Applicability of Rice Husk Residue Generated by the Silica Extraction Process to Anaerobic Digestion for Clean Energy Production

Abstract

Rice husks are a feedstock of biogenic silica because of their high silica content. After silica extraction, a solid residue which consists of mostly carbohydrates and lignin is present. The valorization of the solid residue is important to a closed-loop system of using rice husk and minimal negative impacts on the environment. In this study, we investigated the applicability of solid rice husk residue generated by silica extraction on an anaerobic digestion to produce biomethane. The rice husk residue obtained was characterized in terms of total solids, volatile solids, pH, composition, and particle size for application to anaerobic digesters. By changing the characteristics, the biogas production increased by 2.48-fold compared to that of untreated samples. The residue produced 166.4 mL-biogas/g VS and 100.4 mL CH 4 /g VS in the biochemical methane potential test, which are much higher values than those reported in other studies. Microbial community analysis was performed to investigate the biological reasons for increased biogas and methane production. Increased Bacteroidetes levels were found in the rice husk samples. Among the archaeal communities, a higher distribution of Bathyarchaeota was observed in all rice husk samples than that in the inoculum. Rice husk residue showed a higher operational taxonomic unit than other samples in the rarefaction curve. These changes in the microbial community significantly influenced the anaerobic digestion of rice husk residue and led to improved methane production. The results of this study provides clues for the cleaner utilization of rice husk residue to produce a renewable energy.

Keywords: Rice husk, Anaerobic Digestion, Biochemical methane potential, methane, Microbial community, Pyrosequencing