Study On Performance And Facilities Optimization Of"Wetland Ecological Purification System Constructed With Four Pools" Treating Rural Scattered Sewage

With the rapid development of the national economy, the rapid progress of the integration of urban and rural construction and well-off society, the improvement of life quality of rural residents, rural environmental problems have become increasingly prominent. Based on Rural environment work, and forced on the south area of the middle and lower reaches of the Yangtze River in China, the purification efficiency and influence factors of wetland ecological purification system constructed with four pools that was using for rural sewage treatment project was studied in this research, aiming to, provide a scientific basis for optimizing "wetland purification system’". The main results are summarized as following:(1) Different concentrations of artificial simulation sewage were treated using three grid septic-tank.when the concentration of pollutants in the sewage water increased from200mg/L to500mg/L, the degradation rate of three grid septic-tank was affected and the degradation of CODcr from59%gradually reduced to41%. which indicated that the content of pollutants in wastewater affect the CODcr degradeation. Therefore.the concentration of pollutants in wastewater should be considered for designing " three grid septic-tank’(2) Purification effect of artificial sewage using " three grid septic-tank " at different hydraulic retention time showed that the degradation rate of pollutants increased with more hydraulic residence time and then remained when certain hydr-aulic retention time was reached. Faster CODcr degradation with CODcr concentra-tion in effluent from200mg/L reduced to76mg/L was achived at hydraulic retention time of4days (the first collection pool for2d. the second grid anaerobic fermentation tank for1d, the third cell sedimentation tank1d).(3) artificial sewage treatment tests at different natural temperature showed that, CODcr, ammonia nitrogen, total nitrogen and total phosphorus degradation rates increased at higher ambient temperature in the anaerobic fermentation process tank. CODcr degradation rate of58%was achieved at the best suitable temperature of20-30℃.(4) Comparison tests of actual rural sewage treatment using conventional’" three grid septic-tank" and optimized one showed that the latter provided a better treatment efficiency. When original sewage (CODcr.308.6mg/L;NH4+-N,25.8mg/L; TN,31.5mg/L; TP3.8mg/L) was treated using the conventional’" three grid septic-tank processing, ammonia nitrogen. CODcr. TN and TP degradation rates were10.7%,41.6%,10.8%and11.2%, respectively; When original sewage was treated using optimized " three grid septic tank ", ammonia nitrogen, CODcr, TN and TP degra-dation rates was25.5%,60.9%,17.3%and18.9%, respectively. Treatment effect of optimized " three grid septic-tank " was better than that of the conventional one with CODcr degradation rate of only41.6%, while CODcr degradation rate in the optimized one was60.9%.(5) After tests, the design of" wetland ecological purification system constructed with four pools" was optimized:unit volumes of " three grid septic-tank" of2.6m3,1.3m3and1.3m3, effective depth of1m; wetland system5m2with effective depth of0.7m built with PVC plastic plate, steel or concrete.(6) When domestic sewage (ammonia nitrogen,25.8mg/L; CODcr,308.6mg/L; TN.31.5mg/L; and TP,3.8mg/L) was treated using wetland purification systemafter treatment constructed with four pools, ammonia, CODcr, TN and TP concentration in effluent was7.4mg/L,49.1mg/L,15.1mg/L and0.97mg/L, and the degradation rates were71.1%,84.1%,52.1%and74.2%. respectively. The pollutants concentration were below the maximum allowable emission concentration based on Standard B of Standard Urban Sewage Treatment Plant Pollutant Discharge Standards (GB18918-2002).