Direct current (DC) initiated flocculation of Scenedesmus dimorphus

Despite their superior efficiency, chemical flocculants introduce foreign chemicals, such as metals, into harvested microalgae, posing downstream application challenges. To overcome this, a simple direct current (DC) initiated flocculation technology is proposed for microalgal harvesting. This method applies a DC electric field across titanium plate electrodes to promote microalgal cell aggregation by polarizing their electrical double layer. Scenedesmus dimorphus cultivated in Bold's Basal Medium was tested under various voltage gradients (58, 116, 174, and 233 V/m) and energizing times (20, 40, and 60 min with DC applied), resulting in up to 94% flocculation efficiency based on dry algal biomass, significantly higher than controls. Microbubbles formed due to water electrolysis, but their impact on algal cell separation was minimal. Unlike electrocoagulation, DC-initiated flocculation uses inert electrodes and, thus, introduces fewer Fe or Al ions. This study is anticipated to facilitate research on electrochemically assisted algae harvesting and processing technologies.