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relation to water and chemical consumption, water consumption pattern, necessary water

quality and wastewater characterization, economic conditions as well as the general situation

of the enterprises. Based on the answers and on interviews of the enterprises 7 potential

primary plants and 6 potential secondary plants were selected to participate in the project.

The identification of the grey water resources of the potential primary plants indicated that

institutions such as swimming baths, public schools and sports centres can contribute considerable

grey water resources as it is seen from Table 0.1.

Table 0.1 Survey of potential primary plants and their grey water resources in the municipality

of Herlev.

Primary plants Grey water resources

[m 3 /year]

Type of water

Swimming baths

3.200 – 5.500

1.200 – 2.100

Shower water

Filter rinse water

Public schools 1.000 Shower water

Sports centres (Icerink) 1.200 Cleaned ice*

Hospital 22.000 Rain water**

Industrial production enterprises

4.400

RO-concentrate (dilute),

distillation water

750 Conc. cleaning water

* Seasonal grey water resource (1/9 – 1/4).

** Rain water was included as a potential grey water resource due to a large existing water collection

facility.

A spot check analysis of the grey water from 4 potential primary plants was performed for

determination of pertinent physical-chemical and microbiological parameters.

Grey water from swimming baths and other institutions, where the principal source of the

grey water production comes from showering, is estimated to contain a certain potential for

microbiological after-growth in situations where the grey water is to be collected and stored

in equalizing tanks (COD: 50 – 100 mg/l, SS: 100 – 200 mg/l, total – N: 5 – 10 mg/l, total –

P: 1 – 2 mg/l). Due to technical problems it was only possible to analyse the filter rinse

water from swimming baths and the quality of shower water from institutions having typically

a large consumption of water for showering was consequently estimated based on

other studies of similar types of grey water.

At industrial manufacturing enterprises slightly polluted wastewater from production-like

conditions was classified as grey water. However, the quality of the grey water varies much

dependent on which type of process the water comes from. For example, the quality of grey

water from a medical production enterprise was found to almost meet the requirements of

the Executive Order on Drinking Water (Danish Ministry of Environment). Another enterprise

manufacturing cleaning materials produced less amounts of grey water during their

cleaning of the process tanks, but in this case a considerable degree of pollution was seen in

relation to COD (> 3.000 mg COD/l).

Rainwater – collected at the Herlev County Hospital – was also included in the study because

of an important surplus production. This type of water was estimated to be periodically

very unhygienic because of a heavy after-growth of microbes in certain periods. Due

to a low hardness, conductivity and salinity, however, the technical water quality was estimated

to be high apart from the winter periods, where salt is sprinkled.

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