Effect Of Biochar And Its Different Components On Reduction Of Fe(Ⅲ) By Geobacter Sulfurreducens

Microbial Fe(Ⅲ)reduction plays an important role in iron and carbon cycle in sediments and soils.During anaerobic respiration,biochar can act as electron shuttles to transfer electrons from microorganisms to extracellular electron acceptors,thus achieving long-distance electron transfer.When biochar is applied to the soil,the dissolved black carbon(DBC)will be gradually separated from the undissolved fractions(UBC).Both DBC and UBC have redox activity.However,the importance of different biochar fractions in the electron shuttle process has not been clearly elucidated so far.Therefore,in this study,rice straws were selected as raw materials to prepare biochars at 300℃,400℃ and 550℃(BC300,BC400,BC550)using pyrolysis method,and the DBC(DBC300,DBC400,DBC550)and UBC(UBC300,UBC400,UBC550)fractions were also isolated.The influence of biochar and its fractions on the reduction of hematite by Geobacter sulfurreducens was examined.Using scanning electron microscopy(SEM),infrared spectroscopy(FTIR),X-ray diffraction(XRD),electron paramagnetic resonance(EPR),and electrochemical analysis,the mechanisms related to the promotion effects of biochar and its fractions on microbial reduction of Fe(Ⅲ)were explored.This paper mainly concludes that:(1)Containing abundant oxygen-containing functional groups,the biochars had redox capacity and chemically reduced a small amount of Fe(Ⅲ).In the process of hematite reduction,the biochars mainly functioned as electron shuttles.Compared with the control group,the addition of biochar significantly promotes the reduction degree of hematite.BC400 demonstrated the most significant promotion effect on microbial reduction of hematite.The characterization results showed that BC400 had more free radicals and smaller resistance than other biochars.so it had a stronger electron transport ability.The content of adsorbed Fe(Ⅱ)in the microbial reduction experiment was much higher than that of dissolved Fe(Ⅱ).BC550 had the strongest adsorption capacity for Fe(Ⅱ).XRD analysis showed that biochar not only accelerated the reduction of hematite but also resulted in the phase transformation of hematite.(2)The effect of pyrolysis temperature on UBC-mediated microbial reduction of hematite was similar to that of biochar.But the promotion effect of UBC on Fe(Ⅲ)reduction was much weaker than that of biochar.The promotion effect of UBC on Fe(Ⅲ)reduction was as follows:UBC400>UBC550>UBC300.The EPR analysis showed that UBC400 had the most free radicals.Among them,semiquinone radicals play an important role in the electron transport of microbial-UBC-hematite.(3)The enhancement effect of DBC on hematite reduction was weaker than that of biochar and UBC.Cyclic voltammetry of the reaction solution showed that reduction and oxidation peaks existed at-0.3 and-0.1 V,respectively,indicating the reduction of Fe(III).The XRD results demonstrated that DBC addition did not lead to the phase transformation of hematite,which may be because DBC had less promotion effect on the microbial reduction of hematite and the structure of hematite was relatively stable.