## Active Or Exchange Zone

Figure 16.2 is the same figure illustrated in a previous chapter under carbon adsorption. The length of the active zone was derived in that chapter and is reproduced next.

where 8 Vx

Vn+1 Vn

A, length of active zone total volume of water or wastewater treated at complete exhaustion of bed

= volume treated at breakthrough

= influent concentration to 8 total volume treated at time tn+1 total volume treated at time tn concentration of solute at effluent of 8 at time tn+1 concentration of solute at effluent of 8 at time tn surficial area of exchanger bed FIGURE 16.2 Active zones at various times during adsorption and the breakthrough curve.

pp = pack density of ion exchange material

(X/M )ult = ultimate exchange capacity of the bed or simply, the exchange capacity of the bed.

It should be emphasized that to use the equation [Co], [Cn+j], and [Cn] should be the total concentration of ions. For example, if the influent is composed of the ions Ca2+ = 50 mg/L, Mg2+= 60 mg/L, and Zn2+= 2 mg/L, then [Co]meq in meq/L is 50/(Ca /2) + 60/(Mg/2) + 2/(Zn/2).

Example 16.2 A breakthrough experiment is conducted for a wastewater producing the results below. Determine the length S of the active zone. The diameter of the column used is 2.5 cm, and the packed density of the bed is 750 kg/m . [Co] is equal to 2.2 meq/L. (X/M)ult = 6.5 meq/g.

 C, meq/L V, L 