Microalgae for biofuels via thermochemical conversion processes: A review of cultivation, harvesting and drying processes, and the associated opportunities for integrated production

Biofuels can be derived from waste biomass feedstocks, such as municipal, agricultural, forestry and industrial waste. There are several advantages in switching to microalgae for biofuel production. Microalgae has a rapid growth rate, so is more productive, so requires smaller areas for cultivation per unit of biomass produced. Microalgae can absorb “waste” CO2, does not compete with food crops (for land and freshwater), and can be cultivated in wastewater, doubling as a wastewater treatment. This paper gives an overview of microalgae cultivation, focusing on the early energy-intensive stages: growth, harvesting and drying. The harvesting and drying steps constitute a significant economic bottleneck, due to their high energy costs. This review also covers microalgal cultivation and its integration with wastewater treatment, carbon and energy sources, and the utilization of microalgal biofuel co-products from thermochemical conversion, as this route is the most likely to mitigate the techno-economic downsides of microalgal biofuel production.