Cleaning of Organically Fouled Anion Resins

This process involves a partial caustic regeneration and displacement, followed by a 150 °F, 15% NaCl treatment. The process is repeated until the maximum color eluted during the brine step drops to 1/5 of the highest color eluted during the first treatment. Details of the procedure described above are as follows:

The anion bed is backwashed, then regenerated with 2%-5% NaOH. The amount of caustic must be limited to approximately 1/3 of the normal dosage. The flow rate should be about 0.2 gpm per ft³. For ten minutes after this step is completed, a slow rinse or displacement should occur at the same 0.2 gpm per ft³. Then, 150 °F, 10-15% NaCl solution should be injected at 6.5-8 pounds per ft³. This should also be at a 0.2 gpm per ft³ flowrate. Finally, the “slow rinse or displace” step described earlier should be repeated. This time, however, note the time at which the eluted color is the highest. This observation should be about the most concentrated salt in the effluent. This process should be repeated (without backwashing) until the color eluted during the salting period is 1/5 of that observed during the first treatment.

It is important to realize the procedure is best completed on a regular or periodic schedule before the anion resin is appreciably fouled. If organic matter in the affluent is high, the above steps should be taken every 15 to 30 days. Note that if the underdrain is made of stainless steel, the HCl will attack it, and the resin will have to be moved to an alternate treatment vessel.