Avaliação da eficiência de tanque séptico no tratamento de esgoto sanitário e proposição de tecnologia complementar por meio de modelo de apoio multicritério à decisão

Abstract

The present work evaluated the efficiency of the Septic Tank as primary treatment in the domestic sewage treatment plant of Campina das Missões - RS and proposed the definition of low cost technology implementation based on the multicriteria decision support (AMD) methodology. decision tree. Initially to evaluate the efficiency of the process, samples of the sanitary sewage were collected from April to November of 2016 at the entrance and exit points of the Septic Tank. The following parameters were evaluated: temperature, color, turbidity, suspended and sedimented solids, dissolved oxygen, chemical oxygen demand, biochemical oxygen demand, hydrogen ionic potential, absorbance, oils and greases, electrical conductivity, total coliforms and thermotolerant. Then the results obtained in the different points were compared with Resolutions 357/2005 and 430/2011 of CONAMA and Resolution 128/06 of CONSEMA. The results indicated an average removal efficiency of 26.44% for chemical oxygen demand, 30.72% for biochemical oxygen demand, 19.69% for oils and greases, 40.47% for sedimentable solids, 61.24% For solids in suspension and 94.13% for thermotolerant coliforms. In general, the performance of the Septic Tank proved to be inefficient for sewage treatment. The results demonstrated the need for improvements in the sewage treatment plant, as well as the addition of post-treatment to enable the values of the parameters analyzed to comply with the current environmental legislation. Finally, based on the AMD decision tree, it was suggested the possibility of installing the following technologies: (a) anaerobic filter (AF) after septic tank; (B) horizontal flow WC followed by vertical TS post; (C) WC of horizontal flow followed by vertical post treatment system of TS and FA; the installation of lagoons was initially discarded due to the area available in the ETE. Such technologies may help improve the quality of sanitary sewage prior to its launch in the water body.