VIEWS: 320 PAGES: 95



                          S.M.S.M.K Samarakoon

         A thesis submitted in partial fulfillment of the requirements for the
                          degree of Master of Engineering

     Examination Committee:    Prof. C. Visvanathan (Chairperson)
                               Prof. Nguyen Cong Thanh
                               Dr. Preeda Parkipan

                 Nationality: Sri Lankan
            Previous Degree: Bachelor of Science in Civil Engineering
                              University of Peradeniya
                              Sri Lanka.

         Scholarship Donor: The Government of Netherlands

                       Asian Institute of Technology
            School of Environment, Resources and Development
                                 May 2005


The author first wishes to express her profound gratitude, deepest respect and sincerest
appreciation to her advisor Prof. C. Visvanathan for his persistent guidance, precious
suggestions, encouragement and friendly discussions, all of which enable to accomplish
her study.

Author extends her wishes to examination committee members, Prof. N. C Thanh and Dr.
Preeda Parkpian for their valuable advices, comments, suggestions and encouragement
throughout the thesis work. Author specially offers her sincere appreciation and gratitude
to Dr. Ken Fukushi, counter part of EEM – SACWET project, University of Tokyo, Japan,
providing her technical and financial support for the experimental work.

Sincere appreciation is extended to Royal Netherlands Government for awarding a
scholarship and research fund during Master’s program in AIT.

Author continues her sincere thanks to lab supervisors, Kun Salaya and Kun Tin Win,
technician, Kun Tam for their assistance and cooperation during research period.

Author is grateful to doctoral student Ms. Kwannate and all other advisees of Prof. C.
Visvanathan for their valuable and critical suggestions and discussions.

Finally, the author dedicates this small piece of work to her beloved father, mother,
husband and sisters, especially, her best friend, S.K Weragoda whose unceasing support,
encouragement and scarifies made her success in this effort.


Most of the existing decentralized wastewater treatment options have been mainly
developed based on the septic tank concept. Extensive use of this technology is not
currently advocated in urban and peri-urban areas due to its unsolved deficiencies. This
research study was mainly focused on the incorporation of aerobic membrane bioreactor to
overcome deficiencies. The use of the new concepts of ecological sanitation with this
system helps to solve problems related to nitrogen introducing urine separation toilets.
Furthermore, scarcity of water in the urban centers leads to reuse of membrane based
treated wastewater for secondary purposes.

The experiment was designed for the treatment of domestic wastewater on a laboratory
scale using aerobic MBR. In this study, domestic wastewater and organic fraction of
kitchen waste were combined prior to the treatment. It could be found that the retained
kitchen waste combined with wasted sludge led to have methane production potential as
400 NmL CH4/ 1 g VS.

Aerobic MBR was operated with 10 g/L of MLSS concentration and average 650 mg/L of
influent COD. Experimental runs were investigated for HRT 2, 4 and 6 hours. It was noted
that regardless of HRT, COD removal efficiencies were more than 98 %. Besides to that 95
% of TKN removal efficiency could be achieved, when the system was running for HRT 4
hours .Similarly, in terms of total phosphorous removal efficiency HRT 4 hours provided
the removal of 93%. Furthermore, effluent water quality of each run was compared with
standards and effluent from HRT 4 hours was more potential to reuse.

The main issue faced in this experiment was the faster clogging of the membrane. It was
found that in HRT 6, 4 and 2 hours membrane was clogged after 19,17 and 5 days of
operation, respectively. In addition to that, sludge characteristics were measured in terms
of EPS, SVI and CST. It could be clearly seen that there was significant increase in
bounded protein while moving to HRT 2 hours and under that condition, faster fouling
was observed. In order to diminish fouling problem, coupling and attached growth system
with MBR was investigated, which gave promising results.

                                 Table of Contents

Chapter   Title                                                             Page

          Title Page                                                             i
          Acknowledgements                                                      ii
          Abstract                                                            iii
          Table of Contents                                                    iv
          List of Tables                                                      vii
          List of Figures                                                    viii
          List of Abbreviation                                                 ix

1         Introduction                                                          1
          1.1 Background                                                        1
          1.2 Objectives                                                        2
          1.3 Scope                                                             2

2         Literature Review                                                    3
          2.1 Introduction                                                     3
                  2.1.1 General                                                3
                  2.1.2 Domestic wastewater                                    3
                  2.1.3 Solid waste                                            5
                  2.1.4 Centralized wastewater treatment system                6
                  2.1.5 Decentralized wastewater system                        7
                  2.1.6 Comparison of on-site verses off-site                  7
          2.2 Onsite wastewater treatment options                              8
                  2.2.1 Technology options                                     8
                  2.2.2 Management of onsite wastewater treatment             10
                  2.2.3 Problems of existing on-site wastewater               11
                        management programs
                  2.2.4 Strategies for on-site wastewater treatment           12
          2.3 Ecological sanitation                                           13
                  2.3.1 Concept and methodologies used                        15
                  2.3.2 Urine separation and different treatment concept      15
          2.4 On-site treatment processes and systems                         17
                  2.4.1 Septic tanks                                          17
                  2.4.2 Imhoff tank                                           18
                  2.4.3 Intermittent sand filters                             19
                  2.4.4 Nutrient treatment unit                               20
                  2.4.5 Disinfection units                                    21
                  2.4.6 Aerobic Treatment Units                               22
                  2.4.7 New technologies for on-site wastewater treatment     22
                  2.4.8 Nutrient removal in MBR                               26
                  2.4.9 Energy requirement for MBR process                    27
                  2.4.10Recent development in MBR for wastewater              28
                  2.4.11 Wastewater reuse                                     29

3   Methodology                                                    30
    3.1 Introduction                                               30
    3.2 Preparation of synthetic wastewater                        30
    3.3 Kitchen waste                                              30
    3.4 Activated sludge                                           31
    3.5 Lab-scale experimental study                               31
           3.5.1 Acclimatization of biomass                        32
           3.5.2 Experimental set-up                               32
           3.5.3 Optimum HRT and sludge characteristics            34
           3.5.4 Experimental runs                                 34
           3.5.5 Analytical analysis                               35
    3.6 Membrane cleaning                                          36
           3.6.1 Membrane resistance                               36
    3.7 Sludge settling                                            37
           3.7.1 DSVI                                              37
    3.8 Sludge dewatering                                          37
    3.9 Extra Cellular Polymer Substances                          37
           3.9.1 Measurement of EPS                                37
    3.10 Biological methane production test (BMP)                  38
           3.10.1 Materials needed to conduct BMP test             38
           3.10.2 BMP test procedure                               39
    3.11 Initial study on minimizing fouling                       39
           3.11.1 Overall experiment                               40
           3.11.2 Experimental set up                              40
           3.11.4 Process description                              41

4   Results and Discussion                                         42
    4.1 Initial membrane resistance                                42
    4.2 MLSS and MLVSS variation                                   42
    4.3 Hydraulic retention time                                   43
    4.4 Transmembrane pressure                                     43
    4.5 Sludge characteristics                                     45
    4.6 Dissolved oxygen and pH                                    46
           4.6.1 DO variation                                      46
           4.6.2 pH and temperature variation                      47
    4.7 Removal of organic matter, nitrogen and phosphorus         47
           4.7.1 Organic removal                                   47
           4.7.2 Nitrogen removal                                  48
           4.7.3 Total phosphorous removal                         51
    4.8 Effluent nitrate and nitrite                               51
    4.9 Comparison of effluent quality with standard               52
    4.10 Incorporation of moving media to the system to minimize   53
           4.10.1 TMP variation                                    54
           4.10.3 Removal efficiency                               55
           4.10.4 DO and pH variation                              55
    4.11 Proposed treatment unit design                            55
    4.12 Methane production potential of solid waste               56

5   Conclusions and Recommendations                                59

5.1 Conclusions                         59
5.2 Recommendation for future studies   60

References                              61

Appendix A                              66
Appendix B                              69
Appendix C                              71
Appendix D                              73
Appendix E                              77
Appendix F                              84

                                List of Tables

Table   Title                                                           Page

2.1     Residential water uses by activity for an average five-person      4
2.2     Characteristic of typical residential wastewater                   5
2.3     Percentage of food waste in solid waste in three Asian             6
2.4     Treatment options for domestic wastewater in decentralized         9
        sanitation concepts
2.5     Advantages and disadvantages of ecosanitation                     15
2.6     Pros and cons of aerobic units                                    22
2.7     Advantages and disadvantages of MBR configurations                24
2.8     Characteristics and operating conditions of aerobic MBR           26
2.9     Energy consumption in different MBR systems                       27
2.10    Three generation of MBR design criterion                          28
2.11    Water quality parameters of concern for water reuse               29
2.12    Water reuse options and limitations in Australia                  29
3.1     Composition of synthetic wastewater                               30
3.2     Daily requirement of kitchen waste                                31
3.3     Characteristics of MBR                                            32
3.4     Permeate Flux at different HRTs                                   34
3.5     Analysis of various parameters                                    35
3.6     Frequency of analysis                                             35
4.1     Sludge characteristics                                            45
4.2     Effluent characteristics                                          53
4.3     Initial membrane resistance                                       54
4.4     Technical data                                                    56

                               List of Figures

Figure   Title                                                        Page

2.1      Range of possible sources of household wastewater showing       3
2.2      Wastewater flow pattern in Single household (USEPA, 2002)       4
2.3      Per capita municipal solid waste variations                     5
         (Visvanathan and Trankler, 2004)
2.4      Management of OWTS                                             10
2.5      Schematic of Decentralized user with membrane-based water      11
         and wastewater treatment connected telemetrically to
         centralized management unit
2.6      Onsite system design strategy                                  12
2.7      The options in a fully functional ecosan household             14
2.8      The sewerage system used in Bjorsbyn, Northern Sweden          16
         (Hanaeus et al, 1997)
2.9      Main components of conventional septic tank system             17
2.10     Cross section of an Imhoff tank                                19
2.11     Schematic of typical IFS                                       20
2.12     Generic disinfection diagram                                   21
2.13     MBR configurations                                             23
3.1      Overall experiments                                            31
3.2      Batch system                                                   32
3.3      Continuous system                                              33
3.4      Loading rate variation in three runs                           34
3.5      Thermal extraction method                                      38
3.6      Overall experiments                                            40
3.7      Experimental set up                                            41
4.1      MLSS and MLVSS variation in MBR                                42
4.2      MLSS and MLVSS variation in Anoxic tank                        43
4.3      TMP variation in Run 1(HRT = 6 hours)                          44
4.4      TMP variation in Run 2(HRT = 4 hours)                          44
4.5      TMP variation in Run 3(HRT = 2 hours)                          44
4.6      Days for clogging                                              45
4.7      Variation of EPS in three runs                                 46
4.8      Variation of DO in MBR and Anoxic tank                         47
4.9      Variation of COD removal efficiency, influent and effluent     48
         COD concentration
4.10     TKN variation in three runs                                    49
4.11     Schematic diagram for Nitrogen balance                         50
4.12     Nitrogen mass balance                                          50
4.13     Total phosphorous variation in three runs                      51
4.14     Variation of nitrate and nitrite                               51
4.15     Variation of TMP in attached growth reactor and suspended      54
         growth reactor
4.16     Variation of bounded EPS in the system                         55
4.17     Schematic diagram of proposed unit                             56
4.18     Cumulative methane production in kitchen waste                 57

                                   List of Abbreviations

AIT        Asian Institute of Technology
BMP        Biological Methane Production Potential
BOD5       Biochemical Oxygen Demand
COD        Chemical Oxygen Demand
CST        Capillary Suction Time
DO         Dissolved Oxygen
EPS        Extra cellular polymer Substances
GC         Gas Chromatography
HRT        Hydraulic Retention Time
ISF        Intermittent Sand Filter
MBR        Membrane bioreactor
MLSS       Mixed Liquor Suspended solids
MLVSS      Mixed Liquors Volatile Suspended Solid
MSW        Municipal Solid Waste
N          Nitrogen
N mL CH4   Methane generation at standard temperature and pressure
OWDTS      Onsite Wastewater Differential Treatment Systems
OWTS       Onsite Wastewater Treatment Systems
P          Phosphorous
SRT        Sludge Retention Time
SVI        Sludge Volume Index
TKN        Total Kjedahl Nitrogen
TMP        Trans Membrane Pressure
TP         Total phosphorous
UASB       Up flow Anaerobic Sludge Blanket
VS         Volatile Solids

                                         Chapter 1


1.1 Background

Most of the peri-urban and rural areas in Asian countries have lack of proper sanitation
systems. As a result of this, the effective management of domestic wastewater and solid
waste is becoming a critical problem. Principal technologies for domestic wastewater
treatment can be classified as on-site sanitation (decentralized) and off-site (centralized)
sanitation systems. Traditionally, decentralized systems have been used in non-sewered
areas and now increasingly in sewered areas. Recently, onsite wastewater treatment system
has become a significant alternative to off site system because of its comparative
advantages. These advantages include cleaning wastewater immediately after delivery, low
investment and operational cost, direct visibility of defects to operator and simple

On-site treatment options can be classified as septic tank, Imhoff tank, anaerobic filters,
disinfection units, latrines, urine separation toilets…etc. Septic tank and absorption field is
the most popular conventional treatment facility among them. Septic tanks remove most
settable and floatable material and function as an anaerobic bioreactor that promotes partial
digestion of retained organic matter. However, it is very difficult to achieve high level of
effluent quality by using the septic tank, because this effluent contains significant amount
of pathogens and nutrients. Consequently, ground water contamination, enhancement of
algal growth in surface water bodies and spreading disease is experienced.

Incorporation of the use of aerobic membrane bioreactor is one of the attractive solutions
to overcome deficiencies in septic tank system. However, the usage of the new concepts of
ecological sanitation with this system helps to solve problems related to nitrogen by
introducing urine separation toilets and use it as a fertilizer. Furthermore, scarcity of water
for human needs in the urban centers leads to reuse wastewater for secondary purposes
such as toilet flushing, lawn watering after suitable treatment.

On the other hand, solid waste management also has been created a crucial impact on
human health, in addition to wastewater treatment. The food waste is mostly disposed of as
solid waste forming a large portion that causes handling and storage problems owing to
biodegradable nature. The handling of the waste and separation of the recyclable would be
easier when the major portion of the putrisible waste has been diverted. Consequently, the
overall cost of collection, transport and downstream handling of the municipal solid waste
would be reduced as well as scavenging by animals and aesthetic nuisance from the
decayed waste. The organic portion of the solid waste would be drastically reduced in the
municipal waste stream if it is planned to divert the kitchen waste to the septic tank or the
organic waste tank within the periphery of the residence. About 40-50% of the municipal
solid waste (MSW) stream gets reduced enabling better options for recycle and disposal
either by incineration of the combustibles or land filling of the entire waste.

Various experiments have been carried out to find the performance of MBR system for
domestic wastewater treatment excluding kitchen waste. This experimental research was
focused on replacement of septic tank by aerobic MBR to treat grey water, brown water
and organic fraction of the kitchen food waste except yellow water. Normally, yellow

water consists of high amount of nitrogen and it has economical value as fertilizer. So the
yellow water can be separated from black water. Generally, 70% of kitchen waste can be
considered as organic and which can be pulverized by using a grinder. Once pulverized
food waste is formed it can be disposed from kitchen sink and mixed with brown water and
grey water as influent to the system. Solid fraction of the waste stream is screened out and
sent to anaerobic digestion and colloidal matter is further treated aerobically.
Consequently, it can be obtained high quality effluent for reuse and to reduce the quantity
of food waste entering to the main waste stream.

1.2 Objective of the study

Objectives of this study can be listed as follows:

   1. To develop an aerobic MBR for small-scale domestic wastewater treatment in
      tropic regions;
   2. To investigate performance of the aerobic MBR for domestic wastewater including
      grey water, brown water and pulverized food from kitchen sink;
   3. To compare the quality of the effluent using different operation conditions;
   4. To reduce the quantity of food waste release to solid waste stream.

1.3 Scope of the study

In experimental phase, laboratory scale aerobic membrane bioreactor was installed to treat
grey water, brown water and pulverized food. Synthetic wastewater was used as feed
wastewater combined with kitchen waste juice.

The performance of the aerobic MBR was preliminary investigated by measuring the
physical, chemical and biological characteristics of the effluent and modification of the
setup was made for better performance.

                                               Chapter 2

                                          Literature Review

2.1. Introduction

2.1.1 General

Every community produces both liquid and solid waste and air emission. Majority of the
liquid part consists of wastewater generated after using water supplied to the community
for different applications. From the standpoint of source of generation, wastewater may be
defined as a combination of liquid or water-carried waste removed from residences,
institutions and commercial and industrial establishments.

In addition both untreated wastewater and poorly managed solid waste is a threat to public
health and the environment. Waste also contains nutrients, which can enhance the growth
of aquatic plants and may contain toxic compounds that may be mutagenic or carcinogenic.
For these reasons immediate and nuisance-free removal of the waste from its source of
generation followed by treatment, reuse or disposal into environment is required to protect
public health and environment.

2.1.2 Domestic wastewater

Domestic wastewater derives from number of sources as shown in following Figure 2.1.
Wastewater generated from toilet is termed as black water and it has high content of solids
and contributes a significant amount of nutrients (nitrogen and phosphorous). Black water
can be further separated as feces and urine, where urine is called yellow water and feces
with water is known as brown water. Grey water consists of water from bathing/showering
and from the kitchen.


                      Urine                                                                      Storm


                  Kitchen         Dishwasher        Bath              Cloth      Miscellaneous
                  sink                             shower             washer

                                                      Grey                     sewage

                        Black water


  Figure 2.1 Range of possible sources of household wastewater showing wastewater
Residential dwellings exist in a variety of forms, including single and multi-family
households, apartment houses and cottages or resort residences .The wastewater flow from

residential dwellings due to different activities can be quantified in terms of average daily
flow and individual activity flow. The average daily wastewater flow from a typical
residential dwelling has been found as 185-265 L/cap/day (USEPA, 2002). Individual
wastewater generating activities within a household are the main contributors to produce
the total household wastewater discharge. It has been found that average water use by a
household, which is directly related to the wastewater discharge as shown in Table 2.1.

Table 2.1 Residential water uses by activity for an average five-person household
                                                                       Average for a
  Activity                            Average use (L/Cap/d)
                                                                      household (L/d)
                       (A) Grey water and brown water
  Toilet flush                        61.3                                   306.5
  Bathing                             34.8                                   174.0
  Clothes washing                     37.8                                   189.0
  Miscellaneous uses                  25.0                                   125.0
  Sub total                          158.9                                   794.5
                        (B) Kitchen waste
  Dish washing                        12.1                                   60.5
  Garbage grinders                     4.5                                   22.5
                                      16.6                                   83.0
  Total water use(A+B)               175.5                                   877.5
Source: USEPA, 1980

The flow of wastewater is generally variable with peak flow coinciding with high
household activities in the morning and evening; when in the night minimum flow occurs.
Pollutant load may vary in the similar manner. The typical wastewater flow pattern can be
considered as shown in Figure 2.2 (USEPA, 2002). The variation in flow rate controls the
volume of flow equalization tank and the variation in concentrations.







                  0   3          6         9         12          15     18       21        24
                                               Time of Day/(h)
                          Figure 2.2: Wastewater flow pattern in single house hold (USEPA,2002)

The effective management of residential wastewater flow requires a reasonably accurate
knowledge of its characteristics. Detailed characterization data regarding wastewater flows
are necessary to facilitate the effective design of wastewater treatment and disposal
systems.Table 2.1 shows characteristic of typical residential wastewater flow (USEPA,

  2002). Generally, the nitrogen from toilet is almost 60% in domestic wastewater while
  phosphorus contribution from toilet is about 34%. The value of nitrogen is given by:
                                   [V * N a − Vtw * N t * N % ]
               N Concentration = w                                     Eq: 2.1
         Vw -Total volume of wastewater from a five-member household
         Vtw -Volume of toilet flush water
         Na -Average nitrogen concentration
         Nt - Nitrogen concentration in toilet fraction
         N% - Urine contribution of nitrogen

  Table 2.2 characteristics of typical residential wastewater
    Parameter                              Concentration range (mg/L)
    Total solids                                     500-880
    Volatile solids                                  280-375
    Suspended solids                                 155-330
    Volatile suspended solids                        110-265
    BOD5                                             155-286
    COD                                              500-660
    Total nitrogen                                    26-75
    Ammonia                                            4-13
    Total phosphorus                                   6-12
   Source: USEPA (2002)

  2.1.3 Solid waste

  Rapid urbanization of the developing countries has increased the urban population
  significantly resulting in the growth of the industrial enterprises for the production of the
  different consumer’s products. As a result, huge amount of solid waste being generated
  daily from urban areas have put pressure in the environmental management. The primary
  fraction of the waste generated is dominated by biodegradable portion, which either ends
  up in the barren land or in some other non-engineered landfill. Following figure 2.3 shows
  the range of MSW generation in three countries.




Figure 2.3 Per capita municipal solid waste variations (Visvanathan and Trankler, 2004)

The composition of municipal solid waste differs for different countries and regions, and
developing countries have generally high food and yard waste (Table 2.3), whereas
developed counties have a large fraction of paper and plastic content (Visvanathan and
Trankler, 2004). Identification of waste composition is crucial for the selection of the most
appropriate technology for treatment, taking essential health precautions and space needed
for the treatment facilities.

Table 2.3 Percentage of food waste in solid waste in three Asian countries

 Country                            Percentage of food waste in solid waste (W/W %)
 China                                                    50
 Thailand                                                 55
 India                                                    49
Source: Visvanathan and Trankler (2004)

Henze (1997) has highlighted that there is a requirement of optimal handling of kitchen
waste in today’s society. Because, traditional methods of handling may not be optimal. For
an example, compostable fraction of the solid waste from kitchen can either alone or
combined with part the traditionally waterborne kitchen wastes be kept separate, for later
composting or anaerobic treatment. Nowadays there is a trend of incorporation of
compostable fraction of kitchen waste into wastewater by use of garbage grinders. But
conveying solid waste using sewer, it cannot be reduced the total load produced by
household. However, it can be reduced that significant occupational health problems
associated with transport of this putrisible matter.

Anaerobic digestion is one of the attractive solutions to handle the solid waste. Methane
production potential is the important parameter to be considered in these processes. Several
batch methods exist for measuring methane potentials of waste. The basic approach is to
incubate a small amount of the waste with an anaerobic inoculum and measure the methane
generation, usually by simultaneous measurements of gas volume and gas composition.
(Hassen et al, 2004).

The main goal is to determine the methane potential in terms of STP (STP: standard
temperature and pressure) ml CH4 per gram of organic waste expressed as volatile solids
(VS). The determination should be reliably with a reasonable incubation period and with a
minimum workload. The methane generation as a function of time may also be of interest
for identification of inhibition or adaptation. These priorities have encouraged a procedure
including extensive homogenization of the solid waste sample, a large inoculum,
incubation at 350 C for 50 days, and direct measurement by a gas chromatograph (GC) of
CH4- mass-produced.

2.1.4 Centralized wastewater treatment system (off-site sanitation systems)

The centralized approach is very much suitable for countries, which can afford the huge
costs for construction, operation and maintenance of wastewater collection and treatment
systems. So, it is not possible in low-income or developing countries. Centralized large-
scale infrastructures have been installed in the cities of industrial countries past 150 years
to provide water services. These systems are initially designed to protect public health and
provide fire safety, have been extremely successful in these respects (Harremoes, 1999).

There are instances, however, where off-site sanitation is deemed necessary, because of
unsuitable ground or housing conditions for on-site systems, or because of a community’s
commitment to an off-site system. There is a certain amount of prestige in having an off-
site connection; peer pressure is often a significant motivating force. Once the decision has
been made to implement an off-site system, sewers become a necessity.

2.1.5   Decentralized treatment system

Decentralized wastewater management employs collection, treatment and disposal/reuse of
wastewater from individual homes, clusters of homes, isolated communities, industries or
institutional facilities, as well as from portions of existing communities at or near the point
of waste generation. Decentralized systems maintain both the solid and liquid fraction of
the wastewater near their point of origin, although the liquid portion and any residual
solids can be transported to centralized point for further treatment (Tchobanoglous, 2003).
It consists of wastewater pretreatment, wastewater collection, wastewater treatment,
effluent reuse or disposal and bio solids and septage management. But, every decentralized
system does not consist of all of above elements. Although the components are the same as
the centralized systems, the difference is the type of technology used.

Decentralized wastewater treatment systems have been applied in rural and urban areas for
several decades both in developed and developing counties because of their low investment
costs and their simplicity in operation and maintenance. For an example, USEPA (2002)
emphasizes that 25 million (or 24 % of the total) households in US have applied onsite
sanitation systems. Especially in Vermont, Maine and North Carolina, where about 50% of
the households are equipped with either septic tanks or cesspool. Similar application rates
of the system are found in the rural areas of the European counties. In developing counties,
for example Philippines, Tanzania, Thailand, etc, installation of this system can range from

2.1.6   Comparison of on-site versus off-site

Mahar and Lustig (2003) and Huber (2004) have compared the centralized and
decentralized wastewater treatment concepts as follows:

   •    Design and construction of sewer systems usually take several years. Since a
        centralized sewage treatment plant is naturally useless without sewer systems, the
        benefit starts after a long time lag. Decentralized plants start cleaning the
        wastewater immediately after the delivery, which takes only a few weeks for
        standardized products. Such construction provides a direct and immediate benefit.
   •    The investment and operational costs of decentralized plants are lower than
        centralized plants and they are calculable and directly coupled with the requested
   •    Centralized sewage treatment enhances careless handling of the own wastewater,
        which results in ever-rising expenses for wastewater that contains increasingly
        difficult-to-treat components. Decentralized system prevents such carelessness, as
        the consequences of wrong handling have an immediate and directly visible effect
        for operator.
   •    Decentralized systems promote better watershed management by avoiding large
        water transfer from one watershed to another as centralized systems.

   •   Combined wastewater flow in the centralized approach makes the treatment
       complicated and expensive. Individual flow treatment in decentralized system is the
       reasonable alternative. It provides the possibility to collect pollutant in a small and
       concentrated flow and treat the flow individually.
   •   Decentralized system can provide cost-effective solution for the areas that require
       advanced treatment, such as nutrient removal or disinfection, while recharging local
       aquifers and providing reuse opportunities close to the points of wastewater
   •   Perceived disadvantage of decentralized systems when compared with centralized,
       that is harder to ensure that the owner operate and maintain them properly.
   •   Large-scale treatment plants create large amounts of treated wastewater that need to
       be disposed in one area. This limits the potential for reuse of the treated effluent
       and the wastewater is often disposed of directly into the ocean, sea or river, which
       in turn lead to algal blooms and eutrophication.
   •   Decentralized systems offer an appropriate solution for wastewater treatment in
       low-density areas not for densely populated areas.
   •   Simple faults at a centralized sewerage system can often lead to a breakdown in
       treatment process and release poorly treated effluent into the environment.
       However, decentralized system fails the amount of pollutant will be small. The risk
       to people and to the environment will be much less.

Lens et al (2001) have summarized that various researcher have recently presented ideas
and innovative concepts (For examples, Larsen and Gujer, 1997; Otterphol et al., 1997;
Zeeman, 2000) to overcome the obvious shortcomings of centralized approach and to lead
the way towards an integrated, ecologically and economically sound water/wastewater
management system. Theses proposals have in common:

       •   Integration of water, wastewater and household waste management systems
       •   Separate collection and treatment of the various categories of waste settlement
           generated in the catchment area (house, dwelling, settlement: factory, industrial
       •   Recovery of valuable substances for further and most direct use (For an
           examples, water, compost, biogas and fertilizer).

2.2 Onsite wastewater treatment options

2.2.1 Technology options

Decentralized wastewater treatment alternatives for small communities can be broadly
defined into three categories that represent the basic approaches to conveyance, treatment
and /or disposal (Lens et al., 2001).

   •   Natural systems that utilize soil as a treatment and disposal medium, including land
       application, constructed wetlands and subsurface infiltration. Some sludge and
       septage handling systems, such as sand drying bed, land spreading and lagoon, are
   •   Alternative collection system that uses lightweight plastic pipe buried at shallow
       depths, with fewer pipe joints and less complex access structures than conventional
       gravity sewers. These include pressure vacuum and small diameter gravity sewer

   •     Conventional treatment systems that utilize a combination of biological and
         physical processes employ tanks, pumps, and blowers rotating mechanisms and / or
         other mechanical component as part of the overall system. These include suspended
         growth, fixed growth and combination of the two. This category also includes some
         sludge and septage management alternatives, such as digestion, dewatering and
         composting systems and appropriate disposal information.

Lier and Lettinga (1999) have summarized treatment options for domestic wastewater in
decentralized sanitation concepts associated with integration of environmental protection
and resource conservation technologies (Table 2.4). Environmental protection and resource
conservation technologies focus on a minimum of consumptive use of energy, chemicals
and water and a maximum of reuse of treated wastewater and minimum residues. In their
investigation, they have presented possibilities of above concept using anaerobic treatment

   Table 2.4 Treatment options for domestic wastewater in decentralized sanitation

                       Treatment of separated concentrated wastewater
                            a. Treatment and post-treatment of slurries (Black water)
                            b. Toilet wastewater + kitchen waste

    Anaerobic pre-treatment
            a. Accumulation type digester (for concentrated slurries)
                        - Conventional system,
                        - Improved modules systems,
            b. Compartmentalized systems (for less concentrated slurry)
                        - Accumulation type digester
                        - Sludge bed modules
                        - Anaerobic filter modules.
                        - Hybrid modules,
    Post-treatment of anaerobic effluent, for effluent polishing:
                        - Removal and recovery nutrients
                        - Removal of remaining COD
                        - Removal of pathogens

                      Treatment of totally mixed domestic wastewater
       Anaerobic pre-treatment, sludge mineralization and storage, bio production.
                          - Sludge bed modules (treatment, mineralization, storage)
                          - Anaerobic filter models
                          - Hybrid modules.
       Post-treatment anaerobic effluents
                          - Wetland systems
                          - Ponds
                          - Slow sand filters
                          - Aerobic method
   Source: Lier and Lettinga (1999)

2.2.2 Management of onsite wastewater treatment systems

The primary objective of management of the onsite wastewater treatment system (OWTS)
is to ensure the protection of environment and public health. Management of OWTS is a
combination of three functions as Figure 2.4. Without having effective management, even
the most costly and advanced technologies will not be able to meet goals of the

                            Figure 2.4 Management of OWTS

(a) Operational aspects

Operation comprises all activities related to steering the technological processes.
Considering the operation of small treatment plants, it is well understood that the treatment
performance is strongly influenced by the operator. Experience in USA by Kerri (1993)
has shown that an adequate training program could achieve considerable improvements for
the plant operators. In reality, however, it is not possible to have that type of training
programs. In this respect, it is important to have automatic monitoring and control devices.
Furthermore, it is possible to have reliable system combined with a centralized
organization for plant operation and this may be an optimal solution (Boller, 1997).

(b) Monitoring

Monitoring of the treatment system is the frequent observation of all on-site wastewater
treatment components. Example of monitoring is, knowing what goes down the drain,
reading and recording the results of a flow meters, checking baffles, screen and pumps and
proper alarm for proper function, noting wet spots near the drain field or mound, recording
the date and condition of the septic tank when it is pumped, or sampling and testing
effluent from a performance system and reporting the information to local agencies.

(c) Maintenance

Maintenance is the work of doing periodic upkeep on the system. It includes the repair,
replacement, and cleaning existing components. It can also be the addition of new
components to enhance performance. However, sludge removal forms the major part of the
maintenance, which should be done periodically. Personnel involvement is essential in
every part of the maintenance (Fastenau, 1990).

Generally, the systems owner has done management of conventional onsite wastewater
treatment systems. However, new technological development has been shown that service

provider can do the management automatically. For an example, Fane and Fane (2004)
have highlighted that decentralized user with membrane-based water and wastewater
treatment can be connected telemetrically to a centralized management unit (Figure 2.5).
Then, service provider will provide maintenance as well as technical service.
                Water supply line

                                             MWT               Telemetry

                                          Decentralized                 Centralized
                               Reuse      Individual user               Management
                                          Or Cluster                    Monitoring and

            Reuse                          MDWWT

Figure 2.5 Schematic of Decentralized users with membrane-based water and
wastewater treatment connected telemetrically to centralized management unit.
(MWT=membrane water treatment and MDWWT= membrane-based decentralized
wastewater treatment)

2.2.3 Problems existing in onsite wastewater management

Onsite wastewater systems have experienced two primary failures: operational and
functional failure. The operational failure is because of lack of monitoring of the systems
after installation and the deficiency of the discharging of wastewater to environment.
Functional failure occurs when system continues to remove wastewater prior to the
discharge into receiving water body. The inappropriate use and disposal of wastes from
onsite waste wastewater treatment system (OWTS) can have number of adverse impact
including spread disease, contamination of ground water and surface water, degradation of
soil and vegetation, odor and insect problems and potential litigation.

Typical causes of failure include unpumped and sludge-filled tanks, which result in
clogged absorption fields, and hydraulic overloading caused by increased occupancy and
greater water use following the installation of new water lines to replace wells and cisterns.
Full-time or high use of vacation homes served by systems installed under outdated
practices or designed for part-time occupancy can cause water quality problems in lakes,
coastal bays, and estuaries. Landscape modification, alteration of the infiltration field
surface, or the use of outdated technologies like drywells and cesspools can also cause
contamination problems (USEPA, 1980).

Newer or “alternative” onsite treatment technologies are more complex than conventional
systems and incorporate pumps, recirculation piping, aeration, and other features (e.g.,
greater generation of residuals) that require ongoing or periodic monitoring and
maintenance. However, the current management programs do not typically keep an eye on
routine operation and maintenance activities or detect and respond to changes in
wastewater loads that can overcome a system (USEPA, 2002).

   Nowadays, weak points of traditional OWTS are expected to be overcome by using onsite
   wastewater differential treatment systems (OWDTS). The environmental and health
   principles supporting the management of OWDTS including, ecological sanitation,
   ecologically sustainable development, resource recycling (nutrient and water), water cycle
   management, total catchment management, conservation of water resources, protection of
   public health and prevention of public health risk. (Albrechtsen, 2002)

   2.2.4 Strategies for on-site treatment systems

   USEPA, 1980 has presented onsite system selection strategy is based on the assumption
   that subsurface soil absorption field is preferred onsite disposal option because of its
   greater reliability with a minimum of attention. Onsite system design strategy can be
   categorized into three major sections such as preliminary system screening, system
   selection and system design. Further more, it can be divided into sub categories as shown
   in figure 2.6.It can be seen that there is no obvious changes has been happened to strategies
   by reviewing USEPA 2002.

Preliminary system screening

                                                                                              Design system
                                                                                          •     Treatment
                                                                                          •     Disposal
                                         Initial site                                     •     Residuals

                                       Preliminary                                                            Selection of
                                      Screening of                                    Selection of             treatment
                                                               Detailed site        disposal option
                                     Disposal options           evaluation                                    component

                                                                                       System selection
                                                        Figure 2.6 Onsite system design strategy
                               •   Preliminary system screening

   In preliminary system screening, initially most appropriate system has to be selected to
   make up the system. Since the disposal method is required to give priority, detailed site
   evaluation has to be carried out. However, the site characteristic must be evaluated
   simultaneously with the disposal method. To effectively screen the disposal options, the
   wastewater to be treated and disposed must be characterized and initial site investigation
   made. From the wastewater characteristic and the site information gathered in this step,
   preliminary screening of the disposal options can be made. The potentially, feasible
   disposal options are identified by nothing which one perform effectively under all the
   given constrain.
       • System selection

   Detailed site evaluation is needed to provide sufficient information to select the most
   appropriate treatment and disposal system from the potentially feasible system options.

When suitable soil does not exist as soil discharging filed, surface discharge of water may
be one alternative. In order to discharge water to surface water body, wastewater quality
has to be maintained in high quality. Selection of the most appropriate treatment option is
based on performance and cost. Further, Residual produced from treatment processes also
requires safe disposal. Once all the components are selected, system should be selected.

2.2.5 Challenges in the implementation of Decentralized wastewater management

In many case, small    communities have limited economic resources and expertise to
manage decentralized   wastewater treatment systems (Tchobanoglous and Crites, 1998).
Problems are often      experienced in design, contracting, inadequate construction
supervision, project   management, billing, accounting, budgeting, operations, and

While implementation of decentralized wastewater systems is terrible, from an economic
and social point of view, the engineering involved is equally challenging. To implement
decentralized wastewater management systems, the designer must not only be
knowledgeable about the elements involved in the design of conventional centralized
wastewater management systems, but must have additional information about such items
as septic tanks and Imhoff tank, used for the pretreatment of household wastes: alternative
wastewater collection systems, including the use of pressure and small-diameter.

2.3 Ecological Sanitation

2.3.1 Concept and methodologies used

Ecological Sanitation or “ecosan” is a holistic approach with a set of basic principles. It
can be viewed as a three-step process: containment, sanitization and recycling of human
excreta. Almost all known treatment technologies for municipal and industrial wastewater
can be included in ecosan systems. The key objective of this approach is not to promote a
certain technology, but rather a new philosophy of dealing with what has been regarded as
waste in the past. (

Ecosan represents a conceptual shift in the relationship between people and the
environment; it is built on the necessary link between people and soil. Ecological sanitation
principles are not new. In some cultures, for example in parts of East Asia, ecological
sanitation systems have been widely used for hundreds of years, and in the case of China,
for a few thousand years.

Eco sanitation technology includes wastewater treatment and disposal, vector control and
other disease-prevention activities. It means keeping the eco-cycle in the sanitation process
closed. It is also a low-energy approach that uses natural processes. The systems of this
approach are based on the implementation of a material-flow-oriented recycling (circular
flow) process as alternative to conventional solutions. Ideally, ecological sanitation
systems enable the complete recovery of all nutrients from faeces, urine and grey water to
the benefit of agriculture, and the minimization of water pollution, while at the same time
ensuring that water is used economically and is reused to the greatest possible extent,
particularly for irrigation purposes.

In this system, excreta are processed on site until they are free of pathogenic (disease-
causing) organisms. Thereafter using them for agricultural purposes recycles the sanitized
excreta. Key features of ecosan are therefore:

 • Prevention of pollution and disease caused by human excreta.
 • Treatment of human excreta as a resource rather than as a waste product.
 • Recovery and recycling of the nutrients.

(Ortterpohl, 2003) has summarized the basic principles for the design of real ecosan
systems as follows:

• Efficient use of water and prevention of water pollution.
• Containment and sanitization of faecal matter.
• Reuse of urine and faecals often with bio waste after appropriate treatment usually on
  agricultural land to restore soil and its fertility thereby protecting the water bodies.
• Reuse of urine on sufficiently large areas of land, from around 50 to 400 m² per person
  depending on the crops and the number of harvests.
• Appropriate treatment of grey water, reuse if needed.
• Energy efficiency trough savings in treatment, freshwater transport and in avoidance of
  industrial fertilizer production, if feasible biogas production.

Ecological systems are designed around true containment and provide two ways to make
human excreta harmless: dehydration and decomposition. The preferred method will
depend on climate, ground water tables, amount of space and intended purpose for
sanitized excreta.

Ecosanitation for Grey Water Treatment and Composting of Household Organics

The ecosanitation approach can be broadened to cover all organic material generated in
household (kitchen food wastes) as described in the website (2004). If
these organic materials are sorted within the home, rather than mixed with solid waste and
dumped, they became valuable recyclable material once composted, grey water can be
treated biological systems. Figure 2.7 shows the options in a fully functional ecosan

            Figure 2.7 The options in a fully functional ecosan household.

Advantages and disadvantages of eco sanitation
Advantages and disadvantages of the ecological sanitation can be listed as in Table 2.5.

Table 2.5: Advantages and disadvantages of eco sanitation

                   Advantages                                  Disadvantages
 •   Removal of pathogens from the              •   Users do need to be taught how to use
     domestic environment.                          them properly.
 •   Elimination foul odors-if properly         •   Faeces need to be treated in the correct
     constructed.                                   manner; otherwise they pose a health
 •   Diseases are destroyed, not just               risk.
     contained.                                 •   High-density urban areas don’t always
 •   No potential to contaminate other              have the capacity to use the byproducts
     water sources.                                 produced.
 •   Use very little or no water.
 •   Nutrient and organic matters are
 •   Very cheap to build and operate, with
     very few components which can
Source: Earle (2004)

2.3.2 Urine separation and different treatment concepts

(a) Urine separation

Human urine is the largest contributor to household wastewater. It has been found that
urine contributes to approximately 88% of the nitrogen, 67% phosphorus and 46% of
organic carbon in a wastewater from toilets (Earle, 2004). There exists a number of
technical options for separating and reusing nutrients; compost, vacuum and urine
separating and reusing anthropogenic nutrients. (Lens et al, 2001). For various reasons,
urine separation technology appears to be the most viable alternative, since urine
separation can be achieved within the existing infrastructure, treatment is easier for
separated fraction, and there is a good chance that the technology will be generally
accepted. Also the separation of faeces and/or urine from the domestic wastewater can be
considered as the most important step towards sustainable water concept. It can
significantly decrease the nutrient load on wastewater treatment system. As a result of
this, there will be a decrease in an extra input of energy and physical resources required for
the nutrient removal in wastewater treatment systems. Furthermore, use of human urine, as
a fertilizer will be a good solution to replace mineral fertilizer that is costly in

As Jonsson et al (1997) has described that source separation of human urine is based on
toilets equipped with two bowels, a front one for the collection of urine and a rear one for
fecal material. These source separation toilets is connected to two sewer pipes, one for
urine and flush water from the front bowel and one for faecal matter and flush water from
the rear bowel. Storage tank is kept as temporary storage of urine. For an example,
Hanaeus et al., (1997) has studied urine separation system in an ecological village in
Northern Sweden and the existing sewerage system is shown in Figure 2.8. Further in their

study, they have found that the successful operation of a urine separation system is very
dependent on well-designed toilets and user behavior that promotes a high degree of
                                 Urine separation toilet
              Kitchen sink                                     Rear bowel

                         Septic tank                                       bowel(Urine)
                                                                                          Urine tank

                                                           Sludge for

       Infiltation bed    Distribution box

                                                           Grazing field

         Figure 2.8 The sewerage system used in Bjorsbyn, Northern Sweden
                               (Hanaeus et al, 1997).

As mentioned in the website (2004), model of double-vault urine
diversion toilet has been used in China, India, Vietnam and Mexico. It takes an average
family six months to fill one of the vaults. Then the second vault is used. The first vault is
emptied following an additional six months of sanitization and the material is taken to soil
compost. Urine is never mixed in this toilet but continuously diverted into a separate
container and later used in diluted form as plant fertilizer. The dry eco toilet meets all
necessary health and environmental protection criteria and goes well beyond what
conventional approaches can offer saving water and preventing water pollution. It produces
no smell, does not attract flies and is an affordable solution inside and outside of dwellings
throughout the world.

(b) Other treatment concepts

(1) Composting toilets

Composting toilet has been developed for an ecological sanitation system without using
flush water as well as minimizing odor problem, and aimed for a total recycle of waste
material in rural areas. Choi et al., (2003) conducted a study for the functional analysis of a
compost toilet developed for remote areas where no sewers are available by using lab scale
model. This study included the evaluation of overall performances of the compost toilet
operated with and without heating operations. Unlike the traditional toilet, no odor problem
has been reported in compost toilet. The compost toilet has become a reliable treatment
method for feces and urine and used for single dwellings and public places in Korea.

Composting toilets make use of the process of decomposition, a biological process carried
out by bacteria, worms and other organisms to break down organic substances. In a
composting environment, the competition between organisms for available carbon and
nutrients continues until the pathogens are defeated by to the dominant soil bacteria. Soil-

composting toilets are constructed using shallow, reinforced pits where soil and ash are
added after each use.

(2) Vacuum-biogas system for urban areas

Otterpohl (2003) has highlighted that there are many viable options for ecosan in rural and
less densely populated peri-urban areas, whereas there are still a fairly limited number of
concepts available for urban areas. The key issue is to find toilets that do not dilute too
much and still allow transport of faeces or backwater over distances of some hundreds of
meter or some kilometers. An interesting technology is the vacuum toilet combined with a
backwater-vacuum pipe. Such a system is used on a very large number of ships for up to
thousands of passengers on ships. Such systems can be installed even in very densely
populated areas in combination e.g. with MBRs (membrane bioreactors) for grey water
treatment. This type of technology is becoming more reliable and economic and does
include sanitization. Consequently, Grey water can be reused.

(3) Black water cycle: good potential for urban areas

Otterpohl (2003) has emphasized that separate collection and treatment of black water and
grey water is the foundation of the method “black water cycle process” .The idea of
appropriate treatment and reclaiming the toilet flushing water for toilet usage renders a
very high concentration of nutrients during daily operation possible. This can be an
important contribution for a new viewpoint in domestic wastewater management.

2.4 On-site treatment processes and systems

2.4.1 Septic Tank

                             Inspection port    Scum       Distribution box

                                     Wastewater              Outlet
                                                                          Drainage field

                                Sludge layer             Septic tank

           Figure 2.9 Main components of conventional septic tank system

Conventional septic systems (Figure 2.9) have been used in worldwide since 1970, mostly
in low densely populated areas. However, considerable technological development in the
systems cannot be seen to up-to-date. Further, sedimentation and anaerobic biodegradation
are the two principle treatment processes involved in and 60-80 % suspended solid
removal and 30-50 % BOD removal can be achieved from this system (USEPA, 2002).
These systems use gravity to treat and distribute wastewater in the soil.

Zaveri et al., (2002) has highlighted that failure of the conventional septic tank system
occurs due to several reasons including lack of maintenance, unfavorable site topography
and soil characteristics, poor design and construction, and inadequate capacity.
Consequently, odor and vector problems as well as surface and ground water pollution may


   •   Simplicity, reliability and low cost.
   •   Low maintenance requirements.
   •   Nutrients in waste are returned to soil.
   •   A properly designed, well-maintained system can last for more than twenty years.
   •   It does not consist of any movable components and require very little routine


   •   Enhance algal growth in surface water bodies, due to enrichment of effluent with N
       and P. (Negligible amount of removal of Nitrogen and phosphorous).
   •   Improperly functioning systems can introduce high nitrogen, phosphorus, organic
       matter, and bacterial and viral pathogens into the surrounding area.
   •   Setting limitations have to be considered for septic systems include natural soil type
       and permeability, bedrock and groundwater elevations, and site topography.
   •   Septic tank cannot remove disease-causing microorganisms.
   •   Septic Tanks are not a good solution for use in dense urban areas.

Improvements in septic tank system

Various approaches that have been carried out to improve the treatment performance of the
conventional septic tank system, such as modification of the soil adsorption system,
treating the septic tank effluent with an addition or alternative unit such as a bio filter, a
constructed wetland (Perdomo et al, 1994) or sulfur lime stone filter and modification of
the septic tank configuration through recirculating filters (Zaveri et al., 2002).
Furthermore, application of up flow anaerobic sludge blanket (UASB) septic tank system
is another alternative to the conventional system (Bogte et al., 1993 and Lettinga et al.,
1993) to improve physical removal of suspended solid as well as to improve
biodegradation of dissolved component.

2.4.2 Imhoff tank

The Imhoff tank (figure 2.10) was developed to correct the two main defects of the septic
tank including it prevents the solids once removed from the sewage from again being
mixed with it, but still provides for the decomposition of these solids in the same unit and
it provides an effluent amenable to further treatment.

Imhoff or Emscher tanks are typically used for domestic or mixed wastewater flows above
3 m 3/d.The tank consists of settling compartment above the digestion chamber. Funnel –
like baffle walls prevent up flowing sludge particle from getting mixed with the effluent

and form causing turbulence. Mainly, there are three processes involving in the Imhoff
tank including sedimentation, protection against up flow of the sludge particles and
fermentation of bottom sludge.

The effluent remains fresh and odorless because the suspended and dissolved solid do not
have an opportunity to get in contact with the active sludge to become foul and bad
smelling. Tanks are designed with a retention period of less than two hours during peak
loads in order to ensure this effect. Additional baffles are provided to reduce velocity at the
inlet and to retain suspended matter at the outlet. Desludging is necessary at regular
intervals. Leaving some bottom sludge behind in the tank helps the starting up process.

The Imhoff tank has no mechanical parts and is relatively easy and economical to
operate. It provides sedimentation and sludge digestion in one unit and should produce a
satisfactory primary effluent with a suspended solids removal of 40 to 60 percent and a
BOD reduction of 15 to 35 percent.




 Sedimentation inside
      the funnel

                       Figure 2.10 Cross section of an Imhoff tank

2.4.3 The intermittent sand filter (ISF)

This method is one of the oldest methods of wastewater treatment (Figure 2.11). They are
alternatives to conventional methods when soil conditions are not conductive for proper
treatment and disposal of wastewater. It can be used in sites that have shallow soil cover,
inadequate permeability, high groundwater, and limited land area. Further, it also provides
advanced secondary treatment of settled wastewater or septic tank effluent prior to
subsurface discharging. A well-operated intermittent sand filter will give a clear, sparkling
stable effluent almost completely oxidized and nitrified. Over-all plant removals of 95
percent or more of the BOD and suspended solids in the raw sewage can be expected.


   •   ISFs produce a high quality effluent, which can be reused in irrigation.
   •   Drain fields can be small and shallow.
   •   ISFs have low energy requirements.
   •   ISFs are easily accessible for monitoring and do not require skilled personnel to
   •   No chemicals are required.
   •   If sand is not feasible, other suitable media can be substituted and may be found
   •   Construction costs for ISFs are moderately low, and the labor is mostly manual.
   •   The treatment capacity can be expanded through modular design.
   •   ISFs can be installed to blend into the surrounding landscape.


   •   Land area required may be a limiting factor.
   •   Regular maintenance is required.
   •   Odor problems could result from open filter configurations and may require buffer
       zones from inhabited areas.
   •   If appropriate filter media are not available locally, costs could be higher.
   •   Clogging of the filter media is possible.
   •   ISFs could be sensitive to extremely cold temperatures.

                            Figure 2.11 Schematic of typical IFS
2.4.4 Nutrient removal

Nitrogen may be found in domestic wastewater as organic nitrogen, as ammonium, or in
the oxidized from nitrate and nitrite. Usual forms of phosphorus are organic phosphate,
orthophosphate and pyrophosphates. The removal or transformation of nitrogen and
phosphorous in wastewaters has been subjected to intensive research. However,
conventional on-site wastewater treatment such as septic tank, are not effective with
respect to nutrient removal.

There are larger number of processes have been found for nitrogen removal but few for
phosphorous. Currently, iron-rich intermittent sand filter (ISF) media and sequencing batch
reactors (SBR) are used to reduce phosphorous. These systems are capable of removing
phosphorus to an effluent value of 1 to 2 mg/L with proper maintenance. Basically,
nitrogen removal process can be biological treatment systems, physical/chemical treatment
system (iron exchange, reverse osmosis) and source separation system. Processes that
remove 25 % to 50 % of the total nitrogen include aerobic biological systems and media
filters, especially recirculating filters. Usually, the minimum total nitrogen standard that
can be regularly met is about 10 mg/L (USEPA, 2002).


   •   Andreadaris (1985) has studied the performance of an on-site sewerage treatment
       and disposal system consisting of a septic tank, a gravel filter, a sand filter and soil
       absorption trenches. Average BOD, suspended solid and nitrogen (biological
       nitrification and denitrification) removal efficiencies were 92.9 %, 93.4 % and 70
       % respectively.

   •   Wakatsuki et al (1993) has suggested multi-soil-layering method for nutrient
       removal from domestic wastewater. It has been obtained 80 % removal of nitrogen
       and 90 % of phosphorous removal.

2.4.5 Disinfection

Disinfection of wastewater is required to remove pathogenic organisms in the wastewater
stream. A number of methods can be used to disinfect wastewater including chemical
agents, physical agents, and radiation. For onsite applications, only a few of these methods
have proven to be practical (i.e., simple, safe, reliable, and cost effective). Most commonly
used methods are chlorination and ultraviolet radiation (figure 2.12). Although ozone and
iodine can be and have been used for disinfection, they are less likely to be employed
because of economic and engineering difficulties.

                       Figure 2.12 Generic disinfection diagrams

Disinfection is generally required in three stages in onsite-system. The first is after any
process that is to be surface discharged. The second is before a subsurface wastewater
infiltration systems where there is inadequate soil (depth to ground water or structure too
porous) to meet ground water quality standards. The third is prior to some other immediate
reuse (onsite recycling) of effluent that requires some specific pathogen removal (e.g.,
toilet flushing or vegetation watering).

2.4.6 Aerobic treatment units

Aerobic systems are similar to conventional septic systems in that they both use natural
processes to treat wastewater. But unlike septic anaerobic treatment, the aerobic treatment
process requires oxygen. For this reason, aerobic systems are costly to operate and need
more routine maintenance than most septic systems. However, when properly operated
and maintained, aerobic systems can provide a high quality wastewater treatment
alternative to septic systems. Aerobic Wastewater Treatment may be a good option when
the soil quality is not appropriate for a septic system, there is high groundwater or shallow
bedrock, a higher level of wastewater treatment is required, a septic system has failed and
there is not enough land available for a septic system. Table 2.6 shows advantages and
disadvantages of Aerobic Treatment Units.

Table 2.6 Pros and cons of aerobic units

                  Advantages                                    Disadvantages
      •    Can provide a higher level of             •   More expensive to operate than a
           treatment than a septic tank                  septic system.
      •    Helps to protect valuable water           •   Additional cost for power
           resources where septic systems                consumption compared to septic tank
           are failing.                                  system.
      •    Provides an alternative for sites         •   Mechanical failure due to break down
           not suited for septic systems                 of components.
      •    May extend the life of a drain            •   Requires more frequent routine
           field.                                        maintenance than a septic tank
                                                     •    May release more nitrates to
                                                         groundwater than a septic system.
  Source: Hanna et al (1995) and USEPA (2002)

2.4.7 New technologies for on-site wastewater treatment

(a) Application of membrane technology

Membrane bioreactor (MBR)

Combining membrane technology with biological reactors for the treatment of wastewaters
has led to the development of three generic membrane bioreactors: for solid separation,
bubble-less aeration within the bioreactor, and for extraction of priority organic pollutant
from wastewater. The coupling of a membrane to a bioreactor has increased interest both
academically and commercially because of the inherent advantages of the process offered
over conventional biological wastewater treatment systems.

MBR process description

A membrane bioreactor process for separation and retention of biological sludge is
generally regarded as one alternative to the conventional activated sludge process. The
combination of activated sludge biodegradation and membrane separation is known as
membrane bioreactor process (MBR). A membrane is manufactured in order to achieve the

reasonable mechanical strength and can maintain a high throughput of a desired permeate
with a high degree of selectivity.

Microfiltration (pore size from 0.1-0.4µm) and ultrafiltration (pore size from 2-50nm) are
the two major types of membrane used in wastewater treatment. There are two
configurations of MBR systems based on the location of membranes modules: (1)
submerged membrane bioreactor system, (2) externally pressured cross flow MBR.

Submerged membrane bioreactor system (Figure 2.13(a)), in which a membrane module is
directly immersed in an aeration tank. In general, permeate is extracted by suction or, less
commonly, by pressurizing the bioreactor. This process can also be easily used to retrofit
the conventional activated sludge process without significant modifications to the existing

(a) Submerge membrane bioreactor          (b) Externally pressured cross flow MBR

                            Figure 2.13 MBR configurations

Externally pressured cross flow MBR (Figure 2.13(b)) is the use of cross-flow membrane
modules in conjunction with mixed liquor in the bioreactor being circulated through the
membrane. Although relatively easy to operate, but they require high-speed pumping
devices. It leads to the high operation cost and impose a high level of shear stress on the
biological suspension. Shear stress usually involves the breakage of microbial floc and
subsequent damage to microbial activities (Cho and Lee, 1996). The advantage and
disadvantage of MBR configurations are listed in the Table 2.7.

Table 2.7 Advantages and disadvantages of MBR configurations

              Submerged MBR                       Externally pressured cross MBR
      •   Aeration costs high (nearly 90%)        • Aeration costs low (nearly 20%)
      •   Very low liquid pumping costs           • High pumping cost (60-80%)
          (higher if suction pump is used         • Higher flux (smaller footprint)
          nearly 28%)                             • More frequent cleaning required
      •   Lower flux (larger footprint)           • Higher operating costs
      •   Less frequent cleaning required         • Lower capital costs
      •   Lower operating costs
      •   Higher capital costs

Advantage and disadvantage of MBR


Membrane will continue to decrease in cost in the coming years. MBR has been proved to
be more efficiency than conventional biological treatment process in the following ways.
(Vivanathan et al, 2000)

•   Very high effluent quality, reuse of wasted effluents comes into view, which makes it a
    sustainable technology. They can be used for cooling, toilet flushing, lawn watering, or
    with further polishing as process water.

•   The absence of the secondary settler, the space required for MBR will be less.

•   In a MBR, sludge retention time can be controlled completely independently from
    hydraulic retention time (HRT). Therefore, a very long SRT can be maintained
    resulting in the complete retention of slow-growing microorganisms such as nitrifying
    or methonogens bacteria. Consequently, a greater flexibility of operation.

•   Biomass concentration can be greater than conventional systems. It can be up to 30g/L
    in MBR. Therefore, the system can tolerate high volumetric loading rate. The reactor
    volume can also be reduced.

•    It can be achieved that high rate decomposition and it can retain soluble material with
    a high molecular weight.

•   Low sludge loads resulting in low sludge production. Low F/M and low wastage of
    biomass are the result of this. Chaize and Huyard (1991) have shown that for treatment
    of domestic wastewater, sludge production is greatly reduced if the age is between 50
    and 100 days.

•   In the membrane filtration process, the removal of bacteria and viruses can be achieved
    without adding any chemical. Because of the process equipment can be kept closed, no
    odor dispersion occurs.

• High capital cost and operating cost.
• Limited experience in use of membrane in wastewater reuse

• Current regulatory standards can be achieved by conventional treatment process.
• Lack of interest by the membrane manufacture.


In all practical membrane filtration applications, as the resistance increase the flux will
decline. This increase in resistance may be due to changes in Rm, Ref, Rif or all three
(Equation 2.2). If the flux decline is not reversible by simply altering operation conditions,
it is termed fouling. It can results from the precipitation of less soluble spices (Scaling),
adsorption of organic membrane surface (organic fouling), and adhesion and growth of
microbial cells at the membrane surface (bio fouling). The fouling causes to reduce
productivity, to shorten the membrane life and to impair the fractionation capabilities of
the membrane.
Total resistance can be expressed as follows:

           Rt = Rm + Ref + Rif                                   Eq: 2.2

          Rm - The resistance of clean membrane, which can be obtained from the pure
                water flux data.
          Ref -The external fouling resistant, this includes concentration polarization and
                deposition of colloids/macromolecules on the membrane surface
          Rif - The internal fouling resistance, due to internal fouling into the membrane
          Rt - Total resistance

Control of fouling is of utmost importance. It can be reduced by maintaining turbulent
conditions, operating at sub-critical flux and /or by the selection of a suitable fouling
resistance membrane material. (Gander et al, 2000)

(b) Factors affecting the MBR process performance

The main objective of the membrane-coupled bioreactor is to improve the efficiency of the
biological process step in such a way that to obtain high quality effluent. Many parameters
have to be considered when optimizing the MBR system including, solid concentration,
sludge age, and hydraulic retention time in the biological step as well as the flux rate,
material costs, and the energy cost of the membrane separation. Further, the treatment and
the method of disposal of sludge have to be considered. It has been also found that the
MBR waste sludge is more difficult to dewater than conventional activated sludge
(Parameshwaran, 1997). Optimization of these parameters is very difficult because of
interrelated nature.

Many researches have been carried out to optimize the MBR system and it has been found
that the permeate flux of membrane filtration is affected by raw materials of membrane and
its pore size as well as operational conditions such as the pressure driving force, the liquid
velocity/turbulence, and the physical properties of mix liquor. Some of the characteristics
and operating conditions of aerobic MBR process (submerge membrane) have been listed
in Table2.8.

Table 2.8 Characteristics and operating conditions of aerobic MBR process
(submerged membrane)

          Wastewater                  Synthetic          Domestic            Industrial

 Membrane configuration           Microfiltartion      Microfiltartion   Microfiltartion
                                  Hollow fiber         Hollow fiber      Hollow fiber

 Pore size (µm)                           0.1                0.4                 0.1

 Filtration area (m2)                     0.9                20                  0.3

 Transmembrane Pressure                   40                  4                20-80

 MLSS (kg/m3)                           10-11               12.9                 4.5

 Flux (L/m2.h)                             9                16.6                 18

 Reference                        Yamamoto et al,      Ueda and          Benitez et al1995
                                  1989                 Hata, 1999

2.4.8 Nutrient removal in MBR

(a) Nitrogen removal

Nitrification has been to be greater in an MBR than with a conventional activated sludge
process owing to the longer retention times of the nitrifying bacteria (high sludge age, low
food/micro organism ratio) and the smaller floc sizes, allowing slightly greater mass
transport of nutrient and oxygen into floc. (Gander et al, 2000). It has been found that at
nitrogen load of between 0.1 and 3.3 kgNH3m-3day-1,ammonia removal is greater than 90
%.( Chiemchaisri et al, 1992).

Denitrification, the reduction of nitrate to various gases end-products such as molecular
nitrogen and nitrogen oxide. It can proceed alongside nitrification if aeration is supplied
intermittently (Chiemchaisri et al, 1992 and Chaize et al, 1994), hydrodynamics are such
that an anoxic area results and high organic loads are added allowing anoxic micro-sites to
develop within the flocs. (Ueda et al, 1996, Chaize and Huyard, 1991). In aerobic MBRs
denitrification can be achieved by addition of an anoxic tank prior to the aeration tank,
with conventional recycling. (Ueda and Hata, 1999, Buisson et al, 1998 and
Parameshwaran, 1997). This produces an environment conducive to the anaerobic
denitrification bacteria to utilize nitrate, giving an effluent much reduced in this nutrient.
As Ueda et al (1996) has suggested, MLSS concentration should be increased to enhance
the denitrification.

(b) Phosphorous removal

Phosphorous removal in MBRs is a major area of interest as the need to reduce nutrient
loads becomes more important. Reported phosphorous removal range from 11.9 %( Cote et
al, 1997) to 75 % (Ueda and Hata, 1999).Assimilation alone does not account for all
phosphorous removal. However, stable phosphorous removal has been demonstrated by
metal coagulant dosing achieving a removal efficiency of 80 % or more at molar ratios of
1:1 Al or Fe: P (Buisson et al, 1998).

2.4.9 Energy requirement for MBR process

Till 1997, the tubular cross-flow membrane has been used in membrane bioreactors (Dijk
and Roncken, 1997) and the typical energy requirement of this membrane is 6-8 kWh/m3.
Recently, researches have been carried out to minimize energy consumption for membrane
separation. Hollow fiber turned out to be effective, but have severe problems with blocking
of the fiber. Incorporation of hollow fiber membranes directly into the suspended solids
bioreactor (Submerged membrane bioreactor) as originally proposed by Yamamoto et al,
1991 enables direct solid-liquid separation without necessitating a recirculating pump. It is
claimed that the reduction to operating costs can make the processes comparable to
conventional activated sludge processes. Two types of submerged bioreactors have been
found so far in terms of membrane separation principles, including suctioned-filtration type
and a gravitational–filtration type. (Ueda and Hata, 1999).The gravitational filtration is a
good alternative for the saving energy. Table 2.9 shows energy consumption in different
MBR systems.

Transfer Flow Module (TFM) is one of the new applications, which can be used to
minimize the typical energy requirement up to 0.1-0.5 kWh/m3. That is ten times less than
in conventional membrane bioreactors. (Dijk and Roncken, 1997).

Table 2.9 Energy consumption in different MBR systems

       Process                       Sub            Sub       Sub        SS          SS
       Membrane                      HF             HF        PF          T          HF
 Pore size                         0.1 µm         0.1 µm    0.4 µm     300kDa      0.1 µm
 Surface area(m2)                     2              4       0.96       0.08        0.39
 TMP(bar)                           0.13           0.15       0.3         2         2.75
 Permeate flux(Lm-2h-1)               8              12      20.8        175         8.3
 Cross flow velocity(ms-1)           ND             ND      0.3-05        3          ND
 Energy consumption
 (Permeate)(kWhm-3                 0.0055          0.23     0.013        9.9        0.045
 Energy consumption
                                     0.14          70       0.0091       2.8         10
 (aeration)(kWhm-3 product)
 Total Energy
 consumption/(kWhm-3                 0.14          70          2          13         10
 Reference                       Visvanathan Ueda et Kishino           Cicek et   Suwa et
                                  et al,1997 al,1997 et al,1996        al,1998    al,1992

2.4.10 Recent development in MBR for wastewater treatment

Membranes have been finding wide application in water and wastewater treatment since
the early 1960s when Loeb and Sourirajan invented an asymmetric cellulose acetate
membrane for reverse osmosis. Many combinations of membrane solid/liquid separators in
biological treatment processes have been investigated.

Crawford et all, (2001) has emphasized that there has been three-generations of MBR
systems that have developed to date and fourth generation that is being more recently
promising. The significant development of MBR systems to date can be defined in terms of
their application, solid retention time (SRT), and mixed liquor suspended solids
concentration (MLSS). The fourth era of development is more related to larger plant
applications and to the evolving roles of owners and equipment suppliers. The initial three-
generation of MBR design are therefore largely based upon the information in Table 2.10.

Table 2.10 Three Generation of MBR Design Criterion

                         1st generation        2nd generation         3rd generation
 SRT (days)              50+                   20+                    <10-15
 MLSS (mg/L)             20,000+               20,000                 10,000
 NH3 Removal             Yes                   Yes                    Yes
 Total N Removal         No                    Yes                    Yes
 P removal               No                    Yes                    Yes
Source: Crawford, 2001

Today MBR systems used widely in Japan with several companies offering processes for
domestic wastewater treatment and reuse, and some industrial applications, mainly in the
food beverage industries where high COD wastes are common. Recently, it can be seen
that the trend of application of MBR for on-site wastewater treatment because of inherent
advantages of the system. Woolard and Sparks (2003) said that a tourists lodge in on the
Kenai Peninsula in the US state of Alaska replaced its septic tank and a mound leach field
system with MBR (ionic membranes with a 0.4 micron nominal pore size) system that
provides flexibility to accommodate seasonal changes and an anticipated increase in
wastewater flow, and continue the option for subsurface discharge.

2.4.11 Wastewater reuse

Fresh water sources are becoming scare in many countries, as a result of population
growth, increasing pollution, poor water management practice, and climatic variations.
Consequently, the development and implementation of wastewater reuse practice around
the world have shown that reclaimed water is a proven, reliable alternative resource, which
can be sold as a new product: recycled water. More importantly, water reuse can bring a
whole new approach to water management. (Lazarova et al, 2001).

A wide range of options for water reuse exists. For small and decentralized wastewater
systems, agriculture and landscape irrigation are the most common forms of water reuse.
Other options are including, industrial reuse, recreational impoundments, ground water
recharge, habitat wetlands, miscellaneous uses (Flushing toilets and fire fighting) and
augmentation of portable supplies (Tchobanoglous and Crites, 1998)

Guidelines and standard for reuse

US EPA Suggested guidelines and standard for reuse has been shown in table
2.11.Generally, water reuse application types can be urban, industrial, agriculture,
environmental and recreational, ground water recharge etc. Table 2.12 presents some of the
reuse options and recommended limit in Australia.

Table 2.11 Water quality parameters of concern for water reuse

                                        Range in secondary              Treatment goal in
                                             effluent                   Reclaimed water
 Suspended solid /(SS mg/L)                      5-50                        < 5 - 30

 Turbidity                                       1-30                        <0.1 -30

 BOD5/(mg /L)                                   10-30                        <10 - 45

 COD/(mg/L)                                    50-150                         <20-90

 TOC/(mg/L)                                      5-20                          <1-10

 Total coliform/(cfu/100 mL)                  < 10 - 107                      <1-200

 Fecal coliform/(cfu/100 mL)                   <1- 106                        <1-103

 Nitrogen /(mg N/L)                             10-30                          <1-30

 Phosphorus/(mg P/L)                            0.1-30                         <1-20
Source: Metcalf and Eddy, 2003, Lazarova, 2001 and Crites and Tchobanoglous, 1998.

Table 2.12 Water reuse options and limitations in Australia

          parameter              Groundwater       Agriculture       Unrestricted      Aquaculture
                                    recharge           reuse         urban used
 COD(mg/L)                       <20               <30              <20                <30
 pH                              6-8               6-8              6-8                6-8
 TSS                             <20               <30              <5                 <20
 Nitrate-N(mg/L as NO3-)         <10               ND               <10                <50
 Nitrite-N(mg/L as NO2-)         <1                ND               <1                 <0.1
 Turbidity(NTU)                  <2                <2               <2                 <2
 Total phosphorus                <0.5              ND               <0.5               <0.5
 ( mg/L as P)

Source: Higgins et al, 2003

                                               Chapter 3

3.1    Introduction

In this study, domestic wastewater as well as organic fraction of kitchen waste was
combined prior to the treatment. However, urine was expected to separate completely from
wastewater as this study was related to ecological sanitation. On the other hand, the
complete urine separation led to cause deficiency in nutrient requirement. As a result of
this, this study was shifted to partial urine separation mode in order to fulfill the nutrient
requirement for microorganisms. Furthermore, 50 % of urine could be separated from
wastewater under this mode.

The daily domestic wastewater and kitchen waste generation were estimated in a real
household prior to the experiment. Consequently, it has been found that domestic
wastewater generation from five-person household as 800 L/d (USEPA, 1980) and 2.75%
of the total amount (22 L/d) was used for one batch of the experiment. On the other hand,
total nitrogen and phosphorous concentration in wastewater after partial urine separation
was 35 mg/L and 5 mg/L, respectively. In fact, synthetic wastewater was prepared to
represent wastewater with partial urine separation and kitchen waste juice was mixed to
form the required wastewater stream.

3.2    Preparation of synthetic wastewater

In this study, synthetic wastewater was used as influent instead of actual wastewater.
Composition of synthetic wastewater is shown in Table 3.1. In this synthetic wastewater,
glucose (50% of COD) and soya protein (50% of COD) were used as carbon sources.
Further, COD of influent without kitchen waste juice was 580 mg/L (USEPA, 2002).
Concentrated synthetic wastewater was prepared once in eight days and stored at 50C.

Table 3.1 Composition of synthetic wastewater
 Component                      Concentration/(mg/L)
 Glucose                                272
 Soya protein                           290
 NH4Cl                                  97.1
 KH2PO4                                 26.1
 CaCl2                                   10
 MgSO4.7H2O                              10
 FeCl3                                    3
 NaHCO3                                 200
Source: Modified Chiemchaisri et al (1992), Nagoka(1999)

3.3    Kitchen waste

Average value of the municipal solid waste generation in Asia is 0.75 kg per capita and
50% of that is food waste (Visuanathan and Trankler, 2004). It could be estimated that
total organic waste in a household of five members as 1.5 kg. Then, 2.75 % of it (45g)
would be used to flush with 2.3 L of water from sink, daily. The required amount of waste
was collected from cafeteria in AIT weekly. Then, it was sorted and stored in refrigerator

at 50C. The components of the kitchen waste were adjusted according to the availability in
Thailand as presented in table 3.2. Further, three types of fruits were used as fruits were
seasonally available.

Table 3.2 Daily requirement of kitchen waste (45g)
  Composition                                  Ratio (%) w/w       Wet weight/(g)
  Carrot                                             18                  8
  Cabbage                                            18                  8
  Fruits(Three types)                                30                13.5
  Bone of thigh and wing of chicken                   8                 3.5
  Dried fish                                         10                 4.5
  Egg shell                                           2                  1
  Boiled Rice                                        10                 4.5
  Used Tea                                            4                  2
 Source: Modified from Imai et al (2003)

3.4      Activated sludge

Activated sludge was collected from wastewater treatment plant in Thammasat University,
Bangkok, Thailand. The sludge was taken from aeration tank of the treatment plant. Then,
it was acclimatized with influent wastewater for two weeks.

3.5      Lab-scale experimental study

The overall experiment can be presented in figure 3.1

                               With partial urine separation

                                     Synthetic wastewater              Kitchen waste juice

      Optimization             Sludge characteristics       BMP test      Measurements of
      of operational                                                          Removal
        parameters                                                           efficiency

                                     MLSS, MLVSS
                                     CST                                            COD
                                     SVI                                            TKN
                                     EPS                                            TP

                                  Figure 3.1 Overall experiments

3.5.1    Acclimatization of biomass

Acclimatization processes was carried out in Ambient Lab, in AIT, under ambient
temperature (26-30 0C). The sequence of the processes was 8 hour aeration and 3 hour
settling. The aeration was supported in order to maintain DO concentration in between 2-
4 mg/L. pH was adjusted in between 7-8 using 0.01 N NaOH solution. After three hours
settling time, supernatant was replaced by the wastewater. Finally, variation of MLSS
concentration was observed in the processes to verify proper growth of microorganisms.

3.5.2    Experimental set-up Membrane bioreactor

Lab scale tank with membrane bioreactor was used for the study. The reactor was made of
transparent acrylic sheet having the dimensions as shown in Appendix – A, Figure A-1.
The working volume was 6 liters. The hollow fiber polyethylene membrane was
submerged in the reactor. Further, table 3.3 shows the characteristic of membrane.

Table 3.3 Characteristic of the MBR
  Item                                           Characteristic
  Type                            Mitsubishi rayon
  Pore size                       0.4 µm
  Surface area                    0.2 m2
  Length of a fiber               0.14 m
  Area occupied by fibers         0.14 X 0.16 m2
  Membrane manufacturer           Mitsubishi Rayon Company, Japan Batch and continuous systems

Experimental setup consisted of two systems.

(1) Batch system

                               Figure 3.2 Batch system

It consisted of kitchen sink, grinder and screen as shown in figure 3.2. The system was
used to grind the kitchen waste once in eight days. Once waste was pulverized, it was
screened out using a screen with 1 mm pore size. Then, the remainder was sent for
anaerobic digestion.

(2) Continuous system


                              Figure 3.3 Continuous system
In the continuous system, synthetic wastewater and kitchen waste juice were mixed in the
mixing tank as shown in figure 3.3. Then, it was sent to the anoxic tank followed by the
MBR. MBR was aerated by the central air supply through stone diffusers while keeping
airflow rate as 5 L/min. Part of the aerated sludge in MBR was recycled back to the anoxic
tank using a pump while maintaining recycling ratio as 200 %.

A suction pump was used to extract permeate from MBR with five minutes suction and
five minutes relaxation sequence. The transmembrane pressure (TMP) was measured using
a U shaped Hg manometer attached to the system.

The samples were taken for analysis from all the sampling ports at mixing tank, anoxic
tank, MBR and permeate outlet. At the same time, pH, DO, temperature and flux were
monitored daily both in MBR and anoxic tank.

The system was cleaned every week to prevent the development and accumulation of
microorganisms in the storage system, which could decrease the concentration of substrate
before entering the system. At the same time, valve and pumps were checked.

3.5.3                               Optimum HRT and sludge characteristics

MBR was investigated for three different HRTs including 6, 4 and 2 hours and permeate
flux at different HRT is presented in table 3.4. In every HRT, average COD of wastewater
was 650 mg/L (Both synthetic wastewater and kitchen waste juice) and MLSS
concentration was maintained in between 9000-10000 mg/L .On the other hand, COD,
TKN, and total phosphorous were measured in influent as well as effluent to assess the
removal efficiency. Similarly, nitrate and nitrite concentrations were measured in effluent.
Finally, effluent water quality was compared with standard for reuse. In addition to that,
sludge characteristics such as MLSS, MLVSS, SVI, EPS and CST were measured at each
run for comparison.

Table 3.4: Permeate Flux at different HRTs

                                                                                Permeate Flux
                        HRT(hours)                   Flow rate (L/d)
                                    6                      25                       0.125
                                    4                      36                       0.187
                                    2                      72                       0.360

3.5.4                               Experiment runs

Basically, the experiment was carried out for three runs as shown in figure 3.4.
COD loading rate(kg/

                                                                                        Run III

                                                                       Run II

                                             Run I

                                                            57                    109         141

                                             Figure 3.4 COD loading rate variation in three runs

Initially, the system was investigated for six hours HRT with 2.7 kg COD/ ( for 57
days. Once, parameter analysis was conducted for the first run, the second run was started
while increasing the COD loading rate up to 3.9 kg COD/( second run was
investigated for four hours HRT for 52 days. Similarly, third run was began with two hour
HRT followed by the second run. In addition to that, time period for the third run was 32

3.5.5   Analytical analysis

Most of the analytical techniques used in this study were mentioned in the standard
methods (APHA et al., 1995). Table 3.5 lists parameters and their analytical methods and
table 3.6 shows the frequency of analysis.

Table 3.5 Analysis of various parameters
 Parameters      Analytical         Analytical            Range        Source
                 methods            Equipment
 pH                                 pH meter              0-14
 DO                                 DO meter
 COD             Dichromate         Titration             20 – 900     APHA et al.,
                 reflux                                   mg/L         1995
 SVI                                1L graduated                            -Do-
                                    cylinder and timer
 MLSS            Dry at 103-        Oven                  9000-        APHA et al.,
                 1050C                                    10000        1995
 MLVSS           Dry at 5500C       Oven                     -         APHA et al.,
 Carbohydrate    UV                 Spectrophotometer       -          Dubois et al.,
                 absorbance         (Hitachi U-2001)                   1956
 Protein         UV                 Spectrophotometer       -          Lowry et al.,
                 absorbance         (Hitachi U-2001)                   1951.
 CST                                CST apparatus           -          APHA et al.,
 TKN             Digestion                                  -               -Do-
 Total                              Direct                  -               -Do-
 phosphorous                        Spectrophotometer
 NO3-                                      -Do-             -
 NO2-                                      -Do-              -
Table 3.6 Frequency of analysis

         Parameters                    Sampling point             Frequency of analysis
 pH                              Anoxic tank / MBR                     Everyday
 DO                              Anoxic tank / MBR                        -Do-
 MLSS and MLVSS                             MBR                    Two times per week
 COD                                  Influent/effluent            Two times per week
 TKN                                        -Do-                   Two times per week
 Total Phosphate                            -Do-                   Two times per week
 Carbohydrate                               MBR                       Once per run
 Protein                                    MBR                           -Do-
 NO3-,NO2-                                Effluent                 Two times per week

3.6       Membrane cleaning

When transmembrane pressure was increased up to 60 kPa, membrane was required to
clean. In fact, chemical cleaning was preferred for the hollow fiber membrane. Because,
chemical cleaning helped to reduce the increases transmembrane pressure back down to a
level close to the initial level and this would enable stable operation over an extended
period of time. Generally, there are two ways of doing chemical cleaning such as in-line
cleaning and out-of-system cleaning. In this experiment out-of-system cleaning was
preferred. Procedure of out of system chemical cleaning as follows:

      •   Cake layer adhere to the membrane was removed by flushing with tap water.
      •   The unit was immersed completely into a chemical cleaning tank with chemical
          solution containing a mixed of sodium hypochlorite (effective chloride about 3000
          mg/L) and 4% (wt/vol) of aqueous sodium hydroxide solutions. It is allowed to
          stand for 6-24 hours.
      •   The membrane was rinsed with water to remove chemicals prior to its installation
          back to the reactor.
      •   Membrane resistance was determined to find recovery.
      •   More than 85 % of recovery was obtained before inserting back to the system.

3.6.1     Membrane resistance

Membrane resistant is the indicator for efficiency of a membrane. It can be measured by
filtrating with pure water at different filtration fluxes and recording corresponding
transmembrane pressure. Membrane resistance is derived from the slope of the linear curve
of transmembrane pressure versus flux as in equation 3.1.
                     J =         ⇒ ∆P = J * µ * Rt                       Eq: 3.1
                          µ * Rt

J : permeate flux(L/m2.h)
∆P : transmembarne pressure(KPa)
µ : Viscocity of the permeate(N.s/m2)
Rt : Total Resistance (m-1)

3.7       Sludge settling

Conventionally, the Sludge Volume Index (SVI) has described the sludge settling
properties. SVI can be calculated using equation 3.2.

                               Settled sludge volume (mL/L) X 1000
                            SVI =                                          Eq: 3.2
                                      Suspended solids (mg/L)

•     SVI = 100 mL/g is considered a good settling sludge
•     SVI >150 mL/g are typically associated with filamentous growth (Metcalf and Eddy,

3.7.1     Diluted SVI (DSVI)

Metcalf and Eddy (2003) has introduced DSVI test as follow: The sludge sample is diluted
n times with process effluent until the settled volume after 30 minutes is 250mL/L or less.
And after that, SVI standard method is applied for this sample.
                 (settled volume of sludge, mL/L)(103 mg/g) mL
        DSVI =                                                 =              Eq: 3.3
                           (suspended solids, mg/L)              g

          SVI = DSVI* n        (mL/g)                                         Eq: 3.4

3.8       Sludge dewatering

The dewatering of sludge is very important in terms of membrane fouling. It helps
assessing the easiness in filterability of the sludge. Capillary suction time test is used to
characterize the sludge dewaterability. The time the filtrate requires to travel a fixed
distance in the filter paper is referred to a CST. A large CST usually implies poor sludge

3.9       Extra cellular polymer substances (EPS)

EPS containing protein and polysaccharide have been considered to be a source of
membrane fouling in MBR process. Therefore, it is important to control the amount of EPS
to reduce membrane fouling during the operation and maintenance of in MBR. EPS has a
relationship with dewaterability of sludge. It has been widely reported that the increase of
EPS in sludge would lower the sludge dewaterability measured.

EPS is considered in two types:

      •   Bound EPS (sheaths, capsular polymers, condensed gel, loosely bound polymers,
          attached organic material).

      •   Soluble EPS (soluble macromolecules, colloids, slimes).

3.9.1 Measurement of EPS

Thermal extraction method was used to measure EPS in this experiment. The whole
processes can be shown in figure 3.5. Basically, this process consists of centrifugation and
thermal extraction. First of all, samples were centrifuged for 25 minutes under 4000 r.p.m
to separate soluble EPS and bound EPS. Then, thermal extraction was carried out at 800C
for 1hour to extract bounded EPS.

      (a) Protein

      Protein in the mixed liquor and bound EPS was measured by Lowry Assay method as
      mentioned in Lowry et al (1951). The range of the sensitivity is 5- 100 µg/mL. The
      absorbance of the color after 30 min was read against a blank at 750 nm.

     (b) Carbohydrate

     Carbohydrate in mixed liquor and bound EPS was measured by phenol/sulphuric acid
     method of Dubois et al. (1956). The color obtained was allowed to develop 30 min,
     after which the sample was read against a blank at 490 nm. The standard curve was
     constructed by using glucose.


                                                           Soluble EPS

                                  Bound EPS

                                              4000 rpm, 25 min

                                                    UV adsorption
                                                     (mg /g SS)

                                                   UV adsorbance

                          4000 rpm, 25 min          Carbohydrate
                                                     (mg/g SS)

                          Figure 3.5 Thermal extraction method

3.10 Biological methane production test (BMP)

3.10.1 Materials needed to conduct BMP test (Hansen et al, 2004)

1.      Grinder to reduce waste particle size into fine solids as possible
2.      A total of 6 glass bottles of 2.5 L to be used as BMP test reactors.
3.      Inoculum was obtained from anaerobic waste treatment plant.
4.      Incubator at 37°C.
5.      Glass syringe of 1mL.
6.      Gas Chromatograph.
7.      Gas mixture of 80% N2 and 20% CO2 was used in flushing the headspace of the
        reactors to ensure anaerobic conditions.
8.      Blank reactors (water + inoculum) and control reactors (avicel and cellulose
        powder + inoculum)

3.10.2 BMP (Biological Methane Production) test procedure

The detailed procedure is described in the following.
   • 5 kg of waste was pulverized to reduce particle size and mixed well (no water
   • 1 kg of waste was measured to determine dry matter (DM) content of the original
   • Water was added to the remaining waste (4kg) and blended further
   • After homogenization, 1kg of waste was measured and diluted to a dry matter
       content of 10% and mixed well. Then, a small sub-sample was used for the
       determination of volatile solid and for methane potential measurement.
   • Duplicate sample was necessary in measuring methane production potential due to
       varying quality of inoculums and heterogeneous quality of waste.
   • Initially, 400ml of inoculums was measured and transferred to all to reactors. All
       reactors contained a uniform of 400ml of inoculums. Then, inoculums were stirred
       constantly because the inoculums may contain many particles and were not a
       homogeneous suspension. Also during stirring, each reactor was supplied with
       100ml of sample. Each reactor contained 2g VS/100ml of sample solution which
       was suitable to avoid acidification of the process.
   • After set-up, the reactors were covered tightly with a cap equipped with thick
       rubber septum. The reactors were flushed for 2 minutes with an anaerobic gas
       containing 80% N2 and 20% CO2 to ensure anaerobic conditions in the headspace
       of the reactor.
   • The reactor was incubated at 37°C. During first week of the experiment close
       monitoring (occasional shaking of the reactor to avoid temperature variations) and
       regular methane content measurement were done daily. The incubation time was 50

3.11   Initial study on minimizing fouling

In this research, the sever problem faced was fast fouling .Hence the research direction was
focused on investigation of mechanism to diminish fouling. Thus, incorporation of moving
media to the system was done to investigate the fouling frequency and to compare the
fouling frequency of attached and suspended growth. Further, the existing reactor was
modified as shown in Appendix-A; figure A-2 in order to provide sufficient space for
media. 0.6 kg of cylindrical shape polypropylene media was used in the experiment
(Tsubone et al, 1994). Further, 50% of reactor was occupied with media.

3.11.1 Overall experiment

Figure 3.6 presents the overall experiment. The experiment was initially carried out for
HRT 2 hours.

                             With partial urine separation

                               Synthetic wastewater          Kitchen waste juice

       With moving media                                 Without moving media

                                  HRT = 2 hours

 Sludge characteristics        Fouling characteristics       Measurements of
                                                             Removal efficiency

      MLSS, MLVSS                        EPS
      CST                                                           NH4

                            Figure 3.6 Overall experiment

3.11.2 Experimental setup

Existing experimental set up was simplified to investigate the clogging frequency as
presented in figure 3.7. In fact, anoxic tank was removed from the system and two new
reactors were installed with 11 liter working volume.



                             Figure 3.7 Experimental setup

3.11.3 Process description

Wastewater was mixed in the mixing tank and sent to two reactors through level control
tank. Two parallel reactors were operated under four hour HRT. At the same time, DO was
maintained in both reactors in between 2-4 mg/L keeping air flow rate 10 L/min.

A suction pump was used to extract permeate from MBR with 10 minutes suction and two
minutes relaxation sequence. The transmembrane pressure (TMP) was measured using a U
shaped Hg manometer attached to the system.

The samples were taken for analysis from all the sampling ports at mixing tank, MBRs and
permeate outlets. At the same time, pH, DO, temperature and flux were monitored daily
both in MBRs.

The system was cleaned every week to prevent the development and accumulation of
microorganisms in the storage system.

                                                           Chapter 4

                                                     Results and Discussion

4.1    Initial membrane resistance

Initial membrane resistance was measured prior to the use. The variations of flux with
transmembrane pressure at ambient conditions are shown in Appendix-B. It could be seen
the linear relationship. The initial membrane resistance value was required to ensure the
proper cleaning.

4.2    MLSS variation

It was important to mention that the experiment was supposed to start with synthetic
wastewater which was under complete urine separation condition. However, it was found
that the amount of nitrogen and phosphorous in the wastewater was not sufficient for the
growth of microorganisms in biological processes. Consequently, required COD: N: P
(100:5:1) ratio was maintained while shifting to the partial urine separation case.

The system was investigated for HRT 6 hours in MBR and HRT 1 hour in Anoxic tank
with 260 % recycling ratio (Parameshwara, 1997). Then, it was noticed that the sudden
increment in MLSS concentration in MBR as well as Anoxic tank as shown in the figure
4.1 and figure 4.2, respectively.

          Concentration(mg/L)X 10

                                                      MLSS           MLVSS
                                         0      10       20         30        40   50   60

                                         Figure 4.1: MLSS and MLVSS variation in MBR

After MLSS concentration increased up to 9000-10000 mg/L range, COD, TKN and Total
phosphorous were measured in influent as well as effluent. Further, the same MLSS range
was maintained throughout the experiment in terms of removing 450 mL of sludge daily.
Consequently, SRT in the system was 13 days in the first run.

         Concentration (mg/L) X 10
                                                      MLSS         MLVSS



                                          0    10      20      30      40      50      60
                                     Figure 4.2: MLSS and MLVSS variation in Anoxic tank

Similar MLSS range was used for the second run in order to optimize the system for HRT.
The second run was started followed by the first run with HRT 4 hours in MBR and 1
hour HRT in anoxic tank with recycling ratio 200 %.Recycling ratio in the system was
adjusted in order to fix the HRT in anoxic tank. After system was stable with respect to DO
pH and MLSS concentration both in MBR and anoxic tank, parameters were measured. To
maintain the required range of MLSS, sludge wastage was performed daily. Further, the
SRT of the system was become as 8 days.

Third run was investigated for HRT 2 hours in MBR and the same was used for anoxic
tank while adjusting recycling ratio as 100 %.As previous case, sludge was wasted daily
and SRT was 6 days.

4.3    Hydraulic retention time

Performance of the MBR system was investigated for partial urine separation stage by
varying HRT including 6, 4 and 2 for Run 1, Run 2 and Run 3 respectively. Flux was
adjusted in each run as 34, 50, and 100 mL/min respectively with five minutes on and five
minutes off cycle, to maintain the HRT values. Transmemebrane pressure variation was
recorded daily. Once, the transmembrane pressure difference exceeded 75 KPa, membrane
was chemically cleaned.

4.4    Transmembrane pressure variation

Transmembrane pressure variation in Run 1, Run 2 and Run 3 can be shown as in figure
4.3, figure 4.4 and figure 4.5 respectively. At the beginning of the first run, transmembrane
pressure was not increased for 22 days. The reason for this was due to the time requirement
for increasing the MLSS concentration in the system. Once, it was finished, it was
increased beyond 60 KPa. Then the membrane was cleaned. It could be obtained 97 %
recovery. During the first run, it was cleaned after 27, 19 and 18 days respectively.

                80                                                       TMP

                      0      10        20 Day 30          40      50        60
                          Figure 4.3: TMP variation in Run 1(HRT = 6 hours)

                                                                  TMP variation




                      0      10        20         30         40          50       60

                           Figure 4.4 Variation of TMP in Run 2(HRT = 4 hours)

                                                         TMP variation




                      0      5       10      15         20        25      30      35

                           Figure 4.5 Variation of TMP in Run 3(HRT = 2 hours)

                                               Air flow rate = 1L/min per 1L of reactor

                                                                                                        1.66L/min per
 Days for clogging(day)    35

                                                                                                        1L of reactor
                                                                                                        Air flow rate
                           30    27
                                        19     18        18
                           20                                      17       17
                           15                                                                          11               10
                           10                                                             6
                                 Run 1(HRT = 6 h)    Run 2(HRT = 4 h) Run 3(HRT = 2 h)
                                               Figure 4.6: Days for clogging

The system was able to run for HRT 4 hours for 17 days without clogging. But, in the third
run, it was only for six and four days respectively. In addition to that, it was also noticed
that DO concentration in the MBR was dropped to 0.5 mg/L .As a result of this, system
was not able to run for aerobic condition. Then, the air flow rate was increased from 1
L/min per 1 L of reactor volume to 1.667 L/min per 1 L of reactor volume, in order to
provide sufficient air supply. Consequently, turbulence inside the MBR was increased.
Because of the turbulence condition developed inside, system was able to run for 11 days
as shown in figure 4.6.

4.5                        Sludge characteristics

Any activated sludge processes requires considerable cost for waste sludge handling and its
disposal. Sludge dewatering is the major technique used to handle the sludge. Ability to
dewater the sludge is reflected by the characteristic of sludge. In this experiment, several
tests were carried out in order to measure sludge characteristics in every HRT as shown in
table 4.1.

 Table 4.1: Sludge characteristics

                                     Run 1            Run II               Run III
               Parameter                                                                       sludge             Reference
                                   (HRT = 6 h)      (HRT = 4 h)          (HRT = 2 h)
                                                                                                                  Liu &
        CST/(S)                        38.60             61.90                 144             21.60
                                                                                                                Medcalf &
        SVI/(mL/g)                      50                 62                  168             108.67

CST and SVI are the two main characteristics which determine the dewaterability and the
settalbility of sludge respectively. It could be seen that the CST of MBR sludge is higher
than the value obtained for activated sludge processes. It implies that the difficulty in
dewatering processes is higher in sludge from MBR than activated sludge. SVI is the
second characteristic which is helpful to identify the settalability of sludge. SVI should be
lesser than 100 mL/g in order to have good settelability. Once, it is beyond 150 mL/g, it is

suspected that there is a filamentous growth in the reactor. According to the results
obtained, SVI is less than 100 mL/g in both first and second runs whereas it is more than
100 mL/g in activated sludge process. In case of third run, it was beyond 150 mL/g.

EPS is another important sludge characteristic which determines the tendency of clogging.
In this experiment, EPS was measured in terms of carbohydrates and protein during each
run and average values were obtained. Figure 4.7 presents the average bounded protein and
carbohydrate variation with HRT. It can be clearly seen that bounded protein in the system
was significantly increased while decreasing HRT to 2 hours. Further, bounded protein in
the system was found as 32.9 mg/g VSS, 33.6 mg/g VSS and 59 mg/g VSS in HRT 6, 4
and 2 hours respectively. This should be the main reason for faster clogging of the

      EPS concentration( mg/ g VSS).



                                                                                       Bounded protein
                                                                                       Bounded carbohydrate
                                                                                       Total bounded EPS

                                             HRT = 6 h    HRT = 4 h        HRT = 2 h

                                                 Figure 4.7: Variation of EPS in three runs

4.6                               Dissolved oxygen and pH variation in the experiment

4.6.1 Dissolved oxygen (DO)

DO and temperature in both MBR and anoxic tank were measured daily. DO in MBR was
significantly decreased while decreasing HRT whereas DO in anoxic tank was varied in
between 0.11 mg/L – 0.30 mg/L as presented in figure 4.8. At the beginning of the first run
DO level was 6.8 mg/L and it was gradually decreased while moving to the second run.
However, there was a sudden decrease in DO level in MBR while moving to the third run
with HRT two hours. Further, it could be observed that DO level was dropped from
3.14mg/L to 0.5 mg/L. This rapid variation may be due to higher consumption of oxygen
because of high organic loading. In fact, organic loading rate in the third run was double
that of the second run. Consequently, air flow rate had to increase up to 1.66L/min per 1 L
of reactor volume in the last run in order to maintain aerobic condition in the system. As
result of this, turbulence condition was slightly improved in the MBR led no rapid fouling

 in last two cycles as mentioned in section 4.4. However, air flow to the system had been
 increased to 1.66 L/min per 1 L of reactor volume.

                                                  Run 1                  Run 2                  Run 3
       DO Concentration (mg/L)...

                                     8        (HRT = 6 hours)        (HRT = 4 hours)        (HRT = 2 hours)








                                         0        20            40           60        80           100       120

                                                                     DO in MBR          DO in Anoxic
                                             Figure 4.8: Variation of DO in MBR and Anoxic tank

 In the case of anoxic tank, DO level was prevailed less than 0.3 mg/L throughout the
 experiment which caused to develop anoxic condition in the system (Metcalf and Eddy,
 2003). Further, it has become a proper nitrogen removal in the effluent.

 4.6.2                              pH and temperature variation

  pH varied in the MBR in between 7.01- 8.02 throughout the experiment while having
 23.4 0C - 29.60C temperature inside the MBR. Further, since required pH existed in the
 system, it supported proper growth of microorganisms. Similarly, quite high temperature in
 the system caused to improve the biological treatment. In the case of anoxic tank, pH
 varied within the range of 7.0-7.88 in this experiment, which was slightly lesser than that
 of in influent.

 Influent pH is also important because, it was the main parameter which determined pH
 both in anoxic tank and MBR. Normally, it was maintained in between 7-8.01.Moreover,
 pH was measured in the influent before released to the system to ensure.

 4.7                                Removal of organic matter, nitrogen and phosphorus

 4.7.1 Organic matter

Variation of influent and effluent COD and percentage of removal efficiency is presented in
figure 9. In this experiment, synthetic wastewaters as well as kitchen waste juice were used
as influent. In addition to that, COD of the synthetic wastewater was 580 mg/L and COD of
combination of both synthetic wastewater and kitchen waste juice altered the within the
range of 590 mg/L to 785 mg/L as show in figure 4.9.This variation resulted mainly because
of kitchen waste juice in which COD varied.

                        90                                                                                   800

                                                                                                                   COD Concentration(mg/L)
Removal efficiency(%)

                        70                                                                                   600
                                            Run 1                 Run 2              Run 3                   500
                                          (HRT = 6 h)           (HRT = 4 h)        (HRT = 2 h)
                        50                                                                                   400
                                                                                   Removal efficiency        300
                        30                                                         Influent                  200
                                                                                   Effluent                  100
                        10                                                                                   0
                             0        5          10      15          20       25           30           35
                             Figure 4.9: Variation of COD removal efficiency, influent and effluent
                                        COD concentration

Effluent COD was quite high at the beginning of the first run as it was carried out with
synthetic wastewater prepared under complete urine separation case. In fact, it was 34 mg/L
and that may be due to low MLSS (5,000 mg/L) concentration in the system and lack of
nutrient for the growth of microorganisms. After shifting to the partial urine separation case,
it could be notice that effluent COD less than 15 mg/L

At the beginning of the first run, it was observed that 94 % COD removal efficiency and it
was increased up to 98 % at the end, once MLSS increased up to 10,000 mg/L. In the
second it was about 98 % and in the third run, it was more than 98%.Therefore, in terms of
COD removal efficiency, third run gave better than other two runs.

4.7.2                        Nitrogen removal

TKN was measured in effluent as well as influent in order to compare the removal
efficiency in each run. Variation can be presented as shown in figure 4.10.Influent TKN was
varied in between 50 mg/l – 60 mg/L during the experiment. This variation was resulted
mainly because of kitchen waste juice. In addition to that, it could be maintained the
required total nitrogen content in each run in order to have proper growth of microorganism.
In the case of effluent, average TKN concentrations were 4.67 mg/L, 3.0 mg/L and 8.2 mg/L
in Run 1, Run 2 and Run 3, respectively.It could be seen that the highest TKN concentration
was obtained in Run 3 and the lowest TKN was observed in Run 2. According to the results,
it can be concluded that Run 2 effluent gives better quality effluent than other two runs.
Further, it can be explained in terms of removal including 91 %, 95% and 86% in Run 1,
Run 2 and Run 3, respectively. The maximum removal efficiency was 95 % and it was in
the second run.

                           80                                                                                     100
TKN Concentration (mg/L)

                                                                                                                        Removal efficiency (%)
                           50                                                                                     60
                           40                                                                                     50
                                        Run 1                       Run 2                     Run 3               40
                                    (HRT = 6 hours)              (HRT = 4 hours)          (HRT = 2 hours)         30
                           10                                                                                     10
                            0                                                                                     0
                                0            5                   10                15              20        25
                                                      Influent         Effluent         Removal efficiency

                                                 Figure 4.10 TKN variation in three runs Nitrogen Balance

Mainly, there are two path ways of removing nitrogen called assimilation into the biomass
and nitrification and denitrification as shown in figure 4.11. During the nitrification
processes, ammonium nitrogen is oxidized to nitrite and nitrate by nitrifying bacteria under
aerobic condition. The amount of nitrogen mass balance can be written as follows:

TKNi + NO2-Ni +NO3-Ni = TKNe + NO2-N +NO3-N + Nitrogen assimilated                                           Eq: 4.1
                         +Nitrogen loss due to denitrification

Eq. 4.1 can be re-written to find out nitrogen lost due to denitrification

Nirtrogen lost in denitrification = (TKNi -TKNe) + (NO2-Ni - NO2-Ne)
                                      + (NO3-Ni + +NO3-Ne –α (BOD5i-BOD5e)                                   Eq: 4.2

Where α = Concentration factor (Ratio of nitrogen to BOD5)
      i = Influent
      e = Effluent

The term α (BOD5i-BOD5e) represents the removal of nitrogen assimilation. It is generally,
accepted that during the aerobic process of organic matter removal, each 100 mg/l of
BOD5 needs 5 mg/L of nitrogen(N) and 1 mg/L of phosphorous. Based on this, BOD/N
ratio (α) can be found as 0.05.In addition to that, the mass balance of nitrogen in the MBR
system has presented in Appendix C as a specimen calculation for Run 1(HRT = 6 hours)
and it can be summarized as shown in figure 4.12.

                                                                                       Outflow of nitrogen compounds
                                                                                       (TKN + NO3-N + NO2-N)


  Inflow of nitrogen compounds                                                              Assimilation of nitrogen into biomass
  (TKN + NO3-N + NO2-N)

                                                          Escape of Nitrous gases due to
                                              Figure 4.11 Schematic diagram for Nitrogen Balance


                                                   Influent nitrogen                   Total Nitrogen in effleunt
       Nitrogen concentration(mg/L)

                                                                                       Nitrogen lost in assimilation
                                                                                       Nitrogen lost by denitrification

                                            In    Out                  In       Out              In        Out


                                            Run 1(HRT = 6 hours)       Run 2(HRT = 4 hours)       Run 3(HRT = 2 hours)

                                                         Figure 4.12 Nitrogen mass balance

According to the results obtained from the nitrogen balance, it can be concluded that Run 2
(HRT = 4 hours) provided the highest nitrogen removal among other runs. Further, it could
be assured that the nitrogen was removed as a gas because of denitrification using the
observation of bubble forming inside the anoxic tank. In addition to that, it is essential to
mention that there were no significant changes in pH and DO level throughout the

    4.7.3 Phosphorous removal

    Total phosphorous variation in three runs has been shown in figure 4.13.Influent total
    phosphorous concentration was varied in between 6 mg/L to 8 mg/L all over the
    experiment. In addition to that, average total phosphorous concentration in effluent was
    0.77 mg/L, 0.58 mg/l and 0.72 mg/L in Run 1, Run 2 and Run 3 respectively. Hence, the
    Run 2 provided the highest quality effluent. Furthermore, total phosphorous removal
    efficiencies can be 87.4 %, 92.6% and 90.6% in Run 1, Run 2 and Run 3 correspondingly.
    Therefore, it can be concluded that Run 2 as the most suitable run for total phosphorous

                                         20                                                                                                    100
                                         18                                                                                                    90
               TP Concentration (mg/L)

                                                                                                                                                           Removal efficiency (%)
                                         16                                                                                                    80
                                         14                                                                                                    70
                                                  Run 1(HRT = 6         Run 2 (HRT = 4 hours)                Run 3 (HRT = 2 hours)
                                         12                                                                                                    60
                                         10                                                                                                    50
                                          8                                                                                                    40
                                          6                                                                                                    30
                                          4                                                                                                    20
                                          2                                                                                                    10
                                          0                                                                                                    0
                                              0          2        4     6          8             10         12        14        16       18
                                                             Influent              Effluent                       removal efficiency

                                                         Figure 4.13 Total phosphorous variation in the experiment

    4.8 Nitrate and Nitrite

                                                                                                                                                     Nitrite concentration(mg/L)


                                              Run 1 (HRT= 6 hours)          Run 2 (HRT= 4 hours)                  Run 3 (HRT= 2 hours)
  Nitrate and DO



                                 0                                                                                                              0
                                         0           2            4         6           8              10           12          14         16
                                                                                       Day              Nitrate            DO        Nitrite

                                                               Figure 4.14 Variation of nitrate and nitrite

Nitrate and nitrite concentrations in effluent were measured to compare with the reuse
standards. Variation has been presented in figure 4.14. It can be clearly seen that effluent
nitrate concentration was decreasing while increasing HRT whereas nitrite was raised up.
The main reason for sudden increment in nitrite may be due to the insufficient dissolved
oxygen in the reactor to convert nitrite in to nitrate. Hence, the nitrite was released without
formation of nitrate.

Furthermore, this can be explained considering the dissolved oxygen variation while
increasing HRT as shown in figure 4.14. In the Run 3, air flow rate had to be raised up to
10 L/min in order to provide sufficient oxygen.

In the Run 1 and Run 2, average nitrate concentrations were 10.2 mg/L, 7.8 mg/L whereas
nitrite concentrations were 0.138 mg/L and 0.143 mg/L, correspondingly. However, Run 3,
nitrate 3.72 mg/L and nitrite was increased up to 2.5 mg/L in the last run.

4.9    Comparison of effluent water quality with standard

Reclaimed water applications range from pasture irrigation to augmentation of potable
water supplies. Water reclamation and reuse criteria are principally directed at health
protection and it may vary from country to country. In this study, Reuse guidelines in
Australia were considered as the root.

In this study, it was focused on water reuse options including ground water recharge,
agriculture, aquaculture and unrestricted urban reuse. In addition to that, effluent water
quality was measured in terms of COD, Total phosphorous, Nitrate and Nitrite and
compared with standards as shown in table 4.2. Hence, the most suitable operating
condition of the system was determined.

In the case of ground water recharge and unrestricted urban reuse, effluent from Run 1
(HRT = 6 hours) and Run 3 (HRT = 2 hours) were not adequately treated, because nitrate,
nitrite and total phosphorous level in the effluent exceeded the standard valve.
Furthermore, the effluent nitrate concentration should be considered prior to the discharge
as it would cause significant impact on health causing blue baby syndrome. However,
COD concentration in effluent in three different runs matched with the required limit.
Hence, it can be concluded that effluent from Run 2 (HRT= 4 hours) was the most suitable
operating condition for reuse for above mentioned two options among them.

Effluent water qualities in three different runs were compared with standard values to find
the fitness in agriculture reuse. It can be found that effluent from both Run 1(HRT= 6
hours) and Run 2(HRT= 4 hours) were more suitable for agriculture reuse as effluent water
quality parameters matched with standard.

In the case of aquaculture reuse, effluent nitrite level should be lesser than 0.1 mg/L but
throughout the experiment, it was beyond the limit. Similarly, total phosphorus
concentration was over the required value in three different runs. Hence, the effluent from
this system was not viable for reuse water. Because, excess nitrite concentration can give a
toxic effect on aquatic life.

Table 4.2 Effluent characteristics

                      Operating condition                    Reuse options(Higgins et al, 2003)
                    Run 1 Run 2      Run 3                Ground water
    Parameter       (HRT=        (HRT=       (HRT=        recharge     &
                    6 hours)      4 hours)   2 hours)                      Agriculture   Aquaculture
                                                          urban reuse
 COD/(mg/L)         13.5          10.33        10             <20             <30           <30
 TKN(mg/L)          4.67           3.0        8.0             ND              ND            ND
 TP/(mg/L)          0.77          0.55        0.72            <0.5            ND            <0.5
 NO3-(mg/L)         10.4           7.4        3.72            <10             ND            <50
 NO2 (mg/L)         0.12          0.143         -              <1             <1            <0.1
 Turbidity(NTU) 0.21               0.3        0.31             <2             <2             <2
Note: ND = not defined

So far, the operating conditions were compared according to the key constitute such as
nitrate, nitrite, COD, turbidity and total phosphorus. But, it is essential to compare it with
respect to effluent coliform. As influent to the system was free from micro organism,
effluent coliform concentration was not significant in this study. However, MBR sludge
itself consisted of lesser amount of micro organisms. As micro filtration was capable of
removing pathogenic micro organisms, effluent water was free from bacteria.
Nevertheless, Parameshwara (1997) obtained 100 % of micro organism removal regardless
of operating condition (HRT, transmembrane pressure etc) using 0.2 µm micro filtration
membrane for actual domestic wastewater. Further, both fecal and total coliform in the
effluent were lesser than 2/100 mL. Therefore, it can be concluded that in terms of effluent
coliform concentration, there is not significant health impact on flora and fauna from the
effluent of the system.

4.10   Incorporation of moving media to the system to minimize fouling

In this research, at low HRT significant fouling was notes as presented in section 4.4.
Hence the research direction was focused on investigation of mechanism to diminish
fouling. Thus, incorporation of moving media to the system was done to investigate the
fouling frequency and to compare the fouling frequency of attached and suspended growth.
The moving media was used mainly, because it will be an attractive as a cost effective
method. Further, existing reactor was modified as shown in Appendix-A and Appendix-D
in order to provide sufficient space for media.

Initial membrane resistances were measured in both membranes prior to the start. Table 4.3
presents initial membrane resistance of two membranes and the basic step of determination
of initial membrane resistance has been presented in Appendix-D.

Table 4.3 Initial membrane resistances

 Reactor                       Initial membrane resistance x 1011( 1/m)
 Attached growth                                2.2105
 Suspended growth                               2.4315

4.10.1 TMP variation

In this study, MLSS concentration was maintained around 9000 – 10000 mg/L range with
air flow rate of 1.88 L/min per 1L of reactor volume. Initially, experiment was carried out
for HRT 2 hours and the effluent flow rate from each reactor was 110 mL/min. Besides,
TMP variation in both reactors with attached growth and suspended growth was observed
as presented in figure 4.15. Accordingly, it could be experienced faster clogging in reactor
with suspended growth than that of attached growth. Further, suspended growth system
was clogged after two days while attach growth system was clogged after seven days of
operation. It can be concluded that attach growth provides the necessary environment in
the reactor to resist the faster clogging.

                                     Attach growth reactor
                   90                Suspended growth reactor




                        0        5         Day     10                15
       Figure 4.15 Variation of TMP in attached growth reactor and suspended
                                  growth reactor

Though, attached growth reactor proved lesser fouling compared to the suspended growth,
the frequency of fouling was still higher. For this reason, further studies on this system
should be carried out in the future to find the optimum operational parameters.

4.10.2 Sludge characteristics

EPS is one of the important characteristics which can be used to interpret about fouling.
EPS itself consists of carbohydrate and protein in soluble form as well as bounded from.
However, it has been found that bounded EPS in the system is predominant in fouling.
Figure 4.16 shows the variation of bounded EPS component. Hence, it can be found that
the bounded EPS in both attach and suspended growth as 49 mg/ g VSS and 51 mg/ g VSS
respectively. Similarly, it can not be observed a significant difference of bounded EPS in
both reactors. Thus, it can be concluded that EPS is not a dominant parameter in the case
of faster fouling of reactor with suspended growth.

CST plays a vital role in sludge handling as certain amount of sludge was removed daily
from the system. At, the beginning of the experiment, CST was 250 second in the attached
growth reactor and it was decreased up to 105.3 second in the second week. However, in
suspended growth reactor, it was found as 50.2 second at the beginning and it was
increased up to 69.84 seconds in the second week. Once CST becomes higher, lesser the
opportunity of dewatering. Here, sludge removed attached growth reactor will be more
difficult to dewater than that of suspended growth.

                                                             Bounded protein

            EPS component
              (mg/g VSS)
                                                             Total bounded EPS
                                 Attached growth
                      Figure 4.16 Variation of bounded EPS in the system

4.10.3 Removal efficiency

Removal efficiency of COD and NH3 were determined in this study to find the
performance of the system. It could be obtained average 96.5 % of COD removal from
attach growth reactor and 96 % of COD removal from suspended growth reactor. It reflects
that although clogging frequency is different, removal efficiency remains almost the same.
In the case of NH3 removal, reactor with attached growth provided the 87 % whereas
reactor with suspended growth provided 83 % removal. Therefore, it can be concluded that
reactor with attached growth higher capability of removing ammonia.

4.10.4 DO and pH variation

DO and pH variation in both reactors were measured using DO and pH meter daily. It
could be seen that pH in the attached growth system varied 6.6 - 7.30 and 6.85 - 7.32 pH
variation was observed in suspended growth. Hence, there was not significant difference in
pH in both reactors. DO concentration in reactor with suspended growth varied 3.1- 4.4
mg/ L .In the reactor with attached growth; DO level varied 1.7 - 3.1 mg/L. Thus, it was
noted slightly higher DO level in suspended growth than attached growth.

4.11   Proposed treatment unit design

One objective of this research study was to develop a package treatment unit for a
household with the aid of the experimental findings. The treatment package unit was
designed based on concept described by Woolard and Sparks (2003). Figure 4.17 presents
the schematic diagram of the proposed package treatment unit for a household of five
members and table 4.4 presents technical data. Further, basic calculation steps of
dimensions and the energy requirement have been presented in Appendix E. This system
was further modified after application of moving media (cylindrical polypropylene media)
to the system as shown in the following figure.

                  (a) Perspective view

                     (b) Plan view

Figure 4.17 Schematic diagram of proposed treatment unit

Table 4.4 Technical data

  Domestic wastewater                  Unit                        For a household of five
  treatment unit                                                   members
  Daily wastewater flow rate           m3/d                                  0.8
  Total height of the unit             M                                     1.2
  Space required                       M2                                    0.5
  Air flow                             L/ min per I L of reactor             1.0
  Recycling ratio                      %                                     200
  Average Influent COD                 mg/L                                  650
  Effluent COD                         mg/L                                   12
  Membrane (Hollow fiber )
      • Pore size                      µm                                   0.4
      • Area                           m2                                   4.4
  Power consumption                    KWh/day                              22.2

4.12 Methane production potential (Lab scale)

Methane production potential was measured for source-separated organic household waste.
The experiment was carried out as a batch experiment and duplicates were used as the
waste was not homogeneous. In addition to that, the methane content in the reactor was
measured regularly using gas chromatography. Finally, average methane production
potential was determined.

Figure 4.18 shows curves obtained for the organic fraction of kitchen waste and sludge
removed from MBR and the calculation steps has been presented in Appendix F. Although,
the methane production potential is defined as the maximum of methane produced during
the 50 days of the experiment, it took more than 50 days for the completion of the
generation in this experiment. Nevertheless, there was not significant increment of
methane production observed after 30 days.

It could be obtained 401 mL of CH4/ g VS of methane production in this experiment under
standard temperature and pressure. It reflects the higher biodegradability in kitchen waste.
However, Hassen (2004) has found methane production potential of household waste
as 495 mL CH4/ g VS, which was quite high compared to the value obtained in this
experiment. Variation can be due to use of non-standardized inoculums and waste
              Methane production

               ( NmL/ g VS)

                                   0   20           40      60        80
            Figure 4.18 Cumulative methane productions in kitchen waste

The BMP test incorporated favorable environmental condition for the microorganisms such
as pH, and temperature. Therefore, it can be used to determine the maximum methane
could be obtained for the certain amount of volatile solid. The methane potential represents
a guide to the target results. However, it is not practical to achieve this limit in reality.

BMP test is a benchmark in anorobic digestion to recovery energy using methane gas.
Similarly, energy recovery is one objective of ecological sanitation for sustainable
development. However, the amount of methane produced should be feasible to recover
energy from waste considering as a resource.

Tanikawa et al (2004) has found that the amount of methane produced in actual anaerobic
digestion facilities varied 110–160 m3/ tonne of kitchen waste. Further, they have found
that 0.135 m3 of methane produced per 1 kg of kitchen waste practically. But, it could be
obtained 0.305 m 3 of methane gas per 1 kg of mixture of kitchen waste and sludge
wastage from the lab scale BMP test. According to that, in reality, there is a 44 %
reduction in methane production. The amount of methane produced using this waste can be
found as 6.05 m3 for a month as shown in Appendix E. Moreover, it is expected to produce
the maximum 55.7 KWh energy using waste from a household in a month. (Appendix
F).Besides, Pachauri (2004) has estimated average monthly household energy requirement
(five people household) in India as 275 KWh. Therefore, it can be concluded that 20 % of
energy requirement can be supplied from anaerobic digestion of kitchen waste.

                                         Chapter 5

                           Conclusions and Recommendations

5.1    Conclusions

This research study was mainly focused on the applicability of aerobic membrane
bioreactor to over come the deficiencies appeared in existing conventional decentralized
sanitation system. Initially, the deficiencies in conventional decentralized sanitation
systems were reviewed. However, in this study, it was attempted to develop an
ecologically viable sanitation system which can be applicable in urban and peri-urban

One objective of this research study was to investigate the performance of the lab scale
aerobic membrane bioreactor prior to the application in the field. Performances were
investigated for three different hydraulic retention times as 2, 4 and 6 hours. It could be
found that regardless of HRT, COD removal efficiencies were more than 98 % .Besides,
better TKN removal efficiency could be achieved when the system was running for HRT 4
hours and it was 95 %. Similarly, In terms of total phosphorous removal efficiency, HRT 4
hours provided removal of 92.6 % from wastewater. Finally, it was justified that HRT 4
hour was the best operating condition among them.

Effluent water quality of each experimental runs was compared with standard values to
find the suitability of wastewater for reuse in selected options. Consequently, effluent from
HRT 4 hours had more potential to reuse water in agriculture, unrestricted urban areas and
ground water recharge except aquaculture. As micro filtration was concerned in this study,
there was no health risk to the public as well as secondary disinfection was not required.

Fast fouling was the major issue faced all over the experiment. Therefore, initial studies
on attached growth system with MBR were started to find the exact reason for clogging. It
could be found that the attached growth with MBR gave promising results. However, it is
required to carry out further studies on this matter.

Methane production potential of mixture of kitchen waste and sludge wastage was
determined as 400 mL CH4/1 g VS. The amount of energy produced from mixture of
kitchen waste and sludge wastage per month per household was 55.7 KWh. It could be
satisfied 20 % of monthly energy requirement of a household. As kitchen waste can be
used to produce energy, the amount of waste released to the main stream will be reduced.

Incorporation of ecological sanitation in to the system is another objective of this study by
applying urine separation toilets to use urine as a fertilizer. According to the experimental
studies, 50% of total urine generation can be used as fertilizer. Remaining 50 % is required
to send to the treatment unit. Further, in this study energy was recovered from kitchen
waste considering waste as a resource. Similarly, it is an outcome of ecological sanitation.

5.2       Recommendations for further studies

      •   Fouling was the sever problem faced all over the experiment. The secondary study
          has been started to find out a mechanism to diminish fouling with attached growth.
          Because of the time limitation, system was able to run only for HRT 2 hour. This
          research study can be continued to find of the exact reason of fast fouling. Further,
          system can be optimized for HRT.

      •   Experiment was carried out fixing MLSS concentration at 10,000 mg/L. Effect of
          MLSS variation and air flow rate on fouling should be investigated as a future
          study. MLSS concentration and airflow rate can be optimized.

      •   A microbiological aspect of the sludge in MBR was not mainly focused in this
          research study.

      •   Before introducing package treatment unit to public, cost benefit analysis is
          required to carry out. In addition to that, need of equalization tank while inserting
          package treatment unit to a household is required to study critically.

      •   As daily organic kitchen waste generation per household is not a significant amount
          for higher amount of methane production, co-anaerobic digestion will be attractive
          on this case for a household.

      •   It was expected that scrubbing effect of air would lead to act as one barrier for
          fouling. However, it was not able to get the benefit of scrubbing effect, although
          the membrane structure had been constructed accordingly. Therefore, membrane
          structure can be modified in order to decrease the working volume in a reactor.
          Besides, it will also attractive in the case of package treatment unit reducing the
          size while incorporating of attached growth to the system.

      •   It is required to do a study on scale up effect using a pilot scale study.

      •   Before applying the package treatment unit to a household , it is required to check
          the amount of oil and grease in the effluent because, higher oil content in the
          wastewater leads to generate addition problems in the membrane system.
          Therefore, it is recommended to use a pretreatment to remove oil and grease prior
          to the main treatment.


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          Appendix - A

Aerobic membrane bioreactor design

                                                  Working volume 6 liters
                                                                                                 Dimensions are in millimeters

                                                                                        hole for air line     0




67                                     sludge
                                       withdraw           aeration
                                                          stone input


                      45   140          45                       27     45         28
                 15        260               15                         100
                                 Figure A-1 Dimensions of the reactor


Figure A-2 MBR design for attached growth (All dimensions are in millimeters)


Initial membrane resistance measurement

Table B-1: Initial membrane resistance

                                    Different TMP              Filtration flux
   Flux(mL/min)                                                                        TMP (KPa)
                                       (mmHg)                     (L/m2.h)
        17                                58                          5                    7.7
        63                                67                        18.9                   8.9
        93                                72                        27.8                   9.6
        120                              76.5                       36.0                   10.2
        150                              85.5                       45.0                   11.4
        189                              91.3                       56.6                   12.2

Initial membrane resistance = 3.94286 X10+11 m-1



              TMP (kPa)

                                                               y = 0.0599x + 6.8642
                          4                                            2
                                                                    R = 0.9997

                               0           20             40               60         80
                                                Filtration flux (L/m .h)

                               Figure B-1 Variation of TMP with filtration flux

  Appendix C

Nitrogen Balance

Main steps of calculation of Nitrogen balance for Run 1 are shown below.

Nitrogen compounds in influent:

TKN (mg/L)                          = 55.63
NO3-N (mg/L)                        = 0
NO2-N (mg/L)                        = 0
                                    = 55.63
Nitrogen compounds in effluent:

TKN (mg/L)                          = 4.67
NO3-N (mg/L)                        = 10.1
NO2-N (mg/L)                        = 0.138
                                    = 14.9

Nitrogen lost by assimilation:

BOD5-Inffluent (mg/L)               = 375
BOD5-effleunt (mg/L)                = 6

Nitrogen lost by assimilation (mg/L) = 0.05(375-6)
                                     = 18.45

According to the Eq.4.1

Nitrogen lost by denitrificaton
                                    =Total nitrogen to influent - Total nitrogen in effluent
                                           - Nitrogen assimilated into biomass
                                    = 55.63 – 14.9 – 18.45
                                    = 22.28 mg/L

             Appendix D

Suspended and attached growth reactors

1. Initial membrane resistance of the membrane used in attached growth reactor

Table D-1 Variation of flux with TMP

                                                    Filtration flux
     Flux (mL/min)                  TMP (mm                                TMP (kPa)
                164                    88                  49.1              11.7
                128                    82                  38.5              10.9
                 93                    78                  27.9              10.4
                272                    98                  81.6              13.1

        TMP (kPa)

                    11                                 y = 0.0496x + 9.093
                    10                                      R = 0.9857
                         0        20          40           60         80      100
                                         Filtration flux (L/m .h)
                             Figure D-1 Variation of TMP with filtration flux

Initial membrane resistance                   = 2.2105 X 1011 m-1

2. Initial membrane resistance measurement for suspended growth system

Table D-2 Variation of flux with TMP

                                   Different TMP        Filtration
     Flux (ml/min)                                                         TMP (kPa)
                                     (mm Hg)          flux(L/m2.h)
                48                       61                 14.4               8.1
               112                       67                 33.5               8.9
                63                       61                 18.8               8.1
               159                       74                 47.7               9.9



         TMP (kPa)


                     8                                y = 0.0539x + 7.2269
                                                             R = 0.979

                          0        10      20        30           40     50         60
                                           Filtration flux (L/m .h)

                              Figure D-2 variation of TMP with filtration flux

Initial membrane resistance = 2.4315 x 1011 m-1

                                    (a)                                       (b)

Figure D-3 Reactor with suspended growth (a) and reactor with attached growth (b)

                 Appendix E

Calculation of dimensions of the treatment unit

1.      Design of a package treatment unit for a household of five people

Average daily wastewater flow
from a household in Asia                               = 0.8 m3/d (Halls, 2005)

From the experiment,
Considering HRT 4 as the most suitable operating condition,

Daily treated flow rate for HRT 4 hours                = 72 L /d
Membrane area                                          = 0.4 m2
Filtration rate                                        = 0.18 m3/m2/d

For the proposed treatment unit,
Required membrane area for the MBR                     = 0.8/0.25 m2
                                                       = 4.4 m2
Expected pore size of the membrane                     = 0.4 µm

Working volume of the reactor                          = 0.8 * 4/24 m3
                                                       = 0.15 m3

Width: Length: Height of MBR in the experiment         = 2:3:4(Refer figure 3.3)
                           Width                       = 0. 4 m
                           Length                      = 0.55 m
                           Height                      = 0.75 m
                             Scale up Ratio            = 1: 25

Moving media has been applied to the MBR unit for the 50 % of the volume.

2.      Calculation of energy required to the system

     Power requirement of the pump is:

     Power (KW) = (Q x ρ x H /η) …………………..Eq: 1

     Where,     Q = pump capacity (L/min)
                ρ = density of water (kg/ m3/)
                H = total head (m)
                η = Efficiency of the pump (%)

     Bernoulli's Equation

     P + ρgH + V2/2g = Constant
     P= Pressure (KPa)
     V= Velocity (ms-1)
     G= Gravitational acceleration (ms-2)

 P/ρg                +H                + V2/2ρ    = Total head (Constant)

Pressure head + Elevation head + Velocity head = Total head (Constant)

In this case, elevation head and velocity head is negligible.
From the experiment, the maximum TMP was 75 KPa
Pressure head              = 75 x1000 / (1000 x 9.81) m
                           = 7.64 m

Pump power           = Flow X Head X Gravitational force
                     = 0.8/ (24 x 3600) m3/sec X 7.64 m X 1000 Kg/m3 X9.81msec-2
                     = 0.7 W

Assuming pump efficiency is 65 %
Energy required for pump                  = 0.7/0.65 W
                                          = 1.07 W

From the experiment,
   5 minutes on and 5 minute off cycle
Pump working time per day              = 12 hour/day
Energy required per day                = 1.07 *12
                                       = 12.8 Wh/day
Energy required for suction pump       = 12.8 Wh/day
                                       = 0.0128 KWh/day

From the experiment,
Percentage of recycling               = 200 %
Flow rate through recycling pump      = 1.6 m3/d
Energy requirement for recycling pump = 25.6 Wh/day
                                      = 0.0256 KWh/day

Energy requirement for supplying air

In the experiment,
    Reactor size                             =6L
    Air flow rate                            = 1 L/min/ 1L of reactor * 6L
                                             = 6 L/min
Using Hg manometer pressure obtained         = 86 mmHg
                                             = 1.65 psi
                                     55 psi = 38, 668.8 kg/m2
                                             = 1160 kg/m2

In the package treatment unit,
Amount of air supplied to the system           = 1 L /min/ 1 L of reactor
Volume of the proposed reactor                 = 0.15 m3
Amount of air required to the proposed reactor = 150 L/min

Expected pressure difference                      = (1160 / 6)*150

                                                   = 29002 kg/m2
  Total pressure head                              = (29002 kg/m2)/ (1.165kg/m3)
                                                   = 33, 786 m
 Power required by the air compressor pump is:

 Power (KW) = (Q x ρ x H) / 6,130.25
      Q = pump capacity (L/min)
       ρ = density of air (kg/ L)
       H= total head (m)
Conversion factor = 6,130.25

 Considering, density of air as 0.001165 kg/L at 30°C

 KW (air compressor) = (150 x 0.001165 x 33, 786)/ 6,130.25
 KW (air compressor) = 0.96 KW

 Total energy required per day = 0.96 X 24 KWh
                              = 23.11 KWh/day

 Total energy required to the treatment unit = Energy required for suction +
                                                   Energy required for recycling +
                                                   Energy required for compressor
                                             = (0.0128 +0.0256 + 23.11 KWh)
                                             = 23.14 KWh

         Appendix F

Methane production calculation

                                   Specimen calculation

1. Calculation of moisture content in kitchen waste

Amount of the kitchen waste used                       = 1000 g
Weight of the sample 1 with container                  = 1262.3 g
Final weight of the sample with container after drying = 399.3 g
Water content in the sample 1                          = (1262.3 – 399.3)
                                                       = 863.2 g
Moisture content (%) of sample 1                       = 863.2/1000*100
                                                       = 86.3 %

Table E- 1: Determination of moisture content in kitchen waste

Sample no    Initial weight(g) Final weight(g)        Moisture content (%)
    1              1262.3             399.3                      86
    2              1258.4             405.1                      85

2. Calculation of volatile solids in kitchen waste

Amount of waste in grab sample                                    =2g
Weight of the sample 1 with container                             = 68.64g
Weight of the sample 1 with container after keeping 1050C furnace = 68.62 g
Weight of the sample 1 with container after keeping 5500C furnace = 67.131 g
Volatile solid in sample 1                                        = (68.62-67.131)
                                                                  =1.489 g
% of Volatile solids in sample 1                                  = 0.15 *100
                                                                  = 74.5 %
Table E-2: Calculation of percentage of volatile solid

                             Weight of the
 Sample       Initial                             Weight of the sample
                             sample after                                Volatile solid (%)
   no        weight(g)                              after 5500C(g)
    1          68.64            68.62                   67.131                   74.5
    2          84.88            83.84                   83.263                   78.9

3. Calculation of Methane production potential

Step 1: Determination of mass of CH4 in 0.2 mL sample

 Standard curve for determination of CH4 mass in sample;
Mass CH4 (g)          = Area (CH4 peak in chromatogram)*K
               K      = Constant = 1.7759*10-10
Area, before removal (at day 0.79) = 67072
Mass of CH4 in sample=m (sample) 0.79= 67072*1.7759*10-10

                                         = 11.91 µg

Step 2: Determination of CH4 mass in reactor (Before and after removal)

Volume of the head space (V)           =2150 mL
Mass of CH4 in reactor                 = m (reactor) 0.79 =V/0.2* m (sample)
                                       = 2150/0.2*11.91
                                       = 0.128 g

Step 3: Determination of amount of removal

mi (removal) = mi(before removal)-mi(after removal)
Where,    i = day
Eg: Removal at 4th day
m4(removal) = 1.0332- 0.8534
             = 0.1798g

Step 5: Determination of cumulative gas production (In standard temperature and

Gas law equation
                     PV =        RT                                            Eq: E.1

                                 P : Standard pressure (1 atm)
                                 V : CH4 production in volume (L in STP)
                                 m : CH4 production in mass(g)
                                 M: Molecular weight of methane
                                 R : Universal Gas Constant( 8.2057*10-2 L.atm.mol-1.K-1)
                                 T : Standard temperature(250C)

                      V=         PRT

                     V 0.79=         *1 * 8.2057 *10 −2 * 298 = 195 .7 NmL

Step 6: Calculation of methane potential

Methane potential (NmL) = Methane production (Sample) – Methane production (Blank)
                                            g of VS in reactor

 CH4 potential in day 0.79 = 195.7 – 9.39
                           = 18.63 NmL/ g VS

Table E-3: Calculation of methane production in reactor which consists of Sample with innoculum

                                                                                                                              Cumulative   Cumulative
Run time      Chromotographic area of CH4     Mass of CH4 in 0.2 mL (µg)      Mass of CH4in the reactor (g)   Amount of                                        volume
                                                                                                                             mass removal mass production
 (days)                                                                                                       removal(g)                                     production
                                                                                                                                  (g)           (g)
             Before removal After removal Before removal After removal Before removal After removal                                                         (NmL/reactor)
         0                 0             0          0.000         0.000         0.0000         0.0000               0.0000         0.0000          0.0000            0.00
      0.79             67072         67072         11.911        11.911         0.1280         0.1280               0.0000         0.0000          0.1280          195.70
         2            516511        516511         91.727        91.727         0.9861         0.9861               0.0000         0.0000          0.9861         1507.02
         3            531915        531915         94.463        94.463         1.0155         1.0155               0.0000         0.0000          1.0155         1551.96
         4            541200        447000         96.112        79.383         1.0332         0.8534               0.1798         0.1798          1.0332         1579.05
         5            562063        482564         99.817        85.699         1.0730         0.9213               0.1518         0.3316          1.4046         2146.72
         8            581234        471534        103.221        83.740         1.1096         0.9002               0.2094         0.5410          1.4412         2202.66
        10            591300        285200        105.009        50.649         1.1288         0.5445               0.5844         1.1254          1.6699         2552.10
        18            601321        465444        106.789        82.658         1.1480         0.8886               0.2594         1.3848          2.2734         3474.44
        20            502300        502300         89.203        89.203         0.9589         0.9589               0.0000         1.3848          2.3437         3581.98
        25            511521        401123         90.841        71.235         0.9765         0.7658               0.2108         1.5956          2.3614         3608.88
        30            523087        456430         92.895        81.057         0.9986         0.8714               0.1273         1.7228          2.5942         3964.73
        40            534374        534374         94.899        94.899         1.0202         1.0202               0.0000         1.7228          2.7430         4192.15
        50            541394        541394         96.146        96.146         1.0336         1.0336               0.0000         1.7228          2.7564         4212.63
        60            551111        551111         97.872        97.872         1.0521         1.0521               0.0000         1.7228          2.7749         4240.98

Table E-4: Calculation of methane production in reactor which consists of only innoculum (Blank)

                                                                                                                            Cumulative     Cumulative
                                                                                                             Amount of                                        volume
           Chromotographic area of CH4     Mass of CH4in 0.2 mL(µg)           Mass of CH4in the reactor(g)                    mass            mass
                                                                                                             removal(g)                                     production
                                                                                                                            removal(g)    production(g)
Run time                                                                                                                                                   (NmL/reactor)
(days)      Before removal After removal Before removal After removal Before removal After removal
          0               0             0         0.0000         0.0000        0.0000         0.0000                0.000         0.000           0.0000            0.00
       0.79            3220          3220         0.5718         0.5718        0.0061         0.0061                0.000         0.000           0.0061            9.39
          2            3578          3578         0.6354         0.6354        0.0068         0.0068                0.000         0.000           0.0068           10.44
          3            4039          4039         0.7173         0.7173        0.0077         0.0077                0.000         0.000           0.0077           11.78
          4            6163          6163         1.0945         1.0945        0.0118         0.0118                0.000         0.000           0.0118           17.98
          5            8039          8039         1.4276         1.4276        0.0153         0.0153                0.000         0.000           0.0153           23.46
          8           11163         11163         1.9824         1.9824        0.0213         0.0213                0.000         0.000           0.0213           32.57
         10           13585         13585         2.4126         2.4126        0.0259         0.0259                0.000         0.000           0.0259           39.64
         18           18781         18781         3.3353         3.3353        0.0359         0.0359                0.000         0.000           0.0359           54.80
         20           21802         21802         3.8718         3.8718        0.0416         0.0416                0.000         0.000           0.0416           63.61
         25           23273         23273         4.1331         4.1331        0.0444         0.0444                0.000         0.000           0.0444           67.90
         30           43822         43822         7.7823         7.7823        0.0837         0.0837                0.000         0.000           0.0837          127.86
         40           66034         66034        11.7270        11.7270        0.1261         0.1261                0.000         0.000           0.1261          192.67
         50           71275         71275        12.6577        12.6577        0.1361         0.1361                0.000         0.000           0.1361          207.96
         60           77000         77000        13.6744        13.6744        0.1470         0.1470                0.000         0.000           0.1470          224.66

       Table E-5: Calculation of net methane production by the sample

             Methane production                Methane       Methane
 Run time       Sample +                    produced from produced from
  (days)      innoculums                       sample        sample
              (mL/reactor)                   (mL/reactor)   (NmL/gVS)
         0                 0          0.000               0            0
      0.79           195.70           9.395         186.30         18.63
         2          1507.02          10.439        1496.58       149.66
         3          1551.96          11.785        1540.18       154.02
         4          1579.05          17.982        1561.07       156.11
         5          2146.72          23.455        2123.27       212.33
         8          2202.66          32.570        2170.09       217.01
        10          2552.10          39.637        2512.46       251.25
        18          3474.44          54.797        3419.64       341.96
        20          3581.98          63.611        3518.36       351.84
        25          3608.88          67.903        3540.98       354.10
        30          3964.73         127.859        3836.87       383.69
        40          4192.15         192.667        3999.48       399.95
        50          4212.63         207.958        4004.67       400.47
        60          4240.98         224.662        4016.32       401.63

4. Calculation of amount of energy produced using a household waste monthly

Average value of the municipal solid waste generation in Asia is 0.75 kg per capita and
50% of that is food waste (Visuanathan and Trankler, 2004). It could be estimated that
total organic waste in a household of five members as 1.5 kg.

Waste generated in a household food waste            = 1.5 kg/day
Waste generated in a month                           = 45 kg

In the case of sludge remove from a reactor, sludge consists of 10 g/L solid

Considering HRT 4, from the experiment
Amount of solid removed from the reactor             = 0.125 L /d / 1L of reactor
Working volume of the proposed treatment unit        = 150 L (Appendix –D)
Amount of sludge wastage per day                     = 18.75 L
For a month                                          = 563 L
Amount of solids in sludge                           = 5.7 Kg

Amount of total waste (kitchen waste +Sludge)        = 50.7 Kg
From table C-2
% of volatile solid                             = 76.7 %
Amount of volatile solids                       = 50.7*1000*76.7/100 g
                                                = 38887g VS
From BMP test, considering 30 days methane production as 399 mL/ g VS

Amount of methane generated for month        = 399 mL/ g VS * 38887 g VS
                                             = 15.5 m3
After, including 44 % reduction
Amount of methane produced                   = 6.87 m3

From Kulkarni (2003)
Net Calorific value of biogas                = 5000 Kcal/m3
Amount of energy produced                    = 6.87 m3 *5000 Kcal/m3
                                             = 34135 Kcal
                      One Kcal               = 1.63 Wh
                                             = 55.7 KWh


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