The considerable increase in biodiesel production worldwide in the last 5 years resulted in astoichiometric increased coproduction of crude glycerol. As an excess of crude glycerol hasbeen produced, its value on market was reduced and it is becoming a "waste-stream" insteadof a valuable "coproduct". The development of biorefineries, i.e. production of chemicals andpower integrated with conversion processes of biomass into biofuels, has been singled out asa way to achieve economically viable production chains, valorize residues and coproducts,and reduce industrial waste disposal. In this sense, several alternatives aimed at the use ofcrude glycerol to produce fuels and chemicals by microbial fermentation have beenevaluated. This review summarizes different strategies employed to produce biofuels andchemicals (1,3-propanediol, 2,3-butanediol, ethanol, n-butanol, organic acids, polyols andothers) by microbial fermentation of glycerol. Initially, the industrial use of each chemical isbriefly presented; then we systematically summarize and discuss the different strategies toproduce each chemical, including selection and genetic engineering of producers, andoptimization of process conditions to improve yield and productivity. Finally, the impact ofthe developments obtained until now are placed in perspective and opportunities andchallenges for using crude glycerol to the development of biodiesel-based biorefineries areconsidered. In conclusion, the microbial fermentation of glycerol represents a remarkablealternative to add value to the biodiesel production chain helping the development ofbiorefineries, which will allow this biofuel to be more competitive.Source:
http://www.biotechnologyforbiofuels.com/rss/