Page 264 - Materials Chemistry, Second Edition

Groundwater Remediation 247

(e) Use Equation (6.24) to determine the NTU value:

 S    C in   S 1 1 
− 
NTU =   ln    +  (for G in = 0)

 S −  1   C out   S   S 
 3    50   31 1 
− 
=   ln       +  = 9.75
− 
 31   0.05  3  3 
(f) Use Equation (6.22) to determine the packing height:

Z = (HTU) × (NTU) = (3.77 ft)(9.75) = 36.8 ft
Discussion:
1. The typical hydraulic loading rate, 20 gpm/ft , is much higher than
2
that for the activated-carbon adsorbers, 5 gpm/ft .
2
2. The required packing height of 36.8 ft will make the total
height of the air stripper well over 40 feet. This may not be
acceptable in most project locations. If this is the case, one may
consider having two shorter air strippers in series.

6.5 Ex Situ Biological Treatment
6.5.1 Description of the Ex Situ Biological Treatment Process

Biological processes can be used to remove biodegradable organic com-
pounds from water. With regard to groundwater remediation, the impacted
groundwater can be treated biologically in the in situ or the ex situ mode.
This section covers the ex situ biological treatment, while the in situ bio-
remediation of the impacted aquifer will be covered in the next section.
Aboveground biological reactors can be employed to remove organic COCs
from the extracted groundwater. In general, the bioreactors for removal of
dissolved organics from water/wastewater can be classified into two groups:
suspended growth and attached growth. The most common type of sus-
pended growth is the activated-sludge process, while that for the attached
growth is the trickling-filter process.
Biological systems used in groundwater remediation are usually much
smaller in scale compared to those in municipal or industrial wastewater
treatment plants. The trickling filters consist of packing materials to support
the bacterial growth. Since the biological process is relatively complicated
and affected by many factors, a feasibility study as well as bench- and/or
pilot-scale testing are recommended before the process is seriously consid-
ered as a viable remedial alternative.