Aplicação de tanino como tratamento terciário no polimento de esgoto sanitário secundário

Abstract

The discharge of untreated domestic wastewater is one of the main sources of water resource degradation, making it essential to adopt treatment systems capable of reducing pollutant loads before disposal into receiving water bodies. Although conventional biological treatment processes are highly efficient in removing organic matter and suspended solids, nutrient removal is often limited, which may represent an operational challenge. Furthermore, secondary treated domestic wastewater may still exhibit characteristics that reduce its potential for water reuse applications. In this context, the present study aimed to evaluate the application of tannin as a natural coagulant in tertiary treatment for improving the quality of secondary domestic wastewater from the Wastewater Treatment Plant (WWTP) of the Federal University of Fronteira Sul (UFFS), Erechim Campus, with emphasis on the removal of turbidity, apparent color, total organic carbon, and phosphorus. The study also assessed the operational performance of the treatment plant using monitoring data collected between 2023 and 2025. The WWTP operates with an activated sludge system under extended aeration and achieved average removal efficiencies of 92.4% for BOD, 92.0% for COD, and 89.4% for total suspended solids, while presenting a low average phosphorus removal efficiency of 17.6%. Laboratory coagulation/flocculation tests were conducted using different tannin dosages (25, 40, 55, 70, 85, and 100 mg/L), evaluating total phosphorus, turbidity, apparent color, pH, total organic carbon, and toxicity. The results demonstrated that tannin promoted significant removals of turbidity and apparent color, exceeding 90% in most treatments, in addition to providing complementary reductions in total organic carbon. Ecotoxicological assays using Artemia salina indicated that tannin application did not increase the toxicity of the treated effluent. Therefore, tannin can be considered a technically viable alternative for tertiary treatment of domestic wastewater, contributing to the improvement of final effluent quality.