Study On Chemical Enhanced Phosphorus Removal In Advanced Sewage Treatment

There is a contradiction between biological nitrogen and phosphorus removal in most sewage treatment plants,which results in the concentration of phosphorus in effluent can not meet the discharge standard.Therefore,deep chemical phosphorus removal has become a research hotspot.In this study,the effluent from campus water stations,municipal sewage treatment plants and laboratory water distribution were taken as the main objects,and the surface water standard?was taken as the standard.Ferric trichloride,ferrous sulfate,aluminium sulfate,calcium carbonate,calcium hydroxide,polyaluminium chloride?PAC?,polyferric chloride?PFC?,polyferric sulfate?PFS?were selected as dephosphorizing agents to investigate different types of dephosphorizing agents.The effects of coagulation conditions,initial phosphate concentration,dosage of phosphate remover,temperature,initial pH value and dosage mode on the phosphorus removal efficiency of Phosphate Remover were investigated.The optimal dosage of Phosphate Remover and its optimal dosage were found out.The economy of each Phosphate Remover was calculated according to the dosage of phosphate remover.By comparing the phosphorus removal efficiency of different types of phosphorus removal agents,it was found that the phosphorus concentration of treated water could reach the surface class IV water standard when iron and aluminium salts were added separately.The ratio of the dosage of phosphorus remover to the amount of phosphorus removed is FeCl₃>Al₂?SO₄?₃>PFS>KAl?SO₄?₂>PFC>FeSO₄>PAC.FeCl₃ and Al₂?SO₄?₃ with better phosphorus removal effect were selected and compounded phosphorus removal agents were made according to n?Fe:Al?of 1:2,1:3,2:3 and 3:1.The phosphorus removal efficiency was compared.It was found that the compound use of phosphorus removal agents had better phosphorus removal effect than that of single addition,and the effect was the best when n?Fe:Al?=3:1.Using n?Fe:Al?=3:1 Dephosphorizer to carry out the experiment of influencing factors of dephosphorization efficiency of dephosphorizer,it is found that n?Fe:Al?=3:1 Dephosphorizer has strong adaptability to the initial pH value of water sample,and has good dephosphorization effect at pH=6⁸.With the increase of temperature,the dephosphorization effect of n?Fe:Al?=3:1 Dephosphorizer becomes worse,but the temperature of municipal wastewater is 7²5?,in this temperature range,temperature does not affect the dephosphorization efficiency of dephosphorizer.The lower the initial phosphate content is,the more dephosphorizing agents are needed to remove phosphate per unit mass.The effect of phosphorus removal is better when the phosphorus removal agent is added twice or three times.The phosphorus removal rate is 1.88%,0.44%and 1.5%higher when the phosphorus removal agent is added twice than when the phosphorus removal agent is added three times or four times.With the increase of adding times,the increasing trend of phosphorus removal efficiency decreases gradually.Simulating the pre-removal and side-flow removal of phosphorus in the actual process system,it was found that when the phosphate content was 15 mg/L,the phosphate concentration after treatment was 7.16 mg/L,and the phosphate removal agent was 12.65 mg per mg of phosphorus removal;when the initial phosphate content was 20 mg/L and the phosphate concentration after treatment was 7.07 mg/L,the phosphate removal agent was 11.15 mg per mg of phosphorus removal.When the phosphate content was 30 mg/L,the phosphate content was 5.06 mg/L,and the molar ratio of Phosphate Remover to phosphorus was 1.82.Linear regression analysis was made on the relationship between initial phosphate concentration?X₁?,pH value?X₂?and phosphate concentration?X₃?after completion of the experiment and the dosage of phosphorus removal agent?Y?,and regression equation was established to predict the dosage of phosphorus removal agent.When the allowable error is 15mg/L,the hit rates of each regression equation are 76.9%,57.69%,73.08%and 69.23%respectively;when the allowable error is 20 mg/L,the hit rates of each regression equation are88.46%,73.08%,80.77%and 80.77%,respectively.F-test was carried out on the regression equation Y=18.905X₁+17.275 with the best adaptability and the regression equation Y=11.28X₁-244.443X₂+1802.298 with the best correlation.It was found that at 95%confidence level,the regression equation Y=18.905X₁+17.275 was significantly correlated,and the regression equation Y=11.28X₁-244.443X₂+1802.298 was also significantly correlated.