Research On Nitrogen Removal And N₂O Emission In The Multiple Anoxic And Aerobic Process

With the organic carbon of acetate (SBR-A) and propionate (SBR-P) to the low nitrogen removal efficiency and N2O emissions of the traditional wastewater treatment, effects of carbon source, effects of organic carbon sources, initial nitrogen concentration and electron acceptor on nitrogen removal and N2O emission in the multiple anoxic and aerobic process were investigated. The theroy of controlling netrogen realese and N2O emissions reduction in wastewater treatment processes were provided.With a cycle of 6h, the sludge age of 20d, the influent COD concentration of 200 mg/L, NH4+-N concentration of 45 mg/L, PO43--P concentration of 10 mg/L,the nitrogen removal percentage in the SBR-A and SBR-P reactor was 66.7% and 67.1%, and the removal percentage of phosphate was 51.1% and 28.9%, respectively. During nitrification, the NH4+-N oxidation rate and NO3--N generation rate in the SBR-A reactor were higher than in the SBR-P reactor, while NO2--N and N2O accumulation rates in the SBR-A reactor were lower than in the SBR-P reactor. During nitrification, N2O emission factor in both reactors was less than 0.23%. During denitrification, the denitrification rate in the SBR-A reactor was higher than that in the SBR-P reactor, and the N2O emission factor was very low. Concurrent with the release of phosphorus, little effect occurred on the denitrification rate in SBR-A, while had a high influence on the SBR-P reactor with a lower rate than that without the release of phosphorus. Through high-throughput sequencing, the dominate bacteria in a phylum level were Proteobacteria and Bacteroidetes in both reactors, and in the genus level, the functional bacteria were Thauera, Dechloromonas, Bdellovibrio and Nitrospira etc.For SBR-A and SBR-P reactor, with the influent COD concentration of 200 mg/L, NHU+-N concentration of 45 mg/L, PO43--P concentration of 5 mg/L, the original period reduced from 6h to 4h, SRT shortened from the original 20d to 15d, the nitrogen removal percentage was 72% and the removal percentage of phosphate was 97% and 85.4%, respectively in the two reactor after long-term performance. During nitrification, NO2--N accumulation rate increased with the initial NH+-N concentration increasing. Resulting in N2O accumulation rate and emission factors were increased. Under different carbon sources conditions, N2O emission factors in the SBR-A reactor increased significantly from 0.40% to 2.57%, and SBR-P reactor also increased from 0.36% tol.40%. N2O accumulation rates in the two reactors increased with initial NO2--N concentration increased. N2O emission factors in the SBR-A reactor increased significantly from 1.43% to 4.66% and SBR-P reactor also increased from 0.68% to 2.08%. During exogenous carbon denitrification, when using NO3--N for electron acceptor, there appears obvious nitrite accumulation in the two reactors. NO3--N denitrification rate, NO2--N accumulation rate and PO43--P release rate of the SBR-A reactor were much higher than that in the SBR-P reactor. N2O accumulation rates and emission factors were significantly lower than reactor.When using N02--N for electron acceptor, NO2--N denitrification rate, N2O accumulation rate and emission factors of the SBR-A reactor were much higher than that in the SBR-P reactor.In endogenous denitrification, when using NO3--N for electron acceptor, NO3--N denitrification rate, PO43--P uptake rate, N2O accumulation rate and emisson factor of SBR-A reactor were higher than that in SBR-P reactor, when using NO2--N for electron acceptor, NO2--N denitrification rate, PO43--P uptake rate were higher than that in SBR-P reactor. However, N2O accumulation rate and emisson factors in the SBR-A reactor were lower than that in SBR-P reactor.Experiment results demonstrated that the sludge load were improved in the second operation mode. MLVSS in the SBR-A reactor increased from 1.61 g/L to 2.09 g/L, and MLVSS in the SBR-P reactor increased from 1.64 g/L to 2.35 g/L. The nitrogen removal percentage in the two reactors were improved 5%. The removal percentage of phosphate in the SBR-A reactor was improved 45.9%, while the removal of phosphate in the SBR-P reactor was significantly improved 56.5%. During nitrification, effects of sodium acetate on NOB activity was smaller than sodium propionate. During denitrification, the phosphate accumulating bacteria and denitrifying bacteria existing simultaneously had a greater influence on the denitrification activity and N2O emissions in the SBR-P reactor. The denitrification rate in the SBR-A reactor changed little, but the denitrification rate decreased and N2O accumulation rate and emisson factors significantly increased in the SBR-P reactor. In the two operation modes, DO concentration of the two reactors in the first modes was maintained at more than 2mg/L. DO concentrations of the aerobic section in the first modes was generally higher than that in the second modes. The N2O emission factors in the first operation modes were lower.