Continuous foam flotation harvesting with enhanced drainage: Overcoming the recovery-enrichment paradox

Abstract

Microalgae are promising sources of sustainable biofuels, however high harvesting and enriching costs hamper economic competitiveness. Foam flotation––a low-cost, low-energy adsorptive bubble separation technique––may bridge this gap, yet its efficiency and adoption is compromised by a perceived trade-off (based on batch operation) between two key performance indicators: recovery percentage (R%) and concentration factor (biomass enrichment ratio; CF). Previously, we challenged this ‘recovery-enrichment paradox’ under continuous operation (R% 95, CF 173), but performance fell short of expectation. Here, we present a redesign based on the concepts of process intensification, by incorporating a drainage riser, delivering concomitantly high R% (91) and CF (722), retaining low power consumption (0.052 kWh m−3 of algae culture) with high total suspended solids yield (14.6%). This compares very favorably with other dewatering/harvesting techniques, overcoming the ‘recovery-enrichment paradox’. Our significant intensification of the foam flotation process will accelerate the advent of economically sustainable microalgae derived biofuels.