The packed bed of adsorbent can be regenerated. If the organic material is volatile, the carbon bed may be regenerated by steaming. However, it is more conven-tional to remove the carbon and reprocess the material through a furnace.In large installations, the furnace is installed as part of the carbon installation; in smaller installations, the carbon may be discarded, or removed and returned to the manufacturer for reprocessing. Packed beds of ion-exchange resin are regenerated with brine, causing the ion-exchange beads to shrink and expel
the adsorbed organic matter. Because adsorption reactions are relatively slow, particularly in cold water, packed beds are usually operated at lower flows than niters and ion exchange systems, usually below 2 gal/ min/ft3 (0.27 m3/min/m3). Bed depths
over 4 ft are common so that the retention
time in the bed for adsorption may vary from 10 to 30 min. In evaluating the performance of granular beds of adsorbent, pilot plant studies are required.
If organics are to be removed from a waste stream, the testing program may be extensive, since data must be obtained not only on the removal efficiency of the adsorbent itself, but also on the capability of the exhausted adsorbent to be regenerated and the relative performance of the various commercially available materials. Tests for commercial carbons used for color removal show variations in the KF value from 6.9 to 13.4 and in \/n exponent from 0.42 to 0.62.
Although adsorption may seem most often to be related to reaction of an adsorbent with colloidal substances, activated carbon and some other adsorbents react with molecules, too. This makes adsorption an effective waste treatment process in chemical, petrochemical, and other industries handling chemicals that may find their way into the plant sewer.
When carbon is used, regeneration by reburning is a difficult process to evaluate by pilot plant; assistance by the carbon supplier may be needed. On the other hand, the testing of an ion-exchange-type adsorbent is simple, since regeneration is accomplished with brine. The tests should be repeated for a long enough period of time to indicate whether the capacity of the resin is completely reclaimed each regeneration, and therefore to what extent and how frequently replacement of resin may be necessary. Tests of this kind are usually performed in glass tubes approximately 1 in (2.5 cm) in diameter, with a bed of 30 in (76 cm) of resin adsorbent. The tube is provided with end connections to permit normal downflow processing, backwashing for cleaning, and elution of accumulated organic material with brine. A typical test setup is shown in Figure A plot of organic removal by a packed column of resin, regenerated with brine,