Analysis On The Current Situation Of Sewage Treatment In Villages And Towns In Southern Shaanxi And Study On The Optimal Operation Of Typical Processes

In recent years,the construction of the South-to-North Water Transfer Project and the environmental protection work in Qinling Mountains have been steadily promoted,and the water environment quality in southern Shaanxi has been significantly improved.However,with the rapid development of rural economy,the problem of domestic sewage treatment of rural residents has become increasingly prominent.In order to further consolidate and improve the effectiveness of water environment protection in southern Shaanxi,and guard the sustainable northward movement of clean water,this study carried out a one-year field investigation on more than 70 rural sewage treatment facilities in this area,analyzed in detail the common problems of rural sewage treatment in southern Shaanxi,and put forward the regulation technical route for the optimal operation of rural sewage biological system in combination with the actual problems of a typical town level sewage treatment plant.It realizes the purpose of reducing consumption,increasing efficiency and stable operation of the plant area,and provides a technical idea for rural sewage treatment in southern Shaanxi.The specific research results of this paper are as follows:（1）The investigation results of the operation status of rural sewage treatment facilities in southern Shaanxi show that compared with other rural domestic sewage,the concentration of pollutants in this area is lower and changes significantly with seasons.When the concentration of COD,NH₄⁺-N,TN and TP reaches the peak in winter,the average values are only 134.7,28.5,32.1 and 2.3 mg/L;The fluctuation law of 24h water inflow in the plant area is significant,and there is basically no domestic sewage produced by residents at night.The village and town sewage treatment facilities have a cut-off time of more than 16 and 6 hours per day respectively,and the daily treatment water of most stations is less than 50%of the design value,which is in low load operation for a long time;The average removal rates of COD,NH₄⁺-N,TN and TP in the town level sewage treatment plant with specially assigned personnel are 19%,13%,8%and 13%higher than those in the village level in the inspection mode respectively;In addition,the problems caused by the shortage of construction and operation and maintenance funds,such as the lagging construction of pipe network at some stations,the low sewage collection rate and the lack of professional training for operation and maintenance personnel,are also important factors for the stable operation of rural sewage treatment facilities.（2）According to the previous investigation,under the objective factors of intermittent water cut-off and low pollutant concentration,there is still excessive aeration in most stations,making it more difficult for the activated sludge system to operate stably.In view of the above problems,an optimal operation mode of microbial population structure based on intermittent aeration in the cut-off period is proposed,and the optimal operation is studied in a 1000 m³/d typical town sewage treatment plant.After 161 days of optimized operation,the results show that the removal effect of pollutants is stable when the exposure stop ratio of the fan is controlled at 5:5 during the cut-off period of the system,in which the average removal rates of COD and NH₄⁺-N are 83.67%and92.43%,the removal rates of TN and TP are basically maintained at more than 75%and70%in the later stage of operation under this working condition,and the effluent concentration of each pollutant meets the limit of class I a emission standard.The sludge sedimentation and adsorption performance is good,and the richness and diversity of microbial communities are significantly improved.The relative abundance of nitrifying bacteria dominated by Nitrosomonas and Nitrospira,Acidovorax and Hydrogenophaga and other bacteria that can denitrify under anoxic conditions increased significantly,and the ability of nitrogen and phosphorus removal has been further enhanced.（3）In the aerobic activated sludge treatment process,the energy consumption of the aeration system will directly affect the overall operation cost of the plant.In this study,the measures of regulating the system aeration/shutdown ratio during the rural sewage cut-off period have effectively reduced the fan operation energy consumption while achieving the stable and up to standard discharge of all pollutants in the system.Compared with the original operation scheme of the plant,it can eliminate the external expenses such as adding carbon source,reduce the overall operation time of the aeration system,and increase the overall economic benefit of per ton of water treatment by 0.7Yuan.Based on the treatment water volume of 400 m³/d,the annual operation cost can be saved by more than 100000 Yuan,and the environmental economic benefit can be greatly improved.