Valorization of carbon dioxide via the organic electro-refinery concept: Demonstrating the feasibility of a sustainable process

In this study, we present a successful demonstration of carbon dioxide transformation into carboxylate-rich solutions through a sequential process integrating biological and electrochemical technologies. The process comprises three main stages: (1) CO₂ fixation via algal cultivation, (2) electrochemical conversion of the algal biomass into carboxylates, and (3) separation and purification of the resulting acids using electrodialysis. Each stage was systematically evaluated to determine process efficiency and yield. First, atmospheric CO₂ was effectively fixed into algal biomass at varying cell retention times (2–10 days), with a 5-day retention time yielding the highest productivity, up to 37.65 mg day⁻¹ at an air flow rate of 4.1 L h⁻¹ . Shorter retention times led to biomass washout, limiting fixation efficiency. Second, the algal biomass was electrochemically transformed into carboxylate-containing solutions. The formation of these compounds followed a bimodal distribution: an initial release of native carboxylates from the algal matrix, followed by electrolytic generation via oxidation of organic matter, consistent with the organic electro-refinery concept. Acetate and malonate were predominantly associated with the first phase, while formate and oxalate were linked to the second. Finally, carboxylates were successfully recovered using electrodialysis with anion-exchange membranes. Recovery efficiency was strongly influenced by the applied current density, with up to 60 % of the carbon introduced via the algal suspension recovered as purified carboxylate solutions. These findings demonstrate the technical feasibility and promise of a fully solar-powered, integrated biological-electrochemical platform for CO₂ valorization, offering a novel and sustainable pathway for climate change mitigation. • C O 2 fixation via algae followed by electro-biorefinery transformation into carboxylates. • 3D printed cells for simultaneous generation and purification of carboxylic acids. • Separation and purification of carboxylates by electrodialysis