| Modified A~2+OSA step-feeding process is further optimized for modified A~2/O step-feeding process, which is characterized by anaerobic sludge retention tank fixed in the process of returning activated sludge. It is expected the process both can realize sludge reduction in situ and can improve the rates of nitrogen and phosphorus removal of system. The features of modified A~2+OSA step-feeding process were introduced in this paper, and are compared with that of modified A~2/O step-feeding process; the effects of the two treatment processes on the removal of the main pollutants in sewage and the variation of the different pollutants were investigated; the material balance on the carbon and phosphorus in the two process system were carried out, which were also researched; the main influencing factors of biological phosphorus removal were discussed, and the kinetic model of anaerobic phosphorus release, aerobic phosphorus uptake and denitrifying phosphorus removal of two systems under different influencing factors was established, and parameters of the kinetic models were determined and analyzed.The effects of pollutant removal of the two systems were studied by continuous flow pilot test device. Using synthetic wastewater and remaining influent distribution as1:1, it is found that CODCr, NH3-N, TN and TP of the two process systems have achieved a better removal performance in the condition of sludge and mixture return ratios being 100% and 300% respectively. The result showed that the effluent concentrations of CODCr, NH3-N, TP and TN in modified A~2+OSA step-feeding process system were respectively 41.78mg/L,3.91 mg/L,11.90 mg/L and 0.24 mg/L, that the average removal rates were 92.72%, 92.25%, 90.14% and 96.85%. It also showed that the effluent concentrations of CODCr, NH3-N, TP and TN in modified A~2/O step-feeding process system were respectively 38.78mg/L, 2.49 mg/L, 13.89 mg/L and 0.29 mg/L,that the average removal rates were 92.91%, 94.97%, 82.95% and 96.22%. The removal effects of modified A~2+OSA step-feeding process are better than that of modified A~2/O step-feeding process.The carbon balance was calculated for each functional tank of the modified A~2+OSA step-feeding process system and the modified A~2/O step-feeding process system. System balance rate were 84.53% and 71.43% respectively. It is found that the carbon sources discharging in the form of CO2 of the two systems are 59% and 46%respectively, discharging with the excess sludge both accounts for 15%, discharging with the effluent are 11% and 10% respectively. CODCr of modified A~2+OSA step-feeding process system is removed in anaerobic tank is 23.91%, in anoxic tank is12.39%, in aerobic pool is 22% and in sedimentation tank is 26.21%. CODCr of modified A~2/O step-feeding process system is removed in anaerobic tank is 19.01%, in anoxic tank is 10.84%, in aerobic pool is 15.32% and in sedimentation tank is 26.24%.The phosphorus balance was calculated for the overall system of the modified A~2+OSA step-feeding process and the modified A~2/O step-feeding process, system balance rate were 84.53% and 71.43% respectively. The result shows that phosphorus was discharged mainly with the excess sludge and effluent, discharging with the excess sludge accounts for 74% and 62% respectively, with the effluent are 11% and 10%respectively. Determination of phosphorus content in excess sludge was conducted of two systems; it is found that the excess sludge of modified A~2+OSA step-feeding process system contains more phosphorus.The effects of carbon source concentration, carbon source type, anaerobic degree,pH, NO3-and NO2-on biological phosphorus removal were explored. Through static sequencing batch test and data analysis, the anaerobic phosphorus release kinetic models were achieved and the parameters were determined with different carbon source concentration, carbon source type and anaerobic degree of two systems; the kinetic models of aerobic phosphorus uptake and denitrifying phosphorus removal with different NO3- and NO2- and pH were established and the model parameters were determined. The influence rules and level of different factors on the biological phosphorus removal process were studied by inquiring the kinetic model parameters of biological phosphorus removal in the same system. The further study was conducted on the reasons for the differences in the biological phosphorus removal between two process systems by comparing and analyzing the model parameters of the two process systems. |
PDF Full Text Request