A laboratory-scale model for evaluating effluent toxicity in activated sludge wastewater treatment plants

Abstract

Laboratory-scale wastewater treatment systems were used to assess the potential contribution of a specific waste source, a detergent manufacturing plant, to wastewater treatment plant (WWTP) effluent toxicity. Laboratory-scale, continuously-fed activated sludge treatment systems (CAS units) were established and seeded with sludge from one of two activated sludge WWTPs. The CAS units were fed influent from these WWTPs supplemented with detergent manufacturing plant waste (plant waste). CAS unit effluent toxicity was measured with the 7 day Ceriodaphnia dubia survival and reproduction test and the 4 day Selenastrum capricornutum population growth test. Control (ambient WWTP influent) CAS unit and actual WWTP effluents had similar toxicity, indicating the CAS units generated effluent toxicologically similar to actual effluent for the two species tested. Untreated WWTP influent was supplemented with atypically high concentrations of plant waste in an attempt to establish a dose-response relationship between influent plant waste levels and effluent toxicity. However, there was no trend toward increasing effluent toxicity to Ceriodaphnia or algae with increasing influent plant waste concentrations. Thus, the detergent manufacturing plant waste is not contributing to the toxicity of the municipal WWTP effluent. This case study demonstrated the utility of CAS units for assessing the impact of WWTP influent sources on final effluent toxicity.