Life cycle assessment of seaweed-based biorefineries: environmental impacts, hotspots, and pathways for a circular bioeconomy

Abstract

Seaweed-based biorefineries are increasingly recognized as promising contributors to the circular bioeconomy, offering renewable pathways for fuels, materials, fertilizers, cosmetics, and bioactive compounds. This review synthesizes approximately sixty life cycle assessments (LCA) studies covering diverse product categories, including biofuels, bioplastics, fertilizers and biostimulants, cosmetics, protein and feed, construction materials, food additives, and biochemicals. Across these applications, drying and energy-intensive extraction/crosslinking processes consistently emerge as dominant hotspots, often accounting for 50–70% of total GWP. Consequently, analysis shows that substituting greener solvents (reducing GWP by 20–40%) and implementing renewably powered drying (reducing GWP by ∼15–25%) are the most critical levers for impact reduction. Fertilizers and biostimulants show potential to reduce greenhouse gas emissions through substitution of synthetic inputs, while bioplastics and biofuels highlight trade-offs between energy use and co-product valorization. Cosmetics, food additives, and construction uses remain underexplored but demonstrate niche opportunities for high-value and low-carbon products. Cross-cutting analysis reveals methodological gaps, including inconsistent functional units, narrow impact category coverage, and limited integration of techno-economic analysis. Cultivation-focused LCAs further underscore the influence of farming practices, seasonality, and feedstock quality on downstream performance. Key challenges include high moisture content, ash and salt constraints in thermochemical conversion, insecure feedstock supply, and fragmented system modeling. Addressing these requires harmonized LCA methodologies, improved pretreatment strategies, and integration of techno-economic analysis to bridge environmental and economic performance. Compared to previous reviews, this study advances the field by synthesizing product-specific LCAs alongside cultivation studies, highlighting underrepresented products such as biostimulants and construction materials, and framing hotspots at process, system, and policy levels. Seaweed biorefineries present significant opportunities for climate mitigation, resource efficiency, and sustainable industry development, provided that future assessments expand in scale, scope, and methodological rigor.