Enzyme-based carbon capture: as easy as breathing

Over the past few years, the impact of the climate crisis has never been far from the front pages. From wildfires in Hawaii to flooding in Libya, 2023 has been dubbed the ‘worst year on record’ for climate disasters. The COP28 climate conference taking place in Dubai this month will take stock of the world’s progress in tackling climate change and will once again attempt to design a roadmap to achieving global carbon ‘net zero’.

While reducing our reliance on fossil fuels should remain a priority for ‘net zero’ goals, current renewable energy sources are not yet able to keep up with demand, and likely won’t be for at least a few decades. While we wait for this gap to be filled, we remain reliant on fossil fuels.

If we keep up the current rate of fossil fuel usage for another 20 years, we lose any chance of curbing global warming to even 2°C (a critical threshold for avoiding catastrophic climate consequences). Therefore, while finding long-term renewable energy sources remains important, we also need to deal with the reality of our continuing fossil fuel usage and implement practicable solutions to reduce their impact on the climate.

Expansion of carbon capture and storage (CCS) facilities is included in all major forecasts for how we will achieve ‘net zero’. At least 36 CCS projects are currently in operation globally, with 18 under construction and another 206 in development.

Traditional CCS methods use an amine-based solvent, most commonly monoethalolamine, to separate CO2 from flue gas after the fuel is burnt. The CO2-rich solvent is then heated to release the CO2 and regenerate the solvent. The released CO2 can then be stored, to prevent its release into the atmosphere.

These traditional CCS methods have been employed and optimised for decades. However, they still possess several drawbacks including reliance on environmentally harmful solvents, and a need to purify flue gases before separating CO2. The biggest problem, however, is cost. Current CCS systems are extremely expensive to deploy, and highly energy intensive to run.

If we want to successfully scale-up our carbon capture capabilities, then innovation in this area is crucial. As with many technological problems, nature may offer a solution.

Our natural ability to separate CO2 from the air around us as we breathe is something we take for granted every moment of the day. The secret to our ability to do this is an enzyme called carbonic anhydrase. Carbonic anhydrase is a highly efficient enzyme that converts CO2 into bicarbonate (HCO3-), which can be safely transported around the body, and then back into CO2 in our lungs to be exhaled.

The theoretical possibility of engineering naturally occurring carbonic anhydrase for use in capturing carbon from industrial processes has been recognised for a couple of decades, with patent applications dating back to the 1990s. However, recent innovation in the field of synthetic biology is turning this theory into reality.

Synthetic biology or “SynBio” refers to the design or construction of new biological entities, or the redesign of existing biological systems. SynBio approaches are widely applicable to modern day problems, and show promise in tackling climate change.

One of the major challenges with using carbonic anhydrase – or any enzymes – in industrial processes is thermo-sensitivity. Enzymes are very sensitive to temperature and work best within a very specific temperature range. For typical commercially available carbonic anhydrases, this temperature is around 37°C, meaning these enzymes are not stable at the high temperatures faced in industrial processes.

To overcome this, researchers have turned to bacterial extremophiles. In particular, they have looked to bacteria thriving in deep sea hydrothermal vents. These bacteria can grow at high temperatures (70°C and higher), making them a perfect starting point to develop industrially useful enzymes.

To further improve the thermostability and efficiency of carbonic anhydrase, directed evolution approaches have been employed. Directed evolution is an iterative process which aims to mimic natural selection. Proteins are subjected to multiple rounds of mutagenesis and selection, with the best variants being selected to continue to the next round. Using this approach, carbonic anhydrase enzymes have be engineered with significantly improved tolerance to temperature and pH, while retaining highly efficient CO2 conversion activity.

As a result of this research, engineering company Saipem have successfully developed a commercially available enzyme-based carbon capture technology: BluenzymeTM 200, marking a major milestone in the carbon-capture landscape. Based on technology developed by Canadian company CO2 Solutions Inc., and in partnership with biotech company Novozymes, BluenzymeTM 200 offers a ‘plug-and play’ carbon capture system, that is reported to be able to capture up to 200 tonnes of carbon per day.

It’s still early days in the development of enzymatic approaches for carbon capture, and as with any fledgling technology, significant investment and development will be essential to support scalability. Only time will tell whether carbonic anhydrase corners the carbon capture market, but with the pressure on to find solutions to our escalating climate problems, this natural carbon converting machine may offer a much-needed lifeline.