| In recent years,in order to meet the needs of people's agricultural and sideline products and raise crop yields such as grain and other crops,chemical fertilizers and pesticides have been widely applied in agricultural production.chlorpyrifos is the largest pesticide in the world.It has the characteristics of high efficiency and low toxicity.While chlorpyrifos in the protection of crops,part of the environment to different degrees of destruction of agro ecology,endangering human health.As a new sewage treatment technology,constructed wetland system has been widely applied to agricultural non-point source pollution control,river and lake ecological management and restoration.In view of this,the artificial wetland treatment system of chlorpyrifos in this paper,the investigation and analysis of different conditions of pH,matrix type and planting density,the degradation characteristics of chlorpyrifos in artificial wetland system;combined with the results of single factor experiments,and the basic principle of response surface analysis method,orthogonal experiment,optimization of degradation conditions;at the same time,combined with the analysis of microbial community structure under optimal conditions in the system and the dynamic change of high-throughput sequencing technology,in order to provide the basis for system optimization and molecular ecology study on purification mechanism.The results were as follows:1)Under different conditions,such as pH 4.5,6,7,8,and 9,when pH was 8,The best degradation effect of chlorpyrifos in water,and when pH was 7,Absorption of chlorpyrifos on plants and Adsorption of chlorpyrifos by substrate was the best;with the increase of pH,TN,TP and COD removal rate increased first and then decreased slowly,when pH was 8 higher in removal rate;the urease activity was the highest when pH was 8,and was significantly positively correlated with the removal rate of TN.When pH was 9,phosphatase activity was the highest;when pH was 7,the highest activity of catalase.2)Under different conditions,such as the sand/natural soil of 0:1,1:1,1:2,1:3 and 2:1,when the sand/natural soil of 1:1,degradation of chlorpyrifos in water,absorption of chlorpyrifos on plants and adsorption of chlorpyrifos by substrate were the best,the removal rates of TN,TP and COD were basically the same.When the sand/natural soil of 1:1,the removal efficiency of TN,TP and COD was the best.When the sand/natural soil of 1:1,TN,TP and COD removal effect of the best at this time,phosphatase and catalase activity and urease were highest;the activity of urease and phosphatase had a significant positive correlation with the removal rate of TN and TP3)Under different planting densities of 57,114,171,228 and 283 plant/m2,the planting density was 171 plant/m2,degradation of chlorpyrifos in water and absorption of chlorpyrifos on plants were the best and the planting density of 283 plant/m2 adsorption of chlorpyrifos by substrate was optimal;TN,TP and the removal rate of COD increases with the increase of planting density were first increased and then decreased slowly,the planting density of 171 plant/m2 optimal removal efficiency;planting density of 171 plant/m2,283plant/m2,228 pltant/m2,urease,phosphatase,catalase activity was the highest;the urease activity had a significant positive correlation with the removal rate of TN.4)The multiple regression analysis of degradation of chlorpyrifos in water,absorption of chlorpyrifos on plants and adsorption of chlorpyrifos by substrate showed that the model was very significant and the better fitting degree.In each factor level of the experiment,the influence of each factor on the degradation rate of chlorpyrifos in water order was pH>planting density>substrate type.The influence of plants on chlorpyrifos absorption and adsorption of chlorpyrifos by substrate order was pH>substrate type>planting density.5)Combined with the response surface method,the best chlorpyrifos degradation conditions in the constructed wetland system were pH = 8.69,sand/natural soil of 1.36:1,and planting density 173.73plant/m2.The optimal chlorpyrifos degradation rate was predicted to be 73.05%.The actual rate was found to be 75.68%.No significant difference was observed between the predicted and actual value.Thus,the model could effectively predict the experimental results.6)High-throughput sequencing showed that the number of microbes was increased with the extension of operating time of the constructed wetland system where Proteobacteria and Actinobacteria were the main chlorpyrifos degraders. |
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