Bio-flocculation: A cost effective and energy efficient harvesting technique for algal biofuel production and wastewater treatment

Microalgae are one of the most effective biomass sources for the creation of third-generation biofuel because of their high lipid content and area productivity. However, cost-effective solutions are required for the large-scale cultivation of microalgal biomass. Colloidal characteristics, negative charge on the surface, and low sedimentation velocity of microalgae make it difficult to harvest. Harvesting of microalgal biomass generally accounts for about 20 to 30 % of the total cost of cultivation, thereby acting as a major hold-up at the commercial level. Among the various harvesting techniques adopted (centrifugation, coagulation, and flocculation), bio-flocculation has appeared as a cost-effective, eco-friendly, industrially suitable process for microalgal harvesting. Eco-friendly methods of algal biomass harvesting for instance algal-yeast, algal-fungal, and algal-bacterial bio-flocculation for biofuel production have been debated in the present review. The utilization of fungal, yeast, and bacterial flocculants has been documented to increase the algal harvesting efficiency along with the removal of toxic substances from biomass. The only limiting factor is the pathogenic nature of some bio-flocculants which restricts its utilization in the food and pharmaceutical industries. There is a substantial need for further research to perceive an economic and non-toxic bio-flocculant for harvesting a large number of microalgae that can be employed in all sorts of industries. This review attempts to analyze information on the utilization of microalgae as a viable and efficient way for wastewater treatment due to its capacity to transform wastewater nutrients into valuable chemicals, low energy requirements, sustainability, and adaptability to a variety of environmental situations.