Mesophilic biohydrogen production from calcium hydroxide treated wheat straw

•Dark fermentation of wheat straw pre-treated with 7.4% (w/w) Ca(OH)2 at 20 °C.•Ca(OH)2 pre-treatment and adding Accellerase-1500® yielded 58.78 mL-H2 g-VS−1 straw.•Ca(OH)2 pre-treatment and adding Accellerase-1500® increased VFA production 10-fold.•CaCO3 significantly lowered biohydrogen yields and increased acetic acid production.

The use of Ca(OH)2 pre-treatment to improve fermentative biohydrogen yields, from wheat straw was investigated. Wheat straw was pre-treated with 7.4% (w/w) Ca(OH)2 at ambient temperature (20 °C) for 2, 5, 8, and 12 days, prior to 35 °C fermentation with sewage sludge inoculum. Biohydrogen yields were evaluated during dark fermentation and simultaneous saccharification fermentation (SSF) of total pre-treated straw material and compared to those from separated solid and hydrolysate fractions. Ca(OH)2 pre-treatment followed by SSF, exhibited a synergetic relationship. On average, 58.78 mL-H2 g-VS−1 was produced from SSF of pre-treated and filtered solids. This was accompanied by approximately a 10-fold increase in volatile fatty acid production, compared to the untreated control. By omitting pre-treatment hydrolysate liquors from SSF, H2 production increased on average by 35.8%, per VS of harvested straw. Additional inhibition studies indicated that CaCO3, formed as a result of pre-treatment pH control, could promote homoacetogenesis and reduce biohydrogen yields.