Fatberg: The Fatty Monster of The Sewer

Blockages in sewers are pretty common in cities across the globe. But how large a congealed mass of filth has to be before it gets its own name?

In 2013, after a 15 ton mass of wet wipes, condoms, sanitary products, and other trash that people shouldn’t flush down their toilets was removed from a London sewer under Kingston upon Thames, a new term was born—fatberg.

A worker cradles a fatberg in her arms in a London sewer. Photo credit: Adrian Dennis/AFP

So what is a fatberg exactly? It’s a mass of cooking oil, fat and grease that combine and solidify in the alkaline environment of the sewers together with all sorts of materials in the sewer, especially “flushable” wet wipes (which constitute more than ninety percent of the fatberg), female hygiene products, cotton pads, and toilet paper to form a large, immovable mass that’s as hard as concrete.

Fatbergs usually start forming against the rough edges of the sewer walls, around bends, protruding obstructions such as tree roots and anything that can snag debris. London’s Victorian-era brick-built sewers are especially susceptible to this problem. While wet wipes and sanitary pads make up the bulk of the fatberg, the secret ingredient in the mix is fat and cooking which people pour down their kitchen sink. The alkali in soap and detergent combine with the fat and turn it into a sticky and gooey mass that acts as an adhesive binding all garbage together into a one solid lump. 

Disposal of fats, oils and grease—known as fogs in the sewage business—has long been a problem within the industry, but it never gets much publicity and so the public remains largely oblivious to what they can and cannot flush through their sewers. It was only after the 15-ton ball of congealed fat was found under London’s street, that the subject received some media attention and the word “fatberg” was coined.

“Nobody cares about Fogs,” says Vyki Sparkes of the Museum of London. “You can talk about Fogs until the cows come home. But start using the term ‘fatberg’ and it comes alive; people can visualise it.”

Fat collects in a London sewer. Photo credit: The Guardian

Part of the Whitechapel fatberg. Photo credit: Thames Water/PA

But worse was still to come. In September 2017, a 250-meter long monstrous fatberg weighing 130 tons was found blocking a sewer in Whitechapel in East London. It took workers nine weeks to remove the solidified mass. That same month, another mass of congealed fat and garbage was discovered under the streets of Baltimore, in the United States, causing toilets to clog and spill millions of liters of sewage.

The Whitechapel fatberg became a source of international fascination. A tiny chunk of the infamous fatberg was even acquired by the Museum of London and showcased in an exhibition as an appalling reminder of the “environmental destructiveness of our throwaway age”, and as an educational tool to inform people of what not to flush down the toilet or pour down the sink.

“It's frustrating as these situations are totally avoidable and caused by fat, oil and grease being washed down sinks and wipes flushed down the loo,” said Matt Rimmer, the head of the company responsible for keeping London's sewer’s clean. “The sewers are not an abyss for household rubbish and our message to everyone is clear - please bin it - don't block it,” he added.

In 2018, a special edition manhole cover was installed to commemorate Thames Water’s victory over the infamous 130 tonne Whitechapel fatberg. Photo credit: Thames Water

The vast majority—over ninety percent—of the grease found in sewers come from restaurants and eateries because of faulty or nonexistent grease traps allowing grease, oil and food scraps to find their way into pipes and drains. The other contributing factor are wet wipes, which are often marketed as “flushable” but they are not biodegradable like toilet paper.

The only silver lining in this story is that fatbergs can be converted to biofuel. The Whitechapel fatberg produced about 10,000 liters of biofuel enough to power 350 double-decker London buses for a day.