Advances on the processing of microalgal biomass for energy-driven biorefineries

Microalgae have been largely used as a source of human and animal food, essential fatty acids for the treatment and prevention of diseases, and as a source of pigments for natural colorants. They have also been considered a promising feedstock for the production of liquid biofuels, as they can achieve oil yields considerably higher than oilseed crops. However, microalgae-based biofuels are not yet economically feasible due to high operating costs and large energy demands, which result in poor net energy returns and unattractive internal rates of return. Biomass cultivation, nutrient recycling, water usage, and biomass harvesting are critical process issues. Refining the biomass in its various constituents presents an opportunity for making microalgal lipids economically viable for bioenergy production, supported on high added-value co-products. Hence, this review aims to consolidate the public information on microalgal biomass processing and to present an analysis of the best options for integrating individually studied processes in an energy-driven biorefinery. From this analysis, a preliminary proposal of a biorefinery flow diagram is presented, along with recommendations for further research and technology development in the critical areas for accelerating the development of microalgae biorefineries.