Impacts Of Hematite On Microbially Mediated Nitrate-Reducing Fe(Ⅱ) Oxidation By Acidovorax Sp. Strain BoFeN1

Iron is one of the most abundant elements in the Earth’s crust as well as the essential nutrient for almost all known organism.The Fe（II）oxidation process driven by Fe（II）-oxidizing microorganisms is an important part of globe iron cycle.Under neutral and anoxic conditions,the Fe（II）oxidation and nitrate reduction mediated by the nitrate-reducing Fe（II）-oxidizing（NRFO）bacteria has a far-reaching significance for environmental protection due to its ability of coupling organic pollutant degradation and heavy metal transformation.The Fe（II）oxidation processes driven by NRFO bacteria including the biological process via oxidation by the Fe（II）oxidoreductase in the NRFO bacteria and chemical process via oxidation by the nitrite produced by microbial reduction.Previous studies have shown that minerals can mediate the electron transfer between iron-reducing bacteria and electron acceptors,and enhance the extracellular respiration process of bacteria.However,little was known about the role of minerals in the Fe（II）oxidation and nitrate reduction driven by NRFO bacteria.In this study,a typical NRFO bacteria,Acidovorax sp.strain BoFeN1,was used as a model bacterial strain,and hematite as the model mineral because of its stable structure and properties.According to the kinetics,secondary minerals of the system,the study investigated the impact of mineral on Fe（II）oxidation and nitrate reduction with NRFO bacteria.The main conclusion obtained are as follows:（1）The Fe（II）oxidation and nitrate reduction rate increased when added hematite in condition of Fe（II）as the solo electron donor;the nitrate reduction rate not changed when added hematite in condition of sodium acetate as the solo electron,suggesting that the hematite may enhance the Fe（II）oxidation process of BoFeN1,the bacteria took more electron from Fe（II）oxidation to reduce nitrate.The Fe（II）oxidation and nitrate reduction rate also increased when added hematite in condition of Fe（II）and sodium acetate as electron donor.（2）The Fe（II）oxidation and nitrate reduction rate increased with increasing hematite concentrations.Different kinds of mineral had obvious different influence for NRFO process of BoFeN1,the hematite and titanium dioxide significantly enhanced the NRFO process,no influence was observed on treatment with aluminum oxide.The surface and bulk catalysis of minerals might enhance the process of Fe（II）oxidation of BoFeN1.（3）Hematite enhanced the reaction of Fe（II）and nitrite,and the present of bacteria not influenced the reaction rate of Fe（II）+NO₂^-or Fe（II）+NO₂^-+α-Fe₂O₃,suggesting that the nitrite reduction was a chemical process driven by Fe（II）when Fe（II）as the solo electron donor.（4）The present of hematite influenced the formation of secondary minerals during NRFO process driven by BoFeN1.The cell encrustation was mitigated and little Amorphous mineral found when add hematite in the NRFO process driven by BoFeN1,and found more goethite during the chemical reaction of Fe（II）and nitrite.