Research On The Emission And Reduction Control Of N₂O From Denitrifying PhosPhate Removal System

In recent years, with the continuous improvement of urbanization and industrialization, wastewater with low C/N, C/P ratio is increasing. Due to the lack of carbon sources, the effect of conventional sewage treatment process is not very good. So people pay more attention to water pollution coercion.Because traditional nitrogen and phosphorus removal System is difficult to reconcile competition and conflicts amony the aspects of SRT, nitrate, carbon source, microorganisms, it can not meet the requirements of nitrogen and phosphorus removal. Denitrification and phosphorus removal System as a new type of efficient low-power biological nutrient removal technology became a hot topic because of the advantages of saving the amount of aeration and reducing the sludge production. Recently, many studies have found that the denitrifying phosphorus removal system will produce a large number of N2O. N2O is an important greenhouse gas, the greenhouse effect is300times than CO2. So it is necessary to study the release of N2O, but the Literature of denitrifying phosphorus removal process to deal with N2O emissions in the process of the low C/N of urban sewage is rare, especially in comparison with traditional nitrogen removal process. Therefore, the subject compares the effect of Sewage treatment of A2/N-SBR and A/O-SBR and analyzes N2O emission mechanism and differences. Finally, form the aspect of optimization of process operating conditions, the Literature gives a practical N2O reduction control strategy.The research shows that the removal efficiency of nitrogen and phosphorus by the A2/N-SBR denitrifying dephosphatation processes is higher than the normal A/O-SBR nitrogen removal, and the removal efficiency of COD are both higher than90%.The rates of denitrogenation and phosphorus removal by the A2/N-SBR denitrifying dephosphatation processes are both larger than90%, but rate of denitrogenation by the normal one is only58%, phosphorus removal rate is48%. Such as it is, but from the other analysis, the A/O-SBR nitrogen removal generates few N2O.The A2/N-SBR system N2O is mainly produced in the denitrifying nitrogen removal phosphorus uptake phase and aerated nitrification stage, but its release occurs mainly in aerated nitrification stage. In A/O-SBR reactor N2O is mainly produced in the aerated nitrification stage. In denitrifying nitrogen removal phosphorus uptake phase N2O production in A2/N-SBR reactor is far higher than that of A/O-SBR reactor, while in the aeration stage, N2O production in A2/N-SBR reactor is less than that of A/O-SBR reactor. Within one cycle of the N2O output, A2/N-SBRshould be slightly higher than that of A/O-SBR reactor. In denitrifying nitrogen removal phosphorus uptake phase of A2/N-SBR and A/O-SBR the production of N2O have obvious difference. Another study found that in the external carbon source nitrate, nitrite and N2O reduction rate will be higher than that of with no carbon source (PHAs as carbon source). In denitrifying nitrogen removal phosphorus uptake phase, N2O production were greater than that of a conventional denitrification process, mainly because denitrifying phosphorus accumulating bacteria use intracellular polymer PHAs as the carbon source for denitrification. PHAs degradation rate is slow and it can not provide enough electronics in unit time, which lead to nitrate, nitrite and nitric oxide reductases in electronic form competition in the denitrification process, While the ability on electronic competition of nitrous oxide reductase significantly weaker than that of the nitrate and nitrite reductase Nitrous oxide reductase can not get enough electronics so that the process of N2O reduction for the N2suffocate, N2O appear to accumulate.Therefore, the competitiveness of reducase to electron could be weaken by the way of continuously charging water in the initial stage of oxygen denitrification instead of instantaneous water, consequently the fewer accumulation of nitrite nitrogen and the fewer quantity of N2O. The main reason of the production of N2O in aeration stage is that the lower DO lead to the nitrifying bacteria denitrification. So the production of N2O could be dcreased by changing the aeration amount.