Ethanol can be produced in two different ways, either by Direct Microbial Con­version (DMC) [180] or by Simultaneous SSF process. Novel bioreactors con­sisting of more than one bioreactor along with genetic recombination techniques are being developed at laboratory and pilot scale to improve the yield and pro­ductivity of bioethanol [25, 102]. Thermophilic fermentation seems to be a promising technique [122]. Additionally, the use of supercritical CO2 as a pre­treatment option has increased the ethanol yield by 70% [207].

9.7.13 Boiethanol Refinery

The conversion of by-products into value added products under a biorefinery concept may further reduce the associated process costs with additional energy in the form of fuels, heat, and electricity such as formation of xylitol from xylose, methyl fuorate from furfural and plastic from hydroxylmethyl furfural. Never­theless, estimation of greenhouse gas emissions of these products as they are shaped into marketable products is required. The main technological issues have been summarized recently by Kumar [102]. Prasad [144] described the pros and cons of various pretreatment options for ethanol production from lignocellulosic biomass. Moreover, the availability of the feedstock and related logistics influence the effectiveness of bioethanol technology [180].