Page 266 - Materials Chemistry, Second Edition

Groundwater Remediation 249

Information needed for this calculation:

• Rate constant, k
• Influent COC concentration, C in
• Effluent COC concentration, C out
• Design liquid flow rate, Q

Example 6.13: Sizing an Aboveground Bioreactor for
Groundwater Remediation
A packed-bed bioreactor is designed to reduce the toluene concentration
in the extracted groundwater from 4 to 0.1 mg/L (100 ppb). The packing
depth has been selected to be 3 ft. Determine the required diameter of the
bioreactor.
Use the following information in calculations:

• Rate constant = 0.9 (gpm) /ft at 20°C (for 2-ft packing depth)
0.5
• Temperature of the water = 20°C
• Groundwater extraction rate = 20 gpm

Solution:
(a) Use Equation (6.27) to adjust the rate constant:

2
 D 1  0.3   0.3 0.5
k 2 = k 1    = (0.9)   = 0.80(gpm)/ft
 
 D 2 3
(b) Use Equation (6.25) to determine the surface loading rate, Q/A:

0.1
C out −0.5 −0.5
QA)
= exp[ −kD QA(/ ) ] = = exp[ −(0.80)(3)(/ ]
C in 4
Q/A = 0.423 gpm/ft 2
(c) Use Equation (6.26) to determine the required cross-sectional
area:

Q 20 gpm
= = = 47.2 ft 2
A bioreactor 2
surfaceloading rate 0.423 gpm/ft
Diameter of the bioreactor packing = (4 × A/π) 1/2
= (4 × 47.2/π) = 7.76 ft
1/2
So, d = 8 ft