Glycerol-based biorefinery for fuels and chemicals

The rapidly expanding market for bioethanol and biodiesel is remarkably altering the cost and availability of glycerol. In general, approximately 10 pounds of crude glycerol are formed for every 100 pounds of biodiesel produced. Bioethanol process also generates glycerol up to 10% (w/w) of the total sugar consumed as a byproduct. Crude glycerol has thus been widely recognized as an attractive sustainable resource for chemical industries. Glycerol-based biorefinery is the microbial fermentation processes using inexpensive and readily available glycerol as the raw material to produce fuels and chemicals. A major challenge in fermentation of the low-grade crude glycerol is to obtain microbial strains tolerant to undesirable inhibitory components such as salts and organic solvents that present in crude glycerol. There have been several attempts to explore anaerobic microbial assimilation of glycerol using reconstructed microbial systems via microbial screening and metabolic pathway engineering. As a result, fuels as well as some high-value products were found to be produced by microbial fermentation of glycerol. This review describes biological processes using glycerol that produce fuels and chemicals including 1,3-propanediol, ethanol and organic acids.