Improving Biodegradation of Rice Straw Using Alkaline and Aspergillus niger Pretreatment for Methane Production by Anaerobic Co-Digestion

Abstract

Rice straw, an agricultural waste, is readily available as a potential feedstock for the production of fermentable sugars. However, the recalcitrant nature of the lignin during digestion has been the major hindrances for the feasibility of the anaerobic process. At the same time, conversion of animal manure to value added product like biofuels is an important breakthrough for alternative treatment of such materials. Considering the aforementioned statements, in this study, we propose a combined use of alkaline and biological pretreatment of rice straw followed by the subsequent anaerobic co-digestion with pig manure for the production of methane. 1.5M NaOH was used for alkaline pretreatment which improved the delignification of the rice straw by removing 45.5% of the lignin content. Aspergillus niger BCRC31130 was employed for the biological pretreatment. Alkaline pretreatment followed by five days of biological pretreatment and subsequent thermophilic co-digestion resulted in the highest amount of methane and reducing sugars production 1834.20 mL and 2.23 g/L respectively. Methane production of the proposed process was 3.17 times higher than that obtained from the untreated rice straw. These results suggested that the enhancement of biodegradation of the rice straw through the combined use of alkaline and biological pretreatment led to higher production of reducing sugars which were converted to methane during co-digestion.