Simultaneous Decolorization And Biohydrogen Production From Xylose By Klebsiella Oxytoca GS-4-08 In Presence Of Azo Dyes

Biohydrogen production from the pulp and paper effluent containing rich cellulosic material could be achieved by fermentation process.Xylose,an important cellulosic hydrolysis product,is less used efficiently as substrate for biohydrogen production.Moreover,azo dyes are usually added to fabricate anti-counterfeiting paper,which further increases the complexity of the wastewater.This study wasaims to report that xylose could serve as the sole carbon source for a pure culture-Klebsiella oxytoca GS-4-08 to realize simultaneous decolorization and biohydrogen production,which indicatesa potacial method forreal industry pulp and paper water treatment.With 2 g l^-1 of xylose as substrate,a maximum xylose utilization rate(UR_Xyl)and hydrogen molar yield?HMY?,93.99%and 0.259 mol H₂ mol^-1xylose,were obtained respectively.For growing cells,theUR_Xyl,HMY and the yields of two main fermentation products?ethanol and acetate?were not affected by presented methyl orange?MO?,but were inhibited in presence of methyl red?MR?.These data demonstrate that biohydrogen pathwaysin presence of azo dyes with sulfonate and carboxyl groups were different.Most importantly,the azo dyes were completely reduced during the biohydrogen production period whether in presence of MO or MR.In order to explain the specific degradation and metabolism mechanism,we proposed a hypothesis diagram of simultaneous biohydrogen production and decolorization with xylose as substrateby Klebsiella oxytoca GS-4-08.The D-xylose was intracellularly isomerized and phosphorylated to D-xylulose-5-phosphate,and then fermented to glyceraldehyde-3-phosphate?Gly-3P?through PPP.However,in this case,under anaerobic condition,the electrons may be transferred through the respiratory chain and catalyzed by azoreductase?AzoR?to achieve the unspecific extracellular reduction of MO.MR penetrates and intracellular inhibits on dehydrogenase,hydrogenlyase and etc.,during PPP and pyruvatefermentation pathway,but this inhibition effect may be relieved by increasing the initial cell concentration.However,the decolorizationof sulfonated azo dye i.e.,MO was independent of the glycolysis and biohydrogen pathway,most likely due to the extracellular reduction.The feasibility of hydrogen production from pulp and paper effluent by the strain was proved if the xylose is sufficient,and we anticipate the present finding may offer a promising energy-recycling strategy for treating pulp and paper wastewater especially those containing azo dyes.