Methodology : APOS vs Cut-off system model

The APOS and cut-off methodologies are used in attributional LCA. They differ in their approach to the distribution of the environmental burden between different system functions, particularly in the case of recycling and valorization of a flow. While recycling enables waste to be given a new function, valorization consists in recovering materials or energy from waste (which is used as fuel, for example). In fact, the functions associated with recycling and valorization lie at the interface between two successive life cycles: the production of the flow, and the recuperation of this flow. This makes the allocation of impacts between producer and consumer complex to determine.

The APOS (Allocation at the point of substitution) methodology concerns activities generating several output flows, some of which require treatment to be valorized and transformed into co-products. This approach involves extending the system to include the treatment activity as well as the resulting co-product. Impacts are then split between the main product and the treated co-product.

This approach is quite complex to understand, and can sometimes produce unexpected results. It is therefore important to check the consistency of the results by comparing them with those of a simpler methodology, for example.

The cut-off methodology applies the "polluter pays" principle. This means that the activity generating the flow is considered to be entirely responsible for the impacts, even if the output product is recyclable or recoverable. Consequently, the output flow is considered free of environmental burdens and can be reused without generating additional impacts. If it has to undergo treatment, it is the system that collects the flow that will be responsible for the impacts of the treatment.