The appropriate management and treatment of wastewater, before their disposal, are essential for every society. In Greece, especially in small and isolated rural areas, the lack of drainage infrastructure and wastewater treatment systems is a frequent phenomenon.

This paper deals with the wastewater management of a mountainous settlement in the municipality of Georgios Karaiskakis; Panagia Diasellou. This settlement faces problems due to the lack of drainage infrastructure and septic tanks. Initially, the appropriate treatment methods for small settlements are presented and then the most proper one is selected. Finally, the sewage processing units are measured for two different scenarios and the optimum alternative is selected according to the total investment cost.