Civil Engineering Reference
In-Depth Information
1.0
Breakthrough
Threshold
Flow Processed, gal
Fig. 17-5.
Typical breakthrough curve
through, showing the breakthrough curve in effluent concentration (see Fig. 17-5). The
bed is exhausted when the effluent concentration reaches the target treated water con-
centration.
For some limited applications, two GAC contactors may be designed to operate in
series in order to use the full adsorptive capacity of the respective beds (see Fig.
17-6). Contactor 1 continues to serve as lead unit until it reaches capacity (complete
breakthrough). At this point contactor 2, the lag contactor, serves as the polishing unit.
Contactor 1 is taken off-line and regenerated while contactor 2 becomes the new lead
unit. Once regenerated, contactor 1 becomes the new lag or polishing unit. By switch-
ing the lead and lag function, both GAC units can operate until reaching capacity.
The contactor depth is determined by the shape of the breakthrough curve, since
it determines the ability to operate the bed until full capacity is reached (see Fig.
17-7). A sharp curve (for which breakthrough appears rapidly) means that a relatively
Flow In
Saturated GAC in
Equilibrium with Feed
Polishing Continues
Contactor 1
Contactor 2
Transfer Zone
Flow Out
Polishing in Breakthrough
Curve or Transfer Zone
Fig. 17-6.
Series operation of GAC contactors
