Experimental Study On Treatment Of Rural Domestic Sewage By Coupled Constructed Wetland With Anoxic-Waterwheel Driven Rotating Biological Contactor

This paper coupled biological and ecological technology advantages,to build a treatment model of"anoxic-waterwheel driven rotating biological contactor coupled constructed wetland".The biological section focuses on removing organic pollutants.The ecological section of economical crops to build pollution-purifying agriculture,which uses nitrogen and phosphorus elements in sewage recycling.This model can achieve sustainable treatment of rural domestic sewage.This paper aims to optimize the design of aerobic unit reactor,the configuration of constructed wetland substrates,and the operation of coupled processes,and conduct in-depth research on the pollutant degradation laws of different reaction units,dominant microbial populations,and long-term operation of coupled processes.The main research contents and conclusions are as follows:The flow pattern experimental research of an improved aerobic device was studied,which named bilateral baffle type biological contactor driven by waterwheel（wdb RBC）.The results show that the hydraulic flow regime of wdb RBC tends to be push-flow,the dead zone rate of the reactor is greatly reduced,and the hydraulic flow pattern is improved.The anoxic tank（ANF）and wdb RBC were started-up with activated sludge inoculation,and the removal rates of COD and nitrate nitrogen of ANF reached more than 70%stably on the 15th day;the removal rates of COD and ammonia nitrogen of wdb RBC was stabilized at about 90%on the 20th day.The green zeolite-aerated concrete wetland CW₁ and the gravel wetland CW₂ as the control were constructed and started by the natural film-hanging method.In the 31 days of culture,the average removal rates of COD,ammonia nitrogen,TN,TP in the CW₁ system were 64.32%,83.29%,67.11%and 78.96%,respectively,while the CW₂ system were 54.59%,46.33%,41.29%and 46.55%,respectively.The influences of HRT_{wdb RBC},reflux ratio,and disk speed on the operating efficiency of the ANF-wdb RBC system were studied.Taking into account the removal effect and energy saving,the optimal operating parameters of the ANF-wdb RBC system are determined as follows:the HRT_{wdb RBC} is 4h,the reflux ratio is 100%,and the disk speed is 3 rpm.Under this condition,the average removal rates of COD,ammonia nitrogen and TN by the ANF-wdb RBC system are 87.61%,79.57%and 41.95%,respectively.The ANF-wdb RBC system effluent concentrations of COD,ammonia nitrogen and TN are 29 mg·L^-1,8.79 mg·L^-1 and 25.45 mg·L^-1,respectively.The variation of concentration along the process showed that the degradation of COD and TN concentration mainly occurred in the ANF and first and second compartments of wdb RBC,and the ammonia nitrogen concentration degradation mainly occurs in the rear compartment of wdb RBC.The effluent TN and TP of the ANF-wdb RBC system required further treatment by subsequent constructed wetland units.To explore the influence of hydraulic load and substrate type on the treatment effect of horizontal subsurface flow constructed wetland.The results show that the COD removal rate of CW₁ and CW₂systems increases first and then decreases with the increase of hydraulic load.The removal rate of TN and TP is negative with the hydraulic load.The ammonia removal rate of CW₁ and CW₂ systems varies with the hydraulic load.The ammonia removal rate of CW₁system gradually decreases,while the ammonia removal rate of CW₂ system increases first and then decreases with the increase of hydraulic load.Under different hydraulic loads,the effluent pollutant concentration of the CW₁ system is lower than that of the CW₂system.indicating that the substrate type significantly affects the pollutant removal efficiency of constructed wetland.Finally,considering the effluent quality,pollutant removal rate and pollutant removal volume,the optimal hydraulic load of the CW₁ system is 0.4 m³·m^-2·d^-1～0.5 m³·m^-2·d^-1,and the optimal hydraulic load of CW₂ system is 0.1 m³·m^-2·d^-1～0.2 m³·m^-2·d^-1.When the bio-ecological coupling process runs continuously under the optimal condition,the average removal rates of COD,ammonia nitrogen,TN and TP are 91.52%,92.83%,81.41%and 77.34%,respectively,and the average effluent concentration is 21 mg·L^-1,2.68 mg·L^-1,7.99mg·L^-1 and 0.66 mg·L^-1,respectively.The COD,ammonia nitrogen,TN and TP of the effluent concentration from the coupling process meet the first level A standard in the"Water Pollutant Discharge Standard for Rural Domestic Sewage Treatment Facilities"（DB32/3462-2020）in Jiangsu Province.The contribution rates of COD,ammonia nitrogen,TN and TP removal by biological section were 87.60%,76.48%,45.16%and 15.54%,respectively.It can be seen that the biological unit is the main body of organic matter degradation in the coupling process,which greatly reduces the processing load of the ecological unit,and the ecological unit also further removes nitrogen and phosphorus elements.There are multiple functional microorganisms in each unit of the coupling system,each of which undertakes the corresponding pollutant removal function,and the coupling process runs stably.In this paper,through the improvement and performance optimization of the bio-ecological coupling process device,and the selection of optimal operating conditions,in order to provide theoretical reference for the engineering application of the bio-ecological coupling process.