Turning the Tide on Sargassum: A BioSTEAM Techno-Economic Analysis for a Sargassum Biorefinery

Abstract

Recurring pelagic Sargassum overblooms impose substantial environmental and economic burdens on coastal communities across the Atlantic. Existing operations already recover a profitable liquid biostimulant from the pressate fraction of mechanically processed Sargassum. The pressed cake solid fraction remaining after biostimulant extraction, however, constitutes a significant waste stream with associated disposal costs. This thesis presents the first BioSTEAM-based techno-economic model evaluating whether this solid waste stream can be valorized through anaerobic digestion and downstream fermentation, simulating a floating platform processing 15,000 wet metric tonnes per day across two parallel pathways: a methanogenic route producing biomethane, and an acidogenic route producing volatile fatty acids subsequently fermented by Yarrowia lipolytica into crude microbial oil. Both standalone pathways proved economically unfavorable under base-case assumptions. The best-performing methanogenic case using combined peroxide-enzymatic pretreatment yielded a biomethane MSP of $30.92/MMBtu, more than twice the highest regional market reference price. The acidogenic pathway achieved a base-case microbial oil MSP of $15.99/kg, well above the $1.50/kg soybean oil benchmark. In the integrated model, full allocation to the methanogenic route consistently maximized NPV, with positive returns achievable only when feedstock tipping fees, biostimulant revenue, or access to higher-value biomethane markets were included. These results suggest that the pressed cake waste stream can contribute towards economic revenue, but biological performance improvements and waste-management framing of the feedstock remain critical enablers of economic viability.