Improved Biohythane Production from Rice Straw in an Integrated Anaerobic Bioreactor under Thermophilic Conditions

This study evaluated the feasibility of continuous biohythane production from rice straw (RS) using an integrated anaerobic bioreactor (IABR) at thermophilic conditions. NaOH/Urea solution was employed as a pretreatment method to enhance and improve biohythane production. Results showed that the maximum specific biohythane yield was 612.5 mL/g VS, including 104.1 mL/g VS for H₂ and 508.4 mL/g VS for CH₄, which was 31.3% higher than the control RS operation stage. The maximum total chemical oxygen demand (COD) removal stabilized at about 86.8%. COD distribution results indicated that 2% of the total COD (in the feed) was converted into H₂, 85.4% was converted to CH₄, and 12.6% was retained in the effluent. Furthermore, carbon distribution analysis demonstrated that H₂ production only diverted a small part of carbon, and most of the carbon flowed to the CH₄ fermentation process. Upon further energy conversion analysis, the maximum value was 166.7%, 31.7 times and 12.8% higher than a single H₂ and CH₄ production process. This study provides a new perspective on lignocellulose-to-biofuel recovery.