Waste represents an output from a human Activity that has zero or negative market or non-market value (utility). This value-based distinction separates waste from products, which by definition possess positive value. The concept of waste in Life Cycle Assessment requires careful consideration due to the complexity of legal definitions and the practical needs of physical modelling.
There are many different definitions of waste across jurisdictions and regulatory frameworks, some of which carry significant legal implications. National and international legislation often defines waste in ways that serve regulatory purposes but may not align with the needs of neutral physical modelling in LCA. These legal definitions can create complications when attempting to model material flows consistently across different geographical contexts or regulatory regimes.
In neutral physical modelling for LCA purposes, it is therefore preferable not to make a sharp distinction between waste and By-products. Both represent outputs from activities that are not determining products, and from a system modelling perspective, the treatment of these flows often follows similar principles. This pragmatic approach avoids the complications arising from variable legal definitions whilst maintaining the ability to accurately model material flows and their environmental consequences.
However, the conceptual distinction based on value remains relevant. The definition of a Product implies that any activity output with positive market or non-market value qualifies as a product. Conversely, an output that provides no value or requires payment for its acceptance (negative value) falls outside this definition and must be classified as waste. This value-based criterion provides a theoretically sound foundation for classification, even when practical modelling choices blur the distinction between waste and by-products for analytical convenience.
