ABSTRACT
The most recent, third-generation bioethanol production is an emerging technology using microalgae feedstock and cyanobacteria. The main components for bioethanol production are cellulose and hemicellulose fractions. To produce bioethanol, lignocellulosic material has to undergo different processing steps, which are pretreatment/delignification, hydrolysis/saccharification, fermentation, and downstream processing. The main pathways for bioethanol production using microalgae are yeast fermentation using microalgal inoculum, enzymatic hydrolysis, metabolic pathway in dark environment, and photo fermentation (conversion of organic substrate to biohydrogen by photosynthetic bacteria). Bioethanol production can be carried out through the following steps: preliminary biomass treatment, hydrolysis technique, fermentation processes, and product recovery mechanisms. The second- and third-generation bioethanol production processes have tremendous scope for fulfilling the existing requirements of bioethanol such as for mixing with gasoline, direct use as fuel, for portable purpose, etc. Currently, second-generation industrial plants are in operation in various parts of the world.
