Experimental Study On AOA-SBBR Process For Treatment Of Rural Domestic Sewage

With the rapid development of economy,the changes in rural lifestyles will inevitably generate more domestic sewage,but the level of construction of rural sewage collection and treatment facilities is low.A large amount of rural domestic sewage and livestock breeding wastewater are simply treated by septic tanks or even directly discharged without treatment.It has caused serious pollution of the rural water environment,which not only has a negative impact on the development of agriculture and aquaculture,but also endangers the health and normal production and life of rural residents,and even restricts the development and progress of the rural economy.The composition of rural domestic sewage is relatively simple,with the characteristics of good biodegradability,small output,large fluctuations and almost no toxic and harmful pollutants.Therefore,when treating rural domestic sewage,it is necessary to adapt measures to local conditions and choose a sewage treatment process with low investment,low cost,strong impact resistance,and convenient management.The main purpose of this experiment is to study the feasibility of Anaerobic/Aerobic/Anoxic-Sequencing Batch Biofilm Reactor（AOA-SBBR）process in treating rural domestic sewage,to master its main rules in actual operation,and to perfect the existing theory,it provides theoretical basis and technical reference for practical engineering application.Taking simulated Ningxia rural domestic sewage as the treatment object,through analyzing operating data,the effects of influent COD/influent TN（C/N）,operational cycle,DO concentration,operational temperature and drainage ratio on the efficiency of simultaneous nitrogen and phosphorus removal of AOA-SBBR system were investigated to determine the optimal operating parameters and the optimization method of system operating conditions,and thus further improve the nitrogen and phosphorus removal performance of the AOA-SBBR system.The study on the influence factors of the effect of nitrogen and phosphorus removal effect in the AOA-SBBR system showed that when the C/N was 6,the removal effect of TN and PO₄^3--P was better,and the average removal rates were 99.40±0.80%and 73.67±13.89%,respectively;The efficiency of nitrogen and phosphorus removal decreased with the shortening of the operational cycle;When the DO concentration increased from0.9～1.1mg·L^-1to 1.4～1.6mg·L^-1,the removal efficiency of NH₄⁺-N,TN and PO₄^3--P was improved,NH₄⁺-N and TN achieved a removal rate of 100%,and the average removal rate of PO₄^3--P was 81.56±6.49%.But at this time,there was a secondary phosphorus release phenomenon in the post-anoxic section.By increasing the concentration of DO to2.9～3.1mg·L^-1or adjusting post-anoxia time,the effluent quality of the system can reach to the first class level A standard of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant（GB18918-2002）.As the temperature down from 30℃to 20℃,the removal effect of NH₄⁺-N and TN has decreased,the average removal rates were 92.28±3.13%,91.63±2.86%,respectively.And the removal effect of the PO₄^3--P increased significantly with the decrease of temperature,the average removal rate was 96.03±3.63%;Under the same other operating conditions and only increasing the drainage ratio,when the drainage ratio increased from 3/8 to 6/8,the effect of nitrogen and phosphorus removal in the system was decreases obviously,and even the effluent quality exceeded the second class standard of GB18918-2002.Based on the analysis of nitrogen changes in a typical period,it was considered that the denitrification in reactor was Simultaneous Nitrification and Denitrification（SND）,and Nitrite Type Simultaneous Nitrification and Denitrification（Nitrite Type SND）was the main type.Through the restarting experiment of the reactor,it can be determined that the high DO concentration not only can solve the problem of NH₄⁺-N accumulation,but also can inhibit the secondary phosphorus release in the post-anoxic section,reduce the effluent PO₄^3--P concentration,and thus improve the PO₄^3--P removal efficiency.And the SBBR system still had a stable SND effect when running in the absence of management and changeable environmental factors.In addition,the process experiment under anaerobic condition showed that there was no anaerobic ammonia oxidation reaction in the reactor,the decrease of NH₄⁺-N concentration at the beginning of each period was mainly due to biofilm adsorption and microbial storage.And there were denitrifying dephosphatation and endogenous denitrification in the reactor.Through the analysis of the simultaneous denitrification and phosphorus removal effect of the AOA-SBBR process under different working conditions,it was concluded that the optimization methods of the system operation conditions were as follows:First,when the denitrification effect of the system was good and the phosphorus removal effect was poor,the removal efficiency of phosphorus can be improved by increasing the C/N or increasing the DO concentration.If the low phosphorus removal efficiency was due to the secondary phosphorus release in the post-anoxic section,the secondary phosphorus release can be avoided by shortening the anoxic time;Second,increasing the DO concentration can make the removal efficiency of nitrogen and phosphorus increase synchronously in the system;Third,the effect of phosphorus removal at low temperature in winter was good but the effect of nitrogen removal was poor,which can improve the efficiency of nitrogen removal by prolonging the operational cycle;Fourth,the system can keep the good nitrogen and phosphorus removal efficiency by increasing the drainage ratio while prolonging the operational cycle,and can also improve the daily treatment capacity of nitrogen and phosphorus.The results indicated that there were the following five optimal operating conditions of the system for nitrogen and phosphorus removal:1)20℃,C/N=6,DO=（1.4～1.6）mg·L^-1,the operational cycle of 12h,the drainage ratio of 3/8;2)room temperature（26～28℃）,C/N=6,DO=（3.9～4.1）mg·L^-1,the operational cycle of 8h,the drainage ratio of 3/8;3)room temperature（27～29℃）,C/N=6,DO=（2.9～3.1）mg·L^-1,the operational cycle of 8h,the drainage ratio of 3/8;4)room temperature（25～26.5℃）,C/N=4,DO=（1.9～2.1）mg·L^-1,the operational cycle of 8h,the drainage ratio of 3/8;5)room temperature（24～26℃）,C/N=4,DO=（1.9～2.1）mg·L^-1,the operational cycle of 12h,the drainage ratio of 6/8;Under these five conditions,the effluent quality can reach to the first class level A standard of GB18918-2002stably.