12 The toxicity of municipal wastewater to the receiving water bodies is still unknown, due to 13 the lack of regulated toxicity based index for wastewater discharge in China. Our study aims at 14 gaining insight into the acute toxic effects of local municipal wastewater on alga, Scenedesmus 15 obliquus. Four endpoints, i.e. cell density, chlorophyll-A concentration, superoxide dismutase 16 (SOD) activity and cell membrane integrity, of alga were analyzed to characterize the acute 17 toxicity

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... fects of wastewater from municipal wastewater treatment plants (WWTPs) with 18 different treatment techniques: sequencing batch reactor (SBR), Linpor and conventional activated 19 sludge. Influent and effluent from each treatment stage in these three WWTPs were sampled and 20 evaluated for their acute toxicity. Our results showed that all three techniques can completely 21 affect the algal chlorophyll-A synthesis stimulation effects of influent; the algal cell growth 22 stimulation effect was only completely removed by the secondary treatment process in 23 conventional activated sludge technique; toxic effects on cell membrane integrity of two influents 24 from WWTPs with SBR and conventional activated sludge techniques were completely removed; 25 © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ the acute toxicity on SOD activity was partially reduced in SBR and conventional activated sludge 26 techniques while not significantly reduced by Linpor system. As to the disinfection unit, NaClO 27 disinfection enhanced wastewater toxicity dramatically while UV radiation had no remarkable 28 influence on wastewater toxicity. Our results illustrated that SOD activity and chlorophyll-A 29 synthesis were relatively sensitive to municipal wastewater toxicity. Our results would aid to 30 understand the acute toxicity of municipal wastewater, as well as the toxicity removal by currently 31 utilized treatment techniques in China. 32