4.4.3 Bioventing and Biosparging
Bioventing is a form of biostimulation in which gaseous stimulants, such as air, oxygen, or
methane are added to vadose zone soils, generally by pumping them into wells in the soil.
Biosparging essentially is bioventing in the saturated zone. Biosparging can be used to add
biostimulants, improve aeration, and promote aerobic conditions in the overlying unsaturated
soil. Both of these approaches involve equipment and operations costs.
4.4.4 Biobarriers
Biobarriers are permeable "walls" formed by placing biologically active material in a trench in
the flow-path of shallow groundwater. Conditions in the permeable barrier enhance the
degradation of contaminants. Biobarriers have been created by placing readily oxidized organics
in the trench so that the conditions are sufficiently reduced to degrade halogenated compounds in
shallow groundwater.
4.4.5 Approaches that Require Excavation of Soil
Landfarming is the spreading and mixing of contaminants, contaminated soils, or wastes into a
surface, such as non-contaminated soil. The area is underlain with a barrier of some sort, such as
a natural or constructed clay layer, to prevent leachates from contaminating the groundwater.
The soil is plowed or disked to provide mixing, aeration, and moisture. If the concentration of
the contaminant is too high for easy biodegradation, plowing or disking also helps reduce its
concentration. Finally, if coupled with biostimulation or bioaugmentation, plowing or disking
gives a more uniform distribution of fertilizer and microbial inoculant, respectively.
Composting is the use of aerobic, thermophilic microorganisms in constructed piles of soils with
a bulking agent into windrows to degrade contaminants. The piles are physically mixed and
moistened periodically to promote microbial activity and enzyme-contaminant contact.
Pile bioventing relies on air injected into stockpiled soils to stimulate aerobic degradation. It can
be considered a combination of landfarming and composting. It takes less space than
landfarming, and pumping air into the pile supports aerobic growth without physical mixing.
Bioreactors are large tanks or vessels that can hold excavated contaminated soil, water,
nutrients, substrates and, if necessary, microorganisms. Conditions can be controlled and
optimized in bioreactors, but the volumes that can be contained are relatively small.
5. Cost Assessment
5.1 Cost Reporting
Table 4 lists costs for rhizosphere-enhanced remediation as implemented in this demonstration.
Section 5.3 compares these costs to some alternative conventional treatments.
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