Australia’s worst drought on record paved the way for new technologies in recycled water, but how should authorities deal with the mix of products and services? Toli Papadopoulos reports.
It’s ground zero and all eyes are on Australia as the nation fearfully awaits the day where the taps turn off. We have run out of water.
It may be reassuring to think this scenario wouldn’t have played out during the Millennium drought – one of Australia’s worst droughts on record. But that was cold comfort for water authorities who were under immense pressure to secure water supplies for states and territories nationwide. No longer would Australia be reliant on its flourishing dams, but a network of new water infrastructure and programs to change consumer behaviour.
While not entirely a nationwide drought, it affected most of the country and much of the Murray-Darling basin. As different cities experienced varying levels of drought, the years 2006 to 2008 were the driest on record for many parts of the country. Fortunately, the waterless scenario never came to fruition, as Australia transitioned to a wet La Niña period in 2010 – marking the end of the drought.
Despite the rains arriving, the reaction to the nation’s crisis marked the dawn of a new era. It was an era characterised by new technologies, including desalination plants to provide rainfall independent supplies and recycled water, stormwater and groundwater. Desalination plants were invested in heavily during the Millennium drought, including in the Gold Coast, Perth, Sydney, Binningup in WA, Adelaide and Melbourne. The plants involve taking the salt out of water to make it drinkable via water distillation and membrane processes.
With population growth comes numerous challenges. As we move towards an urbanised future – an eclectic mix of technologies could be required to aid the transition. One of the most significant is the provision of affordable water in the midst of more stormwater and sewage generation, which places pressure on the existing infrastructure.
According to Briony Rogers, Senior Lecturer with Monash University’s School of Social Sciences and research leader with the Cooperative Research Centre for Water Sensitive Cities, many states acted quick enough with water conservation and desalination, but if the rains hadn’t come, a more severe management response would have been required.
“It was certainly a wake up call and we had to make decisions around desalination in a crisis context,” she says.
“There wasn’t time to have extended discussion on the best way forward. If water authorities had a longer lead time, they would have been able to explore a range of decentralised water recycling technologies.”
As there are many technologies for the future, Waste Management Review discusses these in further below.
URBAN ENVIRONMENTS
Melbourne is expected to reach five million residents by 2025 and overtake Sydney’s population growth in the 2050s. By then, both cities will house more than eight million residents. The recent projections are a stark contrast to the 1998 Australian Bureau of Statistics Population Projects, which had initially projected both populations under five million by 2051. Sydney is already at five million and Melbourne is creeping close at 4.8 million.
Dealing with this population growth requires a multipronged approach. In its Melbourne Water System Strategy, Melbourne Water highlights that sewage and stormwater are no longer considered waste products – sewage can generate recycled water, biosolids and biogas. Last year, City West Water, South East Water, Yarra Valley Water and Melbourne Water predicted that in the lowest supply and highest demand scenario, Melbourne will have a shortfall of water of more than 450 billion litres of water.
The document, Water for a future-thriving Melbourne, explains how recycled water can be used to irrigate farms and parks, flush toilets and in industrial processes. The benefits range from reducing the volume of polluted stormwater and treated sewage discharged into waterways and bays, to taking pressure off the water needed from the water supply system.
RECYCLED WATER LEADERS
One of the progenitors of recycled water in Australia has been WA – headed by the state-owned authority Water Corporation WA. A Water Corporation spokesperson tells Waste Management Review that WA didn’t experience the Millennium drought seen on the east coast in the 2000s, but rainfall has been steadily declining since the 1970s. Since then, May to July rainfall in the south west of WA has reduced by around 19 per cent, but streamflows to dams have declined much more dramatically.
The state-owned Water Corporation supplies water to two million people in Perth, the Goldfields and agricultural region and some parts of the south-west.
The 2016 Future Opportunities for Water Services in Perth report showed a water shortage predicted in the drought-ridden city, highlighting that the city must more than double the amount of drinking water it supplies to meet its growing population by 2050. The Water Corporation spokesperson says investment in climate independent sources has been a crucial part of its work to tackle climate change, as outlined in its 10-year Water Forever plan – a three-pronged approach, which includes working with the community to reduce water use, increasing the amount of water recycled and developing new water sources. It complements a 50-year plan to tackle water supplies to meet its target of 30 per cent recycled wastewater by 2030.
Contrary to a nationwide trend towards desalination, Perth responded with additional wastewater treatment facilities, such as the Beenyup wastewater treatment plant. This plant uses groundwater replenishment – a concept where treated wastewater is further treated to drinking water standards. It includes processes such as ultrafiltration, reverse osmosis and ultra violet treatment to remove suspended soils, viruses and bulk and trace organics, and for final disinfection.
The water is then recharged into the natural underground aquifer where it will remain for potentially decades before being drawn out at another location, treated at a water treatment plant and added to the water supply scheme.
TYPES OF RECYCLED WATER
There are several types of water recycling in Australia, including non-potable reuse – water that can be used for industrial purposes, agriculture or landscape irrigation, or flushing toilets.
Direct potable reuse is safe for drinking and other purposes and indirect potable reuse is water that is reclaimed and returned into the current/natural water cycle.
Indirect potable reuse can be returned into a natural water system, such as a groundwater aquifer, to treat the water for human consumption.
It is used in projects such as the Queensland Government-owned Western Corridor Recycled Water Project, which is followed by treatment processes such as microfiltration, reverse osmosis and advanced oxidation.
No Australian urban water supply uses direct potable reuse to treat its sewage – but the option was investigated further in a study by the Australian Academy of Technological Sciences and Engineering. Its review of existing Australian legislation and frameworks found a well-designed and operated direct potable reuse project could be used as a water resource management option.
Ian Wright, Senior Lecturer in Environmental Science at Western Sydney University, says Perth is sourcing more of its supplies from groundwater replenishment.
“Perth and Adelaide are really water stressed and I think they’re a good example for us in the east – Sydney, Brisbane and Melbourne in particular.”
“South Australia had to rely on flows down the Murray, which got really unreliable in the Millennium drought, while both Melbourne, Sydney and south-east Queensland had desalination ready to flick the switch.
“Perth does too – but they realised there’s a lot less salt in sewage. You can actually treat that and I honestly think that’s the answer.”
Ian says desalination is probably more expensive because of the energy, membranes and chemical engineering required. He adds that extracting that fresh water from salty is hard work.
“With the shortage of electricity we face now, that’s one of its biggest drawbacks.”
The Water Corporation spokesperson says its Southern Desalination Plant, which produces up to 100 billion litres of water each year, uses energy recovery devices to capture the hydraulic energy from the high pressure reject stream of the seawater reverse osmosis process. They said these devices transfer this energy to low-pressure feedwater, which reduces the overall amount of energy required in membrane desalination by up to 60 per cent.
NO SILVER BULLET
Briony believes that there is no single answer when it comes to selecting from a host of recycled water technologies, but the key is building climate resilient systems.
She says desalination is suitable for handling larger volumes of rainfall-independent water and more sustainable when supported by renewable energy. Lower energy technologies such as recycled stormwater can be useful for environments where there are catchments available and hard surfaces for the stormwater to run off and collect.
Ian says it’s important to adapt to future climate change coming our way. He says the Western Treatment Plant in Melbourne is a good example of this.
He says there is also potential for Melbourne Water Western Treatment Plant to be used further for non-potable reuse and indirect potable reuse with careful treatment – meaning it would be a drinkable water source.
REVERSE OSMOSIS
Ian says reverse osmosis is one of the new and emerging technologies for sewage. Reverse osmosis is used to remove contaminants from water by pushing this water under pressure through a semi-permeable membrane.
“The old treatment for sewage still had high nutrients in it, but it took a lot of the biological oxygen demand so you didn’t get that unhygienic effluent.
“Now we’ve moved to advanced water treatment with reverse osmosis as the last step and that is the future,” he says, adding that he predicts huge investment in this area.
Ian says Perth has been the leader in recycled water, relying heavily on desalination and groundwater for its water supply.
Perth diversified its water supply, with desalination and groundwater extraction providing about 90 per cent of the city’s water supplies. About 10 per cent of Perth’s sewage is recycled via advanced treatment and replenishment into groundwater supplies.
The Water Corporation spokesperson says works on an Australian first-of-its-kind groundwater replenishment scheme in Perth’s northern suburb of Craigie was completed last year.
It has the capacity to recharge up to 14 billion litres of drinking quality water to Perth’s aquifers.
“Work on the Stage 2 expansion of the scheme is under way, which will see the scheme’s capacity doubled to be able to recharge up to 28 billion litres of water each year,” the spokesperson adds.
By 2060, groundwater replenishment could supply up to 20 per cent of Perth’s drinking water, or around 115 billion litres each year.
COMMUNITY CONSULTATION
Ian says longstanding concerns about drinking recycled sewage can be allayed, as many dangerous waterborne diseases, such as cholera, are incredibly rare in Australia.
“Investment in advanced water treatment is in the millions and there is quite a lot of discomfort in the wastewater industry about a lot of governments going for desalination when it is likely more efficient to turn sewage into a useful product, rather than desalinate water,” he says.
“Brisbane, Melbourne, Sydney and Canberra have a fair bit of water in their storages, but in many ways we’ve become complacent. We’ve got populations expanding whether we like it or not, yet there is huge concern we might have less rainfall and runoff under climate change.
“Nobody has suffered like Perth – they have suffered progressively over 50 years. Their inflow to their surface storages have dropped every decade since 1974.”
He says recycled water offers a reliable alternative to Australia’s water needs, as sewage flow is predictable when compared to rainfall.
Briony highlights direct potable and indirect potable reuse are already happening in cities around the globe, including in Singapore. She adds that the technology to support recycled drinking water is already well established, it is now a matter of encouraging more community dialogue in Australia. In her research, the community has shown an interest in pursuing recycled water.
She says drinking recycled water could be part of a portfolio of options for cities in the future.
“Climate change is leading to lower overall rainfall and extended periods of drought, not only impacting on our water storages, but drying the catchments so that when it does rain, less water ends up running off into the dams.
“From a flooding perspective, when it does rain it will come in more intense, shorter periods, so drainage infrastructure will come under greater pressure from flash flooding.”
Ultimately, it’s about a shared vision, she says, with organisations and the community unified by a common direction and commitment to action for improving our climate resilience and city liveability through water innovations.