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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.