Study On The Relationship Between The Dosage (Fe/P) Of Chemical Enhanced Phosphorus Removal And The Residual Phosphorus Concentration In Municipal Sewage Treatment Plant

Enhanced biological phosphorus removal process(EBPR)is a widely used biological phosphorus removal technology in municipal wastewater treatment plants in China.However,due to the characteristics of water quality and operation conditions,most of the wastewater treatment plants can not stably meet the first class a standard in the national discharge standard for pollutants from urban wastewater treatment plants(GB18918-2002),and chemical enhanced treatment of biological phosphorus removal system has become a city The main method of municipal wastewater treatment plant upgrading.However,the quantitative or excessive dosing method used in the operation of chemical enhanced phosphorus removal process results in the waste of chemicals,the increase of sludge output and the increase of operation cost.In this study,the amount of phosphorus removal agent,the treatment effect and the direction of phosphorus in the chemical enhanced A~2/O treatment system of Xi'an No.4 sewage treatment plant were investigated,measured and analyzed,and then the relationship between the amount of phosphorus added(Fe/P)and the concentration of residual phosphorus and the influencing factors were discussed in the laboratory.The results show that:(1)Xi'an No.4 Sewage Treatment Plant has a good effect on strengthening phosphorus removal by adding chemical phosphorus removal agent to A~2/O process.Under the conditions of Fe/P(mol/mol)and Al/P(mol/mol)of 3.476 and 0.765respectively,the phosphorus removal rate reaches 98%;The combined phosphorus removal rates of chemical precipitation,enhanced biological phosphorus removal(phosphorus accumulating bacteria)and microbial proliferation are 7%,45.07%and47.92%respectively.The chemical phosphorus removal system of the sewage treatment plant is in a state of over dosing of chemicals and needs improvement and optimization.(2)The amount of metal salt added(Fe/P)is an important factor affecting the residual phosphorus concentration in the process of phosphorus removal.The results of single factor coagulation test show that when the dosage of metal salt(Fe/P)is 1.753,the concentration of residual phosphorus in wastewater can reach below 0.5mg/l,and the phosphorus removal efficiency can reach 98%.(3)pH value is an important factor affecting chemical phosphorus removal.The concentration of residual phosphorus in wastewater changes with the pH value.When the pH value is 7.2,the chemical phosphorus removal efficiency is the highest.(4)Through the study on the aging test of hydrated iron oxide flocs(HFO),it can be seen that the adsorption effect of HFO surface active sites on phosphate is one of the important mechanisms of chemical phosphorus removal;the aging of HFO flocs will reduce its surface adsorption sites,reduce the total phosphate adsorption,and increase the residual phosphorus concentration in waste water under the same metal salt dosage(Fe/P)compared with fresh HFO.(5)The process of chemical enhanced phosphorus removal is a slow dynamic process composed of dissolution,precipitation,floc aging,adsorption and coprecipitation.Based on the experimental results and kinetic analysis of the reaction process,the quantitative relationship between the residual phosphorus concentration and metal salt dosage(Fe/P),pH value and aging time of hydrated iron oxide floc is established as follows:(?)(6)The empirical formula of the dosage of metal salt was verified by several groups of data under different operating conditions.The relative error between the theoretical calculation value and the measured residual phosphorus concentration value was between 1.76%and 37.68%.The empirical formula can be used as a prediction tool for the dosage of iron salt medicament,and can be used as a reference for practical application.