Summary: | Toxicity of Municipal Wastewater Treatment Plant Effluent (MWWTPE) was evaluated using bioassay with Daphnia Magna (D. Magna). Acute toxicity tests were performed on effluent samples of Urmia municipal wastewater treatment plant (Biolac system) according to the USEPA methods and 24, 48, 72, and 96 hr lethal concentration 50% (LC50) were calculated by application of Probit analysis. Also interrelationship between main effluent physicochemical parameters of wastewater (BOD5, COD, and TSS) and 24hr-LC50, were studied. Results showed that the effluent was safe to be discharged to the surface water in regard to physicochemical parameters and acute toxicity unit (TUa), according to the standards of Iranian Department of Environment (DOE). Relationship between effluent COD and 24hr-LC50 show that, increase in effluent COD resulted in increase in wastewater toxicity and there was not relationship between BOD5, TSS and toxicity of effluent. Keywords: Wastewater, Effluent, Acute toxicity, Daphnia Magna, Physicochemical parameter
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