Deep beneath the surface of the Malabar wastewater treatment plant, behind a rusted metal bulkhead door and waist-high water, lies a mass of congealed waste that has become a public health headache for the city. This massive accumulation of fats, oils, and grease—known as a fatberg—is believed to be the source of the “poo balls” that have sporadically washed up on some of Sydney’s most iconic beaches, forcing closures at Bondi, Coogee, and Manly.
The fatberg occupies a 300-cubic-metre underground chamber, described by Fiona Copeman, the plant’s hub manager, as the “four-bus area” due to its immense scale. While Sydney Water has attempted to map the mass using drones, the effort was thwarted by turbulence from sewer gases and the rapid flow of treated effluent heading toward a deepwater ocean outfall (Doof) located 2.3km offshore.
The presence of the fatberg has triggered a pollution reduction program from the NSW Environment Protection Authority (EPA), which in February required Sydney Water to undertake significant works to remove the fats from the bulkhead area. The incident highlights a systemic struggle with urban waste management, as the Malabar plant currently processes approximately 40% of Sydney’s sewage.
The Mechanics of a ‘Sloughing Event’
The path from a subterranean chamber to a sandy beach is a result of what engineers call “sloughing events.” According to the corporation’s working theory, chunks of the fatberg are dislodged when You’ll see rapid changes in pumping pressure, often triggered by heavy rainfall or sudden power losses.
Once these pieces break away, they are forced through diffusers—large, upturned shower-head-like structures on the ocean floor—and released into the sea. Depending on wind and wave conditions, these debris balls are carried back to the shoreline. In late 2024 and early 2025, this process resulted in the closure of multiple beaches across the Sydney coastline.
Accessing the core of the problem is a logistical nightmare. Most of the outfall tunnel is deemed unsafe for human entry. To fully remove the fatberg, Sydney Water suggests the only option would be to shut down the city’s largest ocean outfall for several months and divert primary-only treated sewage to the cliff face. However, a secret August 2025 report indicated that this approach is no longer considered acceptable and has never been successfully executed.
The Daily Struggle of Waste Management
The Malabar plant operates on a scale that makes precision cleaning difficult. During dry weather, the facility processes 485 megalitres of wastewater daily—roughly 194 Olympic swimming pools. During wet weather, that volume surges to 1,300 megalitres. This increase in volume reduces the time sewage spends in sedimentation tanks, which in turn means fewer solids are removed before the effluent is sent to sea.
To mitigate this, Sydney Water has implemented a series of operational workarounds. Crews can access a slight five-metre chamber behind the bulkhead door during lunar low tides and periods of minimal rainfall. Every four to six months, a team of six people pumps out rainwater and uses a hose to remove a small amount of “spillover” fat.
A more efficient method involves using a gas vent to lower a hose 20 metres down to suck up fat in front of the stopboards. This method was used to remove 53 tonnes of material in April 2025. Despite these efforts, the main mass beyond the stopboards remains undisturbed, and new fats continue to accumulate.
Operational Capacities at Malabar
| Weather Condition | Daily Volume (Megalitres) | Olympic Pool Equivalent |
|---|---|---|
| Dry Weather | 485 | 194 |
| Wet Weather | 1,300 | ~533 |
Source Control and Future Upgrades
The crisis is not merely a failure of infrastructure but a reflection of changing urban habits. Reports indicate that fats, oils, and grease (FOGs) in the Malabar catchment have risen by 39% over the last decade. Ben Armstrong, Sydney Water’s principal manager of environment, notes that treating these volumes at the end of the pipe is inherently difficult, emphasizing that removal must happen at the source.
To address the issue, Sydney Water is investing $3 billion in upstream plant upgrades to divert sewage away from Malabar. Within the Malabar plant itself, “scum” transfer pumps are being improved, and sedimentation tank scrapers are being upgraded. The facility also utilizes an onsite cogeneration plant that converts FOGs into energy, powering roughly 80% of the plant’s operations.
Despite these technological strides, the human element remains. Copeman, who has managed the facility for nearly 15 years, describes the material as varying between “gritty” and “scummy.” For the staff who work in the “meaty fug” of the sedimentation rooms, the environment is a constant challenge. “I reckon you’re either built for sewage, or you’re not,” Copeman says.
The immediate goal for the city is to prevent further “sloughing events” that threaten the cleanliness of the coast. While the deepwater ocean outfall has significantly improved the visual quality of the water compared to the old cliff-face discharges of the 1990s, the persistence of the fatberg means the risk of debris balls returning to the shore remains. Sydney Water continues to run public campaigns urging residents to keep fats and oils out of their sinks to slow the growth of the underground mass.
The next critical phase involves the completion of the EPA-mandated pollution reduction program, which focuses on the removal of fats from the bulkhead area and the upgrading of primary treatment scrapers. Official updates on the progress of these works are typically managed through the Sydney Water corporate portal and EPA regulatory filings.
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