# Simultaneous Electrochemical Removal of Selenium and Strontium from Aqueous Solution
## 4 Discussion
### Scale-Up  
The scalability of EC reactors is influenced by a multitude of factors for which the maintenance of electrical, geometric, kinematic, and thermal similarity criteria are crucial [42; 43; 44]. The uniformity of the current distribution across the electrodes is vital for ensuring that the electrochemical reactions occur evenly throughout the reactor volume. If the current distribution is not maintained during the scale-up, it can lead to localized overheating, inefficient coagulation, and reduced overall treatment effectiveness. The design of the electrode configuration, including the spacing and arrangement of anodes and cathodes, plays a significant role in achieving a uniform current distribution [45; 46]. Moreover, the electrochemical kinetics of the reactions occurring at the electrodes must also be taken into account. The rate of electrochemical reactions is influenced by factors such as the electrode surface area, the concentration of reactants, and the applied current density. Thus, maintaining similar current densities and electrode surface areas relative to the reactor volume is necessary. Failure to do so can result in changes in the reaction rates, leading to inefficiencies in contaminant removal [47]. Geometric similarity ensures that the physical dimensions and configurations of the reactor maintain proportional relationships that influence the overall performance and efficiency of the system. This concept is particularly important because deviations from geometric similarity can lead to significant changes in the flow dynamics, mass transfer, and reaction kinetics, which can adversely affect the treatment process [46; 48]. The distance between the anodes and cathodes significantly affects the electric field strength and the mass transfer rates of ions in the EC process. If the spacing is not maintained proportionally during the scale-up, it can lead to variations in the current density and, consequently, the efficiency of the contaminant removal [49]. The Reynolds number, which characterizes the flow regime, should remain consistent across scales to ensure that the flow remains either laminar or turbulent as intended. This is particularly important for the mixing efficiency and mass transfer rates [50; 51]. In general, the maintenance of geometric similarity helps to achieve similar Reynolds numbers [48; 51]. Similarity in the Froude number ensures that the effects of gravity on the flow behavior are consistent across different reactor sizes, which is particularly important in systems where buoyancy-driven flows are significant, such as in EC flotation processes [52]. Maintaining thermal similarities ensures that the temperature distribution, heat transfer characteristics, and thermal dynamics remain consistent across different reactor sizes. One of the primary aspects of thermal similarity is the heat transfer coefficient, which describes how effectively heat is transferred between the fluid, electrodes, and reactor surfaces. The heat transfer coefficient can be influenced by factors such as the fluid velocity, temperature gradients, and physical properties of the fluid. If the heat transfer characteristics differ significantly between scales, it could lead to variations in temperature profiles, which may affect the solubility of electrolytes and the kinetics of the electrochemical reactions occurring within the reactor. Additionally, the thermal effects associated with electrical operations must be considered. The Joule heating effect, which occurs due to the passage of the current through the resistive electrolyte, can lead to temperature increases that affect the EC process. Ensuring that thermal management strategies are in place to handle the heat generated during operation is crucial for maintaining the desired electrical characteristics and preventing thermal degradation of the reactor components [53]. By ensuring that these parameters are consistent across different scales, engineers can predict the performance of the larger reactor based on the data obtained from smaller models.