Third-Generation Biofuels: Bacteria and Algae for Better Yield and Sustainability

Abstract

Biofuels have been commercialized, predominantly bioethanol and biodiesel, in pure form or admixed to regular fuels gasoline and diesel, respectively. Mostly, they are based on edible feedstock such as corn, sugarcane, rapeseed, and soybean (so-called first-generation (1G) biofuels). The arising competition over arable land with food crops has caused significant debate, as well as a net contribution to climate change, where it was found that sometimes 1G biofuels perform even worse than petroleum-based fuels, due to land use change, fertilizer usage, and process yields, for instance. Biofuel research has hence targeted lignocellulosic feedstock, which exists in abundance. Due to the stability of these biopolymers, cost-effective 2G (second generation) biofuels are now only at the verge of commercialization. Processes to break up the biomass into fuels are thermochemical and biochemical, using enzymes. 3G (third generation) biofuels have been envisioned, where microorganisms are deployed. For instance, since algae can form up to more than an order of magnitude more biomass per area than terrestrial biomass, they hold great promise for future biofuel production on marginal land or in the ocean. In this chapter, 2G and particularly 3G biofuel concepts, where bacteria and algae are used to obtain biofuels, are discussed. Standard industrial processes, like ethanol fermentation through microorganisms for regular 1G biofuels, and transesterification of various oils to fatty acid methyl esters (FAME, biodiesel) are not covered here. Alternative biofuels from bacteria and algae, such as biomethanol or biohydrogen, are also addressed.