Removal Of Two Kinds Of Pesticide By An Integrated Ecological Ditches With Constructed Wetland System And Engineering Design

Farmland runoff,one kind of agricultural non-point source pollution,is becoming one of the main contributors of water pollution.Besides nitrogen and phosphorus,the problem of pesticide residues also can not be igored.In this study,an integrated ecological ditches with constructed wetland system was applied for the treatment of farmland runoff,the removal efficiency of COD,nitrogen and phosphorus especially thiamethoxam and nitenpyramr was detailedly investigated.Based on the results,the farmland runoff pollution control project design of Lianhuadang orgnic rice base was carried out.The removal efficiency of COD,NH4+-N,NO3--N,TP by "ecological ditches+horizontal subsurface flow constructed wetland "and " ecological ditch+vertical subsurface flow constructed wetland " system was initially investigated.Experimental results showed that a higher removal COD,NH4+-N,NO3--N,TP efficiency was obtained in "ecological ditches+vertical subsurface flow constructed wetland"system,with the removal effiency of 76%,97%,92%,95%and 88%,respectively(HRT=2 d).The removal of COD and NO3--N in ecological ditches is higher due to the oxic/aerobic conditions.The abundance of Betaproteobacteria and Anaerolineae in eco-ditches were 11%and 10%,respectively,Bacillaceae,Nitro bacteraceae,Rhodospirillaceae and Rhizobiaceae accounted for not less than 1%.While the removal of NH4+-N,TN and TP was found mainly in the wetland due to the resorption by substrates.The exisistance of pesticide had no significant effect on the removal of common pollutants.The effect of hydraulic retention time(HRT)on the removal of thiamethoxam and nitenpyram was investigated.The removal efficiency of pesticedes increased as the increase of the HRT.When the HRT was 2 d,2.5 d and 3 d,the removal efficiency of thiamethoxam and nitenpyram was 40%,43%,48%and 93%,100%,100%,respectively.The decrease of thiamethoxam favored its removal.The nitenpyram is prone to hydrolyze,so it was not be detected in the outlet in the case of HRT>2 d.Photolysis and hydrolysis is not obvious for thiamethoxam,so the removal was due to the adsorption of substrates and plants as well as the biodegradation.System run early hollow brick layer pesticide removal rate is higher,as the system is running,soil layer+fine zeolite and zeolite layer removal efficiency increased significantly,hollow brick layer removal efficiency decreased obviously.Finally,based on the above results,the farmland runoff pollution control project design of Lianhuadang orgnic rice base was carried out.The farmland covers an area of 28960 m2.And the volume of runoff is 482 m3/d.The detailed treatment process was:faruland runoff-ecological Iitche-storage pool-gravel bed-storage module-artificial wetland.The unit design and project estimate was finished.The project cost was 208,810,000 yuan.