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It’s the height of summer in Sydney, a time when tourists and locals are usually flocking to the city’s famous beaches.
But nine beaches were shut to the public this week – including well-known Manly – after more ball-shaped debris washed ashore.
Similar sticky round globules have been found on many of the city’s beaches over the past six months, forcing some of them to close temporarily.
The New South Wales environment minister, Penny Sharpe, has said the balls remain a “genuine mystery”.
But there’s a growing number of experts and observers who believe Sydney’s unusual sewerage system is to blame.
“We know it’s a sewage source,” says the water policy expert Prof Stuart Khan. “The combination of different chemical contaminants, human hair, is a very strong indicator that sewage is ultimately the source.”
In October last year, thousands of black balls washed up on several eastern suburbs beaches including Bondi, Bronte, Coogee and Tamarama.
Those balls were initially widely reported to be “tar balls” comprising crude oil until testing coordinated with the Environment Protection Authority (EPA) revealed they were consistent with human-generated waste.
While the EPA says it hasn’t been able to identify the source of the balls, Khan suspects they are from sewage discharged through outfall pipes or washed offshore with stormwater after heavy rain.
Khan, who heads the school of civil engineering at the University of Sydney, says Australia’s biggest city is “out of step” with the rest of the country when it comes to the way it handles sewage.
Sydney’s sewage is only given “primary” treatment at the wastewater plants in Bondi, Malabar and North Head before it is flushed out to sea through “deepwater outfall” pipes that reach between 2km and 4km off the coast.
Those pipes were built in the 1990s. At the time, Khan says, bureaucrats dealing with water pollution had “two main options” – upgrading the treatment process, or maintaining the level of treatment but building the longer outfall.
“We didn’t go the treatment route mostly because of the differences in cost,” Khan says. “That was seen as the less attractive option.”
Primary treatment involves physical processes such as pumping sewage through a screen to remove solid waste. Secondary treatment – not used at the Bondi, Malabar and North Head plants – involves finer filtration and biological processing to break down the sewage.
Sydney Water says its water treatment plants are operating normally. It is also investigating potential illegal dumping into the wastewater network or stormwater system.
The agency says it has developed a “long-term” plan to upgrade Sydney’s wastewater networks with $30bn over the next 10 years.
Khan says it’s a “reasonable theory” that the balls are formed from waste coming from the outfall pipes, but he doesn’t suspect anyone of “hiding anything”.
The environmentalists Dr Richard Gosden and Prof Sharon Beder take a different view – Gosden accuses the EPA and Sydney Water of knowing “exactly what’s happening”.
Gosden and Beder were part of a group called Stop the Ocean Pollution (Stop) who campaigned in the 1980s to have “secondary” treatment added to the Bondi, Malabar and North Head plants before the outfall pipes were built.
Stop garnered significant support, including from the 250,000 people who Gosden said attended the Turn Back the Tide protest concert in Bondi in 1989, but ultimately were unsuccessful.
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“Sydney invented beach culture,” Gosden says. “It’s Australia’s single cultural invention that’s been properly exported. And all the time, it’s been conducted in diluted sewage.”
Beder wrote her PhD on the history of the engineering of Sydney’s sewerage system. As part of it, she examined the link between the city’s sewage and ocean pollution. In 1989, she published a book about her research and said she presented her findings to the relevant government authorities.
“They denied the whole lot,” she says. “As they’re in denial now about these so-called mystery balls.”
Beder says the government needs to step up and improve sewage treatment and better police the “toxic” manufacturing waste she says is put into the sewers by heavy industries.
“The government is just unwilling to do what is necessary to clean up the waste,” she says. “It’s obviously from the sewers. That’s where the faecal matter and the oils and the grease and all the stuff that’s in these balls.”
The balls have all been slightly different, depending on the beach where they’ve been found.
Green, grey and black balls washed up in Kurnell, in Sydney’s south, in early December. The ones found on the northern beaches this week were described as white and grey and “marble-sized”.
A few balls were found at Bondi, Coogee, Maroubra and Cronulla beaches last weekend, the government said. Most of them were only the size of a pea.
Dr Sharon Hook, a CSIRO principal research scientist, says it’s too soon to say where the debris is coming from or to blame Sydney Water.
“They seem to be somehow related to sewage, because they have so much human-derived waste in them,” she says.
Hook says the balls would have formed when fats and oils and other materials that don’t mix well with water are added to sea water. Where they wash up depends on the currents.
Hook says people shouldn’t touch them and they should avoid beaches that are closed.
“I don’t know what it is, but it could be illegal dumping,” she says. “It would be the equivalent of walking through a crime scene.”
The EPA and Sharpe were contacted for comment.
