## 6 Summary and Outlook
Focusing on a future hybrid process that includes photo-electrocatalysis or electrocoagulation may be an effective strategy for addressing this special issue. * Optimizing operational parameters such as pH, current density, and applied voltage is crucial to improve eNO\({}_{3}\)R and their effects should be examined in real environments as in the case of brackish groundwater. Additionally, further studies are needed, especially on the challenge of anode and cathode passivation which results in fouling of the electrodes and seriously decrease the efficiency of nitrate reduction, notably on the application of electric pulses and the specific type to ensure the performance of the process and prevent metal leaching. This can enhance nitrate removal efficiency, minimize by-product formation, and promote a sustainable process. * Selecting the configuration type for the cell, divided or undivided, can greatly impact the efficiency and selectivity of the reduction process. Divided cells are more effective at nitrate reduction, and they could be the suitable choice for ammonia generation as they prevent re-oxidation of the reduced nitrate in the anode and concurrently, we recover the ammonium that migrates through the cation exchange membrane (CEM). However, the drawbacks associated with divided cells are fouling and scaling of the membrane in complex water matrices as the case in brackish groundwater, additionally, the limited availability of ammonium-selective membranes needs to be addressed in future research. The alternative pathway for eNO\({}_{3}\)R to ammonium in brackish groundwater can be employed in undivided cells, providing a specific anode that prevents the production of chlorine radicals and active chlorine. These anodes are currently being developed, especially for large-scale applications. On the other hand, undivided cells remain the optimal choice for eNO\({}_{3}\)R to N\({}_{2}\) due to their effectiveness in minimizing energy consumption and operational costs, while also simplifying system design and maintenance. * Reactor design and the components of the cells, such as shapes, dimensions of electrodes, and their placement in the flow channel are essential for the success of the process due to their role in ensuring fluid dispersion, current distribution, and mass transport. Mathematical approaches to designing electrochemical reactors have been adopted for different technology using numerical tools such as computational fluids dynamics (CFD) since we can test the various reactors with different components before the experimental characterization in laboratory-scale cells and then, during the scale-up of pilot plants. Therefore, the use of CFD simulation to visualize surface-phase changes during electrode reactions, including the mass transport and current distribution during eNO\({}_{3}\)R is crucial to increase the knowledge and performance of the process. Furthermore, designing a new reactor to lower the ohmic resistance and thus reduce unnecessary energy consumption is also a desirable approach. * Researchers who focus on the conversion of eNO\({}_{3}\)R for ammonia production to pursue subsequent utilization should consider the concentration of nitrate in water. Using renewable energies for cost minimization remains advantageous. However, in waters with low nitrate concentrations, it is preferable to prioritize the production of drinking water, specifically through the pathway of converting nitrates into nitrogen. Nevertheless, the generation of ammonium from chemical industry waste, sewage, and the site of calcite one with high nitrate concentration is the most effective approach to address \"two birds in one stone\", removing nitrate and producing ammonia. * The operating cost requires special consideration for large-scale applications, especially raw materials, transportation, and post-treatment costs. Also, the electrical energy consumed during nitrate electroreduction represents a large proportion of the total cost.