When Australia’s first large-scale desalination plants faced concerns about algal blooms and marine die-offs, engineers dived in to design effective solutions.
As the Millenium Drought put Australia’s water supplies and management to the ultimate test, desalination technology was held up as both a saviour and a scapegoat.
On the one hand, it could make seawater drinkable, providing a seemingly limitless supply of fresh water for a parched population. On the other, there were speculations that the discharge of concentrated seawater in the form of brine (a by-product of the desalination process) might devastate marine life.
Thanks to strong governance and innovative engineering solutions, it was possible to design solutions that deliver the benefits without the drawbacks.
“Australia has generally been really good in implementing marine monitoring programs to not only confirm that there is no environmental impact, but also to properly assess potential long-term effects,” said Jerome Douziech, Vice President of Operations and Performance at SUEZ, which designed, built and now operates with its partners both the Perth Seawater Desalination Plant (PSDP) and the Victorian Desalination Plant (VDP). “The most advanced of marine monitoring programs is in place at the VDP.”
By combining the monitoring of process water quality, diffuser performance and marine ecology, the VDP’s marine monitoring ensures the plant operates according to its certified design and its EPA operating licence.
The design of the inlet and outlet structures constitutes the first step in mitigating the risk associated with drawing seawater in and discharging brine.
The plant’s automated control system, the second barrier, is designed to detect and address any issues with water quality to ensure that only brine that meets the required quality specifications goes back into the marine environment.
The marine monitoring program collects data from sensors and instrumentation within the plant, around the discharge points and across the wider marine environment. This information, combined with the ecological monitoring at multiple locations both inside and outside the mixing zone, “provide a comprehensive understanding of local marine processes, ensuring there is no impact from the discharge of those desalination plants”, according to Douziech.
What began as understandable public concern eventually became a model for environmental engineering as it produced positive outcomes.
By the numbers
The Victorian Desalination Plant:
- Is capable of delivering 150 billion L of drinking water annually, which equates to 164 Olympic swimming pools per day
- Can satisfy up to one-third of Melbourne’s annual drinking water demand
- Has produced more than 500 GL of water to date
- Sends water through an 84 km, two-way pipeline to Melbourne
- Has had a 2025/26 order placed by the Minister for Water for 50 GL
Engineering the marine structures
Two inlet structures, located on the seafloor approximately 20 m below sea level, are fitted with velocity caps to ensure a low-speed water intake, preventing the entrapment of marine life.
The brine is discharged back into the marine environment through two seabed outfall structures designed to ensure effective mixing, allowing salinity to return to background levels within a short distance of the discharge point.
Getting the outfall engineering right is critical. This required a focus on two key design elements. One was the outfall tunnel itself, which had to survive the rigours of subsea conditions and operational requirements. The other was providing assurance that the brine was sufficiently diluted before discharge.
Comprehensive modelling supported the design of these structures and verified that they would provide the required brine dispersion across all production scenarios and seawater conditions.
The outfall consists of two nine-metre diameter concrete structures connected to a 1.5 km, four-metre diameter underground tunnel. Each structure is equipped with calibrated nozzles that provide the required discharge velocity to achieve the proper brine dilution.
“You’re designing a structure that sits under the sea, exposed to marine growth, strong currents, mechanical stresses and corrosion constraints,” he said. “It’s actually a dream job for an engineer. Part of our job also involves deploying specialised divers to regularly inspect the integrity of the structures, as well as the associated instrumentation.”
These inspections, combined with continuous salinity and ecological monitoring, have confirmed that the plant operates in accordance with its certified design and EPA operating licence, so the marine environment in the vicinity of the plant remains healthy.
VDP ecological focus is not limited to the marine environment. The design of the plant also delivers significant outcomes on land, with a unique ecological rehabilitation achievement for the 225 ha surrounding the plant.
“The project design includes a significant architectural and landscape component to achieve the plant’s seamless integration within its surrounding coastal environment,” Douziech said.
This led to the establishment of an ecological reserve through the largest single ecological restoration project of its kind ever undertaken in Victoria, restoring and enhancing the natural habitat and creating a new coastal park.
Prior uses of the area over a century, including grazing and mining, had created a large break in the otherwise continuous line of coastal vegetation of the region. This revegetation project is restoring that cleared area back to the ecological state that existed before settlement. By reconnecting important coastal reserves, the region’s habitat values have been enhanced. Returning wildlife has been observed, including kangaroos, wallabies, wombats, koalas and emus.
Energy challenge
The major sustainability challenge with desalination, Douziech said, is its energy-intensive nature. Both plants are 100 per cent offset as their electricity consumption is compensated by wind farm energy generation. But the goal is to continue to reduce their energy needs over time.
“High pressure pumps are used to push seawater through reverse osmosis membranes at approximately 60 bars [870 psi]. These pumps require a lot of energy,” he said. “There is now significant research and development focused on optimising energy consumption.
“One major advancement in both plants has been the implementation of energy recovery devices. These systems use the residual high pressure within the process to recover energy, rather than wasting it, helping to optimise and reduce overall energy consumption.”
Research is also being conducted on the membranes themselves, with a focus on developing new materials that could reduce the energy required to push water through them.
“Among membrane suppliers, it’s a highly competitive environment,” Douziech said. “When they manufacture membranes, they offer a set of performance features, including flow capacity, guaranteed salt rejection and energy consumption. As an operator selecting membranes, we look closely at those three parameters – flow, permeate quality and energy.”
Other research and pilot projects include brine mining, which involves the recovery of various minerals from the brine before it is discharged. These minerals may include those required to rebalance the desalinated water before it becomes drinking water, as well as minerals with commercial value, such as magnesium.
Essential or nice to have?
Often considered in Australia as a product of the Millenium Drought, desalination plants are one of two essential future inclusions outside of traditional water infrastructure such as dams, according to Adam Lovell, Executive Director of the Water Services Association of Australia.
“In the move towards climate-resilient water supplies, seawater desalination and purified recycled water are the two big sources that could offer a relatively stable supply,” Lovell said. “We know that seawater desalination can provide a very good yield, and it’s a well-established technology.
“We’ve seen a lot of desalination suppliers moving beyond nameplate capacity and driving bigger plants beyond what they were originally designed for. This is a great indictment of the fabulous technical skills that exist within the industry, nationally and internationally.”
The desalination story in Australia, from early fears to advanced monitoring, energy recovery and brine mining, reflects a broader evolution in engineering itself. While climate change, sustainability concerns and deeper engagement with stakeholders bring greater challenges at the start, engineers are designing and innovating better to deliver positive outcomes on all fronts.
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