Extracellular polymeric substances as key enablers for microalgal treatment and valorisation of malting and brewery wastewater

Malting and brewery wastewaters present environmental and economic challenges to the brewing industry due to their high organic loads and variable nutrient content, with chemical oxygen demand (COD) values ranging from 328 to 4500 mg/L and 910 to 8926 mg/L, respectively. Conventional treatment methods are limited by high energy consumption, sludge generation, and most importantly, a lack of resource valorisation. This review critically examines the role of extracellular polymeric substances (EPS) as key functional enablers in microalgae-based treatment of these effluents. Microalgal EPS enhance pollutant removal through biosorption mechanisms, facilitate biomass harvesting via natural self-flocculation, and represent valuable bioproducts with applications in the food, pharmaceutical, and environmental sectors. Integrating these functions within a circular biorefinery framework offers a holistic strategy that shifts traditional linear treatment methods toward circular resource utilisation pathways. Key technical and economic barriers to implementation are also identified in this review, including process scale-up, low-energy EPS extraction, and market development for EPS products.