Construction Of High-efficiency Ecological Ditch System And Its Removal Performance For Typical Agricultural Non-point Source Pollutants

In recent years,the proportion of agricultural non-point source pollution in China’s water pollution has been increasing,mainly due to the loss of nitrogen and phosphorus caused by the use of chemical fertilizers and pesticides in agricultural production activities,which brings surplus nutrients to rivers and lakes,causing serious environmental pollution.As a green,low-energy and low-cost technology,ecological ditches do not need additional land.At the same time,they can effectively intercept and purify pollutants,and have multiple functions such as irrigation and hydrological regulation.In this study,Jiangxi Province was selected as the research area,and the removal performance of typical agricultural non-point source pollutants(NH₄⁺-N,TN,TP,Cr⁶⁺)in ecological ditch system was investigated by constructing three different types of ecological ditch system.By analyzing the impact of different factors on the operation of ecological ditches,the mechanism of pollutant removal by ecological ditches is deeply explored by integrating the joint action of plants,substrates and microorganisms.On this basis,common vermiculite,montmorillonite,biochar and other self-made modified iron-based composites were used to enhance the removal performance of the ecological ditch system.The main results obtained in this paper are as follows:（1）The constructed rectangular ecological ditch has a good removal effect on agricultural non-point source pollutants,and the purification of pollutants is mainly played by substrate,plants and microorganisms.No.1rectangular ecological ditch used volcanic stone,limestone,medical stone and zeolite as the substrate and planted Calamus,Barracuda and Pennisetum.The removal rates of NH₄⁺-N,TN,TP,and Cr⁶⁺were 100%,42%,77%and 33%,respectively.The filling matrix of no.2 rectangular ecological ditch was the same as that of No.1 ecological ditch,and the removal rates of NH₄⁺-N,TN,TP,and Cr⁶⁺were 100%,52%,88%and 50%,respectively,when planting Calamus,Canna and Pennisetum.No.3 ecological ditch was trapezoidal,using zeolite,slag and ceramic as the substrate,and planting Calamus,Barracuda and Pennisetum,the removal performance of pollutants was worse than that of rectangular ecological ditch,and the overall removal capacity of NH₄⁺-N,TN,TP,and Cr⁶⁺in rectangular ecological ditch was 5 times,5 times,60 times and 9 times of trapezoidal ecological ditch,respectively.（2）Different operating conditions have great influence on the removal effect of pollutants in ecological ditches.Under static condition,the initial pollutant concentration has the greatest influence on the removal effect of ecological ditch,followed by the water level and water layer of ecological ditch.Under dynamic operation conditions,the initial pollutant concentration also has the greatest influence on the removal effect of ecological ditches,followed by hydraulic retention time and water level of ecological ditches.（3）The addition of vermiculite modified iron-based composites enhanced the stability of the ecological ditch system and significantly improved the removal rates of NH₄⁺-N,TN,TP,and Cr⁶⁺in ecological ditch system.After 5days of static operation,the removal rates of NH₄⁺-N,TN,TP,and Cr⁶⁺were100%,49.2%～56.4%,80%～90.1%and 47.8%～59%,respectively.The removal rates of NH₄⁺-N,TN,TP,and Cr⁶⁺were 87.5%,26%～28.7%,52.4%～51%and 21.4%～25.2%,respectively,in the enhanced ecological ditch system after 12h dynamic operation.The high-efficiency ecological ditch system constructed in this paper has a good removal effect on typical agricultural non-point source pollutants and can provide technical support for rural non-point source pollution control.