Comparison of horse mulch to wheat straw as feedstocks for solid-state anaerobic digestion

Wheat straw is one of the most commonly used bedding materials in horse stall. The finished straw bedding materials, or horse mulch, has lower cellulose and hemicellulose contents, whereas higher total volatile fatty acids (total VFA) concentration than wheat straw. Biogas production from solid-state anaerobic digestion (SS-AD) of horse mulch and wheat straw was compared in this study. The SS-AD tests were conducted at 22% total solids (TS) content using effluent from a liquid AD as inoculum at three feedstock-to-inoculum (F/I) ratios of 2.0, 4.0 and 6.0. Daily methane yield of horse mulch peaked earlier than that of wheat straw. The highest methane yield of 150.0 L/kg volatile solids (VS) was obtained from horse mulch at FII ratio of 4.0, which was 56.2% higher than that of wheat straw. The corresponding cellulose and hemicellulose degradations of horse mulch were 24.1% and 49.4% higher than those of wheat straw, respectively.