How temperature effects rinse down.
The time it takes to rinse a resin down to a given purity level varies somewhat with the temperature of the water. As the water temperature drops the diffusion rates are lower and it takes longer for the traces of regenerant to come out of the resin beads. For relatively low purity standards this doesn’t have much of an impact. However, for high purity water system that must be rinsed down to quality levels better than 100,000 ohms, the water temperature begins to play a significant role in determining the length of the rinse down curve.
Cation resins are not as affected by water temperature as anion resins. New resins are not affected much by temperature changes. It is the anion resins that have been partially oxidized or have some organic matter on them that are most affected by temperature changes. Weakly basic resins are more affected than strongly basic resins. Anion resins that have been in service for a while almost always have a certain amount of weakly acidic groups attached to them. This can be in the form of organic acids due to organic fouling or oxidation of the polymer itself. During regeneration with sodium hydroxide, these weak acid groups are converted to their sodium salts.
During the rinse of an anion resin, these salts hydrolyze in water until they return to the hydrogen form. While this is going on, they are giving off sodium ions. The rate of hydrolysis is a direct function of temperature. Higher temperatures increase the rate of hydrolysis and allow the process to be completed in less time. This means that in warm weather it takes less time to rinse down the resin than it does in cold weather.
Given that the rate of hydrolysis is largely unaffected by the rate of water flowing through the bed, a higher rinse rate may only give what appears to be a better quality effluent because it is diluting the sodium ions in a larger volume of water. The sodium leakage from the bed while rinsing at the same flow rate as the service rate is a more meaningful number.
Water can be conserved by using a warmer temperature for regeneration and using slower flow rates for the rinse water rate to carry the hydrolysis product out of the bed. This can be accomplished by using warm water regeneration and a warm water displacement rinse. This could be extended to 2 or 3 times the normal time required for the displacement rinse. The benefits are that the higher temperature allows the hydrolysis to occur more rapidly; the slower flow rate during the extended displacement rinse and shorter fast rinse conserves water.