The grime balls were a symptom of an ailing sewerage network. The cure could be to drink recycled water

The Age

29-05-2025

If Sydneysiders want clean beaches and a swimmable harbour, they might need to start drinking purified recycled water.
That's the view of Sydney Water, which is pitching a proposal to take wastewater, treat it to a high standard and then return it to the dams. It's an approach also backed by independent water engineers and scientists.
The thousands of dark debris balls found at Coogee and other beaches last year were a symptom of an ageing sewerage network straining at the seams – and that's before you add projected population growth from 4.9 million people in 2021 to 6.3 million by 2041.
Professor Stuart Khan, head of civil engineering at the University of Sydney, says the system is reaching capacity, and using purified recycled drinking water beats the alternative.
'If we don't pull more water out of that system, then we're going to get to the point where we need to start building big, new sewers from Western Sydney to bring more sewage to the coast to discharge into the ocean,' Khan says. 'That's going to be a lot more socially difficult in the 2020s than it was in the 1990s.'
One sign of the straining system is that a big pipe carrying sewage from western Sydney to Malabar now regularly overflows at Mill Pond, making nearby Foreshore Beach in Botany Bay consistently one of the dirtiest in Sydney.
Testing last year revealed the debris balls to be a mix of fats, faeces and other pollutants found in sewage. In April, the NSW Environment Protection Authority concluded that the balls originated in the sewerage system, after ruling out sources such as passing cruise ships.
The environmental watchdog ordered Sydney Water to assess its deep ocean outfall systems at Bondi and Malabar and its sewerage pipe network to find the fault, and convened a wastewater expert panel to provide independent scientific advice.
Khan, who was appointed as chair, says a key question is whether the balls originated in the wastewater treatment plants or from the sewerage pipes overflowing into stormwater during rain. Upgrading either could cost billions.
Wastewater treatment
Water experts call the wastewater treatment plants at Malabar, Bondi and North Head 'the dirty three' because they only provide primary treatment, while all other big cities in Australia provide at least secondary treatment.
Khan says primary treatment is mostly about removing solids under gravity. Other plants provide secondary treatment – using bacteria for biological degradation – or even tertiary. The definition of tertiary is less defined, he says, but usually involves sending the water through another physical filter such as sand.
Each of the dirty three has a deep ocean outfall built in the early 1990s, so the plume of effluent is now released further out to sea. This makes the beaches more pleasant than the bad old days when Malabar was permanently closed and swimmers at Bondi had to dodge turds in the surf, known as 'Bondi cigars'.
Yet there is more pollution because the population has grown. As of 2021, the Malabar plant serves 68,247 hectares in southern Sydney as far south-west as Campbelltown and treats the wastewater of 1.9 million people.
Sally Rewell, the water resource recovery lead at Sydney Water and manager of the Malabar plant, says the average flow treated at the site in dry weather is about 450 megalitres a day, but it can peak at 1200 megalitres a day in wet weather. The plant may discharge to the cliff when flows reach 800 megalitres a day but Rewell says it has not needed this emergency measure in the past decade.
Kurnell resident Sarah-Jo Lobwein from Sutherland-based environment group SoShire says her beach clean-up group has collected detailed data on the type of rubbish and its source since 2018.
SoShire volunteers have been noticing debris balls for years, Lobwein says, but they were mostly greyish white and the size of marbles rather than black and the size of tennis balls like the ones that washed up on nearly every beach from Bondi to Little Bay last October.
'When there's a swell, we used to get angular chunks of the fat, oil and grease … while on calmer days with lots of rain, we would find the circular ones,' Lobwein says.
'There's this idea that … the ocean will dissolve it and spread out the problem, but as we've seen, that's not happening, so we are getting some of the effects of it.'
John Gemmill, chief executive of Clean Ocean Foundation, says Sydney's 'dirty three' deep ocean outfalls stand out in the national data from all outfalls around Australia.
'It's embarrassing for Australia to have those, and totally at odds with how we see ourselves as a beach-loving, ocean-loving country,' Gemmill says.
The Clean Ocean Foundation is calling for all water treatment plants to be upgraded to 'quarternary', which Europe has committed to do by 2045. This refers to advanced treatment beyond tertiary, focused on removing micropollutants such as pharmaceuticals, pesticides and the PFAS family of synthetic cancer-causing 'forever chemicals' now found in the bodies of virtually every NSW resident.
Khan says Europe is upgrading to advanced treatments such as ozone and activated carbon, but the focus is on inland areas to protect rivers. For example, Switzerland is treating water to a high level before returning it to the catchment of the Rhine River, which flows through Austria, Liechtenstein, Germany, France, the Netherlands and out to the North Sea.
In the United States, the Clean Water Act of 1973 effectively outlaws the discharge of anything less than secondary treatment into the ocean, Khan says, though there are cities such as San Diego that have been applying for and receiving exemptions year after year.
He agrees with the 'dirty three' descriptor for Malabar, Bondi and North Head, but says sending the effluent 4-6 kilometres further out to sea has environmental benefits because the strong currents ensure the water is dispersed.
Professor Ian Wright, a water expert at Western Sydney University, says the contaminated plume rarely comes to the surface, making it hard to know how far its footprint stretches.
'Only every now and then will something like the tar balls come [up] and give us an indication of what's actually going on,' Wright says.
Wright believes contaminants including PFAS and microplastics are accumulating in food chains in the ocean, including seafood consumed by humans. His research proves this is happening to platypus in rivers in the Sydney catchment and that sewage outfalls are the source.
The pipes
There has been a concerted political effort to open up more swimming places in the Nepean, Georges and Parramatta rivers and Sydney Harbour, from Barangaroo to Penrith Beach.
But every time there is heavy rain, the sewage overflows into stormwater. At the coast this is flushed away fairly quickly, but it takes longer in the rivers and harbour, so the general advice is not to swim for three days after rain.
Several popular swimming spots – including Balmain, Barangaroo, Nielsen Park and Redleaf – had dangerous levels of bacteria associated with human waste even when it had not been raining when this masthead commissioned independent testing earlier this year.
Kate Miles, head of system planning and land acquisition at Sydney Water, says when there is too much water in the sewerage pipes, it overflows to stormwater, and this is necessary because it prevents pressure building up and damaging the sewer. The part that can be changed, she says, is how much water gets into the sewer in the first place.
In theory, there should be no extra, since people don't use the toilet or the dishwasher more when it rains and might do less laundry. In reality, breaks in the sewer pipes allow rain or stormwater to enter.
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Khan says many of the sewer pipes were laid in the 1930s-1950s and ones on properties are often made of terracotta.
'The older the system gets, the more breakages and leakages that you get,' Khan says. 'Sewage breaks and leakages also tend to flow into the stormwater system, which ultimately leads to beaches or other waterways.'
Many property owners also, whether knowingly or unknowingly, have illegal connections that connect drainpipes from the roof to the sewer instead of the stormwater. Sydney Water can detect this with smoke tests, but the problem is large and dispersed.
Purified recycled drinking water
Sydney Water believes that one way it can reduce ocean pollution is to reduce the wastewater arriving at Malabar.
Miles says this can be achieved by treating the sewage further upstream, for example at the Glenfield and Liverpool treatment plants.
'Initially, we're working with the EPA around increasing the environmental discharges from those plants, but with the view that in the future, once customers are confident in it and embrace the idea as much as we do, the intention would be to convert those plants to purified recycled water plants, and then take that water to Prospect Reservoir,' says Miles.
Khan says significantly reducing the volume of sewage will also make it practical to upgrade the Malabar plant for higher-level treatment. Any upgrade at the current volumes, Khan says, would be enormous and 'extremely ugly', taking up valuable real estate or encroaching on the national park. Upgrading Bondi, where the wastewater treatment plant is built into the cliff face, and North Head, which is in national park, would also be difficult.
Miles says purified recycled water is now used in about 30 cities around the world, including London, Los Angeles, Singapore and Perth. Sydney Water is working on an environmental impact statement for its own proposal, which will be ready later this year.
'Purified recycled drinking water is cheaper than desalination and environmental standards are increasing ... so we have to treat wastewater to a higher and higher standard anyway,' says Miles. 'Why aren't we taking that and actually then just adding a little bit more treatment to it to make it clean enough that we can start to integrate it back into the water cycle?'
The Quakers Hill Purified Recycled Water Discovery Centre, which opened last year, allows members of the public to see the purification process in action – though until the law changes, they can't drink the clean water it produces.
Sydney Water senior project manager James Harrington, who took this masthead on a tour of the facility, says the purified recycled water would not be provided directly to customers but returned to the dams where it would be diluted by fresh water from natural waterways.
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In both the millennium drought and the 2017-2020 drought, Harrington says, Sydney's dams fell to about half capacity and that decline was getting steeper as the population grows.
As well as removing other impurities, the treatment would remove nearly all PFAS. However, Harrington says the proposal is to discharge the PFAS back to the ocean in a brine, while currently it goes into inland waterways.
Wright says he would be 'so happy' to see purified recycled drinking water in Sydney, or at least an expansion of the recycled water scheme where residents are provided water for gardens through a separate mauve tap. However, he has great concerns about sending PFAS to the ocean, especially in a highly concentrated form.
'We're robbing Peter to pay Paul … if we're going to take the PFAS out and then send it to the ocean,' Wright says. 'As the platypus shows, it's a really dangerous bio-accumulator, so with those slow-living marine species, there's a very good chance they're going to cop it.'
Fatbergs
It's not all on Sydney Water. The fats, oils and greases are in the system because consumers wash them down the sink, instead of following advice to put them in the bin. They also regularly flush hair or consumer items such as wet wipes down the toilet. When they clump together, they create 'fatbergs'.
'There's 20,000 blockages of fatbergs and wet wipes in the wastewater network every year, which costs us $27 million,' Rewell says.
An analysis by Sydney Water of 2023-24 data identified a significant increase of fat, oil and grease concentrations in wastewater, especially at Malabar, compared with the previous nine years. But the utility says it is still compliant with its licence.
Sydney Water believes the increase is because of population growth and successfully preventing seawater ingress at Malabar. Miles says people were also cooking more at home since the pandemic, rather than eating in restaurants where the kitchens have grease traps.
In a recent survey, the utility found 26 per cent of men aged between 18 and 29 believe it is acceptable to flush wet wipes, compared with 2 per cent of women the same age.
In beach clean-ups since 2018, Lobwein's group has collected thousands of cotton buds that had been flushed down the toilet and snapped at an exact length that matched the spacing between the physical filters in Cronulla's tertiary water treatment plant.
Lobwein says this data helped convince the NSW government to ban plastic cotton buds. She would like to see more public education campaigns, but also wants to see washing machines have filters to remove microplastics and PFAS so it doesn't enter wastewater.
A cautionary tale
Even if Sydneysiders did not care about water pollution or need to drought-proof their water supply, the sewerage network still needs maintenance.
The situation in Britain provides a cautionary tale. Khan says decades of severe underinvestment meant the sewerage systems could no longer cope with the volume of sewage being generated, and there were massive overflows of raw sewage into waterways.
'All over England, there are severely contaminated waterways because of these leakages, and there is no money to fix it,' Khan says. 'It's a consequence of national privatisation of water under the Thatcher government in the '80s.'