Enhanced Hydrogen And Methane Production From Corn Starch Wastewater By Redox Mediators And Microbial Mechanisms

Corn starch wastewater contains a large amount of monosaccharide,starch,protein and vitamins,which is an ideal raw material for biomass energy production.Because hydrogen can be burned without pollution,it is an ideal zero-carbon energy source.But the process of hydrogen production from dark fermentation of organic matter is accompanied by the production of volatile acids,which can be further utilized and converted into methane.In this study,the fermentation conditions（sludge ratio,initial pH and NH₄Cl concentration）were optimized for hydrogen production by anaerobic fermentation using corn starch wastewater as the substrate.The efficiency of hydrogen production and methane production from corn starch wastewater was enhanced by RMs and the strengthening mechanism was revealed by microbial analysis.In this study,the effects of inoculated sludge ratio,initial pH and NH₄Cl on hydrogen and methane production by the anaerobic fermentation of corn starch wastewater were firstly investigated.The results showed that anaerobic sludge showed a good hydrogen production efficiency when tha ratio of granular sludge and flocculent sludge was 10:0.In addition,the initial pH 5.0 and NH₄Cl of 20 mg/L are suitable for hydrogen production,and butyrate-type fermentation was formed.The experimental results of methane production of hydrogen-producing fermentation liquid from corn starch wastewater showed that when the ratio of granular sludge to flocculent sludge was 1:9,the methane production efficiency was the highest.In addition,the initial pH7.0 and 100 mg/L of NH₄Cl were suitable for methanogenesis,and the cumulative methane production reached 70.4 mL,which was higher than that of the control by 80%.Secondly,the effect of redox mediators（RMs）on hydrogen production from corn starch wastewater fermentation is explored.The results showed that menadione,lawsone,AQS,AQDS,graphene and methyl violet could improve the activity of acidproducing fermentation bacteria during the corn starch wastewater fermentation.Among them,AQS had the most significant promotion effect,with a cumulative hydrogen production of 54.5 mL,which was higher than that of the control by 19%.In contrast,humic acid and riboflavin inhibit their activity.This paper further investigates the effects of different concentrations of AQS on hydrogen production from fermentation of corn starch wastewater.The results showed that when the AQS concentration was 1～10 μmol/L,the cumulative hydrogen production increased with the increase in AQS concentration.The cumulative hydrogen yield of corn starch wastewater by dark fermentation reached the maximum（53.2 mL）under the condition of 10 μmol/L AQS,and the butyrate-type fermentation was formed.The results of highthroughput sequencing analysis showed that the main bacterial genera under 10 μmol/L AQS conditions were unclassified＿Anaerolineaceae,Clostridium＿sensu＿stricto＿1,Proteiniphilum,Trichococcus.Furthermore,this thesis investigated the effects of RMs on the methane production efficiency of fermentation liquid from corn starch wastewater.The results showed that menadione,lawsone,AQS,graphene,humic acid,riboflavin and methyl violet as RMs could improved the methane production efficiency from corn starch wastewater fermentation liquid.The cumulative methane yield of these fermentation systems reached 54.8 mL～63.6 mL after 30 d of culture.The mechanism of different concentrations of AQS affecting methane production efficiency from fermentation liquid was further investigated.The results showed that the methanogenesis efficiency of fermentation liquid showed a trend of first increasing and then decreasing with the increase of AQS concentration in the range of AQS concentration of 1 μmol/L～500μmol/L.At the AQS of 10 μmol/L,the cumulative methane yield reached a maximum of 63.9 mL.Microbial community structure analysis showed significant differences between microorganisms in the control,10 μmol/L AQS and 500 μmol/L AQS systems.The dominant bacterial genera under 10 μmol/L AQS conditions were Methanosarcina,Bacteroidetes＿vadin HA17,unclassified＿Methylophilaceae,unclassified＿Longilinea,unclassified＿Gemmatimonadaceae,Nitrospira,Methylotenera.