Green technology

The microorganisms that eat CO2 and spit out green energy

A DTU team has developed a unique bioreactor that uses microorganisms to convert CO2 into methane, which can be used as biogas and biofuels in the green transition.

Hariklia Gavala from DTU Chemical Engineering has many years of experience in gas fermentation research. Photo: Bax Lindhardt


Electricity, heat and fuels for buses

The great strength of the bioreactor is that it can be used in many different contexts. The methane output can be converted into electricity and heat in a gas turbine and thus replace the use of fossil natural gas. The Danish Energy Agency expects biogas to make up 70% of Danish gas consumption in 2030 compared to just 20% in 2021.

Biogas typically only has a methane content of 45-75% whereas the rest is primarily CO2 but since the methane holds the energy, the biogas must be upgraded by cleansing the CO2 before using it in the gas grid. Most times, the upgrading process simply releases the COto the atmosphere. The bioreactor valorizes almost all the carbon and converts it to pure methane and that also makes the costly upgrading process redundant.

"We have produced methane of a grade that can be used directly in the gas grid," says Hariklia Gavala.

Both methane and ethanol can be used in biofuel. In Sweden – which is one of the EU countries that invests most heavily in biofuels for the public transport sector – a large proportion of buses run on fuels produced from food waste, wastewater and residual products from the paper and forest industries. But conventional bioreactors only extract a limited part of the energy in the biomass, and DTU Chemical Engineering’s bioreactor is far more efficient.

"We can make better use of all types of biomasses, including biomasses that cannot easily be converted into methane in biogas plants. Also, industries that generate off-gases, such as heat and power plants, cement plants, and the steel industry will be able to implement this technology and turn the gas into something useful,” says Hariklia Gavala.

Produces 40 times as much microalgae

Hariklia Gavala and her colleagues have already tested the bioreactor on a scale 35 times bigger than in the lab and proven that the process can work on an industrial scale, and this has gotten several companies intrigued.

Hariklia Gavala has had preliminary talks with Danish companies and the Greek business Solmeyea has also seen great potential in the bioreactor – they’ve already reached an agreement with DTU to use it commercially. Solmeyea manufactures microalgae, which are single-celled algae that use photosynthesis to consume CO2 and produce a range of useful bio products from plant-based foods to biofuels.

So far, they’ve grown microalgae in a way similar to crops by placing the algae in water in large glass vessels where the sunlight makes them multiply. By utilizing DTU Chemical Engineering’s bioreactor they are now able to grow the microalgae much more efficiently – 40 times more microalgae than in conventional production. Another benefit is that the bioreactor takes up much less space than the large glass vessels.

“This bioreactor is a very robust way of getting the microalgae to eat CO2. The productivity is much better, they occupy less space, and the process is not dependent on the sun shining,” says Diego Grumbach, biotechnology engineer at Solmeyea.

For now, the algae are producing lipids which can be used in plant-based foods as alternatives to meat, fish and eggs, but the long-term plan is for the algae to also produce biofuels and bioplastics. Solmeyea has already started a demo plant where they will use the bioreactor.

"The potential is even larger in biofuels than in food. Many biofuels are produced from crops which competes with the food sector, so we need to find a better way of producing biofuels. That's what the microalgae offer," says Diego Grumbach.


The bioreactor was developed at DTU Chemical Engineering by Associate Professors Hariklia Gavala and Ioannis Skiadas and their co-workers. It is the result of a broad collaboration across several fields such as biotechnology, kinetics, reactor engineering and thermodynamics to name a few.

Research and development of the bioreactor has been funded by the Innovation Fund Denmark and supported by the participation of several industrial partners. There are multiple ongoing research projects related to the bioreactor, funded by DTU, Novo Nordisk Foundation and the EU’s European Innovation Council.


Hariklia N. Gavala

Hariklia N. Gavala Associate Professor Department of Chemical and Biochemical Engineering Phone: +45 45256196 Mobile: +45 21171323