Abstract
Today’s society is based on the use of fossil resources for transportation fuels. The result of unlimited consumption of fossil fuels is a severe depletion of the natural reserves and damage to the environment. Depleting fossil reserves and increasing demand for energy together with environmental concerns have motivated researchers towards the development of alternative fuels which are eco-friendly, renewable and economical. Bioethanol is one such dominant global renewable transport biofuel which can readily substitute fossil fuels. Conventionally, bioethanol has been produced from sucrose and starch rich feedstocks (edible agricultural crops and products) known as 1st generation bioethanol; however this substrate conflicts with food and feed production. As an alternative to 1st generation bioethanol, currently there is much focus on advancing a cellulosic bioethanol concept that utilizes lignocellulosic residues from agricultural crops and residues (such as bagasse, straw, stover, stems, leaves and deoiled seed residues). Efficient conversion of lignocellulosic biomass into bioethanol remains an area of active research in terms of pretreatment of the biomass to fractionate its constituents (cellulose, hemicellulose and lignin), breakdown of cellulose and hemicellulose into hexose and pentose sugars and co-fermentation of the sugars to ethanol. The present review discusses research progress in bioethanol production from sucrose, starch and cellulosic feedstocks. Development of efficient technology to convert lignocellulosic biomass into fermentable sugars and optimization of enzymatic hydrolysis using on-site/ in-house enzyme preparation are the key areas of development in lignocellulosic bioethanol production. Moreover, finding efficient fermenting microorganisms which can utilize pentose and hexose sugars in their metabolism to produce ethanol together with minimum foam and glycerol formation is also an important parameter in fermentation. Research has been focusing on the application of genetically modified strains, thermoanaerobes and mixed cultures of different strains in bioethanol production from sucrose, starch and lignocellulosic feedstocks.
Highlights
Energy sources and their utilization determine the economic status and growth of developing countries all over the world [1]
Sweet sorghum bagasse (SSB) in dilute NaOH Cellulose 34% - 45% solution (2% w/v) Hemicellulose 25% - 27% autoclaving at 121 ̊C Lignin 18% - 21 % [54] for 60 min and H2O2 immersing using Celluclast supplemented with β-glucosidase followed by fermentation using Active dry yeast at 30 ̊C and inoculum at 1:10 volume ratio of yeast medium to
Depleting fossil reserves and deleterious effects of fossil fuel burning on the environment led to the search for alternate fossil fuels which must be ecofriendly and renewable
Summary
Energy sources and their utilization determine the economic status and growth of developing countries all over the world [1]. Depleting fossil reserves and increasing demand for energy together with environmental concerns have led to focused research on the development of alternative fuels which are eco-friendly, bio-degradable and economical. The use of renewable resources to produce liquid biofuels offer attractive solutions to reducing greenhouse gas emissions, decreasing reliance on foreign oils, addressing energy security concerns, strengthening rural and agricultural economies and increasing the sustainability of the world transportation system [2]. Bioethanol is the dominant global renewable transport biofuel and offers greenhouse gas savings of up to 80% over conventional fossil fuels depending on the feedstock. Bioethanol is currently produced from traditional food crops such as corn (USA), sugar cane (Brazil), wheat (France, England, Germany, and Spain), cassava (Thailand, Nigeria) and sorghum (India), the feedstock depending on location and dominant agricultural product [4]. The bioethanol produced from these sucrose-and starch-containing feedstock is classified as 1st generation bioethanol (ethanol from corn and sugarcane) and those produced utilizing cellulosic feedstock is 2nd generation bioethanol (ethanol from corn stover, rice straw, palm empty fruit bunches and other lignocellulosic biomass) [https://www.iea.org/publications/freepublications/publication/2nd_Biofuel_Gen.pdf]
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