Rice straw pretreatment with dilute organic acid for enzymatic hydrolysis and simultaneous saccharification and fermentation

To date, much research has revealed the need for pretreatment of lignocellulosic biomass to overcome recalcitrance of lignocellulose and enhance bioethanol yield. Different pretreatment methods including physical, physicochemical, chemical, and biological have been experimented on different substrates. But for ethanol production, acid pretreatment is more attractive because of removing hemicellulose as dissolved sugar, disrupting lignin structure and increasing reaction rate of sequential cellulose hydrolysis process beside availability and low cost. Despite different advantages of strong inorganic acid (especially sulfuric acid), however, generation of inhibitors such as H2S causes some problems. Using weak organic acid for lignocelluloses pretreatment seems to be an interesting method. Organic acids are environmentally friendly to use and improve quality of the by-product stream.The aim of this study was to identify effect of four organic acid (acetic acid, butyric acid, lactic acid, propionic acid) pretreatment at two temperatures (100 and 140°C) and two concentration (1 and 4%). All pretreated and untreated samples were hydrolyzed with cellulase enzymes. Hydrolysate was analyzed by HPLC for sugar content. The amount of ethanol which was produced by substrates in a SSF process after 72h was also measured by HPLC. Pretreating with lactic acid 4% at 140 °C increased glucose concentration in hydrolysate from 5.5 gL-1 to 14.6 gL-1 in comparison to untreated one. Also significant increases in reduced sugar achieved after hydrolysis by other organic acids. After 72 SSF, the best result for ethanol production was related to the substrate pretreated with lactic acid 4% at 140 °C.