Cellulosic Biomass Hydrolysis - Fermentation Coupled Hydrogen Production

Efficient conversion of wheat straw wastes into biohydrogen gas by cow dung compost was reported in this paper. Several environmental factors, such as pretreatment conditions of substrate, initial pH and substrate levels, were selected as target factors in this study. Before the raw wheat straw wastes were degraded by microorganisms, first they were pretreated with HCl concentration of 2.0% by microwave heating of 8.0 min, then the pretreated wheat straw wastes were effectively converted into hydrogen by microbes at fixed initial pH 7.0, substrate concentration 25g/L and fermentation temperature 36±1℃. Maximum hydrogen production yield of 68.1ml H2/gTVS was observed, the value is about 136-fold as compared with that of raw wheat straw wastes. The maximum hydrogen concentration in biogas was about 52% (v/v) and there was no significant methane observed in the biogas throughout the study. In addition, biodegradation characteristics of the substrate were also discussed. The biohydrogen gas was evolved with the formation of acetate, butyrate, and ethanol by decomposition of the pretreated wheat straw wastes. Our experimental results demonstrated that the pretreatment of the substrate plays an essential role in the conversion of the wheat straw wastes into biohydrogen by the composts generating hydrogen.In order to understand biodegradation trait of the substrate, reductive sugar and total sugar content in the raw wheat straw, the pretreated substrate and the fermented residue were analyzed as well as hemi-cellulose, cellulose and lignin. Compared with raw wheat straw, reductive sugar in the pretreated wheat straw increased by about 5.2 times, and after fermentation the reductive sugar decreased 96.2% .Total sugar in the pretreated wheat straw and the fermented residue decreased. Hemi-cellulose and cellulose in the wheat straw declined after pretreatment, however, lignin hardly any changed. Hemi-cellulose, cellulose and lignin in the wheat straw scarcely dropped after fermentation. The results showed that hydrogen-production anaerobic bacteriamostly converted reductive sugar of wheat straw into hydrogen and can't utilize hemi-cellulose, cellulose and lignin in the pretreated substrate to produce hydrogen. Because the content of reductive sugar in the raw wheat straw is low, its hydrogen yield is only 0.5mlH2/g straw. Partial total sugar, hemi-cellulose and cellulose in the raw wheat straw can hydrolyzed to produce reductive sugar after pretreatment, which remarkably improve the hydrogen-production potential of wheat straw.