Perth’s Water Corporation has commissioned expanded advanced water recycling facilities that will inject 14 billion litres of treated wastewater into aquifers annually, making it one of the world’s largest indirect potable reuse systems.

The expansion uses reverse osmosis and advanced oxidation processes to treat wastewater to purity levels exceeding most drinking water standards. The highly purified water is then recharged into underground aquifers where it mixes with groundwater and can be extracted later for drinking water supply.

The project addresses Perth’s water supply challenges as a growing population and declining rainfall strain traditional surface water and groundwater sources. Recycling water that would otherwise be discharged to the ocean creates a new, climate-independent water source.

Perth’s Water Challenge

Perth receives less rainfall than any other Australian capital city, and rainfall has declined about 20% since the 1970s due to climate change. Traditional water sources including dams and aquifers are increasingly stressed, requiring new approaches to water security.

Perth pioneered desalination in Australia, building its first plant in 2006. Two desalination plants now provide about 45% of the city’s drinking water, reducing dependence on rainfall and groundwater. But desalination is energy-intensive and expensive.

Water recycling offers a complementary approach. The source water is reliable regardless of rainfall, and treatment energy requirements are lower than desalination because wastewater has lower salt content than seawater.

Perth’s groundwater replenishment began as a trial in 2017, injecting 7 billion litres annually. The expansion doubles capacity based on operational success and water quality monitoring showing the system performs as designed.

Dr Neale Sutton, who manages the program for Water Corporation, said extensive monitoring over eight years has demonstrated that recharged water meets all health and environmental requirements. Public confidence in recycled water has grown as the system’s safety record accumulated.

Treatment Process

The advanced treatment train removes contaminants from wastewater far beyond what conventional treatment achieves. The process includes several steps, each targeting different contaminant classes.

First, secondary treated wastewater undergoes ultrafiltration, which removes bacteria, viruses, and suspended particles. Ultrafiltration uses membranes with pore sizes around 0.01 microns, small enough to exclude microorganisms but large enough to allow reasonable flow rates.

Next, reverse osmosis removes dissolved salts, organic chemicals, and micropollutants including pharmaceuticals and personal care products. Reverse osmosis membranes have pore sizes measured in angstroms, blocking essentially all dissolved substances except water molecules.

The reverse osmosis process produces highly purified water but also concentrated waste brine containing the removed contaminants. This brine is treated and discharged to the ocean through a deep ocean outfall designed to achieve rapid dilution.

Finally, advanced oxidation using ultraviolet light and hydrogen peroxide breaks down any trace organic chemicals remaining after reverse osmosis. This provides an additional safety barrier ensuring organic contaminants are destroyed rather than just removed.

The multi-barrier approach provides redundancy. Each treatment step alone achieves high removal of most contaminants. Together they provide multiple layers of protection ensuring water quality even if one barrier underperforms.

Aquifer Recharge

Treated water is pumped to infiltration basins where it percolates down to the aquifer about 50 metres below surface. The journey through soil provides additional treatment as bacteria in the soil break down any organic matter and minerals react with dissolved substances.

The aquifer provides substantial buffering volume, mixing recharged water with existing groundwater. By the time water is extracted from production wells, recharged water is typically diluted to less than 10% of the total, with the rest being natural groundwater.

Residence time in the aquifer averages several months before extraction, providing additional purification time. Monitoring wells track water quality throughout the aquifer, verifying that recharged water maintains quality and doesn’t negatively affect the aquifer environment.

The recharge locations were selected based on hydrogeological studies ensuring the aquifer can accept the water volumes without causing problems like waterlogging or groundwater mounding. Computer models of aquifer flow patterns predicted how recharged water would move and mix.

Water Quality and Safety

Water quality monitoring is extensive and ongoing. The system includes automated analysers testing water at multiple points in the treatment train, laboratory testing of samples collected daily, and quarterly monitoring of the aquifer at dozens of wells.

More than 200 different chemicals are monitored including metals, organic compounds, pesticides, and industrial chemicals. Microbial testing checks for bacteria, viruses, and protozoan parasites. Monitoring has consistently shown that recharged water meets Australian drinking water guidelines.

Some micropollutants are detected at trace levels in the treated water, typically nanograms per litre, thousands of times below health concern levels. These trace detections demonstrate the sensitivity of modern analytical techniques rather than indicating health risks.

Independent review by health authorities and expert panels has verified the system’s safety. The multiple treatment barriers and aquifer residence time provide redundancy ensuring water quality even if individual treatment steps perform below optimal levels.

Public acceptance has grown as the system operated safely over time. Initial public opinion research showed significant concern about drinking recycled water. More recent surveys show increased acceptance as residents gained confidence in the rigorous treatment and monitoring.

Economics and Energy

The recycling scheme costs about $1.50 per kilolitre to operate, including treatment, pumping, and monitoring. This is somewhat more expensive than groundwater extraction, which costs about $0.80 per kilolitre, but less than desalination at approximately $2.20 per kilolitre.

Capital costs for the expansion were approximately $200 million, including treatment facilities, pipelines, and infiltration basins. The investment provides water supply security worth far more than the capital cost given Perth’s dependence on stable water supplies.

Energy consumption is moderate compared to desalination. The recycling scheme uses about 1.5 kilowatt-hours per kilolitre compared to 3.5-4 kWh per kilolitre for desalination. Lower energy use means lower carbon emissions and operating costs.

Water Corporation operates solar farms providing renewable energy for water operations including recycling and desalination. The utility aims to achieve net-zero carbon operations by 2030, requiring renewable energy for all major facilities.

Environmental Impacts

Water recycling provides environmental benefits by reducing the volume of treated wastewater discharged to the ocean. The discharged wastewater, while treated to environmental standards, still contains nutrients and other substances that can affect marine environments.

Extracting less groundwater from aquifers also provides environmental benefits. Many Perth aquifers support groundwater-dependent ecosystems like wetlands. Reducing extraction pressure helps maintain water levels supporting these ecosystems.

The reverse osmosis concentrate disposal to ocean requires careful management to avoid environmental impacts. The system discharges through deep ocean outfalls with diffusers providing rapid dilution. Monitoring shows no detectable environmental impact from the discharges.

Energy use creates carbon emissions, though renewable energy reduces this impact. The net environmental benefit versus alternative water sources depends on comparing embodied energy, carbon emissions, and ecological impacts of different supply options.

Life-cycle assessments suggest that water recycling has lower overall environmental impacts than desalination but higher impacts than using surface water where it’s available. For Perth where surface water is limited, recycling offers one of the better environmental profiles among available options.

Future Expansion

Water Corporation plans further expansion to 28 billion litres annually by 2030 if current operations continue performing well. This would provide about 10% of Perth’s total water supply from recycling.

There’s a theoretical limit to how much wastewater can be recycled based on the total volume available. Perth generates about 150 billion litres of wastewater annually. Not all of that is available for recycling because some must be discharged to maintain environmental flows and system flexibility.

Realistically, recycling might eventually provide 15-20% of Perth’s water supply with the remainder coming from desalination, groundwater, and surface water. A diversified portfolio of sources provides security against system failures and climate variability.

Other Australian cities are watching Perth’s experience with interest. Melbourne, Sydney, and Brisbane all have advanced water recycling schemes planned or under consideration. Perth’s operational success provides confidence that the technology works safely and reliably.

International water utilities also reference Perth’s program when planning recycling schemes. Singapore’s NEWater and Orange County California’s groundwater replenishment are similar systems operating at comparable scales. The growing number of successful examples increases confidence in the approach.

For Perth residents, water recycling has become an accepted part of the city’s water supply portfolio. The expansion proceeds with little controversy, reflecting public confidence built through transparent operations and consistent water quality performance. In a city facing ongoing water challenges, recycling has proven to be a valuable solution.