The decision of choosing a facility location among possible alternatives can be understood as a multi-criteria problem where the solution depends on the available knowledge and the means of exploiting it. In this sense, knowledge can take various forms, where the imprecise nature of information can be expressed by degrees of intensity in which the alternatives satisfy the given criteria. Hence, such degrees can be gradually expressed either by unique values or by intervals, in order to fully represent the characteristics of each alternative. This paper examines the selection of biogas plant location based on a decision support model capable of handling and exploiting both interval and non-interval forms of knowledge. Such model is built on a fuzzy approach to weighted overlap dominance, where an interactive procedure is developed allowing the individuals to explore and put into perspective how their different attitudes affect the final ranking of alternatives.