UK supermarket will be the first to disconnect from the grid, use electricity generated entirely by its own rotten food
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A supermarket in the UK will become the world’s first to be powered entirely by its own food waste. At the end of the day, any leftover food — after the good stuff has been given to charity — will be transported to a nearby anaerobic digester, where it will be turned into electricity and sent back to the store via a privately owned one-mile-long power line. When the anaerobic digester is turned on, the large grocery store will sever all connections to the national power grid and rely purely on the electricity generated by bacteria feasting on rotten food. Cool.
An anaerobic digester, as you may have worked out if you did high school biology, digests biological matter (i.e. just about anything that you eat or excrete) with anaerobic organisms. These are special bacteria and yeasts that, when no oxygen is present, break down the biological matter into a wide range of interesting chemicals. Ethanol is one such chemical (yes, anaerobic digestion is used to make beer!), but in this case we’re much more interested in another product that is common in anaerobic digestion: Biogas.
Biogas is a mix of methane and carbon dioxide that is naturally produced by manure, the rotting of food waste, and all sorts of other common biological processes. An anaerobic digester is basically a human-made vessel that speeds up this process by providing the ideal environment for methanogen bacteria to feast upon all of that supermarket waste. It is not inaccurate to say that an anaerobic digester is a lot like a cow’s stomach. The biogas produced by the digester, which can be up to 75% methane, can then be used in much the same way as natural gas, such as heating and cooking, powering a combustion engine vehicle, or generating electricity with a steam turbine or combustion engine generator.
Back to the story. In this case, Sainsbury’s — one of the UK’s major supermarket chains — will be powering its Cannock, Staffordshire store entirely with electricity generated from biogas. At the end of the day, after any usable food has been given to charity or sold to animal feed companies, the remaining waste is sent to a nearby anaerobic digester operated by Biffa (a UK waste management company). The bacteria do their job and the resulting methane powers an on-site generator. The electricity is then be piped back to the grocery store, which is about a mile away.
Sainsbury’s says the new setup will provide enough electricity that the grocery store no longer needs a connection to the national power grid — and, in fact, it will even sell any excess electricity back to the grid,. It isn’t entirely clear how much food waste is being consumed to produce that much electricity, but it’s probably quite a lot. Sainsbury’s says it’s already using anaerobic digestion to produce enough electricity to power 2,500 homes — but presumably that electricity is just being sold back to the grid at the moment, rather than used to power its stores.
Zooming out to the larger picture, biogas is one of the best alternative sources of energy. As you may know, cows (and their manure) produce a lot of methane — and methane is a lot more potent than carbon dioxide when it comes to the greenhouse effect. By using biogas, rather than digging up coal, oil, or natural gas, we could significantly reduce our total carbon footprint. One study found that 100 billion kilowatt hours of electricity could be generated per year — enough to power millions of homes — if we scooped up all of the cow manure in the USA and put it into an anaerobic digester. Biogas couldn’t replace all of our power generation (we just don’t produce enough waste), but it would definitely be a good step towards carbon neutral, or even carbon negative.