Microalgae cultivation and harvesting: Growth performance and use of flocculants - A review

Abstract

Energy and cost effective cultivation and harvesting technologies are important to improve the economic viability and environmental impact of microalgae. Understanding the combined influence of photobioreactor designs and growth conditions on biomass yield and lipid productivity is essential to overcome the above hurdles. The efficiency of microalgae cultivation in photobioreactors under different growth conditions and harvesting efficiency of various flocculants on four selected microalgae species/strains were critically reviewed. Biomass yield, lipid productivity and economic implications of microalgae cultivation and flocculation were analysed. It was found that light intensity and carbon dioxide are prominent factors. However, efficient optimisation of photobioreactor's design and better understanding of the influence of growth conditions on different microalgae species will help in achieving low cost and high productivity of algae biomass and lipid accumulation. Existing technologies and processes seem not to have addressed the inverse proportionate nature of biomass yield and lipid accumulation during cultivation, as high biomass yield compensates low lipid accumulation. Adopting a two-stage cultivation process has shown potential to overcome the problem, but further improvement is required. Flocculation can be one of the most efficient ways of harvesting microalgae from mass culture. The application of flocculants in microalgae harvesting and cell disruption can reduce harvesting costs. The economics of microalgae cultivation and harvesting in photobioreactors were studied; highlighting the importance of optimisation of unit processes with suggestions of areas for further improvements.