Abstract
Microbial lipid production from oleaginous yeasts is a promising process for the sustainable development of the microbial biodiesel industry. However, the feedstock cost poses an economic problem for the production of microbial biodiesel. After lipid extraction, yeast biomass can be used as an organic source for microbial biodiesel production. In this study, volatile fatty acids (VFAs), produced via anaerobic digestion of a lipid-extracted yeast (LEY) residue, were utilized as a carbon source for the yeast Cryptococcus curvatus. The response surface methodology was used to determine the initial pH and inoculum volume for the optimal VFA production. The experimental result for VFA concentration was 4.51 g/L at an initial pH of 9 and an inoculation 25%. The optimization results from the response surface methodology showed that the maximal VFA concentration was 4.58 g/L at an initial pH of 8.40 and an inoculation of 39.49%. This study indicates that VFAs from LEY can be used as a carbon source for microbial biodiesel production, with the potential to significantly reduce feedstock costs.
Highlights
The prospect of converting microbial lipids into biodiesel has attracted attention from many researchers because of the renewable potential of biofuel sources such as microalgae, fungi, and yeasts
The maximum theoretical yield of microbial lipid yield is quite low and one-third carbon is released by CO2 producing Acetyl-CoA, which is the building block of fatty acids, during glucose
Bioenergy and biofuel are advantageous for reducing greenhouse gas emissions and carbon neutrality. Their widespread utilization is hindered by economical limitations, the feedstock cost
Summary
The prospect of converting microbial lipids into biodiesel has attracted attention from many researchers because of the renewable potential of biofuel sources such as microalgae, fungi, and yeasts. Considering a microalgal lipid content of 50%, the per-liter production cost of biodiesel from algal oil varies from USD 1.08 to USD 1.34 [6,7]. Yeasts such as Cryptococcus albidus [7,8,9], Cryptococcus curvatus [10,11,12], Yarrowia lipolytica [13,14], and Rhodosporidium toruloides [15,16], which can use low-cost volatile fatty acid (VFAs) materials (USD 20–100/ton) as carbon sources, can produce biodiesel at a cost of $0.3–$1.26/L [7]. The maximum theoretical yield of microbial lipid yield is quite low (around 0.32 g/g from glucose) and one-third carbon is released by CO2 producing Acetyl-CoA, which is the building block of fatty acids, during glucose
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