Technological Improvement For Enhanced Biological Phosphorus Removal Of Municipal Wastewater In North Of Zhejiang Province

It is agent to improve the discharge standards of wastewater treatment plants (WWTPs) in north of Zhejiang province since there is great threat of eutrophication for these areas.The process performance of enhanced biological phosphorus removal (EBPR) in municipal wastewater treatment plants were investigated to find out the key problems in WWTPs,while research on the sludge activity and relevant microorganism characteristics were conducted to illustrate mechanism related to EBPR improvement in WWTPs.Then,all the data concerning EBPR performance microbial populations and operational parameters was analyzed by Statistical Package for Social Science(SPSS) to determine the relevance of these data and the more important operational parameters affecting EBPR performance.Finally,technological scheme aiming at improving the performance of EBPR in municipal WWTPs was put forward.The results showed that HRT in some of the WWTPs is too short to ensure the sufficient P release and uptake.Due to high proportions of industrial wastewater in influent,more than half of the WWTPs's VFAs were below 20mg/L,accompanying with low nutrients concentrations(average TP_INF and TN_INF 2.946mg/L and 23.53mg/L respectively),which leads to a more difficult situation for operation of municipal WWTPs in the investigated aera.COD_EFF excessed discharge standars seriously,mean TP_EFF and TN_EFF were 0.817 mg/L and 9.95mg/L,but with significant difference in sludge performance.P release and uptake rates were varied from 0.22mg/gVSS/h to 7.90mg/gVSS/h and 0.43mg/gVSS/h to 8.11mg/gVSS/h respectively.Proportions of Accumulibacter(4.8%±2.0%) and Competibacter(4.8%±6.4%) were found.So it's a great challenge for these wastewater treatment plants to meet higher requirements in discharge.Anoxic phosphorus uptake was appeared in two-thirds of the sewage plants, DNPAOs(Denitrifying Polyphosphate Accumulating Organisms) accounted for 30.4%-71.4%of PAOs(Polyphosphate accumulating organisms).There were significant linear correlations between the influent acetic acid concentration vs.acetic acid uptake rate,Accumulibacter proportion vs.anaerobic phosphorus release rate,anaerobic phosphorus release rate vs.aerobic/anoxic phosphorus ratio,indicating that phosphorus release rate was an effective indicator to characterize EBPR performance.The availability and proportion of carbon in sewage wastewater showed great impact on EBPR activity.It is worth noting that there was no direct competiton between PAOs and GAOs(Glycogen Accumulating Organisms GAOs) in this study,DNPAOs could be accumulated in municipal wastewater treatment plant without special process.Due to relatively lower carbon source and higher Competibacter fraction,TN_INF and the fraction of Accumulibacter was negatively correlated while there was no significant correlation between PAOs and anaerobic acid uptake rate.The strategies of reducing industrial wastewater,paying attention on the concentration of VFAs in influent to get appropriate VFAs to TP ratio, N to P ratio,avoidance the HRT being too short and application of separate pre-denitrifying tank are recommended to favor EBPR system.