The Strategy Of Rural Domestic Sewage Treatment In Gansu Province

With the continuous improvement of rural living standards in Gansu,the volume of rural domestic sewage continues to increase,and the quality of the sewage is more complicated.To build a beautiful village and improve the rural living environment,the thesis established a standard discharge system suitable for rural sewage in Gansu,through investigations in the Gansu Qinba Mountains,Longdong-Longzhong Loess Hilly Region,Gannan Pastoral Area,and Hexi Corridor.Pilot construction project was carried out in Xihe County,Longnan of Gansu Province,to verify the feasibility of the rural sewage treatment in Gansu,to promote and apply in whole province.The main results are as follows:?1?Rural domestic sewage in Gansu Province has the following characteristics:First,the fluctuation of water volume is large:usually in the evening and during the day,the amount of domestic sewage generated increases significantly in winter;second,the water quality is relatively stable:the water quality fluctuation due to the impact of domestic water is small,the average pH is7.69,the average COD_Crr is 138 mg/L,the average BOD₅ is 59.2 mg/L,the average SS is 13.9mg/L,the average ammonia nitrogen is 29.1 mg/L,the average total nitrogen is 48.7 mg/L.The average value of total phosphorus is 3.7mg/L,and the average value of animal and vegetable oil is1.9mg/L,which is highly biochemical;Thirdly,the discharge form is random,mainly discharged into nearby river channels through sewage pipes,open channels,and underground channels;natural evaporation or infiltration into the soil.Fourth,due to the differences in economic development and lifestyles,the quality and quantity of rural domestic sewage in different areas are quite different.?2?The standards for the treatment and discharge of rural domestic sewage treatment in Gansu Province have been formulated through the investigation of the existing rural domestic sewage treatment facilities in Gansu Province.It was found that the average pH of the effluent was8.00;the average SS was 7.33 mg/L;the average COD_crr was 56.00 mg/L;the average ammonia nitrogen was 19.73 mg/L.The average value of total nitrogen is 30.38 mg/L while the average value of total phosphorus is 1.48 mg/L,and the average value of animal and vegetable oil is 0.40mg/L.Based on this investigation,the rural life in Gansu Province has been formulated from the aspects of standard classification level,index selection,standard customization,etc.The sewage treatment discharge standard applies to the management of pollutant discharge of rural domestic sewage treatment facilities with a scale of less than 500m³/d?excluding?.The control indicators are:pH,suspended solids,chemical oxygen demand(COD_Cr),ammonia nitrogen,and total nitrogen,Total phosphorus,animal and vegetable oils,and the emission standards are divided into first,second,and third grade standards.?3?The two pilot projects for rural domestic sewage treatment are the centralized treatment model,and the ecological treatment model established in Xihe County,Gansu.After one year of operation,the effect of treating rural sewage is good.In the pilot centralized processing model,the average removal rate of COD,TN and TP reached 95.50%,87.21%and 89.23%,respectively.While the ecological model recorded the average removal rate of COD TN and TP as 89.35%,78.08%and 85.94%respectively.The effluent quality of the two models can meet the first-level standard of Gansu Province's landmark"Discharge Standard of Water Pollutants for Rural Domestic Sewage Treatment Facilities".