Multienzymatic Platform for Coupling a CCU Strategy to Waste Valorization: CO₂ from the Iron and Steel Industry and...

Ongoing climate crisis demands the development of carbon capture and utilization (CCU) technologies that emphasize simplicity, eco-sustainability, and cost-effectiveness. Enzymatic CO₂ reduction emerges as an alternative to biotransforming this cheap raw material into high-value products under milder conditions. This work proposes a multienzymatic platform to reduce CO₂ to formate by formate dehydrogenase (FDH) and oxidize glycerol to dihydroxyacetone (DHA) by glycerol dehydrogenase (GlyDH), allowing for efficient cofactor regeneration. Through studies such as pH operating range, enzyme stability, FDH/GlyDH ratio, and reaction medium engineering to achieve optimal soluble CO₂ concentrations, the reaction with a gas mixture of 24% CO₂ yielded 5.7 mM formate and 6 mM DHA after 30 h, achieving a 92.3% CO₂ conversion. To evaluate the feasibility under industrially relevant conditions, a synthetic gas mixture mimicking the composition of the iron and steel industry off-gases (24.5% CO₂) and crude glycerol (64% v/v) from biodiesel production was tested as substrates. The simultaneous production was successful, yielding 3.1 mM formate and 4.4 mM DHA. Formic acid was subsequently purified using liquid-liquid extraction, employing the green solvent 2-methyltetrahydrofuran (2-MTHF). For the first time to our knowledge, a CCU strategy has been successfully coupled with industrial waste valorization, obtaining two high-value molecules by means of a robust, profitable, and easily manageable multienzymatic system.