Estudo Comparativo de Sistema de Eletrocoagulação Operando por Batelada e em Fluxo Contínuo no Tratamento de Águas

Abstract

The increasing presence of recalcitrant compounds in water and wastewater, such as heavy metals, dyes, fluorides, and pharmaceuticals, has highlighted the limitations of conventional treatment methods due to low efficiency, high consumption of chemical inputs, and the generation of by-products. In this context, electrocoagulation (EC) has emerged as a promising alternative, as it enables in situ generation of coagulants, operational simplicity, and high removal efficiency for a wide range of pollutants. This dissertation aimed to investigate, evaluate, and compare constructive, operational, and hydrodynamic parameters of EC systems operating in batch and continuous-flow modes, in order to support the design of continuous reactors based on batch-scale data. The study was structured into three complementary stages. In the first stage, a systematic scientometric review based on the PRISMA protocol was conducted, analyzing 60 articles indexed in the Scopus and Web of Science databases. The most frequently studied pollutants were chemical oxygen demand (COD), turbidity, and apparent color, with a predominance of aluminum and iron electrodes. Initial pH and electrode spacing were identified as parameters with a positive effect on process efficiency, whereas poorly adjusted increases in current density and electrochemical area negatively affected performance and energy consumption. In the second stage, a cylindrical batch reactor with concentric aluminum electrodes at three different heights (20, 40, and 60 cm) was constructed and operated using filter backwash water (FBW) from a drinking water treatment plant. Experiments conducted under different current densities (3.18 to 9.55 A/m²) demonstrated that the shortest reactor height (20 cm) achieved the highest removal rates, exceeding 97% for turbidity and 93% for apparent color, with kinetics well described by a first-order model. Statistical analyses (ANOVA and Tukey’s test) revealed significant differences among reactor heights only at the initial stages of the process, with removal efficiencies converging at longer reaction times. In the third stage, batch-optimized parameters were transferred to an electrocoagulation reactor operating under continuous-flow conditions, which was previously subjected to hydrodynamic characterization using pulse tracer tests with Methylene Blue. Residence time distribution (RTD) analysis indicated predominantly plug-flow behavior with moderate axial dispersion, with the real hydraulic retention time (4.24 min) close to the theoretical value (4.67 min) and an axial dispersion number of 0.154, demonstrating adequate hydraulic performance for continuous EC application. The performance of the continuous reactor was evaluated at hydraulic retention times ranging from 3 to 7 min using a synthetic solution containing 10 mg/L of fluoride, achieving removal efficiencies of up to 98.25%, higher than those observed in batch operation, along with up to 40% reduction in energy consumption. The transposition coefficients ranged from 1.64 to 1.11, indicating greater performance convergence at higher hydraulic retention times. It is concluded that the transposition of electrocoagulation from batch to continuous-flow operation is technically feasible, provided that structural, operational, and hydrodynamic adjustments are properly implemented to ensure flow stability, high removal efficiency, and energy optimization. The results provide robust guidelines for the design and scale-up of continuous electrocoagulation systems for real water and wastewater treatment applications.