Trommels are used in the field of the waste management, in particular for biological treatment processes. The trommel is the basic facility implemented to sort out impurities through size classification. It is implemented in the process for compost sorting after the biological degradation as well as for the primary sorting of waste. Research in the field of process analysis of waste treatment is at its beginnings. The development of a phenomenological model for trommels dedicated to municipal solid waste will allow a more accurate knowledge of the performance of such facilities. Results of the modelling allow to take into account both the characteristics of the trommel and the characteristics of the waste input to predict the quantity and the quality of the output products. Included to the simulation platform of the Usim Pac software, the model is able to predict the performance of a trommel, to optimise its operation, as well as to study the effects of the addition or the substitution of one trommel in a given treatment process. This model is an aid tool for process analysis for designers, experts and managers of municipal solid waste treatment.