Page 216 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 199

500 ppmV and 5%, respectively. Estimate the percentages of diesel removal
by volatilization and by biodegradation from this bioventing process.

Strategy:
Same as gasoline, diesel is a mixture of hydrocarbons. Diesel is heavier
than gasoline, and the boiling points of diesel compounds range
from 200°C to 338°C, compared to 40°C to 205°C for gasoline [7].
Diesel is mainly composed of C –C hydrocarbons. In this example,
15
10
dodecane (C H ) is used to represent diesel, and it has a molecular
12
26
weight of 170, which is heavier than that of gasoline (100) used ear-
lier in this book.
Carbon dioxide is the dominant greenhouse gas of concern. Even the
ambient CO concentration has been increasing; it is still slightly less
2
than 400 ppmV. This background concentration is much smaller than
5% in the extracted air, so it is excluded in the following calculation.
Solution:
(a) MW of diesel [C H ] = (12)(12) + (1)(26) = 170 g/mole
12
26
At T = 20°C and P = 1 atm,
1 ppmV of diesel = (MW of diesel/24.05) mg/m 3
= (170/24.05) mg/m = 7.069 mg/m 3
3
500 ppmV of diesel = (500 ppmV)[7.069 (mg/m )/ppmV]
3
= (500)(7.069) = 3,534 mg/m 3

(b) MW of CO = (12)(1) + (16)(2) = 44 g/mole
2
At T = 20°C and P = 1 atm,

1 ppmV of CO = (MW of CO /24.05) mg/m 3
2
2
= (44/24.05) mg/m = 1.830 mg/m 3
3
5% = 50,000 ppmV of CO
2
= (50,000 ppmV)[1.830 (mg/m )/ppmV]
3
= (500)(1.830) = 91,500 mg/m 3
(c) The stoichiometric amount of CO produced from biodegrada-
2
tion of diesel can be found from:
C H + 18.5O → 12CO + 13H O
2
2
2
26
12
Every mole of C H biodegraded will produce 12 moles of CO .
26
12
2
In other words, every gram of CO comes from biodegrada-
2
tion of 0.322 g of diesel [= 170 ÷ (12)(44)].