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The teenage inventor making solar disinfection more accessible

An Australian inventor has developed a new way to accurately measure UV exposure for solar disinfection of drinking water – and she’s just 18 years old.

Currently representing Australia in the Stockholm Junior Water Prize this World Water Week, Macinley Butson said she had always been interested and involved in science, but it was learning some shocking statistics that drew her attention to water.

“I knew about water issues, but I didn’t know the extent of the problem,” Butson said.

“I came across two statistics that struck me to the core. These were that 80% of diseases in developing communities are related to poor water quality, and that the World Health Organisation (WHO) estimates that one in five people who undergo a minor or major surgery in a developing community will pass away as a result of infection due to a lack of sterile water.”

Macinley Butson speaking at Ozwater'19.

Determined to help tackle the problem, Butson developed the SASS (sanitation and sterilisation) system. This is a portable, solar-powered unit that provides clean, safe potable water and sterile water for medical use.

Water is passed through a chemical filter before going through a solar disinfection (SODIS) process, which uses the UV in sunlight to kill bacteria. The water can then be sterilised in a pressure cooker, which is powered by the attached solar panel.

“The system can be flat packed, it can be chucked in the back of a car and taken wherever necessary,” Butson said.

“People have said it could be used for disaster relief or in areas where water has been compromised. For me, this project became less about the fact that I invented something and more about the idea that it is possible to develop solutions to these problems.”

However, the amount of time required to successfully perform the SODIS process depends on a range of factors, including location, season, time of day, weather conditions and altitude. 

“For solar disinfection, the WHO recommends you put the water in the sun for six hours,” Butson said.

“This is very vague, especially if you’re living in the Himalayas or in Africa – those two conditions are very different. Solar sterilisation is a process that isn’t dependent on the amount of time, but is dependent on the exposure, which between those two places vary significantly.

“I wanted to look at a cost-effective way to monitor this. We have UV meters, but if you’re living in a developing community there are more pressing things to spend your money on.”

The SODIS sticker

Butson developed her own solution to this problem: the SODIS sticker. It was this invention that saw her named the 2019 Australian Stockholm Junior Water Prize winner.  

The SODIS sticker is able to accurately measure whether water has been exposed to an appropriate amount of UV to be safe for potable use.

It works by combining a transparent UV-sensitive film, typically used for radiotherapy, with a partial UV blocking filter. Butson said this means both incident and reflected light can be measured.

The SODIS sticker during testing.

“Every other detector can only measure directly incident UV radiation because the detectors have opaque backing, or because the detector is a solid-state detector that cannot measure reflected UV radiation being only unidirectional,” she said.

“However, initial results show that when a reflective material is placed behind the water, up to 25% extra UV is reflected back through the water.

“This UV will only be measured by the SODIS sticker and not other detectors … This design is a significant step forward for SODIS UV water disinfection measurement.”

The doughnut-shaped sticker includes a coloured ring attached to a white sticker base. The inner circle (or doughnut hole) contains the film, which changes colour depending on the amount of UV exposure it has received.

When developing the SODIS sticker, Butson said it had to meet a strict criteria, including:

  • able to be placed on or next to a PET water bottle; 
  • small enough not to block UV radiation to the bottle; 
  • have a film that can be seen easily;
  • be water and dirt resistant; 
  • be simple to use and interpret; 
  • and be cheap to make.

The result is an invention that ticks all these boxes and costs less than US$0.01 to produce, making it appropriate for use in developing countries. 

The SODIS sticker on a water bottle.

And this is the cost of Butson producing the sticker at home, having purchased the materials at retail prices.

“I expect that with wholesale and large volume purchases, the cost will be significantly reduced,” she said.

After testing the SODIS sticker in Australia, Butson said the next step would be to see it used in the field. She is also working on an improved UV filter to work in conjunction with the UV sensitive film.

“I am very excited at the possibility of the use of a thin film or coating that I have developed, which can provide the appropriate filtration to produce a viable improved SODIS sticker that does not require the use of a separate UV filter,” Butson said.

“[My] results show the SODIS sticker is an effective way to determine the solar biological disinfection of water and could potentially significantly further improve the sanitation of drinking water for those in need and improve their quality of life.”

The winner of the 2019 Stockholm Junior Prize will be announced on Tuesday, 27 August.

The Australian Stockholm Junior Water Prize, sponsored by Xylem, is open to students between the ages of 15 and 20 who have conducted water-related projects of environmental, scientific, social or technological importance. To find out more and to enter, click here.