The fate of some chosen chlorinated hydrocarbons in the biological sewage purification was determined. Fixed quantities (250 µg/l waste water) of the different volatile compounds such as chloroform, trichloroethylene, chlorobenzene, hexachloro-1, 3-butadiene, 1,2-dichlorobenzene, 1,2, 3-trichlorobenzene, hexach lorobenzene, 2,4-dichlorophenol and γ-hexachlorocyclohexane were dosed into the aeration tanks of the pilot plants. Chlorinated hydrocarbons in the inflow, waste air, effluent and excess sludge were extracted and tested for by GC/ECD. The results of these experiments were adapted with the results of recovery experiments. The balances of the low volatile and volatile compounds also had to be adapted by the means of correction factors because of condensation effects. For example more than 50 % of 250 µg/l water of chloroform or 1,2-dichlorobenzene escaped out of the open sampling bottles which were kept in a refrigerator during the sampling period of 24 hours. The balances of the non-volatile chlorinated hydrocarbons were reaching about 100%. The very hydrophilic and low volatile chloroform was found up to 16% in the waste air, 63% in the effluent and 21% adsorbed on sludge. The very lipophilic and non-volatile hexachlorobenzene was found up to 16% in the effluent and 74% adsorbed on sludge. No hexachlorobenzene was found in the waste air. Biochemical degradation was observed for some of these compounds.

The behavior of the chlorinated hydrocarbons in biological sewage purification depended on their volatility and lipophilic property, and also the intensity of aeration and sludge loading has been of great importance. Balancing of volatile chlorinated hydrocarbons should be done by spot sampling. Bottles for composite samples should be stored in the refrigerator during the sampling period and should be sealed.

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