Page 272 - Materials Chemistry, Second Edition

Groundwater Remediation 255

Assuming no nutrients are available in the groundwater for bioremedia-
tion and the optimal molar C:N:P ratio has been determined to be 100:10:1,
determine the amount of nutrients needed to support the biodegradation of
gasoline. If the plume is to be flushed with 100 pore volumes of oxygen- and
nutrient-enriched water, what would be the required nutrient concentration
in the water for reinjection?

Solution:
Basis: 1 m of aquifer
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(a) From Example 6.14, the total mass of gasoline in the aquifer =
225 g/m 3

(b) Assume that the gasoline has a formula the same as heptane,
C H :
16
7
MW of gasoline = 7 × 12 + 1 × 16 = 100
Moles of gasoline = 225/100 = 2.25 g-mole
(c) Determine the number of moles of C:
Since there are 7 carbon atoms in each gasoline molecule, as indi-
cated by its formula, C H , then:
7
16
Moles of C = (2.25)(7) = 15.8 g-mole
(d) Determine the number of moles of N needed (using the C:N:P
ratio of 100:10:1):
Moles of N needed = (10/100)(15.8) = 1.58 g-mole
Amount of nitrogen needed = 1.58 × 14 = 22.1 g/m of aquifer
3
Moles of (NH ) SO needed = 1.58 ÷ 2
4
4 2
= 0.79 g-mole (each mole of ammonium sulfate contains two
moles of N)
Amount of (NH ) SO needed = (0.79)[(14+4)(2) + 32 + (16)(4)]
4
4 2
= 104 g/m of aquifer
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(e) Determine the number of moles of P needed (using the C:N:P
ratio of 100:10:1):
Moles of P needed = (1/100)(15.8) = 0.158 g-mole
Moles of Na PO ⋅12H O needed = 0.158 g-mole
4
3
2
Amount of phosphorus needed = 0.158 × 31 = 4.9 g/m of aquifer
3
Amount of Na PO ⋅12H O needed
2
4
3
= (0.158)[(23)(3) + 31 + (16)(4)+ (12)(18)]
= 60 g/m of aquifer
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