Biochemical conversion of rice straw into bioethanol - an exploratory investigation

Abstract

A good amount of research has been carried in recent years on the production of ethanol from lignocellulosic mass because it is not only a viable and eco-friendly alternative for the fossil fuels but also offers a solution to biomass waste management. Biochemical conversion of cellulosic biomass to ethanol can be done either by simultaneous saccharification and fermentation (SSF) or by separate enzymatic hydrolysis and fermentation (SHF) processes. In the present study, the readily available rice straw was chosen as a lignocellulosic biomass and pretreated with sulphuric acid and ammonium hydroxide to remove lignin for enhancing porosity and hence enzyme permeability. The pretreated straw was characterised by FT-IR and TG studies. Ethanol was produced from the acid pretreated straw by SHF method using acid and cellulase enzyme catalysis successively for saccharification and Baker's yeast (Saccharomyces cerevisiae) for the subsequent fermentation of the obtained sugar. Ethanol produced was estimated spectrophotometrically and compared with the theoretical yield. The greater degree of thermal degradation in the temperature range 200–400°C for the acid pretreated rice straw compared to the virgin sample impliedthe former's decreased structural integrity and improved flexibility. This was corroborated by the enhanced ethanol yield from the SHF process for the combined successive acid and enzymatic saccharification compared to the SHF process involving enzymatic saccharification only. The economic viability of this method has also been discussed in the present study.