Lignocellulose Essay

Lignocellulose is a major component of plant biomass and is composed of lignin, cellulose and hemicellulose. Lignocellulosics represent the most abundant renewable and inexpensive source of energy, derived from agricultural residues, forest waste and municipal solid wastes (Sánchez, 2009). It has been estimated that the amount of energy from the sun, fixed as carbon in photosynthetic biomass is 10 times the world usage

(Kumar et al., 2008a). Globally, 1.3  1010 metric tons of wood is produced by terrestrial plants, which is equivalent to two-thirds of world’s energy requirement (Demain et al., 2005). Accumulation of such large quantities of lignocellulose creates disposal problems and raises environmental concerns. Usually, a major portion of lignocellulosic waste is burnt for disposal, resulting in loss of valuable material. Alternatively, this vast resource can be judiciously used for the production of various commodity chemicals and liquid biofuels (Menon and Rao, 2012).

Due to increase in price, negative impact on environment and uncertainty in the availability of fossil fuels, alternatives like biofuels are gaining prominence. Technologies are being developed for the bioconversion of renewable lignocellulosic feed stocks into biofuels. These second generation biofuels are more sustainable and economical when compared to first generation biofuels which are obtained from edible biomass (Cherubini, 2010). One of the major bottlenecks associated with biofuels is the poor economics involved in the process for bioconversion of lignocellulosic materials.

The economic viability of biofuels production from lignocellulosics is hindered by the high cost and complexity of processes associated with the conversion of recalcitrant biomass ...

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...id pretreatment of xylans hydrolyzes hemicelluloses to monomeric sugars like xylose arabinose, galactose etc. The resultant heterogenous mixture has to undergo several purification steps to obtain pure xylose. Moreover, the yield of xylitol is only 50 % of the raw material used. Low yield and expensive purification procedures are the major disadvantages of xylitol production by chemical means (Nigam and Singh, 1995).

In the recent times, considerable effort has been put in exploring alternative strategies and the prospect of xylitol production using microorganisms appears attractive. Yeasts are predominant xylitol-producers, although a few reports mentioned xylitol production by bacteria and fungi. Bacterial species like Corynebacterium, Mycobacterium smegmatis,

Enterobacter liquefaciens are shown to produce xylitol (Izumori and Tuzaki,

1988; Yoshitake et al., 1976).