KEY POINTS:
Scientists who have tipped modified cat litter into one of the nation's most polluted lakes say it has reduced phosphorus levels in the water by up to 60 per cent.
The volcanic mineral zeolite is traditionally used for absorbency in chemical spills, sports turf and cat litter.
But it has also been used overseas for treating victims in Bulgaria of the Chernobyl nuclear disaster and for purifying water.
In New Zealand - where too much phosphate from fertiliser, farm run-off, and septic tanks triggers summer-time algal blooms in waterways - it is being used to clean up Lake Okaro, 25km south of Rotorua.
Researchers at the state science company Scion modified 112 tonnes of zeolite from Blue Pacific Minerals at Matamata and dumped it in the lake last September. They boosted its capacity to act as a binding agent for phosphorus and other harmful nutrients.
The mineral effectively capped the lake bed, trapping phosphorus released from the sediment when the deep-water layers lose their oxygen in summer.
This stopped nutrient levels in the water rising to the point where blue-green algal bloom turn the lake into a thick algal soup.
"Algal booms are formed as a direct result of the high levels of nutrients, such as phosphorus, in our lakes," said the Bay of Plenty Regional Council's lakes manager, Andy Bruere.
"We hope to see a significant improvement in Lake Okaro water quality in the next two to three years, without the need for further intervention."
The regional council is now considering a $25 million sediment capping project targeted at the region's tourism icon, Lake Rotorua.
Scion chief executive Tom Richardson said the technology would have a significant pay-off for more than just the region, because nutrient pollutants were a billion-dollar problem worldwide.
And the company that supplied the zeolite, Blue Pacific Minerals, is looking for ways to commercialise the product.
Managing director Dave Hill said: "We think the modified product provides local and national governing bodies with another tool that will help them achieve their objective to clean up New Zealand's waterways."
The Government recently said it would meet about half the total $144.2 million cost to clean up Rotorua's worst-affected lakes.
The trial was funded by the Bay's regional council and supported by researchers from Waikato University, and the National Institute of Water and Atmospheric Research.
- NZPA
