Page 273 - Materials Chemistry, Second Edition

256 Practical Design Calculations for Groundwater and Soil Remediation

(f) The total nutrient requirement = 104 + 60 = 164 g/m of aquifer
3
Void space of the aquifer = V × ϕ
= (1 m )(35%) = 0.35 m = 350 L
3
3
Total volume of water that is equivalent to 100 pore volumes =
(100)(350) = 35,000 L
The minimum required nutrient concentration = 164 g ÷ 35,000 L
= 4.7 × 10 g/L ≈ 0.0005% by wt.
−3
Discussion:
The concentration, 0.0005% by wt., is the theoretical amount. In real
applications, one may want to add more to compensate the loss due
to adsorption to the aquifer material before reaching the plume.
This will make the nutrient concentration fall in the typical range of
0.005% to 0.02% by weight.

6.7 Air Sparging

6.7.1 Description of the Air-Sparging Process
Air sparging is an in situ remediation technology that involves the injection
of air (sometimes pure oxygen) into the saturated zone. The injected air trav-
els through the aquifer, moves upward through the capillary fringe and the
vadose zone, and is then collected by the vadose-zone soil-venting network.
The injected air (or oxygen) serves the following functions: (1) volatilizes
the dissolved VOCs in the groundwater, (2) supplies oxygen to the aquifer
for bioremediation, (3) volatilizes the VOCs in the capillary zone as it moves
upward, and (4) volatilizes the VOCs in the vadose zone.

6.7.2 Oxygen Addition from Air Sparging

As illustrated in the previous sections, the amount of oxygen carried back
to the aquifer by the water, which has been saturated with air or pure oxy-
gen, cannot meet the oxygen demand for in situ bioremediation. An air-sparg-
ing process continuously brings air (or oxygen) directly into the plume.
Consequently, supplying oxygen to the plume to support aerobic biodegrada-
tion is one of the main functions of air sparging. Oxygen-transfer efficiency
(E) is often used to evaluate the efficacy of aeration, and it is defined as:

rate of oxygendissolution
oxygen-transfer efficiency E () = (6.30)
rate of oxygenapplied