Harnessing waste gases to create value

Waste gases are usually the end of the story. But at UQ’s Biosustainability Hub, they are the beginning of something valuable.

Microbes already exist that can consume carbon dioxide and survive in extreme conditions – traits that make them promising tools for transforming waste gases into valuable products.

Dr Lars Puiman and Dr James Heffernan from AIBN are using gas fermentation to harness and boost these natural assets and then partnering with industry to scale them up and test them in real-world environments.

“I’m motivated by the variety of useful products we can make – and seeing the waste gases as an opportunity rather than a problem to be managed,” Dr Heffernan said.

Plastics, proteins and fuels

In the controlled environment of specialised biofermenters, microbes can produce proteins, biodegradable plastics, precursors for fuels and rubber, and chemicals.

In bread and beer making, yeast feeds on sugar during fermentation process. Here, the researchers are using bacteria that feed off gases such as carbon dioxide, carbon monoxide and methane, which can come from organic waste like food and farm waste (biogas) or industrial processes (syngas).

“Microorganisms that exist in nature, they’re already good at performing the processes we’re interested in,” Dr Heffernan said.

Biological flexibility

Microbes can thrive where chemistry struggles, which is a key advantage of gas fermentation compared to conventional manufacturing. Their biological flexibility means they can often tolerate impurities that would quickly disrupt catalysts used in conventional chemical processes.

Just like we take the oxygen we need from the air when we breathe, microbes are well suited to take what gas they need from real-world waste streams that are rarely pure.

“Hydrogen sulphide is an example of a small impurity often found in waste gases that rapidly destroys catalysts – in contrast, microbes often tolerate or can use these trace contaminants’,” Dr Heffernan said.

“With a bioreactor you don't need to worry about a ‘dirty’ gas.”

“This flexibility enables us to use the gas at the source. For example, bioreactors can be located onsite, next to steel mills, refuse or sewerage processing plants to convert their waste gases into byproducts with minimal steps.”

Fine-tuning, not reinventing

While genetic modification can be used to improve product yields, that is only part of the story.

Researchers are working with organisms that have evolved over millennia with useful natural abilities that can be optimised for industrial conditions.

“There are vast numbers of organisms in our soil and water that feed on gases – we use strains which were isolated decades ago for their smart and well-established properties,” Dr Heffernan said.

“Typically, the native version already performs well in our process but we can use genetic engineering to increase resilience, optimise yields or make non-native products.”

The challenge of scale

For Dr Puiman, the promise of gas fermentation lies not just in what it can make, but in the challenge of making those products viable at industrial scale.

“We use gases that are cheap and we also produce products that have to compete with rival established industries, including those that benefit from subsidies,” Dr Puiman said.

“To succeed, we need to make sure that our processes are of the highest efficiency, cost efficient and commercially relevant.”

One of the biggest technical challenges is delivering gases efficiently to the microbes. Because the microorganisms grow in liquid while their food is supplied as gas, researchers need to design systems that maximise contact between the two – and do so in a way that remains efficient, affordable and scalable for industry.

Those challenges are significant, but so is the potential, as demonstrated by the ‘origin story’ of gas fermentation at the Biosustainability Hub. In 2012, LanzaTech came to AIBN with a bold idea to use microbes to convert industrial waste gases into fuels and chemicals.

Case study #1 – Sustainable aviation fuel

Together, the Biosustainability Hub and LanzaTech offer a powerful demonstration of how investing in a sustained research-industry collaboration can deliver enduring value for people, industry and the planet.

Professor Esteban Marcellin, now director of the Biosustainability Hub, recalls when he and Professor Lars Nielsen were approached by LanzaTech.

“They wanted us to build a mathematical model to understand the microbes’ metabolism that turns carbon emissions into ethanol,” he said.

The researchers contributed expertise in systems biology, metabolic engineering and synthetic biology at a formative stage of the company’s development.

They worked alongside LanzaTech scientists to understand how the anaerobic gas fermenting microbes Clostridium autoethanogenum functioned at a fundamental level.

Waste gases are captured from industrial sources and are metabolised by C. autoethanogenum in situ, for example at steel mills or oil refineries.

This close collaboration has now translated into LanzaTech’s commercial-scale gas fermentation capabilities generating thousands of tons per year of fuel-grade ethanol, used to power cars or planes.

The technology has been licenced to multiple companies and is now deployed at an industrial scale across multiple continents.

Case study #2 – Food for fish

The case for a more sustainable alternative for fishmeal in fish farming is strong.

Fishmeal is often made from wild-caught fish, placing pressure on marine ecosystems and relying on long, emission-intensive supply chains.

The researchers use carbon dioxide and methane derived from anaerobic digestion of organic waste streams to grow microbial cells.

The cells themselves are the product.

Once harvested called ‘single-cell protein’ – a protein-rich biomass which could replace the fishmeal and reduce overfishing.

Using both gases simultaneously

At the Biosustainability Hub, the researchers have patented a method for an integrated system where different microbes work together to consume both methane and carbon dioxide.

This makes the system more adaptable to using naturally occurring biogas from green waste and sets it apart from competitors working with single gases.

“By co-culturing two organisms in the one reactor to do the jobs together, we have the best of both worlds – both methane and CO₂ are consumed,” Dr Puiman said.

Big protein boost

Single-cell proteins currently on the market for humans include yeast flakes, and Quorn mycoprotein – a meat substitute, made by fermentation of the fungi Fusarium venenatum.

And the researchers believe a high-quality version of their protein could one day be used in human food, with applications in cattle feed and pet food coming sooner.

“Farm-grown soy protein is a competitor, but gas fermentation is much more efficient.

"The cells we grow are 75 per cent protein, use less water and minimal land so you get a thousand-fold more protein per square metre,” said Dr Puiman.

“Our process just needs proximity to a gas source, so farms could be an ideal setting where food or agricultural waste is used to generate biogas.”

Testing it out

The researchers have patented their lab-scale process for producing fish protein and are now looking for investment to help take the technology further.

“The next step is to scale up production so we can make enough fish feed to test how the fish grow after eating it.”

Case study #3 – Bioplastics

Making bioplastics with gas fermentation is a new frontier.

Bioplastics are already made using biofermentation but using sugars as the food. The most successful bioplastic on the market is arguably PLA - polylactic acid, used for 3D printing.

“More recently, people have started to think we could also produce plastic from waste gases, not just from sugar – there’s a big potential there,” Dr Puiman said.

Under certain conditions, bacteria such as Cupriavidus necator can be encouraged to make a biodegradable plastic called polyhydroxybutyrate (PHB).

“When you limit certain nutrients, the bacteria go into hibernation mode and naturally make PHB granules in the cell as an energy reserve,” Dr Puiman said.

“There are really high yields as the bacterial produces it as 80 – 90 per cent of its body weight, our technical challenge is extracting it.”

Unlike petroleum-based plastics, PHB-based bioplastics break down naturally and safely in the environment, so when we use waste gases to make it, the circular process is complete.”

The future – scaling up and testing

Both researchers agree that the future requires competitive processes, with academia and industry working together.

“To make it really happen, we need to unify all sources of knowledge, then have access to more pilot facilities to prove these technologies can work at scale.”

With the right partnerships and pilot facilities, these tiny microbes could be the biological solution to some of the world’s toughest environmental challenges.

The UQ Biosustainability Hub uses synthetic biology to help the world’s biggest businesses transition to net zero.

Funded by government, industry and UQ, the $70 million Biosustainability Hub is a one-stop-shop for big companies to transform their production practices and create carbon neutral economically viable products and materials.