Study On The Phosphorus Release Of The Returning Sludge And The Effects Of Sludge Side-stream Assisted With Chemical Phosphorus Removal On Mainstream Biological System

A~2O system deterioration was usually caused by the competition between anoxic dinitrifying bacteria and PAOs for carbon source,which led to fail to meet the discharge standard.However,the problem can be solved through combinations of biological and chemical phosphorus removal process.The Phostrip is a well-known process equipped with side-stream chemical phosphorus reomoval or recovery,part of the returned sludge that is rich in phosphorus content,enters an anaerobic tank,releasing phosphorus to the bulk liquid and then the phosphorus is precipitated or crystalized for recovery,the sludge returned to the main biological reactor after separation.Whereas,to make an evaluation of the Phostrip process,it is necessary to further investigate the mechanism of the phosphorus release in the side-stream and the potential effects of chemical phosphorus removal on the main biological system.In this study,the experiment was based on a lab-scale continuous AO reactor equipped with enhanced biological phosphorus removal process,fed with synthetic wastewater.50%of the returned sludge was led to the side-stream system.The mechanism of the phosphorus release in the side-stream was discussed and the effects of the added side-stream on the biological system were investigated.The feasibility for phosphorus recovery was analyzed.The study is to provide guidances for designs of side-stream phosphorous recovery from waste water treatment plants.The main results and conclusions are shown as following:1 The concentration of phosphorus in the side-stream before precipitation was merely 3.66mg/L,which was less than half of that in influent of 8mg/L.It was difficult for precipitation and phosphorus recovery.Theoretical phosphorus recovery rate can only be 6.76%.2 In absence of external carbon source,phosphorus release process in the side-stream was affected by residence time and aerobic time of the main biological reactor.Within 6h,the amount of released phosphorus increased with time.Reduction of the aerobic time of the main biological reactor impoved the phosphorus release from5.79mg P/g MLSS to 6.74 mg P/g MLSS.3 The whole phosphorus removal efficiency was enhanced from 96.0%to 97.9%,through the additional side-stream and side-stream assisted with chemical precipitation.COD removal efficiency was hardly improved.4 The sludge settleability had been improved since the side-stream system was introduced,SVI decreased from 300mL/g to 210mL/g,and then to 110mL/g.The metabolism of the microorganisms was greatly affected by the additional side-stream and side-stream assisted with chemical precipitation.The main internal energy substances involved in phosphorus removal transferred from PHAs to glycogen.