Case Study The Grey Water System At Linacre College Oxford

Linacre College built a great new 'green' building as a hall of residence, gym and restaurant in 1995. Anglian Water decided to use this building as a test bed for their innovative grey water system. This consisted of a two-stage process, in which stored grey water is passed through a sand filter to remove solids, then through a hollow fibre membrane separation process, which removes soap, bacteria and some dissolved organic material. Despite the fact that these filters produced a relatively high quality of water, the design of the system as a whole had serious defects including:

• the underground concrete grey water collection pit was acting as an anaerobic culture vessel, and very quickly rendered the grey water into a condition that was impossible to treat;

• the pipe run from the building was too long and shallow, allowing time for bacterial regrowth;

• the length of time the water was remaining in the tank was too long. Chlorine disinfection upstream was found not to have any effect and was environmentally undesirable;

• the organic material present in grey water changed into a form that was able to pass through the membrane and be assimilated later, in the distribution network. This resulted in the fact that while the treated water was itself clear and sterile, there was sufficient organic material present to allow regrowth later in the system, as the distribution network could never be totally sterile without excessive use of chemicals.

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