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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.