Development of a method for biohydrogen production from wheat straw by dark fermentation

Lignocellulosic biomass contains approximately 70-80% carbohydrates. If properly hydrolyzed, these carbohydrates can serve as an ideal feedstock for fermentative hydrogen production. In this research, batch tests of biohydrogen production from acid-pretreated wheat straw were conducted to analyze the effects of various associated bioprocesses. The objective of the pretreatment phase was to investigate the effects of various sulfuric acid pretreatments on the conversion of wheat straw to biohydrogen. When sulfuric acid-pretreated solids at a concentration of 2% (w/v) were placed in an oven for 90 min at 120 °C, they degraded substantially to fermentative gas. Therefore, wheat straw that is pre-treated under the evaluated conditions is suitable for hydrolysis and fermentation in a batch test apparatus. Five different conditions were evaluated in the tests, which were conducted in accordance with standard batch test procedures (DIN 38414 S8): fresh straw, pre-treated straw, supernatants derived from acid hydrolyzation, Separate Hydrolysis and Fermentation (SHF) and Simultaneous Saccharification and Fermentation (SSF). The SSF method proved to be the most effective and economical way to convert wheat straw to biohydrogen. The hydrogen yield by this method was 1 mol H₂/mol glucose, which resulted from 5% carbon degradation (η_{C, gas}) or the equivalent of 64% of the hydrogen volume that was produced in the reference test (glucose equivalent test). This method also proved to have the shortest lag phase for gas production. The supernatants derived from acid hydrolysis were very promising substances for continuous tests and presented excellent characteristics for the mass production of biohydrogen. For example, a 1.19 mol H₂/mol glucose (76% glucose equivalent) yield was achieved along with a 52% carbon degradation.