1 5 1 5 2 10 0 0
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 0 0
Avoid landfill 5 5 25 5 25 5 25 1 5 2 10 5 25 5 25 5 25 0 0
Minimise carbon foot print 5 3 15 2 10 1 5 4 20 2 10 1 5 1 5 3 15 0 0
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 2 6 1 3 3 9 0 0
Overall 142 126 107 111 65 77 73 122 0 0
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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25 year strategy - West London digestion
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 4 16 5 20 3 12 3 12 1 4 3 12 2 8 3 12 2 8 2 8
RCV 3 2 6 1 3 3 9 4 12 5 15 1 3 3 9 3 9 5 15 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 2 4 3 6
Ease of Promotion 3 3 9 5 15 3 9 3 9 1 3 4 12 4 12 5 15 3 9 4 12
Minimise customer impacts 5 3 15 3 15 3 15 4 20 4 20 2 10 1 5 2 10 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 3 15 5 25 5 25 5 25 4 20 4 20
Minimise carbon foot print 5 4 20 3 15 2 10 4 20 3 15 2 10 1 5 3 15 5 25 4 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 5 15 1 3 1 3 3 9 5 15 4 12
Overall 138 130 110 117 99 82 74 121 146 138
25 year Strategy - N London (digestion)
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 4 16 5 20 3 12 3 12 1 4 3 12 2 8 3 12 2 8 2 8
RCV 3 2 6 1 3 3 9 4 12 5 15 1 3 3 9 3 9 5 15 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 2 4 3 6
Ease of Promotion 3 3 9 5 15 3 9 3 9 1 3 4 12 4 12 5 15 3 9 4 12
Minimise customer impacts 5 3 15 3 15 3 15 4 20 4 20 2 10 1 5 2 10 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 3 15 5 25 5 25 5 25 4 20 4 20
Minimise carbon foot print 5 4 20 3 15 2 10 4 20 3 15 2 10 1 5 3 15 5 25 4 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 5 15 1 3 1 3 3 9 5 15 4 12
Overall 138 130 110 117 99 82 74 121 146 138
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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25 year strategy - NE Provinces (digestion sites)
Business Driver weight THP APD MAD Pyrolysis, Thermal destruction Composting Co-composting Co-digestion Digestion + thermal Co-digestion +
gasification destruction thermal destruction
score total score total score total score total score total score total score total score total score total score total
Cost (capex) £M/tonne 4 4 16 5 20 3 12 2 8 1 4 2 8 2 8 2 8 2 8 2 8
RCV 3 2 6 1 3 3 9 5 15 5 15 3 9 3 9 3 9 4 12 5 15
Cost (Opex) 2 5 10 4 8 3 6 2 4 1 2 1 2 1 2 3 6 3 6 3 6
Ease of Promotion 3 3 9 4 12 3 9 3 9 1 3 4 12 5 15 4 12 2 6 4 12
Minimise customer impacts 5 4 20 3 15 3 15 3 15 1 5 1 5 1 5 2 10 5 25 4 20
Maximise energy production 5 5 25 4 20 3 15 4 20 2 10 1 5 1 5 4 20 5 25 5 25
Avoid landfill 5 5 25 5 25 5 25 1 5 2 10 5 25 5 25 5 25 2 10 4 20
Minimise carbon foot print 5 4 20 2 10 1 5 4 20 2 10 1 5 1 5 1 5 5 25 4 20
Minimise environ impacts 3 4 12 3 9 3 9 5 15 2 6 2 6 1 3 3 9 5 15 4 12
Overall 143 122 105 111 65 77 77 104 132 138
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Appendix 4
Sensitivity Analysis
In order to test the robustness of the original options assessment methodology it was agreed
to undertake a sensitivity analysis of the weightings given to certain business drivers. In the
original options assessment, a weighting was applied to each business driver according to
significance as determined from meetings with Thames Water Senior Managers and Directors
including representatives from Entec.
The sensitivity analysis has involved the following changes to the original weightings as a
double check that the accepted methodological approach is fit for purpose (i.e. able to ensure
that changes to the weightings are ‘real’ and not distorted by the ranking process):
• Option 1 - Change the weighting for the driver 'maximise energy production' from '5'
to '4' ' for the 10-year horizon. This was on the basis that the weighting should take
into account that the need to reduce energy use would become greater for the 25-
year horizon. This resulted in no change to the preferred options for each sub region.
• Option 2 - Change the weighting for the driver 'Cost (Opex)' from '2' to '3' for the 10-
year horizon. This was changed to reflect a different perspective within the business
that the day-to-day operating costs should have been given more importance. This
resulted in no change to the preferred options in each sub regions with the exception
of Mogden as shown in Table 3.
• Option 3 - Change the weighting for the driver 'Cost (Opex)' from '2' to '3' for the 25
year horizon, as per the reasons above. This resulted in no change to the preferred
options for many of the regions with the exception of the sites detailed in Table 4
where the order of the options changed.
• Option 4 - Change the weighting for the driver 'minimise environmental impacts' from
'3' to '4' for the 10-year horizon. This reflects a view that more importance should be
placed on minimising impacts beyond regulatory compliance. Again, this resulted in
no change to the preferred options for all regions.
• Option 5 - Change the weighting for the driver 'minimise environmental impacts' from
'3' to '4' for the 25-year horizon, as per the reasons above. Again this resulted in no
change to the preferred options for many regions with the exception of those given in
Table 4 where the order of the options changed.
Table 3. Summary of changes to the preferred options - 10-year horizon
Region Original (10 yr) Option 2 (10 yr)
Mogden 1. Digestion with thermal 1. Digestion with thermal
destruction destruction / THP
2. THP 2. Pyrolysis, gasification
3. Pyrolysis, gasification
Table 4. Summary of changes to the preferred options - 25-year horizon
Region Original (25 yr) Option 3 (25 yr) Option 5 (25 yr)
Mogden 1. Digestion with thermal 1. Digestion with thermal 1. Digestion with thermal
destruction destruction destruction
2. Enhanced co-digestion 2. THP 2. Enhanced co-digestion
with thermal destruction with thermal destruction /
3. Enhanced co-digestion THP
3. THP with thermal destruction
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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Region Original (25 yr) Option 3 (25 yr) Option 5 (25 yr)
Maple Lodge 1. Digestion with thermal 1. Digestion with thermal 1. Digestion with thermal
destruction destruction / THP destruction
2. Enhanced co-digestion 2. Enhanced co-digestion 2. Enhanced co-digestion
with thermal destruction with thermal destruction with thermal destruction /
THP
3. THP
Southern Region 1. THP 1. THP 1. THP
(digestion)
2. Digestion with thermal 2. Digestion with thermal 2. Digestion with thermal
destruction / enhanced co- destruction destruction
digestion with thermal
destruction 3. Enhanced co-digestion 3. Enhanced co-digestion
with thermal destruction with thermal destruction
South East Region 1. Enhanced co-digestion 1. THP
(lime) with thermal destruction
2. Enhanced co-digestion No change
2. THP with thermal destruction
2. Digestion with thermal 3. Digestion with thermal
destruction destruction
West London 1. Digestion with thermal 1. Digestion with thermal 1. Digestion with thermal
destruction destruction destruction
2. Enhanced co-digestion 2. THP 2. Enhanced co-digestion
with thermal destruction with thermal destruction /
3. Enhanced co-digestion THP
3. THP with thermal destruction
North London 1. Digestion with thermal 1. Digestion with thermal 1. Digestion with thermal
destruction destruction destruction
2. Enhanced co-digestion 2. THP 2. Enhanced co-digestion
with thermal destruction with thermal destruction /
3. Enhanced co-digestion THP
3. THP with thermal destruction
East London 1. Digestion with thermal 1. Digestion with thermal 1. Digestion with thermal
(digestion) destruction destruction / THP destruction
2. Enhanced co-digestion 2. Enhanced co-digestion 2. Enhanced co-digestion
with thermal destruction with thermal destruction with thermal destruction /
THP
3. THP
The sensitivity analysis has shown that in spite of rescoring the weightings given to selected
business drivers the overall preference for the original options is largely unchanged and only
some change to the order of options has occurred.
Thames Water Utilities Draft Strategic Proposals for Sludge Management
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