Cities turn to tech to keep sewers free of fatbergs

Swaddled in wet wipes, ensconced in congealed cooking grease and able to transform into pipe-blocking masses so hard as to require excavation equipment to dislodge, fatbergs are truly the bean-and-cheese burritos of the sewage world. They can cause havoc on a town’s bowels, achieving lengths that outspan bridges and accumulating masses that dwarf double-deckers. Fatbergs are a modern problem that have civil engineers increasingly turning to tech in order to keep their cities’ subterranean bits clear of greasy obstructions.

Fatbergs — a portmanteau of fat and iceberg — are a relatively recent but fast-growing problem in the world’s sewers. They form when FOG (fats, oil, grease) poured down drains comes in contact with calcium, phosphorus and sodium to create a hard, soap-like material. This calcium soap then accumulates on non-degradable flushed items like wet wipes, sanitary pads, condoms, dental floss, clumps of hair, chunks of food waste, and diapers as they travel through a municipal waste disposal system. Though their components may start off soft and pliable (albeit damp) once ‘bergified, they harden into a mass tougher than concrete, requiring sanitation workers to employ high-pressure water jets, shovels and pickaxes in order to break it up.

“These huge, solid masses can block the sewers, causing sewage to back up through drains, plugholes and toilets,” Anna Boyles, operations manager at Thames Water, told RICS in October. “It can take our teams days, sometimes weeks, to remove them.”

They can also offgas toxic compounds such as hydrogen sulfide. Forensic analyses of dislodged fatbergs have also revealed concentrations of all sorts of chemicals including bodybuilding supplements and the metabolites of illicit drugs — not to mention myriad bacterial species. Not only do these deposits constitute a direct health hazard to the workers tasked with demolishing them, fatbergs can cause pipe blockages and force wastewater to overflow aboveground where the contagion can spread.

A blockage in Maryland in 2018 caused more than a million gallons of wastewater to spill into local waterways (it cost $60,000 to clear the 20-foot obstruction) while a similar backup in Michigan flooded the University of Michigan with 300,000 gallons of the stuff.

These cholesterol-like deposits can reach monumental proportions if left unchecked. Thames Water, which manages sewers in both London and the Thames Valley, told the BBC last February that it spent £18m a year clearing 75,000 blockages from its systems. One of the largest bergs to date was pulled from beneath Birchall Street in Liverpool, UK in 2019. It measured 820 feet in length, weighed 440 tons and required more than four months to clear. The month before, a 200-foot long fatberg was discovered under Sidmouth, a popular coastal tourist location in Devon, UK.

“It is the largest discovered in our service history and it will take our sewer team around eight weeks to dissect this monster in exceptionally challenging work conditions,” South West Water director of Wastewater, Andrew Roantree, told The Guardian in 2019. “Thankfully it has been identified in good time with no risk to bathing waters.”

“If you keep just one new year’s resolution this year,” he added, “let it be to not pour fats, oil or grease down the drain, or flush wet-wipes down the loo. Put your pipes on a diet and don’t feed the fatberg.”

These obstructions are just as problematic on this side of the pond. In 2018, officials in Charleston, South Carolina pulled a 2,000 pound, twelve-by three-foot berg from the city’s sewers. The same year, officials in Macomb County, Michigan removed a 100-foot fatberg from one of its 11-foot diameter Lakeshore Interceptor pipes at a cost of $100,000.

"To put it simply, this fatberg is gross. It provides an opportunity, however, to talk with people about the importance of restricting what goes down our sewers. This restriction was caused by people and restaurants pouring grease and similar materials down their drains. We want to change that behavior," Public Works Commissioner Candice S. Miller said at the time.

However, the problem is apparently not universal. “The city of Atlanta does not have ‘fatbergs’ within our sewer system,” a spokesperson from Atlanta’s Department of Water Management told Engadget via email. “Fatbergs are common in other countries.” Any blockages that are encountered within the city’s sewers are disposed of using, “high pressure water and/or rodding equipment.”

This rodding equipment, commonly known as hydrojets, are high-powered versions of the pressure washers used to clean siding and walkways. They’re capable of producing pressures in excess of 4000 ppi and spray omnidirectionally so that they’ll blast detritus from the entire interior surface of a pipe as they’re fed forward. That fecally caked slurry is then sucked out of the main using a truck-mounted vacuum system and stored in an onboard tank for later disposal – as you can see in the 2010 video from the City of Carlsbad, California below. It’s the same basic idea as the trucks that service Port-A-Potties but, again, a more robust version.

A major contributor to the fatberg problem are wet wipes which were first invented in Manhattan in 1957 by Arthur Julius. He went on to found the Nice-Pak company and, by 1963, had partnered with KFC to offer his company’s pre-moistened Wet-Nap towelettes as an after-meal hand sanitizer to the fried chicken chain’s greasy-fingered customers. In subsequent decades Nice-Pak expanded its offerings to include products such as baby wipes and EPA-rated hand and surface disinfectants. As of 2020, the global market for wet wipes runs an estimated $24 billion annually, according to a recent report from Grandview Research.

“Wet wipes may be convenient, but flushing them is a major cause of sewage blockages. On top of this they contain plastic and can find their way into our seas where they pose a threat to wildlife,” Friends of the Earth spokesperson Julian Kirby explained to The Evening Standard in 2019. “Wet wipe manufacturers should be required to make their products plastic-free and clearly label them as ‘do not flush.'”

While the Museum of London has seen fit to preserve part of the famed Whitechapel fatberg for posterity, most municipalities want them gone, flushed and forgotten, but the fatbergs have to be found first. Typically, that involves visually inspecting the sewer mains either by sending down crews or remotely operated cameras like the modular Rovver X from Envirosight or the IRIS Portable Mainline Crawler from Insight Vision. Alternately, the SL-RAT (Sewer Line Rapid Assessment Tool) from Infosense Inc, relies on sonar technology to check sewer lines for obstructions.

Relying on sound waves offers a number of advantages over conventional visual systems. The SL-RAT is set up at through the access points at either end of a length of sewer main.The transmitting unit blasts a series of tones through the pipe where the receiving unit measures the tonal differences between the two sets to determine the extent of any potential blockage. Since utilities don’t have to physically send people or drones into the pipes when using the SL-RAT, crews can inspect more of the sewer network in less time.

The city of Irvins, Utah, for example, used to expend 6,000 gallons of water daily to flush the entirety of its 50-mile wastewater system, done in order to dislodge blockages occurring in only about 5 percent of the network.

“Just to prevent one blockage, we were cleaning the whole system,” Ivins Public Works director Chuck Gillette told St George News in October. “You’re cleaning every pipe.”

With the city’s implementation of the SL-RAT system in 2020, city crews could more precisely locate clogs to dislodge. A process that used to take weeks and 1,100 labor hours is now done in a few days and 320 labor hours. “It’s less [noise] than the sound of a cleaning truck,” Gillette continued, “and there is zero water usage.”

While municipal authorities beg people to help prevent fatbergs from forming in the first place by following the 3Ps — as in, the only things that should go in the loo, are pee, paper and poo — a team of Canadian researchers are looking at converting the ‘bergs into biofuels once they’ve been harvested from sanitation pipes.

“This method would help to recover and reuse waste cooking oil as a source of energy,” University of British Columbia researcher Asha Srinivasan told Smithsonian Magazine in 2018. The UBC team’s method involves first heating a fatberg chunk to between 90 and 110 degrees Celsius to loosen everything up, then adding hydrogen peroxide to break down organic components and free trapped fatty acids, then breaking those acids down into methane using anaerobic bacteria. This is similar in methodology, albeit on a much smaller scale, as to how some wastewater treatment facilities produce natural gas from methane captured during the cleaning process.