Beyond the Fossil Fuel Era: On the Feasibility of Sustainable Electricity Generation Using Biogas from Microalgae

摘要

In this century, biofuels will play an important role as fossil fuel alternatives. However, the long-term sustainability of large-scale biomass-based energy production chains is largely unknown. The current study evaluates the effect of nitrogen and phosphorus nutrient recovery on net energy ratio (NER) and land use, comparing a prospective industrial-scale microalgae production system with established maize agriculture. The functional unit was the delivery of 1.0 TWh of electrical energy using biomethane firing. Nutrient recovery was modeled by embedding anaerobic digestion (AD) as downstream processing step in the biomass production chains. The main finding was that maize-based biomethane electricity provision outperforms a prospective microalgae system in terms of NER, estimated at 4.9 and 3.2, respectively, when utilizing cogenerated heat, In the absence of external fossil fuel input, the renewable maize- and microalgae-based systems would require surface areas of 6.2 X 10~4 and 3.9 X 10~4 ha, respectively. Sustainability of microalgae-based biofuel production is not set by areal productivity or microalgal lipid content but rather by nutrient recovery, which is an important finding that requires prioritization in microalgae research.