Biotechnological Aspects of Soil Decontamination - Biotechnologies and Biomimetics for Civil Engineering - page 380

remove heavy metals from an oil contaminated soil (Mulligan et al. 1999a ). The
first two agents are produced by bacteria, while the last is produced by yeast.
Biosurfactants are also able to remove metals from the sediments. Caustic sur-
factant could be used for removing the organically associated metals, while foam
surfactant can be employed for extracting metals bound to carbonates and oxides
(Dermont et al. 2008 ; Wang and Catherine 2004 ). Since these agents are biode-
gradable, they are able to enhance hydrocarbon removal, and can potentially be
produced in situ, as they have a great potential for soil washing and soil flushing.
This technology yet needs to be performed on commercial scale.
17.4.5 Bioventing
This technique can be applied in situ with a source of oxygen necessary to initiate
the processes. It injects air into the contaminated media necessary to run the
process at a rate designed to maximize in situ biodegradation. It eliminates the off-
gassing of volatilized contaminants to the atmosphere (Khan et al. 2004 ). The
simulation of decontamination of several organic pollutants including variety of
petroleum refinery products by bioventing was performed by Sui et al. ( 2007 ).
Unlike biosparging, which involves pumping air and nutrients into the saturated
zone, bioventing pumps the air only into the unsaturated or vadose zone (USEPA
1998 ). Bioventing also degrades less volatile organic contaminants and, because a
reduced volume of air is required, it allows for the treatment of less permeable
soils. During the application of bioventing in volatile solute transportation in soils,
volatilization has an important role in the first day followed by biodegradation
after this period (Suko et al. 2006 ). Baker and Moore ( 2000 ) have reported the
optimized performance and effectiveness of in situ bioventing. Diele et al. ( 2002 )
have discussed numerical models and their applications in bioventing system
design and operation. Any aerobic degradable substance can be treated by bio-
venting and ultimately leading to biodegradation. Bioventing is most successful on
mid-weight petroleum products like diesel since lighter products tend to volatilize
quickly, while the heavier products generally take longer time to biodegrade. If the
contaminant has to be cleaned to a level lower than 0.1 ppm or if total petroleum
hydrocarbon (TPH) has to be reduced to greater than 95 %, bioventing at that site
may not be effective, and some other method may be needed for this saturated zone
(USEPA 1998 ).
17.4.6 Phytoremediation
In the past few years, green plants have shown several response patterns to the
presence of potentially toxic concentrations of heavy metal ions. Most are sensi-
tive even to very low concentrations; others have developed resistance and