Page 293 - Materials Chemistry, Second Edition

276 Practical Design Calculations for Groundwater and Soil Remediation

or

MW
°
3
1ppmV = × 10 −6 [lb/ft ]at32F
359
MW
= × 10 −6 [lb/f] at 68 °F
3
t
385 (7.8)
MW
= × 10 −6 [lb/ft ]at77F
°
3
392
where MW is the molecular weight of the compound.
Example 7.3: Determine the Mass Removal Rate
by the GAC Adsorbers
Referring to the remediation project described in Example 7.2, the discharge
limit for xylene is 100 ppbV. Determine the mass removal rate by the two
55-gal GAC units.

Solution:
(a) Use Equation (7.8) to convert the ppmV concentration to lb/ft :
3
Molecular weight of xylene (C H (CH ) ) = 12 × 8 + 1 × 10 = 106
3 2
4
6
106
×
−6
°
1ppmV = × 10 −6 = 0.27 10 lb/ft 3 at77F
392
800 ppmV = (800)(0.27 × 10 ) = 2.16 × 10 lb/ft 3
−6
−4
(b) Use Equation (7.6) to determine the mass removal rate:
3
3
×
−4
R removal ≈ (G in )Q = (2.16 10 lb/ft)(200 ft /min)
= 0.65 lb/min = 93 lb/day

7.2.6 Change-Out (or Regeneration) Frequency
Once the activated carbon reaches its capacity, it should be regenerated or
disposed of. The time interval between two regenerations or the expected
service life of a fresh batch of GAC can be found by dividing the capacity of
GAC with the COC removal rate (R removal ) as:

T = M removal (7.9)
R removal