The Commission decided to issue separate guidance on the issue rather than include a definition of by-products in its proposal for revising the waste framework Directive because this leaves existing case law in place and thus allows "greater legal certainty".
The first step in deciding whether a material is a by-product or a waste is to decide whether the manufacturer deliberately chose to produce the material in question. If so, at least three other conditions must be met for it to be classified as a by-product: it must be certain that the material will be used further, that no further processing is needed before reuse, and that the material must form part of a continuous production process.
Several factors are listed that help indicate whether a material is waste. These include cases where a material’s use has a high environmental impact, where the manufacturer perceives the material to be a waste, or where it seeks to limit the quantity of material produced.
Examples of wastes and non-wastes are given in an annex. Blast furnace slag, for example, can be classified as a by-product because the iron production process is adapted to ensure that the slag has the necessary technical qualities and the slag can be used at the end of the production process without further processing. But dust extracted during steel production is a waste because its metallic content cannot be fed back into the production process until the dust filters are cleaned.