Marine macroalgae in a circular economy context: A comprehensive analysis focused on residual biomass

The accumulation of Marine Macroalgal Waste (MMW) - drifted marine macroalgae - is a growing phenomenon. The lack of appropriate management protocols for this residual biomass leaves it mostly unmanaged or disposed of in landfills. Such inappropriate solutions lead to negative environmental impacts, health concerns and coastal degradation, representing an opportunity to develop the bioeconomy. Although a relevant number of studies exists on the use of edible marine macroalgae for several purposes, there is generally a lack of information concerning MMW valorisation, at both local and global scales. This review thus explores the ecological and biotechnological potential for the establishment of a new approach for MMW valorisation based in the circular and blue economies. It is supported in literature on the use of residual biomass whenever possible and also includes studies with fresh biomass to extrapolate, considering known characteristics of MMW; consequently, a roadmap for its utilisation is provided. The review includes characteristics of various seaweeds, MMW accumulation worldwide and traditional uses, together with the development of alternative and integrated valorisation strategies. By analysing a large number of studies, it was possible to perceive a clear potential to explore MMW to obtain renewable fuels, especially biogas and bioethanol and for use in agricultural activities. Allied to this, the extraction of value-added compounds, such as lipids, pigments, phenolic compounds and specific polysaccharides is highlighted, aiming to contribute to the development of an economically feasible zero-waste biorefinery approach.