EDI System Balance Assessment, Adjustment, And Maintenance

An EDI system operates at an equilibrium state where the total number of incoming ions equals the total number of outgoing ions. This is macroscopically manifested as relatively stable operating ranges across three zones, without significant fluctuations. Changes in module operating conditions require a considerable amount of time to reach this equilibrium.

Adjustable factors during system operation include influent flow rate, concentrate flow rate, and voltage.

Increasing the influent flow rate increases the module's operating pressure. If this pressure exceeds the EDI's processing range, the effluent quality will significantly deteriorate. Therefore, when the influent conductivity is high, appropriate adjustment of the influent flow rate is necessary. Conversely, when the influent conductivity is low, the influent flow rate can be increased within the EDI system's pressure tolerance range to improve permeability.

Changes in concentrate flow rate are another factor affecting system equilibrium, particularly directly impacting the system's current. The concentrate flow rate also influences the removal of the weakly charged Si ion. Since the solubility of Si in water at 25°C and a pH of 6-8 is 120 mg/L... Therefore, once the concentration ratio of the influent reaches a certain level, Si will become saturated in the concentrate, preventing deeper silica removal. This is one of the conditions for determining the lower limit of the concentrate flow rate.

If the voltage decreases or the total ion level of the influent increases, the resin in the system will exchange more ions, and the corresponding operating range will shift towards the effluent side until a new equilibrium is reached or breakthrough occurs. During this process, the effluent conductivity will change, with an increase in the amount of weakly charged ions in the effluent being the most obvious manifestation. If the voltage increases or the influent ion level decreases, the system's operating range will shift towards the influent side, resulting in better effluent quality and a decrease in the content of weakly charged ions. Therefore, the equilibrium state of the system can be determined by changes in effluent quality and the amount of weakly charged ions leaking out, which can be explained by the shift in the operating range.