Modelling approaches for consequential life-cycle assessment (C-LCA) of bioenergy: Critical review and proposed framework for biogas production

Conventional life-cycle inventories (LCIs) are static models not considering any mechanism of revenue maximisation and price equilibrium under external constraints. An additional demand of a given commodity, irrespective of the amount, can always be supplied by the average supplier under fully elastic market assumption. This constitutes a recognised limitation for the application of LCA to the assessment of the environmental consequences of changes applied to complex systems, like agro-systems. In the so-called consequential LCI (C-LCI), the relationships between the activities and processes of a life-cycle are no longer seen as essentially technical connections, based on average data; instead the determining socio-economic mechanisms are considered via market information and eventually economic models (partial or computable general equilibrium). The practical implementation of C-LCI is however still obscure to many practitioners and the complementarities and overlaps between the different C-LCI modelling approaches have not been completely clarified so far. aper aims at filling this gap. The first part of the paper provides a survey of a number of applications using different equilibrium models. Afterwards we critically review the main variables and parameters supporting the definition and implementation of the C-LCI modelling approaches. In the last part of the paper we propose a methodology to integrate economic modelling and LCA in order to perform a C-LCA of biogas production, specifically addressing the indirect land use change (ILUC) issue. Finally we describe the application of this methodology to a case study dealing with the production of biogas in Luxembourg.