What are the differences in the requirements for the concentration of the regeneration fluid between forward regeneration and reverse regeneration?

Generally speaking, during regeneration in the downstream direction, the concentration of the regeneration solution should be slightly higher. This is because the regeneration solution first comes into contact with the resin at high saturation; if its concentration is low, the resin at lower saturation levels in the lower part cannot be fully regenerated, which will affect the quality of the effluent. For counter-current regeneration, the concentration of the regeneration liquid can be lower. This is because the regeneration liquid first comes into contact with the resin having a low saturation level, allowing the resin in the lower layer to be fully regenerated. As the regeneration fluid moves upward, its concentration decreases, but since it comes into contact with resin of high saturation, good regeneration can still be achieved. Obviously, the utilization rate of the regeneration liquid is also high.

I agree with the opinion above, but from an operational perspective, downstream regeneration is still recommended.