Study On Phosphorus Removal Of AB Process Municipal Sewage Treatment Plant Effluent

In recent years, people show more concern for eutrophication. The eutrophication makes water not only lose its function, but also deteriorate towards the direction which is not conducive to people. The restrictive factor which resulting in eutrophication is phosphorus. Thus removing phosphorus can be an effective method to solve the eutrophication.The technologies of phosphorus removal are biological and chemical methods. But the biological phosphorus removal is not satisfactory. Thus the chemical phosphorus removal is always introduced to reach the effluent standard. The secondary effluent from some wastewater treatment plant of AB craft was selected as the test water samples.The test studied the law of transformations in various stages of the sewage treatment process. FeCl₃, PAC, Al₂(SO₄)₃ were chosen as coagulants, the phosphorus removal effect for the secondary effluent by coagulant tests were carried out. The test learned the best coagulant and suitable reaction conditions.The tests provided theoretical support and technical parameters for the treatment system design and in-depth study.The results showed that:1,The phosphorus concentration in each process of the wastewater treatment plant of AB craft was measured. The TP of the raw water was about 12.8 mg/L. The concentrations of TP in the A section influent and A section effluent were 13.52mg/L and 5.55mg/L, the phosphorous removal rate of A section was 58.9%. The concentrations of TP in the B section effluent was 4.95 mg/L , the phosphorous removal rate of B section was 10.8%.The test showed that the phosphorus removal of AB craft based on A section. The concentrations of TP in pre-concentrated tank and after- concentrated tank were 8.58 mg/L and 38.84 mg/L. After the supernatant returning of pre-concentrated tank and after- concentrated tank, the TP concentration increased by 1.01mg /L. The TP increase was 8%. Even if the TP in the supernatant of pre-concentrated tank and after- concentrated tank were removed completely, the effluent could not meet the integrated wastewater discharge standard.Thus for AB technology,the phosphorus removal system should be placed on the effluent treatment process.2,The test that not adjusting pH, the raw water added coagulant directly showed that the optimal dosage of FeCl₃, PAC(to Al2O3 account), Al₂(SO₄)₃ were 75mg/L, 75 mg/L and 125mg/L respectively, the phosphorous removal rate were 92.5% , 90.5% and 92.3% respectively, the TP concentration after treatment were 0.37mg/L,0.47mg/L and 0.38mg/L respectively.The TP concentration all met the integrated wastewater discharge standard after treatment of three coagulants.FeCl₃ was the most effective coagulant for phosphorus removal, the next were Al₂(SO₄)₃ and PAC. The test water samples weren't added any coagulants, only pH value was adjusted to 10.5, which could meet the integrated wastewater discharge standard also.The reason was the hardness of the water.3,The test that experimented with the water samples prepared with distilled water and tap water respectively, showed that the optimal pH of FeCl₃ were 5 and 10.5.The former was acidic,while the latter was alkaline, the difference was significant. The TP concentration after treatment were 0.67mg/L and 0.42mg/L respectively, the phosphorous removal rate were 86.46% and 91.5% respectively.To sum up, when the same coagulant treated different waters that had the same TP concentration, the phosphorus removal effect and optimum conditions were quite different.4,The test that FeCl₃ coagulation floc size distribution showed that the size of 0.1-0.5mm were the most, accounting for 70% ⁸0% of the total floc. With the increase of the dosage of FeCl₃, 0.1-0.5mm floc gradually decreased, while the particle size of 0.5-5.0mm and >5.0mm floc gradually increased.