Pelagic sargassum, a brown macroalgae, has become an environmental and economic challenge due to recurring beaching events that disrupt coastal ecosystems, tourism, and aquatic life, while also releasing greenhouse gases (GHGs) such as CO₂, NH3, CH4, H₂S upon decomposition. To address this, we propose a sustainable bioconversion strategy that begins with low-energy offshore harvesting, followed by the bioconversion of sargassum into biodiesel using Black Soldier Fly Larvae (BSFL) as a biological processing agent, culminating in supercritical CO₂ (SCO₂) lipid extraction and trans-esterification/esterification reaction. BSFL efficiently metabolize organic substrates, including sargassum, converting them into lipid-rich biomass with up to 58% lipid accumulation per BSFL dry weight. Pretreatment strategies, such as microbial inoculation and glycerol supplementation, enhance bioconversion efficiency by breaking down complex polysaccharides and improving carbon accessibility. Upon reaching the pre-pupae stage, BSFL lipids are extracted using SCO₂, an eco-friendly and selective method that eliminates toxic solvents while preserving bioactive compounds. The extracted lipids then undergo trans-esterification/esterification to produce fatty acid methyl esters (FAMEs), yielding biodiesel with low sulfur content, a high cetane number, and minimal environmental impact. Compared to traditional algal and non-algal biofuel processes, this pathway significantly reduces energy consumption by eliminating costly auto-hydrolysis, drying steps, pyrolysis and gasification. A techno-economic analysis (TEA) and life cycle assessment (LCA) will further validate that this approach minimizes GHG emissions, enhances process efficiency, and promotes circular bio-economy integration by leveraging co-products such as defatted BSFL for animal feed and bio-fertilizers from sargassum residue (frass). This study presents a scalable pathway for sargassum valorization with a reduced carbon footprint, offering a viable alternative to fossil fuels while mitigating the environmental impacts of excessive sargassum beaching events.
