Macroalgae biorefineries as a sustainable resource in the extraction of value-added compounds

Beyond the commercial exploitation of macroalgae as food and as a source of phycocolloids, this bioresource could represent a third-generation feedstock to obtain a wide range of bioactive compounds as well as biostimulants and bioenergy from biomass valorization. However, seaweed biorefineries are less advanced than those based on terrestrial biomass and validation of this concept must address not only technical feasibility but also environmental and economic sustainability. In this context, the valorization of macroalgae should be demonstrated as a cost-effective alternative, where it would be possible to produce several target products with reduced operational costs and environmental burdens compared to their counterparts. This review aims to address a comparative study including the most recent extraction options based on a sequence of cascading stages of both conventional and advanced techniques. The potential products from the valorization of macroalgae considered in this review correspond to pigments, lipids, proteins, polysaccharides, biostimulants and biogas. Each of these has been evaluated separately to identify which technologies have been used for their extraction/production, analyzing their main advantages and disadvantages, and giving an overview of which technological aspects are most relevant to ensure their potential in the market value chain. This review also provides valuable information on the current macroalgae valorization facilities being developed, in different TRLs, and with the identification of the market sectors of the products obtained. It is hoped that this critical review will be useful to evaluate the possibility of using macroalgae as feedstock in production systems within a biorefinery approach.