Water from plughole to paddock an Aussie first

TREATMENT PLAN: Wastewater in Alice Springs is now being converted into a usable flow of irrigation water.
TREATMENT PLAN: Wastewater in Alice Springs is now being converted into a usable flow of irrigation water. Simon Young BUN140913SEW8

WHEN it comes to growing a horticulture industry in the centre of Australia, water is most likely the first challenge you think of.

That's why a government tender opportunity closing this week is potentially so exciting. The Department of Primary Industry and Resources has offered for lease some 30ha of horticultural land along with a plentiful supply of clean water.

The prospective patch is sited at the Arid Zone Research Institute to the south of Alice Springs township, not far from the airport.

But the water to be used there won't further deplete the drinking water aquifers so crucial to the town's survival.

Instead, the proposal aims to use water recycled from wastewater already generated by the Alice Springs population - in other words, water that otherwise goes down the plughole.

And that means frontier recycling technology to turn such wastewater into a usable flow of irrigation water.

Luckily, such technology already exists.

"The water we use for horticulture comes from a leading-edge water recycling project,” says manager of the AZRI site Stuart Smith.

"It meets strict quality guidelines and is safe for use with crops.”

Australia has huge potential to use water that is recycled via what is called managed aquifer recharge, as a large proportion of our landscape is covered in favourable sedimentary soil deposits.

So far, however, there is only the one operational scheme in Australia, and that is at Alice Springs.

It all started in about the year 2000 with community concerns over leakage and overflows from the Alice Springs sewage treatment ponds into nearby waterways. In addition, there were annual problems with mosquito breeding.

The combined issues forced the managing utility, Power and Water, to rethink its approach and adopt a water recycling strategy.

The centrepiece of the strategy is the futuristic- looking Alice Springs Water Reclamation, which first turned over its pumps in 2008.

The site, which features large open stretches of water called settling ponds, is hugely attractive to migratory birds and a favourite spot for twitchers the world over.

Water is taken from the ponds to a mixing tank, where its pH is lowered and a coagulant added to remove solids from the effluent.

Air is then mixed with the fluids in a special tank and the collected solids skimmed from the surface. The water is chlorinated and sent to a reclaimed water tank from where it is used to irrigate the enormous expanse of nearby Blatherskite Park, which plays host to major events like the Alice Springs Show.

The remaining water is pumped 6.2km to the AZRI site further south, where another phase of treatment begins.

Altogether, about 600ML a year of treated water is piped from the sewage treatment ponds and the Alice Springs Water Reclamation Plant.

The idea was also to help reduce growing pressure on the existing Alice Springs drinking water aquifers, where levels were declining by about a metre per year.

Once the piped effluent reaches the AZRI site, it undergoes a process called soil aquifer treatment, or SAT, followed by underground storage. The pre-treated water coming into the site fills up SAT "basins” that have been specially prepared using earthmoving equipment.

The water percolates the ground surface and infiltrates the soil of the aquifer, which is not connected to any other aquifers or water supplies.

Fresh water can then be drawn at a later date from the volume stored in the aquifer.

The project kicked off in 2008 with four such SAT basins. A fifth was added in 2009 and the area of recharge increased in 2011, so that by 2012 the surface of ground under recharge was measured at 38,400sq m.

The benefit of the scheme is that the water is naturally purified because it is filtered through the earth.

Much like rainwater when it falls on the ground, the treated water percolates through layers of soil, eventually to be stored deep underground. As the water moves through the soil, it undergoes a significant improvement in quality.

The system is well suited to the desert, because little is lost to evaporation and the water can be stored for years.

The water has already been used to trial lucerne.

"The water has an electrical conductivity of about 1.8 decisiemens per metre, which is the same as recycled water from Adelaide or Melbourne,” says Mr Smith.

"The aim of our trial is to find out what this quality of water will do to the local soil under a cropping regime.

"We started with lucerne because it is a local crop with a long history in the area, it is not for human consumption and we can use it on-farm for our animals.”

"Our biggest concern is build-up of salinity, but we hope to be able to manage this with crops that take up a lot of ions from the soil and regular flushing with better quality water.

"The quality of recycled water is getting higher and higher as technology improves and Power and Water upgrade their treatment systems so the risks are almost non-existent.”

Recent research published in the journal Water reveals there are still challenges, among them a general lack of Australian research on the effectiveness of SAT and MAR systems, as well as the problem of clogging up the soil when using water high in dissolved solids.

Pre-treatment of the water used to recharge the aquifer has helped to minimise such clogging.

In fact, rates of recharge have been improved some 40-100% by a 2013 upgrade of the Ilparpa plant to include sand filtration and UV disinfection of the wastewater at Ilparpa before it is piped to AZRI.

As water becomes scarcer under climate change on a continent where it is already scarce, this project is certainly one to watch.

Topics:  alice springs glenn morrison heartbeat horticulture rural water

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