# Practical Methodology for a Three-Dimensional-Printed Hybrid Desalination System
## 3 Results
### Performance of the Hybrid RED-ED System  
The hybrid system was assembled using a single RED unit cell and a single ED unit cell, which were connected exclusively through an electrical circuit, with no fluid exchange between the units. The solutions used in each reactor were described in Sections 3.2 and 3.3; the RED unit used two solutions of different concentrations (H and L), while the ED unit used a saline feed solution for desalination. In this configuration, the RED unit generated the electrical energy required to power the ED reactor for desalination. \begin{table}
\begin{tabular}{c c} \hline \hline
**Flow Rate (mL/min)** & **Salt Removal (\%)** \\ \hline
20 & 8.13 \\
40 & 10.84 \\
60 & 11.56 \\
80 & 12.46 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Salt removal efficiency at different flow rates. Figure 8: Conductivity variation during ED desalination at different flow rates. The RED reactor was tested in batch and continuous modes to determine whether the mode of operation influenced the energy supply to the ED reactor and, consequently, the desalination performance. In the batch mode, the salinity gradient in the RED reactor can decrease over time due to recirculation, which may reduce the energy available to drive the ED process. By comparing this setup with continuous mode operation in the RED reactor, where the salinity gradient is maintained more consistently, the experiment sought to understand if maintaining continuous operation in RED would be more favorable for consistent desalination in ED. The ED reactor was operated in batch mode, with both the desalinated and brine solutions being recirculated. The recirculation aimed to increase desalination efficiency by enhancing the contact time between the feed solution and the membranes, thus promoting higher ion removal rates. Figure 9 illustrates the hybrid setup: Figure 9 shows a schematic of the system, highlighting the electrical connection and the independence of fluid circuits in each reactor, while Figure 9 displays a photograph of the complete experimental setup. The ED desalination process, powered entirely by the RED reactor, was evaluated under two different operational configurations for the RED system: continuous and batch modes. The flow rate selected for the RED reactor was 80 mL/min, based on prior studies. The ED process was conducted in batch mode at two different flow rates, 40 mL/min and 80 mL/min. Figure 10 illustrates the progression of desalination over time for the hybrid system under both experimental conditions. Figure 10 shows the performance of the system when the ED unit was operated at a flow rate of 40 mL/min. The purple lines represent the experiments with the RED reactor in batch mode, while the blue lines represent those conducted with RED in continuous mode. Figure 10 presents the results for the ED process at 80 mL/min, where the pink lines indicate batch operation of the RED reactor, and the green lines correspond to the continuous process. Figure 9: Schematic and experimental setup of the hybrid RED-ED system: (**a**) schematic diagram of the hybrid system, showing the RED and ED reactors connected electrically but operating with independent solutions; (**b**) photograph of the experimental setup, illustrating the RED and ED reactors connected, peristaltic pumps, multimeter, and the power resistor. In both sets of experiments, the batch mode exhibited superior desalination performance compared to the continuous mode, indicating that in shorter experiments, the decrease in the salinity gradient in the batch mode did not significantly impact desalination efficiency. The graphs in Figure 10 show a consistent decrease in conductivity in the desalinated compartment and an increase in the brine compartment, demonstrating effective ion transport under the energy supplied by the RED reactor.