Study On Removal Effect Of Three Kinds Of Pesticides By Constructed Wetlands

As a large agricultural country,the widespread use of pesticides has brought great economic benefits to China's agricultural production.At the same time,a large number of pesticides enter the natural environment inevitably,polluting the water,the atmosphere and the soil.Pesticides in agricultural non-point source pollution not only damage the ecological environment,but also endanger human health.However,current conventional wastewater treatment technologies cannot yet control agricultural non-point source pollution effectively and economically.The application of constructed wetland technology for the treatment of agricultural non-point source pollution has the advantages of low operating costs,ease of management,and ecological landscape benefits.Pesticides can be divided into insecticides,fungicides,acaricides and herbicides according to different control objects.Typical pendimethalin,chlorothalonil and thiamethoxam represented herbicides,bactericides and insecticides are used in large quantities,hard to degrade and have a wide range of hazards.Based on the construction of different types of constructed wetlands,this study examined the removal rates of penicillin,chlorothalonil,and thiamethoxam in wastewater from vertical and subsurface flow constructed wetlands,as well as pesticides in wetland substrates and plants.Cumulative situation,and analyzed the way of removal of pesticides in pesticide wastewater by constructed wetlands.At the same time,this study examined the removal rate of conventional pollutants from pesticide wastewater and the change of bacterial populations in wetlands using constructed wetlands,and measured the toxicity of the wetland system effluent on protozoan Paramecium for the application of artificial wetland technology to agricultural surfaces.Source pollution governance provides a theoretical basis.The main conclusions of this study through experiments and analysis are as follows:1.Agricultural non-point source pollution often contains many kinds of pesticides.At present,there are no reports of the simultaneous detection methods of the three pesticides of pendimethalin,chlorothalonil,and thiamethoxam by liquid chromatography.For the sake of the successful conduct of the later experiments,the study used liquids.Phase extraction and high performance liquid chromatography(HPLC)technology have explored a method for simultaneous detection of pendimethalin,chlorothalonil and thiamethoxam in water.2.The vertical flow and subsurface flow constructed wetlands are batch cycled and the hydraulic retention time is 3 days.In summer,the removal rates of COD,total nitrogen,ammonia nitrogen,nitrate nitrogen,and total phosphorus from conventional wetland systems reached 83.2%-95%,71.2%-92.7%,91.5%-100%,and 81.2%-100%respectively.77.2%-86.4%;autumn reached 77.8%-85.3%,67.9%-86.27%,81.6%-87.2%,77.2%-85.5% and 58.4%-66%;winter reached 57.3%-65.4%,59.11%-67.35 %,59.41%-71.33%,56.4%-68.3% and 39.72%-47.4%.In the study,natural river water bodies were also simulated as controls.The removal rates of the above-mentioned conventional pollutants by the control were 3.6%-13.6%,3.7%-11.3%,2.9%-13.1%,1.3%-7.5% and 1.2%-4.5%.The results showed that there was no significant difference in the removal rate of conventional pollutants between the two types of wetlands,but the removal rate of the two wetlands was higher than that of the control.The seasonal change of conventional pollutant removal rate for the two wetland systems is: summer> autumn> winter.During wetland operation,the amount of bacteria,fungi,actinomycetes,and nitrogen-removing nitrites,nitrates,and denitrifying bacteria in the substrate was examined.The results showed that the number of bacteria,nitrite,and nitrate in the two wetlands increased rapidly with the batch injection of wastewater,the total number of actinomyces grew slowly,and the number of fungi and denitrifying bacteria increased with the increase of pesticide concentration in the sewage.Increase first and then decrease.3.In the summer high temperature period,the mid-autumn temperature periodand the winter low temperature period,two types of wetland removal experiments for pesticides were conducted.The removal rate of pendimethalin in the two wetland systems was 77.9%-91.3% in summer,72.52%-90.23% in autumn and 60.9%-85.1% in winter,and the removal rate for chlorothalonil was 80.47%-98.26% in summer and66.57 in autumn.%-91.1% and winter 58.5%-79.05;the removal rate of thiamethoxam was 71.6%-91.6% in summer,58.62%-89.18% in autumn,and 40.6%-73.58% in winter.The removal rate of penicillin against the control of natural rivers was0.73%-4.5%,the removal rate of chlorothalonil was 0.58%-3.74%,and the removal rate of thiamethoxam was 0.85%-8.43%.The results showed that there was no significant difference in the removal rates of the three pesticides between the two types of wetlands,but the removal rates of the pesticides in both wetland systems were higher than those in the control.The seasonal changes of removal rates of the three pesticides by the two wetland systems are: summer> autumn> winter.To further evaluate the toxicity of the effluent from the two wetlands,the turbidity of the wetland system was used to culture the paramecium,and the growth curve of the paramecium was determined.The original control was the non-addition group.The results showed that the growth curve of Paramecium lucidum cultivated in wetland treated pesticide wastewater was closer to that of the original control group than that of non-wetland treated pesticide wastewater.The parasitoids cultured in wetland treated pesticide wastewater showed the maximum population at the 5-7th day.However,with the increase of the pesticide concentration in the wastewater and the decrease of the pesticide removal rate,the maximum population size of the paramecium grown using the wetland effluent was observed.Obviously reduced,the maximum time appears to be delayed.Paramecium has a high sensitivity to the effluent quality of wetland systems.4.The wetland system mainly removes pesticides through matrix adsorption,microbial degradation and plant absorption.Through data analysis,the matrix adsorption ratio is 38.87%-81.6%,the microbial degradation ratio is 0.28%-35.47%,and the plant absorption ratio is 0.02%-4.62%.The results show that the contributionof the three major components of wetland to the removal of pesticides is expressed as:matrix> microorganism> plant.