Impact of impurities in biodiesel-derived crude glycerol on the fermentation by Clostridium pasteurianum ATCC 6013

Abstract

During the production of biodiesel, crude glycerol is produced as a byproduct at 10% (w/w). Clostridium pasteurianum has the inherent potential to grow on glycerol and produce 1,3-propanediol and butanol as the major products. Growth and product yields on crude glycerol were reported to be slower and lower, respectively, in comparison to the results obtained from pure glycerol. In this study, we analyzed the effect of each impurity present in the biodiesel-derived crude glycerol on the growth and metabolism of glycerol by C. pasteurianum. The crude glycerol contains methanol, salts (in the form of potassium chloride or sulfate), and fatty acids that were not transesterified. Salt and methanol were found to have no negative effects on the growth and metabolism of the bacteria on glycerol. The fatty acid with a higher degree of unsaturation, linoleic acid, was found to have strong inhibitory effect on the utilization of glycerol by the bacteria. The fatty acid with lower or no degrees of unsaturation such as stearic and oleic acid were found to be less detrimental to substrate utilization. The removal of fatty acids from crude glycerol by acid precipitation resulted in a fermentation behavior that is comparable to the one on pure glycerol. These results show that the fatty acids in the crude glycerol have a negative effect by directly affecting the utilization of glycerol as the carbon source, and hence their removal from crude glycerol is an essential step towards the utilization of crude glycerol.

Optimization of decoloring conditions of crude fatty acids recovered from crude glycerol by acid-activated clay using response surface method

“…Although refined glycerol can be obtained by purifying crude glycerol and then utilized in the cosmetic, paint, automotive, food, pharmaceutical, and pulp industries [1], it is not a complete solution because crude fatty acids are also generated. Intensive studies on bioconversion of crude glycerol to value-added products by means of fermentation have found that crude fatty acids are toxic to microorganisms and, thus, partially purified (fatty acid-free) crude glycerol is a better fermentation substrate than that of crude glycerol [3,4]. Therefore, we cannot avoid the generation of crude fatty acids as waste when utilizing crude glycerol.…”

Effective production of low crystallinity Poly(3-hydroxybutyrate) by recombinant E. coli strain JM109 using crude glycerol as sole carbon source

“…One mole of glycerol is produced with the production of every 3 mol of methyl esters (i.e., biodiesel), resulting in 10% by weight (wt%) of the total crude glycerol produced (Melero et al, 2012). This crude glycerol stream contains major impurities such as methanol, salts, soaps, heavy metals and residual fatty acids (Venkataramanan et al, 2012;Yang et al, 2012). The increased production of biodiesel has resulted in excess of glycerol with significant drop in the cost of crude glycerol along with simultaneous decrease in demand.…”

Isolation of New Strains of Bacteria Able to Synthesize 1,3-Propanediol from Glycerol

“…Crude glycerol includes many substances that may act as inhibitors of microbial growth and metabolism. These include sodium salts, heavy metal ions, soaps, methanol and free fatty acids [40,42]. Therefore, the next steps in characterising the bacterial strains were to verify the best isolates using crude glycerol as a substrate.…”