Removal Of Organochlorine Pesticides From Soil By NZVI-enhanced Microbial Fuel Cell Technology

Organochlorine pesticides are persistent and toxic organic pollutants that pose a potentially huge hazard to ecosystems and human health,causing serious global environmental pollution problems.Microbial fuel cells（MFCs）are an emerging technology for contaminant removal,and their use for remediation of soil contaminated sites has become a hot topic of research.However,there are few studies that have applied microbial fuel cells to soil contamination by non-degradable organochlorine pesticides.In this study,soil microbial fuel cell（SMFC）was used to remediate soil contaminated with the organochlorine pesticide HCH,and the performance of SMFC was enhanced using anode modification and addition of exogenous organic matter.Target modified anodes were successfully prepared using a mixture of polytetrafluoroethylene and polyvinyl alcohol as a capping agent to load nano zero valent iron（n ZVI）particles onto the surface of a graphite felt substrate,which is less susceptible to oxidation,stable and highly electroactive.The SMFC devices with high load graphite felt（17.27%n ZVI）,low load graphite felt（10.82%n ZVI）,graphite felt coated with coating agent only and original graphite felt as anode were built.After 101 days of operation,the power production and pollutant removal capacity of the SMFC with n ZVI modified graphite felt as anodes were greatly improved,and the increased n ZVI content effectively reduced the internal resistance of SMFC device,resulting in higher maximum power density,greater power production,enrichment of the number and diversity of the anode-producing microbial community,and improved the removal rate of the organochlorine pesticide HCH in soil.Within 101 days,the maximum power generation output voltages of the four groups of SMFC were434.88 m V,357.06 m V,1.76 m V and 1.29 m V,respectively.And the maximum power densities were 16.76 m W·m^-2,3.50 m W·m^-2,0.92 m W·m^-2 and 0.76m W·m^-2.The internal resistance of SMFC constructed with high or low loading n ZVI graphite felt electrodes was 496.03Ωand 1044.23Ω,respectively.With the increase of n ZVI load,the internal resistance of the battery decreased by110.52%The average power generation of high loading SMFC was 912.89 C,which was 91.35%higher than that of low loading SMFC（477.07 C）.The effectiveness of SMFC in degrading pollutants was shown by the removal rates of HCH in soil.The removal rates of all four HCH isomers in SMFC with different anode materials reached maximum values in SMFC constructed with highly loaded n ZVI graphite felt modified anode:75.82%（α-HCH）,55.52%（β-HCH）,84.12%（γ-HCH）,and 82.27%（δ-HCH）.Meanwhile,high-throughput sequencing results showed that the abundance of microbial communities around the modified anodes loaded with n ZVI was enhanced,and microorganisms with high correlation with electricity production and HCH degradation became the dominant genera under the SMFC operation.It was found that the content of n ZVI would have a certain impact on the microbial communities,and could directly or indirectly promote or inhibit some microorganisms.Glucose was used as an exogenous organic matter and was regularly added to the soil substrate of the SMFC devices.After 54 days of operation cycle,the removal rates of the four HCHs（α-HCH,β-HCH,γ-HCH andδ-HCH）corresponding to the highly loaded SMFC with or without glucose addition were 59.79%vs 48.95%,61.51%vs 28.37%,70.09%vs 49.89%,respectively.The removal rates of the four HCHs were 52.74%vs 20.31%,35.83%vs10.60%,66.13%vs 40.72%and 40.82%vs 39.66%for the low loading SMFC with or without glucose addition,respectively.By the addition of exogenous organics,the removal rates of the four HCHs were increased in the high loading SMFC by 10.84%,33.14%,20.2%and 22.93%respectively,and 32.43%,25.23%,25.41%and 1.16%respectively in the low loading SMFC.In terms of power generation,the average power generation of the high-load SMFC with exogenous organic additions（300.31 C）was 54.74%lower than that of the high-load SMFC without additions（663.59 C）.The average power generation of the low-load SMFC with exogenous organic additions（192.27 C）was 53.43%lower than that of the low-load SMFC without additions（412.85 C）.The addition of exogenous organic matter was effective in increasing the degradation rate of HCH pollutants by SMFC.However,no positive effect was observed in terms of electricity production.