Effluent trial to begin

Queenstown Lakes District Council capital works manager Ken Gousmett inspects a spray nozzle that will irrigate a crop of lucerne with treated effluent from the Lake Hawea sewerage plant. Photo by Mark Price.
Queenstown Lakes District Council capital works manager Ken Gousmett inspects a spray nozzle that will irrigate a crop of lucerne with treated effluent from the Lake Hawea sewerage plant. Photo by Mark Price.
When Lake Hawea people flush their toilets tomorrow they will, for the first time, be helping to feed sheep and cattle in the Upper Clutha basin.

Instead of the town's treated liquid effluent being left to seep into the ground, and then the Hawea River, it will be sprayed over a 2.3ha lucerne paddock.

And when the lucerne grows, it will be harvested and sold to farmers.

Using nitrogen-rich human waste as a fertiliser for animal fodder crops is far from new, but it has never been in fashion in Otago where effluent has traditionally gone into waterways and landfills.

The Queenstown Lakes District Council's $450,000 ''add-on'' to its Lake Hawea sewage-treatment system is the first in the province to change that.

Capital works manager Ken Gousmett said the new Lake Hawea system was a trial but, if it panned out, a similar system could be used for Wanaka's effluent.

He said other Otago local authorities would be watching with interest.

The existing Hawea sewerage system is centred on a ''pretty conventional'' oxidation pond built in 1988.

The wind, and some machinery, aerate the effluent in the pond, allowing ''the bugs'' to break it down.

The sludge sinks to the bottom while the water, or treated effluent, runs out of the pond into trenches and then soaks into the ground.

The new system simply takes this treated effluent and pumps it into a spray-irrigation system with risers and nozzles, laid out across a piece of council-owned ground soon to be sown in lucerne.

Mr Gousmett says the treated effluent should help produce three, four or even more crops per year.

''It has a lot of good things in it, as well as bad things like pathogens."

Safeguards are in place to ensure the spray does not drift on to the neighbouring farm. Spray nozzles are large to avoid creating a fine mist, and a weather station will shut down the system when winds reach 30kmh. It will also operate only at night.

The system will also be shut down for two days before the lucerne is mown and baled, and those doing the work will need to be dressed appropriately and work in certain ways.

The lucerne will be cut, baled and carted away, and stock will not graze the crop directly.

Fonterra does not allow crops grown with the assistance of ''human wastewater'' to be fed to lactating cows.

The dairy giant did not respond to an Otago Daily Times question about why it had such a rule.

Mr Gousmett said the irrigated crop would be fenced off from the public.

''It's treated effluent but it still has lots of bugs in it - pathogens - and it's not suitable for human contact."

Mr Gousmett said one of the main drivers for the new system was the Otago Regional Council's gradual strengthening of consent conditions to improve water quality in waterways.

The disposal of effluent, and particularly sludge, has been a major issue in the Lakes district for several years, and the Lake Hawea trial is partly about boosting public confidence in using it in agriculture.

Mr Gousmett hoped it would demonstrate how treated household effluent could be used by farmers safely, beneficially and without upsetting their neighbours.

''We need to prove it. We need to show it. It will take a couple of years to do that. It's not going to happen in one summer."

The Taupo District Council leads the way in New Zealand, spraying treated effluent on pastures on a large scale.

The Taupo system produces 9000 bales of haylage and provides the council there with $400,000 of income annually.

Mr Gousmett said how much farmers would pay for the Lake Hawea lucerne had yet to be seen. An agricultural consultant was handling that part of the process.

However, he said, the lucerne production was secondary to the main aim of disposing of effluent in a way less likely to harm the environment.

mark.price@odt.co.nz