Commercializing lignocellulosic bioethanol: technology bottlenecks and possible remedies

Abstract

With diminishing oil supplies and growing political instability in oil-producing nations, the world is facing a major energy threat which needs to be solved by virtue of alternative energy sources. Bioethanol has received considerable attention in the transportation sector because of its utility as an octane booster, fuel additive, and even as neat fuel. Brazil and the USA have been producing ethanol on a large scale from sugarcane and corn, respectively. However, due to their primary utility as food and feed, these crops cannot meet the global demand for ethanol production as an alternative transportation fuel. Lignocellulosic biomass is projected as a virtually eternal raw material for fuel ethanol production. The main bottleneck so far has been the technology concerns, which do not support cost-effective and competitive production of lignocellulosic bioethanol. This review sheds light on some of the practical approaches that can be adopted to make the production of lignocellulosic bioethanol economically attractive. These include the use of cheaper substrates, cost-effective pre-treatment techniques, overproducing and recombinant strains for maximized ethanol tolerance and yields, improved recovery processes, effi cient bioprocess integration, economic exploitation of side products, and energy and waste minimization. An integrated and dedicated approach can help in realizing large-scale commercial production of lignocellulosic bioethanol, and can contribute toward a cleaner and more energy effi cient world.

Bioethanol Production with Cellulase Enzyme from Bacillus cereus Isolated from Sesame Seed Residue from the Jazan Region

“…These results showed that there was a higher concentration of ethanol when B. cereus was used to degrade the sesame seed residues, which suggested there was a higher conversion of the substrate to reducing sugars. Banerjee et al (2010) explained that enzymatic hydrolysis is done by cellulase enzymes that are highly substrate specific. The obtained yield can be compared with the yield obtained from other wild-type bacteria.…”

Bioethanol Production from Lignocellulosic Waste-A Review

“…Moreover, no inhibitory by-product is formed in enzymatic hydrolysis [30]. However, enzymatic hydrolysis is carried out by cellulase enzymes that are highly substrate specific [31]. Here cellulase and hemicellulase enzymes cleave the bonds of cellulose and hemicellulose respectively (Cellulose contains glucan and hemicellulose contains different sugar units such as mannan, xylan, glucan, galactan and arabinan).…”

Next-generation cellulosic ethanol technologies and their contribution to a sustainable Africa

“…This allows switching between products according to market conditions, which is practised in some Brazilian sugar mills, and has also been suggested for sweet sorghum processing in Northern China [100]. Potential benefits of combined fermentation -distillation processes for ethanol production from lignocellulose may include (i) replacing exogenous nutrient supplements with sugar juice and/or molasses, which are rich in nutrients [88], (ii) mixing of sugars from juice and lignocellulose to increase ethanol concentrations at the end of the cellulose fermentation, and (iii) scale-up of ethanol purification/distillation to achieve economies of scale and improve energy efficiency [99]. Similar integration possibilities also exist in grain (small grains, corn, etc.)…”