Clever thinking creates cleaner water

June 6, 2012

Clever thinking creates cleaner water

Two chemists from the University of Waikato have come up with an innovative method for treating bore water on Waikato farms.

Along the way, they may have hit upon a low-cost solution for developing countries, where many people have limited access to clean and affordable water.

Associate Professor Alan Langdon and post-doctoral researcher Dr Hilary Nath decided to try using electrochemistry to remove the iron and manganese prevalent in bore water from Waikato’s peaty soils.

The residues give the water its typical browny-orange colour, and generally make it undrinkable without expensive treatment using aerators, filters, ion exchangers and tanks.

The researchers came up with a simple system that uses electric current passing between two perforated titanium electrodes to turn naturally occurring chloride ions in the water into chlorine.

The chlorine then oxidises and precipitates out the metal contaminants, and also disinfects the water passing through the system, making it safe to drink.

Best of all, the whole system can be powered by a car battery.

“By bringing the electrodes closer together than anyone else has been able to we can reduce electrical resistance and consume less power,” says Dr Nath. “And because the flow path through the cell is very short, we can achieve good water flow at modest pressure.”

The system is known as PEFT – perforated electric flow through – and patents are pending. A prototype will be on show at one of two University of Waikato stands at Fieldays later this month; the university is a strategic partner at Fieldays which this year runs 13-16 June.

Drs Langdon and Nath now plan to test the prototype on a Waikato farm, but the invention’s real value may lie in its application in developing countries.

The researchers noticed that the closer together the two electrodes were positioned, the higher the electric field generated between them. And the higher the electric field, the more potent the chlorine being produced.

The two together were so powerful they could kill bugs in the water at much lower chlorine levels than normally required – the electric field was able to puncture the membrane of a bug making it 100 times more susceptible to the disinfecting effect of the chlorine.

“What this means is that you can disinfect water with chlorine levels much lower than can be tasted,” says Dr Nath.

At slightly higher applied voltages the PEFT cell can also disinfect water by the electric field alone, with no need to produce any chlorine.

The researchers can see huge benefits in this discovery for the food industry, particularly for cold pasteurising liquid food products without the need for costly heating and cooling units.

“It’s low technology, but it’s very clever nevertheless,” says Dr Langdon.

WaikatoLink, the University of Waikato’s commercialisation arm, is helping with the development and funding of a working prototype. The Kiwi Innovation Network (KiwiNet) – a collaboration focused on research commercialisation – is also providing support as well as investment from the Ministry of Science and Innovation’s PreSeed Accelerator Fund (PSAF).

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