Page 262 - Materials Chemistry, Second Edition

Groundwater Remediation 245

and there are also empirical equations available to estimate the value of K a.
L
Values of K a in common air-stripping columns used in groundwater reme-
L
diation range from 0.01 to 0.05 s . HTU has a unit of length and can be deter-
−1
mined as:
HTU = Q L (6.23)
( Ka)
L
where Q is the hydraulic loading rate in length/time.
L
The NTU value can be determined by using the following formula:
*
 S   C ( in −G / H )  S −  1 1 
in
NTU =   ln    + 
*
 S −  1   C ( out −G / H )  S  S  
in
 S    C in   S 1 1 
− 
=   ln      +  (for G in = 0) (6.24)

 S −  1   C out   S S 
where S is the stripping factor, H* is the Henry’s constant in dimensionless
form, C is the COC concentration in liquid, and G is the COC concentration
in air.
The following procedure can be used to size an air-stripping column:

Step 1: Determine the required cross-sectional area of the air stripper
by using Equation (6.21). Then, determine the diameter of the
column corresponding to this calculated area. Round up the
diameter value to the next half or whole foot.
Step 2: Use the newly found diameter to calculate the cross-sectional
area and, then, the hydraulic loading rate. Use Equation (6.23) to
find the HTU value.
Step 3: Determine the stripping factor, if not known or specified, by
using Equation (6.20).
Step 4: Use Equation (6.24) to find the NTU value.
Step 5: Use Equation (6.22) to find the packing height, Z.

Information needed for this calculation:

• Henry’s constant
• Stripping factor, S
• Design hydraulic loading rate
• Design liquid flow rate, Q L
• Overall liquid-phase mass-transfer coefficient, K a
L
• COC concentration in the influent liquid, C in