Bacteria Could Provide Cheap, Clean Hydrogen
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Record heatwaves across the northern hemisphere have renewed calls for action on climate change as it becomes apparent that we face unprecedented levels of global warming.
News of a renewable carbon-free energy source which can cheaply convert cane sugar into hydrogen with pure water as the only by-product, is a welcome breakthrough.
Bio-hydrogen production is in its infancy and in Macquarie University’s new synthetic biology innovation, the bacteria are not just the fastest hydrogen-producing microbes around, they are also happy to sit around with no food for months on end – then launch into action to produce on-demand energy.
“There’s already early interest from sites that use diesel generators, such as remote and island communities,” says Professor Robert Willows, a synthetic biologist in Macquarie University’s Department of Molecular Sciences.
The team is developing a prototype and early results suggest that the technology will be cheap to run, quiet and be very low-maintenance.
The genetic engineering of the microbes is partly funded by a $1.1 million grant from the Australian Government’s Renewable Energy Agency (ARENA) and supported by industry partners BOC Australia and Bioplatforms Australia.
The team is also exploring bio-solar cells – a way to make hydrogen using just water, sunlight and bacteria.
Hydrogen energy has received support from both sides of politics, with several states releasing roadmaps for a hydrogen future and chief scientist Alan Finkel considering it the country's next multibillion-dollar export opportunity.
How bio-hydrogen works
“This is renewable energy that uses a two-part system; first, the bacteria consume the sugar and as it digests the sugar it produces the hydrogen gas,” Willows explains.
“Then, we funnel that hydrogen gas into a hydrogen fuel cell which generates electricity.”
It is very common for a range of microorganisms, like bacteria and archaea, to produce gases such as methane as a side-effect of digesting their energy source. In fact, this methane is a potent greenhouse gas emission from agriculture and landfill. It is less well known that bacteria and algae also produce hydrogen and it is this process that Willows and his team have harnessed to produce the climate-benign and useful hydrogen gas.
Farming bacteria to produce hydrogen also has economic and environmental advantages – in the right setting, bacteria rapidly multiply, they are cheap to create and don’t need much space.
The University team has used genetic engineering approaches to change the DNA of certain strains of E. coli bacteria to produce hydrogen from sugars.
By accelerating the metabolism of the bacteria and finding the optimum conditions for production, they have produced a strain that makes hydrogen at rates higher than any previous published rates of bacterial bio-hydrogen.
Many bio-hydrogen developers are using algae to produce hydrogen but Willows says that bacteria have the advantage of much faster production and lower inputs – they also don’t require big ponds for cultivation.
The strain that the team has developed is also very stable, he adds. “We have bacteria that we made more than four months ago that are still producing hydrogen at the same rate,” he says. “They are not growing or dividing – this is exciting as all of the enzymes that are required within the bacterial cell seem to be stable for about three or four months, or possibly longer.”
Unlike ethanol – a fuel that must grow new yeast for each new batch – Macquarie’s bacterial hydrogen producers can keep brewing gas without a fresh biological agent added for each batch.
“We think we may need to regenerate the bacteria every six months or so,” Willows says.
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The technology has a range of applications, Willows says. His team have been part of the CSIRO ON program which helps focus ground-breaking research on outcomes to help target potential research and industry partners.
“We have a couple of models, one is a mobile cartridge which would feed sugar in to produce the hydrogen and then use that hydrogen directly to generate electricity,” he explains.
This model uses the bacteria to produce hydrogen in a demand-driven system. The bacteria produce a certain concentration of hydrogen, then stop, he explains. “This is so much safer because you don't have to store the hydrogen, you just have to make sure the sugar is supplied at the right speed.”
Why bacteria-produced hydrogen fuel cells are so exciting
Hydrogen fuel cells were invented nearly 50 years ago and are a reliable, clean and silent power source that works by splitting hydrogen atoms to produce an electric current and generating heat and water.
NASA space shuttles and the International Space Station are powered by hydrogen – but at present around 95 per cent of the world’s hydrogen is produced using fossil fuels.
There is huge interest globally in using hydrogen as a renewable energy fuel thanks to its high-efficiency production of on-demand zero-emission electricity.
Car manufacturers including Toyota, Hyundai and Honda all make hydrogen-fuelled vehicles, trucking companies Kenworth and Nikola are planning long-haul hydrogen-fuelled trucks, and Boeing and other aerospace companies are testing its use in jet engines.
Hydrogen gas would be an ideal power source for today’s world: except that it remains costly and difficult to transport or store. Most hydrogen is currently manufactured in processes powered by coal, oil or gas, so it is expensive and has a high carbon footprint.
Willows says that genetically-engineered bacteria can overcome these issues because they produce hydrogen on demand (overcoming the storage problem) from renewable raw materials like sugarcane.
Skipping sugar to make bio-solar energy
The team is also exploring a new concept: creating a bio-solar cell, where hydrogen can be created from just sunlight, water and bacteria.
“That’s our long-term vision: to create a biological system that harvests sunlight to supply the electrons to make hydrogen, rather than using sugars,” Willows explains.
Many bacteria species actually produce their own energy by photosynthesising sunlight, and scientists have attempted to harness photosynthetic algae and bacteria for their potential industrial hydrogen-making use for decades. But these species stop working long before they make a useful amount of hydrogen, and the challenges seemed insurmountable.
“Like plants, algae and bacteria grow under varied light conditions so they optimise photosynthesis to work somewhere in the middle,” Willows says.
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Photosynthetic organisms have evolved protective mechanisms to compete with other organisms across a range of conditions. Attempts to fiddle with the DNA of likely-looking bacteria and algae to push them harder has not resulted in any significant gains, Willows explains. “It’s very difficult to get them to do things because of the regulatory controls around their light harvesting and energy conversion systems.”
Willows and his colleague, Associate Professor Louise Brown, have approached the problem from a different angle.
Using recombinant DNA techniques, they have progressed a long way towards introducing chlorophyll (the pigment used by plants to convert sunlight into energy) into traditionally non-photosynthesising bacteria so they can use sunlight to produce their own energy.
The team used a strain of bacteria that doesn’t photosynthesise – specifically a strain of E.coli, a species favoured by synthetic biologists working to recombine DNA because it is so well studied.
“The advantage is we can bypass all of the normal limitations that evolution has imposed on photosynthetic organisms,” Willows says. “By isolating them where they're not competing with other organisms in the environment, they work really well as solar collectors, and then we can then use that energy to make hydrogen in a closed, sterile system.”
“A few years down the track, we think we can engineer bacteria that run on water and don’t even need the sugar – we could make solar cells that are just sealed collections of bacteria, which are really cheap to grow, to produce hydrogen gas,” he says.
For now, with just a couple of spoonfuls of sugar slipped into a two-litre tank of water-loving bacteria, the team’s bio-hydrogen cell can power a mobile phone for a couple of weeks.
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