Modelagem computacional e validação experimental do escoamento de um reator UAHB em escala de bancada

Abstract

The present work aimed to evaluate the hydrodynamic behavior of an Upflow Anaerobic Hybrid Sludge Blanket (UAHB) reactor on a bench scale (5.7 L), through the integration of stimulus-response experimental tests and computational modeling (CFD). The research sought to characterize the flow inside the reactor, identify hydraulic anomalies, and validate the application of numerical simulations for this type of system. The reactor, constructed of plexiglass and operated continuously, was subjected to different theoretical Hydraulic Retention Times (HRT: 0.6, 1, and 2.33 hours). The hydrodynamic tests used tap water as effluent and eosin Y as a tracer, with concentrations determined by spectrophotometry at 516 nm. The experimentally obtained Residence Time Distribution (RTD) curves were fitted to the uniparametric theoretical models of dispersion (Small and Large Intensity) and tanks-in-series (N-CSTR). The test results revealed the presence of a "long tail" effect in the concentration curves, indicating the existence of dead zones and preferential paths. The N-CSTR model showed the best fit to the experimental data (correlation coefficients r² > 0.95), suggesting a predominant flow regime of complete mixing, with the reactor behaving equivalently to 3 or 4 perfect-mix reactors in series. The analysis of hydraulic anomalies indicated dead zone volumes with negative percentage values, which suggests the strong influence of hydraulic short-circuiting. The hydraulic efficiencies (λ) ranged from 0.18 to 0.86, being classified as satisfactory, good, and unsatisfactory, respectively for the HRTs of 0.6, 1, and 2.33 hours. The Reynolds number confirmed the laminar flow regime under all conditions. The CFD modeling, performed in ANSYS CFX 2025 software based on the actual reactor geometry, allowed visualization of the velocity field and estimation of dead zones (between 15.2% and 26.5% of the total volume), which were concentrated near the reactor inlet. However, the quantitative comparison between the dead zone volumes obtained experimentally and via CFD revealed divergences greater than 150%, possibly related to the adopted boundary conditions. It is concluded that the combination of experimental techniques and computational simulation proved robust for the hydrodynamic characterization of the UAHB reactor, providing valuable insights for the improvement of design and operation of anaerobic reactors aiming for higher efficiency in effluent treatment.