Humic substances affecting the limitation of the activated sludge process for removal of micropollutants

In our previous investigation with the Bacillus subtilis rec-assay, a stron g DNA-damaging potential was found in effluents of municipal wastewater tre atment plants and nightsoil treatment plants using the activated sludge pro cess. We hypothesized that the presence of non-biodegradable humic substanc es in the influent and the association of micropollutants inducing DNA-dama ging chemicals to them may cause the comparatively lower removal rate of mi cropollutants than that of primary organic substrates. In this research, a batch type activated sludge process was set up in the laboratory to examine the fate of these toxic micropollutants and to evaluate the effect of humi c substances. As neutral and polar micropollutants, pyrene and I-aminopyren e was respectively selected, and their speciation (i.e., free, sorted onto dissolved organic matters including humic acid, and sorbed onto activated s ludge) was investigated. Almost all pyrene was sorbed onto activated sludge without any biodegradation. It was observed that the effect of humic subst ances made both pyrene and 1-aminopyrene leave the process in forms sorbed onto humic acid and free in the effluent. This complexity of the fate of mi cropollutants and the significant effect of humic acid leads to the necessi ty of further investigation not only in the activated sludge process but al so into the other various natural environments. (C) 1998. Published by Else vier Science Ltd. All rights reserved.