Effects Of Chemical Synergistic Phosphorus Removal On The Performance Of Activated Sludge In Urban Sewage Treatment Plant

While chemical synergistic phosphorus removal can improve the phosphorus removal effect of sewage treatment plants,there are problems such as excessive dosage of phosphorus removal agent,which leads to the increase of excess sludge production and affects the denitrification and phosphorus removal performance of activated sludge.At present,the actual dosage rate of chemical phosphorus removal is mostly 2～3 times or even higher than the theoretical dosage rate.Due to the different requirements for phosphorus removal in sewage treatment plants and different dosage strategies of phosphorus removal,it will affect the degree of excessive dosage of phosphorus removal.Therefore,in this study,we discussed the characteristics and optimization strategies of chemical synergistic phosphorus removal based on the analysis of the impact of excessive addition of phosphorus removal agent on the performance of activated sludge in the process of chemical synergistic phosphorus removal.Taken a sewage treatment plant in Xi’an as the research object（the sewage plant was operated by both CASS and A²/O processes after the upgrading and renovation）.Firstly,we discussed the influence of excessive dosage of phosphorus removal agent on the characteristics of wastewater treatment,and analyzed the effects chemical synergistic phosphorus removal on phosphorus concentration distribution along the process of sewage treatment plant,nitrogen and phosphorus removal performance of activated sludge and phosphorus composition;Secondly,a Jab-scale SBR reactor was used to treat the simulated sewage,and the anaerobic-aerobic（A/O）process was used to analyze the chemical synergistic phosphorus removal when the TP concentration of the effluent was less than 0.3 mg/L.we analyzed the effect of synergistic phosphorus removal and the biological phosphorus removal performance of activated sludge;Finally,the batch experiments were used to analyze the impact of simultaneous and post-dosing of phosphorus removal agent on phosphorus removal effect,and optimize the dosing strategy of phosphorus removal agent,in order to provide a theoretical basis for the selection of phosphorus removal agent dosing position in actual sewage treatment projects.The main conclusions were as follows:（1）In order to clarify the effect of chemical synergistic phosphorus removal in the actual sewage treatment process and its influence on the output of excess sludge,the dosage of phosphorus removal agent,phosphorus concentration distribution along the route and excess sludge output of the CASS and A²/O processes of the wastewater treatment plant were investigated.analysis.The phosphorus removal agent used in this plant is an iron-aluminum composite phosphorus removal agent（Yiwei phosphorus）,of which Fe³⁺is the main component（90.43%）.The CASS process phosphorus removal agent is pre-dosing,and the A²/O process phosphorus removal agent The dosing method is synchronous dosing.The analysis results of the dosage of phosphorus removal agent and the output of excess sludge show that the actual dosing rate（calculated by the concentration of phosphate at the dosing point）of the pre-dosing and synchronous dosing is 1.60 and 6.25 mol Fe/mol P,respectively.According to the effluent phosphorus concentration and the relationship between the remaining dissolved phosphorus and Fe/P molar ratio required by different dosing methods of each process,it can be known that the optimal dosing rate Fe/P molar ratio of phosphorus removal agent in CASS and A²/O systems should be 1.4 respectively.and 3.2.Therefore,the phosphorus removal agent in each process of the sewage treatment plant was in a state of excessive addition,and the excess addition of phosphorus removal agent resulted in an increase of 13.69%in the output of excess sludge（calculated with a moisture content of 80%）.（2）In order to analyze the effect of excessive dosage of phosphorus removal agent on the performance of activated sludge,the denitrification and phosphorus removal capacity of activated sludge in CASS and A²/O processes was analyzed.The results show that the excessive dosage of phosphorus removal agent has no great influence on the stability of the CASS and A²/O processes and the biological denitrification capacity of the sewage treatment plant.However,in terms of biological phosphorus removal ability,compared with another sewage treatment plant without chemical phosphorus removal agent,the average phosphorus release and absorption rate of CAST and A²/O process is 6.50 mg P/（g VSS·h）,this paper the phosphorus activity of the activated sludge from the CASS and A²/O processes of the WWTP was reduced by50.16%and 54.42%,respectively.Therefore,excessive dosage of phosphorus removal agent will significantly weaken the biological phosphorus removal ability of activated sludge.（3）In order to further analyze the characteristics of chemical synergistic phosphorus removal,a Jab-scale SBR reactor operated by A/O（anaerobic-aerobic）process was built.Add phosphorus remover to make the TP concentration of the effluent less than 0.3 mg/L.The results showed that increasing the dosage ratio of phosphorus removal agent had no obvious effect on the concentrations of COD,TN and NH₄⁺-N in the effluent.Compared with 4.52 and 3.95mg P/（g VSS·h）when the maximum phosphorus release/absorption rate in the reactor without phosphorus removal agent was added,when the phosphorus removal agent addition rate was 3.6 mol Fe/mol P（60mg/L）and 6.0 mol Fe/mol P（100 mg/L）,the maximum phosphorus release rate in the reactor decreased by 52.87%and 64.60%,and the maximum phosphorus absorption rate decreased by 48.60%and 62.02%,respectively.When the phosphorus removal agent was stopped for 7 days,the maximum phosphorus release/absorption rate in the reactor recovered to the levels of 68.58%and 74.17%in the initial stage.This shows that the chemical synergistic phosphorus removal will weaken the biological phosphorus removal ability of activated sludge,but this weakening is reversible.（4）In order to reduce the influence of excessive dosage of phosphorus removal agent on the biological phosphorus removal ability,the dosing strategy of phosphorus removal agent was optimized,and batch experiments were carried out to analyze the effect of simultaneous dosing and post-dosing on the effect of chemical synergistic phosphorus removal.The results showed that when the same as dosage rate of phosphorus removal,the TP removal rate of post-dosing was 9.61%higher than that of synchronous dosing,and post-dosing can prevent the phosphorus removal from entering the biological treatment system.Combined with the analysis of the synergistic phosphorus removal effect of different processes in the sewage treatment plant and the results of continuous running test,the post-dosing was more suitable for this sewage treatment plant than the synchronous dosing.