From batch to continuous electrocoagulation: integrating hydrodynamics and process parameters for efficient fluoride removal and reactor scale-up

Abstract Electrocoagulation (EC) is a promising technology for water treatment; however, the reliable transposition of parameters from batch to continuous systems remains a critical challenge for process scale-up. This study presents an integrated experimental and mechanistic evaluation of batch and continuous EC reactors for fluoride removal, combining electrochemical optimization with hydrodynamic characterization. Experiments were conducted using synthetic water containing 10 mg L⁻ 1 of fluoride in reactors equipped with concentric cylindrical aluminum electrodes. Optimal batch conditions were identified at a current density of 13.06 A m⁻ 2 and a hydraulic retention time (HRT) of 6 min, achieving 98.25% fluoride removal with a specific energy consumption of 5.97 kWh m⁻ 3 . These parameters were subsequently used as a reference for continuous flow operation, where HRTs between 3 and 7 min were evaluated. Residence time distribution (RTD) analysis revealed a predominantly plug flow regime with moderate axial dispersion ( D / uL = 0.154), with the real HRT close to the theoretical value. The continuous system outperformed batch operation under all evaluated conditions, with removal efficiency gains of up to 17.7% and energy savings of up to 40%. A relationship between HRT and the batch-to-continuous conversion factor was established, indicating convergence of system performance at higher residence times. These findings demonstrate that the integration of hydrodynamic behavior and electrochemical parameters provides a robust basis for predicting reactor performance and enables reliable scale-up of EC systems.