Microbes pave way for green flight

Instead of burning biowaste, we should let microorganisms turn waste into CO2-neutral fuel, chemicals, and proteins.

Greta Thunberg will soon take to the skies on CO2-neutral fuel—just one of many good pieces of news from a green transition that is well underway. This is the message from one of the frontrunners in the bioeconomy.

“Soon bacteria, yeast, and fungi will become the factories that produce not only fuel, but also a wide range of chemicals, plastics, and even proteins,” says Professor Irini Angelidaki, DTU Environment.

An important realization in the bioeconomy is that the idea of replacing fossil products directly with bioproducts with the same properties is outdated. For decades, attempts have been made to replace petrol and diesel with various biofuels, and each on each occasion biofuels have been shown to be disproportionately expensive. That is why researchers have begun to turn everything upside down: it is now a question of deriving maximum value from the individual biological raw material. Since biofuel must ‘simply’ be burned off, it should not be the main product, but rather a by-product from the production of other higher value products.

The research team at DTU Environment has previously developed a technology with Nordzucker which has sugar factories in Denmark and throughout Northern Europe. The company was already working on using sugar beet plant waste to produce bioethanol. The researchers analysed the processes and were able to demonstrate that the company could use the same raw material and essentially the same plants to produce succinic acid instead. Among other things, succinic acid is used as a softener in the production of paints, polymers, and cosmetics. Currently, the starting point is predominantly crude oil.

“Succinic acid has a significantly higher market value compared to ethanol. As a result, the operating economy of reprocessing has increased significantly,” says Irini Angelidaki, adding that the example shows the importance of combining technical developments with economic analysis:

“We can’t rely on subsidies. The new solutions must be competitive.”

The technology is patented—and in a new EU-funded project—DTU Environment, in cooperation with the Spanish partners Norvento and IVEM, will bring the technology to market.

CO2 as useful raw material

Producing aviation fuel from biomass will require a number of steps.

“Currently, we have a large production of biogas. Instead of burning the gas to get electricity and heat, it can be upgraded to methane by removing CO2 (from the biogas, ed.). Methane can be used directly in the natural gas grid, but it can also be processed into methanol. Furthermore, catalytic methods exist to produce aviation fuel from methanol,” explains Irini Angelidaki.

Admittedly, planes will emit CO2 when the fuel is burned, but this CO2 is in turn captured by plants and bacteria earlier in the process.

“Protecting the climate is an important argument for the bioeconomy. Unlike the use of fossil fuels which simply lead to higher CO2 emissions, we recirculate CO2 through plants and microorganisms.”

The climate is the starting point for long-term cooperation between the City of Copenhagen and DTU Environment. The municipality is working to become CO2 neutral by 2025. It is impossible to make all activities CO2 neutral, so if you want to be CO2 neutral overall, you have to establish activities that capture CO2. The answer is not to pump this CO2 underground, says Irini Angelidaki:

“CO2 storage may make sense in some countries, but I don’t think it will be an appropriate solution for Denmark. We actually need CO2 as a raw material in the bioeconomy!”

Utilizing CO2 is precisely the purpose of the research eFuel project. Here we are trying to use excess CO2 from biogas plants to produce methane which can be used as a raw material in future production—e.g. in fossil-free, liquid fuels. The project is supported by the Energy Technology Development and Demonstration Programme. Irini Angelidaki and her colleagues from DTU Environment are participating in the programme and cooperating with the companies Nature Energy and Biogasclean—as well as the University of Southern Denmark and several others.

Bacteria and catalysis can be combined

The bioeconomy has only just started in earnest, stresses Irini Angelidaki:

“It’s not entirely clear which products will prove to be the best to produce from residual biomass. Moreover, there’s no guarantee that production in microorganisms will be the best way in all cases—for example, there are also many ways of converting biomass using thermochemical catalysis, which other researchers at DTU are interested in. Here, researchers have a head start and have achieved high efficiency in a number of processes.”

Both approaches have pros and cons.

“While thermochemical catalysis has high efficiency, it requires high temperature and therefore the supply of a significant amount of energy. Production in microorganisms is typically carried out at room temperature and is thus more energy efficient. A further advantage is that the microorganisms thrive in water. This means that we can exploit slurry, wastewater, and other wet fractions directly, thus avoiding energy consumption for initial drying which is inherent in thermochemical catalysis.”

In other words, it is not either-or, concludes Irini Angelidaki:

“I can easily imagine that it would make sense to use different methods for different steps—e.g. microorganisms handle the initial degradation of biomass and also some of the later stages—while the final conversion of methanol into an aviation fuel could perhaps be done by catalysis. So exactly what methods we are going to use remains to be seen, but Greta Thunberg will take to the air on 2nd-generation biofuels. Of that there’s no doubt!”

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