Microbial utilization of crude glycerol for the production of value-added products

Abstract

Energy fuels for transportation and electricity generation are mainly derived from finite and declining reserves of fossil hydrocarbons. Fossil hydrocarbons are also used to produce a wide range of organic carbon-based chemical products. The current global dependency on fossil hydrocarbons will not be environmentally or economically sustainable in the long term. Given the future pessimistic prospects regarding the complete dependency on fossil fuels, political and economic incentives to develop carbon neutral and sustainable alternatives to fossil fuels have been increasing throughout the world. For example, interest in biodiesel has undergone a revival in recent times. However, the disposal of crude glycerol contaminated with methanol, salts, and free fatty acids as a by-product of biodiesel production presents an environmental and economic challenge. Although pure glycerol can be utilized in the cosmetics, tobacco, pharmaceutical, and food industries (among others), the industrial purification of crude glycerol is not economically viable. However, crude glycerol could be used as an organic carbon substrate for the production of high-value chemicals such as 1,3-propanediol, organic acids, or polyols. Microorganisms have been employed to produce such high-value chemicals and the objective of this article is to provide an overview of studies on the utilization of crude glycerol by microorganisms for the production of economically valuable products. Glycerol as a by-product of biodiesel production could be used a feedstock for the manufacture of many products that are currently produced by the petroleum-based chemical industry.

Utilization of biodiesel-derived glycerol or xylose for increased growth and lipid production by indigenous microalgae

“…The only product for which there is a nearly insatiable market is some type of fuel. Indeed, the heterotrophic production of ethanol, butanol and hydrogen using fungi or bacteria has also been reported (Dobson et al 2012;Ghosh et al 2012;SabourinProvost & Hallenbeck 2009). Heterotrophic cultivation of the alga Chlorella protothecoides showed equivalent growth on pure or crude glycerol (Y.-H. Chen & Walker 2011).…”

“…The availability of crude (or technical) glycerol as a cheap carbon source has led to many studies evaluating the use of crude glycerol as feedstock for the biological production of valuable chemicals as dihydroxyacetone, citric acid, vancomicin, cephalosporine and others (Dobson et al 2012;Liu et al 2013;Morgunov et al 2013;Shin et al 2011;Zeng et al 2013). However, if these conversion processes are successful, the value of their products, produced at enormous levels, would also fall precipitously.…”

Bioprospection of bacteria and yeasts from Atlantic Rainforest soil capable of growing in crude-glycerol residues

“…The world market of "green/clean" energy is increasingly counting on biodiesel as a viable alternative to fossil fuels for environmentally sustainable development (Dobson et al, 2012;Yang et al, 2012). However, around 10% of the biodiesel production results in crude glycerol as the main by-product of this process (da Silva et al, 2009).…”

“…Such variation and the chemical nature of these contaminants make the direct use of crude glycerol unviable for food, pharmaceutical, chemical, and synthetic material industries (Ashby et al, 2011), which commonly use pure glycerol. Thus, the use of crude glycerol in other applications and/or in its bioconversion to other products with economic value appear to be the best alternative for its processing in biodiesel production facilities (Johnson and Taconi, 2007;Min et al, 2010;Dobson et al, 2012).…”

“…As noticed from these studies, the use of microorganisms capable of degrading/converting crude glycerol has been a major strategy proposed (Pagliaro et al, 2007). The predominant type of work reported in recent years employs pre-selected and/or already established strains of microorganisms for glycerol-bioconversion processes (Mu et al, 2008;Rymowicz et al, 2010;Gungormusler et al, 2011;Ashby et al, 2011), which is relevant in view of the urge of developing biotechnologies able to efficiently cope with the waste of biodiesel production (Yazdani and Gonzalez, 2007;Dobson et al, 2012). However, the screening for new strains of microorganisms showing greater or more rapid degradation of crude glycerol, or even displaying novel metabolic features in terms of value-added compounds they can generate directly from growth on this residue, should not be relegated in this context.…”