Electrocoagulation flocculation

Electrocoagulation flocculation Electrocoagulation flocculation (ECF) is an alternative technique for the use of metal coagulants and relies on the release of iron or aluminium ions from a sacrificial anode (Vandamme et al. 2013). When using an aluminium anode during ECF, aluminium hydroxides are generated and when using an iron anode, ferric and/or ferrous hydroxides are formed (Vandamme et al. 2011). As the aluminium or iron anodes are oxidized, the main reaction at the cathode is the reduction of water, which generates hydrogen gas. Comparison of the recovery of two marine microalgae species Chlorococcum sp. and Tetraselmis sp. was carried out (Uduman et al. 2011) by electrocoagulation. High recoveries of up to 98 and 99% for Chlorococcum sp. and Tetraselmis sp., respectively, were obtained. The technique was also evaluated for harvesting the marine microalga P. tricornutum (Vandamme et al. 2011). In this study, the aluminium anode proved to be more efficient than the iron anode and under optimal conditions (pH 4, sedimentation time of 30 min and stirring speed of 150 rpm) the time required to initiate flocculation as well as the final recovery efficiencies were reproducible. Finally, the flocculation obtained was as effective as when using alum, though with the advantage of a limited aluminium content in the harvested biomass (below 1%). Electrocoagulation flocculation has low electricity consumption when used in seawater and therefore could be a promising low-cost technique for harvesting microalgae. Fayad et al. (2017) also found out that aluminium electrodes were best for harvesting C. vulgaris. 100% algae recovery was achieved within 50 minutes by using a steering speed of 250 rpm, an inter-electrode distance of 1 cm and a current density of 6.7 mA/cm2. This same study also optimized the operation parameters to minimize energy consumption down to 1 kWh/kg microalgae: aluminium electrodes were used with a current density of 2.9 mA/cm2, a stirring speed of 250 rpm and an inter-electrode distance of 1 cm at pH 4 for 60 min electrolysis. ECF harvesting of C. vulgaris in this study did not affect significantly the amount of lipids, chlorophyls A and B, and carotenoids.