By Angus Dalton
The mass closure of beaches due to the discovery of mystery grime balls should trigger a rethink of Sydney’s sewage system, according to a leading water policy expert, who said the reliance on “primary” treatment was unusual for a major developed city.
Nine beaches from Manly to North Narrabeen were closed on Tuesday after the discovery of white and grey marble-sized debris. It came just months after black balls washed up on beaches from Bondi to Botany Bay.
Most of the white debris balls found on the northern beaches were marble-sized and shared some physical characteristics with last year’s black grime balls, the EPA said.Credit: James Brickwood
The white globs shared some physical characteristics with the balls that closed eastern Sydney beaches last year, the NSW Environment Protection Authority said, but it was too early to draw conclusions.
One thing was made clear from the analysis of the sticky balls that washed up in October, however – their source was, at least partly, us.
The black balls comprised fats, oils and calcium, with traces of pesticides, human hair, hypertension medication, animal drugs, steroids, THC from marijuana and methamphetamine.
“These are things that my research group and others have known for a long time are really good indicators of sewage,” said Professor Stuart Khan, head of the School of Civil Engineering at the University of Sydney.
Workers cleaning up mystery balls in Dee Why on Wednesday.Credit: Louie Douvis
“There’s clearly a wastewater source involved. Potentially, it’s from a large ship, but I think that’s unlikely … it requires a fairly large wastewater catchment to bring all those different chemicals together.”
Khan, whose expertise is in water treatment, said Sydney’s wastewater system was unusual for a major city in a developed nation. Sewage is only given “primary” treatment at the wastewater centres in Bondi, Malabar and North Head.
“We really are out of step with the rest of the developed world, discharging primary-treated effluent into the Pacific Ocean. You can’t do that in California,” said Khan, who called for better treatment and recycling of wastewater.
Primary treatment relies on physical processes such as screening out solids and allowing sludge to settle to the bottom while fat and grease float to the top. Secondary processing involves detailed biological processing and filtration and can rid wastewater more thoroughly of fat and grease.
After primary processing, wastewater at the three centres is pumped kilometres out to sea to deep ocean outfalls built in the 1990s. (Another centre in Warriewood releases wastewater off Turimetta Head but that undergoes secondary treatment and disinfection.)
“One of the [primary] processes that they do employ is skimming the top to remove fat, oil and grease. But still, a lot of it can be dissolved, and it’s suspended in the water. You’re not going to remove all of it,” Khan said.
“There’s a big outfall off Malabar, which is not far from Coogee, and there’s a big one off North Head, which is not far from the northern beaches. Under the right conditions, you’re going to be discharging a lot of fat and grease into the ocean.
“It’s not too far-fetched to think about how that might congeal into these types of balls.
Sedimentation tanks at Bondi Wastewater Treatment Plant, which relies on “primary” treatment before wastewater is pumped out to sea.Credit: Steven Siewert
“I think the bottom line is that Sydney Water should take much more seriously the proposition that they could be formed from discharged sewage effluent ... rather than dismissing it.”
Another possibility was that sewage had ended up in stormwater through leakage, Khan said, and then flowed into the ocean. Sydney was drenched last week with its heaviest rain this summer.
Sydney Water confirmed there were no operational issues with the Warriewood or North Head treatment centres but said it is working with the EPA to identify potential sources of the northern beaches’ balls and their similarities to last year’s washed-up debris.
The organisation has engaged an external modelling expert to help find the origin of the balls. Illegal dumping into wastewater and stormwater networks is also being investigated.
Black balls washed ashore at Gordons Bay in Sydney in October 2024.Credit: Janie Barrett
“Sydney Water is taking the matter seriously and is continuing to work with the EPA to investigate possible causes of the grease balls,” a spokesperson said.
University of NSW associate professor Jon Beves, the chemist who led the testing of the eastern suburbs balls, has requested samples of the northern beaches debris.
“I don’t know how they compare to the ones that we analysed from Coogee Beach last year. Perhaps they’re similar, but at the moment, we don’t know,” he said.
Beves said the black balls had not come from an oil spill. “It’s from human-generated waste, the type of stuff you’d find in a sewer.”
The EPA’s analysis of the grease balls last year initially revealed bacteria associated with wastewater, but an “oil fingerprinting” test showed petroleum hydrocarbons similar to heavy fuel oils often used in shipping, complicating the mystery.
“This is a phenomenon that’s not being seen anywhere else in the world,” Environment Minister and Acting Premier Penny Sharpe said, adding no obvious pollution events at sea had been identified. “This is an odd situation that remains a mystery that we’re getting to the bottom of.”
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