New water purification device could help future-proof food supply

University of Canterbury researchers are hopeful a new device using solar energy to purify water more efficiently could revolutionise hydroponic farming and improve climate-resilient crops in the future.

The water treatment device, developed by a team of University of Canterbury (UC) researchers in collaboration with agriculture industry organisations, is unique as it automatically converts solar energy harnessed during sunny days into chemical energy that removes pollutants from water, which can then be used to grow plants in instead of soil.

The process of growing plants in water with some nutrients added instead of soil is known as hydroponics — and has become an increasingly important technology internationally as a way to grow food in an urban centres and environments protected from storms, pests and disease.

University of Canterbury chemical and process engineering professor Alex Yip told 1News that hydroponics technology could be used to "supply the food chain", but was reliant on the plants absorbing completely clean, toxin-free water.

"So the root of the plant doesn't actually contact with the soil, it only contacts with the water and the benefit of doing so is it then can absorbs the nutrients very quickly and efficiently," he said.

"With a closed system with recirculating water, it is very important to keep the water clean, especially from emerging micropollutants, which is what we are targeting with our new device. These micropollutants include pesticides, endocrine-disrupting chemicals and long-lasting pollutants."

He said while using solar energy to trigger a chemical reaction has been widely researched around the world, their photoelectrochemical device was the first of its kind to automatically switch to using stored electricity as a power source during the night or overcast weather conditions.

"Our New Zealand team is the first one to put this together to form the device that can handle various weather conditions, so the engineering design of it is innovative."

The intention of the project, funded by Ministry for Business and Innovation and Employment (MBIE), was to make hydroponic farming more affordable for operations of all sizes and even could be used in homes, which Yip said could be a "catalyst" to enable a climate change resilient food supply.

"I think it is an enabling technology, so it enables hydroponics to be used widely in the public and not to worry about the potential of water contamination."

Yip said the project team had already found the device worked in a laboratory setting when trialled on plants — including strawberries and microgreens — and would soon test the device in a real-world hydroponic system.

"Currently we are trialling the 'light mode' and the 'dark mode' separately. So we already know the photocatalytic side which is the trigger using the sunlight works. At the same time, during night-time in a dark environment, we can trigger the reactions using electricity.

"We are in the final year of the project of putting these two together. With the prolonged sunlight situation we know that it's working, but the challenge would be whether the smart device [was] really doing something really smart to switch between dark and light mode.

"So we are currently testing the conditions where we have only intermittent sunlight, but not continuous sunlight," he said.

Global benefits to hydroponic farming

A woman checking the salad greens in a hydroponics pod (file photo). (Source: istock.com)

Yip said hydroponic farming was important because it had the potential to decarbonise the food chain by growing food in city centres that did not have to be transported long distances.

"Growing plants efficiently and sustainably within the city would help cut down some of the carbon emissions or 'food miles' associated with transportation," he said.

"It would also mean plants could be grown any time of the year rather than just within the season for that fruit or vegetable, allowing off-season cultivation of high-value produce."

He said lack of clean water in other countries around the world was a "major hurdle" in adopting hydroponics technology.

"Therefore they still rely on the traditional farming, and especially in the urban regions, you do have a water contamination. And in some countries like that, especially Southeast Asia, that becomes the major hurdle of adopting the adopting the technology.

Yip hoped their smart water purification device could change that, saying it could also be used in individual households instead of, or in addition to, water filters.

"So if we have a very good device that can treat water, what it means is that they will then be feel comfortable and safe to use hydroponics."

Yip said the device and its use in hydroponics has been a "collaborative effort" with multiple institutions, including Lincoln Agritech, the University of Malaya, and the New Zealand Institute for Plant and Food Research.

"The project team also involved an advisory board of field leaders, including Bluelab, Aqualinc Research, eClean Technologies, and 26 Seasons."

Yip said the next steps were to seek further funding from the Government or private investors to scale up the project once testing was complete.

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Taxonomy

• Agriculture Company
• Agriculture
• Hydroponics
• Sustainable Agriculture
• Sustainable Agriculture