Current advances in microalgae harvesting and lipid extraction processes for improved biodiesel production: A review

Microalgae have been considered as a potential feedstock for biodiesel production, since its cultivation uses less land than other traditional oil crops and has a higher growth rate. A great challenge is a choice of an effective approach for microalgae biomass recovery and lipid extraction, since the scheduling of these practices are critical and require an economical and environment friendly route. Flocculation has evolved as an efficient and economic approach for harvesting microalgae biomass. This review discussed the recent progress of chemical flocculants including organic and inorganic, bio-flocculants and nanomaterials-based processes for biomass recovery. In addition, the present review describes modifications made in conventional methods for lipid extraction. Several pre-treatment methods such as mechanical, chemical integrated with various solvents and nanoparticles are vastly investigated for lipid extraction. Use of green solvents namely, ionic liquids, supercritical fluids and switchable solvents are also reviewed, with the focus on cleaner biofuel synthesis. Furthermore, the article discusses policies implemented for the advancement in biofuel production, major challenges and considers future directions in microalgae harvesting and lipid recovery processes. This is the first study that extensively compares the recent approaches for biomass and lipid recovery. The present work intended to serve a long-term adaptation of the innovative techniques for copious economic benefit. Thus, this review emphasizes on advanced techniques that influence the microalgae biomass separation and cellular disruption for proficient lipid removal from microalgae, which deliberates towards the development of sustainable microalgae biofuel and heighten the bio-economy strategy.