Influencing Factors And Intensification Technologies For The Degradation Of Chlorpyrifos From Soda Saline-alkaline Paddy Drainage In Subsurface Flow Constructed Wetlands

Chlopyrifos is one of frequently-used pesticide,which has been detected in the drainage from paddyfield.With the effects from policy and marketing guidances,more paddyfield appeared and accompanied with large amount of drainage from paddyfield.The co-existing nutrients and chlopyrifos under soda saline-alkaline conditions in the drainage make a considerable impact on the downstream waterbody and wetland ecosystems.The aim of this study is to explore the degradation performance of chlopyrifos and its toxic hydrolytic metabolite 3,5,6-trichloro-2-pyridinol(TCP)in the subsurface flow constructed wetlands(SFCWs).The physicochemical and adsorption characteristics of six substrates were investigated to screen the optimal substrate.The distribution and degradation characteristics of chlopyrifos and TCP in SFCWs were evaluated respectively.The effects of inflow characteristics on the degradation performance were explored in detail.The mechanism of degradation was discussed and the intensification technologies were developed to enhance the treating performance of CWs.Main conclusions were listed as follows:(1)The chlorpyrifos isothermal adsorption capacities of six substrates were: vermiculite > Fe-C >> volcanic > slag > ceramsite > gravel.Slag is the optimal substrates for the removal of chlorpyrifos.Vermiculite and Fe-C are more suitable for the utilization on the intensification.The distribution comparison of chlopyrifos in macropytes were root > stalk > foliage.And the absorption performance of TCP by the three macropytes were cattail > canna > reed.Canna can simutanously absorb both chlorpyrifos and TCP and hence acting as the optimal macropyte.(2)Constructed wetlands can remove chlopyrifos effectively.The removal of chlopyrifos in the constructed wetlands mainly happened in the first 2 h,and chlopyrifos removal percentages on hydraulic retention time(HRT)24 h and 8 d were above 90 % and above 99 %,respectively.The concentration of chlopyrifos in the top layer was lower than that in the bottom layer.The contribution proportions of microbial degradation,chemical hydrolysis,absorption by macropyte and adsorption of substrate were > 66 %,~ 20 %,< 4 % and 6 – 10 %,respectively.The concentrations of TCP in the water column of constructed wetlands increased to the maximum value(HRT 1 – 2 d)and then decreased to 2 ?g L-1(HRT 8 d).Slag can improve the removal performance of TCP,while the microbial degradation happened in the central of CWs was a significant pathway of TCP.(3)The removal of chlopyrifos and TCP were impacted by the increasing of influent chlopyrifos concentration.The existence of co-existing nutrients can restrain the degradation of chlopyrifos.The degradations of chlopyrifos and TCP were enhanced under soda saline-alkaline condition.(4)Liquid microbial agent and Fe-C are the optimal microbial agent and substrate for intensification.Shortening hydraulic retention time to 4 d was achieved by the addition of microbial agent.The relative abundance of Proteobacteria reached over 50 %,which meant Proteobacteria was probably the main phylum of degrading microbial community.The existence of Fe-C strongly affected the microbial community structure.The dominant fungus on the Fe-C were Thiobacillus,Acidovorax,Aquabacterium and Noviherbaspirillum which may participate in the process of ferric oxidation of iron-carbon micro-electrolysis or can survive in micro-electrolysis environment while the degradation process.(5)Intensification technologies of degradation chlopyrifos and TCP in SFCWs were presented based on the conclusions of this study.The technologies can effectively enhance the degradation of chlopyrifos and TCP by reducing HRT to 4 d with better removal performances.The technologies can provide theoretical basis on the pollution control of chlopyrifos in the paddyfield drainage.