Assessment of Fresh and Dry Rice Straw for Biogas Potential by Anaerobic Digestion

To simplify the procedure of biogas production using agricultural straw as raw materials, the biogas performance of both dry and fresh rice straw (RS) was assessed during batch anaerobic digestion (AD) at 35 °C. The results showed that biogas production from fresh RS was 400.5 mL/g volatile solids (VS), which was 40.9% larger than that from dry RS substrate. Meanwhile, the methane content in biogas from fresh RS was 56.05% (approximately 2.5% larger than for dry RS), and the VS removal rate from feedstock was 72% (which was 7.2% greater than for the dry RS substrate). Moreover, the scum volume resulting from digestion of dry RS was 3.16 times the volume from fresh RS at the end of AD, indicating that RS feedstock in a fresh state was more readily biodegradable and more easily used as a substrate by microorganisms. Therefore, compared with dry RS, fresh RS as AD feedstock has practical application value and should be included in further research on the AD of biomass resources.