Study On The Purification Of Rural Disorderly Discharged Wastewater By Aquatic Vegetable Constructed Wetland

In recent years,with the effective control of point source pollution in the Taihu Lake basin,the situation of non-point source pollution in agriculture has become increasingly severe.The rapid development of the rural economy in the Taihu Lake Basin has caused a large number of pollutants from rural residential areas to be discharged into the Taihu Lake with the collection of rainfall and runoff,which has intensified the eutrophication of Taihu Lake.Based on the current economic situation of rural residents in the Taihu Lake Basin and the characteristics of large impact loads,high concentrations of nitrogen and phosphorus,and high randomness,the study proposed a combined system of ecological ditches and improved constructed wetlands.Ecological ditches have been transformed from traditional agricultural irrigation ditches.Constructed wetland is an“aerobic/anaerobic/aerobic three-stage submerged aquatic vegetable type constructed wetland”(abbreviated as OAO new type of aquatic vegetable artificial wetland).Aerobic/anaerobic/aerobic alternate structures to increase the efficiency of nitrogen and phosphorus removal.Based on the existing research of the research group,the study mainly focuses on the treatment effect of the ecological ditch,the influencing factors of the constructed wetland,the optimized conditions,the treatment effect of the combined system,and the mechanism of nitrogen and phosphorus removal during the actual operation of the combined system.The following main conclusions have been made:1.To study the long-term purification effect of ecological ditches on sewage discharged from villages.The characteristics of influent water pollutants and removal rates were analyzed,and the purification effects of pollutants along the ecological ditches were studied.The results showed that the removal rates of COD,ammonia nitrogen,nitrate nitrogen,total nitrogen and total phosphorus by ecological ditches were 23.22%,19.81%,22.80%,20.48%and 48.73%,respectively.The COD,ammonia nitrogen,nitrate nitrogen,total nitrogen concentration decreased rapidly before the 40m,and the total phosphorus concentration decreased rapidly in the first 20m.2.The influencing factors of the actual operation of the OAO new type of aquatic vegetable artificial wetland were studied.The results showed that the optimal hydraulic load of constructed wetland was 0.3 m~3/(m~2·d).Under this load,the removal rates of COD,ammonia nitrogen,nitrate nitrogen,total nitrogen and total phosphorus were 40.65%,55.02%,and 77.12%respectively.For 57.62%and 61.79%,the corresponding removal loads were6.14 g/(m~2·d),0.15 g/(m~2·d),0.21 g/(m~2·d),0.590 g/(m~2·d),0.07 g/(m~2·d),respectively.With the decrease of seasonal temperature,the removal rates of COD,ammonia nitrogen,nitrate nitrogen and total nitrogen gradually decreased,and the total phosphorus removal rate was higher in autumn than in summer.After the addition of greenhouse insulation in winter,the removal rates of COD,ammonia nitrogen,nitrate nitrogen,total nitrogen and total phosphorus have all increased.3.The optimization measures of OAO new aquatic vegetable artificial wetland were studied.After natural ventilation,the removal rates of COD,ammonia nitrogen,total nitrogen and total phosphorus increased by 4.92%,3.23%,2.1%and 1.02%,respectively,and the removal rate of nitrate nitrogen decreased by 1.74%.With the two-point influent,the removal rates of COD,ammonia nitrogen,nitrate nitrogen,and total nitrogen increased by 3.01%,4.51%,7.32%,and 5.61%,respectively,and the total phosphorus removal rate decreased by3.9.%.Under the conditions of optimal load and optimization measures,the removal rates of COD,ammonia nitrogen,nitrate nitrogen,total nitrogen,total phosphorus and SS in the combined system were 57.69%,59.64%,70.31%,64.19%,78.13%and 92.62%,respectively.4.The removal mechanism of nitrogen and phosphorus in the new OAO artificial wetland constructed wetland was studied.The results show that the performance of constructed wetland in the removal of phosphorus is better than the performance of nitrogen removal by adsorption.The average absorption rates of nitrate nitrogen and ammonia nitrogen were 0.347 mg/(g?d)and 0.511 mg/(g?d)for water spinach,and the average phosphorus absorption rate for water spinach was 0.12 mg/(g?d).The nitration intensity and denitrification intensity of constructed wetlands were consistent with the density distribution of nitrifying bacteria and denitrifying bacteria.Ammonia removal takes place in the first and second stages,and nitrate removal occurs mainly in the middle.