Study On Enhanced Phosphorus Removal Efficiency Of Secondary Biochemical Effluent By Different Phosphorus Removal Agents

In order to solve the problem that the phosphorus in the secondary biochemical effluent of a municipal sewage treatment plant is difficult to reach the first class a standard,chemical enhanced phosphorus removal measures are often used.In this study,through optimization and compounding,the effect of various phosphorus removal agents on TP removal efficiency was explored,aiming to find a phosphorus removal agent with high phosphorus removal efficiency,less secondary pollution and economic benefits among different chemical phosphorus removal agents.The main results are as follows.Batch experiments were carried out on simulated wastewater with different single phosphorus removal agents.The results showed that:considering the initial pH value of actual wastewater,TP removal efficiency and agent cost,ferric chloride,aluminum sulfate,polymerized ferric sulfate,commercial composite aluminum salt and composite iron salt were selected as phosphorus removal agents for secondary biochemical effluent research.Taking the secondary biochemical effluent of a municipal sewage treatment plant as the research object,the removal efficiency of TP and COD_Cr was studied from three aspects of initial pH value,dosage and reaction temperature.The results showed that the appropriate initial pH values of ferric chloride,aluminum sulfate,polymeric ferric sulfate,composite aluminum salt and composite iron salt for TP removal were 7,7,7.5.7.5and 7.5.The suitable initial pH values for COD_Cr removal and TP removal were not completely consistent.In order to meet the requirement that the concentration of TP reaches the first class a standard,the dosage of ferric chloride,aluminum sulfate,polyferric sulfate,composite aluminum salt and composite iron salt should be at least 45mg/L,60mg/L,45mg/L,120mg/Land 90mg/L respectively.The increase of temperature promoted the removal of TP and fluctuated the removal of COD_Cr.Through the orthogonal experiment of various factors,it was found that the dosage of ferric chloride,polymerized ferric sulfate,composite aluminum salt and composite iron salt had the greatest influence on TP removal,while the initial pH value had the greatest influence on aluminum sulfate.When the molar ratio of iron to aluminum as 3:1,2:1,1:1,1:2,1:3,in order to meet the first grade a standard of TP concentration,the initial pH value of wastewater is 7.5,the molar ratio of ferric chloride and aluminum sulfate is 1:1,and the suitable dosage is 50mg/L.The molar ratio of aluminum is 1:3,and the dosage is 65mg/L.Taking the secondary biochemical effluent of a municipal sewage treatment plant as the research object,the suitable initial pH value of the wastewater with the compound phosphorus removal agent is consistent with the research results of the simulated wastewater,both of which are 7.5;in order to meet the requirement that the TP concentration in the wastewater after the reaction reaches the first class a standard,the compound dosage of ferric chloride and aluminum sulfate,polymerized ferric sulfate and aluminum sulfate is at least 55mg/L and 65mg/L,and the TP removal rates are 77.5%and 78.4%.The removal rates of COD_Cr were 39.1%and 37.4%respectively;with the increase of temperature,the removal rates of TP were improved by the two kinds of compound agents,the removal rates of COD_Crby the combination of ferric chloride and aluminum sulfate increased with the increase of temperature,and the removal rates of COD_Cr by the combination of polyferric sulfate and aluminum sulfate increased with the increase of temperature;through the orthogonal experiments of various factors,it can be seen that the two kinds of compound agents have the greatest impact on the removal effect of TP All of them are dosage.Considering the effect of phosphorus removal and the cost of adding agent,the single phosphorus removal agent is polyferric sulfate,while the compound phosphorus removal agent is ferric chloride and aluminum sulfate.The research results of this paper can provide reference for the selection of phosphorus removal agent in urban sewage treatment plants.