Page 253 - Materials Chemistry, Second Edition

236 Practical Design Calculations for Groundwater and Soil Remediation

Discussion:
1. The bulk density of activated carbon is typically in the neighbor-
hood of 30 lb/ft . The amount of activated carbon in a 55-gallon
3
drum is approximately 160 lb.
2. The adsorption capacity of 0.01 kg/kg is equal to 0.01 lb/lb or
0.01 g/g.
3. Care should be taken to use matching units for C and q in the
isotherm equations.
4. The influent aqueous COC concentration, not the effluent concen-
tration, should be used in the isotherms to estimate the adsorption
capacity.

6.3.3 Design of an Activated-Carbon Adsorption System
6.3.3.1 Empty-Bed Contact Time
To size the liquid-phase activated-carbon system, the common criterion used
in design is the empty-bed contact time (EBCT). The typical EBCT ranges
from 5 to 20 min, mainly depending on the characteristics of the COCs. Some
compounds have a stronger tendency to adsorption, and the required EBCT
would be shorter. Taking PCBs (polychlorinated biphenyls) and acetone as
two extreme examples, PCBs are very hydrophobic and will strongly adsorb
to the activated-carbon surface, while acetone is very soluble in water and
not readily adsorbable. The required EBCT for acetone would be much lon-
ger than that for PCBs.
If the liquid flow rate (Q) is specified, the EBCT can be used to determine
the required volume of the activated-carbon adsorber (V activated carbon ) as:

= Q EBCT()( ) (6.10)
V activatedcarbon
6.3.3.2 Cross-Sectional Area
The typical hydraulic loading rate to carbon adsorbers is set to be ≤5 gpm/ft .
2
This parameter can be used to determine the minimum required cross-sectional
area of the adsorber (A activated carbon ):

Q
=
A activatedcarbon (6.11)
surfaceloading rate
6.3.3.3 Height of the Activated-Carbon Adsorber
The required height of the activated-carbon adsorber (H activated carbon ) can then
be determined as:

= V activatedcarbon (6.12)
H activatedcarbon
A activatedcarbon