Multi-objective optimisation for generating sustainable solutions considering total effects on the environment

This contribution presents and discusses two multi-objective optimisation approaches considering total (direct and indirect) effects on the environment. Sustainability metrics, conventionally measuring direct harmful effects on the environment, are now upgraded with indirect effects in order to measure the unburdening the environment, e.g. due to the substitution of harmful with benign products. The first approach, based on a relative direct sustainability index, is now upgraded to a total sustainability index, and the second one, based on a concept of eco-cost and net profit, is extended to a recently introduced concept of eco- and total profit. These approaches are illustrated through a case study of the supply chain synthesis for producing biogas from organic and animal wastes. The results indicate that considering total effects enables obtaining more realistic solutions, than in those cases when only direct effects are considered. An appropriate trade-off between economic and environmental criteria can be established when performing a maximisation of total profit.