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D2) Grey water reuse in buildings

F. Derrien francois.derrien@cstb.fr Div. Water and Buildings, CSTB, France

Abstract

The increase of water consumption and the simultaneous decreasing of rainfall in some parts of Europe lead to water saving measures. Between them the use of water saving devices and the diagnosis of installations in order to fight against leaks are now widely used. Rain water reuse or grey water treatment are techniques that become widespread, in spite of the brake coming from technical or regulatory barriers. Grey water reuse has the advantage that it is a possible technique where water scarcity is a daily concern.

This paper presents an example of grey water reuse in a house. This in situ experiment delivers data that are important for the knowledge of technical, economical and health parameters. The challenge is to define an acceptable water quality compared to different existing references like potable water or public baths requirements. The possible uses will depend on these parameters and their acceptance by health authorities.

Keywords

Grey water, water saving, sustainable development

1 The state of the art of grey water reuse

1.1 The reasons for grey water reuse

Water consumption has widely increased in industrial countries until the concept of sustainable development has been understood and starts to be practiced in the field of building equipments. Today, in Europe this water consumption stabilises around 150 L/inhabitant/day whilst it is still around 300 L/inhabitant/day in North America. However, the awareness of water scarcity in some regions of the world, or simply a better management of water resources according to sustainable development principles lead to a control of water use in buildings. Different solutions like using water saving devices (dual flush toilet cisterns, pressure reduction systems, tap with lever stop) or reusing rain water, or reusing grey water are now commonly used. Although widely used in Germany, gray water reuse is not popular in France because of cautiousness

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opposition from health authorities. Looking at figure 2 explains why grey water reuse is particularly interesting. Comparison of right and left parts of the figure shows equilibrium in quantities between the resource (shower and bath grey water) and its possible use for flushing toilet, washing machine and watering garden. After a first experiment in a commercial building, the first installation in a single family house has been started in France. CSTB has followed this experiment in order to collect the values of different parameters and gather information for health authorities.

Figure 1 – Water consumption

Figure 2 – Distribution of water usage

1.2 Water quality and regulation

It is difficult to require for grey water quality the same criteria than for water intended for human consumption. Technically and economically, is is not profitable. However, installing a second piping system in a building for this purpose will lead to ask the question of this water quality. But using it for flushing toilets, washing clothes or watering the garden suggests to choose the same criteria as for bathing water quality (see table 1). In addition, Germany has established specific guidelines for theses

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applications where more severe criteria for Pseudommona aeroginosa are established (less than 1/mL).

Table 1 – Comparison of guidelines for drinking water and bathing water quality Potable water Bathing water

Directive 98/83/CE

Directive 2006/7/CE intended to repeal

76/160/CE at the end of 2014 Directive 76/160/CE

Colony count 22°C 100/mL Colony count 37°C 20/mL

Total coliforms 0/100mL <10000 /100 mL

Escherichia-coli 0/100mL between 500 et 1000

UFC/100 mL Faecal coliforms <2000/100mL

Enterococci 0/100mL between 200 and 400

UFC/100 mL Faecal streptococci

100/100mL Anaerobic sulfato reducing bacteria 0,5/mL

Légionella 1000 UFC/L Pseudomona aeruginosa 0/250mL

Staphylocoques 0/100mL Surface active

substances Between 0,3mg/L and

no lasting foam between 0,3mg/L and no

lasting foam Ammonia nitrogen 0,1mg/mL

Conductivity < 2500

Colour

Acceptable to consumers and no abnormal change No abnormal change No abnormal change

Turbidity 1 NFU Taste and odour acceptable

Hardness > 15 °F Nitrates 50 mg/L Nitrites 0,5 mg/l

Oxidisability 5 mg/l O2 pH Between 6,5 et 9 Between 6 and 9 Iron 200 μg/l

Mineral oils Between 0,3 mg/L and no visible film on water surface

Phenols 0,005 mg/L Transparency Between 1 and 2 m

Dissolved oxygen 80 to 120% of saturation Floating residues No

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1.3 The existing techniques

Recycling grey water has started in 1970. The first systems have been developed by NASA and were using a filtration on diatomaceous earth added with active carbon adsorption. The possible treatment techniques can be classified in two different families : physico-chemical ones and biological ones.

- Physico-chemical treatment techniques : sand filters or membranes (micro-filtration and ultra-filtration). These techniques are usually coupled with UV light devices for final disinfection purposes. Membrane filtration systems are more performant than sandfilter ones because they eliminate organic pollution and turbidity. However they generate energy consumption (mainly for reaching sufficient pressure). Consideration shall also be taken for clogging problems.

- Biological treatment techniques : they act on biodegradable matters. They can be membrane bio-reactors or aerobic biological filters. These biological techniques permit a satisfactory reduction of total coliform bacteria, do not need energy consumption because no pressure increase is necessary. However, they need an additional disinfection.

2 The in situ tested system

2.1 Description

The house where the experiment is carried out is a single family house with six rooms and 125 m2 living space. The sanitary installation comprises two bathrooms (one bath, one shower and two wash basins), 2 toilets of which one with a hand wash basin, one kitchen with a sink and a dish washing machine. In the basement, one laundry with washing machine and washing trough. Grey water is collected from the shower and wash basins. After treatment it is used for washing machine, washing trough and garden watering. The grey water treatment apparatus is shown on figure 3. It is a relatively big apparatus, difficult to install in narrow space. Grey water is directed to it via a PVC line, additional drinking water arrives via the copper pipe and treated water goes out via the other copper pipe painted in green and with the signs "non potable water" on it.

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Figure 3 – Water treatment system

Figure 4 shows the principle of functioning.

Figure 4 – Water treatment system

The different steps of the process are the following:

1. pre-filter destinated to eliminate coarse impurities like hair or plushes. It is equiped for backwashing.

2. first chamber for treatment. It contains the substrate on which microorganisms in aerobic conditions grow.

3. (also number 2 on figure 4) second chamber for treatment. It has the same function as the first chamber and constitutes a second level in the process.

4. UV lamp, installed on the entry of treated water in the clear water container.

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2.2 Installation

Figure 5 shows a typical installation of the system.

Figure 5 – Typical installation of the system

2.3 Impact on piping system in the house

Figure 6 shows the installation before and after the greywater recycling installation, especially the modification due to backflow prevention. On the left, recycled water can be mixed with potable water in the tap. Furthermore, the level of tap outlet is below the overflow level creating a risk of back siphoning dirty water contained in the trough into potable water pipe. On the right, two taps have been installed, totally disconnecting the two piping systems, and the taps exits are more than 2 cm above spill over level of the washing trough.The indication "non potable water" is visible on the recycled water pipe, also painted in green colour.

Figure 6 – Backflow prevention

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3 Experimental results

3.1 Water analysis

Water anlyses have been made during the first month at weekly intervals and afterwards with one sampling each month until 1st of March 2007. The results are shown on table 2, for grey water and table 3 for treated water. Grey water contains coliforms, enterococci and pseudomona, all of them being eliminated by the treatment except pseudomonas in 4th December analysis. Grey water turbidity is comprised between 7 and 146. Compared with the process specifications, the analyses for treated water are in line with bathing water quality given in European Directive 76/160/CE and table 3 of specification table given in paper H 201 of german Fachverienigung Betriebs-und Regenwassernutzung. No more pseudomona are detected in and after 1st March analysis. Turbidity is comprised between 2 and 4. Table 2 – Grey water analysis results

Date 04/12/20

06 11/12/20

06 18/12/20

06 08/01/20

07 15/02/20

07 01/03/20

07 pH 7.4 7.7 7.7

Temperature (°C) 14

Mesure impossib

le 13 15

Turbidity (NTU) 7.58 18.00 85.50 146 42.2

Total coliforms (n/100 mL)

1 900 000 >100 000

3 600 000 370 000 114 000

Thermotolerant coliforms

(n/100 mL) 104 000 >100 000 65 000 5 400 800 Enterococci (n/100 mL) 20 <10

Pseudomona Aeruginosa (n/100 mL) 114 Legionella (UFC/L)

Legionella Pneumophila

(UFC/L) Nitrogen Kjeldahl

(NTK) (mg/L) Phenols (mg/L)

Orthophosphates (PO4)

(mg P/L) Salmonella Absence

Anionic detergents

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(mg/L LAS) Cationic detergents

(mg/L) Non ionic detergents

(mg/L)

Table 3 – Treated water analysis results

Date 04/12/20

06 11/12/20

06 18/12/20

06 08/01/20

07 15/02/20

07 01/03/20

07 pH 7.8 7.2 7.4 7.8

Température (°C) 16.2 14 12.5 14

Turbidity (NTU) 4.22 2.49 2.13 4.17 2.52

Total coliforms (n/100 mL) <100 <100 0 0 0

Thermotolerant coliforms

(n/100 mL) <100 0 0 0 0 Enterococci (n/100 mL) <2 0

Pseudomona Aeruginosa (n/100 mL) 6 200

indétectable 100

Legionella (UFC/L)

Non détectés

<500

Non détectés

<500 Legionella

Pneumophila (UFC/L)

Non détectés

<500

Non détectés

<500 Nitrogen Kjeldahl

(NTK) (mg/L) 12 2 Phenols (mg/L) <0.01 <0.01

Orthophosphates (PO4)

(mg P/L) <2.5 2 Salmonella Absence Absence

Anionic detergents (mg/L LAS) <0.10 <0,10

Cationic detergents (mg/L) 0.5 0,6 à 1,5

Non ionic detergents (mg/L) 0.4 0,1

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3.2 Water consumption

Two water meters have been installed, one on the additional drinking water entry, and the second one on the treated water (figure 7). Comparison of both leads to the understanding on how often potable water is necessary in addition to treated grey water, for satisfying the needed volumes.

Figure 7 – Water meters

The measured water volumes are plotted on figure 8 and 9. The addition of these volumes between 15 February 2007 and 1st March at 9h45 equals to 1285 litres for treated water and 0 for potable water. Between 1st March at 10h15 and 15 March, the total is 1718 litres for treated water and 11 litres for potable water. This additional potable water consumption corresponds to one drawing on 4 March and follows the consumption of treated water (see table 4). Table 4 : Water volumes and temperature measured on 4th March 2007 at 21h

Date et heure

Température (°C) Chambre

prétraitement Température (°C)

Chambre traitementCompteur eau traitée

Compteur eau

d'appoint 04/03/07 21:02 18,2 16,8 0 0 04/03/07 21:03 18,4 16,9 3 0 04/03/07 21:04 18,4 16,8 0 3 04/03/07 21:05 18,5 16,8 0 0 04/03/07 21:06 18,2 16,8 5 1 04/03/07 21:07 18 16,8 0 3 04/03/07 21:08 17,8 16,8 0 1 04/03/07 21:09 17,8 16,8 0 0 04/03/07 21:10 18,1 16,8 0 0 04/03/07 21:11 18,4 16,8 0 0 04/03/07 21:12 18,2 16,8 0 0 04/03/07 21:13 18,1 16,8 2 2 04/03/07 21:14 18 16,8 0 1 04/03/07 21:15 17,8 16,8 0 0

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Figure 8

Température et comptage d'eau

0

5

10

15

20

25

30

15/02/07 00:00 17/02/07 00:00 19/02/07 00:00 21/02/07 00:00 23/02/07 00:00 25/02/07 00:00 27/02/07 00:00 01/03/07 00:00

Date et heure

°C et L

T° chambre prétraitement (°C) T° chambre traitement (°C) Comptage d'eau traitée (L) Comptage d'eau d'appoint (L)

Figure 9

Température et comptage d'eau

0

5

10

15

20

25

30

35

01/03/07 00:00 03/03/07 00:00 05/03/07 00:00 07/03/07 00:00 09/03/07 00:00 11/03/07 00:00 13/03/07 00:00 15/03/07 00:00

Date et heure

°C et L

T° chambre prétraitement (°C) T° chambre traitement (°C) Comptage d'eau traitée (L) Comptage d'eau d'appoint (L)

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3.3 Temperature

Temperature measurements during a period of one month are plotted on figures 8 (from 15 February2007 to 1 March 2007) and 9 (from 1March 2007 to 15 March 2007). Temperature peaks in pre-treatment chamber reflect the temperature of grey water coming from the shower. Temperature in pre-treatment chamber fluctuates in the same way. In both chambers, temperature stabilises around 15 °C, which is favourable to non proliferation of pathogenic organisms and for the good functioning of treatment process.

5 Conclusions

Grey water reuse is a way of saving water. Water consumption statistics show a good adequation between the quantities of grey water produced by the use of showers and wahs basins with the intended use in WC flushing, washing machines and garden watering. This first experiment, carried out in France in a single family house leads to the observation of good results for treated water analyses, corresponding to the fixed objective of bathing waters. It also shows the importance of adapting the house piping system in order to prevent any contamination of potable water. Treated water production was sufficient, except for only a few litres during a period of 3 months. The experiment will be continued in order to study the stability of the system performance.

6 Aknowledgments

The author thanks the society Pontos® GmbH for participation to the experiment and the authorisation for reproducing documents.

6 References

1. Fachvereinigung Betriebs-und Regenwassernutzung. Hinweisblatt H201. Avril 2005

2. A. Lakel. Recyclage des eaux grises dans l'habitat. Technologies de traitement rencontrées. CSTB Internal report. Janvier 2004

3. Recyclage des eaux grises. Techniques et Sciences Municipales n° 9 –septembre 2003

4. Recyclage de l'eau : Station pour l'habitat et le tertiaire. Les cahiers Techniques du Bâtiment. N° 266 Décembre-janvier 2007

5. Berghütte scont Naturressourcen. Sanitär Heizungstechnik 10/2003

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6 Author presentation

Francois Derrien is working at Centre Scientifique et Technique du Bâtiment (France) where he is responsible of the division "Water and Buildings". The activities of this division are focused on certification for water treatments including anticorrosion processes, disinfection, assessment of maintenance or diagnosis actors.