The chunks of fat, oil, and grease build-up—affectionately(?) referred to as "fatbergs"—have been an ongoing problem in London's sewer system. When the waste isn't just clogging up drains, it's making its way down further and clogging up the sewers. But now, a new power station is set to generate 130 gigawatt hours a year from the clogs—enough to power almost 40,000 homes. And that's a good enough excuse to go sewer-grease mining.
Some of the fat-generated energy will go back into running the local sewage works where the chunks of fat-ore are being mined, establishing a gross little cycle that should benefit just about everyone involved. Except maybe the grease-miners. And while using food-waste to produce energy is great, you'd ideally set up a way to do it that doesn't involve first clogging and then de-clogging sewers. But in the meantime this is a solid solution. More here.