Toxicity Reduction of Municipal Wastewater by Anaerobic-anoxic-oxic Process

Objective This study was conducted to optimize the operational parameters of anaerobic-anoxic-oxic （A2/O） processes to reduce the toxicity of municipal wastewater and evaluate its ability to reduce toxicity.Methods A luminescent bacterium toxicity bioassay was employed to assess the toxicity of influent and effluent of each reactor in the A2/O system.Results The optimum operational parameters for toxicity reduction were as follows:anaerobic hydraulic retention time （HRT）=2.8 h,anoxic HRT=2.8 h,aerobic HRT=6.9 h,sludge retention time （SRT）=15 days and internal recycle ratio （IRR）=100%.An important toxicity reduction （%） was observed in the optimized A2/O process,even when the toluene concentration of the influent was 120.7 mg·L-1.Conclusions The toxicity of municipal wastewater was reduced significantly during the A2/O process.A2/O process can be used for toxicity reduction of municipal wastewater under toxic-shock loading.