Biomedical Engineering Reference
In-Depth Information
halorespiration also decreases with decreasing chlorine number. It seems reasonable that
bioaugmentation will be most successful for contaminants with similar characteristics, and
there likely will be relatively little competition from any indigenous bacteria.
The following sections review successful field-scale bioaugmentation strategies based
on pollutant type. The sections address the use of bioaugmentation to remediate organic
contaminants, metals and mixed pollutants. The discussion focuses on field studies of bioaug-
mentation to the extent possible, since promising microcosm approaches have not always
proven successful under field conditions.
1.7.1 Petroleum and BTEX
Petroleum products consist primarily of aliphatic hydrocarbons, although they also contain
toxic and carcinogenic aromatic hydrocarbons (notably benzene, toluene, ethylbenzene and
total xylenes, known as BTEX compounds). The major petroleum compounds are not neces-
sarily difficult to biodegrade in most natural environments, and degradation pathways for most
petroleum constituents are well-established. Petroleum contamination is widespread but usually
can be treated biologically through natural attenuation or biostimulation alone, as oxygen and
inorganic nutrients are typically the limiting factors (Swannell and Head,
1994
). However, this
depends on the site parameters, as bioaugmentation also has been shown to accelerate the
bioremediation of diesel pollution (Bento et al.,
2005
). It is often desirable to remediate spills
and leaks quickly and efficiently, so there long has been a perceived need for bioaugmentation
cultures, and there are a variety of commercially-available products to bioremediate oil spills
(Table
1.1
). Like chlorinated solvents, petroleum hydrocarbons and BTEX are among the better
studied pollutants in terms of remediation strategies. The Exxon Valdez spill increased public
awareness of the idea of bioremediation and bioaugmentation, though bioaugmentation at the
spill was not the critical step (Glaser,
1993
). Most sites, even in pristine areas, contain bacteria
ready to degrade petroleum hydrocarbons.
As mentioned earlier (Section
1.2.1
), careful field studies generally have not shown a need
or significant benefit from bioaugmentation for petroleum product removal (Van Hamme
et al.,
2003
). Plant-assisted bioaugmentation might prove more successful, as plants are both
aesthetically more pleasing and are often already present at the interfaces typically present at
petroleum spills (Cohen,
2002
; Juhanson et al.,
2007
). Bioaugmentation and phytoaugmentation
also could be implemented as precautionary measures around areas prone to leaks and spills
(Lendvay et al.,
2003
). Bioaugmentation could be more useful in removing petroleum product
cocontaminants, like BTEX, rather than the petroleum itself (Park et al.,
2008
). Petroleum-
related contamination also can coincide with other petroleum product wastes, like cyanide and
heavy metals. In these cases, metal resistant bacteria might need to be added if the indigenous
community is inhibited by the metals.
1.7.2 Polycyclic Aromatic Hydrocarbons (PAHs)
PAHs are found in wood preservatives, mothballs and some petroleum products. They are
composed of multiple aromatic rings in various conformations. Among the most common
PAHs are anthracene, chrysene, naphthalene, pyrene and benzo[a]pyrene. These compounds
are often toxic, mutagenic and lipophilic, making them difficult contaminants to treat, as they
accumulate in soil organic matter and therefore are not readily bioavailable for microbial
degradation (Cerniglia,
1992
; Wilson and Jones,
1993
; Bamforth and Singleton,
2005
). There are
mixed reviews on the efficacy of bioaugmentation for PAH degradation, and it has yet to
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