Study On Biological Nitrogen And Phosphorus Removal By The A/O Process And SBR Process Under Low DO Condition

Along with eutrophication aggravating, nutriment removal, such as nitrogen and phosphorus, has become a most important mission for municipal sewage treatment plant. SND is a new applied nitrogen removal technology which has studied in recent years, it can economize carbon source, and benefit in nitrogen removal, so, it is considered a low carbon source demanded and low energy consumed sewage treatment technology. A large number of studies indicate that low dissolved oxygen state is able to promote SND process and improve nitrogen removal efficiency. But, the biological phosphorous removal property under low DO condition is rather scarce, which limits the application of this technology.Therefore, this test chooses the A/O process and the SBR process respectively for the representative of the continuous flow system and the batch-flow system, studies on biological nitrogen and phosphorus removal effect under low DO condition. From the aspects of saving energy and satisfying actual operation, this paper compares the nitrogen and phosphorus removal effect of the A/O process with that of the SBR process for municipal wastewater under low DO condition to look for a energy saving sewage treatment. And, this study is conducted from the aspects of operating stability and the sludge settlement ability. The results show that:①The effect of each researchful factor to organism removal is small, the removal rates of the A/O system and SBR system under every conditions are about 90%.②The anaerobic(anoxic) time influences the nitrogen and phosphorus removal effect. In the A/O process and the SBR process, 2 hours of anaerobic(anoxic) time can satisfy phosphorus removal and achieve good phosphorus removal effect.③DO affects biological nitrogen and phosphorus removal effect. Within the testing range of DO, obvious SND happens in the low DO tank of the A/O process and low DO phase of the SBR. In the A/O process, the lower the dissolved oxygen, the better the removal rate of TN, when the concentration of DO is 0.5mg/L, the removal rate of SND is 23.9%, and the removal rate of TN is 63.8%. In the SBR process, when the average concentration of DO is 0.7mg/L, the removal rate of SND is maximal, is 32.3%, and the removal rate of TN reaches to 74.5%. In general, the removal rate of TP in the A/O system is low, the effluent can not meet the standard. In SBR system, the phosphorus removal effect is good. When DO is 0.7mg/L, the phosphorus removal effect is hightest. The long-term results indicate that the concentration of DO increases above 2mg/L before the end of aeration ensuring phosphorus admitted completely in the SBR system.④The HRT(T) affects the ammonia nitrogen removal effect obviously. The longer the HRT(T), the greater enhanced degree of the ammonia nitrogen removal effects of two systems. The higher HRT results in better nitrogen removal effect, but when the HRT of the A/O system exceeds 9 hours, the removal rate of nitrogen increases slowly, when the T of the SBR system is greater than 8 hours, the removal rate of nitrogen increases also seldom. When the HRT of the A/O system is 9 hours, the phosphorus removal effect is better, but the effluent can not meet the standard. When the T of the SBR system is 8 hours, the phosphorus removal effect is good, the average effluent concentration of TP is 0.5 mg/L. Therefore, it is suggested to adopt the SBR system for good nitrogen and phosphorus removal effect.⑤To the A/O system and the SBR system, SRT affects the removal effect of ammonia nitrogen, nitrogen and TP, which are identical. The longer the SRT, the better the treatment effect of ammonia nitrogen and nitrogen, but the longer SRT results in worse effect of TP. The proper SRT is 20d.⑥Under low DO condition, the SVI of the A/O process is always higher, during 150~200. Low temperature in the winter results in bulking sludge. In the SBR process, the sludge settling ability is fine, the SVI does not increase, within 100~150, and the treatment effect is stable.⑦The SBR process is better than the A/O process, whether in ascepts of technical economy and stabilization or nitrogen and phosphorus removal effect. The results show that when the anaerobic(anoxic) time is 2 hours, DO=0.7mg/L, T=8h, SRT=20d, the SBR system realizes nitrogen removal by SND and phosphorus removal under low DO condition successfully, achieves good nitrogen removal effect by SND and phosphorus removal effect...