Experimental Study On A / O Biological Contact Oxidation And Vertical Flow Constructed Wetland For Treatment Of Domestic Sewage

People's demand for water resources with the development of our country's economy and the rapid growth of population is gradually increasing.At the same time,the pressure of natural water environment caused by a large amount of untreated domestic sewage discharge is growing.Urban infrastructure construction in China,especially for sewage treatment works of medium and small town,starts lately.The small and medium-sized cities have small amount of sewage and low degree of industrialization.The research and development of suitable wastewater treatment process have important environmental and social significance.This paper mainly studies the "A/O biological contact oxidation and vertical flow constructed wetland" combination process treating sewage.The test is divided into three stages,the first stage includes quick start-up of both processes.The second stage studies the treatment effect of A/O biological contact oxidation process under different working conditions.The treatment effect and mechanism of the combined process under continuous operation are studied in the third stage.So the application and popularization of the combined process can provide experimental and theoretical basis for small and medium-sized towns.The conclusions are as follows:?1?A/O biological contact oxidation process strated up with artificial inoculation,the water temperature was from 22 to 25?and the DO wasmaintained at around the set point 2-3mg/L,the inflow was increasing gradually,at the same time,the sludge age was gradually decline,At the influent concentrations of COD?NH₄⁺-N and PO₄^3--P were 84.2²43.8mg/L?27.4⁶4.8mg/L and 2.49⁶.56mg/L,on the twenty-second day,the removal rate of COD,NH₄⁺-N were respectively 86.8%,78.2%,and tends to be stable,by the side,the removal rate of PO₄^3--P was stable and up to 73.79%,which indicated the success of the system start-up.The vertical flow constructed wetland started up with natural hanging membrane,the inflow was intermittent in the early,then made it gradually increasing to the design flow load,after 28 days,at the influent concentrations of COD and NH₄⁺-N were 121²30mg/L and 32.6³2.6mg/L,finally the effluent COD and NH₄⁺-N concentration were stable and below 40 mg/L and 20 mg/L,the removal rate were 75% and 60% respectively,plants grow well at the same time,which indicated the success of the vertical flow constructed wetland start-up.?2?Under the normal temperature 22²7?,with the gas water ratio of 7:1,the reflux ratio of 100%,at the HRT of 12 h,the removal of COD had the best treatment effect,at the HRT of 9h,the removal of NH₄⁺-N and TN had the best treatment effect,at the HRT of 7h,the removal of PO₄^3--P had the best removal effect.With the hydraulic retention time of 9h,reflux ratio of 100%,at the gas water ratio of 12:1,the removal of COD and NH₄⁺-N had the best treatment effect,at the gas water ratio of 7:1,the removal of TN and PO₄^3--P had the best treatment effect.With the hydraulic retention time of 9h,gas water ratio of 7:1,at the reflux ratio of 200%,the removal of COD and TN had the best treatment effect,at the reflux ratio of 150%,the removal of NH₄⁺-N had the best treatment effect,at the reflux ratio of 100%,the removal of PO₄^3--P had the best treatment effect.?3?Under the low temperature 8¹2?,with the gas water ratio of 7:1,the reflux ratio of 100%,at the HRT of 12 h,the removal of COD?NH₄⁺-N and TN had the best treatment effect,at the HRT of 6h,the removal of PO₄^3--P had the best treatment effect.With the hydraulic retention time of 9h,reflux ratio of 100%,at the gas water ratio of 9:1,the removal of COD and NH₄⁺-N had the best treatment effect,at the gas water ratio of 7:1,the removal of TN had the best treatment effect,at the gas water ratio of 4:1,the removal of PO₄^3--P had the best treatment effect.With the hydraulic retention time of 9h,gas water ratio of 7:1,at the reflux ratio of 150%,the removal of COD?NH₄⁺-N and TN had the best treatment effect,at the reflux ratio of 50%,the removal of PO₄^3--P had the best treatment effect.By comprehensive consideration,the best condition of combination process was at the the hydraulic retention time of 9h,gas water ratio of 7:1 and the reflux ratio of 100% at low or normal temperature.?4?The load of 1.2m³/m²·d in vertical flow constructed wetland,the inflow was continuing,at the normal temperature 22²7?,at the average influent concentrations of COD,NH₄⁺-N,TN and PO₄^3--P were 256.4 mg/L,61.4mg/L,70.1mg/L and 5.02mg/L respectively,the average effluent concentrations of COD,NH₄⁺-N,TN and PO₄^3--P in the combination process were 14.6mg/L,1.4mg/L,12.7mg/L and 0.43mg/L.The removal of COD,NH₄⁺-N and TN all achieved the corresponding standard A.At the low temperature 8¹2 ?,at the average influent concentrations of COD,NH₄⁺-N,TN and PO₄^3--P were 269.7mg/L 57.8mg/L,66.1mg/L and 4.69mg/L respectively,the average effluent concentrations of COD,NH₄⁺-N,TN and PO₄^3--P were 29.6mg/L,9.9mg/L,19.9mg/L and 0.88mg/L.The removal of COD also still achieved the corresponding standard A,the removal of NH₄⁺-N and TN only achieved the corresponding standard B.?5?In the conbination process,the pollutants removal were mainly through the A/O biological contact oxidation reactor,but it was much affected by temperature,at the normal temperature 22²7?,the average contribution of the ramoval COD,NH₄⁺-N,TN and PO₄^3--P by the A/O biological contact oxidation reactor were 91.5%,92.3%,76.2% and 92.3% respectively,at the low temperature 8¹2?,the average contribution of the ramoval COD,NH₄⁺-N,TN and PO₄^3--P by the A/O biological contact oxidation reactor were 88.4%,72.9%,58.7% and 72.9% respectively.The A/O biological contact oxidation reactor which in the front of the combination process was greatly reduced the pollution load,which could reduce the possibility of reduced congestion and make the constructed wetland that play a better role in the process,at the same time,the vertical flow constructed wetland which in the back of the combination process could make up for the removal of nitrogen and phosphorus,which could make the effluent achieve the corresponding standard.