Industrial decarbonization is essential to achieving climate and net-zero emissions goals, with Carbon Capture and Storage (CCS) one the key strategies to handle on-site emissions. From 2045, Sweden aims negative goal emissions, which makes even more relevant the fast development of strategies on permanent carbon storage processes. The Swedish forestry industry, in particular the pulp and paper sector, tops among the largest players in the world. Nevertheless, it produces yearly hundreds of thousands of tons of by-product, such as lime mud, green liquor sludge and lime grits which landfilled, bringing both economic and environmental costs.

The aim of this work was to explore the potential of enzymatic routes combined with residues from the paper-making industry for carbon dioxide capture, and to assess carbon storage using CO2-rich media and relevant minerals within Sweden. Carbonic anhydrase (CA), an ubiquitous enzyme that catalyzes CO2 hydration, was used to evaluate its enhancement effect on CO2 capture. Four distinct residues tested with DvCA8.0 lysate showed a CA-boosting effect on CO2-equivalent capture of up to 4-fold under open-air conditions and 2.2-fold in CO2-rich experiments, reaching concentrations of up to 0.5 g/L and 0.74g/L, respectively. Element leaching, particularly Ca2+ and Mg2+, positively correlated with CA addition, likely due to enzyme-enhanced H+ production promoting the dissolution of residue components such as CaCO3 and MgO, further demonstrating the compatibility of CA with the tested materials.

Despite their high specificity, enzymes are sensitive and costly to produce, posing challenges for large-scale applications. To address this issue, DvCA8.0 was immobilized on nanomagnetic particles to improve stability, enhance productivity, and enable biocatalyst recycling. CO2 capture experiments with lime mud (0.4%) showed that the immobilized enzyme remained active for up to ten consecutive cycles, exhibiting productivity 2.4 times higher than the free enzyme, highlighting the potential of the CA immobilization strategy.

System optimization was followed using lime mud. Variables such as gas flowrate, residue concentration, CA lysate load and type, and time were assessed to identify the most suitable condition for both increasing carbon capture and CA-effect. Tests were firstly conducted in a continuous flow and ambient pressure mode, and showed a CA

enhancement of up to 70% higher when compared to non-catalyzed conditions. At optimized conditions, a total of 5.1 g/L of bicarbonate was measured in the supernatant, with CA-boosting effect of 1.4-fold. Later, tests under distinct CO2 partial pressures and temperatures were performed to evaluate kinetics of CO2 capture for both enzyme and non-enzyme assisted systems, which led to an increase on the rate of CO2 uptake in 2-fold (40 °C and 14 bar). Other four enzymes were tested, and ApCA, a carbonic anhydrase from Aeribacillus pallidus, showed the best performance, with a enhancement of 4-fold when compared to non-CA added systems. Finally, a multicycle experiment was performed and revealed a CO2 uptake of 10.3 g/L in the CA presence.

In addition, the carbon storage potential of different minerals was evaluated. Batch tests with olivine and bicarbonate-rich solutions showed a modest 6.9% increase in mineral carbonation with DvCA8.0, likely limited by the low bicarbonate concentration and mildly acidic pH. Finally, 10-bar CO2 batch experiments with Swedish rock samples confirmed carbon storage in stable carbonate forms, such as Ca- and Fe-carbonate forms, demonstrating the feasibility of coupling enzymatic CO2 capture with long-term mineral storage in integrated CCS processes for Sweden.