Mesophilic and Thermophilic Biohydrogen Production from Xylose at Various Initial pH and Substrate Concentrations with Microflora Community Analysis

Abstract

Anaerobic dark fermentation biohydrogen production from xylose was investigated under mesophilic (35 °C) and thermophilic (55 °C) conditions at various initial pH (5.0–10.0) and substrate concentrations (2.5–12.5 g/L). In addition, the microbial community structure variations under different temperatures were analyzed. It was demonstrated that the maximum hydrogen yield (1.24 mol-H2/mol-xylose) was obtained with substrate concentration of 7.5 g/L and initial cultivation, pH 7.0, at 35 °C, with butyrate, acetate, and ethanol as the major byproducts. The increase of substrate concentration resulted in accumulation of volatile fatty acids (VFAs), especially propionate, and a decrease in final pH under mesophilic conditions. However, the hydrogen yield increased along with the increase of substrate concentration at 55 °C with butyrate and ethanol as the main metabolite. Stable pH of the system could be maintained even at high xylose concentration up to 12.5 g/L due to a low level of VFAs accumulation. A lower hydrogen yield of 1.14 mol-H2/mol-xylose was obtained at thermophilic condition, while a stable operation condition could be achieved and maintained more easily. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis showed that microbial community structures of both systems were dominated with bacterial species related to Clostridium, while the thermophilic system had fewer hydrogen-producing microbial species than that at mesothermal condition.

Effect of fermentation temperature on hydrogen production from xylose and the succession of hydrogen‐producing microflora

“…Peak hydrogen yield obtained at 55°C revealed that thermophilic hydrogen‐producing bacteria have been enriched by repeated batch cultivation. High hydrogen production efficiency gained at 55°C could be attributed to higher bioactivity in the thermophilic range . Higher hydrogen production with few by‐products has also been observed under thermophilic conditions in comparison with mesophilic conditions in a previous study .…”

“…High hydrogen production efficiency gained at 55°C could be attributed to higher bioactivity in the thermophilic range . Higher hydrogen production with few by‐products has also been observed under thermophilic conditions in comparison with mesophilic conditions in a previous study . Although, with lower hydrogen yield at 60°C (1.04 mol H 2 mol −1 xylose consumed ), heat pretreatment was not needed to inhibit methane‐producing bacteria during repeated batch culture at 60°C and at 65°C.…”

“…Based on our previous study, xylose solution of 30.0 g L −1 was used as carbon source . Sufficient inorganics (mg L −1 ) were prepared in the substrate to provide the essential nutrients and trace elements for H 2 ‐producing consortia: 382.1 NH 4 Cl, 87.7 KH 2 PO 4 , 260.0 CaCl 2 · 2H 2 O, 320.0 MgSO 4 · 7H 2 O, 125.0 FeSO 4 · 7H 2 O, 0.3397 Zn 2+ , 0.3365 Ni 2+ , 1.5747 Co 2+ , 0.2661 B 3+ , 2.8646 Mn 2+ , 5.7380 I − , 0.1920 Cu 2+ , 0.5950 Mo 6+ …”

“…The hydrogen‐producing sludge samples were taken from the mixed culture after repeated batch cultivation with constant hydrogen yield at each culture temperature. The samples were taken for PCR‐DGGE analysis using the method described in our previous study . Total DNA of the sludge samples was extracted with a Soil DNA Isolation kit (Soil gDNA kit, Biomiga, USA).…”

“…Various anaerobic mixed cultures have been enriched for fermentative hydrogen production using xylose or other substrates . Temperature, pH, hydraulic retention time, organic loading rate and substrate concentration are the major environmental and operating factors in the hydrogen fermentation process . Among these, temperature is one of the most important environmental factors which could affect hydrogen production activity, xylose utilization, liquid metabolites distribution or microbial community.…”