Simultaneous Decolorization and Biohydrogen Production from Xylose by Klebsiella oxytoca GS-4-08 in the Presence of Azo Dyes with Sulfonate and Carboxyl Groups

Abstract

Biohydrogen production from the pulp and paper effluent containing rich lignocellulosic material could be achieved by the fermentation process. Xylose, an important hemicellulose hydrolysis product, is used less efficiently as a substrate for biohydrogen production. Moreover, azo dyes are usually added to fabricate anticounterfeiting paper, which further increases the complexity of wastewater. This study reports that xylose could serve as the sole carbon source for a pure culture of Klebsiella oxytoca GS-4-08 to achieve simultaneous decolorization and biohydrogen production. With 2 g liter Ϫ1 of xylose as the substrate, a maximum xylose utilization rate (UR xyl ) and a hydrogen molar yield (HMY) of 93.99% and 0.259 mol of H 2 mol of xylose Ϫ1 , respectively, were obtained. Biohydrogen kinetics and electron equivalent (e Ϫ equiv) balance calculations indicated that methyl red (MR) penetrates and intracellularly inhibits both the pentose phosphate pathway and pyruvate fermentation pathway, while methyl orange (MO) acted independently of the glycolysis and biohydrogen pathway. The data demonstrate that biohydrogen pathways in the presence of azo dyes with sulfonate and carboxyl groups were different, but the azo dyes could be completely reduced during the biohydrogen production period in the presence of MO or MR. The feasibility of hydrogen production from industrial pulp and paper effluent by the strain if the xylose is sufficient was also proved and was not affected by toxic substances which usually exist in such wastewater, except for chlorophenol. This study offers a promising energy-recycling strategy for treating pulp and paper wastewaters, especially for those containing azo dyes.IMPORTANCE The pulp and paper industry is a major industry in many developing countries, and the global market of pulp and paper wastewater treatment is expected to increase by 60% between 2012 and 2020. Such wastewater contains large amounts of refractory contaminants, such as lignin, whose reclamation is considered economically crucial and environmentally friendly. Furthermore, azo dyes are usually added in order to fabricate anticounterfeiting paper, which further increases the complexity of the pulp and paper wastewater. This work may offer a better understanding of biohydrogen production from xylose in the presence of azo dyes and provide a promising energy-recycling method for treating pulp and paper wastewater, especially for those containing azo dyes.KEYWORDS xylose, Klebsiella oxytoca, decolorization, biohydrogen production

Stoichiometry and Thermodynamic Analysis on Biohydrogen Production from Xylose by Klebsiella oxytoca GS-4-08

“…The results indicate that the fermentative products and biohydrogen production for growing cells in the presence of MR were thermodynamic controlled. The plausible reason is that enzymes for both acid production and hydrogen generation were repressed, , and additional experiments were performed to confirm the accuracy of this assumption (Figure S4).…”

“…As shown from Table S2, the error is only 6.92% in batch experiments with poor biohydrogen production. The highest recovery of the electron balance might due to that only a small fraction (less than 30%) of xylose was being degraded and few byproducts being generated. , However, large errors were involved in those batch experiments with good hydrogen generation. For example, the errors were as high as 10.16% and 19.55% for the batch experiments without azo dyes and with 0.3 mM of MO, respectively.…”

“…After centrifugation (8000 g , 15 min) at 4 °C, the pellet was washed twice by 50 mM of phosphorus buffer solution (pH = 7.0). For preparation of resting cells and growing cells with various inoculum sizes, the method we used was according to previous study . After inoculum, 100 mL of the biohydrogen production medium in 250 mL of serum bottles were purged with high purity N 2 gas for 15 min, and the bottles were capped with butyl rubber stoppers and placed in incubator shakers (140 rpm) at 35 °C.…”

“…Biohydrogen production from renewable biomass is getting more attention today due to the increasing importance of renewable energy. , Three biohydrogen production methods are currently available, i . e ., direct photolysis, photo fermentation, and dark fermentative biohydrogen production. − Compared to direct photolysis and photo fermentation, more previous efforts were made on dark fermentative biohydrogen production due to the higher hydrogen production efficiency and potential for industrial application. , Some key parameters, such as hydrogen molar yield (HMY) and maximum hydrogen production in hexose fermentation, were extensively investigated. − However, dark fermentative biohydrogen production from xylose, the second most abundant sugar in lignocellulosic biomass after glucose, is less efficient for fermentation by both prokaryotes and eukaryotes. , …”

“…Simultaneous decolorization and biohydrogen production from xylose was achieved in our previous study, but the biohydrogen production mechanism with special inhibitor i . e ., carboxyl azo dye is still unclear …”