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Good bacteria: Why sustainability engineers are turning to microbes

Joseph Flaig

From making vegan leather and lighter materials to eating plastic and generating electricity, armies of bacteria are helping engineers in the fight for a more sustainable future (Credit: Shutterstock)
From making vegan leather and lighter materials to eating plastic and generating electricity, armies of bacteria are helping engineers in the fight for a more sustainable future (Credit: Shutterstock)

Humanity’s fingerprints on our planet are increasingly hard to ignore.

Microplastics are everywhere, from fresh Antarctic snow to every human placenta tested in a trial. Greenhouse gases continue to build up at frightening rates, as we live through what some have called the Anthropocene.

We have some solutions to these issues – but those solutions often have their own issues. Mining metals for electric vehicle (EV) batteries, for example, often causes environmental degradation. We need to make the most of available materials to prevent unnecessary damage to the planet.

“Minimising waste and maximising resource reuse are crucial, particularly in sectors such as construction and electronics, due to their significant environmental impact,” says Dr Adenike Akinsemolu, sustainability researcher and honorary associate professor at the University of Birmingham.

To tackle these challenges, an increasing number of engineers are turning to bacteria. Like the microorganisms that play a vital role regulating our health, engineered bacteria could help heal the environment by making manufacturing processes cleaner, boosting recycling rates, and tackling pollution.

From making vegan leather and lighter materials to eating plastic and generating electricity, armies of bacteria are helping engineers in the fight for a more sustainable future. For some projects, the question now is how far they might go.

Charging up EV recycling

In Edinburgh, bacteria are hard at work extracting valuable metals from a used Nissan Leaf battery. If successfully scaled up, researchers at the University of Edinburgh say the method could feed into a “new UK-based supply chain for rechargeable vehicle batteries”, reducing reliance on mining and importing raw cobalt, manganese, nickel, and lithium.

“If we're going to spend all those resources, all that energy, digging the metals out of the ground, we have to keep using them. That's basically the difference between this petrochemical dependent society and a metal dependent society,” says research leader Professor Louise Horsfall.

“Unfortunately, at the moment, all the green technologies that we've come up with seem to depend on the same metals. They have become particularly critical for this green transition, so they're becoming more competitive to access, and they are becoming more valuable.”

Using a fermenter, bacteria are added to battery leachate – the liquid that remains after the initial processing stages – to simulate a natural biological reaction. During the process, the bacteria produce nano-sized particles of the metallic compounds, resulting in a sediment that can be separated and filtered out from the residual liquid.

The process is based on new genetic technologies able to sequence huge numbers of extremophiles, combined with the ability to synthesize DNA, says Professor Horsfall.

A recent lifecycle assessment on the recovered manganese found that the biological method had a carbon footprint 100-times lower than chemical methods. The assessment, carried out by collaborators at the University of Leicester, also found the method had lower water usage.

Self-healing concrete

Instead of reusing materials, some engineers are using bacteria to prevent the use of new materials – and their associated emissions. A team at Drexel University in Pennsylvania aims to achieve that with BioFiber, a new material that could heal cracks in concrete to extend its lifetime.

The network of polymer fibres is encased in a bacteria-laden hydrogel, surrounded by an impermeable polymer shell coating. Activation happens when the shell is broken by cracking and deformation in the concrete, which releases the bacteria to ‘seal and heal’ the crack by producing calcium carbonate.  

The brittleness and flexibility of the coating will be tuned for different applications to ensure the bacteria are not prematurely released, says Mohammad Houshmand, lead author of the work. BioFiber will be used in pavements and bridge decks at first, he adds, as residential buildings have different performance requirements.

“There’s a saying that we have two types of concrete – cracked concrete, and concrete that’s about to crack. Whatever type of concrete and material that you want to use, it's going to crack at some point,” Houshmand says.

BioFiber could extend the lifetime of structures, making other repairs unnecessary. It could also prevent disruptions to traffic and the environment from road closures, Houshmand added.

The researchers are now incorporating the product into concrete for structural testing, analysing the healing timeframe and recovery strengths afterwards. The work is on a lab scale for now, but the team hopes to get funding to boost the scale of production and apply it in larger structures.

Carbon recycling

Bacteria are also converting waste into useful materials, such as in a project at the University of Nottingham where bacteria are turning textile, greenhouse and microplastic waste into acrylic molecules, which can then be mixed with other monomers to create polymers. Those recycled materials could then have an unlikely second life as additively-manufactured parts in medical devices.

The Materi-8 project team, funded by the Federal Agency for Disruptive Innovation in Germany, aim to build a ‘containerised’ system that could be used around the world, including in countries that receive waste from elsewhere.

Some projects are even directly targeting emissions with bacteria. LanzaTech in Illinois, for example, uses bacteria in a ‘carbon recycling’ process that converts plant emissions into fuels and other chemicals. The company’s products include sustainable aviation fuel (SAF) and polyethylene for packaging. It has reportedly produced a proprietary strain at scale, which can produce isopropyl alcohol for production of polypropylene.  

‘Vast opportunities’

“The opportunities to use bacteria to improve sustainability are vast,” says Dr Akinsemolu. “The versatility of microbes to adapt to different environmental conditions makes them particularly valuable.”

Scaling up is likely to be the biggest challenge for most projects however, with Professor Horsfall referencing a lack of facilities and a need for more collaboration.

Many microbial technologies demonstrate promising results in controlled, small-scale experiments but face hurdles in maintaining efficiency and effectiveness at larger scales, adds Dr Akinsemolu. Other challenges include economic viability and studying their long-term environmental impact.

Read the full Q&A with Dr Adenike Akinsemolu.

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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.

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