Enhancement of biodiesel yield and characteristics through in-situ solvo-thermal co-transesterification of wet microalgae with spent coffee grounds

Abstract

This study evaluated in-situ co-transesterification of wet spent coffee ground (SCG)/microalgae mixture for enhanced biodiesel production. SCG and microalgae showed lipid contents of 16.0 and 23.6 wt%, respectively. A total of 27 transesterification runs were performed using wet SCG:algae (1:1, w/w) at different temperatures, times, and solvent ratios. Box-Behnken quadratic model suggested 198 °C, 6 mL solvent g^-1 biomass, and reaction time of 132 min as the optimum conditions for maximum biodiesel yield. At different SCG/microalgae blend ratios, pure microalgae showed the highest biodiesel yield of 20.15 wt%. Increase of SCG ratio resulted in significant reduction in the biodiesel yield, reaching the lowest value of 11.2 wt% using pure SCG. On the other hand, SCG showed better biodiesel characteristics than microalgae regarding iodine value, cetane number, and oxidation stability. The present results confirmed that SCG-algae blend results in dual effect of enhancing biodiesel yield and quality, comparing to the individual transesterification.

Keywords: Biofuels; Circular economy; Optimization; Renewable energy; Waste recycling.