

Experts are calling for an upgrade of Sydney’s sewage system after a second round of beaches were closed upon the discovery of balls of debris washed ashore.
Black balls of debris were first seen along Coogee and Bondi in October, and were later determined to be a mixture of fats, oils, human hair, soap scum, human faeces, and recreational drugs.
Beaches along Sydney’s north were closed again on Tuesday as the balls- this time white and grey- made its return, and although they share some similarities with those found last year, the NSW Environmental Protection Authority says it’s too early to draw any conclusions.
Professor Stuart Khan, head of the school of civil engineering at the University of Sydney and specialises in water treatment, told the Sydney Morning Herald that the debris analysed in October are good indicators of sewage.
“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 says that Sydney’s wastewater system was unusual for a major city in a developed nation, as sewage is only given “primary” treatment at wastewater centres in Bondi, Malabar, and North Head.
This primary treatment involves physical processes, such as screening out solids and allowing sludge to settle to the bottom, while fat and grease floats to the top. Secondary processing relies on detailed biological processing and filtration, and can rid wastewater more thoroughly of fatty substances.
After primary processing, wastewater is pumped kilometres out to sea to deep ocean outfalls constructed in the 1990s.
“We really are out of step with the rest of the developed world, discharging primary-treated effluent into the Pacific Ocean,” said Khan. “You can’t do that in California.”
“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.
“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.”
Investigations continue into source of mystery balls of debris
Sydney Water confirmed that there were no operational issues with the Warriewood or North Head treatment centres, and it working with the EPA to identify potential sources of the debris on Tuesday and their similarities to those found last year.
They’ve also engaged an external modelling expert to help find the origin of the balls.
Associate Professor Jon Beves at the University of NSW led the testing of the balls along the eastern suburbs last year, and has requested samples of the northern beaches debris for testing.
“I don’t know how they compare the ones that we analysed from Coogee Beach last year. Perhaps they’re similar, but at the moment, we don’t know,” he said. “It’s from human-generated waste, the type of stuff you’d find in a sewer.”
Environment Minister and Acting Premier Penny Sharpe said no obvious pollution events at sea had been identified.
“This is a phenomenon that’s not being seen anywhere else in the world,” she said. “This is an odd situation that remains a mystery that we’re getting to the bottom of.”