Towards sustainable biomass-for-bioenergy supply chains by trading off between multiple objectives

Optimisation of biomass-for-bioenergy supply chains (BSC) is a way forward for the bioenergy industry to make a greater contribution to the energy market. OPTIMASS is a mixed integer linear programming model developed to come with optimal strategic dimension of such BSC. In addition to existing models, OPTIMASS takes into account changes in biomass characteristics due to harvest and pre-treatment operations which are needed to meet the requirements set to biomass products delivered at a conversion facility. Moreover OPTIMASS considers the re-injection of by-products from conversion facilities which can play a decisive role in the determination of a sustainable supply chain. Sustainability of supply chains has emerged as a concern for their design. This implies the trade-off between different, conflicting objectives. This paper describes the integration of OPTIMASS and the multi-objective optimisation method ‘Compromise Programming’. Compromise programming has been selected because it doesn’t require any interference or preference of the user and intends to determine the most objective, neutral optimal solution. To illustrate the application and behaviour of OPTIMASS as a multi-objective model, an optimisation exercise considers the chain through which biomass derived from low input high diversity (LIHD) biomass systems is supplied to anaerobic digesters and composting facilities in the Limburg province (Belgium). The objectives at stake are maximum net energy output, maximum economical profit and minimum global warming potential. The analysis (considering equal weights attributed to the objectives) indicates that the energetic objective drives the decision making process when it is included in the multi-objective optimisation. This is mainly because this objective forces the supply chain to deliver as much energy as possible which entails the use of all available anaerobic digesters. When the energetic objective is not considered, the resulting supply chains are characterised by features of the economically and environmentally optimised supply chains. Comparison of the single objective and multiple objective optimised supply chains makes clear that the configuration of the supply chain differs according to the objectives included in the optimisation. So, adding the multi-objective optimisation method to OPTIMASS has pointed out to be a valuable action because a real trade-off is needed between the considered objectives and it will increase the attractability to stakeholders since they are usually interested in more than one objective.status: publishe