(CNN) What used to be a disgusting subterranean mass of congealed waste -- also known as a fatberg -- will soon be on display at a London museum.

The peculiar exhibit is but a fragment of one of the largest such objects ever found, measuring 820 feet long and weighing 130 tons, as much as 11 double-decker buses. It was removed last year from the sewers underneath the East London district of Whitechapel, after it caused a severe blockage.

"It will be displayed in a sealed unit," said Sharon Robison, head of conservation at the Museum of London.

"It's been in quarantine for a total of around nine weeks already and we'll undertake some more scientific analysis before the exhibition."

The Whitechapel monster

Fatbergs (the word is a portmanteau of fat and iceberg) form over time as items such as wet wipes, nappies, condoms, sanitary products and various types of greases and oils are flushed or washed down drains instead of disposed correctly.

Thames Water, which operates the water system in London, says it spends £1 million a month , or nearly $1.4 million, to clear blockages of this kind. To reduce their occurrence, it has started a campaign called " Bin it - don't block it " to educate the public on which items should be discarded as regular garbage rather than flushed down the toilet.

The Whitechapel sewer during removal of the fatberg

The worst offenders are cooking oils and fats -- coming mostly from restaurants and other food outlets -- and wet wipes, which are often marketed as "flushable." But unlike toilet paper, these wipes take years to break down as they often contain plastic, and shouldn't be flushed at all.

When it cools down, the fat tends to solidify around other flushed items such as wet wipes. The resulting mass then sticks to the sewer walls and hardens until it becomes as hard as concrete. The 47 inch by 27 inch sewer pipe in Whitechapel, 11 feet underground, was completely blocked by the fatberg, which spanned the length of two football fields.

Removal took nine weeks. "People think this comes out of the sewer as a massive lump, but the team that has extracted it had to break into small pieces and suck it up through a hose," said Robinson.

Powering buses

After extraction, rather than ending up in a landfill, the fatberg fragments were turned into biofuel at a special facility in Scotland. "We're the only people in the world who can turn the stuff into biodiesel," said Dickon Posnett of Argent Energy . "It's difficult, it's not cheap, it takes a lot of work, but every ton of biodiesel displaces a ton of normal diesel, which saves over three tons of greenhouse gas emissions."

The fatberg fragments are first melted, then the solids and plastics are removed before it's converted into an oil. It's then filtered and blended at 20 percent with standard diesel.

A Thames Water sewer engineer working on a fatberg in London in 2014.

Posnett estimates that the Whitechapel fatberg might have yielded up to 10,000 liters of fuel, some of which has since powered London buses. But he says he'd much rather collect the fat from grease traps, devices that prevent solids and greases from entering watersystems. "That would mean that what goes down into sewer is genuine sewer waste. But there's very limited legislation in the UK to enforce the practice of collecting oil with grease traps at the outlets into the sewers from restaurants and hotels and such."

A piece of London history

Museum of London took several precautions after acquiring the fragments, including monitoring the gases coming from the lumps and performing x-ray scans to make sure no sharp bits were hiding inside: "The fatberg itself is actually quite toxic, so we had to be certain that we weren't going to put something in a display case that would be releasing dangerous or flammable gases -- but it doesn't smell very much anymore," said Robinson.

The results of the various tests will be part of the exhibit, for which Robinson expects a mixed response: "There will be people who'll wonder why on earth we've chosen to display this, but also people who understand this is a serious London issue and that we have a role to play in telling that story and to reach a wide audience.

"This is an important London story about what we're doing to the city, about population growth and the way the British diet has changed to include more fats, oil and grease that end up into the sewer system, posing a challenge for the Victorian infrastructure that the city is built on."

Posnett agrees: "It's such an interesting story, putting it into a museum and showing what happens to the stuff we flush down the toilet can be an eye opener to what goes on under the streets and help people learn about landfills and waste and greenhouse gas emissions," he said.

"It's a brilliant way of highlighting the problem."