Application And Study On Performance Of Pollutants Removal From Agricultural Runoff By Surface Flow Wetland

This study aims at the serious pollution of agricultural non-point source and the lack of ecological structure in the Erhai buffer zone.Based on the investigation of Erhai agricultural non-point source.The paper selects the typical buffer zone between Baihe and Mexi stream in the western Erhai basin,and the farmland in the region is the main land use method.the purification effect of surface flow wetland is studied for control the agricultural runoff in the lake area,and the structural parameters of Erhai buffer wetland and the microbial response of the wetland were studied.The conclusions are as follows:(1)The survey found that the nitrogen pollution load of agricultural runoff was heavy,which concentrated in the village and vegetable fields,especially in the initial storm runoff.The average concentration of total nitrogen,ammonia nitrogen and total phosphorus was 5.11,2.42 and 0.48mg/L,which was inferior to the grade of V water,which could not be directly discharged into Erhai.(2)the results of surface flow wetland study showed that:(1)the concentration of nitrogen in each wetland system was decreased gradually.The concentration of COD in the plant system increased along the course,and the concentration of phosphorus in the plant system of the Hydrilla verticillata wetland increased gradually in summer.(2)The removal efficiency of total nitrogen and nitrate in the wetland system with plants is better than that in the blank system.The removal of nitrogen is the most stable in the plant system of the Nymphoides peltatum wetland,and the average removal rate of total nitrogen,ammonia nitrogen and nitrate nitrogen in a year is 83.1%,79.29% and78.57%,the Phragmites communis wetland is second to the removal of nitrogen,and the average removal rates of total nitrogen,ammonia nitrogen and nitrate nitrogen in a year are 73.9%,77.97% and 68.85%.The Hydrilla verticillata wetland system had better removal effect in summer and autumn.There was no significant difference in ammonia nitrogen concentration in effluent of each plant system.The Phragmites communis wetland system has the best effect to remove phosphorus,and the annual average removal rate is 47.71%.The removal efficiency of phosphorus is better inSeptember to April in second year.The average removal rate is 46.4%.The concentration of COD in the wetland system is rising along the range.(3)The biomass increment of 3591.75 g,1477.55 g and 9054.55 g were respectively increased.The nitrogen content of Chinese cabbage is between 9.22-17.72g/kg and phosphorus content is 1.32-2.59g/kg.The nitrogen content of the algae is between 6.52-24.79g/kg and phosphorus content is 1.65-2.69g/kg.The nitrogen content of Phragmites australis is between 10.42-20.50g/kg and phosphorus content is 1.33-2.23g/kg.The removal rate and the width of the system are simulated.It is found that the plant wetland system can meet the requirements of water quality entry into the Erhai lake,and the blank wetland system does not meet the requirements.The optimum width of the Nymphoides peltatum,Hydrilla verticillata,blank and Phragmites communiswetland system is 7.04 M,8.64 m,11.65 m and 6.92 m.(4)The contribution rate of Phragmites communiswetland to nitrogen and phosphorus removal was the most,the total contribution rate of nitrogen and phosphorus was 28.26% and 21.12%.The total contribution rate of Nymphoides peltatum and Hydrilla verticillata to nitrogen and phosphorus removal was 5.88% and11.36%,3.23% and 5.81%.The nitrogen removal rate of marsh,black algae and reed wetland is 1.3,1.14 and 1.14 times of the blank wetland system.(5)The analysis of microbial community structure found that: The total number of microbes was negatively correlated with the water quality of nitrogen and phosphorus.The removal of nitrogen was related to the number of nitrifying Spirillum,acidophilus,buomonas,floating fungus,verruca,microphylla and thick walled bacteria.Plants can significantly increase the number and species of microorganisms in wetlands,the effect of microbe on water quality in summer is stronger than that in winter.(3)According to the characteristics of West Erhai high and low East buffer belt,the pretreatment tank is separated from the processing system,and the potential energy is used to provide power.The existing reservoirs and fishponds in the area should be transformed to deal with agricultural runoff and reduce the water load of Erhai into the lake.Combined with pilot study and field conditions,the design of wetland 1 and wetland 2 days were 162.5m3 and 250m3 respectively.Wetland plants choose reeds.Fillers are made of phosphorus removal fillers.