Waikato scientists' pure gold

16:00, Dec 09 2012

Water, water everywhere, nor any drop to drink. The Waikato, with its mighty river and verdant pastureland, does not immediately spring to mind as a place where an ancient mariner or anyone else might struggle for drinkable water.

But the province’s peaty soils can make life difficult in the backblocks, where bore water and untreated surface water are often the only options. In some cases, the amount of contaminants such as iron and magnesium is so bad that the only way you could safely drink the stuff is by installing cumbersome and expensive decontamination equipment.

Then there are those “problem waters”, as Alan Langdon calls them, where even the best current technology would struggle to produce anything remotely useable.

Associate professor Langdon and his colleagues at the University of Waikato’s department of chemistry and engineering have devised an innovative method for purifying water that not only promises to solve that local problem, it has potential commercial export applications in a range of sectors including agriculture and horticulture.

“We’ve had many organisations telling us, ‘yep, this could solve our water problems’,” says Nigel Slaughter, general manager, commercial of the university’s commercialisation arm WaikatoLink. WaikatoLink is part-funding the manufacture and testing of a prototype.

The technology is called PEFT, for Perforated Electric Flow Through. It arose from a decade’s research at Waikato and as Langdon says, “like all science, it hasn’t occurred overnight”.


Essentially it’s an electrochemical purification method that simultaneously removes contaminants and disinfects water. It works by applying a low voltage current — low enough to be produced by a simple car battery — to water flows through an extremely narrow gap between two perforated electrodes, generating chlorine from chloride ions that occur naturally in the water.

In combination with a high electric field, the two-punch effect eliminates contaminants and kills bugs.

Only some of this is innovative, however — and to grasp which is the groundbreaking science you need to know the twists and turns of the 10-year back story.

It was one of Langdon’s postgrad students, Grant Mathieson, who got the ball rolling when he began investigating ways of purifying wastewater, using two well-established electrochemical methods.

Mathieson’s innovation, according to Langdon, was recognition that to make this kind of purifying system economically viable, you had to find a way to cut down the resistance of the cell, either by making the electrodes larger in area or by bringing them closer together.

Matheson went for the second option, using what Langdon describes as “a really novel system” involving a steel flume, aluminium shavings and a fine insulating mesh. “It allowed us to bring the electrodes very close together without them shorting out.”

The catalyst for the next innovation — the one that got WaikatoLink so excited — was the arrival of overseas doctoral student Hilary Nath who had been working on wastewater treatment and green tech in his native Sri Lanka.

Together, Nath and Langdon began devising a solution to Waikato's 'problem waters', using Mathieson’s idea of a fine mesh to bring electrodes closer together. Rather than a flume, however, they wanted to use a conventional cell, sealed against water, with enough current to bring about electrolysis while also being safe and cheap.

But how to get the electrodes close enough to do the business while still allowing water to flow past? Drill patterns of holes in the electrodes and stagger them to shorten the flow's path. This was the project’s big moment.

“We believe we can now develop this technology to make unuseable waters into useable waters,” says Langdon. “And for waters that are more easily treated our system will be quicker and more efficient than conventional treatments.”

Backed with an investment of $92,000 from the Ministry of Science and Innovation’s Pre Seed Accelerator Fund (PSAF), to go with a similar WaikatoLink KiwiNet contribution, prototypes are about to be tested at 10 sites involving various water types and sources around the Waikato.

WaikatoLink is talking to a Hamilton company keen to manufacture.

If all goes to plan, the first commercial applications will be developed for treatment of household water, says Slaughter. “I think that will be the biggest market, but there are lots of other potential applications. It should have a great deal of appeal in agriculture, where irrigation nozzles tend to block up — removing the iron would resolve this problem.”

It could also be handy for decontaminating and disinfecting bore and well water to make it more palatable for stock and, of course, for human consumption.

“Once we’ve got it up and running we’ll be looking to partnerships to take it into various markets. Obviously New Zealand is the test, but there are overseas opportunities, too.”

Langdon sees even more promising applications. One big benefit of the Waikato invention is it works at lower voltages than previously enabled — and it can disinfect at lower chloride concentrations — meaning it could be used in swimming pools without having to make them saline.

“But that’s all fairly straightforward. The thing that has really excited us is that this system is 100 times more efficient than one would expect given the amount of chlorine present.”

In other words, the system can kill bugs at much lower chlorine levels than normal, an effect of the very high electric field effectively rupturing the bugs' membranes.

The result? Clean water without that chlorine taste. Even better, if the voltage was increased just a little, says Langdon, “we could produce fields strong enough to kill bugs without chlorine at all. All of a sudden we are looking at a chlorine-free disinfection process and one starts to think ‘food products’. So it’s a platform technology with several possible directions for further development.”

A lot of, ahem, water has to go under the bridge before then. But it’s looking like a real coup for Waikato science, with bonus export potential.

Consider for a moment how many countries might benefit from a cheaper, more efficient method of purifying drinking water. “This has turned from a minor project into a very exciting opportunity,” says Slaughter.