Sustentabilidade de alternativas de tratamento descentralizado de esgoto em bases militares isoladas: uma abordagem por índice composto

Abstract

The deficit in wastewater treatment in isolated communities is an obstacle to the universalization of sanitation, prescribed by SDG-6 (UN) and by Law 14026/2020 (Brazil), requiring incentives for successful and potentially replicable decentralized wastewater treatment projects in these places. In this sense, remote military installations of the Brazilian Army can contribute. Therefore, the objective of this work was to select the most sustainable alternative for the treatment of domestic sewage from an isolated military base. First, a literature review was carried out on decentralized technologies suitable for isolated communities, in order to combine them in different technological arrangements (scenarios) of treatment. Then, the scenarios were dimensioned for 60 soldiers and the respective construction (CAPEX), operation and maintenance (OPEX) costs were obtained. Finally, the scenarios were evaluated holistically based on a global sustainability composite indicator that aggregated not only economic factors, but also environmental, sociocultural and technical ones. The seven treatment scenarios analyzed were: 1) Septic tank (ST) and anaerobic filter (ANF) with drying bed (dry. bed); 2) ST and horizontal subsurface flow constructed wetlands (HCW) with dry. bed; 3) ST and vertical subsurface flow constructed wetlands (VCW) with dry. bed; 4) French vertical-flow constructed wetland adapted to tropical climates (VFCW); 5) Facultative lagoon (FL); 6) TEvap for blackwater; banana circle (BC) for dark greywater and EvaTAC for light greywater; 7) TEvap for blackwater; BC for dark and light greywater. The results showed that the FL was the most sustainable option, mainly due to its simple and cheap operation and maintenance. This may indicate that there are usually more interesting collective solutions than individual solutions for isolated bases, because the volume of effluents produced is large. The scenarios with intermittent feeding were the most unsustainable (VFCW; ST+VCW and dry. bed). It was also verified that the scenarios with source separation of effluents (6 and 7) have very high CAPEX due to the need for multiple units in parallel (R$ 2,559.60 inhab-1 for TEvap//CB//EvaTAC and R$1,458.16 inhab-1 for TEvap//CB//CB), despite being more sustainable than the Brazilian standardized option of ST+ANF and dry. bed. Thus, it was suggested future studies with a focus on expanding the application scale of these technologies, usually single-family. At the same time, the low cost of the adapted version of the VFCW (CAPEX of R$ 340.47 inhab-1 and OPEX of R$ 55.07 inhab-1year-1) indicated its potential for greater decentralized applications in practice. It should be noted that the composite indicator approach is suitable for decision-making in the military context, as it facilitates the interpretation of the complex problem of selecting the most sustainable treatment alternative for military decision-makers without technical knowledge.