Pretreatment of wheat straw for fermentation to methane

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Abstract
The effects of pretreating wheat straw with gamma-ray irradiation, ammonium hydroxide, and sodium hydroxide on methane yield, fermentation rate constant, and loss of feedstock constituents were evaluated using laboratory-scale batch fermentors. Results showed that methane yield increased as pretreatment alkali concentration increased, with the highest yield being 37% over untreated straw for the pretreatment consisting of sodium hydroxide dosage of 34 g OH−/kg volatile solids, at 90°C for 1 h. Gamma-ray irradiation had no significant effect on methane yield. Alkaline pretreatment temperatures above 100°C caused a decrease in methane yield. After more than 100 days of fermentation, all of the hemi-cellulose and more than 80% of the cellulose were degraded. The loss in cellulose and hemicellulose accounted for 100% of the volatile solids lost. No consistent effect of pretreatments on batch fermentation rates was noted. Semicontinuous fermentations of straw-manure mixtures confirmed the relative effectiveness of sodium and ammonium-hydroxide pretreatments.