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14.10 CHAPTER FOURTEEN

/ i i~iiii~!~i~ii! ~i!iiii!i ~iii ~ ~iii~iii ~iii!!i!ii ~ t Flocculation/ Flocculation/
Settling Settling

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Flocculatlon/
Settling Filters

1
Filters
Filters
~

Prefiltration
Postfiltration Filtration/
Adsorption
FIGURE 14.2 Basic options for locating GAC treatment.

Under certain plant configurations and site-specific conditions, prefiltration adsorption
may be feasible. However, this option has limited applications and benefits and therefore
is not discussed further in this chapter.
The more conventional option for most applications is postfiltration adsorption in which
the water receives complete treatment before GAC application. In this option, the
highest-quality water is applied to the GAC system, the only objective being to remove
dissolved organic compounds. As a result, the carbon usage rate is minimized, as is the
frequency of regeneration, providing for an efficient GAC design.

General Considerations
General design considerations in assessing the feasibility of GAC for a specific applica-
tion include

• Design flow rate and system hydraulics
• Types and amounts of organics to be removed
• Type of GAC
• Breakthrough and empty bed contact time (EBCT)
• Adsorber volume and bed depth
• Surface loading rate
• Backwashing requirements
• Carbon usage rate
• Type of contactor units
• Gravity or pressure units