Harvesting of intact microalgae in single and sequential conditioning steps by chemical and biological based – flocculants: Effect on harvesting efficiency, water recovery and algal cell morphology

Abstract

Quick algae harvesting methodologies relating optimum flocculent dose (DOpt.), percentage harvesting efficiency (%HE) and percentage water recovery (%WRecovery) to the in-situ hydrodynamic properties of water-algae systems are presented. Flocculation of three microalgae in single and sequential steps, using chemical (polymer and ferric chloride) and biological (egg shells) flocculants, was studied. Zeta potential and pH analysis were completed to further understand the flocculation mechanism. Polymer at DOpt. of 7.0 g/kgDS resulted in WRecovery of 90% and %HE of 96.7%. Lower %HE (92.1), %WRecovery (79) and noticeable algal cells deformation was observed for ferric chloride at DOpt. of 7.0 g/kg DS. Bio-flocculant conserved algal structure and resulted in %HE of 96.2 and %WRecovery of 90 at DOpt. of 5.4 g/kgDS. Significant % HE of 99.8, %WRecovery of 99.8%, and up to 95% reduction in DOpt. were achieved in sequential flocculation. The results established the effectiveness and suitability of sequential/ bio-flocculation for algae harvesting. - 2019