Surfactant desorption is key to successful PAH bioremediation
By George Ivey
Figure 1
Formulations which are patented
non-ionic surfactant mixtures
used in the in situ and ex situ
treatment of petroleum hydrocarbons,
chlorinated solvents, heavy metals,
and more recently PAHs, PCBs and
MTBE type contaminated waste are
involved in Surfactant Enhanced
Bioremediation (SEB®) using Iveysol
®. These surfactant formulations have
the ability to enhance soil biodegradation.
During in situ and ex situ bioremediation,
the effectiveness of the bioremediation
process is a function of balancing several
physical and chemical parameters to
achieve effective bio-mineralization of
the target contaminants. The addition of
Ivey-sol to the substrate can aid in the
controlled desorption of the contaminants
making them more bio-available.
As a result, the duration of hydrophobic
organic chemicals (HOC) bioremediation
can be reduced by as much as 30 to
60%, or more.
Normally hydrophobic organic
chemicals exhibit limited bioavailability
to microorganisms as the contaminants
tend to partition onto the soil
matrix. This partitioning can account
for as much as 95% or more of the
total contaminant mass. Thus this limits
the concentration of HOC available
to the microbial population. Hence
certain HOCs such a polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls
(PCBs) and phtalates can persist in the soil matrix for long
periods of time.
The use of Ivey-sol surfactant formulations, as part of a
well designed bioremediation process, will provide a mechanism
to desorb and mobilize the target contaminants from
the surface of soil and bed rock to make them more available
to the indigenous or introduced microbial populations.
Bioavailability is governed by the substrate concentration
that the cell membrane comes in contact with (i.e., what the
microorganisms ‘see’) as well as the rate of mass transfer from
potentially bioavailable (e.g., non-aqueous HOCs) phase to the
directly bioavailable (e.g., surfactant-aqueous HOC) phase.
Surfactant Enhanced Bioremediation affects the sorption of
HOC and surfactants at the solid-liquid interface (i.e., the surface
–H2O–NAPL interface). This mechanism is in part
responsible for the increased bioavailability of the HOC and
surface-bound nutrients. SEB using Ivey-sol is effective at
low surfactant concentrations. It expedites bioremediation of
the contaminated soil and positively affects the
surfactant–soil–NAPL systems (e.g., mass transfer of HOCs,
cell hydrophobicity, and cell attachment at interfaces) while
averting the inhibiting and/or microbial toxic effects associated
with some surfactants (i.e., catonic and anionic) which
are only effective at much higher concentrations.
Ex Situ Bioremediation.
How Ivey-sol technology works
An illustration of how the SEB - Ivey-sol technology
works, is shown in Figure 1. This should be used to augment
one’s present knowledge of bioremediation to understand the
Ivey-sol surfactants’ effects on a microscopic scale in
improving the controlled liberation of hydrocarbons and
nutrients (i.e., surfactant-aqueous HOCs and nutrients-aqueous)
and their controlled availability for mineralization by
the microorganisms present.
This illustration demonstrates how the technology desorbs
contamination in the soil and either dissolves it for in situ or
ex situ applications. In the case of ex situ Surfactant Enhanced Bioremediation (SEB), the surfactants
desorb the contaminants, making them
more bio-available and, as a result,
expedite the biodegradation process.
This mechanism can be described
as follows:
When HOC (i.e., petroleum product)
is absorbed on a soil grain, water
alone will not remove it from the surface.
This is a function of the
hydrophobic characteristics of the
HOC, which repels the water at its surface,
and its inherent low water solubility.
With the addition of SEB Ivey-sol
surfactants, the Ivey-sol hydrophobic
grouping is repelled by the water but
attracted to the HOC on the surface. At
the same time, the hydrophilic grouping
is attracted to the water molecules.
These opposing forces loosen the
HOC from the surface of the soil
matrix and suspend it in the water
phase. Once dissolved, the suspended
HOC is more visible to the microbial
population present.
Once liberated in low concentration
in a ‘surfactant-aqueous HOC’
microscopic outward appearance, it is
more bioavailable to the microbial
population.
Range of applications
Ivey-sol surfactant formulation can
selectively dissolve a broad range of
petroleum hydrocarbons from light, to
medium, to heavy-end HOC type contamination.
In addition, formulations
have also been developed that are very
effective on: chlorinated solvents,
PCBs, PAHs, and MTBE. It has also
been shown to enhance the effectiveness
of in situ soil and groundwater
bioremediation, and ex situ soil (landfarm)
type bioremediation processes
by increasing HOC bioavailability.
Case Study
(PAH & diesel soil remediation)
Ivey International Inc. was retained
by Quinsam Coal Corporation to remediate
over 200,000 kilograms (440,000
lbs) of diesel and PAH contaminated
soil at their mining operation located
near Vancouver, BC. Baseline total
petroleum hydrocarbon concentrations
exceeded 10,000 ppm and several of
the PAH parameters exceeded the
applicable Environmental Standards.
Ivey International Inc. treated the contaminated
soils using their new
Surfactant Enhanced Bioremediation
process. After excavating and bio-piling
the soil, the surfactant enhanced
bioremediation treatment was applied
and the bio-pile was then covered.
Daily aeration was done during the
treatment period. After only 12 weeks
samples taken from the pile showed
that the remediation of the Fueloil/
Diesel and PAH contamination was
completed to BC Environmental
Standards and the soil was safe to reuse
on-site.
Table 1 - Soil washed with Ivey-sol (106 Formulation)
PAH Case Study (bench scale)
During the spring of 2005, Ivey
International’s Research & Development
Division was retained to conduct a
bench-scale testing to determine the
effectiveness of Ivey-sol for the desorption
of PAH contaminants off silty-sand
soils that had originated from an industrial
brownfield site with over 100,000
tons of contaminated soil. The remediation
plan involved a combination of in
situ and ex situ bioremediation of said
soils. The critical barrier associated with
PAH bioremediation is its low bioavailability
due to the fact that 90 to 95% of
PAHs preferentially absorb on to surfaces
versus being dissolved in the aqueous phase. If Ivey-sol could desorb and
liberate the PAHs, it would in effect
increase their bioavailability for microbial
and mineralization.
The bench scale test involved the
mixing of a 20:l volume of PAH contaminated
soil from which a representative
baseline sample was collected
for PAH analysis. Then a 1 L volume
of contaminated soil was washed and
the liquid phase was decanted. A post
Ivey-sol wash sample was then collected
and submitted for analysis (Table 1).
As the bench scale test results
demonstrate, Ivey-sol was effective at
desorbing all 19 PAH compounds. On
average, pre to post PAH concentrations
dropped by >90%. The lowest
desorption/removal was observed for
benzo(ghi)perylene of 84.3%, while
the highest desorption/removal was
observed for 2-methylnaphthalene at
97.3%.
George Ivey is with Ivey International.
He can be reached by e-mail at budivey@island.net.
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