Catalytic Effect Of Redox Mediators On Fermentation Hydrogen Production From Excess Sludge

Excess activated sludge contains a large amount of organic matter,toxic and harmful substances and nutrient elements,which will cause serious pollution to the environment.Anaerobic fermentation using excess activated sludge as substrate can not only reduce sludge discharge,but also obtain clean energy-hydrogen.Therefore,excess activated sludge from sewage treatment plant is used as substrate and sludge from anoxic tank is used as inoculation sludge for fermentation hydrogen production by anaerobic microorganisms.On the basis of determining the of excess activated sludge dosing ratio,the effects of redox mediator(ROMs)on fermentation hydrogen production from excess activated sludge and the effects of initial p H and NH4 Cl on fermentation hydrogen production from ROMs-mediated excess sludge were investigated.The microbial community structure characteristics in fermentation hydrogen production from excess activated sludge were analyzed by using high-throughput sequencing technology.The current study firstly investigated that the effects of the different ratio(0%,20%,40%,60%,80%)of excess activated sludge on anaerobic fermentation hydrogen production.The results showed that the cumulative hydrogen production of anaerobic fermentation of excess activated sludge showed a trend of increasing first and then decreasing with the increase of the ratio of excess activated sludge.Under the excess activated sludge dosing ratio of 60%,the cumulative hydrogen production reached the maximum value of 4.72 m L.And the liquid terminal fermentation products contained ethanol,acetate,propionate and butyrate.As increasing in the ratio of excess activated sludge,the percentage of propionate was reduced firstly and then was increased.The content of ethanol and butyrate showed a opposite trend with propionate.When the radio of excess activated sludge was 60%,the percentages of ethanol and butyrate were higher than that of other test experiments by 7.4%~ 28.6% and 2.9%~3.8 times.The results of anthraquinone-2-sulfonic acid(AQS),henna quinone,menadione and graphene oxide(GO)as ROMs enhancing fermentation hydrogen production from excess activated sludge showed that AQS could significantly promote the hydrogen production with the cumulative hydrogen production of 6.18 m L.However,the activity of hydrogen-producing bacteria was inhibited by other ROMs.Microbial community structure showed that all ROMs could improve the diversity of microbial community and Proteiniclasticum was the predominant acidogenic fermentation bacteria in the AQS system.In the range of AQS concentration of 0 to 300 mg/L,the cumulative hydrogen production of anaerobic fermentation from excess activated sludge showed a trend of increasing first and then decreasing with the increase of AQS concentration.The maximum accumulative hydrogen production of 8.22 m L was reached when the AQS concentration was 100mg/L.The microbial community structure showed that the predominant acidogenic fermenting flora at the AQS concentration of 100 mg/L was Longilinea,Proteiniclasticum,and Thermomarinilinea,and their relative abundances were 12.0%,4.7%,and 2.3%,respectively.Furthermore,the effects of initial p H and NH4 Cl on AQS-mediated hydrogen production from excess sludge were revealed.The results showed that a high hydrogen production activity of anaerobic sludge were observed under the initial p H of 6.0 and 8.5 with the cumulative hydrogen production after 156 h of culture was 11.72 m L and 12.13 m L,respectively.However,the analysis results of microbial community structure showed that the major bacterial community was different in these two systems.Under the initial p H of 6.0,Longilina is the predominant acidogenic fermenting bacteria,while Longilina,Proteiniclasticum,Guggenheimella and Youngiibacter are the predominant acidogenic fermenting bacteria under the p H of 8.5.When the concentration of NH4 Cl is 0~800 mg/L,the accumulative hydrogen production of AQS-mediated excess activated sludge fermentation showed a trend of first increase and then decrease with the increase of NH4 Cl concentration,and reached the maximum value of 10.3 m L under thecondition of 60 mg/L NH4 Cl concentration.Longilinea(17.9%),Proteiniclasticum(9.5%),Guggenheimella(4.1%)and Youngiibacter(4.0%)were the predominant acidogenic fermenting bacteria under this condition.