Behaviour of persistent organochlorine micropollutants during primary sedimentation of waste water.

The removal of polychlorinated biphenyls and the organochlorine insecticides gamma-HCH, aldrin, dieldrin and endrin during primary sedimentation of raw sewage has been studied using a pilot plant facility. A matrix of sixteen experiments was performed, where the pilot plant was operated at four different hydraulic loadings with four different influent suspended solids loadings. Significant removals of micropollutants into the primary sludge were observed, although no particular relationship with the removal of suspended solids was evident. It is concluded that a proportion of the organic microcontaminants present in raw sewage were associated with non-settleable solids and were also in the dissolved form. The significance of the behaviour of organochlorine micropollutants in waste water treatment processes and the hydrological cycle are discussed in the context of water re-use operations.