Mild Acid Hydrolysis of Rice Straw for Highly Efficient Methane Generation with Hydrolysates

Glucose and xylose are the dominant hydrolysis products of lignocellulose, and they can be used as a potential substrate for biogas generation. To reveal the acid hydrolysis metabolism and enhance the methane production, mild acid hydrolysis of rice straw was conducted to obtain hydrolysates with different glucose to xylose ratios. The methane production and microbial metabolism process using mixed sugars and hydrolysates were investigated. The results showed that the cellulose and hemicellulose in the rice straw were converted to the desired sugars by controlling the acid hydrolysis conditions. The glucose to xylose ratios tested were 70:30, 60:40, 50:50, 40:60, and 30:70. The anaerobic digestion process had the highest methane yield with the 40:60 glucose to xylose ratio in the mixed sugars and hydrolysate, which were 334.1 mL/g and 318.2 mL/g based on the chemical oxygen demand (COD), respectively. The metabolic process with the 40:60 glucose to xylose ratio had good butyrate type fermentation and a high COD removal rate. The corresponding acid hydrolysis conditions were 1% HCI and a 7.5% solid loading at 60 degrees C for 48 h. Therefore, the mild acid hydrolysis conditions can adjust the glucose to xylose ratio in the hydrolysate for high methane production.