Treatment Of Typical Neonicotinoid Pesticides Wastewater By Constructed Wetland And Microbial Fuel Cell System

Neonicotinoid pesticides are a new class of pesticides with advantages of broad spectrum,high efficiency and resistance,making them widely used in the global agricultural field.However,a large number of neonicotinoid pesticides have been detected in the water environment to increasingly cause serious environmental problems in recent years.Thus,how to economically and effectively remove neonicotinoid pesticides from water is a concern in water treatment and ecological protection.The constructed wetland coupled microbial fuel cell（CW-MFC）system can use the bioelectrochemical effects of MFC to enhance the traditional CW when MFC is embedded into the CW,which allows the CW-MFC not only improve the effectiveness of CW for wastewater treatment,but also convert organic matter in wastewater into electricity.In this study,imidacloprid,a typical neonicotinoid pesticide with a high proportion of agricultural use,was taken as the target pollutant while a CW-MFC system（Z-GE system）using activated carbon as wetland substrate was constructed to explore the ability and capacity on imidacloprid removal.Investigations include different circuit connection conditions（Opened-circuit state:Ⅰ-1,Ⅰ-2;Closed-circuit state:Ⅱ-1,Ⅱ-2,Ⅱ-3,Ⅱ-4,Ⅱ-5）,system effectiveness on different concentrations of imidacloprid,the influence of imidacloprid on the removal of conventional pollutants（COD,NH₄⁺-N,TN,TP）in wastewater,the performance of electricity generation,and the microbial community of the system.The main conclusions are as followed:1)Compared with CW system,CW-MFC system can strengthen the removal of conventional pollutants in wastewater.The strategy of effluent recirculation can improve the reoxidation environment in CW-MFC system,and further improve the removal effect of pollutants（COD removal rate from 91.13±2.07%to 93.20±1.40%,NH₄⁺-N removal rate from 43.64±3.34%to 63.05±4.18%）.2)An ultraviolet spectrophotometry method was established for the quantitative detection of imidacloprid concentration in water.CW-MFC system has a good removal effect on imidacloprid.When the influent imidacloprid concentration is 5 mg/L and 10 mg/L,respectively,the corresponding removal rates are 96.32±0.49%and 91.42±0.65%,respectively,with anode contributed the highest in imidacloprid removal.With the increasing imidacloprid concentration in the influent/wastewater,the removals of COD,NH₄⁺-N and TN were inhibited to varying degrees（especially the COD removal was reduced by 5.79%and NH₄⁺-N removal was decreased by 9.56%）,while the effect on phosphorus removal was not significant.In the later stage of the experiment,CW-MFC system with pyrite as the substrate（Z-PGE）was connected in series with the Z-GE system（CW-MFC with activated carbon as substrate）,the average TP removal rate increased from 68%to 94%,indicating that pyrite as the substrate could enhance phosphorus removal.3)Before imidacloprid was added into the influent,CW-MFC system had good electrical performance,with a maximum output voltage of 448 mV.After exposure to imidacloprid,the output voltage of the system temporarily decreased（433 mV）and then gradually recovered to 502 mV.Under the stress of imidacloprid in 5 mg/L,the maximum internal resistance of the system was 558.92Ω,which was increased by 39.24%（compared with the case of no imidacloprid addition）.Under continuous exposure to imidacloprid,the internal resistance of the system decreased as the concentration increased from 5 mg/L to 10 mg/L,and the output voltage also rose at the same time.The results showed that the electrical energy conversion and output of the CW-MFC system was inhibited under the initial stress of imidacloprid,but the inhibition was temporary.4)The effects of imidacloprid on electrogenic microorganisms in CW-MFC system were investigated,and the information of anode and cathode microorganisms in CW-MFC system was obtained before and after the addition of imidacloprid.Alpha diversity analysis showed that the stress of imidacloprid increased the richness and diversity of microbial species in cathode,but not in anode.At the level of phylum,class and genus,Bacteroidota showed high adaptability to the accumulation of imidacloprid,while Firmicutes were inhibited at the level of phylum.The abundances of Bacteroidia and Bacilli increased with the addition of imidacloprid at class level.Bacillus may help the CW-MFC system to remove imidacloprid.