| In recent years, water pollution caused by eutrophication is still severe in our country, the resulting water environmental damage is also increasing, so phosphorus as an important limitative nutrition factor of water eutrophication must be strictly control the emission. With A2/O process treating domestic sewage, the concentration of total phosphorus in effluent water is about 1.0mg/1 that can’t reach the discharge standard, then the process combined chemical and biological phosphorus removal becomes an important way to achieve the phosphorus standard discharge in urban sewage treatment plant. At present, the main problems using the method of chemical phosphorus removal are the uncertainty affects in the quantity and adding point of reagent, as well as the changes of activated sludge in long running process. The study took the A2/O process as the research object and the combination of biological phosphorus removal and pre chemical phosphorus removal were adopted to investigate the effects of Al2(SO4)3 dosage on the concentrations of TP、COD、TN、NH4-N in effluent and activated sludge characteristics in the reactor under different adding points.The prepositive chemical phosphorus removal experiment took dosing coagulants in front of the bioreactor at room temperature, the results showed that the concentrations of TP、COD、TN and NH4+-N in effluent reached first grade A standards of "Discharge standard of pollutants for municipal wastewater treatment plant" (GB18918-2002) when the molar ratio of P to Al was 1:1 while the concentration of TP in effluent was up to about 2.0 mg/L with the ratio of P to Al was 0.5:1. The value of SVI and Zeta potential reduced from 87.4 mL/g and -4.73 mV to 74.2 mL/g and -7.16 mV before and after dosage respectively, when the molar ratio of P to Al was 1:1, indicating the sedimentation performance of activated sludge was reinforced. And the Oxygen uptake rate increased from 3.185 mg(O2)/(g(MLSS)·min) to 3.462 mg (O2)/(g(MLSS)·min) indicating the activity of sludge was also enhanced. It was also found that the amounts of Extracellular Polymeric Substances (EPS) increased from 66.25mg/g VSS to 105.24mg/g VSS and the ratio of protein to polysaccharide reduced from 5.23 to 2.09, indicating the dewatering performance of sludge was improved. The results of microorganism community structure of sludge taken from reactor before and after dosage showed that microbial species reduced from 8 to 5, indicating some microorganism communities were eliminated due to the maladjustments of sludge environment after dosage and bacterial abundance decreased while the rate of bacteroidetes and chloroflexi increased and became advantage bacterium group together with proteobacteria within the reactor. The prepositive chemical phosphorus removal experiment was took at low temperature, the concentration of TP in effluent was up to about 3.0 mg/L without the coagulants, the concentrations of TP、COD、TN and NH4-N in effluent reached first grade A standards when the molar ratio of P to Al was 1.5:1.The simultaneous chemical phosphorus removal experiment took dosing coagulants at the end of the aerobic pond at room temperature, the results showed that the concentrations of TP、 COD、TN and NH4+-N in effluent reached first grade A standards of "Discharge standard of pollutants for municipal wastewater treatment plant" (GB18918-2002) when the molar ratio of P to Al was 0.5:1 while the concentration of TP in effluent is about 1.5-2.0 mg/L with the ratio of P to Al was 0.25:1. The value of SVI and Zeta potential reduced from 93.75mL/g and-5.5 mV to 81.25mL/g and -11.8 mV, the Oxygen uptake rate increased from 4.246mg(O2)/(g(MLSS)·min) to 6.732mg(O2)/(g(MLSS)·min), the oxygen absorption rate of aerobic sludge from 4.246 mg (O2)/(g (MLSS), min) up to 6.732 mg (O2)/(g (MLSS), min), and the amounts of Extracellular Polymeric Substances (EPS) increased from 66.25mg/g VSS to 105.9mg/g VSS and the ratio of protein to polysaccharide reduced from 5.23 to 2.2 before and after dosage respectively, when the molar ratio of P to Al was 0.5:1, that the changed trend were consistent with that of prepositive chemical phosphorus removal. Taking Al2(SO4)3 before and after dosing reactor sludge microbial community structure analysis, found that aluminum, phosphorus mole ratio was 0.5:1 when the sludge microbial species of coagulant dosage before 8 kinds of reduced to six, Cyanobacteria and Elusimicrobia disappeared, and the proportion of bacteroidetes and Acidobacteria bacteria has increased, while Proteobacteria decreased. The simultaneous chemical phosphorus removal experiment was took at low temperature, phosphorus removal rate was greatly reduced in the bioreactor effluent without the coagulants, the concentrations of TP、COD、TN and NH4-N in effluent reached first grade A standards when the molar ratio of P to Al was 1:1. |
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