‘Fatbergs’ a plague on the sewers of London

Thames Water, the private utility company responsible for the public water supply and waste water treatment in large parts of Greater London, plans to transform waste cooking fat to green energy, in order to tackle London's "fatberg" problem.
In charge of 43,500 miles of sewers underneath London, Thames Water's biggest headache is waste cooking fat poured down through kitchen sinks or toilets.

The cooled cooking fat then clings to wet wipes, plastics, or planks of wood and congeals into a "fatberg" blockage, a large immovable mass.