Plant-based biopolymers: emerging bio-flocculants for microalgal biomass recovery

The production of microalgal biomass and its derived products on a large-scale requires the development of sustainable and cost-effective harvesting technologies. Biomass recovery is the primary step in the downstream processing of microalgae and it is a costly operation because microalgal cultures are stable hydrophilic colloidal suspensions. Bio-flocculation has been proposed as a low-cost technology that can be employed to dewater microalgal cultures thus making secondary harvesting methods like filtration and centrifugation less energy-intensive. This review provides an overview of increasing applications of plant-based biopolymers in microalgal biomass harvesting on laboratory and pilot-scale culture volumes. The structure, preparation, and flocculation activity of natural and chemically cationized plant biopolymers are presented. Recent studies demonstrating microalgal biomass recovery have been summarized discussing the advantages and limitations of plant-based biopolymers as emerging bio-flocculants. Future perspectives on biopolymers with special attention to studies reported on nutrient medium recycling, environmental impact assessment and techno-economic analysis of plant-based bio-flocculants facilitated bio-flocculation have been discussed.