Biological And Chemical Transformation Of Iron And Sulfur During The Simultaneous Reduction Of Sulfite And Iron Oxides And Co-Production Of Ferrous Sulfide By Shewanella Oneidensis MR-1

Coal,oil and natural gas are the main energy materials used by human society at this stage.However,when consuming these fossil fuels,a large amount of gas which contains sulfur dioxide is generated,causing atmospheric pollution.Recovering sulfur resource when purifying sulfur dioxide-containing flue gas meet the demand of waste recovery.Biological flue gas desulfurization can produce elemental sulfur,but the purity issues has become a bottleneck for it's development.The nano-ferrous sulfide has the functions of dehalogenation of organic pollutants,absorption and degradation of toxic substances.The biosynthesis of nano-Fe S has been a major research hotspot for a long time.Meanwhile,the sulfide produced in anaerobic sulfate biological reduction process and ferrous materials added to the system have the potential to synthesize nano-Fe S.In the anaerobic sulfate/sulfite reduction reaction system of biological flue gas desulfurization,the addition of soluble ferrous ions alone has a precipitation problem that affects its reaction with the sulfide produced by reduction.Therefore,in-situ addition of bioreducible iron oxides in this system produces a combination of ferrous ions and sulfur ions,which can avoid or reduce the problem of ferrous precipitation.The simultaneous bioreduction of sulfate/sulfite and iron oxide requires further investigation.In this study,Shewanella oneidensis MR-1 strain with iron oxide and sulfite reduction ability was used as an experimental strain to study the process characteristics of single and simultaneous biological reduction of sulfite and various iron oxides,and to analyze the sulfide and ferrous ion in the reaction concentration changes,in-depth analysis of the biological and chemical reactions between sulfite,iron oxides,sulfides and ferrous ions in the reaction process,and preliminary study of the possible presence of nitrate in the system on the biological reduction of iron oxides And the process of strain MR-1 reducing nitrate and nitrite.The main work and research results are as follows:(1)Strain MR-1 has the ability to simultaneously reduce Fe(III)and sulfite in the a single system and generate Fe S through biological and chemical processes.The proportion of Fe S generated by the biological method of depleting ferrihydrite increases.The strain CMX does not have the function of reducing ferrihydrite,and Fe S is generated by the chemical reaction of ferrihydrite and sulfide.When the ratio of sulfite to ferrihydrite is 3/4.Strain MR-1 can convert the sulfur in the system to Fe S.For the strain CMX that does not have iron oxide reduction function,the sulfide reacts with ferrihydrite through chemical reaction.Finally,88.3% of sulfide can be converted into Fe S.(2)Strain MR-1 can synthesize nano-Fe S through the simultaneous reduction of ferrihydrite and sulfite.Part of the generated nano-Fe S is bound to ferrihydrite and the rest is dispersed in solution.The size distribution in a range of 600-1000 nm,while some particles are distributed below 100 nm,and the dispersion of nanoparticles is outstanding.(3)Strain MR-1 can reduce hematite,goethite and magnetite with high crystallinity to Fe2+,and the overall reaction rate is much lower than that of weakly crystallized ferrihydrite.In the reaction system of using goethite and hematite as the iron source,sulfur undergoes a chemical reaction with iron oxide after biological reduction from sulfite to sulfide.However,the reaction of hematite and goethite with sulfide is limited by the type of iron oxide and crystal structure,and the reaction efficiency is not high,resulting in the accumulation of subsequent sulfide,which is more serious in hematite.(4)The effect of nitrate on the reduction of iron oxide by strain MR-1 was investigated,and it was found that low concentration of nitrate had a promoting effect on the reduction of ferrihydrite.The presence of iron oxide will affect the reduction of nitrate by strain MR-1.The lower the bioavailability of iron oxide,the slower the reduction of nitrate.The process and product of reducing different concentration of nitrite by MR-1 strain were investigated,and it was found that the low concentration of nitrite can be completely reduced to ammonium.When the concentration is higher than 5 m M,the toxicity of nitrite inhibits the conversion of nitrite.