Evaluation of electrocoagulation, flocculation, and sedimentation harvesting methods on microalgae consortium grown in anaerobically digested abattoir effluent

Abstract

Microalgae dewatering is a major bottleneck for biomass production in a large-scale microalgal production system which accounts for 20–60% of production cost. In this study, three dewatering systems of electrocoagulation, flocculation, and pH-induced flocculation were evaluated for microalgal consortium grown in anaerobically digested abattoir effluent at pH 6.5 and 9.5. At the shortest time (15 min) and the highest current density (0.08 A cm−2), the highest microalgae recoveries of 78 and 84% were obtained with the corresponding power consumptions of 1.25 and 1.07 kWh kg−1 for cultures at pH 6.5 and 9.5. For microalgae suspension at pH 6.5, the highest biomass recovery of 77% was obtained when 100 mg L−1 of FeCl3·6H2O (after 15 min) or 100 mg L−1 of Al2(SO4)3·18H2O (after 30 min) was added. However, microalgal recoveries significantly increased when FeCl3·6H2O or Al2(SO4)3·18H2O was used with the culture at pH 9.5. pH-Induced experiments showed that cultures adjusted at pH 10.5 had 36% higher biomass recovery compared to that in cultures at pH 8.5 after 2 h. The results of this study showed that cultures at higher pH (9.5) had a better microalgae recovery in all dewatering systems than cultures at lower pH (6.5).