Dark fermentative hydrogen production from xylose by a hot spring enrichment culture

Dark fermentative hydrogen production by a hot spring culture was studied from different sugars in batch assays and from xylose in continuous stirred tank reactor (CSTR) with on-line pH control. Batch assays yielded hydrogen in following order: xylose > arabinose > ribose > glucose. The highest hydrogen yield in batch assays was 0.71 mol H2/mol xylose. In CSTR the highest H2 yield and production rate at 45 °C were 1.97 mol H2/mol xylose and 7.3 mmol H2/h/L, respectively, and at 37 °C, 1.18 mol H2/mol xylose and 1.7 mmol H2/h/L, respectively. At 45 °C, microbial community consisted of only two bacterial strains affiliated to Clostridium acetobutulyticum and Citrobacter freundii, whereas at 37 °C six Clostridial species were detected. In summary hydrogen yield by hot spring culture was higher with pentoses than hexoses. The highest H2 production rate and yield and thus, the most efficient hydrogen producing bacteria were obtained at suboptimal temperature of 45 °C for both mesophiles and thermophiles.