Effects Of Conductive Materials On Biological Sulfate Reduction Process Under Different Organic Carbon Sources

Biological Sulfate Reduction?BSR?is a technology for reducing Sulfate to sulfide by Sulfate Reducting Bacteria?SRB?under anaerobic conditions.It has the advantages of high treatment efficiency and low energy consumption and commonly used in the treatment of sulfate-containing wastewater.However,the community structure,reaction mechanism and interaction mechanism of SRB and its co-existing microorganisms are insufficient.Organic carbon source,as an important substance for microbial growth and metabolism,has an important influence on the efficiency of sulfate reduction,and the research on the influence mechanism of different types of organic carbon source is still on the comparison of the treatment efficiency.Conductive materials,as an important carrier that can promote electron transfer in biochemical reactions,are also one of the influencing factors of the sulfate bioreduction process.The addition of conductive materials as a new strategy to enhance the biological treatment efficiency of sulfate wastewater has begun to be widely studied.The influence of conductive materials on the metabolic rate and the relationship between microorganisms under different organic carbon sources is not yet clear.In this study,four sets of different anaerobic sequence batch reactors?ASBRs?were run using acetate and ethanol as the organic carbon source respectively and the addition of conductive material?Fe₃O₄?or not,the effects of different types of organic carbon sources and conductive materials on sulfate reduction and organic carbon metabolism were analyzed.Combined with 16S rRNA and metagenomics,the effects of different types of organic carbon sources and conductive materials on the structure of microbial communities and the function of functional microorganisms were analyzed.The functional microorganisms and their interactions in the co-metabolism of organic carbon and sulfate.The theoretical system of BSR technology has been enriched and developed.The test results show that when acetate is used as the organic carbon source,the degradation rates of organic carbon in A-Con?without Fe₃O₄?and A-Fe?with Fe₃O₄?are 27.2%and 20.4%,respectively.And methanogenic activity is not high.The sulfate reduction rates in A-Con and A-Fe are 9.7 mg/?g VSS·h?and 3.6 mg/?g VSS·h?,respectively.The addition of conductive materials slightly inhibited the degradation of acetate and the reduction of sulfate.When ethanol was used as the carbon source,ethanol is completely degraded and converted into propionic acid and acetic acid at a ratio of 1:1,the organic carbon degradation rates in E-Con?without Fe₃O₄?and E-Fe?with Fe₃O₄?were 4%and 62%,respectively.The accumulation of propionic acid and acetic acid in E-Con showed no methanogenic activity.While the removal rates of propionic acid and acetic acid in E-Fe were 58%and 86%respectively,and it's methanogenic activity was higher.The sulfate reduction rate in these two groups of reactors is all about 46 mg/?g VSS·h?.The addition of conductive materials can promote the degradation of organic carbon,but has a small effect on the reduction of sulfate.The results of 16S rRNA analysis showed that the microbial community structure under different organic carbon sources was significantly different,and was greatly affected by conductive materials.When acetate was used as the carbon source,there are two types of SRBs,complete oxidation type?CO-SRB?and incomplete oxidation type?IO-SRB?.Desulfobacteraceae and Desulfuromonas had higher relative abundances.When ethanol was used as the carbon source,it's mainly IO-SRB,including Desulfobulbus and Desulfomicrobium.In the four groups of reactors,the main methanogens are Methanosaeta,Methanosarcina,Methanobacterium,and Candidatus_Methanofastidiosum.When ethanol is used as the organic carbon source,the addition of Fe₃O₄ can increase the relative abundance of these four types of methanogens.According to metagenomic analysis,when acetate was used as an organic carbon source,CO-SRB Desulfococcus is a functional bacterium participating in sulfate reduction and acetate oxidation.The addition of Fe₃O₄ could increase the abundance of Desulfococcus to promote the oxidation of acetate and the reduction of sulfate.The competition between CO-SRB and methanogens was related to the domestication time,and the addition of Fe₃O₄ could improve the competitive advantage of Methanosarcina and Methanosaeta over acetate.When ethanol was used as the organic carbon source,IO-SRB is the main functional bacteria involved in ethanol metabolism and sulfate reduction.The addition of Fe₃O₄ could increase the relative abundance of Methanosaeta,and at the same time promote the methanogenesis process of the acetic acid pathway and the DIET pathway,shows that the“collaboration”relationship of IO-SRB and methanogens mainly through adding the Fe₃O₄ implemented to improve the relative abundance of Methanosaeta,therefore Methanosaeta in E-Fe is the most important functional microbes.