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ACTIVATED CARBON PROCESSES 14.11

Design Flow Rate and System Hydraulics. GAC contractor design is similar to the de-
sign for conventional gravity dual-media filtration. Hydraulically, the design must ac-
commodate the maximum flow of the plant. GAC volume is determined based on design
flow for the GAC facilities and the EBCT established for the flow. Because flow rates
and organic concentrations often vary seasonally, careful analysis is needed to prevent
undersizing or oversizing the contactors.
Types and Amounts of Organic Compounds to Be Removed. Both the type and the
amount of organic compounds to be removed strongly affect the type and level of pre-
treatment prior to GAC adsorption, as well as the rate of adsorption of the contaminant
molecules.
Type of GAC. GAC particles are similar in size to filter media, typically ranging be-
tween 1.2 and 1.6 mm in diameter. General properties of typical types of GAC produced
in the United States are presented in Table 14.3. Some commonly manufactured mesh
sizes available for GAC and their associated size ranges appear in Table 14.4.

Breakthrough and EBCT. Primary factors the designer must consider in determining
the volume required for a GAC adsorber or contactor are breakthrough and EBCT.
Breakthrough. Breakthrough can be defined as the point at which the concentration
of a contaminant in the effluent adsorption unit exceeds the treatment requirement. Total
organic carbon (TOC) is often used as the performance standard defining GAC exhaus-

TABLE 14.3 Properties of Granular Activated Carbon Produced in the United States*
The
Carborundum Calgon Witco
Company Corporation NICIT Chemical
Product name GAC 40 Fitrasorb Hydrodarco Hydrodarco Witcarb
HD-1030 83 Plus 950
Base material Western Bituminous Lignite Bituminous Petroleum
bituminous coal coal coke
coal
U.S. standard sieve 12 × 40 12 X 40 10 × 30 8 X 30 12 X 40
size
Effective size, mm 0.6 0.8 to 0.9 0.8 to 0.9 0.8 to 0.9 0.8 to 0.9
Uniformity coefficient -<1.9 -<1.9 -<1.7 -<1.9 --<1.7
Apparent (or vibrating 0.47 0.4 to 0.5 0.40 to 0.50 0.47 0.46 to 0.53
feed) density, g/cm 3
Washed density, lb/ft 3 25 25 23.5 26 29 to 33
Iodine number, mg/g 1,050 1,050 600 900 1,050
Surface area, m2/g 1,000 to 1,100 1,050 650 1,000 1,000
Available in: 60-1b bags, 60-1b bags, 40-1b bags, 50-1b bags, 50-1b bags,
bulk bulk bulk bulk 200-1b drums,
hopper trucks,
tote bins
*A WWA Standard for Granular Activated Carbon [AWWA B604-74, Journal A WWA 66(11):672, 1974] pro-
vides minimum specifications on the properties of granular activated carbon used as an adsorption medium for
treating drinking water.