# Why food waste is a climate problem and what anaerobic digestion does

> Food rotting in landfill emits methane roughly eighty times more warming than CO2 over twenty years, and England's new weekly caddy collections exist chiefly to feed anaerobic digestion plants.

*Section: Environment — By Elena Marsh (Environment & Climate Correspondent) — Published July 12, 2026 — 4 min read*

Canonical URL: https://dailyjunction.org/environment/why-food-waste-is-a-climate-problem-and-what-anaerobic-digestion-does
Tags: food-waste, methane, anaerobic-digestion, landfill, recycling-policy

## Key takeaways

- Buried food decomposes without oxygen and produces methane, a gas with roughly 80 times the warming effect of carbon dioxide over a 20-year horizon, and landfill gas capture systems recover only part of it.
- The Environment Act 2021 requires English councils to run weekly separate food waste collections, bringing England into line with Wales and Scotland and creating a guaranteed feedstock stream for digesters.
- An anaerobic digester ferments food waste in sealed tanks to yield biogas that is burned for power or upgraded to grid-quality biomethane, plus a nutrient-rich digestate spread on farmland in place of manufactured fertiliser.

The small caddy appearing on kitchen counters across England is usually explained as a recycling measure, a tidier way to deal with tea bags and potato peelings. That undersells it. The weekly food waste collections now required of every English council are the supply chain for an industrial process most households have never heard of, and the reason the government bothered is a gas, not a bin.

When food is buried in landfill it is starved of oxygen. The bacteria that break it down under those conditions do not produce carbon dioxide, as composting in open air does; they produce methane. Over a century, a tonne of methane warms the planet around 28 times as much as a tonne of CO2, and over the 20-year window that matters most for near-term climate targets the multiplier is closer to 80. Landfill operators are required to capture the gas with wells and membranes, and the better sites burn it for electricity, but capture is partial: gas escapes before the wells are drilled, through the cap, and long after a cell is closed. Waste is one of the UK's largest sources of methane, alongside agriculture and leaking gas infrastructure, and food is the single most gas-productive thing in a black bag.

The scale of the input is startling. WRAP, the waste and resources charity that runs the Courtauld Commitment with the food industry, estimates the UK throws away around 10.7 million tonnes of food a year, roughly six million tonnes of it from households. Landfill tax, now above £100 a tonne at the standard rate, was designed to squeeze this material out of holes in the ground, and incineration has taken much of the overflow. But burning food is thermodynamically absurd — it is mostly water — which left policy needing a destination that treats wet organic waste as an asset.

That destination is anaerobic digestion. The Environment Act 2021, implemented through the Simpler Recycling reforms, obliges English councils to collect food waste separately every week, with the last of them coming on stream through 2026. Wales made separate collection near-universal years earlier, which is one reason it posts some of the highest municipal recycling rates in the world, and Scotland imposed a duty on most councils in 2016. England is the laggard finally closing the gap, and in doing so it guarantees millions of tonnes of feedstock a year to a sector that has been quietly building capacity in anticipation.

## Inside the digester

An anaerobic digestion plant does deliberately what a landfill does accidentally. Food waste is pulped, screened for plastic and cutlery, pasteurised, then fed into sealed steel tanks kept at around 40 degrees, where communities of microbes ferment it for several weeks. The product is biogas, typically 55 to 60 per cent methane, captured completely because the tank is the whole point. Some plants burn it on site in gas engines to generate electricity and heat. Increasingly the more valuable route is upgrading: stripping out the CO2 to produce biomethane pure enough to inject into the national gas grid, a route subsidised by the Green Gas Support Scheme and paid for through a levy on gas suppliers. The same molecule that wrecks the climate escaping from a landfill becomes a fossil gas substitute when it is made in a tank instead.

The process leaves a second product, digestate, a wet residue rich in nitrogen and phosphate that is spread on farmland under quality protocols in place of manufactured fertiliser — itself an energy-intensive product usually made from natural gas. The Anaerobic Digestion and Bioresources Association counts several hundred operational plants across the UK, spanning farm digesters running on slurry and maize, water company digesters processing sewage sludge, and the merchant food waste plants the new collections will feed.

## The caveat that keeps the hierarchy honest

Digestion is a good destination for waste; it is a poor excuse for creating it. Growing, chilling and transporting food emits far more than a digester ever recovers, which is why the official waste hierarchy puts prevention and redistribution above energy recovery. WRAP's argument for the caddy is partly psychological: householders who scrape plates into a small visible bin each week confront how much they buy and never eat, and measured food waste tends to fall where separate collection arrives. The digesters get their feedstock either way. The climate does best when there is slightly less of it than the industry would like.

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Daily Junction — https://dailyjunction.org/environment/why-food-waste-is-a-climate-problem-and-what-anaerobic-digestion-does