CO₂and N₂O Overflow Control In The Process Of Urban Sewage Phosphorus And Nitrogen Biological Treatment

Biological nutrient removal at home and abroad for studies are more focused on process optimization and analysis of microbial populations, and less focused on generation of CO2and N2O in biological nutrient removal process. The trial aims to establish a single and a double sludge system, compare the differences of nitrogen and phosphorus removal、CO2and N2O production quantity in the traditional nitrogen and phosphorus removal process and denitrification and phosphorus removal process, so as to provide a theoretical basis for the over control of CO2and N2O in the biological nutrient removal process.The dual-sludge and single-sludge process were established after100days of operation, and the nitrogen and phosphorus removal effeciency were high and stable. The COD removal rates of dual-sludge and single-sludge system were82.04%and81.35%receptively, phosphate removal rates were96.38%and97.34%, and ammonia nitrogen removal rates were96.38%and97.34%. Based on water data analysis, two-sludge system saves54.6%carbon source than the single-sludge.By the comparison of performance on two and single-sludge process, two-sludge system was fit for the treatment of low C/N wastewater, with advantages of saving carbon source and sludge, etc.However, the effluent ammonia concentration was under the impact of water change ratio and the system was difficult to control, incompletely denitrification is the biggest drawback of the two-sludge system. Though the external carbon source was added at denitrification phase of the one-sludge process, the effluent ammonia、 phosphate、nitrite and nitrate concentration can all lower than lmg/L in the180d running days, with shock load capability and simple and controllable process.The generation of CO2in double and single-sludge system was studied by deriving formulas and using calculation method. With anoxic denitrification and phosphorus removal stage as the analysis border, based on effluent datas, the production of CO2in a double and single-sludge process were calculated as3.16×10-4g/d and5.22×10-4g/d, and two-sludge system saves CO2emission39.46%.In the experiments of effects of different denitrification types on N2O overflow, the generation of N2O in denitrification and phosphorus removal system and exogenous denitrification system were0.15and0.20mg/L, accounting0.92%and1.52%of TN removal rate, recepectivly. The carbon source type of denitrification (intracellular polymers and external carbon) had no significant effect on the overflow of N2O.The effects of different influent ammonia concentration on N2O overflow were studied. It showed that when the ammonia concentrations were50,60and70mg/L during the nitrification, the production of N2O of2#and3#sludge under the three conditions were0.20、0.18、0.22mg/L and0.36、0.47、1.39mg/L, accounting10.6%、8.4%、8.6%and9.7%、5.15%、20.2%of the loss of nitrogen.The increase in ammonia concentration had no significant effect on the N2O overflow of2#sludge. However, the N2O emissions of3#sludge increased with the improvement of ammonia concentration and the increased speed was significantly faster than the ammonia concentration. Meanwhile, at the same level of ammonia concentration, the amount of N2O overflow of nitrification sludge were more than the mixed sludge and influenced significantly by the ammonia concentration.