Intensification of Microalgae Harvesting using a Foam Column

Abstract

Large-scale production of microalgae for commercialisation still needs to be improved by challenges in downstream processes, particularly harvesting. This study investigated the feasibility of foam flotation as a cost-effective harvesting technology using a foam riser design. The harvesting of the microalgae Chlorella vulgaris was systematically examined within the foam column. The primary result showed that installing risers in the column significantly increased harvesting efficiency. A flow map was developed showing the relationships between foam structures (discontinuous/continuous), air flow rate, and the CTAB and microalgae concentration. It was found that higher microalgae concentrations required more CTAB and approximately 30% of the free CTAB content remained in the solution. A foam riser with a diameter ratio of 0.25 increased the pressure and liquid fraction within the column. It leads to reduced foam water content and a 95.6% higher concentration factor than the operation without a riser which using air flow rate of 1 L min-1. Notably, the foam's velocity and bubble size increased significantly as it approached and entered the riser. However, the angle of the riser did not have a significant effect on the process due to the foam naturally formed its own angle under the riser. The implementation of a double-stage foam flotation process at an air flow rate of 2 L min-1 resulted in a 30% increase in efficiency compared to a single-stage process. This suggests that using multistage foam flotation as the preferred method for microalgae harvesting can significantly improve the overall efficiency of the process. Overall, a foam riser can be optimized for microalgae harvesting by having a constriction ratio of 0.25, a length of 15 cm, and an angle of 90 degrees. Additionally, a two-stage foam flotation process can enhance its effectiveness and offer the potential for scalability in microalgae harvesting technology.