Analysis of Factors Affecting the Quality of Medical Pure Water

1. The Influence of Raw Water Conductivity on Desalination Efficiency

As the raw water conductivity increases, the conductivity of the EDI effluent also increases. This is because low raw water conductivity results in low ion content, and this low ion concentration leads to a larger potential gradient on the resin and membrane surfaces in the desalination chamber. This enhances water dissociation, increases the limiting current, and generates more H+ and OH- ions, resulting in better regeneration of the anion and cation exchange resins filling the desalination chamber.

2. The Influence of Operating Voltage on Product Water Quality

The quality of the effluent from medical pure water equipment is also related to the operating voltage. If the operating voltage is too low, it is insufficient to remove ions from the desalination chamber before the pure water is discharged. The electrodialysis and resin electroregeneration processes are relatively weak, and ion exchange is the primary process. As the operating voltage increases, the degree of water dissociation increases, and the resin regeneration effect is better, leading to a decrease in the conductivity of the desalinated water. When the operating voltage increases to a certain level, the ion exchange process and the resin regeneration process reach equilibrium, and the product water conductivity further decreases and tends to stabilize. However, excessive operating voltage will cause excessive water ionization and ion back diffusion, thus reducing the quality of the permeate. Therefore, it is recommended that EDI be operated at an appropriate voltage.

3. The Influence of Flow Rate on Permeate Quality

The conductivity of the EDI effluent changes very little with the operating current at different influent flow rates. This is because, in the circuit, the solution phase and resin phase in the dilute chamber are connected in parallel. Since the conductivity of the ion exchange resin is much higher than that of the electrodialysis permeate, the resin phase resistance becomes the determining factor for the dilute chamber resistance. Ion transport mainly occurs through the resin phase, and within a certain range of dilute flow rate, the flow rate has little effect on the resin phase resistance. Therefore, the total current of the membrane stack does not change significantly, and the permeate conductivity changes very little. Consequently, the influent flow rate has little effect on the degree of water dissociation.