Abstract
Biodiesel has gained a significant amount of attention over the past decade as an environmentally friendly fuel that is capable of being utilized by a conventional diesel engine. However, the biodiesel production process generates glycerol-containing waste streams which have become a disposal issue for biodiesel plants and generated a surplus of glycerol. A value-added opportunity is needed in order to compensate for disposal-associated costs. Microbial conversions from glycerol to valuable chemicals performed by various bacteria, yeast, fungi, and microalgae are discussed in this review paper, as well as the possibility of extending these conversions to microbial electrochemical technologies.
Highlights
Consumption of fossil energy is the foundation of modern society, from moving vehicles to lighting bulbs
The glycerol content in waste glycerol is from 27 wt% to 28 wt% with a methanol concentration that can vary from 6.2 wt% to
Intracellular glycerol is converted to dihydroxyacetone (DHA) by a NAD+-dependent glycerol dehydrogenase, and phosphorylated to dihydroxyacetone phosphate (DHAP) by a phosphoenolpyruvate (PEP) dependent DHA kinase (DHAK) [6]
Summary
Consumption of fossil energy is the foundation of modern society, from moving vehicles to lighting bulbs. (2) synthesis of higher carbon compounds with glycerol and other substrates; and (3) industrial combustion [9] These traditional chemical catalytic processes often include expensive metal catalysts, toxic intermediates, and low conversion rates [9]. Compared to direct application and chemical transformation, microbial conversion is a viable alternative that avoids certain disadvantages such as low product specificity, high energy input (pressure/temperature) and intensive pretreatment requirements [1,6]. With the development of the biodiesel industry, new breakthroughs have been made each year using different microbial species and bioengineering techniques to convert waste glycerol to value-added products. The glycerol metabolic pathways of representative bacterial and yeast species will be comprehensively discussed This includes the capability of various microbial species to convert glycerol to value-added chemicals addressed in terms of yield, productivity and final concentration. We introduced and discussed microbial electrochemical technologies that may be used as a strategy for generating value-added chemicals as well as electrical energy directly from glycerol
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