Page 279 - Materials Chemistry, Second Edition

262 Practical Design Calculations for Groundwater and Soil Remediation

Assuming an isentropic efficiency of 80%, the actual horsepower
required is determined by using Equation (6.36) as:
0.31
= hp theoretical = = 0.4 hp
hp actual
E 80%
Discussion:
The energy necessary for an isentropic compression is generally greater
than that for an equivalent isothermal compression. However, the
difference between the inlet and final discharge pressures in most
air-sparging applications is relatively small. Consequently, the theo-
retical power requirements for the isothermal and isentropic com-
pressions should be very similar, as illustrated in this example.

6.8 Biosparging
Biosparging is an in situ remediation technology for aquifers impacted by
biodegradable organics. It enhances the biological activities of indigenous
microorganisms to biodegrade organic constituents in the saturated zone by
injecting air (or pure oxygen) and nutrients, if needed, into the plume. In
addition, to reduce concentrations of COCs in the aquifer, biosparging may
also reduce those in the capillary zone.
The biosparging process is similar to the air-sparging process. However,
the COC removal mechanism of air sparging is mainly volatilization, while
that of biosparging is enhancement of in situ biodegradation. In general,
some degree of volatilization and biodegradation occurs when either air
sparging or biosparging is used. Biosparging can be more effective on semi-
volatile compounds than air sparging. The air injection rate for biosparging
is typically smaller than that of air sparging, and the air can be injected on
an intermittent basis, just to support the biological activities. However, when
volatile constituents are present, biosparging often needs to be combined
with soil-vapor extraction or bioventing for concern of fugitive emission.
Design calculations for biosparging are essentially the same as those for air
sparging. Please refer to the discussion and examples presented in Section 6.7.

6.9 Metal Removal by Chemical Precipitation

Elevated heavy metal concentrations may occur in extracted groundwater
or in wastewater streams. Chemical precipitation is one of the common
methods to remove inorganic heavy metals from groundwater or waste-
water. The hydroxides of heavy metals are formed at high pH and are