Methodology to support the planning of sewage treatment systems within river basins

Selection of sewage treatment systems for protecting water resources within a watershed is a complex problem. It involves environmental, technological, operational and social aspects joint analysis associated with the treatment systems, in addition to raw or treated sewage final disposal receiving watercourses support capacities assessments. The present work proposes a methodology that could help the sewage treatment systems selection process through the combined application of water quality mathematical model, metaheuristic optimization technique (genetic algorithm) and multicriteria analysis method (theory of multi-attribute utility). The study area is the hydrographic basin Benevente River, an important watercourse located in the Espirito Santo state South region, in Brazil. Minimum efficiencies for removing organic matter and nutrients were considered in the sewage treatment systems pre-selection. For the most populous districts, such as Jabaquara, Alfredo Chaves and Alto Pongal, the ordering process, supported by multicriterial analysis, led to the selection of mechanized technologies-activated sludge processes. For all other locations, stabilization pond systems were selected. The methodology described in this work can be generally applied to the planning of wastewater treatment and final disposal in watersheds and subsidize effluents discharge and dilution in watercourses environmental licensing and granting processes.