Greywater Recycling Systems in Germany

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					          Greywater Recycling Systems in Germany
                    Whether or not they are applicable to the Meda Counties

                                          Erwin Nolde*

                *Nolde & Partner, Consultants for Innovative Water Concepts
        c/o Technical University of Berlin, Department of Hygiene, Amrumer Strasse 32
                                   D-13353 Berlin, Germany;
                        Board member of fbr, the German Association
                          of Rainwater Harvesting and Water Reuse

        Although Germany is not considered a water-poor country, there are
        regional differences in the water supply and consumption that exist.
        During the past 15 years, greywater recycling in Germany has been
        approached with varying interest and a degree of success. Besides an
        increased public environmental awareness, water costs also play an
        important role in increasing the demand for advanced greywater treat-
        ment systems especially in buildings and housing schemes. Under fa-
        vourable conditions, the amortisation costs usually lie between 5 and 7
        years. Systems that have been extensively tested and have shown to
        be most reliable are those that employ an advanced biological treat-
        ment followed by a UV disinfection of the recycled greywater. Systems
        based on the membrane technology are being developed and re-
        searched intensively in Germany for municipal wastewater treatment,
        however, so far they play no role in greywater recycling. The most pref-
        erable ones are greywater systems operating under low energy and
        maintenance requirements without the use of chemicals. In Germany,
        greywater recycling systems should be registered at the Health Office
        to prevent cross-connections with the drinking water network. The hygi-
        enic requirements for recycled greywater that is primarily used for toilet
        flushing, are in accordance with the EU-Guidelines for Bathing Waters.
        The use of recycled greywater for irrigation is minor, whereas, its´ re-
        cent reuse in laundry activities has delivered promising results.

        Greywater; Biological wastewater treatment; Amortisation; Quality require-
        ments; Service water; UV Disinfection.

In Germany, the first official water reuse project using greywater started in Berlin in
1989. Resistance against greywater recycling in buildings at first originated from the
Berlin water suppliers who ignored the need for water recycling and in which their only
interest was in selling more water. Among the hygiene experts the opinions were differ-

ent. Some experts welcomed the new concepts and approaches with some reserva-
tions, while others were vehemently against a second water network for the fear of pos-
sible cross-connections. One hygiene expert even prophesied a relapse in times of
plague and cholera if recycled water was to be used in households for toilet flushing.
Today, the Berlin Health Departments deal with recycled water in buildings more objec-

At the beginning of the research on greywater over a decade ago, the main goal was to
supply a few residential dwellings of about 100 persons with recycled greywater for toi-
let flushing. The Technical University of Berlin (TU-Berlin) was the first to define the pro-
ject goals and the general requirements for greywater recycling plants. Later on, the
required investigative parameters for recycled greywater were set up and different con-
cepts were tested. Following 1993, numerous investigation results were made available
for the TU- Berlin and the official authorities. Based on these results, specific quality
requirements were established for recycled greywater that were intended for usage of
toilet flushing in households (Berlin Senate, 1995). Today, about 300 – 400 greywater
recycling systems are operating in Germany under different concepts. Some of them
have been withdrawn following installation while others look back on more than 10
years of successful operation (Nolde, 1996b).

In Germany, the classification of household wastewater into blackwater and greywater
are not yet defined. Here “Greywater“ means - if not otherwise defined - the low-
polluted wastewater from bath tubs, showers, hand-washing basins and sometimes
even washing machines usually excluding wastewater from the kitchen and toilet flush-
ing system. Synonyms used in Germany for recycled greywater are service water or
non-potable water. As a definition, service water is the non-potable water made avail-
able for the use in households from recycled and treated greywater.

Water from recycling systems should fulfil four criteria: hygienic safety, aesthetics, envi-
ronmental tolerance and economical feasibility.

1. Hygienic safety:
     a) Installation aspects:
  •  There should be a guarantee that no cross-connections exist between the drink-
     ing water and the service water supply;
  •  Pipes and tubes have to be properly designated and coloured and the non-
     potable water taps have to be labelled and protected against unauthorised use;
  •  Greywater recycling plants have to be registered at the local health authorities.

       b) Water quality aspects:
 •     Hygiene parameters: the concentrations for E. coli and total coliform bacteria that
       have been adopted during the whole research period are under the EU-
       Guidelines for Bathing Waters (76/160/EEC).
       Total coliform bacteria: < 10.000 / 100 ml; E. coli: < 1.000 / 100 ml; Pseudomo-
       nas aeruginosa: < 100 / 100 ml.
       During the research period between 1989 and 1993 other pathogenic microor-
       ganisms were tested in addition to the above parameters:
       Faecal Streptococcus: 0 / 0.1 ml; Candida albicans: 0 / 0.1 ml, Staphylococcus
       aureus 0/1 ml; Legionella sp.: 0 / 10 ml and Salmonella sp.: 0/ 100 ml.

 •    Physical and chemical parameters:
      BOD7 < 5 mg/l and an O2 Saturation > 50 % to ensure that the water undergoes
      an effective cleaning process and that it could be stored without causing odour
      UV-Transmission at 254 nm (1 cm cuvette) > 60 % as a minimum transmission
      for UV-disinfection.
2. Aesthetic aspects:
   Treated greywater should not be a source of odour and nuisance to its´ consumer
   and it should be as free as possible from suspended solids and colour.

3. Environmental tolerance:
   Many German cities are very proud of their highly efficient and well-maintained wa-
   ter supply systems. Most of them supply drinking water to their communities without
   adopting to chlorination. Therefore, a chemical disinfection and a high energy de-
   mand for a greywater recycling system are principally not acceptable.

4. Economical aspects:
   The maintenance and operation costs of a greywater recycling system should lie be-
   low the costs of the drinking water supply and the wastewater treatment in order to
   ensure that an investment will pay for itself within a certain amortisation period.
   However, it is worth mentioning that water prices in Germany have considerably in-
   creased during the past 20 years compared to the energy prices. In many regions
   for example, the yearly water bill for a 4-people household amounts up to 1,000 € at
   a water price of about 5 €/m3.

The advantage of greywater recycling at household level lies in the fact that costs for
installation are usually less than those required for a larger central systems intended for
multiple households.

The initial optimism of some greywater system manufacturers being that the low-
polluted greywater from bath tubs and showers only requires little aeration to prevent
water from fouling in the storage tank, was misplaced. With these systems, it was not
possible to maintain the above water quality requirements. The users of these systems
refused to continue operating them due to odour nuisance and discomfort. Electro-
chemical disinfection that had been applied later on did not solve these problems. High
AOX concentrations were measured in the water as a result (Deutsche BauBeCon,
1995, 1996).

The investment costs amounted up to 1,100 Euro per household. Out of the 12 investi-
gated systems, 8 systems have been immediately dismantled during the start phase
due to the discontent of the tenants. Of the remaining 4 systems, only one was as-
sessed as being good (Hesse, 2002).

Another concept that was realised for a 8 people household, consisting of a weak single
treatment stage and an eventual UV-disinfection, had also failed. The treated water did
not fulfil the above greywater quality requirements. The water putrified in the pipes sys-
tem and had clogged the inlet devices to the flushing cistern. In addition, the investment

costs for this system (8.000 €) as well as operation costs were relatively high (Hesse,

Greywater recycling systems for multiple-family houses have proved right from the be-
ginning to be the most effective for greywater recycling. The following concept for grey-
water treatment has already proved its efficiency and suitability for over ten years.
Treatment follows a sedimentation stage, a biological treatment stage, a clearing stage
and an eventual UV disinfection as shown in Figure 1.

                                                      washing machine
                                     handwash basin

                                                                          kitchen sink
                Bath tub


                            Sedimen-                                       Engineered wetland
                             tation                                      (vertical-flow soil filter)

                                                                                                       UV-Disin-   Storage
                            Sedimen-                                    Multi-stage       Sedimen-
                             tation                                       RBC               tation      fection     tank

                                                                        Modular multi-stage SBR
                           Sieve / filter                                 (aerated flow-bed)                         toilet flushing
                                                                                                                     house cleaning
                                                      Sludge from                                                    laundry

Figure 1: A recommendable concept for greywater treatment.

Bath tubs and showers are usually the main sources of greywater. In the absence of
enough greywater, an additional drinking water source will guarantee a continuous non-
potable water supply. For a higher need for greywater, washing machines can be also
connected. It is not usual to direct the wastewater from the kitchen into the greywater-
recycling system.

Three systems have proved so far their suitability:

1. Vertical-flow soil filters, with or without disinfection depending on the personal
2. Multiple Rotating Biological Contactors (RBC), and
3. Modular multi-stage Sequencing Batch Reactors (SBR) with an aerated flow-bed.

Only a small amount of sludge is produced in these systems.

Membrane reactors for water recycling are also under development. However, surface
clogging of the membrane still pose many problems. Investigations are underway to
guarantee a clog-free operation.

Plant-covered soil filter:
A 60 m² engineered wetland constructed in the mid of the courtyard of a housing set-
tlement has been operating successfully for 8 years with the full satisfaction of its´ 60
users (Figure 2). Greywater from bath tubs, showers, hand-washing basins and wash-
ing machines enters the plant-covered soil filter where it undergoes biological treat-
ment. UV disinfection has been included as a final safety measure before the use in
toilet flushing (Deutsche BauBeCon, 1995, 1996). Extensive investigations over several
years of operation have shown that the water quality fulfilled all above mentioned qual-
ity requirements even during the winter at temperatures of -20 °C. Within the soil filter,
E. coli concentrations were reduced to over 99 % and all hygiene requirements have
been achieved under the EU-Guidelines for Bathing Waters (76/160/EEC).

Figure 2. Constructed wetland for greywater recycling (Berlin).

One has to take into consideration that in warmer climatic regions considerable
amounts of water evaporate from the reed beds (ca. 15 - 30 mm/d) contributing posi-
tively to the microclimate of a housing settlement. On the other hand, this water is lost
from the system and is not available anymore to the recycling process.

Rotating Biological Contactor (RBC):
Funnel-shaped sedimentation tanks with automated sludge-removing devices proved to
be most effective in treating greywater. Biological treatment follows in a plant-covered,
vertical-flow soil filter or a multi-stage Rotating Biological Contactor (RBC), the latter
then coupled to a clearing tank to remove the biomass. The treated water is eventually
subjected to UV-disinfection before it is stored in the service water tank. Distribution of
service water is achieved with a booster pump.

In densely populated areas with high land price, compact treatment systems are prefer-
entially installed in buildings (specific area requirement about 0.1 m²/Person). One of
the two most extensively researched plants is the first greywater treatment plant in
Germany. The plant is found in a 15 m² basement (Berlin-Kreuzberg) treating the grey-
water from showers, bath tubs and hand-washing basins from 70 people (Figure 3).
Another RBC plant in a housing settlement for 65 people in Kassel has been also inten-
sively investigated confirming the results of the Berlin plant (Bullermann et al., 2001;
Nolde, 1995, 1996, 1999a).

Figure 3. Rotating Biological Contactor (RBC) for greywater treatment (Berlin-
Several investigations have also shown that the use of common personal hygiene
products, household-cleaning chemicals and medicinal baths or even a deliberate con-
tamination of the greywater with faeces and pathogenic bacteria should pose no prob-
lem to a properly and efficiently functioning greywater system (Bullermann et al. 2001;
Nolde, 1999).

On a large scale, the first greywater recycling plant was built in 1996 as an RBC for a
four-star Hotel (Arabella-Sheraton near Frankfurt/Main) with 400 beds (Nolde, 1996).
Investigations have shown that each guest produced on average about 90 litres grey-
water per day. The need for service water for toilet flushing was about 50 litres per
guest and day. The greywater recycling plant was designed to recycle a maximum of
20 m³/d. With an occupancy of 80 %, an initial water price of 4 Euro and an increase in
the water price of 7 % per year, taking into consideration the operation and mainte-
nance costs, the amortisation period is calculated to be about 6.5 years (Figure 4). De-
pending on the interest rate, the recycling system requires another 3 years to make a
profit. Nowadays, after useful experience that has been collected in the field of grey-
water recycling, a similarly high greywater treatment efficiency can be guaranteed with
even less investment.

      Figure 4: Amortisation of a greywater recycling plant for a hotel (Germany).

Modular Greywater Systems:
Greywater systems of the modular type have also been developed in the past three
years which
are suitable for single as well as multiple-family houses. The system consists of an aer-
ated flow-bed reactor, realised as a Sequencing Batch Reactor (SBR), where the bio-
mass is fixed on foam cubes. Interfering particles are held back from the system by an
automated sieve. Sedimentation also takes place during the biological treatment stage.
The system is tightly closed in order to prevent condensation water and air from reactor
to escape into the surroundings.

The majority of the greywater recycling systems that are nowadays being installed in
Germany (about 20 to 60 systems per month) originate from a company that was
founded in 2001. These systems (AquaCycle®, PONTOS) are constructed on a modular
basis for single-family households, housing settlements, hotels and camping sites (Fig-
ure 5). They operate with an output capacity of about 200 – 10,000 litres per day. The
greywater originates from bath tubs, showers, hand-washing basins and occasionally
from washing machines.

Figure 5: Standard AquaCycle 900 Module with a cleaning capacity of 600 l/d.

About 95 % of the modular systems are installed in single and double-family house-
holds with a treatment capacity of about 600 l/d, whereby, most of them are not being
used to their full capacity. The system requires a standing area of 0.81 m² and a room
height of 1.88 m. With investment costs of about 5.000 € (including installation) and low
operation costs of 20 – 25 €/year for energy, 200 m³ of water can be saved yearly if the
system is being used to its full capacity. Experience has shown that with larger systems
the relationship between investment and saving potential has been clearly improved.

The hygiene parameters for E. coli and total coliforms under the EU-Guidelines for
Bathing Waters (76/160/EEC) and which are guaranteed by the manufacturers are con-
tinuously maintained. Investigations have also shown that under laboratory test condi-
tions with synthetic greywater, very high concentrations of E. coli (above 107/ml) are
reduced to below detection levels (0/10 ml). In the system effluent, no E. coli were de-
tectable in 1 ml samples with a UV transmission of 72 – 76 %. During a daily treatment
performance of 600 litre and a system influent of 238 mg/l COD, a COD of 28 mg/l and
BOD7 of 2,4 mg/l were measured in the system effluent (unpublished data). The manu-
facturers of this system recommend the use of this high-quality recycled water for land-
scape irrigation, cleaning and laundry in addition to its use for toilet flushing.

A recent research at the TU Berlin with modular greywater recycling system as shown
above investigated the microbial load of clothes washed with drinking water and those
that were washed with recycled greywater (Töpfer, et al., 2003). The washing machine
temperatures were 30, 60 and 95°C and the laundry was dried indoors as well as in a
dryer. 128 contact samples (CASO-Agar on 25 cm² Rodacplates) were made from
laundry washed and dried under the two different test conditions.

Out of the 84 contact samples that were originated from the dryer, no difference was
found from a hygienic-microbiological point of view between those samples washed and
rinsed with recycled greywater and those washed with drinking water. All samples
yielded less than 5 CFU/10 cm². With samples that have been air-dried indoors (44
samples), higher concentrations have been measured in only 3 samples (8 - 18 CFU/10

cm²) reflecting the air quality of the inhabited room (Control plates: 16 CFU/10 cm² for
24 h).

The above investigations clearly show that clothes washing with recycled greywater
should not be rejected from a hygienic aspect. Although between 40,000 – 50,000 rain-
water harvesting systems are installed yearly in Germany and most of these house-
holds use rainwater for their laundry, at this point in time not much can be said on this
extended form of greywater reuse as regarding its general acceptance among the
population. From an economical and ecological aspect, it is an innovation if greywater
recycling does not remain limited to its sole use for toilet flushing and landscape irriga-

Discussion and Conclusions
On basis of the collected experience, it is clear that an extensive biological treatment of
the greywater is indispensable in order to avoid technical problems and health risks as
well promoting public acceptance for greywater recycling. Following an extensive bio-
logical treatment – independent of the system employed– it is not necessary to add
chemical disinfectants to the treated water which can be used as a non-potable water
source. Several studies have shown that the re-growth of pathogens following UV disin-
fection is not expected and the probability of re-growth is so low that the German quality
requirements are never exceeded (Bullermann, 2001; Nolde and Dott, 1991; Nolde,

Due to the lack of statutory requirements for non-potable water use in Germany and the
lack of extensive risk assessments in this field, it has been accepted that no higher
quality requirements for recycled greywater for use in toilet flushing are needed than
those described in the EU-Guidelines for Bathing Waters (76/160/EEC) and the Berlin
Quality Requirements for Greywater. Even today, these requirements are considered
strict enough as one can see that by keeping to these requirements there is a guaran-
tee that a longer body contact and even an occasional swallowing of this water does not
cause illness.

However, it is of utmost importance that greywater system installations are properly
made in order to exclude cross-connections between the drinking water and the non-
potable water networks. This can easily be controlled at the beginning prior to the op-
eration by a temporary dying of the water using food dyes (Senat, 2003).

On the international level, different quality requirements for recycled greywater exist
depending on the specific use, whether recycled greywater is used for crop or land-
scape irrigation or for toilet flushing. If one compares the German quality requirements
for non-potable water for use in toilet flushing with the American quality requirements
for unrestricted urban reuse (EPA, 1992), it can be seen that the Americans demand
relatively higher requirements for hygiene for unrestricted urban reuse (no detectable
faecal coliforms/100 ml) but at the same time lower requirements for their wastewater
treatment (BOD5 ∗ 10 mg/L). Furthermore, the EPA recommends a residual chlorine of
a minimum of 1 mg/l Cl2 in order to reduce odour, slime, turbidity and bacterial re-

The Australian Office of Housing, Department of Human Services recommended in a
draft specification < 1 virus (Adenoviruses) per 50 litres, < 1 Cryptosporidium per 50

litres, < 1 helminth per litre, total N (incl. NOx, TKN, Ammonia) < 5 mg/l and TP < 0.5
mg/l in a project where treated greywater was to be used for toilet flushing and irrigation
(Office of Housing, 2003).

On the other hand, Heyworth (2001) found that young children from South Australia
drinking tank rainwater were not at a greater risk of gastroenteritis compared to the chil-
dren drinking treated public mains water. Even an increased prevalence of gastroenteri-
tis cases among children drinking solely treated drinking water from the public mains
has been documented by the author warranting further investigations.

Lücke made a comparison between the contamination of non-potable water and that of
food with hygienically relevant microorganisms (Lücke, 1998). He emphasised the fact
that E. coli as well as other pathogenic microorganisms are allowed in food in compara-
tively higher concentrations. He mentions, as an example, unpasteurised cheese in
which 104 E. coli per gram are allowed.

Seeing it from an aspect of health, an extensive risk assessment for the different uses
of non-potable (service) water should be made. Environmental aspects should also be
taken into consideration as it would not be acceptable to meet the water problems and
scarcity in many countries through a higher energy and chemical expenditure.

Last but not least, there are cost aspects that should be considered that are in most
cases detrimental for the adoption and propagation of water recycling systems.
In poorer areas with low water prices and low income, expensive greywater recycling
systems are not affordable to everybody. On the other hand, luxury hotels in tourist ar-
eas have a huge demand for high-grade water from usually scarce water resources.
Water recycling in these facilities will increase the water supply and secure its availabil-
ity at all times without the need for large water reserves.

Therefore, it is worth consideration whether such recycling technologies should be laid
down in a statute in these countries particularly where hotel facilities, comfort and prices
are comparable to those of international standards. For this purpose, these systems
and technologies are already available as has been presented in this information. For
the majority of the population, new and inexpensive concepts and solutions should be
worked out on site based on the positive experience in Germany. However, these cost-
effective concepts should not be put towards the cost of the water quality. Therefore, an
attempt to promote this technology and to reduce its´ costs should be a priority of water
management schemes in these countries.

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