Research On Characteristics Of Enhanced Biological Phosphorus Removal In Urban Sewage Treatment Plant

As a typical technology for phosphorus removal in many Wastewater Treatment Plants at home and abroad,Enhanced Biological Phosphorus Removal（EBPR）has the characteristics of high phosphorus removal efficiency,economy and less sludge,etc.But in actual engineering practice,it is hard for EBPR to meet the emission requirements of Grade-A standard specified in Discharge Standards for Pollutants from Urban Sewage Treatment Plants（GB 18918-2002）due to the influence of inflow water quality,temperature,dissolved oxygen and returned sludge and so on.Generally speaking,chemical phosphorus removal is used to assist EBPR to achieve the purpose of phosphorus removal.However,chemical phosphorus removal agents will not only generate a large amount of unmanageable sludge,but also increase costs of operation.Therefore,it is signification for the efficient and stable operation of urban wastewater treatment plant to explore and research the differences in phosphorus removal efficiency of different water treatment processes and the influence of different electron donor and electron acceptor on enhanced biological phosphorus removal.In this research,the third and fourth WWTP in Xi’an City was taken as the research object.This study compared and analyzed the phosphorus removal efficiency of different sewage treatment processes through the detection of inlet and outlet water quality of different treatment processes,phosphorus concentration of main structures,biological phase of activated sludge,phosphorus release and absorption activity of activated sludge,analysis of phosphorus components in sludge and microbial community structure.At the same time,the effects of nitrate and microbial community structure on enhanced biological phosphorus removal were explored.The main conclusions are as follows:（1）Both the selection pond+modified oxidation ditch process and the A²O+chemically assisted phosphorus removal process can achieve good phosphorus removal.The maximum anaerobic phosphorus release rate of the activated sludge at WWTP III was 4.78 mg P/（g·VSS·h）,the maximum aerobic phosphorus uptake rate was 4.12mg P/（g·VSS·h）and the maximum acetic acid uptake rate was 25.93 mg Hac/（g·VSS·h）,with aΔP/ΔHac of 0.23.The maximum anaerobic phosphorus release rate from activated sludge at WWTP IV was 5.93 mg P/（g·VSS·h）,the maximum aerobic phosphorus uptake rate was 4.75 mg P/（g·VSS·h）and the maximum acetic acid uptake rate was 41.85 mg Hac/（g·VSS·h）with aΔP/ΔHac of 0.11.The phosphorus removal efficiency of both wastewater treatment processes was above 94%.（2）The A²O process is influenced by influent water quality and sludge reflux,and requires intermittent dosing of chemical phosphorus remover in the effluent of the biological tank in order to achieve the same treatment performance as that of the selection tank+modified oxidation ditch process.However,the effect of intermittent dosing of chemical phosphorus remover on biological phosphorus removal is relatively small.（3）Under the condition of sufficient carbon source,NO^-₃-N had little effect on the anaerobic maximum phosphorus release rate of phosphorus accumulating bacteria in activated sludge,while under the condition of limited carbon source,NO^-₃-N has a significant effect on the anaerobic phosphorus release process of phosphorus accumulating bacteria in activated sludge system.However,in the presence of NO^-₃-N,denitrifying phosphorus absorption process will occur,resulting in the reduction of phosphorus concentration.（4）It was found that there was a fermentative phosphorus accumulating bacterium Tetrasphaera in the activated sludge system of the third sewage treatment plant,and the proportion is as high as 16.2%,the proportion of traditional phosphorus accumulating bacterium Ca.Accumulibacter was only 7.8%.Because Tetrasphaera has anaerobic fermentation,it can convert complex organic matter in raw water into acetic acid and produce ATP for anaerobic phosphorus absorption;The fermentation product acetic acid can cooperate with accumulibacter to remove phosphorus,so that it can still meet the effluent standard without chemical phosphorus removal agent.