The Anaerobic Digestion of Microalgae Feedstock, “Life-Cycle Environmental Impacts of Biofuels and Co-products”

Abstract

Anaerobic digestion offers a potential pathway to eliminate some of the overheads for microalgae-based biofuels bio-refinery production systems. It is anticipated that the incorporation and integration of anaerobic digestion with microalgae-based biofuels production is able to attain higher efficiency and improve sustainability in the production of biofuels from microalgae. This chapter investigates several of the technical issues associated with anaerobic digestion of microalgae biomass including the low concentration of biodegradable (digestible) microalgae substrates, cell wall disruption and high lipid concentrations. Also highlighted is when the incorporation of anaerobic digestion into a biofuels bio-refinery concept, several anaerobic digestion-related issues can be addressed by the pre-treatment methods used to process microalgae for liquid and gaseous biofuels. This chapter also discusses other technical issues associated with the anaerobic digestion of microalgae including ammonia inhibition, low C/N ratio and co-digestion. Gas produced by the anaerobic digestion of residual microalgae biomass can be used for electrical or thermal energy within the microalgae biofuels bio-refinery, while the high density microalgae cultures can provide efficient biogas purification. The resulting digestate has been shown to be an ideal nutrient source for the continued growth of additional microalgae biomass, and helps to close the nutrient loop associated with large-scale microalgae biomass production. With a greater understanding of the different microalgae species and their characteristics, the anaerobic digestion of microalgae and their residues must be optimised to play an essential role in the sustainable future of clean energy derived from microalgae biomass.