Abstract
The production of biodiesel results in a concomitant production of crude glycerol (10% w/w). Clostridium pasteurianum can utilize glycerol as sole carbon source and converts it into 1,3-propanediol, ethanol, butanol, and CO2. Reduced growth and productivities on crude glycerol as compared to technical grade glycerol have previously been observed. In this study, we applied random mutagenesis mediated by ethane methyl sulfonate (EMS) to develop a mutant strain of C. pasteurianum tolerating high concentrations of crude glycerol. At an initial crude glycerol concentration of 25 g/l the amount of dry cell mass produced by the mutant strain was six times higher than the amount produced by the wild type. Growth of the mutant strain was even detected at an initial crude glycerol concentration of 105 g/l. A pH controlled reactor with in situ removal of butanol by gas-stripping was used to evaluate the performance of the mutant strain. Utilizing stored crude glycerol, the mutant strain showed significantly increased rates compared to the wild type. A maximum glycerol utilization rate of 7.59 g/l/h was observed along with productivities of 1.80 g/l/h and 1.21 g/l/h of butanol and 1,3-PDO, respectively. These rates are higher than what previously has been published for C. pasteurianum growing on technical grade glycerol in fed batch reactors. In addition, high yields of the main products (butanol and 1,3-PDO) were detected and these two products were efficiently separated in two steams using gas-stripping.
Highlights
Limited availability of fossil resources and increasing global impact from the release of fossil fuel-derived CO2 has increased the development of biological production of renewable alternatives
At an initial crude glycerol concentration of 53 g/l growth by the wild type, MNO3, and MNO10 was almost negligible, while MNO6 and MNO24 were less inhibited than the wild type grown on technical grade glycerol
At an initial glycerol concentration of 75 g/l, MNO6 produced 16.5% dry cell mass compared to the wild type growing on technical grade glycerol
Summary
Limited availability of fossil resources and increasing global impact from the release of fossil fuel-derived CO2 has increased the development of biological production of renewable alternatives. Biodiesel production from plant lipids is considered a renewable alternative to mineral oil-derived diesel (Demirbas 2007). The increasing market for biodiesel has substantially altered the cost and availability of glycerol released from transesterification of fatty acids from lipids. Without purification, this glycerol (crude glycerol), is considered a waste (Johnson and Taconi 2007; Dobson et al 2012) and it is, important that new and sustainable solutions for utilization of the crude glycerol are developed (Pyle et al.2008; Yazdani and Gonzalez 2007; Willke and Vorlop 2008). The organisms best known for producing 1,3-PDO are Clostridium butyricum and Klebsiella pneumoniae, which both can achieve high yields and productivities (Biebl et al 1999; Zeng et al 1994)
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