Bioconversion of carbon dioxide – from greenhouse gas to valuable resource


An article by Dr Martin Langer, BRAIN AG

When we talk about climate change, we are also talking about harmful greenhouse gases. One of these is carbon dioxide (CO2). With approx. 35 billion tons emitted each year, it currently accounts for the lion’s share of greenhouse gas emissions, and its proportion in the atmosphere has risen since the start of industrialisation from roughly 280 ppm (parts per million) to 410 ppm today. A waste product generated during the combustion of fossil fuels, CO2 has a proven impact on the climate and is considered one of the primary causes of global warming. To keep the effects of climate change at a more or less manageable level, climate researchers believe that global warming will need to be limited to an annual average of +1.5°C. Biotechnology can contribute to achieving climate goals, for example by capturing CO2 and using it in a sustainable way – making biotechnology an effective instrument on the path towards a sustainable economy, a bioeconomy.

So what can we do about the surplus CO2? Above all, we must all try to reduce carbon emissions in the first place! Yet we are not currently able to run our transport systems, operate our industries or heat our private households entirely without CO2 emissions – in short, life as we know and love it would not be possible without them. So what we need to do is capture those CO2 emissions that are still unavoidable and make sure that they are not released into the atmosphere where they can do further damage. A crazy idea? Not at all – and many efforts are already being made to use gaseous CO2 as a resource and to incorporate it into a new solid or indeed liquid substance.

Here are a few pertinent examples: Evonik and Siemens are converting CO2. The polymer manufacturer Covestro is using carbon dioxide to produce the polyols that are needed in soft polyurethane foam – which forms the basis for mattresses, for instance. The Swiss start-up Climeworks is working on capturing CO2 from the atmosphere so it can then be used to grow plants or produce carbon-neutral fuels.

Microorganisms become production specialists

What role does biotechnology play in this context? How can it help us extract the gaseous compound that is CO2, or indeed the pure element that is carbon (C), from industrial waste streams – e.g. from flue gases – and use it as a resource? Biotechnology is all about using living organisms such as microorganisms, algae or plant cells, taking advantage of their ability to metabolise one substance into another.

One example is the pure CO2 that is generated during the production of bioethanol: researchers at BRAIN AG are working together with the company Südzucker AG on a BMBF-funded cooperation project (Zero Carbon Foot Print, ZeroCarbFP). They have been looking in a wide range of sources and industrial facilities for microorganisms that use CO2 as the sole source of carbon in their metabolic processes.

And indeed they did find, among the thousands of microorganisms they studied, some that use CO2 to produce substances that could serve as the building blocks for chemical compounds. The team had been confident of finding what they were looking for, as the ratio of oxygen to CO2 on Earth roughly one billion years ago (0.5% oxygen and approx. 20% CO2) was almost exactly the opposite to what it is now. And at that time the only life on our planet was microorganisms that thrived under precisely such conditions.

After studying the metabolic processes of these bacteria, and many other of their properties, the next step involved getting the microorganisms to metabolise CO2 more efficiently, and above all more quickly. To this end, those involved in the project used biotechnological tools – turning normal CO2 consumers into super CO2 consumers. Currently, the Südzucker project is in its third funding phase, which is the pilot phase.

Energy from hydrogen for energy-free CO2

CO2 has so far been described as the end of the carbon cycle, and as a fully oxidised molecule is regarded as “energetically dead”, making any further reaction impossible. The greatest challenge for the researchers, therefore, was to find an energy source that could restore the CO2 to a reduced (energetically useable) state. To this end, they conducted experiments with sulphur, copper and, most recently, hydrogen. The latter was determined to be the best energy source. (It can be obtained by electrolysing water – a process that can be performed cost-effectively using for example solar or wind power in what is known as an electrolyser.)

In biotechnological applications, the microorganisms that use the CO2 quantitatively metabolise the carbon from the CO2 to form an organic intermediate compound that is needed as a building block for further compounds in the chemicals industry, for example. This building block can now be used as a substitute for those previously obtained from fossil resources such as petroleum. Use of these microorganisms thus creates a kind of “bio-refinery” for various methods of producing a large number of substances. The new biotechnological processes have therefore boosted the trend in the chemicals industry towards using biobased building blocks.

Adding value on the basis of biological resources and renewable energies – the use of CO2 from industrial waste streams, as described in this article, is thus in line with the principle of the bioeconomy.

Further information