Enhanced sequestration of carbon dioxide into calcium carbonate using pressure and a carbonic anhydrase from alkaliphilic Coleofasciculus chthonoplastes

CO2 in the atmosphere is a major contributor to global warming but at the same time it has the potential to be a carbon source for advanced biomanufacturing. To utilize CO2, carbonic anhydrase has been identified as a key enzyme. Furthermore, attempts have been made to accelerate the sequestration via pressure. This study aims to combine both approaches to achieve high sequestration rates. The carbonic anhydrase of the alkaliphilic cyanobacterium Coleofasciculus chthonoplastes (cahB1) and bovine carbonic anhydrase (BCA) are introduced into a high-pressure reactor to catalyze the hydration of CO2 at up to 20 bar. The reactor is filled with a CaCl2 solution. Due to the presence of Ca2+, the hydrated CO2 precipitates as CaCO3. The impact of the carbonic anhydrase is clearly visible at all pressures tested. At ambient pressure a CO2 sequestration rate of 243.68 kg(CaCO3)/m(3) h for cahB1 was achieved compared to 150.41 kg(CaCO3)/m(3) h without enzymes. At 20 bar the rates were 2682.88 and 2267.88 kg(CaCO3)/m(3) h, respectively. The study shows the benefit of a combined CO2 sequestration process. To examinate the influence of the enzymes on the product formation, the precipitated CaCO3 was analyzed regarding the crystalline phase and morphology. An interchange of the crystalline phase from vaterite to calcite was observed and discussed.