Avaliação do desempenho operacional dos reatores UASB da ETE da Universidade Federal de Lavras

Abstract

Sewage treatment is an essential basic sanitation service, aimed at protecting the environment and improving life quality. Some large institutions, such as universities, are similar to urban centers in sewage yield and have therefore been investing more and more in their own sewage treatment plants (STPs). In this context, the Federal University of Lavras (UFLA) has a sewage treatment plant, the ETE-UFLA, which comprises preliminary, primary, and secondary treatment, the latter containing six Upflow Anaerobic Sludge Blanket (UASB) reactors followed by six submerged aerated biological filters (SBBFs). In order to assess the proper functioning of these treatment units, constant monitoring of the influent and effluent characteristics of the sewage treatment plant (STP) is essential. Therefore, the objective of this study was to evaluate the efficiency of each UASB reactor and the STP as a whole through physicochemical variables such as alkalinity, acidity, pH, temperature, biochemical oxygen demand, chemical oxygen demand, total nitrogen and solids. These analyses were conducted following the methodologies described in APHA (2023). Samples were taken between 2022 and 2023, collected from the internal pumping station of the sewage treatment plant (influent to the UASB reactors), at the outlet of each reactor, and at the outlet of the sewage treatment plant. Additionally, the sludge in the reactors was characterized to measure microbial growth via total volatile solids. The average flow rate during the analysis period was approximately 118.4 m3 d ⁻1 , which ensured a hydraulic retention time (HRT) of 13.48 h. The results revealed instability in the performance of the UASB reactors, due to a 64% decrease in chemical oxygen demand (COD) removal efficiency from 2022 to 2023. This phenomenon can be attributed to the low volumetric organic load (0.65 kg m⁻3 d ⁻1 ), peak flow rates, and the absence of regular sludge disposal, which caused the entrainment of solids. Although the combined system maintained legal compliance, with overall efficiencies of 79% and 66% and total Kjeldahl nitrogen (TKN) removal exceeding 60%, the unit operated below its potential. Therefore, the system requires operational interventions, such as adjusting the number of reactors in operation to increase the organic load, and implementing a strict sludge disposal schedule to stabilize anaerobic digestion.