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June 28, 2009

Making every drop count

Recycling across Australia

Wastewater has been recycled and used in Australian towns and cities for decades, but usually for watering recreational facilities such as parks and golf courses.

However, a recent proposal for one drought-stricken Australian community to recycle sewage and use it to top up drinking supplies has left a lot of people with a bad taste in their mouths.

In a referendum, residents of the city of Toowoomba in south-east Queensland rejected a scheme to recycle sewage to top up drinking supplies.

The issue divided the small community and roused passions, but it also highlights a major issue facing all Australians. A drying climate due to global warming and a growing population has created the need to find and adopt innovative, sustainable methods to slake our thirst for water.

Overcoming the 'yuk factor'

Researchers and water authorities in Australia say there's no scientific or health reason that recycled wastewater can't be safely used as part of drinking water supplies if treated properly.

But there can be a formidable psychological reason. It's called the 'yuk factor' - based on the thinking that the water in the glass in your hand might have started off in someone's toilet bowl. But should we be worried?

Overseas, it's not unusual for treated wastewater to be part of drinking supplies. The city of London is located downstream from numerous wastewater recycling plants that discharge into the Thames river. Which is why there's a common saying that when you drink a glass of water in London, the water has already passed through several pairs of kidneys.

And recycled wastewater is successfully used to top up drinking water supplies in Namibia, the United States and Singapore.

Many informal 'taste and tell' surveys reveal that most people can't tell the difference between tap water, bottled water and recycled water. So why the fuss? Well, that's what some residents of Toowoomba, in south-east Queensland, and Goulburn, in New South Wales, are thinking.

A tale of two cities

Both Toowoomba and Goulburn were planning to introduce schemes to recycle sewage into drinking water supplies to help their communities overcome chronic water shortages due to drought and long-term, below-average rainfalls.

Toowoomba would have been the first city in Australia to use recycled sewage for drinking water, with its proposal for a new $68 million wastewater treatment plant to top up potable water supplies at Cooby Dam. The Goulburn proposal - which is still being considered - involves building a new wastewater plant as part of a $32 million project to recycle effluent and return it to the Sooley Dam catchment.

But recycling effluent for drinking is an emotive issue. In Toowoomba, a group of concerned citizens collected some 10,000 signatures for a petition opposing the project. That's despite advocates of the proposal saying their recycled wastewater will be so pure it could be used for hospital purposes such as kidney dialysis.

Backers of both proposals also point out recycling is part of much wider water saving strategies that are feasible, sustainable, and necessary - and that they can help drought-proof their communities for decades to come.

How to make wastewater drinkable

There are a number of ways in which to purify water - including sewage water, groundwater or seawater - to obtain drinking water. Methods include distillation, freezing, reverse osmosis, electrodialysis or ion exchange. Each method has advantages and disadvantages, and the method chosen depends on the scale, location, source of water, cost and available energy sources.

Treating wastewater to make it suitable to add to drinking supplies often involves the reverse osmosis process, along with other purification treatments.

In Toowoomba, for example, the wastewater would have been treated using ultrafiltration, reverse osmosis, ultraviolet disinfection and oxidation processes to destroy microorganisms.

During reverse osmosis, water is forced under pressure through very fine membranes which allow water molecules to pass through, but not salts and other matter. The technology is already used around the world to provide water for industrial purposes and drinking water on ships, and there are plans to use it on spaceships.

Using a process called ‘indirect potable reuse’, the recycled wastewater would then top up existing drinking water supplies to be stored at the nearby dam and then undergo conventional water treatments. It would then become part of residents’ daily drinking supplies.

But there are two common concerns with such water purification projects. Firstly, they require considerable amounts of energy. Secondly, there are environmental concerns about what to do with the concentrated salty waste water that is made during the process.

The big picture

Residents of Toowoomba have voted against their wastewater scheme, but the issue is now being looked at on a much wider scale. The publicity involving the Toowoomba poll has helped put the spotlight on other Australia-wide initiatives to quench our growing thirst for water.

Australia is the driest inhabited continent and climate change resulting in below average rainfall and extensive droughts have prompted the search for new, innovative and sustainable water supplies, and ways to curb demand.

Growing demand from agriculture, industry and a growing population, have exacerbated the problem. According to national State of Environment reports, industry and householders are using increasing amounts of water.

As a result, there is a push for new sustainable water supplies taking place at all levels of government in every State. And it's easy to see why. Much of the sewage treated at Australian wastewater treatment plants is fed directly into the sea or rivers - in effect, it goes down the drain.

But water recycling is now set to play a much greater part in the water management cycle. Many states are committed to increasing water recycling targets in years to come.

Although there are differing views, researchers and health authorities say it's possible to recycle water to the relevant standard for whatever use the water is required, be it irrigation, horticulture, agriculture, household use - or drinking water.

What's important, they say, is defining what standards are required for particular uses, and then implementing relevant risk management, quality assurance, and monitoring programs to provide safe drinking water, or alternative uses that spare potable water.

And then there's one other vital issue to consider, which you can sum up with the adage: 'You can lead a horse to water, but you can't make it drink'. Overcoming the yuk factor might turn out to be the most crucial part of the whole process.

1 comment:

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