Effects Of Biocurrent On The Reduction Of Metolachlor And The Bacterial Community Adaptation In Soil

As an agricultural country,the pesticide pollution has always been concerned.The use of herbicide is necessary in the agricultural procession.The pollution caused by the extensive application need be focused.Microbial fuel cells(MFCs)are new type of bioelectrochemical technology for the remediation of polluted soil,using solid electrodes as the electron acceptor.This technology can overcome the low efficiency of pollutant biodegradation caused by the lack of electron acceptor and difficult mass transport in soils.It can remediate the polluted soil with the bioelectricity output.In this study,the performance and degradation effect of soil MFCs were studied with metolachlor as the goal pollutant.The characteristics of the soil,concentration of metolachlor and the microbial communities in soil MFCs were determined to investigate the main factor which influenced the removal efficiency of metolachlor.And the space-time adaptation of the specific microbial communitiesin in soil MFCs was studied.Based on the statistical correlation analysis among soil properties,metolachlor concentration,power generation capacity and microbial abundances,the factors affected the reduction of metolachlor were revealed.The results were as follows:(1)The removal efficiency of metolachlor in the single chamber soil MFCs assembled with a carbon fiber mesh anode and an activated carbon air–cathode was enhanced by 262%(with an initial concentration of 10 mg/kg)and 176%(with an initial concentration of 20mg/kg),respectively.The maximum current density was 78.9±0.6 mA/m~2.Furthermore,the maximum current density in the soil MFCs with a graphite rod–carbon fiber anode was 7–fold higher than that in the former MFCs,was 636.6±19.0 mA/m~2.The highest removal efficiency was 97%.The time of the complete removal of metolachlor was 245(in non–electrode treatments)and 109(in closed-circuit treatments)days calculated by the fitted curve.(2)In soil MFCs,the microbial degradation was the main degradation manner of metolachlor.According to the correlation analysis,Azohydromonas sp.,Pontibacter sp.and Sphingomonas sp.were the potential degradation bacteria which were significantly related to the degradation of metolachlor.The abundances of the potential electricigens(such as Clostridium sp.and Geobacter sp.)were significantly positive correlated to the bioelectricity generation.The adaptation of bacteria community had taken place under the stimulation of biocurrent.Geobacter sp.replaced some of Pontibacter sp.gradually with the increase of biocurrent.Geobacer sp.and Pontibacter sp.promoted each other.Geobacter sp.might play two roles of electricity production and degradation at the same time.The abundance of Geobacter sp.decreased with the reduction of biocurrent while the abundance of Pontibacter sp.and Sphingomonas sp.increased.They continued to act the role of degradation in soils until the complete removal of metolachlor.