Hari Gavala points to a cigar-shaped steel cylinder that is a few meters high and sits behind a glass window in her lab at DTU Chemical Engineering. The cylinder is a bioreactor housing millions, if not billions, of loyal 'employees', that can only be seen by the naked eye when they are lumped together. These microorganisms are the invisible heroes that can convert CO2 and syngas into methane, ethanol, or organic acids, which are building blocks that can be used to produce more sustainable alternatives to anything from fuels to chemicals, plastics and food.
"The process is not much different from brewing beer at a microscopic level, but the potential is enormous for the green transition," says Hari Gavala, associate professor at DTU Chemical Engineering.
Close to full utilization
The inside of the bioreactor is coated with pieces of plastic, which provides a large amount of surface on which the microbes can grow. When you add syngas or CO2 in gaseous form, the microorganisms begin to eat away and convert it into methane through fermentation.
Syngas consists of CO2, hydrogen and carbon monoxide and is produced by gasifying biomass such as wood, straw or organic solid waste such as wastewater or food waste. But syngas cannot be used directly as a fuel in the transport sector, nor can it be used directly in the gas grid as the energy content is too low. So there is great benefit in using the microbes to convert it into methane.
"When we produce methane, close to 100% of the CO2 or syngas is converted into methane, and the production rate is ten times higher than in a conventional biogas plant," says Hari Gavala.
By using different types of microorganisms, you can control what the CO2 will be converted into, and even though Hari Gavala sees enormous potential in methane, it can also be used to produce ethanol or organic acids.
Whereas conventional bioreactors require higher pressure to ensure that the gas molecules move to the liquid where the microorganisms reside, DTU Chemical Engineering's bioreactor is designed to operate under regular atmospheric pressure, making it cheaper and safer to operate.
