Study On The Treatment Of Rural Sewage By Multistage Drop Waterfall Reoxygenation Biological Contact Oxidation

In recent years,the disordered discharge of rural domestic sewage has seriously polluted the water environment and affected the quality of rural living environment.The existing urban sewage treatment technology is not suitable for rural sewage treatment due to its complex operation management and high cost.Many sewage treatment stations have been forced to shut down,resulting in a low rural sewage treatment rate in most areas.In this study,A rural sewage treatment process was developed based on pre-denitrification and nitrogen removal process(A/O process),biological contact oxidation method was used as the prototype,and gravity drop water reoxygenation method was adopted.During the operation of the process,only one sewage lifting pump consumed energy,the treatment effect was stable,the area was small,and the operation and management were convenient.During the start-up and operation of the process,the natural inoculation method was used to culture the biofilm.After about 25 days of operation,the removal rates of COD,ammonia nitrogen and total nitrogen gradually stabilized.The average effluent concentration was 63.9mg/L,8.3 mg/L and 20.8 mg/L,respectively,and the average removal rates were 80.13%,67.43% and 40.43%,respectively.After the stable operation of the membrane,the analysis along the process of COD,ammonia nitrogen and total nitrogen shows that the removal of ammonia nitrogen basically takes place in the tertiary contact oxidation tank.The sewage regulating tank contributes the most to the removal rate of COD and total nitrogen,and the denitrification reaction takes place in it to remove most of the COD and total nitrogen.The removal of COD and total nitrogen in the wastewater conditioning tank accounted for 63.63%and 79.55% of the total removal,respectively.In the study of the optimum conditions of multi-stage drop reoxygenation biological contact oxidation method,it is found that: When the hydraulic retention time is 10 h,the reflux ratio of nitrification liquid is 200%,and the water temperature is kept at 15-20℃,the process has a good and economical removal effect on pollutants,and the removal rates of COD,ammonia nitrogen and total nitrogen are 85.7%,76.6% and 53.8%,respectively.The average effluent COD,ammonia nitrogen and total nitrogen concentrations were 40.0 mg/L,7.4 mg/L and 18.2 mg/L,respectively.The effluent COD reached the GB18918-2002 Grade A standard,and the effluent ammonia nitrogen and total nitrogen concentrations reached the GB18918-2002 Grade B standard.The economic analysis of multistage drop water reoxygenation biological contact oxidation method shows that when the process is running,only one sewage lifting pump consumes energy,and the treatment cost of ton of water is about 0.25 yuan.Compared with the existing rural sewage treatment technology,the cost is lower and suitable for rural sewage treatment.