The Role Of Extracellular Polymeric Substances In Iron Oxide-enhanced Acetic Acid Oxidation And Methanogenesis

Iron oxides can increase the rate of methane production by anaerobic fermentation and affect the production of methane by affecting the microbial extracellular polymer substances in the anaerobic environment.However,the effect of extracellular polymers in the methanogenic process has not been thoroughly studied.At present,many scholars have shown that microbial extracellular polymers play an important role in microbial-mineral interactions,and the transmission of extracellular electrons is related to humus and other extracellular polymers.However,the effects of iron oxides on extracellular polymers during methanogenesis are still unclear.Therefore,this paper used paddy soil and anaerobic sludge as the research object,observed the effect the typical iron oxides(goethite,hematite and ferrihydrite)on anaerobic fermentation system,and explored the effect of iron oxides on the microorganisms and microbial extracellular polymers in methane production system by anaerobic fermentation of paddy soil.This study can provide a theoretical basis for further understanding the interaction between microorganisms and iron oxides,and provide some technical support for improving the methane production efficiency of anaerobic fermentation of organic matter and controlling greenhouse gas emissions.(1)Methane production system by anaerobic fermentation of paddy soil: In the process of methanogenesis,humic acid,fulvic acid and tryptophan-like protein in the extracellular polymer LB-EPS secreted by methanogenic microorganisms were linearly and positively correlated with methane-producing rate and substrate consumption rate,indicateing that humic acid,fulvic acid and tryptophan-like proteins played an important role in the process of adding iron oxides to enhance methane production.The addition of iron oxides can promote the formation of humic acid and fulvic acid in the system,increase the content of humic acid by 30%,thereby increasing the electron transfer capacity of 10% in the system,and increasing the methanogenic rate and substrate consumption rate of the iron oxide group.(2)Methane production system by anaerobic fermentation of sludge: In the process of methanogenesis,the humic acid,fulvic acid and tryptophan-like protein in the extracellular polymer LB-EPS secreted by methanogenic microorganisms played an important role in the process of enhancing methane production by adding iron oxides.The addition of goethite and hematite can promote the formation of humic acid and fulvic acid in the system,increase the content of humic acid by 12%,therebyincreasing the electron transfer capacity of 8% in the system,and improving the goethite group and Methanogenic rate and substrate consumption rate of the hematite group.(3)Humic acid,fulvic acid and L-tryptophan all contain functional groups such as-OH,N-H and-COOH,which all have electronic acceptance ability,and the electronic acceptance ability is not proportional to the concentration change.The electron acceptance of humic acid was the highest when the concentration was 2 mg/L,that of fulvic acid was the highest when the concentration was 10 mg/L,and that of L-tryptophan was the highest when the concentration was 2 mg/L.At the same concentration,the electron acceptability of humic acid is stronger than that of fulvic acid and L-tryptophan.