Rice straw anaerobic co-digestion: Comparing various pre-treatment techniques to enhance biogas production

Study investigates rice straw size impact on co-digestion with four pre-treatments: thermal, hydrogen peroxide, combined thermal and hydrogen peroxide, and hydrogen peroxide followed by thermal treatment. Rice straw is divided into four sizes: 3–5 cm, 1–2 cm, 5–10 mm, and 300 μm. Co-substrates, sewage sludge, and chicken manure are used at a 20 % total solids concentration. Pre-treatment effects on rice straw and volatile fatty acid content post-digestion are assessed by quantifying cellulose, hemicellulose, and lignin content. Thermal pre-treatment, particularly on 1–2 cm-sized rice straw, demonstrates the highest efficacy with biogas production of 389 mL/g-VS. Preferred rice straw sizes for adaptability are ranked: 1–2 cm > 5–10 mm > 3–5 cm > 300 μm. However, pre-treatment fails to enhance biogas production compared to the control, attributed to structural deterioration, accelerated hydrolysis, elevated VFA levels, methanogenic inhibition, and increased hemicellulose content. Co-digestion is recommended over pre-treatment for rice straw anaerobic digestion.