Desempenho de um sistema unifamiliar de baixo custo para tratamento de esgoto: tanque séptico e filtro anaeróbio econômico

Abstract

Domestic wastewater treatment is a pillar of basic sanitation that, currently, few people have access to in the country. This is even more restricted when we talk about rural communities, where is difficult to cover the wastewater collection network for conventional treatment. Therefore, the objective of this study was to evaluate the performance of a decentralized domestic wastewater treatment system, using low cost material, making the system accessible to places with inadequate or nonexistent wastewater treatment. A system containing a septic tank and a cost-effective anaerobic filter (STCAF) and an infiltration trench for final disposal of the effluent was installed. The STCAF system was made with three polyethylene containers straight, the first two being used for the septic tank (two chambers in a row) and the last one for the anaerobic filter, which was filled till half with a stone support. The system received unsegregated wastewater from a four-person household. Sampling and analysis of raw and treated wastewater were performed over a period of 16 months to evaluate the efficiency of each unit and the total efficiency of the system. The average removal efficiencies obtained in the STCAF system were 67%, 54%, 67%, 62%, for BOD, COD, TS and TSS, respectively. For TKN, PO4³--P, total coliforms and E. coli the average removal efficiencies were 35%, 50%, 1.35 log and 0.96 log, respectively. The values obtained were within the range expected by the literature, except COD, the only parameter that had removal below expectations. However, as the concentrations in the raw wastewater were high (strong wastewater), the final effluent presented concentrations higher than those allowed by the Brazilian legislation. The STCAF system constitutes an accessible and efficient alternative, being quite attractive due to its low cost, easy implementation and operation.