Bioconversion of glycerol to ethanol by a mutant Enterobacter aerogenes

In a 20 g/L glycerol TSB, E. aerogenes ATCC 13048 converted 18.5 g/L P-glycerol and 17.8 g/L R-glycerol into 12 and 12.8 g/L ethanol, respectively. In a 50 g/L P-glycerol TSB, it utilized only 15.6 g/L glycerol; but the new strain used up 39 g/L, yielding 20 g/L ethanol after 120 h, an equivalence of 1.02 mol ethanol/mol-glycerol. This is the highest ethanol yield reported from glycerol bioconversion. The result of this P-glycerol fermentation can be duplicated using the R-glycerol from biodiesel production.There is an increasing demand for biofuels alternatives to petroleum-based fuel due to the health and environmental problems of the latter. Moreover, fossil fuel is not renewable; Campbell and Laherrere (1998) predict that petroleum reserves will be completely depleted by 2050. Recently, there has been a significant increase in the production and use of bioethanol and biodiesel. These biofuels - apart from being alternatives to fossil-derived fuels - are secure, renewable, non toxic, have a favorable energy balance and lower harmful emissions and are, therefore, environmentally friendly. Biodiesel is produced from the transesterification of vegetable oils or animal fats using simple alcohols (methanol or ethanol) and alkali catalysts. The process generates a lot of glycerol as a by-product. Specifically, the amount of glycerol generated is about 10% of the biodiesel produced (Yazdani and Gonzalez, 2008). Thus, for every 100 lb of biodiesel produced, 10 lb of glycerol is generated as waste. It is rightly predicted that crude glycerol availability will increase in the near future due to this global growth in biodiesel production (Dharmadi et al., 2006).Crude glycerol from biodiesel production presents great economic and environmental challenges. It is expensive to purify, and its improper disposal can contaminate the lithospheric environment. Yet, its surplus collapses the price of glycerol, which affects the glycerol-producing and -refining industries. Consequentl