Experimental And Engineering Design Of Air-lift A~2/O Biofilm Reactor For Treatment Of Rural Domestic Sewage

At present,with the development of urbanization and toilet revolution in China,the problem of rural water environment has attracted more and more attention.Because the rural villages are scattered,the rural sewage collection pipe network is not perfect and the technology,management and economy are relatively lagging behind,it is difficult to use the unified collection of sewage for centralized treatment like the city,so the use of decentralized sewage treatment technology which can collect,treat and recover rural domestic sewage has attracted more and more attention.A~2/O process is one of the most widely used nitrogen and phosphorus removal processes at present,so this experiment adopts the integrated A~2/O process as the main body,combined with biofilm and efficient and practical air-lift reflux technology to strengthen the removal effect of rural domestic sewage,and carries on the parameter optimization and engineering design of the test.The experiment investigated the removal effect of reactor on COD,nitrogen(including ammonia nitrogen,nitrate nitrogen,TN)and TP in wastewater by controlling the parameters of nitrification liquid reflux ratio,sludge reflux ratio,DO concentration and SRT.Taking into account the efficiency of pollutant removal and energy saving and consumption reduction,the best parameters for reactor treatment of rural domestic sewage were determined,that is,the reflux ratio of nitrifying liquid was 200%,the DO concentration was 2.0 mg/L,the sludge reflux ratio was 60%,and the SRT was 12 d;Under the optimum parameters,the effluent COD,ammonia nitrogen and TN concentration of the reactor can be far lower than the pollutant discharge standard of the GB18918-2002?Standard for Pollutant Discharge from Municipal Sewage Treatment Works?,but the effluent TP concentration can not meet the first class standard of the municipal sewage,so the biological phosphorus removal by adding chemical agent polyaluminium iron is adopted to meet the discharge requirements.Experimental results show that the reactor can maintain high efficiency and stable removal effect after 30d start-up.The change of reflux ratio of nitrification liquid has great influence on the removal effect of reactor TN,mainly on the removal of nitrate nitrogen.With the increase of R from 150%to 250%,the denitrification effect of the reactor is gradually enhanced,but when R is 300%,the denitrification effect of the reactor weakens,and the reactor has the best treatment effect when R?250%.However,considering that the denitrification effect of R is from 200%to 250%,the difference is small,and the problem of energy consumption is taken into account.It is considered that the optimum reflux ratio of nitrifying solution is 200%.The change of DO concentration has a certain effect on nitrogen and phosphorus removal in the reactor.In the process of DO from 2.0mg/L?3.0mg/L,the nitrification effect increases gradually,and the effluent content of ammonia nitrogen and TN decreases gradually.At the same time,the decrease of TN content is mainly due to the decrease of ammonia nitrogen content.However,the removal efficiency of TP increased at first and then decreased.When DO was 2.5mg/L,the removal efficiency of TP was the best,but the difference of TP concentration between 2.0mg/L and 2.5mg/L was small.At the same time,when DO is2.0mg/L,the effluent of COD and N can meet the national first class a effluent standard.Considering the energy saving and consumption reduction of the reactor,it is considered that DO is the best working condition for 2.0mg/L.The change of sludge reflux ratio has a certain effect on denitrification and phosphorus removal in the reactor,from 60%?100%in the r,and the TN effluent content gradually decreases,which all meet the first class a discharge standard of urban sewage;The removal efficiency of TP was 60%?100%in r,and the average removal rate of effluent was70.71%,67.13%and 61.57%,respectively;Considering that the effluent concentration of TP is on the high side,the sludge reflux ratio with the best TP treatment effect is chosen as the best sludge reflux ratio.The change of SRT has a certain effect on the denitrification and phosphorus removal of the reactor,SRT from 12 d?18 d,the denitrification efficiency of the reactor increases first and then decreases,and the effluent nitrogen concentration is the lowest when the SRT is 15 d;And the phosphorus removal effect is shorter mud age is more helpful to biological phosphorus removal.considering the reactor phosphorus removal effect is not good,12 d is the best sludge age.The addition of polyaluminum and iron(measured by al content)at the end of the aerobic tank was 2mg/L,3mg/L and 4mg/L,respectively.The experimental results show that when the dosage of polyaluminum and iron is 4mg/L,the removal effect of TP in effluent is the best,which can meet the requirements of primary a effluent of urban sewage stably,and when the dosage of polyaluminum and iron is 3mg/L,the effluent TP can meet the requirement of primary B effluent of municipal sewage.However,the addition of polyaluminum and iron has a certain effect on the activity of microorganisms,and will affect the removal of organic matter and nitrogen to a certain extent.In this paper,an integrated A~2/O biofilm reactor was designed to treat rural domestic sewage with air hoist as reflux device,and the technological process was artificial grid regulating tank/clear tank ultraviolet disinfection effluent,and the operation parameters of main structures and ancillary structures were designed.