MODELING THE FATE OF PESTICIDES IN MUNICIPAL WASTE-WATER TREATMENT

The fate of two insecticides (lindane and diazinon) and three herbicid es (2,4-D, 2,4,5-T, and atrazine) in municipal wastewater was investig ated in pilot plant experiments. The pesticides were dosed into the wa stewater to provide feed concentrations in the 2 to 10 mu g/L range. T he pilot plant was operated at both 4- and 10-day solids retention tim es (SRTs) in the first of two testing campaigns and at a 4-day SRT in the second campaign. Only lindane was found to be biodegradable to any extent. Loss of pesticides from the system due to sorption to mixed l iquor solids was small. Estimated partition coefficients ranged from 0 .01 to 2 L/g volatile suspended solids (VSS), whereas biodegradation r ates ranged from 0.1 for lindane to 4 E-6 L/g VSS . h for 2,4,5-T. Bec ause the pesticides examined are mostly refractory to activated sludge treatment under the conditions examined, it is desirable to limit the ir entry to wastewater collection and treatment systems to minimize th eir impact on receiving waters.