Page 271 - Materials Chemistry, Second Edition

254 Practical Design Calculations for Groundwater and Soil Remediation

Solution:
(a) From Equation (6.28), 1 mole of hydrogen peroxide can yield a
half mole of oxygen:
H O → H O + 0.5 O 2
2
2
2
Molecular weight of hydrogen peroxide (H O )
2
2
= (1 × 2) + (16 × 2) = 34
Molecular weight of oxygen (O ) = 16 × 2 = 32
2
(b) Molar concentration of 1,000 mg/L hydrogen peroxide
= (1,000 mg/L) ÷ (34,000 mg/mole) = 29.4 × 10 mole/L
−3
Molar concentration of oxygen (assume 100% dissociation of
hydrogen peroxide)
= 29.4 × 10 mole H O /L × (0.5 mole O /mole H O )
−3
2
2
2
2
2
= 14.7 × 10 mole/L
−3
Mass concentration of oxygen in water from hydrogen peroxide
addition
= (14.7 × 10 mole/L) × 32,000 mg/mole = 470 mg/L
−3
6.6.3 Addition of Nutrients to Enhance Biodegradation
Nutrients for microbial activity usually exist in the subsurface. However,
with the presence of organic COCs, additional nutrients are often needed
to support the bioremediation. The nutrients to enhance microbial growth
are assessed primarily on the nitrogen and phosphorus requirements of the
microorganisms. The suggested C:N:P molar ratio is 120:10:1, as shown in
Table 5.2. The nutrients are typically added at concentrations ranging from
0.005% to 0.02% by weight [4].

Example 6.16: Determine the Nutrient Requirement for
In Situ Groundwater Bioremediation
A subsurface is impacted by gasoline. The average dissolved-gasoline con-
centration of the groundwater samples is 20 mg/L. In situ bioremediation
is being considered for aquifer restoration. The aquifer has the following
characteristics:
• Porosity = 0.35
• Organic content = 0.02
• Subsurface temperature = 20°C
• Dry bulk density of aquifer materials = 1.6 g/cm 3