Study On Distribution And Removal Efficiencies Of Heavy Metals In Sewage Treatment Process

Heavy metals in the water is very stable,it is difficult to degradation by microorganisms,Heavy metals are a great pollutant in the water environment.The discharge of municipal sewage is an important way for heavy metal pollutants to enter the water environment Therefore,it is of great significance to study the return characteristics of heavy metal pollutants in sewage treatment.Selected four kinds of metal commonly used in urban sewage（Cd,Cu,Ni and Cr）as a research object,Study on distribution and removal efficiencies of heavy metals in the A and B plants with large differences in the raw water properties was carried out.The main contents and results of the experimental study are as follows:（1）A,B two sewage plants in and out of the water were detected four kinds of target heavy metal pollutants.The contents of Cd²⁺,Cu²⁺,Ni²⁺and Cr³⁺ in the influent of A plant were:4.78μg/L,2.86μg/L,38.89 μg/L and 1.48 μg/L,The contents of the effluent were: 2.76 μg/L,2.55 μg/L,33.51 μg/L and 0.89 μg/L,The removal rates were: 42.21%,10.69%,11.47% and42.21%.The contents of Cd²⁺,Cu²⁺,Ni²⁺and Cr³⁺ in the influent of B plant were : 8.18 μg/L,5.89 μg/L,43.86 μg/L and 2.21 μg/L,The contents of the effluent were : 5.88 μg/L,4.25 μg/L,36.97 μg/L and 1.64 μg/L,The removal rates were: 28.18%,27.78%,28.18% and 27.78%.（2）A,B two sewage treatment plants can remove the four kinds of heavy metals.The contents of Cd²⁺,Cu²⁺,Ni²⁺and Cr³⁺ in A plant from the grit chamber were : 3.53 μg/L,3.37μg/L,36.35 μg/L and 1.34 μg/L,The contents of the effluent in the secondary sedimentation tank were respectively: 2.85 μg/L,2.58 μg/L,33.52 μg/L and 0.89 μg/L.Which the best effect of grit chamber treatment,the removal of heavy metal pollutants can reach a maximum of22.75%.The contents of Cd²⁺,Cu²⁺,Ni²⁺and Cr³⁺ in B plant from the grit chamber were : 6.76μg/L,5.25 μg/L,41.04 μg/L and 1.86 μg/L,The contents of the effluent in the secondary sedimentation tank were respectively: 5.93 μg/L,4.34 μg/L,37.34 μg/L and 1.57 μg/L.Where the secondary settling tank treatment the best,the removal of heavy metal pollutants can reacha maximum of 24.56%.（3）A,B two sewage plants in the four kinds of heavy metals in the water content of the difference between the larger,B plant content was significantly higher than the A plant,Cd²⁺,Cu²⁺,Ni²⁺ and Cr³⁺content higher than 41.56%,51.44%,11.13% and 51.44% respectively.Water content of four kinds of heavy metals and water consistent,B plant content was significantly higher than the A plant,Cd²⁺,Cu²⁺,Ni²⁺ and Cr³⁺content higher than 53.06%,40.00%,9.20% and 40.00% respectively.In A plant,the total removal rates of four heavy metals were 42.21%,10.69%,11.47% and 39.41% respectively.The total removal rate of B was 28.18%,28.78%,15.70% and 30.34% respectively.（4）In different seasons sewage plant were detected target class pollutants of heavy metals in water,treated four kinds of heavy metal pollution has certain removal.A factory in June in water Cd²⁺,Cu²⁺,Ni²⁺ and Cr³⁺,the content of 4.78μg/L,2.86μg/L,38.98μg/L,1.48μg/L,in December of 3.97μg/L,2.2μg/L,31.86μg/L,1.33μg/L.B factory in June in water Cd²⁺,Cu²⁺,Ni²⁺ and Cr³⁺,the content of 8.18μg/L,5.89μg/L,43.89μg/L,2.21μg/L,in December of 6.85μg/L,4.93μg/L,36.53μg/L,2.02μg/L.In general,the four target heavy metal contaminants were higher in September and December at least.In the removal rate,the removal efficiency of Cd²⁺,Ni²⁺ and Cr³⁺was better in June,and the removal efficiency of Cd²⁺,Cu²⁺ and Ni²⁺was better in the secondary sedimentation tank in September.（5）The Cd²⁺,Cu²⁺,Ni²⁺ and Cr³⁺ were accumulated in the sludge of the two sewage plants.the sludge.In A plant,the average concentration of heavy metal contaminants in the anaerobic tank sludge were: 0.95 mg/kg,133.92 mg/kg,79.66 mg/kg and 117.00 mg/kg,The average concentration detected in the sludge concentration tank were: 1.26 mg/kg,152.97 mg/kg,87.80 mg/kg and 113.79 mg/kg.In B plant,the average concentration of heavy metal contaminants in the anaerobic tank sludge were: 1.02 mg/kg,160.46 mg/kg,87.44 mg/kg and128.77 mg/kg,The average concentration detected in the sludge concentration tank were 1.30mg/kg,187.64 mg/kg,116.71 mg/kg and 124.24 mg/kg.B plant sludge heavy metal content higher than the A plant.