A new device which costs just £20 could transform agriculture in remote areas, according to its inventors.
The device makes fertiliser by treating water with ultrasound thanks to work done by chemists and engineers at the University of Glasgow.
They found a way to produce molecules of nitrate using just sound waves, water and air.
The prototype process could be scaled up to enable individual farmers to make their own fertilisers on demand in the future.
That would help reduce the carbon footprint in the sector, which currently relies on complex, expensive and fossil-fuel driven factories for large-scale production of fertilisers like ammonia.
The Haber-Bosch process, which drives most industrial ammonia production, creates around 2% of the world’s annual carbon emissions.
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In a new paper in the in the Cell Reports Physical Science journal, the team explained how they build on a century-old discovery to turn the nitrogen from the air we breathe into nitrate.
It involves bubbling air through deionised water to dissolve nitrogen and oxygen and then uses focused waves of ultrasound to produce tiny bubbles in the water.
The bubbles then heat up and can reach temperatures of 5000°C – as hot as the surface of the sun – during repeated ultrasound pressure-driven implosions. The extreme conditions inside the bubbles break apart nitrogen molecules and fuse them with oxygen, ultimately producing molecules of nitrate.
Professor Mark Symes of the University of Glasgow’s School of Chemistry is one of the paper’s corresponding authors. He said: “Currently, the world relies on factories which can cost hundreds of millions of pounds each to produce vast quantities of fertiliser.
“They have helped feed the world and grow the global population over the past 100 years, but we wanted to explore whether we could make something that produces one farmer's needs for as little capital outlay as possible.
“We’ve been able to show that you can produce nitrates from air and water in a very cheap and simple device using nothing but sound waves. Our hope is that this could lead to a significant decentralisation of fertiliser production, allowing farmers in the developing world to feed their crops by pressing a button and letting ultrasound do the rest.”
Professor Symes tasked his colleague Dr Lukman Yusuf, the paper’s lead author, with building a working nitrate production system as cheaply as possible with off-the-shelf components. Dr Yusuf managed to build a working demonstrator, around the size of a can of coffee beans, for about £20.
Professor Symes added: “The basics of the process we’re using here were first identified in the 1930s, and returned to occasionally in the decades since, but never widely adopted as a method of fixing nitrogen from air.
“Advances in affordable ultrasound technology have opened up new opportunities in sonochemistry – using sound waves to drive chemical reactions – in recent years. Our results constitute a step-change in the effectiveness of sonochemical nitrate production, suggesting that this is an idea whose time has finally come.”
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The team acknowledge that their prototype currently uses proportionately more energy than the Haber-Bosch process, and that further study is required to demonstrate that the nitrate it produces can be used effectively to grow plants.
“Our plan is to spend the next 12 months working intensively to refine the process we’ve pioneered, and reduce the amount of energy it requires,” said Dr Paul Prentice of the University of Glasgow’s James Watt School of Engineering, the paper’s other corresponding author.
“Our paper describes how we’ve managed to produce batches of nitrate one at a time with a pulsing protocol optimised for the reactor system. We’re now working towards building improved prototypes capable of producing nitrate continuously at higher concentrations, making the process more useful for real-world applications.
“We’re also looking to determine just how effective the nitrate we produce will be in helping plants grow, which will help guide our path to commercialising a device for use in the real world in the years to come.”
