Study On The Artificial Submarine Wetland For Tail Water Purification Of Rural Domestic Sewage Treatment In Baiyangdian

In order to build the Xiong’an New Area into a future new city with"blue and green interweaving",improving the water environment quality of the river basin is an important part of it,To this end,Hebei Province had promulgated a more stringent discharge standard of water pollutants in Daqing River Basin.For the sewage treatment facilities in Baiyangdian rural area,the conventional treatment could no longer meet the sewage discharge requirements,and the tail water of the sewage treatment facilities needs to be deeply treated.Due to its reliable effect,simple management and low cost,artificial wetlands can be used as a suitable ecological technology unit for the advanced treatment of tail water of rural domestic sewage treatment in Baiyangdian.In this thesis,two constructed subsurface flow wetlands with different filler filling methods were constructed to study the purification effect of the constructed subsurface flow wetland on the tail water of rural domestic sewage treatment in Baiyangdian,and to investigate the effects of influent hydraulic load,filler filling method and wetland effluent return on the decontamination efficiency of the constructed subsurface flow wetland.The main research results were as followed.Through static adsorption test,the adsorption properties of ammonia nitrogen and phosphorus of zeolite,steel slag,gravel and engineering sand were tested.The results showed that among the four fillers,zeolite has the strongest adsorption capacity for ammonia nitrogen,and the equilibrium adsorption capacity and theoretical saturated adsorption capacity are 0.0641 and 1.9009 mg/g respectively.The steel slag has the strongest adsorption capacity for phosphorus,and the equilibrium adsorption capacity and theoretical saturated adsorption capacity are 0.0627 and 1.0134 mg/g respectively.For the filler types and grading of the constructed subsurface flow wetland,the mixed filler of"zeolite+steel slag"is preferred to realize the adsorption and removal of ammonia nitrogen and phosphorus in the tail water.Through two artificial subsurface flow wetlands filled with different fillers,the decontamination effect of the wetland is compared and analyzed under the conditions of inlet hydraulic load of 0.175,0.25,0.5 m³/（m²·d）and reflux ratio of 100%,200%and400%.It was found that with the increase of hydraulic load,the removal rate of COD,NO₂^--N in the tail water gradually increased,the removal rate of NO₃^--N,TN,TP was gradually reduced,and the concentration of pollutants in the effluent of wetland No.2was lower.The results showed that the optimal hydraulic load of influent water during operation is 0.25 m³/（m²·d）.Under this hydraulic load,the pollutant removal rate of the wetland with functional filler zeolite and steel slag paved in the unit was higher than that of the wetland with zeolite and steel slag concentrated in the inlet and outlet end.The average of the COD,NO₃^--N,NO₂^--N,TN,TP concentration in effluent were 18.34,5.32,2.96,8.51,and 0.01 mg/L.When the influent hydraulic load was 0.25 m³/（m²·d）,add wetland effluent reflux and gradually increase the reflux ratio.The removal of COD,NO₃^--N and TN in tail water by artificial subsurface flow wetland increases first and then decreases.The results showed that reflux could effectively enhance the denitrification effect of wetland.During operation,the optimum reflux ratio is 200%,and the removal rates of COD,NO₃^--N and TN in tail water were 5.58%,6.74%and 9.17%higher than those without reflux.In the low temperature period in winter,the operation effect of the artificial submersible wetland fluctuates,and TN in effluent was difficult to meet the limit requirements.The denitrification effect was enhanced by reducing the influent hydraulic load of wetland.The constructed subsurface flow wetland was operated under three influent hydraulic loads of 0.1,0.175 and 0.25 m³/（m²·d）.It was found that with the decrease of influent hydraulic load,the removal rate of COD in tail water gradually decreases,and the removal rate of TN and TP gradually increases.The results showed that during the operation of the wetland,the optimal influent hydraulic load was 0.175m³/（m²·d）,and all pollutant indexes in the effluent can stably meet the discharge limit requirements.