Enhancing Biodiesel Production from Microalgae and Sewage Sludge Lipids by Adding Waste Coffee Ground Lipids
2023
Go, Y.W. | Yeom, S.H.
The free fatty acid (FFA) content in the feedstock lipids of microalgae (MA), sewage sludge (SS), and waste coffee grounds (WCGs) were 7.6%, 38.5%, and 1.7%, respectively. For a single feedstock lipid, the maximum biodiesel conversion was about 70% for MA lipids using acid or alkaline catalysts, 29.6% for SS lipids using acid catalysts, and 93.5% for WCG lipids using alkaline catalysts. For a mixture of MA and SS lipids, the maximum biodiesel conversion was only 38.6% in the experimental range tested. In contrast, for mixtures of WCG and MA lipids and WCG and SS lipids, where WCG lipids accounted for three-fourth of the mixtures, the biodiesel conversions using an alkaline catalyst were 89.5% and 70.0%, respectively. When MA, SS, and WCG lipids were mixed in equal proportions, 71.8% biodiesel conversion was obtained with 3.0 wt% of an alkaline catalyst. This study shows that WCG lipids, when used with lipids having high FFA content, are crucial for improving the conversion of lipids into biodiesel. In addition, by manipulating the proportion of WCG lipids in the mixture, we were able to use an alkaline catalyst, which has several advantages over an acid catalyst, to produce biodiesel at a relatively high biodiesel conversion.
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