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14.4 CHAPTER FOURTEEN

The uniformity coefficient is a ratio of the size opening that will pass 60% of a rep-
resentative sample of the filter material to the size opening that will pass just 10% of the
same sample. The maximum uniformity coefficient recommended by AWWA is 2.1 af-
ter backwashing and draining a GAC filter. If two types of GAC media have the same
effective size, the one with a larger uniformity coefficient (that is, 1.7 to 2.4) will have a
greater number of fines in the upper layers of a stratified bed and larger particles in the
lower layers. Typical uniformity coefficients for GAC produced in the United States are
less than or equal to 1.9.

Manufacture of Activated Carbon
Activated carbon is made from organic materials having a high carbon content. A wood
product such as sawdust, coconut shells, or wood may be used, or a coal product such as
bituminous coal, lignite, or peat is converted to activated carbon by heating the material
to between 300 ° and 1,000 ° C. The resulting carbon material provides large surface ar-
eas and, accordingly, a large number of adsorption sites.

DESIGN OF POWDERED ACTIVA TED
CARBON FACILITIES

PAC is used by surface water treatment plants either full-time or as needed for taste and
odor control or removal of organic chemicals.

Characteristics of PAC
The apparent density of PAC ranges from 23 to 46 lb/ft 3 (0.36 to 0.74 g/cm 3) depending on
the type of material and the manufacturing process. Iodine and molasses numbers are often
used to characterize PAC. Information needed to evaluate different PACs is shown in Table
14.1, which summarizes the manufacturers' specifications for some commercially available
PACs. In general, the following criteria should be used to evaluate different PACs:

TABLE 14.1 Manufacturers' Specifications of Some Commercially Available PACs
Parameter PAC I a PAC 2 b PAC 3 c PAC 4 d PAC 5 e PAC 6 f
Iodine number, mg/g 800 1,199 600 900 1,000 550
Molasses decolorizing index 9 -- -- 14 18 --
Moisture as packed, % 5 3 5 10 10 4
Apparent density, g/cm 3 0.64 0.54 0.74 0.38 0.38 0.50
Ash content, % -- 6 -- 3 to 5 3 to 5 --
Passing 100 mesh, % 99 -- 99 95 to 100 95 to 100 99
Passing 200 mesh, % 97 -- 97 85 to 95 85 to 95 95
Passing 325 mesh, % 90 98 90 65 to 85 65 to 85 90
aAqua-Nuchar, Westvaco, Covington, W.Va.
bWPH, Calgon Corp., Pittsburgh, Pa.
CAqua, Westvaco, Covington, W.Va.
dNuchar S-A, Westvaco, Covington. W.Va.
eNuchar SA-20, Westvaco, Covington, W.Va.
fHydrodarco B, American Noril, Jacksonville, Fla.
Source: Adapted from I. N. Najm et al., 1991.