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Greywater reuse systems for toilet ushing in multi-storeybuildings over ten years experience in Berlin
Abstract
Water reuse in Germany has gained in signicance in the last 10 years. Several greywater systems, built according to guidelinesintroduced in 1995, operate today with no public health risk. Two greywater treatment systems are described in this paper: a rotary
biological contactor (RBC) built in 1989 for 70 persons, and a uidized-bed reactor for a one-family household built in 1995 as the
biological stage for the treatment of household greywater for use in toilet ushing. Both systems were optimized in the following
years with consideration of a minimal energy and maintenance demand. As numerous investigations have shown, biological
treatment of the greywater is indispensable in order to guarantee a risk-free service water for reuse applications other than potable
water. 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Greywater; Water reuse; Toilet ushing; Service water; Water quality; Biological treatment; Bacterial contamination
1. Introduction
1.1. Background
The exploitation of surface water followed by ad-
vanced treatment for drinking water supply oers no
guarantee for continuous microbiologically and chemi-
cally indisputable drinking water quality (Weller, 1993).
A long list of household chemicals and drugs which are
usually only partly biodegradable nd their way back to
the consumer in drinking water after passing the mu-
nicipal wastewater treatment plant (Stan & Ling-
kerhagner, 1995; Seiler, Zuagg, Thomas, & Howcroft,
1999).
The substitution of drinking water with service water(dened as water with characteristics dierent than
drinking water) used for purposes other than potable
water, e.g., toilet ushing and garden irrigation, helps
support the sustainability of valuable water resources.
Furthermore, considerable amounts of added chemicals,
in addition to sludge which arises during drinking water
treatment, can be minimized. Service water made
available from stormwater or greywater systems can be
cost eective and with proper operation presents no
hygienic risk or comfort loss for the consumer (Lucke,
1998). On the other hand, the treatment and distribution
of service water should not demand more energy and
chemicals than that needed for conventional systems.
Water from recycling systems should fulll four cri-
teria: hygienic safety, aesthetics, environmental toler-
ance and technical and economical feasibility (Nolde &
Dott, 1991). In Germany, the classication of household
wastewater into blackwater and greywater is almost
unknown and both terms are not yet dened. Here
``Greywater'' means if not otherwise dened the low
polluted wastewater from bathtubs, showers, hand-
washing basins and washing machines excluding waste-water from the kitchen and the toilet ushing system.
Some manufacturers of greywater systems assume a
mechanical treatment of the greywater to be satisfactory
(Hildebrand, 1999), whereas others claim a more ad-
vanced treatment technology to be necessary (Zwerenz,
1999; Zeisel, 1999). Some experts from the German
Ministry of Environment (formerly German Federal
Health Department) even prophesied plague and chol-
era when water with non-drinking quality was provided
for toilet ushing or other non-potable uses (Moll,
1991). However, this attitude has changed (fbr, 1998)
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and the rst greywater recycling plants have proved
their eciency and applicability in practice for almost 10
years.
In the meantime, about 76% of the questioned in-
ternational experts within a Delphi study ``Water
Technology in Year 2010'' consider it technically feasi-
ble to use greywater in households by the year 2010 with
no public health risks (Delphi, 1999).
In the last 10 years several greywater plants with
dierent technologies have been developed in Germany
although only a few have been widely investigated and
assessed. During an assessment of dierent plants, the
use pattern as well as the reuse objective should be
considered. A greywater plant at dierent sites may
deliver dierent results.
1.2. Greywater reuse guidelines
Hygienic/microbiological quality standards, such asthose dened in the German ``Trinkwasserverordnung''
do not exist for service water. Reuse criteria directed at
health and environmental protection have been set at
the beginning of these investigations on the rst grey-
water pilot plants in Berlin, Germany in 1988. These
criteria followed the EU-Guidelines for recreational
waters (EU-Guidelines, 1975), complemented with ad-
ditional microbiological parameters for the detection of
P. aeruginosa, Salmonella sp., Legionella sp., Staphylo-
coccus aureus and Candida albicans. Following success-
ful operation of these systems and achievement of the set
criteria, guidelines for service water reuse were then rstintroduced in Germany in 1995 on a local level by the
Berlin Senate Department for Building and Housing
(SenBauWohn, 1995). Parameters were dened among
others for BOD7 ` 5 mg l1, total coliforms
` 100 ml1, faecal coliforms ` 10 ml1 and Pseudo-
monas aeruginosa ` 1 ml1.
In other countries, guidelines and standards for water
reuse in buildings either do not exist or are being revised
or expanded. The US Environmental Protection Agency
(EPA) published in 1992 ``Guidelines for Water Reuse''
which describe the treatment stages, water quality re-
quirements and monitoring tools (EPA, 1992). Accord-
ing to the EPA, reclaimed water used for toilet ushingshould undergo eventual ltration and disinfection. The
euent should have no detectable faecal coliforms in
100 ml of the treated water, a BOD5 of T 10 mg l1 and
a residual Cl2 of P 1 mg l1, whereby Cl2 should be
continuously monitored.
In Tokyo, Japan, the reuse of treated wastewater has
been highly promoted. A typical use of the reclaimed
water is for toilet ushing with about 970 000 m3 year1.
Reclaimed water criteria for use in toilet ushing were
dened in the ``Report on reuse of treated wastewater''
among others for total coliforms T 1000 ml1 and
BOD T 20 mg l1 (Maeda, Nakada, Kawamoto, &Ikeda, 1995).
1.3. Problems with greywater treatment systems
The most technical problems were encountered in
systems in which greywater was not suciently treated.
These systems were merely aerated and mainly built for
single-family dwellings for which a high maintenance
was required. Advanced physical methods for water re-
use, such as ultraltration and reverse osmosis, are very
high energy demanding. On the other hand, using
membrane ltration 0X2 lm which is less energy de-manding, eliminates microorganisms but hardly reduces
the BOD. This will eventually result in slime formation in
the distribution net and in the development of anaerobic
conditions with smell emissions (unpublished data).
Not all biological treatment systems which are al-
ready well established to treat household sewage are
suitable for greywater recycling since the regulatory re-quirements for these systems (COD: 150 mg l1; BOD5:
40 mg l1) which lack hygiene requirements, are less
strict than those required for greywater recycling sys-
tems. As an example, a horizontal-ow planted soil lter
(650 m2 for 200 persons) treating the greywater from
kitchen and bathtub delivered unsatisfactory results
with euent BOD5 concentrations of 1040 mg l1
(Hegemann, 1993). In comparison, an intermittent,
vertical-ow soil lter (20 m2 for 15 persons) working
without the wastewater from the kitchen showed excel-
lent results BOD7 ` 3 mg l1, even following doubling
the number of connected persons to the system with a
daily greywater ow in the soil lter of 7501500 l
(Nolde & Dott, 1992). However, if a polishing pond, an
integral part of a municipal wastewater treatment plant,
is connected to the soil lter from which the service
water is withdrawn, the pond will exhibit extensive algal
growth during the summer months rendering the water
unt for use (Dott, Nolde, & Christen, 1993). Similar to
stormwater systems, light has also a negative eect on
greywater systems and therefore, service water tanks
should be protected against daylight.
2. System concept and methodology
2.1. Greywater system concept
The following concept for greywater treatment has
proved its eectiveness and suitability for over 10 years.
Treatment follows a sedimentation stage, biological
treatment, a clearing stage and eventual UV disinfection
as shown in Fig. 1 (Nolde, 1996a).
Funnel-shaped sedimentation tanks with automated
sludge-removing devices proved most eective. Biologi-
cal treatment can follow in a plant-covered, vertical-ow
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soil lter or a multiple-stage rotary biological contactor
(RBC) (alternatively a trickling lter), coupled to a
clearing tank to remove the biomass. The treated water
is eventually disinfected by UV before it is stored in theservice water tank. Distribution of service water is
achieved with a booster pump.
2.2. Case study
The results from two dierent plants are presented in
this paper. The rst greywater treatment plant (GW 1) is
found in a 15 m2 basement (BerlinKreuzberg, Man-
teuelstrae 41) treating the greywater from showers,
bathtubs and hand-washing basins from 70 persons. At
the beginning of these investigations in 1989, the pilot
plant was not yet optimized and the biological stageconsisted of a two-stage RBC which was replaced in
1997 with a four-stage RBC (Fig. 2) (Zeisel, 1999).
The second greywater treatment plant (GW 2) is a
two-stage uidized-bed reactor (BerlinWedding,
Bornemannstrae 4) treating the greywater from shower
and bathtub of a two-person household. The system has
a total volume of 165 l (stage 1: 105 l; stage 2: 60 l) and
placed above the toilet in the bathroom (Fig. 3). Cube-
shaped polyurethane material was used as biolm car-
rier in both stages.
2.3. Sampling
For all physicochemical parameters, samples were
taken as 24-h quantity proportional mixed samples (GW
1) or as random samples (GW 2), immediately stored
without preservation at 4C and processed within 24 h.
Inuent samples were taken from the sedimentation
tank (or bathtub in GW 2), and the euent samples
from the service water reservoir. For all microbiological
parameters, random samples were taken, stored at 4C
and processed immediately. Decimal dilution series were
prepared in physiological saline (0.9%). Testing for
faecal and total coliforms followed in triplicate serial
dilutions and were quantied using the Most Probable
Number (MPN) method (APHA, 1980). Settled sampleswere taken for all parameters.
2.4. Physicochemical parameters
UV transmission. UV transmission was determined in
the settled samples according to DIN 38404-C3. The
sample was measured in a Shimadzu UV-1201 pho-
tometer (Kyoto, Japan) at a wavelength of 254 nm in 1
cm cuvettes against Millipore water.
Spectral absorption coecient (SAC 254 nm). The
spectral absorption coecient was detected continuously
with a UV-probe Type LXG 139 operating at 254 nm anddevice unit Type LXG 144 (Fa. Dr. Lange, Dusseldorf).
Instead of ltration, the turbidity was compensated
through a reference measurement at 550 nm. As several
investigations have shown, the SAC 254 nm correlates
very well rb 0X9 with the TOC measurements.Total organic carbon (TOC). The determination of
TOC followed DIN 38409-H3. Measurements were
made in TOCOR 100 (Fa. Maihak, Hamburg) run in the
range between 2 and 30 ppm (thermal decomposition).
Injection quantities varied between 40 and 140 ll de-
pendent on sample concentration. The inorganic carbon
portion of the sedimented samples was stripped o with
synthetic air following acidication to a pH below 2. Allmeasurements were given as the arithmetic mean from a
minimum of ve consecutive measurements of a sample.
Chemical oxygen demand (COD). COD measure-
ments of settled samples were carried out photometri-
cally using a LASA Plus photometer and quick test
cuvettes (LCK 414, 560 mg l1; LCK 314, 15150 mg
l1; LCK 114, 1501000 mg l1; Fa. Dr. Lange,
Dusseldorf). The coecients of variation were 1.99%
(LCK 414), 1% (LCK 314) and 0.56% (LCK 114).
Biological oxygen demand (BOD). BOD7 was deter-
mined in the fresh settled sample following DIN 38409-Fig. 2. The four-stage greywater treatment system GW 1 in Berlin
Kreuzberg (Foto: K. Zeisel).
Fig. 1. Recommended concept for greywater treatment.
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H51 based on dilution with allylthiourea (nal concen-
tration in the sample was 1 mg l1). The oxygen con-
centration was measured with a WTW Oximeter OXI 96
and an oxygen probe EOT 196 (Fa. WTW, Weilheim).
Due to technical reasons, BOD measurements were de-
termined following seven days incubation instead of the
usual ve days. It is expected that the BOD 7 value is
either larger than or equal to the BOD5 for the samesample. For inoculated domestic polluted water in a
moderate motion, a conversion factor of 1.17 is used
1 mg l1 BOD5 1X17 mg l1 BOD7 (Imho & Im-
ho, 1990). At rst approximation, this factor can also
be used for greywater.
2.5. Microbiological parameters
Colony forming units (CFU). The determination of the
number of the CFU followed in duplicate serial dilu-
tions using Kochs pour plate method. The DEV-nutri-
ent agar plates were incubated for 44 4 h at 20C and37C. Plates which showed between 30 and 300 colonies
under an 8 magnication were evaluated and thearithmetic means determined.
Faecal and total coliforms. Detection and enumeration
of total coliforms followed in Fluorocult-Lauryl-sulfate
broth using the MPN method. Tubes were incubated at
37C for 48 h and those showing turbidity and gasformation were recorded as positive. For the detection
of faecal coliforms, the medium was made alkaline fol-
lowed by irradiation with a long-wave UV light to ex-
amine uorescence. In the presence of a light-blue
uorescence, an additional test was made to check for
the formation of indole from tryptophan using Kovac's
reagent. All tubes with turbidity, gas formation, uo-
rescence and indole formation were considered positive
for faecal coliforms.
Contamination studies. Several investigations were
made to study the survival of health relevant bacteria in
Fig. 3. The two-stage greywater treatment system GW 2 in a bathroom in BerlinWedding.
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greywater systems. Greywater was articially contami-
nated with faeces from baby diapers and concentrations
of faecal bacteria were measured in the greywater
system.
3. Results
3.1. Greywater qualities
The exact composition of greywater is primarily in-
uenced by the user's behaviour, the implementation of
water-saving measures and is dependent on which
greywater sources have been used. Untreated greywater
usually contains low nutrient concentrations (Table 1)
which are below the regulatory requirements for
euents of modern large sewage treatment plants inGermany Ntotal 18 mg l
1Y Ptotal 1 mg l
1.Although no toilet wastes were introduced into the
above greywater systems, surprisingly high loads of total
and faecal coliforms were measured over some periods
(unpublished data). This has been related to the intro-
duction of faecal bacteria into the system during baby
washing and diaper changing as tenant questionnaires
have shown.
Service water used for toilet ushing can be won from
the usually low-polluted greywater from showers,
bathtubs and hand-washing basins. In GW 1, daily av-
erage values of 3035 l/person were recorded for grey-
water while in GW 2 only 1520 l/person were
available daily (water-saving ttings and habits; ow:
9 l min1).
3.2. Biodegradability of household chemicals in the
greywater system
Fig. 4 shows the degradation of Fa soap, Birkin
shampoo and oliveoil and spice soaps in GW 2. The
organic load in the form of TOC and spectral absorp-
tion coecient (SAC) was biodegradable within a few
Table 1
Dierent untreated greywater qualities measured in Berlin plants
Parameter Unit GW 1 GW 2
Mainly bath and shower Bath, shower and washing
machine with baby diapers
Mainly shower (9 l min1)
TOD mg l1
2695COD mg l1 100200 250430 113633
BOD7 mg l1 50100 150250 70300
Ntotal mg l1 510
Ptotal mg l1 0.20.6
Faecal coliforms ml1 101101 104106 101101
Total coliforms ml1 102103 104106 101103
Total counts (CFU) ml1 105106 106107 105106
Fig. 4. Biodegradation of personal hygiene preparations in the rst stage of the uidized-bed reactor GW 2.
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hours. The TOC as well as SAC (254 nm) of the service
water were slightly higher than those of drinking water
(TOC of Berlin drinking water lies between 3 and 4 mg
l1; SAC between 8 and 10 m1).
Fig. 5 shows that the greywater from washing ma-
chines using Awalan washing liquid, which was intro-
duced in GW 2 for experimental reasons, was almost
ve times more polluted than the bath and shower
water, and more time was needed for biodegradation
(Fig. 4). The almost horizontal curve course at the end
of the biodegradation experiments indicates the rest of
the TOC to be only slowly or non-biodegradable.
3.3. Investigations in a RBC (GW 1)
As a result of the primary investigations on GW 1
which ended in 1993 and in order to establish a modular
greywater system with minimal maintenance, GW 1 was
extensively automated in 1997 and replaced with a four-
stage RBC keeping the same system volume while
achieving a higher system stability especially during load
uctuations. At least two hours per week were necessary
for maintenance of the old two-stage GW 1, but this has
been reduced to below 0.2 h.
BOD7 concentrations of 50250 mg l1 have been
measured in GW 1 inuent (Table 1) while euent
concentrations were always below the 5 mg l1 control
limit. Fig. 6 shows that the treated greywater had a
higher UV transmission in all samples measured com-
pared to the euent of the municipal wastewater treat-
ment plant of BerlinRuhleben. A UV transmission
close to that of the drinking water in Berlin was also
measured.
On the other hand, many service water samples did
not fulll the drinking water microbiological standards
of 100 CFU ml1 (37C) and 1000 CFU ml1 (20C) for
bacterial total counts as can be seen in Fig. 7.
Fig. 6. UV transmission of service water from GW 1 compared to Berlin s drinking water and treated municipal wastewater of BerlinRuhleben.
Fig. 5. Biodegradation of washing-machine liquid in the rst stage of the uidized-bed reactor GW 2.
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Fig. 8 shows that the measured bacterial concentra-
tions in treated water were usually below the control
values. Most values, mainly those of faecal coliforms
and faecal streptococci, were even below the detection
limit of 0.03 bacteria ml1. Only two out of 46 samples
exceeded the limits for P. aeruginosa with 4.3 bacteria
ml1 (Nolde, 1996a).
3.4. Investigations in a uidized-bed reactor (GW 2)
The investigations have shown that, a good service
water quality can be achieved with a smaller greywater
system (TOC: 48 mg l1; BOD7 ` 5 mg l1), even when
the organic load is high as shown in Table 1. A number
of the random samples from stage 1 has fullled the
microbiological requirements for faecal coliforms in
service water without further treatment (Fig. 9), whereas
other samples lay above the limit value, especially when
faecal material is introduced into the system from baby
washing. In addition, the hygienic/microbiological pa-rameters of the Berlin service water quality requirements
were realized following UV disinfection of the treated
water. Signicantly lower coliform bacterial concentra-
tions in GW 2 were rst attained following reduction of
the ow rate in the UV unit (after October 98) as shown
in Fig. 10. A calculated UV dose of 250400 J m2 was
held constant. The requirements were even achieved
following contamination of the system with faeces from
baby diapers in December 1998.
3.5. Behaviour of pathogenic microorganisms in greywater
In addition to the behaviour of household chemicals
in greywater systems, the presence as well as the survival
of potentially pathogenic microorganisms is of much
signicance for the assessment of greywater treatment
plants and the exclusion of any health hazard connected
with greywater reuse.Fig. 8. Concentrations of total and faecal coliforms in service water
tank GW 1 compared to the control values of the quality guidelines.
Fig. 7. CFU of samples taken from the service water tank in GW 1 at
20C and 37C, compared to the German ``Trinkwasserverordnung''.
Fig. 9. Concentrations of total and faecal coliforms in GW 2 (samples from the rst biological stage).
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Since Salmonella (in 100 ml samples), Legionella (in
10 ml samples), Staphylococcus aureus (in 1 ml samples)
and Candida albicans (in 0.1 ml samples) were not de-tected in the treated greywater (GW 1), the water was
articially contaminated with relevant pathogenic mi-
croorganisms in order to investigate their behaviour.
The concentrations of faecal coliforms in the greywater
inuent (GW 1) that has been contaminated on a daily
basis is shown in Fig. 11. After day 7, contamination
was stopped and a reduction of the faecal coliforms was
observed afterwards. However, samples taken from the
toilet ushing system always showed values below the
control limit for faecal coliforms and no regrowth of
the bacteria was detectable in the system.
Further contamination experiments in batch culturesshowed no increase in the number of pathogenic mi-
croorganisms in greywater. Instead, a continuous death
rate was observed with all tested microorganisms. Fig. 12 shows the survival of Salmonella sp. in articially con-
taminated greywater in batch experiments. Very high
start concentrations of 107 were reduced below the limit
of detection within three weeks of incubation at room
temperature in the dark.
4. Discussion
On the basis of the collected experience on dierent
greywater systems over the past 10 years, it is clear thatan extensive biological treatment of the greywater is
indispensable in order to avoid technical problems and
public health risk as well as promotion of public ac-
ceptance.
Dierent quality requirements for non-potable water
uses should be scientically justied and a risk assess-
ment analysis is desirable in every case. With regard to
sustainable water concepts, a lower energy and chemical
demand than that needed for conventional systems
should be achieved in service water systems. For large
greywater systems working with a multistage RBC, the
Fig. 11. Survival of faecal coliforms following continuous contami-
nation of the greywater with faecal material over a period of 7 days.
The vertical line shows the end of the contamination in GW 1.
Fig. 12. Survival of Salmonella sp. in articially contaminated grey-water in batch cultures.
Fig. 10. Concentrations of total and faecal coliforms in GW 2 following UV disinfection compared to the control values of the quality guidelines.
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energy demand for greywater treatment, UV disinfec-
tion and service water distribution was determined to be
less than 1.5 kWh m3 (Nolde, 1996b). Low energy and
maintenance costs can thus be a challenge especially for
smaller greywater plants.
The use of chemical disinfectants (e.g., chlorine
compounds) in greywater systems should be avoided
since treated greywater can be satisfactorily disinfected
with a UV dose ranging between 250 and 400 J m2.
Several investigations have also shown that common
personal hygiene preparations and household-cleaning
chemicals as well as the occasional use of medicinal baths,
or even a contamination of the greywater with faeces and
pathogenic bacteria, cause no problems in properly
functioning greywater systems working with dierent
carrier material (e.g., sand, polyethylene, and polyure-
thane) for biolm xation, followed by an eventual UV
disinfection (Nolde & Dott, 1992; Mehlhart, 1999).
From the author's point of view it is today indispens-
able, that every greywater system be tested once underseveral dierent conditions (e.g., faecal contamination,
application of household chemicals) before operation.
Following installation, a qualied inspection should be
made in which a full compliance to DIN or other stan-
dard-installation regulations takes place. In order to
avoid cross connections with the drinking water network,
it is recommended that the service water is dyed once prior
to operation. The operation of non-registered and un-
tested greywater systems is connected to a potential hy-
gienic risk to the user and the drinking water network.
At this point in time, it is dicult to give general
recommendations regarding planning and design of a
greywater plant, since the user behaviour, volume and
concentration of greywater can vary widely as for ex-
ample in a one-family household and in a hotel. The
greywater systems that have been realized until now
with extensive treatment of the greywater were mainly
prototypes or special productions, whereby the total
costs were decisively dependent on site conditions. As
such it is still dicult to give precise details on the in-
vestment costs of such systems, to which a second pipe
system and additional space are also needed. Dependent
on system size, the specic investment costs beginning
with water treatment and ending with the service water
pump would at a rst approximation be between 300 for large systems and up to 1000 for small ones per
connected person. With drinking water and wastewater
prices in Germany of 5 m3, it can be ensured that
such an investment will pay for itself taking into con-
sideration the operation and maintenance costs.
5. Conclusions
Greywater processing has proved to be technically
feasible. There are enough positive examples which
verify that the total water for toilet ushing (about 15 to
55 l/person/day) can be substituted with service water
without a hygienic risk or comfort loss.
The Berlin quality requirements for service water
have proved to be eective for the reuse of treated
greywater for toilet ushing. Regulatory requirements
for other reuse purposes, such as in washing machines,
are still desirable. These requirements should be in every
case use-oriented and based on a risk assessment.
It should be possible in the future to have a dual
water system in households with two water qualities.
The rst a high quality drinking water originating pri-
marily from natural water resources, and a second wa-
ter quality for all other uses. This should bring with it
an environmental relief on both the water and energy
sectors.
Acknowledgements
This research was mainly supported by the Berlin
Senate Department for Building and Housing. Dipl.
Ing. Jochen Zeisel from Sanitarsystemtechnik, Berlin,
and Dipl.Ing. Rudi Buttner from Fa. Lokus, Berlin, for
greywater system planning and design. Hans Grohe for
supporting investigations on the uidized-bed reactor.
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