Biological hydrogen production from acid-pretreated straw by simultaneous saccharification and fermentation

Abstract

Hydrogen is currently produced in large amounts in the chemical industry, including that from the steam reforming of fossil fuels. Hydrogen must be produced sustainably to be economically feasible. This could be achieved from water through electrolysis powered by photosynthetic or other renewable energy, or by gasification or pyrolysis of biomass. It may also be possible to develop a cost-effective and reliable technology to produce hydrogen directly from renewable biomass or organic waste products through anaerobic fermentation. Lignocellulosic biomass contains approximately 70 to 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 acidpretreated 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 120oC, they degraded substantially to fermentative gas. Therefore, wheat that is pretreated under the evaluated conditions is suitable for hydrolysis and fermentation in a batch test apparatus. Different conditions were evaluated in the tests, which were conducted in accordance with standard batch test procedures (DIN 38414 S8): fresh straw, pretreated straw 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 (ηC 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. H2 yields observed in this study are higher than the H2 yields reported in other studies (the use of mixed culture inocula resulted in a slightly higher yield).