Page 254 - Materials Chemistry, Second Edition
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Groundwater Remediation 237
6.3.3.4 COC Removal Rate by the Activated-Carbon Adsorber
The removal rate by an activated-carbon adsorber (R removal ) can be calculated
by using the following formula:
= C( ) Q (6.13)
R removal in − C out
In practical applications, the effluent concentration (C ) is kept below the
out
discharge limit, which is often very low. Therefore, for a factor of safety, the
term of C can be deleted from Equation (6.13) in design. The mass removal
out
rate is then essentially the same as the mass loading rate (R loading ):
R removal ≅ R loading = ( CQ) (6.14)
in
6.3.3.5 Change-Out (or Regeneration) Frequency
Once the activated carbon reaches its capacity, it should be regenerated or
disposed of. The time interval between two consecutive regenerations or the
expected service life of a fresh batch of activated carbon can be estimated by
dividing the capacity of the activated carbon in the adsorber with the COC
removal rate (R removal ) as:
T = M removal (6.15)
R removal
6.3.3.6 Configuration of the Activated-Carbon Adsorbers
If multiple activated-carbon adsorbers are used, the adsorbers are often
arranged in series and/or in parallel. If two adsorbers are arranged in series,
a monitoring point should be located at the effluent of the first adsorber. A
high effluent concentration from the first adsorber indicates that this adsorber
is reaching its capacity. The first adsorber is then taken off-line and the sec-
ond adsorber is shifted to be the first adsorber. Consequently, the capacity of
both adsorbers would be fully utilized, and the compliance requirements are
met. If there are two parallel streams of adsorbers, one stream can always be
taken off-line for regeneration or maintenance, and the continuous operation
of the process will not be interrupted.
The following procedure can be used to complete the design of an acti-
vated-carbon adsorption system:
Step 1: Determine the design adsorption capacity as described previ-
ously (also see Example 6.9).
Step 2: Determine the required volume of the activated-carbon adsorber
by using Equation (6.10).
