Study On The Purification Of Paddy Field Backwater By Hydroponic Vegetable Type Ecological Ditches

In order to reduce the secondary pollution caused by plant harvesting in traditional ecological Ditches and increase the economic benefits of ecological Ditches,in this study,hydroponic vegetables were used as planting plants in ecological Ditches.Through in door simulated wastewater tests,the substrate fillers and vegetable types of ecological Ditches were optimized to explore the purification effect and removal path of COD_Cr,nitrogen and phosphorus in actual paddy field drainage by the optimized ecological Ditches.The following research results were obtained:Feasibility of different models of ecological Ditch drainage in rice fields:Four different mode Ditch systems,Hydroponic lettuce only,substrate only,direct hydroponic lettuce+substrate filler,and solid substrate hydroponic lettuce+substrate filler,had certain purification effects on COD_Cr,TN,and TP in simulated wastewater.The purification efficiency of the Ditch system with direct/solid substrate hydroponic lettuce+substrate filler for simulated wastewater was significantly higher than that of the Ditch system with only hydroponic lettuce or substrate filler.In terms of operation time and the removal efficiency of COD_Cr,nitrogen and phosphorus by various systems,it was more feasible to use a Ditch system of direct/solid substrate hydroponic lettuce+substrate filler to purify COD_Cr,nitrogen and phosphorus in paddy field drainage.Optimization of matrix fillers in ecological Ditch systems:（1）The purification rate of COD_Crand the adsorption of TN and TP by Ditch systems filled with different matrices were comprehensively selected,and volcanic rock+zeolite,zeolite+gravel were initially selected as matrix fillers for subsequent research on ecological Ditch systems.（2）Based on the impact of different media filling methods on the growth of water spinach and their purification rates for COD_Cr,TN,and TP in wastewater,volcanic rock and zeolite mixed at a ratio of 1:1 was selected as the media for the subsequent study of the ecological Ditch system.Optimization of hydroponic vegetables in ecological Ditch systems:（1）Accor ding to the comprehensive purification rates of COD_Cr,TN,and TP in Ditch systems for hydroponic cultivation of different vegetable seedlings,the water spinach Ditch system was superior to the lettuce and parsley Ditch system.（2）In terms of the purification rates of COD_Cr,TN,and TP in the ecological Ditch system of comprehensively hydroponic cultivation of small parsley with different growth periods,the small parsley Ditch system in the vigorous growth period was superior to the small parsley Ditch system in the slow growth period.（3）Based on the growth habits of water spinach and parsley,water spinach was selected as a hydroponic vegetable in the ecological Ditch system.The purification efficiency of the hydroponic water spinach+matrix filler Ditch system for actual paddy field drainage:（1）After 20 days of hydroponic cultivation,by the end of system operation,the effluent from the hydroponic water spinach+matrix filler Ditch system can meet the Class IV water quality standards specified in the Environmental Quality Standard for Surface Water（GB 3838-2002）,including COD_Cr,NH₄⁺-N,NO₂^--N,NO₃^--N,TN,and TP;Its removal of COD_Cr mainly depended on substrate adsorption,water spinach absorption and utilization,and microbial action,while its removal of TN mainly depended on substrate adsorption,water spinach absorption and utilization,and ammonia volatilization.（2）After 20days of hydroponic culture,by the end of system operation,the effluent from the Ditch system of solid substrate hydroponic water spinach+substrate filler can meet the Class II water quality standard specified in the Environmental Quality Standard for Surface Water（GB 3838-2002）,including COD_Cr,NH₄⁺-N,NO₂^--N,NO₃^--N,TN,and TP;Its removal of COD_Cr mainly depended on substrate adsorption,water spinach absorption and utilization,microbial action,and denitrification,while its removal of TN mainly depended on substrate adsorption,water spinach absorption and utilization,ammonia volatilization,and denitrification.（3）The removal rate of paddy field drainage using the Ditch system of solid substrate hydroponic water spinach+substrate filler was better than that using the Ditch system of direct hydroponic water spinach+substrate filler.The Ditch system of solid substrate hydroponics with water spinach and substrate fillers can be used to control COD_Cr and nitrogen and phosphorus pollution in paddy field drainage.By studying the purification effects and pathways of different Ditch systems on paddy field drainage,the research results can provide technical support for the prevention and control of water eutrophication and agricultural non-point source pollution.