Note: Descriptions are shown in the official language in which they were submitted.
-1- 2~4394 ~
TITLE OF THE INVENTION
Method for the biodegradation of organic contaminants in
a mass of particulate solids and apparatus therefor.
FIELD OF THE INVENTION
The invention relates broadly to the degradation
of organic contaminants present in particulate solids.
More particularly, the invention relates to the
degradation of organic contaminants in soils through
microbiological processes.
BACKGROUND OF THE INVENTION
Bioremediation is the use of living organisms
for detoxication of hazardous wastes. It can involve
either the introduction of specific organisms and/or the
stimulation of indigenous bacteria. The technique was
first experimented in the 1970's to treat contaminated
soils and aquifers. However, hurdles in the regulatory
processes and constant pressure from environmentalist
groups had reduced the use of bioremediation to marginal
levels.
In recent years however, several advantages have
been recognized for bioremediation, particularly in situ
bioremediation. Among others, it has been found that the
technology is specific, relatively cheap and quicker to
use than most other remediation techniques. The technique
can be used to degrade a wide variety of organic compounds
present at various levels in contaminated soils. One of
-2- 20~39~8
the most important advantages of biological degradation
over conventional techniques is the fact that the
contaminants are usually broken down to harmless
substances whereas conventional techniques usually only
temporary displace the problem or transfer the
contaminants to another medium.
Various approaches to bioremediation of soils
have been tested and compared. One preliminary conclusion
that seems to be drawn from those tests is that
microorganisms occurring in nature are so versatile and so
adaptable that most applications of bioremediation could
rely almost exclusively on the use of natural organisms
that have not been modified in any way, thereby avoiding,
at least for now, the introduction in natural systems of
genetically engineered organisms.
The most common technique used in bioremediation
involves the stimulation of naturally occurring bacteria
residing at the site of contamination. It is usually
called "biostimulation". By addition of the appropriate
nutrients, principally oxygen, phosphorus and nitrogen,
and by maintaining optimum growth conditions, it is
possible in some instances to favour increased
multiplication of the communities of indigenous organisms
that together are capable of degrading undesirable
contaminants. Hence, the addition of microorganisms to
the site is not required in biostimulation. A common
-3- 204 3948
variation of the "biostimulation" technique is land-
farming. In land-farming, chemical nutrients are added to
soil, often in an excavated pile, while adequate
oxygenation is assured by frequent turning or dishing of
the soil.
Implementing biostimulation usually requires a
certain amount of laboratory testing, to ensure that there
are sufficient numbers of indigenous microbes on site, and
to determine the optimum conditions to enhance their
growth and biodegradative action. This preliminary
characterization usually leads to treatability studies to
establish that the site can be remediated economically.
In situ bioremediation usually requires extensive
engineering to introduce nutrients to the site, through
injection wells, infiltration galleries and the like.
Land-farming, in contrast, can be accomplished simply by
spraying the nutrients onto soil piles that are frequently
mixed and aerated.
In U.S. Patent 4,849,360, Norris et al. describe
a process using biostimulation for confining contaminated
soils and degrading the hydrocarbons they contain. The
method comprises the use of indigenous microorganisms,
nutrients, water and a suitable gas distribution system.
The amount of contaminated soils to be treated is adjusted
by evaluating the capacity of the gas distribution system
to create optimal aerobic conditions (see column 2, lines
20~39~8
_ -4- 85161-1
47-50). The method also involves evaluating the native microbial
community in the soil and creating proper conditions for this
community to grow as much as possible (see column 4, lines 12-45).
One of the ma]or drawbacks of this method appears to be the fact
that the soils to be decontaminated must be confined in a
container.
Another example of a decontamination system using
biostimulation is described by K. Fouhy and A. Shanley in an
article entitled "Mighty Microbes" (Chemical Engineering, 98(3),
30-35, 1991). For this system, liquids are sprayed on the
contaminated soil pile, and air may be blown or suctioned through
the mass by a system of pipes located under the mass. This is
described as a "wet" technique for the onsite processing of soil.
Contrary to the technique described in U.S. Patent 4,849,360, soil
is not confined to a container. The sprinkling system is used to
add water and nutrients and the air distribution system buried in
the pile increases oxygen supply. Although the method has proven
to be quite interesting for the degradation of some contaminants,
it has been found to be relatively time consuming and somewhat
limited for degrading more chemically stable contamlnants such as
PCB's. As shown at page 33 of the article, decontamination of a
contaminated soil containing PCP and creosote led to a 58%
reduction in contaminants in 3 months. Generally, this is not
.. .
~'"~
-
2~43948
sufficient to meet the levels required by the regulatory
authorities in North America.
An alternative to biostimulation is
"bioaugmentation". This technique consists in introducing
non-native cultures, previously selected from other sites
for their ability to degrade specific wastes. These
microbial products are usually blends of different species
or strains. In recent years, companies have begun selling
microbial blends purported to be active against hazardous
compounds, including use for in situ waste remediation.
Most common are products for degradation of hydrocarbons
and petroleum distillates, but several manufacturers also
sell microbial products with claimed activity against
aromatic compounds and other hazardous chemicals. In
addition to these commercially available cultures, there
are several microbial isolates that have shown success in
the laboratory in degrading hazardous wastes, such as the
white-rot fungus, which can degrade lignins and many other
aromatic compounds.
Waste treatment technologies based on the
principle of bioaugmentation have also been developed. In
U.S. Patent 4,850,745, Hater et al. describe a
bioaugmentation technique by which a system for treating
soil contaminated by petroleum hydrocarbons is designed by
applying in a dry form a suitable bacterial culture
capable of degrading petroleum hydrocarbons to the bottom
6--
2~43g~
of an excavated cavity. A system of distribution piping
capable of supplying nutrients directly to the cultures
and also an air flow through the area containing the
cultures is provided to maintain optimal growth
conditions. The system described by Hater et al. seems to
be operated in a closed circuit. In other words, Hater et
al. do not teach or suggest the subsequent introduction of
microorganisms once the initial inoculation has been made.
In U.S. Patent 4,952,315, another type of
bioaugmentation technique is described. Saab discloses a
process for eliminating hydrocarbons contained in a
contaminated soil. The desired result is obtained by
using a microbiological treatment involving the use of
emulsifiers permitting the separation of the contaminants
from the soil in which they are found. The contaminants
can then be degraded by using a biological process
requiring endogenous bacteria. This approach can be
somewhat lengthy as it is required to bring the
contaminants in a fluid phase before having the
possibility of degrading them through the action of
microorganisms.
One of the most promising applications for
bioaugmentation appears to be in the degradation of oil
spills, since the biology of hydrocarbon degradation has
been well studied. Unfortunately, most of the methods
that were used so far to decontaminate major oil spills
2~4~94~
such as the Mega Borg and Exxon Valdez spills could not
generate conclusive data. Furthermore, although
bioaugmentation allows the introduction of microbes
tailored for a given waste, it has difficulty working in
practice because competition from natural microbial
populations requires large inoculum sizes, and because
cultured organisms cannot always handle the stresses
present in natural environments.
Bioremediation offers some concrete advantages
over competing methods. It is a destructive technology
that offers a permanent solution to hazardous waste
problems, without the need to remove the wastes off-site.
It utilizes a natural process that does not itself create
environmental problems. Even though in si tu
biostimulation requires preliminary laboratory assessment,
it can be implemented quickly and inexpensively at most
sites. Soil bioremediation has been estimated to be far
less expensive than incineration or land disposal, and
competes well with other available options, like
recycling.
However, bioremediation, either through
biostimulation or bioaugmentation, has its limitations.
Hence, bioremediating soil will generally take longer than
excavation for incineration or landfilling. Also,
biostimulation is often insufficient to provide
degradation of contaminants at acceptable levels whlle in
~ -8- ~43~4~
the case of bioaugmentation, one of the major problems
seems to reside in the fact that it is difficult to
maintain the cultures introduced at the beginning of the
process to optimal levels.
SUMMARY OF THE INVENTION
In accordance with the present invention, it has
been found that the periodic irrigation of a contaminated
mass of particulate solids with a culture medium which may
contain one or more appropriate bacterial strains
endogenous or indigenous to the contaminated mass and
having the ability to degrade organic contaminants leads
to substantial improvements in yield when compared to
biostimulation techniques and conventional bioaugmentation
techniques in which the mass to be decontaminated is
inoculated only once.
The present invention therefore relates to a
method for the biodegradation of organic contaminants in
a mass of particulate solids. The method comprises
providing a contaminated mass of particulate solids on an
impervious surface in fluid communication with an
impervious recovery reservoir. The impervious surface has
operating thereon air supply and/or air suction means to
provide suitable and continuous oxygenation of the mass
and/or to remove undesirable vapor emissions from the
mass. The contaminated mass is then irrigated by
periodically applying on its surface a culture medium
9- 2~3~!~8
which may comprise at least one bacterial strain and co-
substrates thereof. The bacterial strain is either
endogenous or indigenous to the contaminated mass and has
the ability to degrade the undesirable organic
contaminants. The medium is drained through the mass and
recuperated in the recovery reservoir and the washings are
to be reused to irrigate the contaminated mass. The mass
is periodically mixed and its temperature and moisture
level are controlled to monitor the biological activity of
the bacterial strain and to permit adjustment of the
biological conditions inside the mass to maintain
bacterial levels suitable for the strains to degrade
undesirable contaminants. The expression "culture medium"
when used herein is entitled to designate a solution
containing various nutrients, co-substrates and optionally
surfactants to be added to the contaminated mass as well
as a vehicle for the bacterium inoculates that may be
introduced periodically to the contaminated mass.
Hence, the process of the present invention
provides a method by which levels of active microorganisms
can be maintained in the contaminated mass to maintain
decontamination conditions which are as optimal as
possible. The bacterial culture applied on the
contaminated mass through irrigation can be applied either
continuously or at periodic intervals, depending on the
-lo- ~ ~ 3~ 8
overall level of contamination and the desired
decontamination time.
Preferably, the impervious surface used in the
method of the present invention is sloped to enable
recovery of the washings drained through the contaminated
mass. Also, the air supply and/or air suction system
preferably comprise a series of perforated conduits
connected to an air compressor operable in suction and/or
compressed mode. The perforated conduits are preferably
located inside a gravel bed and the compressor has an
activated charcoal filter which is operated when the
system is in the suction mode.
The culture medium applied to the mass may
comprise specific nutrients such as nitrogen and
phosphorus and surfactants to improve the efficiency of
the microbial cultures present in the medium and in the
soil. More preferably, the bacterial medium is provided
from a medium delivery unit allowing to maintain the
strains used to decontaminate the mass or from the
recovery reservoir in which it is introduced prior to
initiating decontamination. The culture medium may be
applied on the mass by being pumped from the delivery unit
or the recovery reservoir through a plurality of
sprinklers or a perforated double-partition resilient
irrigation tubing network in fluid communication with the
delivery unit. The sprinklers and resilient tubing are
-11- 2~4 ~ 9~ ~
respectively located above and on the mass to be
decontaminated. The culture irrigated through the mass
can be reused by being pumped from the recovery reservoir
through the sprinklers or the tubing network. The
recovery reservoir can also combine the dual function of
delivery and recovery, in which instance the culture
medium is directly introduced in it and combined with the
washings to irrigate the contaminated mass. The
temperature and moisture level of the mass may be measured
by a plurality of thermocouples and appropriate sensors
inserted in the mass. Other preferred features include
the direct oxygenation of the recovery reservoir to
maintain the bacterial population present in both the
culture medium and the washings as well as the use of an
impervious cover placed over the contaminated mass to
segregate rain water and to assist in maintaining optimal
temperature levels.
Also within the scope of the present invention
is a system for the biodegradation of organic contaminants
in a mass of particulate solids. A known system for the
biodegradation of organic contaminants comprises a sloped
impervious surface having thereon air supply and/or air
suction means to provide suitable and continuous
oxygenation of the mass or to remove undesirable vapor
emissions from the mass. It also comprises an impervious
recovery reservoir in fluid communication with the sloped
- -12- 2 Qq 39 48
impervious surface, a storage container havlng therein a
solution containing nutrients and spraying means connected
to the storage container to irrigate the mass by spraying
the nutrients on the mass, the solution being drained
through the mass and recovered in the reservoir to be
reused to irrigate the mass.
In the system of the present invention, one
improvement comprises substituting the storage container
by a medium delivery unit in which a culture medium may
comprise at least one bacterial strain and co-substrates
thereof is maintained. The system of the present
invention also comprises means to continuously measure the
temperature and moisture level of the mass to monitor the
biological activity of the bacterial strain and to
maintain the activity at levels sufficient for the
bacterial strain to degrade the contaminants in the mass.
As mentioned previously, the means to measure the
temperature and moisture of the mass may preferably
comprise a series of thermocouples inserted in the
contaminated mass. Means to provide suitable oxygenation
of the impervious recovery reservoir which, as mentioned
previously, may be used alone and combine the dual
delivery-recovery function, are also provided.
The following is a description by way of example
of preferred embodiments of the present invention,
reference being had to the following drawings in which:
_ -13- 2 ~q3 9~g
Figure 1 is a side elevation of a preferred
embodiment of the biotreatment system of the present
invention;
Figures 2 and 3 represent a comparison of the
temperature inside and outside the contaminated mass at
various intervals during the decontamination of
hydrocarbons using the process of the present invention;
Figure 4 represents a comparison of the
temperature inside and outside the contaminated mass at
various intervals during the decontamination of
hydrocarbons using the process of the present invention
when the compressor was operated in the suction mode;
Figure 5 represen~s oil and grease concentration
throughout the decontamination of hydrocarbons using the
process of the present invention;
Figure 6 represents chromatograms showing the
progression of PAH's degradation during the
decontamination of hydrocarbons using the process of the
present invention;
Figures 7 and 8 represent side elevations of
another embodiment of the biotreatment system of the
present invention; and
Figure 9 represents a plan view of the
biotreatment system of Figures 7 and 8;
_ -14- ~04 394~
Figure 10 represents the reduction of PCP
concentration during the treatment of PCP contaminated
soil using the process of the present invention;
Figure 11 represents the reduction of oil and
grease concentration during the treatment of PCP
contaminated soil using the process of the present
invention; and
Figure 12 represents the reduction of PCP
concentration in washings from the treatment of PCP
contaminated soil using the process of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a method for
the biodegradation of organic contaminants in a mass of
particulate solids through continuous application of
culture medium on the mass to be decontaminated. It also
relates to a system for carrying such method. The
parameters that usually affect the efficiency of
biodegradation of various wastes such as oily waste
residues include the presence of active organisms, oxygen
supply, the addition of nutrients, the use of surfactants,
the presence of co-substrates, the temperature, the
moisture level and the pH. Hence, the choice of the site
design must take most of these parameters in consideration
to allow maximum efficiency of the bioremediation process.
_ -15- 20439~
Referring now to Figure 1, a preferred
embodiment of the decontamination system of the present
invention, generally designated by reference numeral 10,
comprises a sloped impervious surface 12. The impervious
surface 12 is preferably made of a material such as
concrete, asphalt, polyethylene or other suitable
polymeric plastic and has a sufficient inclination to
permit recovery of the washings, preferably between 1 and
3%. The impervious surface 12 is connected to an
impervious recovery reservoir 14 in which culture medium
washings may be collected. On the impervious surface 12
is installed an air distribution system comprising a
series of perforated pipes 16, 18, 20, 22 and 24 which are
placed in a gravel bed 26. The gravel bed is optional but
it appears to provide better distribution of the air
provided to the contaminated mass. The perforated pipes
16, 18, 20, 22 and 24 are linked to pipe 28 leading to an
air compressor 30. The compressor 30 may be chosen to
allow operation in suction mode as well as compressed
mode. In both the suction and the compressed mode, air is
provided to maintain suitable aeration of the contaminated
mass. However, the compressed mode may also serve to
control the air temperature and hazardous vapor emissions
if required. When the compressor is operated in
compressed mode, air is passed through pipe 32 nd when the
compressor is operated in the suction mode, air is passed
-16- 20439~8
through pipe 34 and activated charcoal filter 36 or a peat
absorbent filter (not shown) to recover gaseous
contaminants.
The decontamination system 10 also comprises an
irrigation system, generally designated by reference
numeral 38. The irrigation system 38 comprises a medium
delivery unit 40 to provide nutrients, surfactants,
bacteria inoculates and required co-substrates to the
contaminated mass. The irrigation system 38 also
comprises a series of sprinklers 42, 44, 46 and 48 in
fluid communication with both the delivery unit 40 and the
recovery reservoir 14. Pumps 50 and 52 are provided to
supply culture medium to the sprinklers 42, 44, 46 and 48
through either the delivery unit 40 or washings
accumulated in the recovery reservoir 14.
To operate the decontamination system of Figure
1, a decontamination site should first be constructed with
a proper slope on which is installed impervious surface 12
in such a fashion as to allow collection of washings in
the recovery reservoir 14. Perforated pipes 16, 18, 20,
22 and 24 are then placed on the impervious surface 12 and
covered with a gravel bed 26. The contaminated mass of
particulate solids 54 is then piled on the gravel bed 26
and irrigated with a culture medium pumped from the
delivery unit 40 through pump 50 and sprinklers 42, 44, 46
and 48. As the microorganisms contained in the culture
2~4394 8
-17-
medium diffuse through the contaminated mass 54 in the
direction indicated by the arrows 56 and 58, compressor 30
is operated to provide suitable oxygen levels to maintain
optimal activity of the microorganisms introduced in the
soil and to provide sufficient oxygenation for the
organisms already present in the contaminated mass. Once
the culture medium pumped through the sprinklers from the
delivery unit 40 has reached the bottom of the
contaminated mass 54, its washings are drained in the
recovery reservoir 14 and may be pumped through pump 52 to
be reused again. Drained culture medium ~or washings) is
therefore recirculated through this system and analysis of
phosphorus and nitrogen levels found in the washings are
used to optimize fresh medium addition.
The frequence at which the contaminated mass is
irrigated and the amount of culture medium that is
provided depends on various factors including the level
of contamination of the particulate mass and the time
within which the contaminated mass is to be
decontaminated. Preferably, the culture includes
nitrogen, preferably of a concentration between 3 and 5
ppm, phosphorous, preferably at a concentration of 0.3 -
0.5 ppm.
The bacterial strains that are used are selected
for their ability to degrade the contaminants present in
the mass of particulate solids. Incubation of the
~ -18- 2043~4~
bacterlal straln can be done on-slte and thermocouples
linked to a digital data collection system as well as
suitable sensors are respectlvely used to monltor
temperature and molsture levels in the contaminated mass.
Another embodiment of the decontamlnatlon system
of the invention is shown in Figures 7, 8 and 9.
Referrlng to Flgure 7, the decontaminatlon
system, generally deslgnated by reference numeral 70, has
an lmpervious surface 92 which usually presents an
inclination of 1 to 3% in order to provide suitable
recovery of the culture medium washlngs. The impervious
surface 92 is preferably either a polyethylene membrane or-
a concrete or asphalt llnlng. The lmpervious character of
the sloped surface 92 ls partlcularly lmportant to avold
the lntroduction of contaminants ln non-contamined soil.
The impervious surface 92 may be sloped ln such a manner
as to taper from the center of the contaminated mass
towards each of its side or from one side of the
contaminated mass to the other. The lmpervlous surface 92
leads to a concrete channel 94 ln whlch the washlngs are
collected. The channel 94 may contaln gravel (not shown).
The channel 94 ls protected by cover 88 to prevent rain
water to be introduced in the system. Channel 94 ls
connected to a recovery reservolr (not shown) that is used
to contain the culture medium and to recover the washings
from the decontamination process. The recovery reservoir
- ~ -19- 2043948
may be oxygenated in order to provlde adequate condltlons
for the mlcroorganisms found in the washings to degrade the
contaminants present in the washlngs. Hence, the culture
rnedium and the washings contained in the recovery reservoir
can be oxygenated either by providing air through suitable
air supply means (not shown) or by adding chemical
substances such as hydrogen peroxide. The culture medium
and the washings are sprayed on the contaminated mass by
being pumped from the collectlng reservolr through the
lrrigation system 82 using a pumping system similar to the
one used in the previous embodiment.
A cover 88 is placed over the contaminated mass
and the irrigation system 82 which is described in further
detail later on. Preferably, the cover 88 may be an
impervious cloth which may be maintained in position using
weights such as sand bags 90 that prevent the cover 88 from
being blown loose by winds. Another arrangement that can be
used to maintain the cover 88 in position is to provide a
hose (not shown) filled wlth water or any sultable liquld,
circling the cover 88 at the bottom of the pile. The cover
88 is used for at least three purposes. Flrstly, it allows
segragation between the rain waters and the waters used in
the decontamination process. Secondly, it prevents the
escape of volatile components generated from the
decontamination process. Thirdly, it provides an
20439~8
,
-20-
isolation feature that enhances the overall efficiency of
the heating of the mass.
The air distribution system, generally
designated by reference numeral 72, comprises a main pipe
dlsposed longitudinally to the pile and designated by
numeral 74 (Flg. 9). A series of perforated transversal
pipes 78 are connected to the main pipe 74 to provide even
oxygenation of the contaminated mass.
The transversal- pipes are preferably spaced
apart by a distance of about 3 meters. Each of the
perforated pipes ls controlled by sultable valve means 100
IFig. 7). The perforated pipes 78 are located underneath
the contaminated mass and on the impervious surface.
The use of gravel to cover the perforated plpes
78 is foreseeable but optlonal, although ln some lnstances
it may increase the speed at which decontamination is
carried out. However, in lnstances where treated soll is
to be removed and new contamlnated soll ls to be added to
the slte, the use of gravel does not appear to be
practlcal. Thls decrease in air distribution efficiency
lncurred from not uslng gravel can be obvlated by
lncreaslng tne num~er of perforated transversal pipes.
' ~0~13q~8
-21-
The perforated pipes 78 are llnked to an angled
member 76 whlch ls llnked to the maln plpe 74. The main
pipe 74 is linked to an air compressor (not shown) whlch
ls slmilar to the air compressor described in the
embodiment shown in Figure 1.
The irrigatlon system, generally designated by
reference numeral 82, ls made of a serles of perforated
double-partltlon lrrlgation tubes 84 and 86 which are best
lllustrated in Flgure 9. Referrlng to Flgure 9, the
lrrlgatlon system 82 comprises a series of transversal and
longitudinal perforated double-partition irrigation tubes
respectively designated by reference nurnerals 84 and 86.
The perforated double-partitlon lrrigation tubes 84 and 86
are usually made of a flexlble materlal slmllar to the
material used to make regular watering hoses.
The tubes 84 and 86 are interconnected through
a series of valves (not shown) that allow for the partial
operation of the irrlgatlon system 82. Thls type of
irrigatlon system allows for contlnuous operatlon of the
apparatus. Hence, in instances where the contaminated
mass to be treated is not provided all at once, the system
can be partially operated and the treated mass can be
removed and replace~ ~y a~ltlonal contaminated mass.
This makes the overall decontamination operation more
flexible.
-22- 204~48
Contrary to the embodiment descrlbed previously,
the irrigation system is not provided with sprinklers.
However, the double-partition irrigation tubes 84 and 86
allow for a slow release of the culture medium, which
cannot be done easily when sprinklers are used. By using
these tubes, the resulting irrigation allows for a more
permanent control of the moisture level of the
contaminated mass as the irrigation rates can be brought
down to very low levels. This is not possible when
sprinklers are used, as one has to irrigate the system and
stop until the sprayed culture medium is infiltrated in
the contaminated mass. At the beginning of the
decontamination process, the system is operated in the
suction mode. The irrigation rates, when using the second
embodiment, may be such that continuous irrigation is
possible. The culture medium itself can be pre-
oxygenated, thereby eliminating the need to initially
operate the system on a compression mode. When volatile
substances are no longer at undesirable levels, the
compression mode may be used. If the system is operated in
cold temperatures, the compressed air is warmer than the
ambient temperature and consequently heats the
contaminated mass. As mentioned previously, the use of
the cover 88 also allows better conservation of the heat
generated by the compressed air.
~~ -23- 20~394 8
Although it may be useful to constantly irrigate
the contaminated mass with the culture medium when the
decontamination process is initiated, constant irrigation
is not required throughout the entire decontamination
process. Hence, irrigation rates may be controlled in two
preferred manners. Firstly, a timer may be used to
activate the irrigation system at regular intervals, for
example every 12 hours, for a predetermined period of
time, for example 1 hour. The rate of irrigation and the
volume of culture medium to be used is calculated and
adjusted depending on the hydraulic conductivity of the
soil and according to the type of soil to be
decontaminated. Alternately, a moisture indicator can be
inserted in the contaminated mass and set to activate the
irrigation system when the moisture reaches a certain
level. The rate at which the culture medium may be
provided varies depending on the amount of liquid which
can be reatined by the particular soil under study. This
capacity is at least a function of the size of the
particles contained in the soil. This varies
substantially depending upon the type of soil. For
instance, clays will retain much more water than sands.
All the poured liquid leaches out after having saturated
the soil with water and waited 24 hours before pouring if
the pouring rate is not superior to the infiltration rate.
Hence, the moisture indicated is to be adjusted to operate
`~ -24- 2~3~4~
only when water in the contaminated mass has an
infiltration pouring rate similar to the infiltration
rate. In other words, the rate of pouring of the medium
is a function of the infiltration rate of the soil to be
decontaminated. The rate at which the culture medium is
added is not particularly related to the level of
contaminants found in the contaminated soil, the purpose
being to effect decontamination as quickly as possible.
Ideally, soil should be constantly irrigated as long as
its macropores are filled with air. This is done by
measuring the "field capacity" (capacité au champs) of the
soil to be decontaminated.
The volume of contaminated mass that can be
decontaminated at once using either embodiment of the
system of the present invention varies depending upon
various parameters, at least as far as width and length
of the mass are concerned. The length of the contaminated
mass is not critical and may be adjusted depending on the
size of the system. With regard to the width, it is
important to consider that, as the contaminated mass has
to be turned periodically, the width may vary with the
means available to turn the mass. Generally, preferred
width varies between 9 and 14 meters. As far as the
height of the contaminated mass is concerned, the optimal
height will range between 2 and 3 meters. Heights
exceeding 3 meters can be foreseen but the efficiency of
~_ -25- 20~3948
the decontamination process is usually reduced as
irrigation and oxygenation of the contaminated mass
becowes more difficult. On the other hand, heights below
two meters are not interesting as the volume that can be
decontaminated at once is reduced, thereby increasing the
costs of the overall operation. Furthermore, a
contaminated mass of reduced height exhibits less thermal
inertia. Decreases in thermal inertia usually mean that
during cold nights, the overall temperature of the
contaminated mass would fall too rapidly.
The volume of air that may be introduced to
oxygenate the contaminated mass may vary from 1/2 to 2
times the overall volume of the contaminated mass an hour.
Optimally, the volume of air introduced in the
contaminated mass every hour should be the same as the
volume of the contaminated mass itself. The air can be
heated to maintain optimal decontamination conditions.
This may be particularly interesting if decontamination is
to be effected in cold climates.
It is important to mention that the compressor
may also be operated permanently or controlled using a
suitable timing system. For example, when treatment of
the contaminated soil is almost completed, not as many air
changes are required as not as many contaminants are to be
degraded. As mentioned previously, at the beginning of
the decontamination process, oxygen can be provided by
-26- ~04 3~g 8
adding an oxygenated culture medium in order to limit
volatilization of the gaseous contaminants. Another
manner in which the escape of volatile gases may be
controlled is by introducing a sensor in the contaminated
mass to determine the rate of volatile products. When the
rate of escape of volatile contaminants is at high levels,
oxygenation through the compressor may be interrupted and
restarted when the rate has decreased to acceptable
levels. Typically, the level of volatile contaminants
should be maintained below 260mg/m3 an hour for benzene,
300 mg/m an hour for naphtalene and 200 mg/m3 an hour for
toluene for example.
With regard to the microorganisms used in the
decontamination process, various types of organisms may be
used depending on the type of contaminant present in the
contaminated mass. Generally speaking, the strains used
are isolated from contaminated sites and assayed for their
ability to degrade a given contaminant. They may be used
either as pure cultures or as mixed cultures, being
mixtures of microorganisms. In the case of hydrocarbons,
for example, various Pseudomonas strains such as
Pseudomonas putida may be used. In the case of PCPs,
various bacterial strains can be used as well as various
spores such as Coriolus versicolor and Sphanerochaete
chrysosporium. Although the selection of the strain is of
some importance, the method by which a given strain is
20439~8
-27-
selected to be used in bioremediation is relatively well
known by those skilled in the art.
The pH of the contaminated soil usually has to
be maintained between 6 and 8. Many ways can be used to
maintain the required pH that will not be harmful to the
organisms in the culture. One example is to use lime.
Anionic or non-ionic surfactants can also be
added to the contaminated soil in preferred concentrations
of about 0.01% in the culture medium in order to reduce
surface tension. The types of surfactants that may be
used are commercially available surfactants that are well
know by those skilled in the art.
The growth medium is incubated after inoculation
with the proper culture for a sufficient period of time to
allow the microorganisms to grow. The microorganisms may
be cultured in a laboratory to a high concentration to
form a stock solution. Alternately, the microorganisms
may be cultured only until a suitable microorganism
culture suspension for carrying out the process is
achieved. For example, in the laboratory, microorganism
concentrations of about 1 X 101 can be produced and
diluted to 1 X 106 or 1 X 107 prior to being used to
irrigate the contaminated mass The culture medium can be
maintained on the site by using appropriate co-substrates.
As far as inoculation rates are concerned, it
has been found that regular inoculation provides more
-28-
adequate conditions for achieving suitable decontamination
levels. Whereas most prior art processes provide designs
that allow only a single inoculation of the contaminated
soils, the process and system of the present invention
contemplates periodic inoculation. Preferably,
inoculation can be effected every two weeks as an average
and typically, the concentration of microorganisms
introduced in the contaminated mass ranges from 10 to 10
per cubic meter of water for each 100 m3 of contaminated
mass.
Important aspects that have been developed to
improve bioremediation of organic contaminants include the
use of a fabric cover, the possibility of constantly
irrigating the contaminated mass by providing an apparatus
allowing low irrigation levels, the possibility of
oxygenating the reservoir in which washings are recovered
and the possibility of controlled moisture levels through
appropriate probing means. It is also important to
mention that the design of the second embodiment allows
one to partially operate the apparatus and to replace
decontaminated soil by other contaminated masses in a
relatively easy fashion.
The process of the present invention provides
means to allow maximum control of the conditions favoring
efficient decontamination of particulate solids while
eliminating the risk of contaminants migration to
~OA~9~8
_ -29-
surrounding ground waters. Furthermore, the availability
of large amounts of bacteria through multiple inoculation
allows the possibility to maintain optimal biological
activity throughout the process.
The following examples are introduced to
illustrate rather than limit the process of the present
invention.
Example 1
Biological remediation of shoreline oily waste from a
marine spill.
On May 8, 1988, the collision of the oil tanker
Czantoria with a dock located in the port of Quebec city
resulted in a 2000 to 3000 barrels spill of light crude
oil in the St-Lawrence river. Subsequently, two types of
shorelines were affected. The first type of shoreline
consisted of beaches mostly composed with granular
materials such as sand, rock and silt. The second type of
shoreline consisted of marshes containing various types of
weeds.
Oily waste was collected separately from those
two types of shorelines for subsequent treatment and
disposal. Approximately 300 m of material was
contaminated with up to 30~ of oil and could not be
disposed of in landfill sites or local incinerators.
2~4~948
- -30-
The decontamlnation operation was done in two
phases using the system illustrated in Figure 1; a first
phase of 10 days in the fall of 1988, and a second phase
from May to November 1989. During the first phase, two
piles of waste were placed on the impervious surface; one
pile of granular material (sand, soil, rocks and silt),
and one pile of weeds and woody material. The site was
operated for 10 days from November 29, 1988 to December 9,
1988. The operation was ended because it was no longer
possible to prevent water freeze-up.
The site was re-opened in May 1989. In June, it
became evident that water flow in the granular pile was no
longer suitable for an efficient activity. The site was
then redesigned to contain only one mixed pile. Mixing
was done again in July and in September based on
temperature variations analysis.
In both phases, a culture medium containing
phosphorous and nitrogen sources, a biodegradable
surfactant having an alcohol polar substituant to increase
the mobility of the contaminants, at least one hydrocarbon
degradating the bacterial strain at a concentration of 10
and a suitable co-substrate at a concentration level of
loo ppm was used.
The pH of the contaminated soil was corrected to
be within the range of 6 to 8 by treating the soil with
dolomitic lime. Inoculation was conducted every day
2~4394~
-31-
during which approximately 240 liters of the medium were
sprayed at a rate of 20 l/min for 2 hours.
The site was closed on November 1989 when
contamination level was below 1%.
Evaluation of the various parameters of the process
1. Temperature
It has often been said that bioremediation only
works within a very narrow time window in cold latitudes
because of problems in maintaining suitable temperature.
This is likely to be the case for landfarming when a thin
layer of waste is spread on a wide surface. However, the
design of the present invention works at much colder
temperatures than what is considered to be the limit for
landfarming. In fact, it seems that the process is
efficient even at -20~C. The reason for this increased
efficiency is the fact that compressed air is warmer and
the pile thickness generates friction that increases air
temperature furthermore. Also, heat created by biological
activity is less susceptible to dissipation in ambient
air. Figure 2 illustrates this phenomenon for the first
days of operation. Sharp decreases in the pile
temperature are caused by periodical addition of nutrient
so 1 u t i on .
Figure 3 shows the temperature curves for the
remainder of the operation. It is important to note that
the pile temperature increases sharply right after each
2~439~8
_ -32-
mixing operation. The decrease in September was caused by
operating the compressor on suction mode.
Figure 4 illustrates the temperature variations
during 13 days while the compressor was operated in this
fashion. Even though lower than during the compressed air
mode, the pile temperature was always kept above ambient
temperature. One of the most important features of this
bioremediation process is the stability of the pile
temperature when in diurnal cycles.
Oil and grease deqradation
Figure 5 shows the evolution of oil and grease
concentrations. The first 10 days represent operation in
the fall 1988 and the remaining 160 days being related to
the 1989 operation. Up to the 68th day, two curves are
shown, one for the granular material and one for weeds.
From the 69th day, only one day is shown representing the
mixed pile, oil and grease concentration.
Initial concentrations were respectively 30.5
and 3.9% in weeds and granular material. Before mixing
the two piles, concentrations were down to 10.0 and 1.7%.
Average concentration of the mixed pile was 6.3%, reduced
to 1.1% at the end of the operations.
It must be pointed out however that oil and
grease analysis is only performed on fine materials.
Table I shows the breakdown of materials found in the
combined waste pile. This was obtained by analyzing a
_ -33- 2~3948
representative sample of 20 kilograms. Rocks and large
pieces of woody material were not tested for oil and
grease. Since these can be considered very slightly
contaminated - oil and grease % weight close to 0 - their
relative contribution to the pile (50%) allows a
redistribution of the tested level of 1.1% of the entire
waste, bringing it closer to 0.52%.
Leachate test results indicated that the
remaining material would not contaminate soil and
groundwater. All tests showed s0.2 ppm oil and grease;
acceptable limits for sanitary landfill sites is 15 mg/kg.
TABLE 1
Fine materials (weeds, clay, sand) 47.3%
Large rocks ( > 5 cm diam.) 15.4%
Small rocks ( ~ 5 cm diam.) 31.4%
Coarse woody material 5.9%
Polyaromatic hYdrocarbons (PAH's)
Figure 6 and Table 2 show the progression of
PAH's degradation during the process. The chromatograms
clearly show the disappearance of the characteristic PAH
_34_ 20439~
absorption peaks. No single PAH was found to be in excess
of the regulated level for residential areas.
The low value for initial naphthalene
concentration (3.8 ppm) is an indication that much of the
original volatile PAH's were lost to the atmosphere during
the first days of the spill.
TABLE 2
PAH's degradation
P.A.H. NOV. 88 JUNE 89 NOV. 89
Naphthalene 3.8 n.d. n.d.
Acenaphtylene 25.6 0.6 n.d.
Acenaphthene 20.7 3.4 0.4
Fluorene 45.8 3.1 1.4
Phenanthrene 97.6 14.5 1.8
Anthracene 27.7 ---- 0.8
Fluoranthene 6.5 0.6 1.2
Pyrene 34.2 18.0 1.0
Benzo(a)fluoranthene 15.5 .06 0.4
Benzo(b)fluoranthene 5.3 0.7 0.1
Benzo(k)fluoranthene ---- 1.4 1.0
Benzo(a)pyrene 0.5 0.7 0.3
TOTAL PAH 283.2 44.0 8.5
~_ -35- 2~43~4~
Biological activity
At various times during the operation biological
activity was measured through bacteria count. At all
times count was maintained above 1 X 107 units/g soil,
with a peak count of 3.6 X 10 units/g in June 1989.
Through growth analysis it was found that 100% of the
microorganisms present in the soil had affinity for
petroleum hydrocarbon substrates. Hence, in instances
where the microflora in the contaminated 50il iS abundant
because of a large variety of carbon sources as it is the
case in this example, the addition of microorganisms may
not be necessary or useful because of competition from
strains already present in the mass.
The present example demonstrates that
bioremediation can be an efficient mean of degradating and
disposing of oily waste from marine spill shoreline clean-
ups. In fact, disposal costs have been shown to be about
4 to 8 times less than transportation and disposal at a
landfill site.
Content in oil and grease can be reduced to
values under 1% with leaching potential of close to 0 ppm.
The actual requirements for sanitary landfill in Quebec
are respectively 5% and 15 mg/kg for oil and grease, and
leaching. Hence, these requirements were met when using
the process of the present invention. It seems that some
of the key factors that were found to be of considerable
2~43~4 8
-36-
importance when operating the bioremediation process of
the present invention were the following:
- sound management practices and tight control are
essential to achieve efficient bioremediation;
- good water drainage is essential to maintain low
compaction and adequate air circulation;
- constant temperature measurement is necessary to
accurately monitor biological activity;
- periodical mixing is indicated from temperature
10readings must be performed to maintain the system at
its peak performance level.
Example 2
Biorestoration of soil contaminated with PCPs.
15The system used in this example was the system
shown in Figures 7-9.
The contaminated soil to be treated was siltous
sand having a relatively weak permeability. Extended
spraying periods were thus required in order to allow
suitable absorption of the nutrients medium to avoid
liquid build-up at the surface of the pile. The
compaction levels of the pile increased as its
permeability decreased, and hence turning the pile was
essential to maintain a soil structure that was as loose
as possible.
2~4394~
- -37-
120 cubic meters of the contaminated soil which
initially exhibited PCP levels of 115 ppm was placed on an
impervious concrete surface having a thickness of 50 mm
and an inclination of 1%. The air distribution system
located between the concrete surface and the contaminated
pile was covered with gravel. This gravel bed was useful
to increase air diffusion and the drainage of the pile.
It turned out that it was only moderately effected when
the pile was turned. A fabric cover made of fabrene was
deposited on the contaminated mass. It turned out to be
suitable to control rain water and to help allow efficient
recirculation of air. Also, the fabric covers increased
the heating efficiency of the pile.
The concrete surface was in fluid communication
with a 2000 liter underground recovery reservoir. A
culture medium containing phosphorous and nitrogen
sources, a biodegradable surfactant having an alcohol
polar substituant to increase the mobility of the
contaminants, a PCP degradating bacterial strain at a
concentration of 106 and a suitable co-substrate at a
concentration level of 100 ppm was used.
The pH of the contaminated soil was corrected to
be within the range of 6 to 8 by treating the soil with
dolomitic lime in an amount of 500 kg for 120 m3 of soil
prior to the first irrigation inoculation. The first
inoculation was conducted on July 13, 1990 during which
~ -38-
~43948
approximately 240 liters of the medium were sprayed at a
rate of 20 l/min for 2 hours. Subsequently, a soil sample
was analyzed previous to each inoculation. On September
25th to October 12th, the contaminated mass was irrigated
every day for 2 hours at a rate of 20 l/m and 3 times in
the week of October 14th, 1990 at a rate of 20 l/m for 2
hours. The last spraying was done on Friday, October
l9th, 1990 at a rate of 20 l/m for 2 hours. The spraying
rate was augmented to increase the concentration of
microorganisms in the contaminated pile toward the final
stages of the decontamination process to enhance
degradation probabilities as the contaminant concentration
had been reduced to relatively low levels.
The pile was turned every 2 to 3 weeks,
depending on the compaction state of the pile and the
availability of the required machinery.
From September 14th, 1990, a heating element was
introduced to maintain the temperature of the contaminated
pile at a suitable level. The heating was controlled by
a thermostat so that the air provided to the contaminated
soil did not exceed 25C. Heating was required until the
end of the decontamination process on November 15th, 1990.
Certain sediments have a tendency to end-up in
the recovery reservoir but they are recirculated after
spraying. In fact, after spraying, allowing the pump to
be constantly operated in the reservoir, homogenizes the
2Q43948
medium. Finally, it is to be noted that during the hot
summer months, operation losses were compensated by
filling the reservoir with fresh water. The results
obtained are shown in Table 3.
TABLE 3
# DATES DAYSPCP O & G WASHINGS
SiteIppm) (ppm) PCP (ppm)
1 900707 0 115 700 n/d
2 900714 7 51,4 600 n~d
3 900718 11 36,4 400 n/d
4 900727 20 8,0 n/d 7,6
900810 34 7,4 n/d n/d
6 900817 41 13,8 300 n/d
7 900829 53 10,8 n/d n/d
8 900907 62 13,6 n/d n/d
9 900914 69 12,7 n/d 0,6
900925 80 6,6 n/d n/d
11 901001 86 6,5 n/d 0,25
12 901009 94 4,5 n/d n/d
13 901015 100 4,6 n/d 0,02
14 901026 111 3,5 n/d n/d
901115 131 1,9* n/d n/d
* NOVALAB Analysis, Montreal.
Note 1: In average, the soil fraction is equal or lower
than 2,38 mm (fraction on which the analysis
were conducted) represented in weight 35% of the
samples. 2/3 of the soil is thus constituted by
large particles.
Note 2: The analysis methods are the following:
- For PCP: EPA 8040
- For oil and greases: Standard Methods 503,
A & E.-
n/d: non-detectable.
2Q1 t~g~
~- -40-
Figures 10-12 respectively show the reduction in
PCP concentration in the contaminated pile, the reduction
in oil and greases and the reduction in PCP concentration
in the washings. It can be seen from the table that the
inoculations made between the beginning of August and mid-
September had a relatively low efficiency as the
contamination level of about 10-12 ppm appeared to be
maintained. The use of a co-substrate in the contaminated
mass helped to provide optimal bacterial activity and this
allowed further decrease in PCP level.
Concentration levels of oils and grease in the
contaminated mass also decreased with time. Since a
concentration of 300 mg/kg is well under residential
criteria for the province of Quebec, measurement of this
parameter was interrupted at this level. The few
measurements provided demonstrate the possibility of
obtaining relatively efficient elimination of oil and
grease contaminants in soil through biotreatment.
Analysis of the washings from the treated pile
showed a decrease in the presence of PCPs as the
decontamination process proceeded to completion. The last
analysis performed indicated a PCP level of 0.02 mg/l in
the washing. This concentration usually meets standard
waste levels recommended by Canadian cities for phenol.
Oxygenation of the reservoir provided means to further
degrade residual PCPs in the washings.
2Q ~?~9~8
- -41-
Hence, the final analyses indicated a 1.9 ppm
residual concentration in PCP, which is substantially
under the 5 ppm norm indicated for industrial lands in the
province of Quebec. All the analyses were performed on
soil particles having 2.3 mm or less in size. The results
obtained are therefore overestimated as soil particles of
this size represent only 1/3 of the total weight of the
contaminated mass while practically containing all the PCP
contaminants. Whereas the smaller particles retain
contaminants through absorption and adsorption, larger
particles are only slightly affected because of a
surfacetvolume ratio that is much smaller. Also, large
particles are relatively easy to treat through repeated
washings. In fact, if one considers the soil to be
treated as a single entity, it would seem realistic to
conclude that its actual decontamination level could be
closer to three times lower than the levels indicated in
Table 3.
A reduction in PCP concentration in contaminated
soil from 115 ppm to 1.9 ppm was achieved. This
represents a contaminant reduction rate of 98% over a four
month period. This is much higher than what has been
previously reported in the prior art and would appear to
open up new possibilities for efficient biological
degradation of highly undesirable contaminants.
Claims to the invention follow.
