Estudo de viabilidade técnica-econômica, social e ambiental para seleção de tratamento de esgoto doméstico em áreas rurais

Abstract

Choosing the best structure of domestic sewage treatment requires a variety of analyses and data involved. In relation to rural and isolated areas, this task is more difficult due to the lack of data and driving analysis that allows decision-making process on the most viable systems for use in areas that embrace rural sanitation. Several planning studies present technological matrices with possible domestic sewage treatment systems, but which system is the best option among the existing ones? Thus, through this study, a survey of environmental, social, technical and economic data and information was carried out, of case studies and pilot projects with technologies applicable in a decentralized way in humid subtropical climate in Brazil. From this data collection, the Analytic Hierarchy Process (AHP) was applied in different scenarios using indicators divided into environmental, social and technical-economic criteria, in order to evaluate the main systems (the priority ones) in each criterion and in general. For the selected criteria and indicators, weights (degree of importance) were defined in order to allow the evaluation of the systems and decision-making of the most priority based on the most sustainable technologies. There were 11 configurations of domestic sewage treatment systems evaluated that contained in a single or more than one stage treatments by anaerobic digestion, wetlands and filters (anaerobic filter and sand filter). In general, among all the scenarios performed (evaluating the sensitivity of the method based on the data and degrees of importance of the criteria used), the system composed by compact Upflow Anaerobic Sludge Blanket, Septic Tank and Anaerobic Filter and Septic Tank and Wetland with vertical subsurface flow were the ones that proved to be the most indicated, compared to the other ones, for the defined study area. Furthermore, the realization of several scenarios caused the priorities in each criterion and in general to change, according to the data of the indicators used for each alternative (each system) and according to the weights of each criterion (degree of importance between them). This variation demonstrates that although the AHP method is valid for the use of the choice of sewage treatment in rural and isolated areas (comparison of different types of systems), the method is sensitive to the data used and degrees of importance judged for criteria and indicators. This does not prevent its use for the objective mentioned, since the greater the number of data used in the indicators, the better and more accurate the application of the method is, and that public and expert opinions can contribute to the definition of the degree of importance of the criteria and indicators used.