Comparative study of different thermal pretreatment techniques for accelerated methane production from rice straw

This study emphasizes the use of different thermal pretreatment methods (i.e., hot air oven, hot water bath, autoclave and microwave) on pretreatment of rice straw prior to anaerobic degradation. These pretreatment methods resulted in reasonably high solubilization of recalcitrant biomass. Maximum solublisation was attained by microwave (190 °C; exposure time-4 min) (66.6%) followed by autoclave, hot air oven and hot water bath methods. Accelerated cumulative methane yield of microwave pretreated sample achieved was 367.71 mL/g-VSadded, which was 160.68 mL/g-VSadded higher than the control. Combining this high temperature conditions with lesser exposure time also improved the energy balance of the process. The physicochemical characteristics of pretreated rice straw were investigated by Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), FESEM analysis showed the increased porosity of the rice straw, FTIR analysis showed the omission of hemicellulose from the matrix and with XRD analysis reduced value of crystallinity index supports the destruction of the crystalline matrix.