By-products are understood, and can therefore be managed, as wastes used as substitutes for commercial products and/or raw materials that can be recovered without any need to submit them to treatment.
This excludes waste applied to soil in agricultural use or in favour of ecology.
For a waste to be managed as a by-product, it must have the resolution of the Agència de Residus de Catalunya declaring it a by-product.

The management of waste as a by-product must involve the replacement of a raw material or an auxiliary product.
Activities intended for recycling waste are those developed by waste managers, and therefore waste management with such entities can not be as a by-product.

Examples:
a) Example of the management of a waste as a by-product:
"A clear example of management as a by-product is the use of lime milk caused as the waste of the process of a company (producer) to neutralise effluents in another company's purifier (receiver), in the place of sodium or calcium hydroxide.
" b) Example management of a waste through a waste manager:
"The use of plastic waste generated in a company (producer) by a company engaged in recycling these materials. In this case, the waste receiver company must be a waste manager of the General register of waste management enterprises of Catalonia".