Regulating Of Multistage AO Process For Low Temperature Wastewater Treatment

Multistage anoxic/oxic?AO? process is a multipoint influent sewage treatment technology based on anaerobic/ anoxic/ oxic?A2O?process.The process owns the advantages of high carbon source utilization,good treatment effect and low energy consumption.However,as a kind of active sludge process,it could not meet the discharged standard at low temperature.So it is necessary to find the regulation measures for multistage AO process to treat wastewater at low temperature.At present,additional measures or process controlling are main ways to enhance wastewater,which were less reported by previous study for the multistage AO process.In this research,the effects of additional measures and process controlling on wastewater treatment at low temperature by multistage AO process were investigated.On this basis,the screening and combination of the strengthening process were carried out.Besides,the continuous dynamic test was optimized and verified to determine the control measures of multistage AO process for low temperature wastewater treatment.The methods of strengthening nitrogen removal by adding nitrifying bacteria and carrier were investigated,and enhancing phosphorus removal was conducted by simultaneous or post chemical phosphorus removal.The results showed that the working time of adding nitrifying bacteria was limitation,the maximum time was maintained only 12 d.While combined or suspended carrier could enhance nitrogen removal efficiency and continuously.Simultaneous or post chemical phosphorus removal can effectively improve the phosphorus removal effect with effluent reaches the 0.5 mg/L.Compared with postposition chemical phosphorus removal using PAC,using Fe SO4·7H2O for simultaneous removal of phosphorus,with low reagent cost,simple process and other advantages,suitable as a means to strengthen the removal of low-temperature sewage treatment by multistage AO process.The effects of sludge reflux ratio,nitration liquid reflux ratio,anoxic oxic volume ratio,sludge retention time and dissolved oxygen?DO?on multistage AO process treating low temperature wastewater were investigated.The results showed that sludge reflux ratio and nitration liquor reflux ratio had no obvious effect on multistage AO process.While reducing anoxic aerobic volume ratio and sludge retention time optimization were effective means to enhance nitrogen removal.The process obtained the best efficiency when anoxic aerobic volume ratio,sludge retention time and DO was 0.40,24 d,and 3±0.5 mg/L,respectively,with the effluent COD,NH₄⁺-N,TN and TP concentration were 23,1.04,10.49 and 1.41 mg/L,respectively.Through the above research,the combination measures of multistage AO process treatment to enhance the low temperature sewage were as follow ing,the ratio of anoxic and aerobic volume was 0.40,sludge retention time was 24 d,and using the Fe SO4·7H2O with Fe/TP dosage of 1.5 for simultaneous phosphorus removal.And the control of the sludge reflux ratio was 60%,the nitration liquor ratio was 50%:150%,the influent distribution ratio was 60%:40%,and DO in the aerobic zone was 3±0.5 mg/L,the effluent COD,NH₄⁺-N,TN,TP and SS were 24,0.55,10.38,0.35 and 8 mg/L,respectively,which can meet the standard A of first level.