Design of an Efficient Harvester and Dewater Mechanism for Microalgae

Abstract

Microalgae have now been widely considered as a promising bio-energy feedstock. The current microalgae harvesting methods used, such as centrifugation, sedimentation and flocculation, have been shown to be effective but are costly, representing between 35 % to 50 % of the total production cost. The aims of this study were: (1) to investigate the effectiveness of two electrocoagulation processes, electroflocculation and electroflotation, as algae pre-harvesting processes; and (2) to design, test and optimize a cost-effective and efficient filtration-based harvesting mechanism for micrioalgae. The principal results of the study showed that: (1) The mean final concentration for electroflocculation of 17.94 gL⁻¹ significantly exceeded (p = 0.0416) that for electroflotation of 9.51 gL⁻¹, indicating electroflocculation to be the more effective process; (2) Microscope images of the algae showed that, for the level of power applied (1 A, 40 V max), electrocoagulation did not appear to have produced any effect on the algae that was significantly different from that by centrifugation and that neither method appeared to have caused any significant cell wall damage or rupture; (3) The most effective configuration for the harvester prototype -- resulting in higher throughput rate (0.303 gh⁻¹), higher efficiency (233.33 gL⁻¹), as well as a lower energy consumption (143.46 kWhm⁻³) -- corresponded with higher concentration of the incoming biomass (21.5 gL⁻¹), lower belt velocity (0.05 ms⁻¹), higher inclination angle (25°) and lower pressure (0 Psi); and (4) The total energy consumption for the harvester prototype, when combined with a preceding pre-harvesting process, of 4.95 kWhm⁻³ was comparable to those reported by others for filtration-based harvesting. The new efficient harvesting mechanism proposed showed significant potential in successfully reducing algae production cost and make biofuels from microalgae economically feasible in the mid to long term in view of the prototype having achieved high output biomass concentration, low energy consumption per unit volume, high throughput rate, and facility of implementation.