Seaweeds as a sustainable source of bioenergy: Techno-economic and life cycle analyses of its biochemical conversion pathways

Abstract

This study evaluates the environmental impacts, economic potential, and merits of producing bioenergy from seaweed via biological conversion pathways, including the: 1) sugar pathway; (2) volatile fatty acids pathway; and (3) methane pathway to produce ethanol, ethanol and heavier alcohols, and heat and power, respectively. The maximum seaweed price and minimum product selling price are both calculated as economic indicators. Overall, results demonstrate that the sugar platform is economically superior, as it provides a higher average maximum seaweed price of USD 121.6/t compared with USD 57.7/t and USD 24.2/t for volatile fatty acids platform and methane platform, respectively. The minimum product selling price calculated for a range of biomass purchase prices (USD 50–150/dry t) and plant scales (100,000–700,000 dry t of seaweed) indicated that the sugar platform is capable of selling ethanol at prices lower than its 2019 wholesale price (USD 1.38/gal) at smaller plant scales and higher seaweed price compared with volatile fatty acids platform. Cradle-to-grave life cycle assessments were conducted to identify the key drivers of its environmental profile. Three scenarios for the preparation and transportation of seaweed were considered, namely: (1) grinding + pumping; (2) chopping + wet transportation; and (3) chopping + dry transportation. Seaweed grinding and pumping in the biorefinery was identified to be the most sustainable mode of transportation. In addition, our results demonstrated that biofuels can lead to better environmental profiles compared with generation of bioelectricity, as a larger burden is displaced by substituting fossil fuels in the transportation sector. © 2021 Elsevier Ltd