sousproduit

A sous-produit, or by-product, is a secondary product generated during the manufacture of a primary product. It is not the main output but may be recovered, sold, or used as an input for other processes.

By-products are typically distinguished from waste by their value and intended use. Whether a stream qualifies as a by-product depends on regulatory definitions and the possibility of reuse with minimal processing, rather than disposal as waste.

Common examples include glycerol produced in biodiesel manufacture; lignin from pulping; sugar beet pulp from sugar extraction; fish by-products such as scales and viscera used for meal or oil; citrus peels used for essential oils or pectin. These materials can be reintroduced into other industrial sectors or markets.

Valorizing by-products supports the circular economy by reducing waste, lowering material costs, and creating additional revenue streams. Realizing this value often requires sorting, purification, and quality control to meet market or regulatory requirements.

In practice, whether a material is treated as a by-product rather than waste depends on jurisdiction and industry. Companies typically maintain documentation to demonstrate continued value, safe handling, and suitability for reuse in order to classify the stream as a by-product.