Page 78 - Materials Chemistry, Second Edition

Site Assessment and Remedial Investigation 61

Determine:
(a) The concentration of benzene adsorbed onto the suspended sol-
ids, and
(b) The percentage of total benzene mass in the dissolved phase of
the unfiltered wastewater.

Solution:
(a) Use Equation (2.26) to find K :
p
K = f K oc
p
oc
= (1%)(85) = 0.85 mL/g = 0.85 L/kg
Use Equation (2.25) to find S:
S = K C
p
= (0.85 L/kg)(5 mg/L) = 4.25 mg/kg
(b) Basis: 1-L solution
Mass of benzene in the liquid phase
= (C)[(volume of the solution)] = (5)(1) = 5 mg
Mass of benzene adsorbed on the solid
= (S)[(Volume of the solution)(suspended solid concentration)]
= (4.15 mg/kg)[(1 L)(5,000 mg/L)(1 kg/1,000,000 mg]
= 2.125 × 10 mg
−2
Total mass of benzene
= mass in the liquid + mass on the solid
= 5 + (2.125 × 10 ) = 5.021 mg
−2
Percentage of total benzene mass in the aqueous phase
= 5/(5.0215) = 99.6%

Discussion:
Almost all of the benzene, 99.6%, is in the dissolved phase because only
a small amount of solids is present, the organic content of the sus-
pended solids is low, and benzene is not very hydrophobic.

Example 2.37: Mass Partition between Vapor, Liquid, and Solid Phases

The vapor concentrations of benzene and pyrene in the void space of the
vadose zone underneath a landfill are 100 ppmV and 10 ppbV, respectively.
The total porosity of the vadose zone is 40%, and 30% of the porosity is occu-
pied by water. The (dry) bulk density of the soil is 1.6 g/cm , and the total
3
bulk density is 1.8 g/cm . Assuming no free product is present, determine
3
the mass fractions of each COC in the three phases (i.e., void, moisture, and