Page 270 - Materials Chemistry, Second Edition

Groundwater Remediation 253

(d) Use the 3.08 ratio to determine the oxygen requirements for com-
plete oxidation of gasoline present (see Section 5.4.4 for details):
Oxygen requirement = (3.08)(225) = 693 g >> 1.08 g
As demonstrated, the oxygen contained in the groundwater of
the aquifer is negligible, when compared to the amount of
oxygen required for complete aerobic biodegradation of the
gasoline present.
(e) If the groundwater is brought to the surface and aerated with air,
the saturated dissolved-oxygen concentration in water at 20°C
is approximately 9 mg/L. When this groundwater is recharged
back to the impacted zone, the maximum amount of additional
oxygen added to the groundwater per m of the aquifer can be
3
found as:
The amount of oxygen added by water saturated with air =
(V)(DO )
sat
l
= (350 L)(9 mg/L) = 3,150 mg = 3.15 g
Amount of oxygen-enriched water needed to meet the oxygen
demand (expressed as the number of pore volumes of the
plume) = (693/3.15) = 247

Discussion:
1. As shown in part (e), the plume has to be flushed at least 247
times with air-saturated water to meet the oxygen requirement.
2. If the extracted water is aerated with pure oxygen, the saturated
DO will be approximately five times higher and the required
flushing will be five times less.
3. Fraction of gasoline in the dissolved phase
= (mass of gasoline dissolved)/(total gasoline in the aquifer)
= (7)/(225) = 3.1%
This shows that gasoline dissolved in the groundwater only
accounts for a small portion of its total mass in the aquifer.

Example 6.15: Determine the Effectiveness of Hydrogen Peroxide
Addition as an Oxygen Source for Bioremediation

As illustrated in Example 6.14, it would take a tremendous amount of
water, whether it is saturated with air or pure oxygen, to meet the oxygen
demand for in situ groundwater bioremediation. Addition of hydrogen
peroxide becomes a popular alternative. Because of the biocidal potential
of hydrogen peroxide, the maximum hydrogen peroxide in the injected
water is often kept below 1,000 mg/L for in situ bioremediation applica-
tions. Determine the amount of oxygen that 1,000 mg/L of hydrogen per-
oxide can provide.