Engineered Ecosystem for Decentralized Treatment of Sewage from Small Generators and Isolated Communities

Abstract

In different regions of the world as well as in many parts of Brazil, high percentage of the
population and sometimes, entire isolated communities do not have access to sewerage
system or sewage treatment. The common scenario is the use of septic tanks and, in many
cases, direct discharge into water bodies. The objective of this study was to develop and test a
low-cost sewage treatment system, appropriate for isolated or poor communities at the same
time, meeting the discharge threshold limits established by the Brazilian regulation. For that, a
compact engineering ecosystem for decentralized treatment of domestic sewage was
constructed and tested in a research unit installed in an environmental protected area in
Grande Island, south coast of Rio de Janeiro State. The system is formed by septic tank,
submersed aerated filter, secondary decanter, and for polishing, vegetated tanks containing
aquatic macrophytes (wetland) and one tank with algae. The results of a 200 day monitoring
period, covering two different flows rates (200 L.h^-1 and 52 L.h^-1) are presented. With the
lower flow (52 L.h^-1), the following removal efficiency was achieved: 87.8% (nitrite); 71%
(nitrate); 47% (Ammoniacal nitrogen); 89% (COD); 40.2% (total phosphorus). After the flow
reduction, most of parameters analysed, met the threshold limits established by the Brazilian
Federal Legislation, which demonstrated that the system fulfilled its purpose.