| At present,the prevention and control of water pollution at home and abroad are mainly based on organic pollutants,nitrogen and phosphorus,and there are few studies on the removal of pathogenic microorganisms.Due to the generally poor economic foundation in rural areas of China's hills,Ecological ditches combined with soil infiltration and constructed wetlands show good application prospects in the treatment of rural domestic sewage.However,there is still no relevant research on pathogen contamination.The pathogenic microorganisms in water have seriously harmed human health,and Escherichia coli is a common strain of such pathogenic microorganisms.In this thesis,E.coli was used to characterize the pathogenic microorganisms in rural domestic sewage,and the effective removal of E.coli was the goal.The experimental study was carried out from the aspects of the percolation of fillers,the wetland plants and the optimization of system operating parameters.The main research results are:1.Screen for infiltration fillers that are suitable for removing pathogenic bacteria.In this study,seven infiltration fillers were used to determine the E.coli removal capacity of different fillers.The results showed that:The ability of different filler media to remove E.coli from domestic sewage from strong to weak was: biochar,anthracite,paddy soil,dryland soil,woodland soil,zeolite,and quartz.The experiment further added different proportions of biochar(0%,2%,5%,10%,20%,50%)in the dryland soil.The optimal proportion of dryland soil + biochar particles based on E.coli removal capacity and removal cost is discussed.The results show:Adding biochar can increase the porosity of wetland soils.Effectively increase the rate of percolation wastewater and E.coli removal rate per unit time,Among them,the effect of E.coli removal is more obvious;Biochar addition can delay the time for the filler to reach saturation and effectively increase the processing capacity of the infiltration packing.Comprehensive consideration of E.coli removal efficiency and bio-char addition costs and other factors,to determine the optimal proportion of bio-char addition of 20%.2.Screen for suitable aquatic plants with efficient removal of pathogens.In this study,the effect of different aquatic plants on the removal of E.coli was studied by combining indoor room temperature pot(30cm diameter)and plant ditches(200m).Firstly,the water plants of lotus root,water hyacinth,cress,wild white,mushroom grass,canna,Iridium,and myriophyllum were usedto determine their ability to remove E.coli.Subsequent field experiments conducted in the field showed that the wastewater was successively treated with wild peony root,rejuvenation flower,shiitake grass,canna,Iris chinensis,Canna indica,Iris chinensis,and wild wolfberry white group.Determination of E.coli removal rate of sewage through various aquatic plant groups.Pot experiment results show:Most of the aquatic plant groups can effectively remove E.coli,and the removal effect of cress was the best.However,not all aquatic plants can effectively remove the total coliform bacteria.The elimination rate of total coliform bacteria after the 5th cycle of L.edodes and P.oleifera was much lower than that of the waterless plants group.Ditch test results show:Reef flowers,Canna esculenta,and Iris grandiflora have higher removal efficiency of total coliform bacteria.In general,the removal rates of E.coli(total coliform and Escherichia coli)are high,including I.glauca,Foxtail algae,re-flowers,water hyacinth,canna and cress.The optional aquatic plant species can be used to remove E.coli contamination from water.3.Use response surface method model design test to analyze the optimal operation parameters of E.coli removal.The test selected packing,inlet pH,and inlet flow rate as influencing factors.For E.coli removal efficiency,Filler selection anthracite,dry soil,quartz sand;influent pH is set to 6.0 ~ 8.0;inlet flow rate is set to 10.0 ~ 30.0 m L/min,Based on response surface methodology(RSM),the effects of different process conditions on the removal of E.coli were investigated,and the operating parameters of the constructed wetland process were optimized.The results showed that the removal rate of E.coli from anthracite was higher than that of quartz sand and upland soil.When pH is neutral,the removal rate of E.coli is generally low;The influent flow rate of the system has no obvious effect on the removal rate of E.coli.Based on response surface analysis,the test conclusions are drawn:When the p H was 6.0,the influent flow rate was 10.0mL/min,and the filler was anthracite,the removal efficiency of the total coliform bacteria was the best.The removal rate was 96.86%.When the influent pH was 8.0,the influent flow rate was 20.0 mL/min,and the filler was anthracite,the best removal efficiency was achieved for E.coli.The removal rate was 93.66%.Overall,it is possible to effectively remove domestic sewage E.coli by screening out suitable fillers and aquatic plants,and controlling the p H of the water body and the hydraulic retention time of the entire wastewater treatment process. |
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