Enhancement of Remediation Technologies with Biosurfactants - Biosurfactants: Research Trends and Applications - page 233

soluble components; (3) chemical treatments for oxidation or detoxification; and
(4) stabilization/solidification with cements, limes, and resins for heavy metal con-
taminants. Phytoremediation, although less developed, has also been used. The most
suitable types of plants must be selected based on pollutant type and recovery tech-
niques for disposal of the contaminated plants.
Most in situ remediation techniques are potentially less expensive and dis-
ruptive than ex situ ones, particularly for large contaminated areas. Natural or
synthetic additives can be utilized to enhance precipitation, ion exchange, sorp-
tion, and redox reactions (Mench et al., 2000). The sustainability of reducing
and maintaining reduced solubility conditions is key to the long-term success of
the treatment. Ex situ techniques are expensive and can disrupt the ecosystem
and the landscape. For shallow contamination, remediation costs, worker expo-
sure, and environmental disruption can be reduced by using in situ remediation
techniques. In this chapter, the addition and effectiveness of various biological
surface agents used to enhance bioremediation, in situ flushing, and soil-washing
processes for soil and sediment remediation will be examined. The main focus
will be on biologically produced surfactants due to their biodegradability, low
toxicity, and effectiveness.
Soil remediation can be performed with or without excavation via soil washing
or in situ flushing (Mulligan et al., 2001a). Solubilization of the contaminants can
be performed with water alone or with additives. The solubility of the contaminant
is thus a key factor. Contaminants such as trichloroethylene (TCE), polycyclic aro-
matic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) are of very low
solubility. Effective bioremediation of organic contaminants leads to complete min-
eralization of the contaminants. Often the process is enhanced by the addition of
nutrients, electron acceptors, or bioaugmentation (addition of bacteria) (Yong and
Mulligan, 2004). Inorganic contaminants such as metals and radionuclides are com-
monly found with the organic contaminants, further complicating the bioremedia-
tion process. The inorganic contaminants may be toxic to the bacteria, cannot be
biodegraded, but may be converted from one form to another.
ENVIRONMENTAL TECHNOLOGIES
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To remove nonaqueous phase liquids (NAPLs) from the groundwater, extraction
of the groundwater can be performed by pumping to remove the contaminants in
the dissolved and/or free-phase NAPL zone. However, substantial periods of time
can be required and effectiveness can be limited. Drinking water standards of the
extracted water can be achieved after treatment with activated carbon, ion exchange,
membranes, and other methods. Extraction solutions can be introduced into the soil
using surface flooding, sprinklers, leach fields, and horizontal or vertical drains to
enhance the removal rates of the contaminants. Water with surfactants or solvents or
without additives is employed to solubilize and extract the contaminants as shown
in Figure 10.2 in soil flushing. These additives include organic or inorganic acids or
bases, water-soluble solvents, complexing or chelating agents, and surfactants.