Recycling activities are treatment activities that supply outputs of by-products that can substitute a reference product as an input to an activity.
Well-known examples of recycling are reuse of glass or plastic bottles. Sometimes recycling is used as a more narrow term covering only material recovery, e.g. remelting of glass or metal. Another very common but less obvious recycling activity is energy recovery.
Like any other treatment activity, recycling activities provide treatment service as their determining product. The physical goods that are produced from the recycling (cleaned bottles, secondary glass or metal, electricity or heat, etc.) are therefore by-products of the recycling activity. These by-products can then be modelled as negative inputs to the recycling activity, representing the resulting reduced demand for the alternative non-recycled (“virgin”) production.
Treatment activities that are not recycling are either intermediate treatment activities (which provide only by-product/waste outputs that are themselves materials for treatment) or final disposal activities (which have no by-product/waste outputs).
As for any other service product, there may be more than one kind of recycling activity for the same material, and some of these may be constrained, so that only some of the recycling activities are the marginal treatment activities for the material. Recycling can not be the marginal treatment for by-product/wastes that are not fully utilised.
The discussions of open vs. closed loop recycling, burdens/credits of recycling, etc., are irrelevant in consequential LCA, since all types of recycling are treated in the same manner, following the actual physical flows and substitutions.