U.S. patent application number 09/047339 was filed with the patent office on 2002-01-24 for method for soil remediation.
Invention is credited to KAWAGUCHI, MASAHIRO, SUGAWA, ETSUKO.
Application Number | 20020009332 09/047339 |
Document ID | / |
Family ID | 27282418 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020009332 |
Kind Code |
A1 |
SUGAWA, ETSUKO ; et
al. |
January 24, 2002 |
METHOD FOR SOIL REMEDIATION
Abstract
The present invention provides a method for remedying soil
containing a region polluted with a pollutant which comprises a
step of injecting into the soil a liquid containing a microorganism
having an activity to decompose the pollutant or a liquid
containing the microorganism and an activation agent for the
microorganism decomposing the pollutant, wherein the step comprises
isolating the region from surrounding soil with a barrier made of a
material that does not allow the pollutant, the microorganism, the
activation agent or water to pass through, and replacing void water
in the isolated region with said liquid.
Inventors: |
SUGAWA, ETSUKO; (ATSUGI-SHI,
JP) ; KAWAGUCHI, MASAHIRO; (ATSUGI-SHI, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
27282418 |
Appl. No.: |
09/047339 |
Filed: |
March 25, 1998 |
Current U.S.
Class: |
405/129.65 ;
405/128.7; 435/262.5 |
Current CPC
Class: |
B09C 1/10 20130101 |
Class at
Publication: |
405/129.65 ;
405/128.7; 435/262.5 |
International
Class: |
B09B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 1997 |
JP |
9-073806 |
Jan 30, 1998 |
JP |
10-018928 |
Mar 20, 1998 |
JP |
10-071995 |
Claims
What is claimed is:
1. A method for remedying soil containing a region polluted with a
pollutant comprising a step of injecting into the soil a liquid
containing a microorganism having an activity to decompose the
pollutant or a liquid containing a microorganism having ability to
decompose the pollutant and an activation agent for the
microorganism, wherein the step comprises: separating the region
from the surrounding soil with a barrier made of a material that
does not allow the pollutant, the microorganism, the activation
agent or water to pass through; and replacing void water in the
isolated region with the liquid.
2. The method according to claim 1, wherein the activation agent
contains at least one of a nutrient and an inducer for the
microorganism.
3. The method according to claim 1, wherein the activation agent is
a culture medium which does not contain a carbon source for said
microorganism.
4. The method according to claim 1, wherein said pollutant is a
hydrocarbon.
5. The method according to claim 4, wherein the hydrocarbon is at
least one of chlorinated aliphatic hydrocarbon compounds and
aromatic compounds.
6. The method according to claim 5, wherein the chlorinated
aliphatic hydrocarbon is at least one of dichloroethylene,
trichloroethylene and tetrachloroethylene.
7. The method according to claim 1, wherein the method further
includes a step for trapping and decomposing the pollutant that has
been driven out of said region by injecting the liquid.
8. The method according to claim 1, wherein the method includes a
step for previously exposing the liquid to oxygen or air prior to
injecting the liquid into the region.
9. The method according to claim 1, wherein the microorganism in a
state of the highest degradation activity for the pollutant is
injected into the region.
10. A method for remedying soil containing a region polluted with a
pollutant comprising a step of injecting into the soil a liquid
containing a microorganism having an activity to decompose the
pollutant or a liquid containing the microorganism and an
activation agent for the microorganism to make the microorganism
decompose the pollutant, wherein the step comprises: separating the
region from the surrounding soil with a barrier made of a material
that does not allow the pollutant, the microorganism, the
activation agent or water to pass through; and injecting into the
region the liquid in an amount 1.1 times or more a void volume of
the isolated region.
11. The method according to claim 10, wherein the liquid is
injected in an amount 1.2 times or more the void volume of the
isolated region.
12. The method according to claim 10, wherein the activation agent
contains at least one of a nutrient and an inducer for the
microorganism.
13. The method according to claim 10, wherein the activation agent
is a culture medium not containing any carbon source for the
microorganism.
14. The method according to claim 10, wherein the pollutant is a
hydrocarbon.
15. The method according to claim 14, wherein the hydrocarbon is at
least one of a chlorinated aliphatic hydrocarbon compound and an
aromatic compound.
16. The method according to claim 15, wherein the chlorinated
aliphatic hydrocarbon compound is at least one of dichloroethylene,
trichloroethylene and tetrachloroethylene.
17. The method according to claim 10, wherein the method further
comprises a step for trapping and decomposing the pollutant driven
off of the region by injecting the liquid.
18. The method according to claim 10, wherein the method further
comprises a step for exposing the liquid to oxygen or air prior to
injecting the liquid into the region.
19. The method according to claim 10, wherein the microorganism in
a state of a highest degradation activity for the pollutant is
injected into the region.
20. A method for remedying a soil polluted with a pollutant
comprising a step of taking the soil in a treatment vessel to
decompose said pollutant by introducing a liquid containing a
microorganism capable of decomposing the pollutant or a liquid
containing the microorganism or an activation agent for the
microorganism, wherein the treatment vessel is composed of a
material that does not allow the pollutant, microorganism, the
activation agent or water to pass through, and the liquid is
injected to replace void water in the soil in the vessel with the
liquid.
21. The method according to claim 20, wherein the pollutant is a
hydrocarbon.
22. The method according to claim 21, wherein the hydrocarbon
includes at least one of an aliphatic chlorinated hydrocarbon
compound and an aromatic hydrocarbon compound.
23. The method according to claim 22, wherein the aliphatic
chlorinated hydrocarbon compound includes at least one of
dichloroethylene, trichloroethylene and tetrachloroethylene.
24. The method according to claim 20, wherein the liquid is
introduced in an amount exceeding the void volume of the soil.
25. The method according to claim 24, wherein the liquid is
introduced in an amount 1.1 times the void volume of the soil.
26. The method according to claim 24, wherein the liquid is
introduced in an amount 1.2 times the void volume of the soil.
27. The method according to claim 20, wherein the liquid contains
an activation agent for the microorganism.
28. The method according to claim 27, wherein the activation agent
is a nutrient for the microorganism or an inducer for the
microorganism to express an ability to degrade the pollutant.
29. The method according to claim 27, wherein the activation agent
contains a culture medium not containing any carbon source.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for remedying
polluted soil. In more detail, this invention relates to a method
for remedying polluted soil in which the pollutant in the polluted
region is decomposed by microbial activities.
[0003] 2. Related Background Art
[0004] Recent rapid developments in science and technology have
produced a vast amount of chemicals and chemical products. These
substances are polluting nature slowly accumulating in the
environment. Environmental pollution is a serious problem spreading
all over the world since water and the air are circulating in the
environment. Examples of hitherto known pollutants are chlorinated
organic compounds (such as dichloroethylene (DCE),
trichloroethylene (TCE), tetrachloroethylene (PCE) and dioxin),
aromatic compounds (such as toluene, xylene and benzene) and fuels
such as gasoline. Chlorinated aliphatic hydrocarbon compounds (such
as dichloroethylene, trichloroethylene and tetrachloroethylene) are
especially used in a large amount as a solvent for cleaning
precision machine members and for dry cleaning, and pollution of
soil and ground water by these solvents have been revealed. In
addition, these organic compounds are so volatile that they may
cause air pollution. It is also pointed out that these organic
compounds are teratogenic and carcinogenic, so that it becomes
evident that they seriously affect living creatures. Accordingly,
an urgent theme is not only to cut off the pollution sources but
also to clean the soil and ground water already polluted with these
organic compounds.
[0005] One of the conventional methods for remedying the soil
polluted with chlorinated organic compounds is, for example, to
scoop out the polluted soil and subject it to a heat treatment.
Although this method enables complete elimination of pollutants
from the dug up soil, it requires much expenses and a long working
period for turning up the soil. It is practically impossible to
take out the polluted soil situated deep under the ground, limiting
the application range of this method. In addition, the chlorinated
organic compounds released from the dug up polluted soil should be
recovered by adsorption onto an adsorbent such as activated
charcoal to prevent secondary air pollution, and the used activated
charcoal requires further processing. For example, when the used
activated charcoal which adsorbed chlorinated compounds such as
DCE, TCE and PCE is incinerated, more poisonous by-products such as
phosgene may be generated. Accordingly, the final processing cost
is predicted to be enormous because of the necessary additional
steps to make the recovered pollutants harmless.
[0006] Vacuum-extraction of the pollutants from the polluted soil
or use of a microorganism having pollutant-degrading ability can
solve one of the problem of the above-mentioned method, i.e.,
limitations of the treating region. These methods do not require to
dig up the soil and can purify the soil at the location where it is
(called "in situ" hereinafter). Actually, these method are cheap
and simple compared with the foregoing dig-up method; only
small-scale work is required such as boring a well for introducing
a vacuum extraction pipe or pollutant-degrading microorganisms into
the polluted soil. The vacuum extraction method has problems that
it cannot remove chlorinated organic compounds in a low
concentration of several ppm or less efficiently, and that further
treatment of the recovered chlorinated organic compounds is
required as in the above-mentioned method.
[0007] On the other hand, the pollutant in soil can be degraded
into harmless substance(s) by the microbial remediation method
using microorganisms native or foreign to the soil. Thus, the
microbial method dispenses the detoxification treatment of the
recovered pollutant that is indispensable in the foregoing two
methods. In addition, this method is highly efficient in degrading
pollutant of a relatively low concentration.
[0008] Accordingly, now the microbial remediation method is
attracting attentions.
[0009] When the native microorganisms (inherently living in the
region to be remedied) are used in the remediation method, it is
necessary to supply the soil region to be treated with activating
agents such as inducers to induce degradation activity of the
native microorganisms, nutrients to enhance the microbial
degradation activity, oxygen and growth stimulating agents. When a
foreign microorganism having the pollutant-degrading ability is
used, it is necessary to introduce into the soil the microorganism
and if necessary activating agents for that microorganism.
[0010] In both cases, it is preferable to introduce the
microorganism or the activating agent in the soil as even as
possible. Usually, soil structure is not so uniform as to allow
uniform diffusion of a liquid containing the microorganism and
activating agent into the soil. For the purpose of solving these
technical problems, the inventors of the present invention have
disclosed an art for uniform distribution in the soil of the
injected liquid containing a microorganism and a microbial
activating agent. Japanese Laid-Open Patent Application No.
8-224566.
SUMMARY OF THE INVENTION
[0011] The inventors of the present invention has found that when a
liquid containing a microorganism and an activation agent is
injected into the soil, a portion of the pollutant present in the
voids (pores) of the soil may be pushed out according to the
injection, and move along the diffusion of the liquid, so that the
polluted region may be expanded by the liquid injection. This
tendency is more evident with volatile pollutants such as DCE, TCE
and PCE. Therefore, enlargement of the polluted region due to the
liquid injection should be prevented as much as possible
irrespective of the pollutant concentrations, especially in in situ
remediation of the soil. As a conclusion, a technical development
has been required to solve this problem.
[0012] Further studying how to solve the technical problems
hitherto described, the inventors of the present invention found a
method for remedying the soil which completes remediation of the
soil in the closed space by isolating the polluted region in situ
from the surrounding soil, or substantially enclosing the soil
within a closed space.
[0013] The object of the present invention, based on the findings
of the inventors of the present invention, is to provide a method
for carrying out high remediation of the soil while preventing
enlargement of the polluted region.
[0014] In accordance with one embodiment of the present invention,
there is provided a method for remedying soil containing a region
polluted with a pollutant which comprises a step of injecting into
the soil a liquid containing a microorganism having an activity to
decompose the pollutant or a liquid containing a microorganism
having ability to decompose the pollutant and an activation agent
for the microorganism, wherein the step comprises:
[0015] isolating the region from surrounding soil with a barrier
made of a material that does not allow the pollutant, the
microorganism, the activation agent or water to pass through;
and
[0016] replacing void water in the isolated region with said
liquid.
[0017] In accordance with another embodiment to achieve the
foregoing object, the present invention provides a method for
remedying soil containing a region polluted with a pollutant
comprising a step of injecting into the soil a liquid containing a
microorganism having an activity to decompose the pollutant or a
liquid containing a microorganism having ability to decompose the
pollutant and an activation agent for the microorganism, wherein
the step comprises:
[0018] separating the region from the surrounding soil with a
barrier made of a material that does not allow the pollutant, the
microorganism, the activation agent or water to pass through;
and
[0019] injecting into the region the liquid in an amount 1.1 times
or more a volume of the void of the isolated region.
[0020] In accordance with the other embodiment, the present
invention provides a method for remedying a soil polluted with a
pollutant comprising a step of taking the soil in a treatment
vessel to decompose the pollutant by introducing a liquid
containing a microorganism capable of decomposing the pollutant or
a liquid containing the microorganism and an activation agent for
the microorganism, wherein the treatment vessel is composed of a
material that does not allow the pollutant, microorganism, the
activation agent or water to pass through, and the liquid is
injected to replace void water in the soil in the vessel with the
liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a schematic drawing of a treatment system.
[0022] FIG. 2 is an illustrative drawing of the method for
hardening the soil.
[0023] FIG. 3 is an illustrative drawing of the test apparatus used
in Example 1.
[0024] FIG. 4 is a schematic drawing showing an example of a system
for carrying out the present invention.
[0025] FIG. 5 is a graph showing TCE decomposition in Example 1,
and Comparative Examples 1 and 2.
[0026] FIG. 6 is a graph showing TCE decomposition in Example 1,
and Comparative Examples 1 and 2.
[0027] FIG. 7 is a graph showing TCE decomposition in Example 1,
and Comparative Examples 1 and 2.
[0028] FIG. 8 is a graph showing TCE concentrations in the sample
collected from the sampling hole 34 in Example 2.
[0029] FIG. 9 is a graph showing TCE concentrations in the sample
collected from the sampling port 35 in Example 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] [Outline of Remediation System]
[0031] With reference to the schematic drawing of FIG. 1, a
remediation system for the polluted soil is explained. The
treatment vessel 8 for pollutant decomposition installed at a site
of the soil pollution is composed of a side wall 1, a bottom 7 and
a lid 2. The treatment vessel 8 contains the polluted soil to
isolate the soil from the surrounding soil. The lid 2 is provided
with two opening 3 and 4, and a liquid injection pipe 5 is inserted
into the vessel 8 though the opening 3 to inject a liquid
containing a microorganism or a liquid containing a microorganism
and an activation agent into the soil for soil remediation. One end
of the liquid injection pipe 5 is inserted into the soil 9 in the
treatment vessel 8 to inject the liquid into it. The other end of
the pipe 5 is connected to a tank 11 containing the liquid. The
liquid is injected into the soil 9 with a pump 10 disposed on way
of the pipe 5.
[0032] A discharge pipe 6 is inserted into the treatment tank 8
through an opening 4 to lead the pollutant or the overflowing
liquid into a pollutant decomposition apparatus 12, where the
pollutant retained in the soil void is pushed out by an applied
pressure due to the liquid injection from the injection pipe 5. A
trap 13 is provided to prevent the discharge of the pollutant from
the pollutant decomposition apparatus 12 into the air.
[0033] It is preferable to construct the pollutant decomposition
treatment vessel 8 so as to enclose the pollution source or the
highly polluted soil in situ (where the soil to be treated exists).
This enables not only efficient remediation of the soil but also
prevention of the diffusion of the pollution. When there is a flow
of ground water, it is effective in preventing spread of pollution
to install the treatment vessel as upstream as possible. The shape
and construction method of the side wall 1 is not limited as long
as the wall is made of a material not permeable by water,
microorganisms and pollutants. For example, an iron pipe may be
driven into the polluted soil to form a iron pipe side wall 1, or
the side wall 1 may be formed by driving four iron plates into the
soil as side walls.
[0034] [Bottom Formation]
[0035] The bottom 7 can be formed, for example, by injecting a soil
hardening agent to harden the soil at the bottom. To form the
bottom, after the steel pipe is driven into the treatment site or
after four steel plates were driven into the site, a soil hardening
agent is injected into the bottom of the region in the pipe or
surrounded by the steel plates. Examples of the soil hardening
agent are water glass, rapidly hardening cement, normal cement and
special purpose cement, which may be properly selected according to
the conditions of the site or the purpose. Admixtures such as
montmorillonite, calcium, an anionic polymer surface active agent
and/or a fluidity accelerating agent may be added to the soil
hardening agent. When the pollutant is a volatile compound such as
a chlorinated aliphatic hydrocarbon compound (for example,
dichloroethylene, trichloroethylene or tetrachloroethylene), it is
preferable to use an water glass type soil hardening agent not
permeable by these compounds.
[0036] [Injection of Hardening Agent]
[0037] Examples of the injection method of the hardening agent into
the ground are the CCP method, jet-grout method and roden jet pile
method. Although these methods can be appropriately selected
depending on the region of the polluted soil and conditions of the
ground, CCP method is preferable since this method enables
injection of the soil hardening agent without outflow of the
polluted soil, thus dispensing the treatment of the outflow.
[0038] The CCP method in forming the bottom of the polluted soil to
be treated by injecting the hardening agent at a high pressure is
described referring to FIG. 2. A rod 57 to which a special jet
equipment is mounted is attached to a boring machine 56, and the
other end of the special jet equipment is connected to a
circulation water tank 60 via a super-high pressure pulse pump 58
and a valve 59. The ground is bored to a depth of injection
position with a rotation speed and a stroke number suitable for the
soil conditions, while continuously sending the circulation water
by keeping the pump discharge pressure at, for example, 30
Kgf/cm.sup.2 or less. When reached to a desired depth, the rod is
disconnected from the circulation water tank and connected to the
soil hardening agent tank 61 by valve operation to inject the soil
hardening agent, for example, at a rotation speed of 10 to 20 rpm
and a discharge pressure of 200 to 400 Kgf/cm.sup.2. The pollutant
decomposing microorganism may be injected, for example, from the
rod connected to the microorganism storage tank 62 and pump 58, or
it may be injected by driving a separate injection pipe into the
treatment region.
[0039] When the construction site has a water impermeable layer
such as a rock-bed, the layer itself may be used as the bottom
7.
[0040] [Top Construction of Treatment Vessel]
[0041] It is preferable that the top of the treatment vessel is a
sealed structure by providing a lid made of the same material not
permeable by the pollutant as the side wall, not to release into
the air the pollutant rising to the earth surface forced by the
rising front of the injected liquid. Diffusion of the pollutant
into the environment from the treatment vessel 8 due to injection
of the liquid can be almost perfectly prevented by constructing
such a treatment vessel at the site of the pollution. It can also
prevent the pollutant-decomposing microorganism and the activation
agent such as a nutrient or an inducer for the microorganism from
diffusing into the environment.
[0042] [Pollutant Decomposition Equipment 12]
[0043] Examples of the decomposition apparatus 12 to decompose the
pollutant extruded from the soil 9 are a bioreactor filled with a
pollutant-decomposing microorganism immobilized on a carrier, a
bioreactor containing a liquid containing a pollutant-decomposing
microorganism to which polluted gas or polluted soil water is
introduced, or a chemical decomposition apparatus using ultraviolet
light or iron.
[0044] [Remediation Method]
[0045] Application of the method according to one embodiment of the
present invention to a remediation method in which microorganism is
introduced into the soil containing the pollutant will be explained
hereinafter.
[0046] The pollutant-degradable microorganism grown in the
fermentation tank 11, together with a liquid medium, is introduced
into the pollutant decomposition treatment vessel 8 through the
injection pipe 5. The injection position and injection method may
be properly selected depending on the soil texture and
consolidation. For example, the liquid medium can be sent up from
the bottom of the treatment vessel using a pump, or it can flow
down from the top of the treatment vessel by hydrostatic pressure.
The liquid medium to be injected into the soil may contain an
activation agent for the microorganism. As the activation agent,
there is a growth medium containing nutrients for the microorganism
or an inducer for the microbial expression of the
pollutant-degrading activity.
[0047] When the pollutant is a volatile compound such as DCE, TCE
or PCE, it is preferable to fill the treatment vessel with the
liquid medium containing microorganism by injecting it from the
bottom of the treatment vessel, so as to achieve soil remediation
more efficiently. The volatile pollutant retained in the soil void
is pushed up by the liquid front, and part of the pollutant moves
toward the earth surface to finally seep from the surface as a gas
or mixed with the liquid. According to the embodiment of the
present invention, however, the extruded pollutant from the soil by
the injected liquid will be guided to the pollutant decomposition
apparatus 12 through the pipe 6 to be decomposed there. The
pollutant remaining in the soil void not excluded by the injected
liquid is decomposed by the microorganism injected into the soil.
Thus, a much higher remediation of the soil is attained according
to the embodiment of the present invention. The number of the
injection port is not limited to one so long as the microorganism
can be distributed in the vessel as uniform as possible. When a
plurality of the injection ports are used, however, it is
preferable that the ports are disposed, for example, upward to the
earth surface so that the pollutant driven by the injection front
can be trapped securely. It is also desirable that the position and
shape of the drainage port for the overflow is properly devised
depending on the injection method.
[0048] The microorganism to be injected into the treatment vessel
has an activity to degrade the pollutant. For example, when the
pollutant is an aromatic compound such as phenol or a halogenated
aliphatic hydrocarbon compound such as DCE, TCE or PCE, a bacterial
strain such as Pseudomonas cepacia strain KK01 (FERM BP-4235),
strain J1 (FERM BP-5102), strain JM1 (FERM BP-5352), strain JMC1
(FERM BP-5960), strain JM2N (FERM BP-5961), strain JM6U (FERM
BP-5962) and strain JM7 (FERM BP-5963) can be used. When the
pollutant is a petroleum fuel, the present invention can be
practiced using, for example, an Alcaligenes species, strain SM8-4L
(FERM P-13801).
[0049] It is preferable that the microorganism for the injection is
in a state having high pollutant-degrading activity by cultivation.
Since the microorganism usually shows the highest degradation
activity to the pollutant in its logarithmic growth phase, it is
preferable to introduce the microorganism in the logarithmic growth
phase into the soil containing the pollutant.
[0050] Meanwhile, degrading chlorinated aliphatic hydrocarbon
compounds, the microorganism is often damaged by the intermediate
products. In such a case, the higher the concentration of the
pollutant is, the more seriously the microorganism is damaged
accompanied by the decrease in decomposition activity. One can
solve such a problem according to the method of the present
invention, that is, when the soil to be treated contains a high
concentration of a pollutant in a treating vessel, an excess amount
of a liquid medium containing the pollutant-degrading microorganism
is injected into the vessel through the injection pipe 5 to fill
all the void in the soil with the medium, thereby extruding the
inherent soil water from the soil in the vessel. Since a liquid
medium injected into the soil migrates through the soil while
partly diluted with the inherent soil water, when the liquid medium
is injected into the treatment vessel in a volume larger than the
total soil void volume in the treatment vessel, it pushes out the
inherent void water from the soil void and further pushes out the
void water diluted with the liquid medium. Thus, extruding water
containing the pollutant in a high concentration from the soil to
be treated, which decreases the concentration of the pollutant in
the soil thus lessens the damage to the microorganism. This also
enables uniform distribution of the liquid medium into the soil in
the treatment vessel.
[0051] The optimum injection amount of the liquid medium containing
the microorganism depends on the soil properties, e.g., moisture
content of the soil, it is preferable that the injection volume is
1.1 times or more, more preferably 1.2 times or more, the total
volume of the soil void. When the injection volume is determined as
described above, a part of the pollutant present in a high
concentration in the soil is washed out along with the overflow of
the injected medium, thereby decreasing the pollutant concentration
in the soil. This procedure lessens the damage of the microorganism
due to the pollutant itself or its intermediate products in
degradation, enabling treatment of the region containing the
pollutant in a high concentration.
[0052] The volume of the void (Vv) of the soil in a given region
can be determined by the following equation (1):
Vv=V-100.multidot.W/((100+.omega.).multidot..gamma.s) (1)
[0053] In the equation (1), V is the total volume of the soil, W is
the total weight of the soil, .omega. is the moisture content of
the soil and .gamma.s is the specific gravity of the soil particles
( of the solid matter). The total weight of the soil can be
determined by multiplying the weight of a unit volume by the volume
of the soil of the region, the former being determined by a
conventional method (for example, a direct measurement method or a
replacement measurement method).
[0054] The moisture content of the soil is determined, for example,
as follows. A prescribed amount of soil is taken from the soil and
placed in a watch glass to weigh the total weight (Wt) (the sum of
the weights of the watch glass (Wp), the soil particles (dry
weight) (Ws) and moisture contained in the soil sample (Ww)). After
drying the soil sample at about 110.degree. C. for 24 hours, it is
weighed again, the weight Wa=Wp+Ws. Therefore, the moisture content
of the soil sample (.omega.) is calculated as follows:
.omega.=100Ww/Ws=100(Wt-Wa)/(Wa-Wp)
[0055] The specific gravity of the soil particles is determined,
for example, as follows. A pycnometer of an inner volume of Vp and
of a weight of Wp is filled with distilled water and its weight
(Wc) is measured, where Wc=Wp+.gamma..sub.WYp (.gamma..sub.W
represents the weight of a unit volume of water). Then, this
pycnometer is filled with the soil sample and water. After
thoroughly deaerated, the total weight (Wt) is expressed by the
following equation (2):
Wt=Wp+(Vp-Vs).gamma..sub.W+Ws (2)
[0056] where Vs is the volume of the soil particles (solid) in the
soil sample and Ws is the dry matter weight of the soil sample. The
specific gravity (Gs) determined by dividing the weight of the unit
volume of the sample soil .gamma.s (=Ws/Vs) by the weight of the
unit volume of water is generally used as the specific gravity of
the soil. Accordingly, the above equation (2) can be converted
to:
Wt-Wp+(Vp-(Ws/Gs.gamma..sub.W)).gamma..sub.W+Ws=Wc +(1-1/Gs)Ws
(3)
[0057] Thus, after the soil sample is taken out from the pycnometer
and dried to determine the dry matter weight Ws, the specific
gravity of the sample soil can be determined using the following
equation (4).
Gs=Ws/(Ws+Wc-Wt) (4)
[0058] It is desirable to collect the soil samples from a plurality
of places for determining the void volume of the isolated soil
region, since construction of the soil isolated by the barrier is
not always uniform. The average of the soil void volumes of the
samples taken from a plurality of places may be used as the void
volume of the isolated soil. When the value of the soil void volume
varies greatly among samples, it is preferable to increase the
sampling number. When the presence of soil layers containing soil
particles of different nature is predicted or known in the isolated
soil region, one can investigate the soil layer constitution
previously to determine respective soil void volume, and use the
sum of the void volumes of soil layers as the total soil void
volume.
[0059] When a microorganism showing the highest activity and in its
logarithmic growth phase is used, the cells consume a large amount
of oxygen in the soil of the treatment vessel. Accordingly, the
oxygen concentration in the soil may rapidly decrease immediately
after the microorganism is introduced. Such decrease in oxygen
concentration may cause decrease in pollutant-decomposing activity
of the microorganism. Therefore, for effective remediation of the
soil, it is preferable to aerate the liquid medium to be injected
with the microorganism into the treatment vessel, with a sufficient
amount of oxygen or air. Otherwise, when the liquid medium to be
injected into the soil contains some nutrients as an activation
agent for the growth of the microorganism, it is effective in soil
remediation to lower the nutrient concentration in order to
suppress the microbial growth in the soil, or to eliminate the
carbon source for the microorganism to substantially halt the
growth of the microorganism in the soil.
[0060] As hitherto described, according to one embodiment of the
present invention, an environment polluted with a high
concentration of a pollutant can be effectively remedied by using a
microorganism. It can also suppress the efflux of the pollutant,
the microorganism and the activation agent for the microorganism
outside the environment to be remedied. According to the other
embodiment of the present invention, more improved remediation of
the polluted environment is possible in addition to the foregoing
advantages.
[0061] Although the present invention will be described in detail
referring to the examples, it is by no means limited thereto.
EXAMPLE 1
[0062] An experimental apparatus as shown in FIG. 3 was assembled
for this example. A 2 litters stainless steel vessel 14 with a lid
was prepared. The contact faces of the vessel 14 and lid 15 were
mirror-polished and a Teflon O-ring 20 was used for sealing up the
vessel. An injection port 16 for the microorganism introduction, a
discharge port 17 and a port 18 for sampling were provided on the
lid 15 and a Teflon tube was attached to the discharge port 17 and
fixed by means of a Teflon seal. Teflon coated rubber was attached
to the sampling port.
[0063] Gravel with a mean diameter of 1 cm was put in the stainless
vessel to a thickness of about 4 cm. The gravel layer 22 was formed
so that its moisture content and porosity (void ratio) were zero
and 53% respectively. Then, the microorganism injection pipe 19 was
driven into the gravel layer 22. Next, 2932 g of fine sand of a
specific gravity of 2.7 was filled so that the moisture content and
the void ratio of the sand layer be 14% and 40% respectively. A
layer of gravel with a mean diameter of 1 cm was further formed on
the sand layer up to the top face of the stainless steel vessel.
The gravel layer also had a moisture content of zero and a void
ratio of 53%. The void volume of the soil in the stainless steel
vessel is determined as follows:
[0064] For the sand layer 21, the following equation can be applied
where its moisture content is 14% and 2932 g of sands of a specific
gravity of 2.7 were used.
[0065] Weight of fine sand (Ws)+Weight of moisture in the fine sand
layer (Ww)=2932 g
[0066] Moisture content (.omega.=100 Ww/Ws)=14
[0067] Specific gravity (Ws/Vs)=2.7
[0068] From the above, the volume (Vs) of fine sand particles in
the fine sand layer is calculated:
Vs=2932.times.100/(2.7(100+14))=952.57(cm.sup.3)
[0069] The void ratio is expressed by: Total volume of the fine
sand layer (V)-Vs)/Total volume of the fine sand layer and
(V-Vs)/V=0.4, then;
V=Vs/0.6=952.57/0.6=1587.6(cm.sup.3)
[0070] and
[0071] The void volume (Vv) of the sand layer=0.4
V=0.4.times.1587.6=635 (cm.sup.3)
[0072] Since the volume of the gravel layer is expressed by the
difference between the volume of the stainless steel vessel and the
volume of the fine sand layer, the volume is calculated as:
2000-1587.6=412.4 (cm.sup.3).
[0073] Since the void ratio of the gravel layer is 53%, the volume
of the void is calculated as: 412.4.times.0.53=218.5 (cm.sup.3).
Therefore, the total void volume of the soil in the stainless steel
vessel is: 635+218.5=853.5 (cm.sup.3).
[0074] The lid 15 was then set up on the stainless steel vessel 14.
The microorganism-injection pipe 19 was passed through the
microorganism-injection port 16 on the lid 15, and the connection
part was sealed with a Teflon seal. The lid was fixed with vises to
ensure sealing of the vessel.
[0075] A reservoir 25 containing 500 ml of an aqueous solution of
50 ppm TCE 26 and a pump 24 were prepared. After connecting a
Teflon tube extending from the discharge port 17 through the
reservoir 25 to the microorganism-injection port 17 by means of a
pipe joint 27 as shown in FIG. 3, the fine sand in the vessel 14
was contaminated with a vapor of TCE sent from the reservoir by
means of the pump 24, at a rate of 1 litter/min. for 25 hours.
After disconnecting the TCE reservoir, a cultivation tank (not
shown) of a pollutant-decomposing strain JM1 (FERM BP-5352) was
connected to the microorganism-injection pipe 19 and the liquid
culture of strain JM1 was slowly injected by means of compressed
air. The injection volume (938.9 ml) was set to be 1.1 times as
much as the total void volume of the sand and injection was
continued until overflow of 445.4 ml (the presumed inherent soil
water present in the void of the sand: Ww=0.14 Ws=0.14.times.2.7
Vs=360 ml)+superfluous amount of the culture liquid medium (0.1
Vv=85.3 ml) flowed out from the discharge port 18. The JM1
cultivation tank was removed after injection and the injection port
and discharge port were sealed. All of the overflow was
collected.
[0076] Immediately after the injection and every 3 hours after, a
0.5 ml liquid sample was taken from each of three sampling ports by
inserting a syringe. Sampling points were the bottom (1 cm above
the bottom gravel layer), the middle (5 cm above the bottom
sampling point) and the top (5 cm above the middle sampling point)
of the sand layer. Each liquid sample was immediately placed in a
bottle containing 5 ml of n-hexane and, after stirring for 3
minutes, the n-hexane layer was collected to determine TCE
concentration by ECD gas-chromatography. The results are shown in
FIGS. 5 to 7 (FIG. 5: Top, FIG. 6: Middle, FIG. 7: Bottom of the
sand layer). The conditions of the culture of pollutant-degrading
microorganism are as follows:
[0077] A 3 day culture of strain JM1 (4.8.times.10.sup.8 cell/ml)
was diluted 2-fold with M9 medium and used for the injection.
1 M9 medium Na.sub.2HPO.sub.4 6.2 g/l KH.sub.2PO.sub.4 3.0 g/l NaCl
0.5 g/l NH.sub.4Cl 1.0 g/l Sodium L-glutamate 20 g/l
[0078] TCE concentration of the trapped overflow measured by the
same method as described above was 20 ppm, indicating that the
overflow contained TCE.
Comparative Example 1
[0079] A stainless steel vessel containing the soil polluted with
TCE was prepared as described in Example 1. The experiment was
carried out in the same manner as in Example 1, except that M 9
medium was used instead of JM1 culture. The results are also shown
in FIGS. 5 to 7.
Comparative Example 2
[0080] A stainless steel vessel containing the soil polluted with
TCE was prepared as shown in Example 1 and the experiment was
carried out in the same manner as in Example 1 except that the
injection of JM1 culture fluid was stopped when the liquid just
come out from the discharge port to prevent overflow, that is, the
injected amount of the culture was 493 ml (the soil void volume
(853.5 cm.sup.3) subtracted with the volume of the void water (360
ml)). TCE concentrations in the sand layer in the stainless steel
vessel were also measured by the same method as in Example 1. The
results are shown in FIGS. 5 to 7.
EXAMPLE 2
[0081] Formation of Pollutant-decomposition System in Simulated
Polluted Soil--Decomposition of TCE
[0082] A preliminary experiment was carried out for determining the
void volume of the soil to be used in the experimental system shown
in FIG. 4. A 36.6 litters stainless steel vessel 28 with a lid was
prepared. The contact faces of the vessel 28 and lid 29 were
mirror-polished and a Teflon O-ring 30 was used for sealing up the
vessel. A soil hardening agent-injection port 31,
microorganism-injection port 32 and TCE-introduction port 33, and
two discharge ports 34 and 35 were provided on the lid 29. A Teflon
tube was fixed to each discharge port with a Teflon seal. A
stainless steel pipe of 13 mm diameter, tapered and provided with
many holes of 1 mm diameter at its lower end, was use as the soil
hardening agent-injection pipe 36. An L-shaped stainless steel pipe
of 14 mm diameter, tapered at the end, was used as the
TCE-introduction pipe 37, where several holes of about 1 mm
diameter were provided in the lower part so as to inject TCE from
the bottom of the stainless steel vessel. A stainless steel pipe
with a diameter of 13 mm was also provided as the
microorganism-introduction pipe 38.
[0083] Gravel was spread at the bottom of the stainless steel
vessel to a height of about 4 cm to form a gravel layer 39. After
setting the TCE-introduction pipe 37 in the layer, fine sand 40 was
put in the stainless steel vessel 28 up to 200 mm from the top of
the stainless steel vessel 28, and an iron pipe 41 of 112 mm
diameter and 200 mm long was driven into the sand layer. To the
same depth as with the iron pipe 41, was driven a soil hardening
agent-injection pipe 36 into the sand layer. After further filling
the vessel with sand to a height of 180 mm from the top of the
stainless steel vessel 28, a microorganism-introducti- on pipe 38
was driven into the sand layer parallel to the soil hardening
agent-injection tube 26. Finally, the vessel was filled with sand
up to the rim. Gypsum 43 was injected around the soil hardening
agent-injection pipe 36, microorganism-introduction tube 38 and
TCE-introduction pipe 37 to fix them not to leave any space between
the sand and pipes. An iron lid 42 was set on the iron pipe 41 so
that the soil hardening agent injection tube 36 and microorganisms
injection tube 38 come through the lid, and the joints were fixed
with gypsum. Each pipe was inserted into the port provided on the
lid 29 of the stainless steel vessel and sealed with a Teflon seal.
The lid was fixed with vises and the tight sealing was confirmed.
The soil hardening agent-injection tube 36 was then connected to
the soil hardening agent tank 50 via a valve 47 and a booster pump
46. A soil hardening agent of water glass type (made by Nitto
Kagaku Co.) was used as a soil hardening agent. After injecting 400
ml of the soil hardening agent from the soil hardening agent tank
50 operating the booster pump 46 at a pressure of 5 kg/cm.sup.2,
the valve was closed and the stainless steel vessel was left
standing for 24 hours. Then, the lid 29 was removed and the iron
pipe 41 was withdrawn to find that the bottom of the iron pipe was
sealed with a hardened product of the water glass type hardening
agent. It was also confirmed that neither gaseous TCE, the liquid
medium containing the microorganism to be used in this example nor
water would not leak from the iron pipe 41.
[0084] The void volume of the soil region isolated from the
surrounding environment by the iron pipe 51 was first determined.
The soil volume was calculated as follows: (11.2/2
).sup.2.times.3.14.times.20=1969 cm.sup.3. The specific gravity,
moisture content and weight of the unit volume of the soil were
also determined using the samples randomly collected from three
points in the isolated soil region. The results were a specific
gravity of 2.7, a moisture content of 14% and an weight of the unit
volume of 1.86 g/cm.sup.3. There were no significant difference
among these values due to the difference of the sampling points.
Therefore, the total soil void volume of the isolated soil region
was calculated to be 779.1 cm.sup.3 from the foregoing equation
(1).
[0085] The test system shown in FIG. 4 was assembled by the same
method as described above. 500 ml of an aqueous solution of 400 ppm
TCE was put in a reservoir 44 and this reservoir 44 was connected
to the TCE-introduction port 33 via a pump 45 using a Teflon tube.
The reservoir 44 was also connected to the discharge ports 34 and
35 using Teflon tubes. Then, the pump 45 was operated to circulate
gaseous TCE at a rate of 1 litter/min. for 24 hours to contaminate
the sand in the vessel. After that, the Teflon tubes connected to
the two discharge ports were removed and an air sample was taken by
inserting a syringe through each discharge port into the sand layer
to a depth of 100 mm. TCE gas concentration was assayed by FID gas
chromatography (trade name: GC-14B, made by Shimadzu Co.). The
result showed that the gas concentrations were 985 ppm and 950 ppm
at the discharge ports 34 and 35, respectively.
[0086] After closing the valves 48 and 49 at the TCE-introduction
port 33 and microorganism-injection port 32, the soil hardening
agent-injection tube 36 was connected to the soil hardening agent
tank 50 via the valve 47 and booster pump 46. A water glass type
soil hardening agent (made by Nitto kagaku Co.) was used as the
soil hardening agent. After sending 400 ml of the soil hardening
agent from the soil hardening agent tank 50 with a booster pump 46
at 5 kg/cm.sup.2, the valve was closed. The vessel was left
standing for 24 hours. Then, the Teflon tubes connecting the
discharge ports 34 and 35 and the reservoir 44 were disconnected
from the reservoir tank 44 by switching the valve 56 and 57. The
Teflon tube extending from the discharge port 34 was connected to a
decomposition apparatus 53 containing 500 ml of the liquid culture
of strain JM1 (FERM BP-5352). The strain JM1 used in the
decomposition apparatus was grown by the same method as used for
soil injection. The Teflon tube connected to the discharge port 35
was connected to the activated carbon column 52.
[0087] Then the liquid culture of strain JM 1 (FERM BP-5352) in the
tank 51, grown in the same manner as in Example 1, was injected
into the isolated region from the pipe 38. The injection volume was
934.9 ml which is 1.2 times as much as the soil void volume. Upon
seeing the overflow of the liquid from the discharge port 34,
injection of the liquid was stopped. The gas exhausted from the
decomposition apparatus during injection was sampled from the
sampling port 55 and the TCE concentration in the gas was assayed
using an FID gas-chromatograph (trade name: GC 14B, made by
Shimadzu Co.), showing a concentration of below the detection
limit. After finishing the culture fluid injection, the valve 48 of
the microorganism-injection tube was closed and the Teflon tube
connected to the activated carbon column was removed, and Teflon
rubber stoppers were attached to ports 34 and 35 to make them
sampling ports.
[0088] An aliquot of 0.5 ml of the soil water was taken every 3
hours after the culture injection, by inserting a syringe from the
sampling port 34 into a depth of 100 mm, and TCE concentration was
assayed by the same method as in Example 1. Gaseous samples were
also collected from the sampling port 35 every 3 hours for TCE
assay by FID gas chromatography. The results are shown in FIGS. 8
and 9.
[0089] At the end of the experiment, an aliquot of 0.5 ml of the
liquid culture 54 in the decomposition apparatus 53 was collected
and, after extracting with n-hexane, TCE concentration was
determined by gas-chromatography. The TCE concentration was 0.01
ppm.
EXAMPLE 3
[0090] Two sets of simulated TCE polluted soil were prepared in the
same manner as in Example 1.
[0091] A colony of strain JM1 (FERM BP-5352) grown on M9 agar
medium containing 1 wt % of malic acid was transferred to M9 liquid
medium containing 1 wt % of sodium glutamate and cultured with
shaking at 15.degree. C. for 2 days. The cell concentration of the
liquid culture after 2 days' shaking culture was 6.times.10.sup.8
CFU/ml. This culture was diluted 2- and 4-fold with M9 medium
containing no carbon source and the dilutions were aerated with
oxygen gas for 10 minutes. Dilutions were injected into the soil in
the above prepared two vessels respectively, by the same method as
described in Example 1.
[0092] After the injection, the injection and discharge ports were
sealed and the vessel was left standing for 48 hours at 20.degree.
C. Using a syringe, samples of 0.5 ml soil water were taken from
three sampling points each provided 1 cm above the lower gravel
layer, 5 cm above the bottom sampling point and 5 cm above the
middle sampling point. Each of the samples was immediately placed
in vessels containing 5 ml n-hexane and stirred for 3 minutes. Then
the hexane layer was collected to determine the TCE content by ECD
gas-chromatography (trade name: GC 14B, made by Shimadzu Co.) The
results are shown in Table 1 and Table 2.
EXAMPLE 4
[0093] Two sets of simulated TCE polluted soil were prepared as in
Example 3. The culture liquid medium of the strain JM1 cultivated
under the same condition as in Example 3 was diluted 2- and 4-fold
with M9 culture medium containing no carbon source and aerated with
air for 10 minutes. These dilutions were injected into the vessels
containing the TCE polluted soil, and the TCE concentration in the
soil was measured by the same method as described in Example 3. The
results are shown in Table 1 and Table 2.
EXAMPLE 5
[0094] An experiment was carried by the same method as in Example
4, except that the culture dilutions to be injected were not
aerated. The results are shown in Table 1 and Table 2.
EXAMPLE 6
[0095] An experiment was carried by the same method as in Example
4, except that the injected culture dilutions of JM1 did not
overflow from the discharge port, and injection was stopped at the
point when the injected liquid appeared from the discharge port.
The results are shown in Table 1 and Table 2.
2TABLE 1 JM1 culture (2-fold dilution) Example 4 Example 3 (exposed
(exposed to to air for Example 5 Sampling oxygen for 10 (no point
10 minutes) minutes) aeration) Example 6 Top 0.03 (ppm) 0.08 (ppm)
0.23 (ppm) 1.10 (ppm) Middle 0.02 0.06 0.09 0.34 Bottom not 0.03
0.1 0.10 detected
[0096]
3TABLE 2 JM1 culture (4-fold dilution) Sampling point Example 3
Example 4 Example 5 Example 6 Top 0.05 (ppm) 0.09 (ppm) 0.12 2.15
(ppm) Middle 0.03 0.08 0.08 0.41 Bottom 0.03 0.05 0.07 0.15
[0097] It was confirmed from the results in Table 1 and Table 2
that a higher degree of soil remediation could be attained by
previously aerating the bacterial suspension to be injected into
the soil with oxygen or air. Moreover, by previously aerating the
culture fluid with oxygen or air and injecting the culture fluid at
a volume 1.2 times as much as the void volume of the soil to be
remedied, the top layer of which remediation is often difficult can
be more efficiently purified.
* * * * *