Australia’s dry climate means water reuse has become increasingly important. Stuart Khan looks at its role in city ambitions for Rainfall Independent Supplies.
The Australian water sector is a frequent adopter of buzzwords, which provide insights into the sector’s collective focus and direction at particular times. Examples from recent decades have included: ‘sustainable development’; ‘resilience’; ‘smart water’; ‘one water’; and ‘water sensitive cities’. There is now a new expression, currently climbing its way to prominence. This expression is ‘Rainfall Independent Supplies’ (RFIS).
Australia’s longest and most severe drought on record is referred to as the Millennium Drought, having lasted from 1997 to 2010. It was during this event that many of the country’s largest cities began to understand that an overwhelming dependence on rainfall to maintain water for growing urban populations was increasingly vulnerable to stress or failure.
The emergence of RFIS
Writing in The Source in 2016, University of Canberra Professorial Fellow Jane Doolan observed that, during the Millennium Drought, efforts in managing water demand and consumer behaviour were “coupled with augmenting urban water supplies and creating a more diverse portfolio of supply options, including use of recycled water, stormwater and groundwater, and building desalination plants as rainfall-independent supplies”.
The expression “rainfall-independent supplies” also appeared in the Victorian State Government’s Guidelines for the Development of Urban Water Strategies in 2016, and, therefore, in many of the urban water strategies that have subsequently been developed in Victoria.
A more recent severe drought, during 2017-2020, has further focused attention on this concept, and RFIS has transitioned from being merely a positive characterisation of some urban water sources to a clear, underlying objective for urban water planning. This is most apparent in the New South Wales Water Strategy, published in August 2021. This document positions the expansion of RFIS as a key strategy to improve capacity to cope with climate variability and change. With reference to the state’s largest city, it says: “The resilience of Sydney’s system can be improved immediately by increasing water conservation and water efficiency and, in the future, by securing more reliable water supplies that include additional rainfall independent sources of water – either desalination and/or recycled purified wastewater.”
“For some cities, groundwater from deep confined aquifers can provide a relatively rainfall independent supply”
The New South Wales Water Strategy indicates that Sydney currently has the capacity to supply 23% of the city’s total water demand from RFIS. This capability is provided by a seawater desalination plant, which can supply 15% of demand, and a portfolio of water recycling projects, which, together, supply 8% of total demand. The document illustrates both the need and the opportunity to expand RFIS for Sydney by comparing these figures with total RFIS capacity as a percentage of total demand for other cities, including Adelaide (49%), Perth (49%), and Melbourne (37%). It states: “Increasing our proportion of rainfall-independent supplies allows us to slow down depletion rates in times of drought, helps to keep our dams full (providing long-term security) and enhances our ability to respond to other shocks in the system, such as water quality incidents.”
For some cities, groundwater from deep confined aquifers can provide a relatively rainfall independent supply. For example, large groundwater resources contribute to the water supplies of Perth and Adelaide. However, significant sustainable groundwater resources are not readily available to other Australian cities, including Brisbane, Sydney and Melbourne.
Desalination and recycling
By far the most prominent form of RFIS for Australian cities is seawater desalination. During the later years of the Millennium Drought, Australia embarked on a major programme of capital investment in seawater desalination. The first major plant was constructed to supply Perth with 45GL/year and became operational in 2006. Perth is now supplied with water from two desalination plants, with the second completed in 2012 to supply 100GL/year.
The Gold Coast Desalination Plant was completed in 2009 to supply 50GL/year. When needed, this water can be transferred to Brisbane via pipe and pumping infrastructure known as the South East Queensland Water Grid. The Sydney Desalination Plant was completed in 2010 to supply 90GL/year, and much of the associated infrastructure has been sized to facilitate a future expansion to 180GL/year. A desalination plant to supply Adelaide was constructed in 2012, able to supply 100GL/year. Australia’s largest seawater desalination plant was built in 2012 to supply Melbourne with up to 150GL/year.
Australia also has some experience with large-scale water recycling schemes. Most significant has been the groundwater replenishment scheme constructed to replenish the groundwater resources relied upon by Perth. This scheme first started operating in 2017, purifying water from a Perth sewage treatment plant by ultrafiltration, reverse osmosis and ultraviolet disinfection prior to injection of 14GL/year to an important drinking water aquifer. The scheme is now undergoing expansion to double capacity to 28GL/year. For this purpose, construction of a second advanced water treatment plant was completed in 2019, along with a new pipeline and recharge and monitoring bores. The expansion is being commissioned and tested throughout 2021, and is expected to become fully operational in 2022.
A larger water recycling scheme was developed in Queensland and is known as the Western Corridor Recycled Water Scheme. This scheme can collect treated effluent from six wastewater treatment plants for treatment at one of three advanced water treatment plants around Brisbane. The scheme was constructed with the capacity to supply 70GL/year, some of which is delivered directly to large industrial water users, including a gas-fired power plant. But the scheme has the capability to produce far more water than these users consume and was designed for the remainder to be used to replenish supplies in the region’s largest surface water storage, Lake Wivenhoe. The infrastructure to deliver this water has been constructed, but has yet to be used for that purpose as, following construction in 2009, adequate supplies (>60% of capacity) were maintained in Lake Wivenhoe from natural inflows until 2019. During this period, the Recycled Water Scheme was largely decommissioned to save ongoing maintenance costs.
Since 2019, water storage in Lake Wivenhoe has been below 60% of capacity and dropped as low as 36% in early 2021. It is anticipated that low water storage will soon trigger a gradual recommissioning of the Western Corridor Recycled Water Scheme. This purified recycled water will be an important RFIS for Brisbane, providing protection against the impacts of future drought.
The water quality dimension
While the growth of RFIS for Australian cities has primarily been in response to periods of drought, the statement in the New South Wales Water Strategy that it “enhances our ability to respond to other shocks in the system, such as water quality incidents” is also well founded. In 2013, Brisbane experienced major flooding in water catchments, leading to high degrees of erosion and extreme spikes in raw water turbidity. Very large quantities of suspended sediment in raw water severely impeded the performance of the water filtration plant, reducing the rate at which treated drinking water could be produced. As a consequence, it has been reported, Brisbane almost ran out of water during the floods, as demand outstripped supply. Relief from this situation was provided by the Gold Coast Desalination Plant, which delivered water into the Brisbane supply network via the South East Queensland Water Grid.
Similarly, following severe bushfires in Sydney’s drinking water catchment, reduced quality raw water has been experienced after heavy rainfall events during 2020 and 2021. While no emergency situations have
been encountered, the ongoing operation of the Sydney Desalination Plant has enabled reduced reliance on the major water filtration plant that supplies drinking water to most of Sydney. Under previously established operating protocols, the desalination plant would normally have ceased producing water once Sydney’s surface water storages were replenished to sufficiently high levels. However, this has not occurred, specifically for the purpose of guarding against spikes in raw water quality, which may impede water filtration performance.
The comparatively low proportion of RFIS capacity for Sydney, as highlighted in the New South Wales Water Strategy, suggests that this city may be less well equipped to manage extended drought and raw water quality incidents than other Australian cities. The fact that RFIS has been recognised as a meaningful measure against which to benchmark our urban water supplies also suggests that future growth in urban water supply capacity will probably be weighted towards increasing RFIS capacity. For Sydney and other cities, this will probably mean further growth in both seawater desalination and purified recycled water. •
Professor Stuart Khan is at the School of Civil & Environmental Engineering, University of New South Wales, and is a member of the Management Committee of the IWA Specialist Group on Water Reuse.
Water Corporation gears up for doubled replenishment capacity
Australia’s Water Corporation, which serves Perth and surrounding areas in Western Australia, brought the country’s first full-scale recycled water Groundwater Replenishment Scheme online in 2017. This 14GL/year scheme has recharged 40 billion litres to date (August 2017-July 2021). Commissioning work is under way on a second phase that will see the capacity of the scheme doubled in early 2022.
Wastewater treated at the utility’s Beenyup Wastewater Treatment Plant in Craigie, in the northern suburbs of Perth, passes to an Advanced Water Recycling Plant. Here, the water undergoes further advanced treatment processes, including ultrafiltration, reverse osmosis and ultraviolet disinfection, to meet Australian guidelines for drinking water.
The expansion includes building a second Advanced Water Recycling Plant at the Beenyup facility, drilling four new recharge bores and four new monitoring bores in Wanneroo and Neerabup, and building a 13km recharge pipeline connecting the Advanced Water Recycling Plant with the new bores. Construction of the new infrastructure was completed in 2019. Commissioning and testing are under way and the second phase is expected to be fully operational early next year.
Reuse project prospects for agricultural reuse
The recent Australian Government federal budget sets out National Water Grid Authority funding prospects for water infrastructure (see www.nationalwatergrid.gov.au/about/news/budget-2021-22). There is a substantial focus on water reuse, especially for agriculture.
Of the four projects approved for construction phase funding, three of them include water reuse:
• VIC – Werribee Irrigation District Modernisation
• VIC – Recycled Water on the Bellarine
• QLD – Warwick Recycled Water for Agriculture
Of the eight projects being funded for detailed business case development, four are water reuse projects:
• VIC – Pakenham Cora Lynn Recycled Water Scheme
• VIC – Sunbury-Bulla-Keilor Agricultural Rejuvenation
• VIC – Tyabb-Somerville Recycled Water Irrigation Scheme
• SA – New Water Infrastructure to Barossa