Bioethanol from Biomass: A Review

As concern about global warming and dependence on fossil fuels grows, the search for renewable energy sources that reduce CO2 emissions becomes a matter of widespread attention. To reduce the net contribution of GHGs to the atmosphere, ethanol has been recognized as a potential alternative to petroleum-derived transportation fuels. Production of ethanol from biomass (bioethanol) is one way to reduce both consumption of crude oil and environmental degradation. It is biodegradable, low in toxicity and causes little environmental pollution if spilt. Bioethanol has higher octane number, broader flammability limit, higher flame speed and higher heat of vaporization than gasoline. These properties allow for a higher compression ratio, shorter burn time and leaner burn engine, which lead to theoretical efficiency advantages over gasoline in an internal combustion engine. Bioethanol currently accounts for more than 94% of global biofuel production. Lignocellulosic biomass is envisaged to provide a significant portion of the feedstocks for bioethanol production in the medium and long form due to their low cost and high availability. Successful utilization of cellulosic materials as renewable resources is dependent on the development of economically feasible process technologies for cellulase production. Cellulase plays a vital role in the production of bioetanol from biomass. Hydrolysis of biomass is usually carried out by the action of cellulolytic enzymes and the sequential process called Simultaneous Saccharification and Fermentation process (SSF). Cellulase production is the most expensive step during ethanol production from cellulosic biomass, and accountes for approximately 40% of the total cost. Significant cost reduction is required in order to enhance the commercial viability of cellulase production technology. Therefore, efforts are to be intensified to produce ethanol efficiently through improved fermentation technologies. Reduction in the cost of cellulases can be achieved by use of cheaper raw materials and economically viable fermentation strategies. Any strategies which can bring down the production cost of cellulases, can significantly reduce the cost of bioethanol. In the present paper, bioethanol production from lignocellulosic wastes and their cost reduction strategies are highlighted.