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Farm irrigation seen as the solution to wastewater problem

Chris McLennan
By Chris McLennan
March 20 2022 - 8:00pm

Converting human sewage into usable irrigation water could be Australia's pot of gold.

Water authorities across the nation are turning to "recycled" water to solve excess wastewater issues as populations grow with the added bonus of growing farm irrigation.

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Where previous generations turned up their nose at the idea, improved science and a better understanding of climate change, has made recycled water the flavour of the month.

Municipal councils are spending millions of dollars upgrading sewage treatment plants to provide irrigation for parks and gardens and take pressure off drinking water supplies.

For instance in NSW, the Goulburn Mulwaree Council has just spent $33 million upgrading its sewage treatment plant to pipe recycled effluent around Goulburn for watering parks and playing fields.

This particular system can be expanded in the future to provide treated effluent for industrial uses.

Even though it is still expensive to source water this way, experts say it is far cheaper than stripping salt from seawater at the huge and costly desalination plants which mostly lay idle near the nation's capitals.

Victoria has taken the plunge into recycled water big time by unveiling a 1.1 gigalitre storage dam to irrigate thousands of hectares of farmland from early next year.

MELTON MILESTONE: Officials said they were turning on the tap for farmers with the construction of this 1.1 gigalitre recycled water storage dam near Melton which is set to irrigate thousands of hectares of farmland from early next year. Picture: Greater Western Water.

The $116 million Western Irrigation Network project near Melton is jointly funded by Victorian and federal governments.

This secure supply will water the already substantial market gardens to the west of Melbourne where high value fruit and vegetable crops are already grown.

There are already big lettuce farms among many vegetable crops, strawberries, apples even turf farms in this region.

Victoria hopes dryland farmers in the area will now invest in irrigation as well.

Combined with existing storages, the dam will be part of a network capable of supplying 18.3 gigalitres of recycled water a year by 2050.

The project includes more than 50 kilometres of pipeline to hopefully convert dryland farms to become a new "food district".

Other works include the construction of infrastructure to connect existing recycled water supplies between the Melton and Bacchus Marsh plants to feed into the network.

Vegetable growing at Bacchus Marsh.

Melton MP Steve McGhie said unreliable rainfall has been a significant issue for local farmers.

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This irrigation water for crops will use Class C recycled water.

In one of Australia's premier wine growing region, the Federal government is looking into the possible construction of a 1350 megalitre recycled water dam to help supply South Australias McLaren Vale district.

There is similar work going on in the Barossa, Eden and Clare valleys.

The $2.5 billion Western Corridor Recycled Water Scheme in Queensland is one of the world's biggest.

The drought-motivated scheme cleans up water for use mainly in power generation.

A project was completed this year at Warwick, south-west of Brisbane, to clean up water for eventual farm use.

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How it is made

Almost all states classify their recycled water the same - Class A is for residential customers for non-drinking purposes such as toilet flushing, garden watering and car washing.

Class B and Class C recycled water is for commercial and agricultural purposes.

To convert wastewater to recycled water the process can last anywhere from eight hours (mechanical treatment plant) up to about 100 days (lagoon based treatment plant).

The first stage of treatment involves removing solids as water passes through a screen, preventing large objects such as bottles and plastic bags from entering the rest of the system.

Water then passes into a tank where remaining solids sink to the bottom and are removed.

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There are already many market gardens west of Melbourne and authorities hope with the availability of more irrigation water more dryland farms will convert to help feed those producing the wastewater.

In the secondary stage, liquid moves into large aeration tanks where oxygen is pumped in to encourage the growth of micro-organisms.

These break down organic matter into simple materials such as water and carbon dioxide.

A floating sludge separates from the water during this process and is sent to a sludge digester where it breaks down. This takes about 15 days.

The remaining liquid from the secondary tanks is moved to stabilising tanks, where remaining solids settle to the bottom.

The last stage involves removing dangerous phosphorous from the brew.

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Phosphorous is a chemical often found in detergents.

Sewage is then filtered one last time and remaining solids (biosolids) are removed. The remaining water is disinfected with chlorine.

This purified water is then pumped into a shallow holding tank, where sunlight penetrates the water killing remaining bacteria.

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Chris McLennan

Chris McLennan

National Rural Property Writer

ACM national rural property writer based in Bacchus Marsh, Victoria. Career journalist. Multi award winner.

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