Study On The Treatment Of Rural Domestic Sewage By An Integrated Expanded Bed Biofilter

Nowadays,problems about water environment pollution become increasingly prominent in China,among which rural domestic sewage has become one of the major sources of pollution.With the improvement of living standard for people in rural areas of China,the discharge of rural sewage has increased rapidly.However,the treatment rate of rural sewage is still at a low level.Large amount of untreated domestic sewage that discharged disorderly caused the rapid deterioration of the surrounding environment in rural areas.Therefore,it is urgent to improve the status of rural sewage treatment.According to the dispersion of rural domestic sewage and the fluctuation of its quality and quantity,aiming at the disadvantages of commonly used sewage treatment technologies for rural domestic wastewater in current times,such as large occupation of space,complex operation and high operating cost,an Integrated Expanded-bed Biofilter?IEBF?was used to carry out the rural domestic sewage treatment experiment,which provided reliable references for practical application.The removal efficiency of pollutants by IEBF in the start-up stage of biofilm formation was studied.The denitrification performance of IEBF was investigated by controlling hydraulic load,reflux ratio and gas-water ratio.Removal effects of biological and chemical phosphorus in the IEBF were studied by changing the dosage of chemical agents.Removal efficiency of pollutants during stable operation by IEBF was also surveyed.The main results are as follows:?1?IEBF aodpted a natural biofilm start-up.After 22 days of start-up,the quality of effluent was good,the removal rate of COD_Cr was higher than 75%,while the removal rate of TN was higher than 50%.?2?Under the testing conditions,the denitrification effect of IEBF decreased with the increase of the intake hydraulic load.The optimum intake hydraulic load was 5 m³/?m²·h?.Increasing the reflux ratio was conducive to improving the denitrification effect.When the reflux ratio was 100%-150%,better denitrification effect was achieved.The removal efficiency of COD_Cr and TN increased first and then decreased with the increase of air-water ratio.When air-water ratio was 5:1,the removal effects of COD_Cr,NH₄⁺-N and TN were better.?3?When IEBF adopted biological phosphorus removal,the average removal rate was62.11%,which met the standard of B in the first grade of"Discharge standard of pollutants for municipal wastewater treatment plant"?GB18918-2002?.When adding 10 mg/L PAC to the inlet end of the third stage filter for chemical phosphorus removal,the average effluent concentration was less than 0.5 mg/L,which met the standard of A in the first grade.?4?During stable operation,the average removal rates of COD_Cr,SS,NH₄⁺-N,TN and TP by IEBF were 90.03%,94.00%,94.20%,64.24%,81.78%respectively.The effluent concentration reached the standard of A in the first grade.?5?The cost of water treatment per ton of effluent from IEBF meeting the standard of B in the first grade was 0.21 yuan.When PAC was added to strengthen phosphorus removal,the cost of water treatment per ton was 0.226 yuan,and the effluent quality met the requirements of the standard of A in the first grade.By analyzing the performance of IEBF for nitrogen and phosphorus removal,the optimum operation parameters were determined,which had positive significance for putting forward its practical application as well as promoting rural domestic sewage treatment.