Weak Acid Hardness Reduction Process
The H&T Weak Acid Cation (WAC) softening process can be used in applications for removal of both iron and hardness in a one-step process, or where softening is needed but an increase in the sodium level cannot be tolerated. Weak Acid Cation resin is extremely efficient and makes excellent use of the regenerant. The resin operates in the hydrogen cycle instead of the sodium cycle, so hydrogen ions are exchanged for hardness instead of sodium. Acid is used for regeneration in place of sodium chloride and, due to the resin
efficiency, only stoichiometric quantities of acid are required. The regenerant waste is virtually neutral and requires very little pH adjustment prior to disposal.
It is necessary to have a favorable hardness-to-alkalinity ratio in order to achieve desired results. Only the temporary hardness, or hardness associated with alkalinity, will be removed. If the alkalinity is not high enough, there will not be enough hardness reduction to make the system viable. However, when the water quality fits the application, this process can be a highly effective way to remove the desired amount of hardness without a corresponding increase in sodium. If the hardness is 400 mg/L and the alkalinity is 300 mg/L, the WAC process will produce water with 100 mg/L of hardness. The exchange of alkalinity generates CO2 in the WAC exchanger, therefore a degasifier is needed following the exchanger to strip the CO2 and raise the pH. Usually, when iron is removed using an ion exchange resin, the resin will be contaminated with iron and require cleaning or replacement. However, in this case, acid is used as the regenerant, so the resin is cleansed of any iron during every regeneration.