Environmental Engineering Reference
In-Depth Information
Although traditional chemical and physical means of treating contaminated soil
have had been in use, biodegradation technology is currently considered as one of
the most effective ways of rendering polluted soil fit for use. Recent attention has
been given to the use of vegetation as a means of remediating contaminated soil
systems (Davis et al.
2002
). Evidence that plant roots and rhyzosphere associated
microbial community are capable of enhancing the degradation of petroleum chem-
icals in soils provides a potentially important approach for the
in situ
treatment of
contaminated sites. Vegetation may act to immobilize water soluble contaminants,
increase their stability in soil structure, and create a favorable environment for deg-
radative microorganisms. Before phytoremediation can be efficiently employed,
more basic research is needed to reveal basic mechanisms involved.
The combined impact of plants and microbes on soil pollutants is numerous, and
many attempts have been made to manipulate enhanced contaminant degradation.
Our approach refers to rhizoaugmentation which is the addition of hydrocarbon
degrading microorganisms to soil with the objective to get them associated with
rhizospheres of plants involved in remediation (Miller and Dyer
2002
; Shaw and
Burns
2007
). However, we have enhanced the aims of such rhizoaugmentation by
using not only simple hydrocarbon degrading microorganisms but that those which
demonstrated an ability to produce biosurfactants.
Biosurfactants have been reported to be effective for environmental bioremedia-
tion (Shin et al.
2006
; Juwarkar et al.
2007
; Das et al.
2009
). Biosurfactants can
enhance bioremediation via two processes, i.e. by solubilization and by increasing
desorption rate constants. The rate of soil bio- and phyto-remediation may be lim-
ited when a spatial separation between contaminants, microbial population and/or
plant roots is present. For example, the contaminants such as polycyclic aromatic
hydrocarbons must be transported to the bacteria, and rhamnolipid has the greatest
effect on the highly hydrophobic contaminants (Rosario et al.
2007
).
In this study, we examined the role of three different plants, a microbial inoculant
containing the association of hydrocarbon degrading and biosurfactant producing
bacteria and pure biosurfactant on a degradation of 10,000 ppm petroleum spiked
into sterilized Absheron soil. It was hypothesized that the addition of plants with
microbial inoculants to contaminated soils would increase petroleum degradation,
and addition of biofurfactant would further increase efficacy of the phytoremedia-
tion system.
2
Materials and Methods
2.1 Soils
Grayish-brown Absheron non-contaminated soil was removed from the surface ho-
rizon (5-20 cm depth) and sieved through a 2-mm screen. Then it was autoclaved
at 121 °C for 1 h and left covered at the room temperature. This was repeated twice
