Recent advances in second generation bioethanol production: An insight to pretreatment, saccharification and fermentation processes

In response to the scarcity of non-renewable energy sources, sustainable and renewable biofuels from biomass have gained utmost attention. Utilization of lignocellulosic biomass for production of varied energy forms (second generation fuels) like biogas, biodiesel, bioethanol, etc has increased in the past decade. Their properties of being naturally abundant and easily accessible throughout the year, makes them an attractive energy alternative. Efficient pretreatment techniques for effective transformation of lignocelluloses to varied products, by increasing digestibility of celluloses and hemicelluloses can be achieved through acid, alkali treatment, enzymatic hydrolysis, and steam explosion. Idea behind optimizing pretreatment protocol is to maximize release of monosaccharide sugars for conversion to valise added products. Tailoring of hydrolytic enzymes through various approaches is well accepted for increasing specific activity of particular enzymatic reaction and can also be clubbed with other pretreatment processes minimizing chemical usage. We at our laboratory are working on optimization of process parameters for enhancing efficiency of saccharification process to obtain maximal monosaccharide sugars that can be converted to bioethanol. Present review compiles various approaches made by prominent scientists for efficient utilization of celluloses and hemicelluloses for ethanol production and also describes recent advanced techniques utilized for the same. Greater emphasis has been led on comparative study on utilization of simple sugars by bacteria and fungi and effect of consolidated bioprocess system on ethanol production from varied agro-industrial wastes.