Electrochemistry 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 on 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.

University of Waikato researchers Dr Hilary Nath and Associate Professor Alan Langdon with their invention.

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,” said 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 is patented in New Zealand with international patents filed. A prototype is currently being tested by Drs Langdon and Nath on a Waikato farm, and results are positive - they’ve seen the total oxidisation of iron during their trial.

“The initial focus will be disinfection of harvested rain water, disinfection of water supplies derived from surface water and bore water contaminated with iron - we need to be very sure our technology is robust before contemplating overseas markets, particularly in developing nations,” said Dr Langdon.

The researchers noticed that the closer together the two electrodes were positioned, the higher the electric field generated between them. 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,” said 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.

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

WaikatoLink, the University of Waikato’s commercialisation arm, is helping with the commercialisation of the technology. 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).