Hydrothermal Pretreatment of Rice Straw with Alkaline Addition for Enhancing Biogas Production in Semicontinuous Anaerobic Digester

This study presents the results of hydrothermal pretreatment of rice straw on its ability to improve the biogas production process in anaerobic digesters. Hydrothermal treatment on rice straw biomass was carried out with the addition of 0%, 3% and 5% NaOH (w/w rice straw) for one hour at a temperature of 140 °C. This study showed that hydrothermal and alkaline hydrothermal pretreatments were able to increase organic degradation of rice straw as indicated by an increase in the dissolution of lignin and hemicellulose from rice straw. Temperature and NaOH worked synergistically to dissolve lignocellulose in the hydrothermal pretreatment process. In the semicontinuous digester fed with pretreated rice straw, NaOH content in the pretreatment stage was found to give significant effect in enhancing biogas production. Average daily biogas production by the untreated rice straw, hydrothermal pretreated without NaOH addition, hydrothermally treated rice straw with 3% NaOH and 5% NaOH was 23.9, 57.1, 95.8 and 108.8 L/kg rice straw, respectively.