A taste for drinking recycled water

Why do our elected leaders wait until crisis point before making decisions about water supply for Australians? We should start talking about solutions to the next drought now.

By Stuart Khan, ABC.net (Australia), 5/5/14

Queensland's Western Corridor Recycled Water Project an example of indirect potable reuse of reclaimed water. It uses 'reverse osmosis' to purify wastewater. Credit: Environment.gov.au

IT WAS ONLY A FEW years ago that Australia was in the grip of the 'Millennium Drought' (approximately 2001 to 2007). As drinking water supplies for some of our major cities dwindled, water supply planning decisions were made with an extreme sense of urgency.

How quickly we forget; much of Australia is now experiencing secure levels of water availability. Now, there appears to be little immediate urgency to identify and assess potential additional water sources.

However, it is essential that such assessment be conducted at this point in the climate cycle, rather than waiting for the next drought to arrive.

Planning early facilitates sober analysis of all issues associated with water supplies. Furthermore, it enables necessary community debate and public awareness-raising to be initiated in the absence of a perceived emergency and with adequate time to proceed.

It is arguable that there are now a number of large water supply infrastructure projects that were initiated during the last decade that are now seen to be an imperfect fit for addressing long-term water management needs. This is reflected in some large water recycling and seawater desalination infrastructure which is currently not producing water or operating well below design capacities.

As the Millennium Drought progressed, some Australian cities began to focus on various approaches to reclaiming municipal wastewaters for reuse to supplement drinking water supplies. This involves taking the treated effluent from sewage treatment plants and subjecting that water very high levels of treatment.

The largest project, known as the Western Corridor Recycled Water Project, collected effluent from six sewage treatment plants around Brisbane, 'polished' that water at three new advanced water treatment plants in preparation for some of it to be used to augment raw water supplies in Lake Wivenhoe, Brisbane's largest drinking water reservoir.

However, soon after the plants were constructed and pipes laid, the drought broke. Water storage in Lake Wivenhoe is now so ample that the Western Corridor project sits idle and the Queensland Government is examining options to free itself from the financial burden of continuing to maintain it.

Unlike the east coast of Australia, the drought in Perth never broke and hasn't for nearly 40 years. During that time, the population was sustained by extensive groundwater extraction until 2006 when the first of two seawater desalination plants began operation.

However, after a successful three-year trial, a large recycled water project is now under development for Perth. This project, known as the Groundwater Replenishment Scheme, will take treated wastewater effluents through an advanced water treatment process and use them to recharge Perth's groundwater supplies. The project is projected to provide up to 20 per cent of Perth's drinking water supplies by 2060.

These two projects represent two quite different approaches to supplementing drinking water supplies with recycled water: either by boosting surface water supplies or by recharging groundwater.

However, they both involve returning highly treated, reclaimed water back to a traditional environmental water source in preparation for it to be re-extracted from that source and then suitably treated for supply as municipal drinking water. Water engineers refer to the environmental water source as an 'environmental buffer' and the overall process as 'indirect potable reuse' (IPR).

An alternative approach that is rapidly gaining interest in Australia, the USA and South Africa is known as 'direct potable reuse' (DPR). That is, municipal wastewater is highly treated to a quality suitable for direct use as a drinking water supply, without the inclusion of an environmental buffer.

In the right mix of circumstances, there appear to be many potential advantages of direct potable reuse compared to IPR. Among the most important are reduced energy requirements, which come largely from the often significantly reduced need to pump water over long distances and uphill to the environmental buffer reserves. With reduced energy also come reduced greenhouse gas emissions and reduced costs.

A recent assessment undertaken by engineering firm GHD revealed that in some circumstances, DPR could provide drinking water with about 30 per cent less energy than required by a comparable IPR scheme and 60 per cent less energy than seawater desalination.

In addition, there are a number of other possible advantages of DPR, which are yet to be explored in detail. These include improved water quality and system reliability as a consequence of reduced vulnerability to environmental factors such as extreme weather events and other catchment-related risks.

Furthermore, DPR has the potential to mitigate flooding for some cities such as Brisbane. By providing a component of drinking water through direct potable reuse, existing reservoirs such as Lake Wivenhoe could be maintained with lower storage volumes without compromising water supply security. If this alternative management approach were applied to the Western Corridor Recycled Water Project, enormous value would be gained by the improved prevention of major flooding events such as those experienced by Brisbane in recent years.

A reliable supply of high quality water is essential for all Australian towns and cities. Secure water availability facilitates agriculture, commerce, recreational activities, improved amenity and healthy lifestyles. As such, safe, reliable water supply is fundamental to the provision of high quality urban living.

The advantages of wastewater recycling and direct reuse would both facilitate our water supply adaptation to climate change as well as reduce our further impacts to climate change resulting from carbon emissions. Along with issues of water quality and costs, these must surely be key priorities as we plan for the future of Australian cities.

Now — not in the middle of the next drought — is the appropriate time for Australia to begin to consider the issues associated with DPR as a potential future water resource. We have much to gain by developing a national taste for drinking recycled water.

Stuart Khan is associate professor in the School of Civil & Environmental Engineering at the University of New South Wales. He is speaking tonight in Adelaide on the topic of recycled water.


Related Story: Recycled water could have stopped Brisbane floods 11 MAY 2012