Influence of alkaline addition on the composition and yield on the hydrothermal treatment of rice straw

Abstract

Agricultural waste is abundantly available in Indonesia, including rice straw. The largest components of rice straw are cellulose, hemicellulose, and lignin, making this material good enough as raw material for production of biogas, bioethanol, and other renewable fuels. The bonds in the cellulose and lignin in rice straw are strong and difficult to degrade which consequently will block the microorganisms to degrade them. In this study, a hydrothermal treatment was performed with the addition of NaOH. The purpose of this study was to investigate the effect of alkaline hydrothermal treatment on rice straw delignification, cellulose and hemicellulose solubility, the formation of reducing and furfural sugars, as well as the degrees of cellulose crystallinity. The variables used were NaOH concentration of 3%, 5%, and 7% (w/w total solid) and temperature were 100 ℃, 120 ℃, and 140 ℃. Treatment was performed using an autoclave with water and rice straw ratio of 8:1 with heating time for 2 hours. The results of this study showed that hydrothermal and NaOH treatment can increase rice straw organic degradation as indicated by increasing delignification of rice straw and increased levels of watersoluble sugars. The higher the temperature and the NaOH concentration, the more lignin and soluble hemicellulose content. Meanwhile, the reducing sugar increases with increasing temperature and NaOH concentration. Thermal decomposition rate has also occurred at lower temperature. It was found that the highest organic rice straw degradation occurs at higher temperature and NaOH concentration.