Integrated valorization of algae biomass and food waste: A circular approach to sustainable bioproducts

This review aims to evaluate and synthesise recent advances in the integrated valorisation of algal biomass and food waste, and to assess their combined potential as sustainable resources for bioproducts, bioenergy and environmental applications within a circular bioeconomy framework. The central hypothesis is that the synergistic use of algal biomass and food waste through integrated valorisation approaches can significantly improve resource efficiency, reduce environmental impacts and create new value streams in the bioeconomy. To address this hypothesis, the review focuses on five main tasks: (1) analysing recent developments in co-processing techniques for algae biomass and food waste, (2) evaluating novel integrated valorisation strategies for the production of high-value bioproducts, (3) assessing the potential of combined algae-food waste systems for bioremediation and nutrient recycling, (4) identifying key challenges and opportunities for scaling up integrated algae-food waste biorefineries, and (5) exploring the circular economy implications of integrated valorisation approaches. Recent developments in co-processing techniques have shown promising results. Codigestion of Chlorella vulgaris with food waste increased biogas yields by 42% compared to mono-digestion, with a maximum methane yield of 0.38 L/g volatile solids at a 1:1 ratio (Zhang et al., 2022). Novel extraction methods using supercritical CO2 and green solvents have achieved high efficiencies in recovering valuable compounds from mixed biomass streams, with extraction efficiencies of 95% for lipids, 88% for proteins and 78% for polyphenols from a mixture of Spirulina platensis and fruit processing waste (Wang et al., 2021). In addition, hybrid systems combining microalgae cultivation with food waste fermentation have demonstrated effective nutrient recovery and wastewater treatment, achieving 92% nitrogen removal and 87% phosphorus removal, while producing valuable algal biomass and organic acids (Li et al., 2023). The red alga Fucilaria lumbricalis offers interesting possibilities for integration into these valorisation strategies. Its high carrageenan content (up to 50% dry weight) makes it an attractive source of hydrocolloids for food and pharmaceutical applications (Smith, 2020). Co-processing F. lumbricalis with food waste could potentially enhance biogas production due to its high carbohydrate content. Furthermore, the ability of the seaweed to accumulate heavy metals suggests potential applications in bioremediation when combined with other waste streams (Johnson & Parker, 2018). Key challenges for scaling up integrated algal/food waste biorefineries include optimising co-processing ratios, developing efficient separation technologies, and ensuring consistent biomass quality. However, the circular economy implications of these integrated approaches are significant, offering opportunities for waste reduction, resource recovery, and the creation of novel bio-based products (Kotler et al., 2021). This review explores these recent advances, evaluates emerging valorisation strategies, and identifies critical research needs to further develop integrated algae-food waste biorefinery systems within a circular bioeconomy framework. The methodology involved a comprehensive literature review of peer-reviewed articles published in Q1 and Q2 journals within the last three years (2020–2023), focusing on key terms such as ‘algae-food waste integration’, ‘circular biorefinery’, ‘integrated valorisation’ and ‘algae waste co-processing’.