The production of most renewable materials involves co-products. Traditionally, the environmental impacts have been allocated between the different co-products according to a more or less arbitrary allocation ratio. Following the new ISO requirements, and based on SETAC recommendations, allocation shall be avoided whenever possible. It has been the general belief that avoiding allocation through system expansion was not always possible for co-products from renewable material production, since the substitutions involved were believed to be too complex, difficult to determine, and sometimes involving endless regressions. However, these perceived problems can be solved by applying a stringent procedure for identifying the affected processes, earlier developed and presented by the author. This paper shows a number of case studies on renewable materials where allocations have been avoided through system expansion. Examples include the notoriously difficult problems of agricultural or industrial by-products applied as fodder (e.g. rapeseed cake, which substitutes soybean production, which again has oil as a by-product) or fertiliser (e.g. organic manure), the co-products from a cow (meat, milk, butter etc.), and the secondary functions of forestry and agriculture (e.g. maintaining rural income, amenity values such as maintenance of landscapes for recreation).
The production of most renewable materials involves co-products. Traditionally, the environmental impacts have been allocated between the different co-products according to a more or less arbitrary allocation ratio. The idea that co-product allocation can be avoided by system expansion has been put forward by Tillman et al. (1991) in respect to waste incineration, and more generally by Heintz & Baisnee (1992). It was given a prominent place in the procedure of ISO 14041, where it reads: “Step 1: Whereever possible, allocation should be avoided by: 1) dividing the unit process to be allocated into two or more subprocesses and collecting the input and output data related to these subprocesses; 2) expanding the product system to include the additional functions related to the coproducts…”
Although avoiding allocation is seen as the preferable option, it has been the general belief that avoiding allocation through system expansion was not always possible for co-products from renewable material production, since the substitutions involved were believed to be too complex, difficult to determine, and sometimes involving endless regressions.
However, these perceived problems can be solved by adapting a stringent procedure for identifying the affected processes, earlier presented in Weidema et al. (1999), leading to the conclusion that allocation can (and shall) always be avoided in prospective life cycle assessments.
