Fatbergs are a sticky problem for sewerage systems – blocking pipes, spawning poo balls, and even forcing the cancellation of a Bryan Adams concert.
When households pour cooking oils, out-of-date milk or the residues of a roast dinner down the sink, it contributes to the buildup of fats, oils and grease – known as FOG – in the wastewater system, and the growth of fatbergs.
“When you get blocked sewers, you get all sorts of problems,” says Prof Stuart Khan, an expert in water quality and treatment at the University of Sydney.
“You get overflow of raw sewage coming out at designated – or undesignated – overflow points within the system.” Digging out fatbergs requires “fairly hands-on maintenance, which increases costs”, he says, and higher fat loads or other types of contamination can affect the performance of wastewater treatment processes.
Water authorities advise that apart from water, only the 3Ps – poo, pee and (toilet) paper – should be flushed or drained.
So how should we dispose of other types of liquid waste?
Forgoing the FOG
Cooking oils and fats may seem liquid as they slip down the sink, Khan says, but in pipes they tend to congeal, solidify and accumulate – sometimes over many years – often binding with other material like wet wipes.
“Sometimes we might be pouring them down the sink without even realising. It’s the washing up, when you’ve cooked a chicken or a turkey and there might be a lot of oil and grease left in the bottom of the tray,” he says.
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A simple solution is to do more wiping than rinsing, says the environmental engineer Prof Faisal Hai, of the University of Wollongong. “If we have a frying pan with some oil or some sticky material, can we use some paper towel to wipe that off and put that into the bin rather than into the sink.”
Larger amounts of oil, stock or other fatty foods can be sealed in a container, and put in the bin. When rinsing dishes, a sink strainer can help to collect and dispose of food scraps in the organics bin. In-sink garbage disposal units increase the load on wastewater systems, and should not be used.
Out-of-date milk
Milk past its use-by date is a common issue for households, Hai says. Like any food or drink that contains fat, milk can also contribute to FOG in the system, and should not be poured down the drain.
The best option is to avoid buying more milk than you need, he says.
Sydney Water’s principal environment manager, Ben Armstrong, says another option is to mix leftover milk with water (diluted on a one-to-one basis) and put it on the garden. Or, simply keep it in the container and put that in the rubbish bin.
Leftover liquids
There are more than 720 sewage treatment plants across Australia. Most rely on biological processes, like natural bacteria and microbes, to help break down organic material and remove pollutants from the water.
“Natural bugs basically eat the organic contents in the wastewater. That’s how they clean it up,” Hai says. But the bugs can only eat so much, and often require oxygen supplied by large blowers. Certain chemicals can interfere with the process, while others pass through treatment and enter waterways.
Paints, solvents, pesticides, motor oil and other chemicals can damage sewerage infrastructure, cause blockages, or pollute waterways if washed down the drain.
“Wastewater treatment plants aren’t designed to break down most types of pesticides and a lot of industrial chemicals present in paints. So they will go through the sewerage treatment plant and into the environment,” Khan says. “That might mean out into the Pacific Ocean or, if you’re inland, it might mean going into a freshwater waterway.”
Medicines should never be flushed down the toilet because they can end up in waterways like rivers and streams, leading to wildlife impacts such as changes in fish bodies and behaviours.
“There’s no simple answer to really solve the problem because even the pharmaceuticals that we take, we tend to excrete part of in our urine. And that all ends up in the sewers, of course, through no fault of anybody.”
Unwanted or expired pharmaceuticals, inhalers, creams and supplements can be dropped off at pharmacies participating in the nationwide Return Unwanted Medicines program.
Clean up your act
It is inevitable that some soap, shampoo and dishwashing liquid will end up down the drain in the process of cleaning, but it is best to avoid disposing of large amounts that way.
Consumer awareness has seen many brands remove or reduce phosphates – which in too-high concentrations can stimulate the growth of algae and other organisms. Look for eco-friendly detergents that have nil or low concentrations.
“Residents play a crucial role in protecting our wastewater system by knowing what they can, and can’t, put down their sinks and toilets,” says Sue Jackman, an executive general manager at Melbourne Water.
“The safest option is to dispose of unwanted liquids and chemicals through household rubbish or council waste facilities, not the wastewater system.”
