title: Effects of pH and substrate concentrations on dark fermentative biohydrogen production from xylose by extreme thermophilic mixed culture.
abstract: Biohydrogen is considered as one of the most promising energy alternatives considering the climate and energy crisis. The dark fermentative hydrogen production from xylose at extreme thermophilic condition (70 °C) using mixed culture was conducted in this study. The effects of initial pH values (ranged from 5.0 to 10.0) and substrate concentrations (ranged from 2.5 to 15.0 g/L) on the hydrogen production, substrate degradation and metabolite distributions were investigated using batch-mode operations. Results showed that initial substrate pH values in the neutral region (6.0-7.0) were beneficial for hydrogen production. The fermentation at initial pH 7.0 and 7.5 g/L xylose reached an optimal hydrogen yield of 1.29 mol-H2/mol-xyloseconsumed. Ethanol, butyrate, and propionate were the major liquid metabolites. The xylose biodegradation efficiency of the mixed culture decreased sharply at high initial culture pH values. The increase of xylose concentration resulted in the accumulation of propionate and an obvious decrease in the final pH value, as well as a low hydrogen yield. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis indicated that hydrogen producing bacteria were enriched by repeated culture under extreme thermophilic conditions. Also, the mixed culture was dominated with bacterial species related to Clostridium and Thermoanaerobacterium.
authors.affiliation: School of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin, 300384, People's Republic of China. qcs254@163.com.|Tianjin Key Laboratory of Aqueous Science and Technology, Tianjin, 300384, People's Republic of China. qcs254@163.com.
authors.forename: Chunsheng
authors.initials: C
authors.lastname: Qiu
authors.affiliation: Tianjin Key Laboratory of Aqueous Science and Technology, Tianjin, 300384, People's Republic of China.
authors.forename: Puyu
authors.initials: P
authors.lastname: Shi
authors.affiliation: School of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin, 300384, People's Republic of China.|Tianjin Key Laboratory of Aqueous Science and Technology, Tianjin, 300384, People's Republic of China.
authors.forename: Shumin
authors.initials: S
authors.lastname: Xiao
authors.affiliation: School of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin, 300384, People's Republic of China.|Tianjin Key Laboratory of Aqueous Science and Technology, Tianjin, 300384, People's Republic of China.
authors.forename: Liping
authors.initials: L
authors.lastname: Sun
mesh_terms: D001419:Bacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D061249:Batch Cell Culture Techniques; D002087:Butyrates / Q000378:metabolism; D003013:Clostridium / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D058645:Denaturing Gradient Gel Electrophoresis; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D006358:Hot Temperature; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D016133:Polymerase Chain Reaction; D046950:Thermoanaerobacterium / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D014994:Xylose / Q000378:metabolism*
chemical_list: D002087:Butyrates; D004269:DNA, Bacterial; D000431:Ethanol; D006859:Hydrogen; D014994:Xylose
keywords: Biohydrogen; Dark fermentation; Extreme thermophilic; Mixed culture; Xylose