Økologisk byfornyelse og spildevandsrensning, 47 – Etablering og drift af anlæg til opsamling, rensning og genanvendelse af gråvand til toiletskyl og maskinvask af tøj - Nordhavnsgården

Establishment and Operation of Installations for Collection, Treatment and Recycling of Greywater for Laundry Machines and Toilet Flushing

Summary and conclusions

The objective of the project was to establish a full-scale test for collection and treatment of grey water to be reused for laundry machines and toilet flushing, in an apartment house, aiming at contributing to increasing the knowledge on the microbiological and the chemical composition of untreated and treated grey water. Thus, the quality of treated and stored grey water for toilet flushing could be determined. Knowledge of the composition of grey water is necessary to determine the possible applications and ways of treatment that would be best suitable for a given type of water. There was not sufficient basis to determine whether the Danish Environmental Protection Agency should prepare guidelines for the use of grey water.

The test facilities were established in the apartment house of "Nordhavnsgården" Østbanegade 153, 2100 Copenhagen Ø, with 295 apartments. At a meeting of tenants in December 2000, a legally competent assembly approved that test facilities should be established for collection and cleaning of grey water in the building. Furthermore, it was decided that the facilities with special funding from FSB should be extended to include approx. 80 apartments instead of 30 as originally proposed. In case of unacceptable odour from the test facilities, the test should be stopped immediately.

In connection with a considerable renovation of the premises at the beginning of the 90's, the entire building was prepared for reuse of grey water. Double waste pipes were established from each apartment and separate piping for the water supply for toilet flushing. Waste water from showers and wash basins are connected to one of the waste pipes (grey water and waste water from the toilet and the kitchen sink was connected to the other waste pipe (black waste water). All piping is carried out according to RC direction 003 " Use of rainwater for toilet flushing and laundry machines in private housing ".

There is no direct connection between the water from the water works and the system for grey water. Feed-water from the existing water system is supplied with a reflux valve (counter and vacuum valve) in the central boiler house. Equipment for refilling of drinking water is mounted in accordance with RC direction 003 with minimum air gab of 20 mm.

The system is a RBC system (Rotating Biological Contactor), see figure 2.8.

Appendix A shows a flow diagram of the system - a thoroughly tested German concept, which uses environmentally friendly and corrosion resistant components. The system is fully automatic and self-cleaning in its day-to-day running, and supplied with numerous alarm functions in case of different kinds of major or minor errors in the system. The alarm signal can be transferred by modem to a PC or a cell-phone. An annual maintenance check of about 6-8 hours is required, as well as 2-3 hours maintenance each month.

The system consists of the following treatment modules:

Collection and sedimentation tanks for grey water, where the primary sedimentation takes place.
Biological cleaning in a RBC system, where a transformation of organic substances takes place.
Secondary sedimentation and clearing with sand filter.
UV-light treatment
Storage tanks for treated grey water

The system was put into operation in June 2001. During the period from June 2001 to April 2002 the treated grey water was led directly to the sewerage system. In order to gain as realistic operating experience as possible during this period, a simulation program was established, which tapped water from the storage tanks in a quantity equal to the expected consumption within a 24 hours period. Large consumption in the morning, in the afternoon and in the evening. During the same period a number of samples were analysed and characterised as untreated and treated grey water.

From April 2002 until the completion of the report, the cleaning system has been in operation, and has delivered treated water to approximately 80 apartments in the building, where it was used for toilet flushing. During the same period a further number of water samples were taken to determine the cleaning effect of the system. Furthermore, a series of samples were taken from toilet cisterns, both the cisterns supplied with treated grey water and the cisterns supplied with water from the water works.

From the overall evaluation of the system appears that the system is very well functioning and requires only minimal supervision and maintenance. There have been no reports of unusual smell during the normal operation of the system, and there have been no complaints from the tenants.

Two tenant surveys were conducted, which included all 80 apartments, as well as a running evaluation of five selected tenants.

The first survey was carried out about 14 days after the commissioning of the system, and included three questions regarding smells, discoloration and lack of water in the toilets.

After 10 months' use of the grey water system, another tenant survey was carried out, this time with the objective to gather the tenants' experience form their use of grey water for toilet flushing.

In general, the system seems to function very well, both from the tenants' and the superintendent's point of view. The system has proven to be operationally stable, and the small inconveniences thatdid °Ccur were easily solved, using the gathered experience.

There is only limited knowledge of the health and hygienic aspects in connection with the use of grey water for toilet flushing. Only very few Danish or foreign surveys area available on these aspects, and there is limited knowledge of the microbiological and chemical composition of different kinds of grey water.

The main objective of the project was to estimate to what extent the treatment system could reduce the number of selected microbiological measuring parameters in grey water, for in this way to determine the microbiological quality of treated and stored grey water supplied to toilets. Further objectives were to obtain an overall evaluation of the operation of the system and the technology, and bad smell, if any . the latter being the cause of operational problems with previous systems for treatment of grey water. Finally, the test results were to contribute with generally increased knowledge of the microbiological and chemical composition of grey water.

An overall and summarising evaluation was carried out of the health and hygienic risks for the tenants from the use of treated grey water for toilet flushing, whereas no risk assessment was made of the failures and errors with the technical system. It should be mentioned, however, that a number of pr°Cedures have been implemented to reduce the risk of failures and operational breakdowns. No significant evaluation was made of the health and working environment for the people who were in charge of the maintenance of the system.

The Danish Environmental Protection Agency decided that the measuring programme for the grey water projects should be carried out in two steps:

A general characterisation of grey water when transferred to the grey water system, before the water was treated. This step included a series of chemical parameters and microbiological standard parameters.
In step two, water samples should be taken from the inlet as well as the outlet to the treatment section of the system. The number of measuring parameters in step two was reduced in comparison to step 1. On the basis of the measuring programme step 1, the most essential parameters should be identified, i.e. the most sensitive or the most describing parameters (parameters as indicators for problematic polluting components), so that a less extensive but more specific measuring programme could be constructed in step two.

The results of the microbiological analyses, which were carried out by ROVESTA Miljø I/S and KVL indicate that the system for treatment of grey water over a long test period was very reliable, and produced water of a quality that was very close to the drinking water quality standards.

On the basis of the project results, the health risks in connection with a possible oral intake of toilet water supplied with treated grey water does not seem higher in comparison with toilet water that had not been supplied with grey water. The contribution from the faecal pollution during a toilet visit is the dominant factor.

On the basis of the project results, it is estimated that the content of possible chemical substances, in particular metals and xenobiotic substances, does not constitute a health risk when using grey water for toilet flushing.

On the basis of the overall result of the project it is estimated that the health risks are exceptionally small for the residents at Nordhavnsgården, who use toilets supplied with treated grey water.

Based on the results derived from the project, an extensive data basis has been formed for evaluation of selected microbiological and chemical parameters with regard to the use of grey water. From repeated comparable analyses appears that the quality of the treated grey water is very high, very close to the required quality of drinking water.

The project contributes with extensive and new knowledge on technologies and microbiological and chemical parameters with regard to the use of grey water, on the basis of which the Danish Environmental Protection Agency together with relevant authorities can decide whether to prepare new guidelines for the use of grey water, along the lines of the guidelines for the use of rainwater in private homes.