Sydney is flushing roughly 1.5 billion liters of sewage into the ocean every day, a practice that harkens back to a bygone era when dilution was considered a solution to pollution. But a recent discovery of “poo balls” washing up on Bondi beach is raising questions about whether this decades-old system is reaching its limits.
Is Sydney’s sewage system a relic of the past, or is it still a viable solution for a modern city?
- Sydney relies on “fast primary treatment,” removing only solids before discharging effluent via ocean outfalls.
- A massive fatberg at the Malabar plant is suspected of causing the recent beach closures.
- Other australian cities, and many globally, employ secondary and tertiary treatment for cleaner discharge.
- Upgrading Sydney’s infrastructure is hampered by cost and limited space.
The unusual approach-pumping largely untreated sewage kilometers offshore-dates back to the mid-20th century, when the Bondi, Malabar, and North Head treatment plants were constructed. Before that, in the late 1800s, sydney simply discharged raw sewage directly into its harbor, creating a notorious public health hazard.
The Primary Problem
University of Sydney Professor Stuart Khan, who chairs the New South Wales government’s autonomous water advisory panel, explains that primary treatment is a fundamentally physical process. “You have a very large tank,and the raw sewage comes in at one end and flows through,” he says. “When sewage is flowing quite slowly and gently, some of the solid material that’s suspended in it will start to sink to the bottom of the tank, just under gravity.”
The remaining liquid, known as effluent, is then discharged into the ocean, where the eastern Australian current is expected to dilute it. The solids scraped from the bottom of the tank, called sludge, are now further treated and used for soil remediation in forestry and agriculture.
Secondary treatment, common elsewhere, utilizes biological processes to break down organic matter, while tertiary treatment adds a final filtration step, typically using sand.
A Brief history of Sydney’s Sewers
The shift from direct harbor discharge to cliff face outfalls in the early 20th century offered some betterment, but the ocean beaches remained famously polluted. “Incidences of ear infections were not uncommon for people swimming at Bondi,” Khan recalls. “Some beaches like Malabar were wholly unswimmable… you wouldn’t go in the water.”
When Sydney considered its options, building deepwater ocean outfalls-extending up to 4 kilometers offshore-proved cheaper than upgrading to secondary treatment. The Malabar outfall opened first in 1990.
Environmentalist Richard Gosden, who campaigned against the outfalls in the 1980s with the group Stop the Ocean Pollution, notes that sydney’s approach was unusual even then. “They had some pretty rough outfalls in Britain, where they only had primary treatment,
