Converting human wastewater into usable irrigation water could be Australia’s pot of gold.
Water authorities across the country are turning to “recycled” water to solve problems of excess wastewater as populations grow with the added benefit of increasing agricultural irrigation.
Where previous generations turned their noses up at the idea, improving science and a better understanding of climate change have made recycled water the flavor of the month.
City councils are spending millions of dollars upgrading sewage treatment plants to irrigate parks and gardens and reduce pressure on drinking water supplies.
For example, in New South Wales, the Goulburn Mulwaree Council has just spent $33 million to upgrade its sewage treatment plant to channel recycled effluent around Goulburn to water parks and playgrounds.
This particular system can be extended in the future to provide treated effluent for industrial purposes.
Although it is still expensive to source water this way, experts say it is much cheaper than extracting salt from seawater in the huge and expensive desalination plants that are for mostly dormant near national capitals.
Victoria has taken the plunge into recycled water by unveiling a 1.1 gigalitre storage dam to irrigate thousands of hectares of farmland from early next year.
The $116 million Western Irrigation Network project near Melton is jointly funded by the Victorian and Federal governments.
This secure supply will water the already substantial market gardens west of Melbourne where high value fruit and vegetable crops are already grown.
There are already large lettuce farms among many vegetable crops, strawberries, apples and even sod farms in this area.
Victoria hopes dryland farmers in the region will also invest in irrigation.
Combined with existing storage, the dam will be part of a network capable of supplying 18.3 gigaliters of recycled water per year by 2050.
The project includes more than 50 kilometers of pipeline to hopefully convert dryland farms into a new “food district”.
Other works include building infrastructure to connect existing recycled water supplies between the Melton and Bacchus Marsh mills to feed into the network.
Melton MP Steve McGhie said unreliable rainfall was a significant problem for local farmers.
In one of Australia’s premier wine regions, the federal government is exploring the possibility of constructing a 1,350 megalitre reclaimed water dam to help supply South Australia’s McLaren Vale district.
Similar work is underway in the Barossa, Eden and Clare valleys.
The $2.5 billion Western Corridor Recycled Water Scheme in Queensland is one of the largest in the world.
The drought-driven program cleans water for use primarily in power generation.
A project was completed this year in Warwick, south-west of Brisbane, to clean water for possible agricultural use.
How it’s made
Almost all states classify their reclaimed water the same – Class A is for residential customers for non-potable purposes such as toilet flushing, garden watering, and car washing.
Class B and Class C recycled water is intended for commercial and agricultural purposes.
To convert wastewater into recycled water, the process can take anywhere from eight hours (mechanical treatment plant) to around 100 days (lagoon-based treatment plant).
The first stage of treatment is to remove solids as the water passes through a screen, preventing large objects such as bottles and plastic bags from entering the rest of the system.
The water then passes to a tank where the remaining solids sink to the bottom and are removed.
In the secondary stage, the liquid moves through large aeration tanks where oxygen is pumped in to promote the growth of microorganisms.
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 decomposes. It takes about 15 days.
The remaining liquid from the secondary tanks is moved to stabilization tanks, where the remaining solids settle to the bottom.
The final step is to remove the dangerous phosphorus from the brew.
Phosphorus is a chemical often found in detergents.
The wastewater is then filtered a final time and the remaining solids (biosolids) are removed. The remaining water is disinfected with chlorine.
This purified water is then pumped into a shallow reservoir, where sunlight penetrates the water killing any remaining bacteria.