Page 275 - Materials Chemistry, Second Edition
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258 Practical Design Calculations for Groundwater and Soil Remediation
2. Despite the relatively low oxygen-transfer efficiency in this exa-
mple, the air sparging still adds a significant amount of oxygen
to the aquifer. With regard to oxygen addition, an air injection
rate of 5 ft /min with an oxygen-transfer efficiency of 10% is
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equivalent to reinjection of air-saturated water at 116.6 gpm.
6.7.3 Injection Pressure of Air Sparging
Injection pressure is an important component for design of an air-sparging
system. The applied air injection pressure should overcome at least (1) the
hydrostatic pressure corresponding to the water-column height above the
injection point and (2) the air-entry pressure, which is equivalent to the cap-
illary pressure necessary to induce air into the saturated media.
P injection = P hydrostatic + P capillary (6.31)
Reported values of injection pressures range from 1 to 8 psig [5].
The following procedure can be used to determine the minimum air injec-
tion pressure:
Step 1: Determine the water-column height above the injection point.
Convert the water-column height to pressure units by using the
following formula:
P hydrostatic =ρg h hydrostatic (6.32)
where ρ is the mass density of water and g is the gravitational
constant (32.2 ft/s ).
2
Step 2: Use Table 2.2 to estimate pore radius of the aquifer media and
then use Equation (2.11) to determine height of capillary rise (or
obtain the capillary height from Table 2.2 directly). Convert the
capillary height to the capillary pressure by using the follow-
ing formula:
P capillary =ρg h capillary (6.33)
Step 3: The minimum air injection pressure is the sum of these two pres-
sure components (P hydrostatic + P capillary ) as stated in Equation (6.31).
Information needed for this calculation:
• Depth of the injection point, h hydrostatic
• Mass density of water, ρ
• Geology of the aquifer material or the pore size of the matrix