The increasing and disorderly urban growth through the years has contributed to the necessity of basic infrastructures in the cities, leading to multiple problems with the disposal of waste and sewage. To solve these problems, wastewater treatment systems are proposed, being the definition of the installation site a complex question. Many physical, chemical, biological and social factors should be emphasized. In this context, multi-criteria analysis can be used to select alternative sites to define where a wastewater treatment plant should be installed. A fuzzy-logic based model is proposed to improve this site selection, where the adopted factors are: distance to urban area, pedology, land cover, altitude and slope. The model was applied as a study case to the city of Criciúma (Santa Catarina State, Brazil). The model presented suitable results, where the site alternatives to the wastewater treatment plant in Criciúma agreed with the City Master Plan.
