The Use of Flocculation as a Preconcentration Step in the Microalgae Harvesting Process

Flocculation is a widely utilized separation technique in colloid chemistry, the chemical industry, and wastewater treatment. However, its application in microalgal biomass production and downstream processing remains limited. Biomass harvesting represents a significant cost factor in large-scale microalgae production, with the separation of biomass from the liquid medium accounting for up to one-third of total production expenses. The use of flocculants as a pre-treatment step has emerged as a promising approach to reducing these costs. Laboratory-scale flocculation is commonly employed to optimize flocculant dosage and assess strain-specific flocculation efficiencies. Meanwhile, pilot-scale flocculation, when applied before centrifugation, provides critical insights into the applicability of specific flocculant–strain combinations and their impact on yield and biomass quality. Numerous studies have investigated the flocculation behavior of various microalgal strains using a wide range of chemically distinct flocculants at the laboratory scale. This review highlights recent advancements in microalgal flocculation as a pre-centrifugation strategy and outlines future perspectives for achieving cost-effective, large-scale microalgal biomass production as a globally viable resource.