Microalgal flocculation; global research progress and prospects for algal biorefinery

: Microalgal research has made significant progress due to versatile and high-value industrial applications of microalgal biomass or its derivatives. However, to explore their full potential and to achieve commercial robustness, microalgal biorefinery needs cost-effective technologies to produce, harvest, and process the microalgal biomass on large scale as higher production and harvesting cost is one of the key hindrances in the commercialization of algae-based products. Among several other algal biomass harvesting technologies, self-flocculation seems to be an attractive, low-cost, and eco-friendly harvesting technology. This review covers various flocculation-based methods that have been employed to harvest microalgal biomass with a special emphasis on self-flocculation in microalgae. Moreover, genetic engineering approaches to induce self-flocculation in non-flocculating microalgae along with the factors affecting self-flocculation and recent research trends have also been discussed. It is concluded that self-flocculation is the most desired approach for the energy- and environment-efficient harvesting of microalgal biomass. However, its poorly understood genetic basis needs to be deciphered through detailed studies to harness its potential for the algal biorefinery.