Technical and economic viability of a compact, partially submersed black water treatment system for floating residences

Riverine populations in the Amazon lack appropriate sanitation technologies due to the challenges imposed by the várzea (floodplain) environment. This compromises their health and the quality of the environment in which they live. This study aims to verify the technical and economic viability of a black water treatment using a septic tank + anaerobic filter (bamboo rings, crushed stone, brick fragments) with locally available components, of small volume and which is partially submersed. The system's pollutant removal efficiency was considered using analyses of pH, temperature, biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrogen, ammonium and phosphorus. Economic viability was calculated using the costs of the systems, compared with the value of a standard residence and family income of residents of the Mamirauá and Amanã Reserves. BOD removal efficiency was similar for the media filter tested (average 77%). COD load removal was between 67 and 83%. Nitrogen and phosphorus concentrations remained high in relation to legal standards, with 59 and 96 mg L⁻¹ of phosphorus for the brick fragment filters, and 230 and 379 mg L⁻¹ of nitrogen for the crushed stone and bamboo ring filters, respectively. The cost for the system was US$ 1,000, about 5% of the cost of a standard residence. The three filter configurations were similar in terms of organic material removal. The technology proved viable in terms of efficiency and cost as it is an accessible option for the várzea environment.