Recycled sewage will play a vital role in securing Australia’s drinking water supplies, says Dr Stuart Khan, Associate Professor at the University of New South Wales School of Civil and Environmental Engineering.
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.
Drinking water supplies in Australia have notoriously experienced ‘boom and bust’ cycles of floods and droughts. During the inevitable prolonged droughts, many water supply planning decisions have tended to be made with an extreme sense of urgency, as conventional drinking water supplies for some of our major cities dwindled.
This sense of urgency in planning restricts the opportunity for detailed options-analysis and severely impedes the ability of governments and water utilities to develop public awareness and appreciation of the benefits of some non-traditional means of supplementing water supplies. As a consequence, it is arguable that there are now a number of large water supply infrastructure projects that were initiated during the past 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 that is currently not producing water, or is operating well below design capacities.
Much of Australia is now experiencing higher levels of water availability than during the most recent extensive drought, termed the ‘Millennium Drought’ (approximately 2001–07).
Consequently, 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.
GLASS HALF FULL
Supplying highly treated reclaimed water directly to a drinking water distribution system is known internationally as direct potable reuse (DPR).
This differs from more established approaches to potable water recycling by the absence of a so-called ‘environmental buffer’ – a practice referred to as indirect potable reuse (IPR). IPR involves the storage of treated reclaimed water in environmental buffers – such as a river, lake, reservoir or aquifer – prior to it being recovered through drinking water treatment plants and distributed to consumers.
It is instructive to observe that there is a number of successfully operating DPR schemes internationally. The most established of these has been operating in Namibia since 1968 without observed negative impacts to public health. More recently, DPR projects have been developed in the United States and South Africa, with both countries now actively considering additional developments within the next few years.
Recent Guidelines for Water Reuse developed by the US Environment Protection Agency state that, “while DPR is still an emerging practice, it should be evaluated in water management planning, particularly for alternative solutions to meet urban water supply requirements that are energy intensive and ecologically unfavourable”.
Potential benefits of DPR, relative to IPR, are likely to be highly case-specific. However, those potential benefits include significantly lower energy requirements, construction costs, and operational costs. DPR can also provide an opportunity to allow potable reuse in situations where a suitable environmental buffer is not available for IPR.
How the benefits of DPR compare to other water supply options, including IPR, seawater desalination, stormwater harvesting and groundwater extraction, will vary across Australia and depend on regional environmental, social and economic factors.
In comparing alternative systems, issues to be considered include:
• Whether public health and safety can be confidently and reliably met;
• The ability to meet all environmental and health regulatory requirements;
• Energy and other costs associated with treating and delivering the water;
• Social acceptance of the water source and trust in the water service provider to manage risk; and
• Any environmental impacts where the water is sourced and where the wastewater is discharged.
The science, technology and engineering associated with DPR have been rapidly advancing in recent decades. DPR is growing internationally and will be an expanding part of global drinking water supply in the decades ahead.
DPR is technically feasible and can safely supply drinking water directly into the water distribution system, but advanced water treatment plants are complex and need to be designed correctly and operated effectively with appropriate oversight. Current Australian regulatory arrangements can already accommodate soundly designed and operated DPR systems.
HEARTS AND MINDS
How recycled water for drinking is viewed across Australia depends on several factors, including the management of health risks, cost-effectiveness and public perceptions. Each of these factors will vary across states and regions. Australian communities are entitled to know the costs, benefits and risks involved in all water supply options.
Increasing energy costs may have a significant impact on future decisions to choose between DPR, IPR, surface water dams, or seawater desalination. A cost–benefit analysis may identify that an appropriately designed DPR scheme is less expensive to construct and operate than other methods of water supply, while still meeting all regulatory requirements.
Public acceptance remains an important and sometimes difficult issue for all planned potable water projects. However, there is evidence to suggest that acceptance is increasing generally, and can be fostered by effective community engagement and communication programs.
Governments, community leaders, water utilities, scientists, engineers and other experts will need to take leadership roles to foster the implementation and acceptance of any DPR proposal in Australia.
This is an edited extract from an Australian Academy of Technological Sciences and Engineering (ATSE) report, Drinking water through recycling (October 2013). The full report is available online.