Bio-refinery of palm kernel expeller waste into attached microalgal biodiesel, the life cycle analysis of waste biomass-to-energy

Abstract

The exploitation of solid carbon waste in the form of palm kernel expeller served two purposes: (i) providing nutrients for microalgal growth and (ii) serving as a medium for the adhesion of microalgal cells. This study examined the life cycle assessment of biodiesel production from attached microalgae, a less explored domain as compared with conventional microalgal system focusing on energy and environmental feasibility aspect. The computed environmental impact indicated that harvesting and lipid production had contributed significantly to the overall impact, though the global warming potential remained low (5.2 × 10−4 kg CO2 eq.). The establishment of scenario analysis had revealed that solvent recovery options resulted in about 48–55 % damage recovery, giving significant decline in the environmental impacts. In terms of energy sustainability, the study revealed a net energy ratio of 0.52, suggesting that the energy output is less than the energy invested. While falling short of ideal energy sustainability, the ratio surpassed that of conventional petroleum diesel and many previous microalgal technologies. Despite challenges, the findings accentuated the importance of continuous improvement in microalgal biofuel processes for enhancing energy efficiency and reducing environmental impact.