Melbourne under attack from subterranean ‘fatbergs’
Melbourne is under attack from the slimy, subterranean threat of "fatbergs".
With up to 2000 tonnes of non-compliant materials, fats, oils and wipes flushed down toilets or tipped into sinks each year, water authorities are spending about $3 million a year busting hundreds of fatberg blockages, with some monster stoppages, including beneath Flinders St Station's north entrance.
Some coagulated messes of fats, wipes, grease and non-biodegradable matter form rock-hard bergs which can cost $10,000 each to remove from the sewer network with high-pressure blast hoses or vacuum trucks.
While most are not measured, the largest fatberg City West Water has tackled recently measured 900mm long and 400mm tall in a 600mm diameter pipe under Flinders Street at the intersection of Elizabeth Street.
Yarra Valley Water's largest fatberg in recent times was about 700kgs, 2.5 meters long and around one metre thick - a 10 per cent portion of lump is currently on display in Melbourne Museum's "Gut Feelings" exhibition.
"Fatbergs are formed when a build-up of fats and oils in the sewer system combine with wet wipes which people think are flushable to form dense and often solid masses of fat that block the sewer system," Yarra Valley Water managing director Pat McCafferty said.
"They're out of sight and out of mind for most people, however, they create expensive damage in the sewer system and can harm the environment, which is why we focus so hard on preventing them."
Mr McCafferty said a 3mtr wide chunk was extracted at Lilydale about four years ago, with the increased consumer use of disposable wipes and dry conditions leading to encroaching tree roots creating problems.
Yarra Valley Water spends almost $1 million a year removing fatbergs across the eastern and northern suburbs and fixing the pipe damage.
Mr McCafferty said Yarra Valley Water customers flush 650 tonnes of wet wipes and rags down the toilet each year and greater education as needed to reduce fatbergs and expensive blockages.
"Over the past five years, City West Water has seen an average of 400 fat blockages in our sewer network each year," City West Water's infrastructure manager Amanda Smith said.
"A typical cost to remove a blockage is around $1000, however there have been instances where single blockages have cost more than $10,000 to remove."
South East Water also responds to an average of four blockages each day caused by fats, oils, wipes and sanitary products in the sewer network.
"In 2018-19 we proactively cleaned around 45 large assets per week, resulting in a cost of around $940,000 for the year," customer service general manager Terry Schubach said.
"We work hard to maintain our sewer pipes and pump stations, and we're installing our Advanced BlokAid sensors in high-risk sections of our network to help detect and enable us to clear blockages early.
"Our customers can help by remembering to only flush the three Ps; pee, poo and toilet paper, and to think at the sink before pouring fats, oils or food scraps down the drain."
Undetected, fatbergs can produce spill-off into the environment, with heavy fats and greases running into storm water, creeks, parkland and roadways.
While Melbourne's sewer system is generally working well and preventive maintenance is helping stop fatbergs growing from smaller to much larger sizes, overseas experience has seen some gigantic examples, including a 130-ton, 250m-long mass under London and a Maryland, US fatberg which caused the spillage of 4.5 million litres of sewage.
Yarra Valley Water treatment plant manager Rob Kinder said as well as foreign solid waste, high-fat diets were impacting the system, both through pan residue tipped down sinks and undigested fat remnants in human waste in toilets.
City West said there was no estimate on the collective weight of fatbergs in the system at any single time but there had been a decline in the past two years, largely attributed to an improvement in commercial customers improving grease traps use.