Production of liquid biofuels, such as bioethanol, has been advocated as a sustainable option to tackle the problems associated with rising crude oil prices, global warming and diminishing petroleum reserves. Second-generation bioethanol is produced from lignocellulosic feedstock by its saccharification, followed by microbial fermentation and product recovery. Agricultural residues generated as wastes during or after processing of agricultural crops are one of such renewable and lignocellulose-rich biomass resources available in huge amounts for bioethanol production. These agricultural residues are converted to bioethanol in several steps which are described here. This review enlightens various steps involved in production of the second-generation bioethanol. Mechanisms and recent advances in pretreatment, cellulases production and second-generation ethanol production processes are described here.

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Lignocellulosic agriculture wastes as biomass feedstocks for second-generation bioethanol production: concepts and recent developments

Bioethanol has been identified as the mostly used biofuel worldwide since it significantly contributes to the reduction of crude oil consumption and environmental pollution. It can be produced from various types of feedstocks such as sucrose, starch, lignocellulosic and algal biomass through fermentation process by microorganisms. Compared to other types of microoganisms, yeasts especially Saccharomyces cerevisiae is the common microbes employed in ethanol production due to its high ethanol productivity, high ethanol tolerance and ability of fermenting wide range of sugars. However, there are some challenges in yeast fermentation which inhibit ethanol production such as high temperature, high ethanol concentration and the ability to ferment pentose sugars. Various types of yeast strains have been used in fermentation for ethanol production including hybrid, recombinant and wild-type yeasts. Yeasts can directly ferment simple sugars into ethanol while other type of feedstocks must be converted to fermentable sugars before it can be fermented to ethanol. The common processes involves in ethanol production are pretreatment, hydrolysis and fermentation. Production of bioethanol during fermentation depends on several factors such as temperature, sugar concentration, pH, fermentation time, agitation rate, and inoculum size. The efficiency and productivity of ethanol can be enhanced by immobilizing the yeast cells. This review highlights the different types of yeast strains, fermentation process, factors affecting bioethanol production and immobilization of yeasts for better bioethanol production.

https://cyberleninka.org/article/n/143136.pdf

Yeasts in sustainable bioethanol production: A review.

Application of response surface methodology and artificial neural network methods in modelling and optimization of biosorption process.

Recent developments in pretreatment technologies on lignocellulosic biomass: Effect of key parameters, technological improvements, and challenges.

Biological approaches to tackle heavy metal pollution: A survey of literature

Enhanced saccharification of rice straw and hull by microwave-alkali pretreatment and lignocellulolytic enzyme production.

Comparative study on ethanol production from pretreated sugarcane bagasse using immobilized Saccharomyces cerevisiae on various matrices

Enzymatic hydrolysis optimization of microwave alkali pretreated wheat straw and ethanol production by yeast

enzyme production and meeting the increase in awareness on energy conservation and recycling. The conversion of cellulosic mass to fermentable sugars through biocatalyst cellulase derived from cellulolytic organisms has been suggested as a feasible process and offers potential to reduce use of fossil fuels and reduce environmental pollution (5), (6). Cellulase production by different organisms in submerged state fermentation has received more attention and is found to be cost-prohibitive because of high cost of process engineering. India is an agricultural country and wheat is one of the most important agricultural crop in India. Every year nearly 78.4 Million Tones wheat is produced. With the processesing of wheat grains a large amount of straw is produced which can be used as a substrate for ethanol production. Currently a most important application of cellulases and hemicellulases in the pulp and paper industry is the biobleaching of pulp, the production of dissolving pulp, the treatment of wastewater and the deinking of recycled waste paper. The potential of enzymatic treatments has been assessed and the processes have proved successful (7), (8). In the present study the production of cellulolytic enzymes by a local isolate of A. heteromorphus on lignocelluloses in submerged fermentation is reported.

/pdf/production-of-cellulases-by-aspergillus-heteromorphus-from-3yyarfjq42.pdf

Production of Cellulases by Aspergillus Heteromorphus from Wheat Straw under Submerged Fermentation

Enzymatic hydrolysis of microwave alkali pretreated rice husk for ethanol production by Saccharomyces cerevisiae, Scheffersomyces stipitis and their co-culture

Anita Singh

Papers

Enhanced saccharification of rice straw and hull by microwave-alkali pretreatment and lignocellulolytic enzyme production.

Comparative study on ethanol production from pretreated sugarcane bagasse using immobilized Saccharomyces cerevisiae on various matrices

Enzymatic hydrolysis optimization of microwave alkali pretreated wheat straw and ethanol production by yeast

Production of Cellulases by Aspergillus Heteromorphus from Wheat Straw under Submerged Fermentation

Enzymatic hydrolysis of microwave alkali pretreated rice husk for ethanol production by Saccharomyces cerevisiae, Scheffersomyces stipitis and their co-culture