Performance of a Municipal Wastewater Treatment Plant During the COVID-19 Pandemic: A Case Study from a Coastal Tourist Region in Rio de Janeiro, Brazil

Resumo

This study assesses the performance of a municipal wastewater treatment plant (WWTP) in Saquarema, Rio de Janeiro, Brazil, between 2019 and 2024, with emphasis on the COVID-19 pandemic period. Using official monitoring data from the Rio de Janeiro State Environmental Institute (INEA), effluent parameters, including flow rate, pH, suspended solids (SS, TSS), methylene blue active substances (MBAS), biochemical oxygen demand (BOD5), and ammoniacal nitrogen (N-NH3), were evaluated against regulatory standards. Statistical analyses indicated operational stability during peak pandemic years, with 94.44% of BOD5 values were below the 40 mg L^-1 limit, likely reflecting reduced hydraulic and organic loads due to lockdowns and decreased tourism. However, non-compliance events occurred before and after the pandemic, especially in 2019, 2023, and 2024, including simultaneous exceedances of BOD5 (up to 141 mg L^-1), TSS, and MBAS. Ammoniacal nitrogen showed the most critical results: from 2022 to 2024, 22.58% of samples exceeded the 20 mg L^-1 legal limit, reaching 35.23 mg L^-1. The late inclusion of N-NH3 in monitoring and its persistent removal inefficiency suggest structural deficiencies in biological treatment. The findings underscore the urgent need for technological upgrades, particularly nitrification and denitrification systems, to ensure regulatory compliance and protect public health and coastal ecosystems.