Continuous conversion of CO2-derived algal biomass into carboxylates via an electro-assisted organic refinery

This study presents a continuous electrochemical-biological process, at early TRL 5, for the conversion of CO 2 -derived algal biomass into carboxylate-rich streams through an integrated electro-assisted organic refinery. The system combines algal cultivation, electrochemical oxidation, and electrodialysis-based separation, operating under steady-state conditions after 6 h and maintaining stable performance for more than 2 days. The influence of key operational parameters, including electrode material, current density, and membrane type, was systematically evaluated. Dimensionally stable anodes (DSA) were found to favor partial oxidation pathways, enhancing carboxylate recovery compared to boron-doped diamond (BDD), which promotes more extensive mineralisation. In the electrodialysis stage, lower current densities improved recovery and increased the mean carbon oxidation state (MCOS), likely due to reduced parasitic reactions in the cathodic compartment. Membrane selection also played a critical role, with FAB-PK-130 anion-exchange membranes outperforming RALEX AMH-PES, attributed to their lower resistance and higher selectivity. Product analysis revealed a distribution dominated by citrate, malonate, oxalate, oxamate, and tartrate, although a small fraction of compounds remained unidentified. The process demonstrated stable operation without significant performance losses during the experimental period, supported by constant cell voltage. The results demonstrate the potential of integrating biological CO 2 fixation with electrochemical conversion and membrane-based separation to produce value-added carboxylates from algal intermediates. This study provides a proof-of-concept framework for the development of electro-assisted organic refineries based on CO 2 -derived biomass.