Greywater Reuse System for Toilet Flushing

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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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