Is compost actually good for the environment — the case against composting, and what to do anyway

You have probably seen 'compostable' printed on a disposable cup or a set of cutlery. For most readers the word means 'this returns to soil'. Read from the standards side, the meaning is much narrower. What an industrial composting standard requires is that, under a specified temperature, moisture and duration, the item disintegrates to a set fraction, biodegrades, and does not inhibit plant growth. Certification therefore guarantees not a property of the material alone but a promise conditional on 'if you give it these conditions'. Taken somewhere the conditions do not hold — a bucket by the back door, a heap that never heats — the certification guarantees nothing at all.

Over six days this series has followed the machinery that treats food scraps as a resource: the methane arithmetic, the history of chemical fertiliser and the landfill, where mandates stumbled, twenty years of Japan's Food Recycling Act, and the economics that decide compost or biogas. What is left for the final day is to doubt the contents that machinery is carrying. The hardest question for composting's advocates is whether composting works at all, and leaving that question to outside critics guarantees it will keep returning as an accusation. Setting out the numbers yourself turns out to be the stronger position.

The criticism is not a matter of sentiment; it separates into four checkable claims. The first is physical: items certified compostable do not break down in real compost the way the label implies. The second is chemical: even when they do break down, substances such as PFAS survive and remain in the finished compost. The third concerns quality: heavy metals and microplastics are detected in compost sold on the market. The fourth is accounting: once the mileage of the collection round and the energy of the processing site are counted, is the climate benefit of city-scale composting as large as it is said to be?

This article takes the four in order and attaches the counter-evidence to each. In fairness, it is worth saying at the outset that three of the four are problems practitioners can fix, and that the remaining one — the climate accounting — currently runs in composting's favour on the available data. The failure mode of an article that reports criticism is to let the force of the criticism flip the conclusion along with it. Here each claim is bounded: how far it holds, and where it stops. The closing section then looks back across the seven days and sets out handles that both an individual and a municipality can actually take up.