U.S. patent application number 10/662363 was filed with the patent office on 2004-07-01 for method for decomposing a pollutant.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Kato, Kinya, Kawaguchi, Masahiro, Kuriyama, Akira.
Application Number | 20040127764 10/662363 |
Document ID | / |
Family ID | 18682535 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040127764 |
Kind Code |
A1 |
Kuriyama, Akira ; et
al. |
July 1, 2004 |
Method for decomposing a pollutant
Abstract
In a process for decomposing pollutants by bringing pollutants
contained in air into contact with air that contains chlorine,
under irradiation by light, at least part of a chlorine-generating
solution present in a chlorine generation region is fed to a means
for forming the functional water by electrolysis to effect
regeneration and is again fed to the chlorine generation region.
Also disclosed is a pollutant decomposition system used in such a
process.
Inventors: |
Kuriyama, Akira; (Kanagawa,
JP) ; Kato, Kinya; (Kanagawa, JP) ; Kawaguchi,
Masahiro; (Kanagawa, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
TOKYO
JP
|
Family ID: |
18682535 |
Appl. No.: |
10/662363 |
Filed: |
September 16, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10662363 |
Sep 16, 2003 |
|
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|
09880760 |
Jun 15, 2001 |
|
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6699370 |
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Current U.S.
Class: |
588/316 |
Current CPC
Class: |
B01D 53/70 20130101;
Y02W 10/37 20150501; Y02C 20/30 20130101; B01D 53/007 20130101 |
Class at
Publication: |
588/205 |
International
Class: |
A62D 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2000 |
JP |
181636/2000 |
Claims
What is claimed is:
1. A method for decomposing a pollutant comprising: a supplying
step for supplying a chlorine-generating solution to a container
with a supply means; a chlorine-generating step for generating
chlorine from the chlorine-generating solution contained in the
container; an irradiation step for irradiating the pollutant mixed
with the chlorine; and a flowing step for flowing, from the
container to the supply means, the chlorine-generating solution
from which the chlorine is being generated or from which the
chlorine has already been generated, wherein the supplying step
adjusts the chlorine-generating solution returned from the
container and supplies the adjusted chlorine-generating solution to
the container.
2. The method according to claim 1, wherein the chlorine-generating
step generates chlorine by introducing a gas to the
chlorine-generating solution.
3. The method according to claim 1, further comprising a
neutralizing step for neutralizing the chlorine-generating solution
returned from the container.
4. The method according to claim 1, wherein the chlorine-generating
solution is an electrolyzed solution and is supplied to the
container in the supplying step.
5. The method according to claim 1, wherein the chlorine-generating
solution contains an inorganic acid and/or an organic acid.
6. The method according to claim 1, wherein a wavelength of the
light for irradiation is from 350 nm to 450 nm.
7. The method according to claim 1, further comprising an absorbing
step for absorbing an air containing the pollutant from soil.
8. The method according to claim 1, further comprising an obtaining
step for obtaining a gaseous pollutant from underground water.
9. The method according to claim 1, wherein the pollutant is an
organochlorine compound.
10. The method according to claim 1, wherein the
chlorine-generating solution returned from the container is
neutralized with alkaline water.
11. The method according to claim 1, wherein the
chlorine-generating solution is a hypochlorous acid aqueous
solution and/or a hypochlorite aqueous solution.
12. The method according to claim 1, wherein the irradiation step
irradiates a gaseous pollutant mixed with the chlorine.
Description
[0001] This application is a division of application Ser. No.
09/880,760, filed Jun. 15, 2001, which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a process for decomposing
pollutants (in particular, organochlorine compounds) and a
pollutant decomposition system used therefor.
[0004] 2. Related Background Art
[0005] With the development of industrial techniques until recent
years, the use of organochlorine compounds such as ethylene
chloride and methane chloride has been widespread. Disposal of
these compounds has become a serious concern. Due to environmental
problems caused by these pollutants, great efforts are being made
to remediate these problems.
[0006] As methods for disposing of such pollutants, for example,
methods are available in which ethylene chloride is decomposed with
an oxidant or a catalyst. Stated specifically, known are a method
in which it is decomposed with ozone (Japanese Patent Application
Laid-Open No. 3-38297) and a method in which it is irradiated by
ultraviolet rays in the presence of hydrogen peroxide (Japanese
Patent Application Laid-Open No. 63-218293). It is also suggested
to use sodium hypochlorite as an oxidizing agent (U.S. Pat. Nos.
5,525,008 and 5,611,642). Also proposed is a method in which sodium
hypochlorite and ultraviolet irradiation are used in combination
(U.S. Pat. No. 5,582,741). Another method is also known in which a
photocatalyst comprised of fine semiconductor particles of an oxide
such as titanium oxide and liquid ethylene chloride are suspended
under an alkaline condition, and the suspension is irradiated by
light to effect decomposition (Japanese Patent Application
Laid-Open No. 7-144137).
[0007] In addition to the foregoing, methods of photodecomposition
by ultraviolet irradiation in a gaseous phase without the use of
any oxidizing agent have already been attempted. For example,
proposed are a method in which a waste gas containing
organohalogenated compounds is subjected to ultraviolet irradiation
to convert it into an acidic decomposed gas, followed by washing
with an alkali solution to make it harmless (Japanese Patent
Application Laid-Open No. 62-191025), and a system in which waste
water containing organohalogenated compounds is subjected to
aeration and the gas being discharged is subjected to ultraviolet
irradiation, followed by washing with an alkali solution (Japanese
Patent Application Laid-Open No. 62-191095). It is also known to
decompose ethylene chloride using iron powder (Japanese Patent
Application Laid-Open No. 8-257570). In this case, it is presumed
that reduction decomposition takes place. Reduction decomposition
is also reported with respect to the decomposition of
tetrachloroethylene (hereinafter abbreviated to "PCE") using fine
silicon particles.
[0008] Chlorinated aliphatic hydrocarbons such as trichloroethylene
(hereinafter abbreviated to "TCE") and PCE are known to be
aerobically or anaerobically decomposed by microorganisms. Attempts
have also been made to decompose or purify by utilizing such a
process.
SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide a
decomposition process that does not require any treatment with
activated carbon or microorganisms and by which pollutants can be
decomposed efficiently, without causing any secondary pollution on
account of the use of air, which contains chlorine and may also
produce a small quantity, of waste water; and an efficient
pollutant decomposition system employing such a process.
[0010] To achieve the above object, the present inventors conducted
extensive studies. As a result, they have reached a new finding
that superior decomposition power can be achieved by subjecting
functional water (e.g., acidic water) to aeration to form air that
contains chlorine, and mixing this air with air that contains
pollutants such as organochlorine compounds, followed by
photodecomposition. The functional water is obtained by
electrolysis of water that is reported to have a microbicidal
effect (Japanese Patent Application Laid-Open No. 1-180293) or the
effect of cleaning contaminants present on semiconductor wafers
(Japanese Patent Application Laid-Open No. 7-51675).
[0011] In the course of continued, detailed experiments to explore
any practically desirable form, it was also discovered that in
order to conduct a simpler and more efficient decomposition, it is
effective to carry out electrolysis on a functional water waste
liquor formed in the course of aeration or after the aeration and
to form functional water that is again usable as a chlorine feed
source. Thus, the water can be reused to carry out the
decomposition, making it possible to greatly cut down the quantity
of waste water and that of the electrolyte to be added.
Accordingly, the present invention has been accomplished.
[0012] More specifically, the present invention provides a process
for decomposing pollutants by bringing pollutants contained in air
into contact with air that contains chlorine under irradiation by
light, the process comprising:
[0013] a chlorine-containing air generation step of generating air
which contains chlorine, by bringing air into contact with a
chlorine-generating solution comprised of functional water (I) or
functional water (II) having been fed into a chlorine generation
region;
[0014] a decomposition step of decomposing the pollutants by
bringing the air which contains chlorine and air which contains
pollutants into contact with each other under irradiation by light
in a decomposition treatment region;
[0015] a regeneration step of obtaining functional water (II) by
regeneration by feeding as functional water waste liquor at least
part of the chlorine-generating solution present in the chlorine
generation region, to means for forming functional water by
electrolysis; and
[0016] a feed step of feeding to the chlorine generation region the
functional water (II) obtained through the regeneration step;
[0017] the functional water (I) and functional water (II) being
water capable of generating by aeration the air which contains
chlorine, and the functional water (I) comprising a solution used
for its formation which does not contain the functional water waste
liquor and the functional water (II) comprising a solution used for
its formation which contains the functional-water waste liquor at
least in part.
[0018] The present invention also provides a pollutant
decomposition system for decomposing pollutants by bringing
pollutants contained in air into contact with air which contains
chlorine, under irradiation by light, the system comprising:
[0019] a chlorine generation region into which a
chlorine-generating solution comprising functional water (I) or
functional water (II) is fed to bring it into contact with air to
generate air which contains chlorine;
[0020] a decomposition treatment region into which the air which
contains chlorine and air which contains pollutants are fed to
bring them into contact with each other under irradiation by light
to decompose the pollutants;
[0021] means for effecting irradiation by light;
[0022] means for forming functional water by electrolysis; and
[0023] means for feeding at least part of the chlorine-generating
solution to the means for forming functional water;
[0024] the functional water (I) and functional water (II) being
water capable of generating by aeration the air which contains
chlorine, and the functional water (I) comprising a solution used
for its formation which does not contain the functional water waste
liquor and the functional water (II) comprising a solution used for
its formation which contains the functional water waste liquor at
least in part.
[0025] The contact of the chlorine-generating solution with the air
in the chlorine-containing air generation step may be the step of
sending air to the surface of the chlorine-generating solution. In
order to improve efficiency, it is preferable to use the step of
enlarging the area of gas-liquid contact. To enlarge the area of
gas-liquid contact, preferably usable is the step of jetting the
chlorine-generating solution into air or subjecting the
chlorine-generating solution to aeration.
[0026] According to the present invention, a pollutant
decomposition process and a pollutant decomposition system used
therefor can be provided by which pollutants such as organochlorine
compounds can be decomposed efficiently, safely and simply in the
gaseous phase under normal temperature and normal pressure, and the
quantity of the electrolyte to be added and the quantity of waste
water can be cut down.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic illustration for describing the basic
construction of a first embodiment of the present invention.
[0028] FIG. 2 is a schematic illustration for describing an example
in which the basic construction of the first embodiment has been
modified.
[0029] FIG. 3 is a schematic illustration for describing the basic
construction of a second embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Embodiments of the present invention are described below
with reference to the accompanying drawings.
[0031] Embodiment 1
[0032] FIG. 1 shows the basic construction of an embodiment of the
pollutant decomposition system of the present invention.
[0033] In FIG. 1, reference numeral 102 denotes an electrolytic
cell serving as a functional-water formation means, which is
internally provided with the cathode 103 and the anode 104.
Reference numeral 101 denotes a decomposition treatment tank having
a chlorine generation region that has an air diffusion means 107
for aerating functional water kept at the bottom, and its
decomposition treatment region is irradiated by light from a light
irradiation means 106.
[0034] First, untreated water held fully in the electrolytic cell
102 is mixed with a high-concentration electrolyte solution fed
from an electrolyte solution feed unit 105 to come into an aqueous
electrolyte solution having a stated concentration. Not shown
particularly in the drawing, a stirrer may be provided in the
electrolytic cell 102, which is preferable because an aqueous
electrolyte solution having a uniform concentration can be prepared
in a short time by stirring the untreated water. In this state, the
cathode 103 and the anode 104 are connected to a direct-current
power unit (not shown) to carry out electrolysis for a certain time
to obtain functional water (I). This water is supplied to the
decomposition treatment tank 101 at one time in its entirety in the
case of batch operation, or at a constant flow rate in the case of
continuous operation.
[0035] The functional water (I) may also be prepared without
relying on electrolysis and by adding hypochlorous acid or the
like. In such a case, the necessary reagent may be added to the
untreated water held fully in the electrolytic cell 102 to form
functional water (I), which is then supplied to the decomposition
treatment tank 101 at one time in its entirety in the case of batch
operation, or at a constant flow rate in the case of continuous
operation. In the case of batch operation, the untreated water may
directly be supplied to the bottom of the decomposition treatment
tank 101 through a water supply means (not shown) and then the
necessary reagent may be added to form the functional water
(I).
[0036] The functional water (I) supplied to the decomposition
treatment tank 101 is aerated by the air diffusion means (aeration
means) 107 provided in the chlorine generation region at the bottom
portion of the decomposition treatment tank 101, so that the
interior of the decomposition treatment tank 101 is filled with air
that contains chlorine and the decomposition treatment region is
formed. Here, the air supplied to the aeration means 107 may be air
that does not contain any pollutants and air that contains
pollutants may separately be supplied to the decomposition
treatment region of the decomposition treatment tank 101. In such a
case, the air that contains pollutants may be supplied to the
aeration means 107 so that mixed air comprised of the air that
contains chlorine and the air that contains pollutants may be
formed in the decomposition treatment region in the decomposition
treatment tank 101. This makes construction simple to some extent.
Then, this mixed air may be irradiated by light from the light
irradiation means 106 for a desired residence time, whereby the
decomposition target substance is decomposed.
[0037] Functional water waste liquor having decreased in the amount
of dissolved chlorine as a result of the aeration in the chlorine
generation region inside the decomposition treatment tank 101 in
the course of or after the desired decomposition reaction is
discharged out of the chlorine generation region of the
decomposition treatment tank 101 through a waste liquor pipe 108 at
one time in its entirety in the case of batch operation, or at a
constant flow rate in the case of continuous operation. Then, a
part of all functional water waste liquor is returned to the
electrolytic cell 102 through a functional water waste liquor
flow-back pipe 109. Also, a storage tank 110 may optionally be
provided in the course of the functional water waste liquor
flow-back pipe 109 so that the functional water waste liquor can
temporarily be stored.
[0038] In the case where it does not flow back in its entirety and
partly flows out, new untreated water must be added to the
electrolytic cell 102 in a quantity corresponding to that of the
flow-out.
[0039] The functional water waste liquor in this embodiment may
have a pH close to 4, depending on the pH of the original
functional water and the feed of pollutants. This waste liquor may
be returned to the decomposition treatment tank 101 and
electrolyzed to form functional water (II), or may be neutralized
and thereafter electrolyzed. In the case where the waste liquor is
drained, it should be subjected to neutralization. As an aqueous
alkaline solution used for such neutralization, an aqueous solution
of an alkali reagent such as sodium hydroxide may be used. Not
shown in the drawing, a means for mixing the alkali reagent in the
functional water waste liquor while monitoring the pH may also
additionally be provided in the course of the waste liquor pipe
108.
[0040] The functional water waste liquor returned to the
electrolytic cell 102 is electrolyzed there, becoming functional
water (II) regenerated as a source from which the air that contains
chlorine is fed.
[0041] When the functional water (II) is formed, the functional
water waste liquor may preferably be regulated in some cases to
have a suitable electrolyte concentration. If the electrolyte
concentration has already been in a proper range, such a regulation
step may be omitted. A means may also be provided for feeding the
electrolyte automatically while measuring the concentration of
dissolved chlorine in the functional water present in the chlorine
generation region at the bottom portion of the decomposition
treatment tank 101 or measuring the concentration of electrolyte in
the electrolytic cell 102 or storage tank 110. However, according
to experiments conducted by the present inventors, it has been
found that the decomposition power of the entire system does not
decrease when the functional water waste liquor is returned and
regenerated in a quantity about five times the quantity of the
functional water in the system and is thereafter again added.
Hence, it is possible to operate the system even if no means for
regulating the electrolyte concentration are provided.
[0042] Then, the functional water waste liquor fed into this
electrolytic cell 102 is electrolyzed to form functional water
(II), which can again be used for the decomposition. This
functional water (II) is further fed into the chlorine generation
region of the decomposition treatment tank 101, and is aerated
according to the same procedure as the above functional water (I)
to generate the air that contains chlorine, where the mixed air
thereof with the pollutants is again formed to carry out the
decomposition under irradiation by light in the decomposition
treatment region.
[0043] Subsequently, such steps of forming the functional water
(II) in the electrolytic cell 102 and decomposing the pollutants in
the decomposition treatment region inside the decomposition
treatment tank 101 are repeated any desired numbers of times. This
makes it possible to greatly cut down the total quantity of waste
water and the quantity of the electrolyte to be added.
[0044] FIG. 2 shows a decomposition system partly modified from the
system shown in FIG. 1. As shown in FIG. 2, the system may be so
constructed that the chlorine generation region, which is the part
where the functional water present at the bottom of the
decomposition treatment tank 101 shown in FIG. 1 is aerated, is
made independent as a functional water aeration tank 201 and the
mixed air comprised of the air that contains chlorine and the air
that contains pollutants, formed here, is sent to the decomposition
treatment tank consisting of only the decomposition treatment
region.
[0045] Not shown in the drawing, the system may also be so
constructed that the air that contains pollutants is directly sent
to any of the above two-type decomposition treatment tanks and the
air that does not contain any pollutants is sent to the aeration
means in the chlorine generation region to generate the air that
contains chlorine, where the mixed air is formed to carry out
decomposition under irradiation by light.
[0046] Embodiment 2
[0047] FIG. 3 shows the basic construction of a second embodiment
of the pollutant decomposition system of the present invention.
[0048] The system shown in FIG. 3 differs from the one shown in
FIG. 1 in that the electrolytic cell 102 is provided therein with a
diaphragm 111 and that the cathode 103 side in the electrolytic
cell 102 communicates with the waste liquor pipe 108 through a pipe
(alkaline-water pipe) 112 at the latter's part on the side upstream
to the part where the waste liquor pipe 108 and the functional
water waste liquor flow-back pipe 109 are joined. As the diaphragm
111, preferably usable is, e.g., an ion-exchange membrane.
[0049] In the case of the construction as shown in Embodiment 2,
maintenance must be performed on for the diaphragm. Also, such a
system has a complicated construction. However, because of such a
construction, the acidic water formed in the vicinity of the anode
104 can be prevented from being mixed with the alkaline water
formed in the vicinity of the cathode 103, so that functional water
can be obtained, which has a higher concentration of dissolved
chlorine and is capable of generating a large quantity of chlorine
gas.
[0050] The functional water waste liquor in the present Embodiment
may also have a pH close to 1, depending on the feed of pollutants.
This waste liquor may be returned to the electrolytic cell 102 and
electrolyzed to form functional water (II), or may be neutralized
and thereafter electrolyzed. In the case where the waste liquor is
drained, it should be subjected to neutralization. As an aqueous
alkaline solution used for such neutralization, an aqueous solution
of an alkali reagent such as sodium hydroxide may be used. The use
of alkaline water formed on the cathode side when acidic water is
formed is preferred because it is unnecessary to use any additional
alkali agent or use any unit for feeding it. This alkaline water
may also be supplied through the alkaline-water pipe 112 to the
functional water waste liquor present in the waste liquor pipe 108
so as to be utilized for the neutralization.
[0051] Also, in Embodiment 2, the basic construction and procedure
for the decomposition are the same as those in Embodiment 1. Also,
in the case of Embodiment 2, like in Embodiment 1, the system may
be so constructed that the decomposition treatment tank and the
functional water aeration tank are separately provided and the
functional water may be aerated with the air that does not contain
any pollutants to generate the air that contains chlorine.
[0052] These steps may be repeated batch-wise any desired number
times, or may be carried out continuously.
[0053] In both Embodiments, the decomposition target substance is
air that contains pollutants, having been vacuum-extracted from
polluted soil, or air that contains pollutants, obtained by
aeration of underground water having been pumped up. Accordingly,
the system may also be so constructed that hydrochloric acid,
sodium chloride and sodium hypochlorite are added to
pollutant-dissolved water such as underground water having been
pumped up from polluted soil, to make up the functional water (I),
which is then subjected to the aeration to form the mixed air of
pollutants and chlorine to carry out the decomposition under
irradiation by light.
[0054] Not shown in the drawing, the waste water may also be
irradiated by light to effect decomposition when in both
Embodiments the waste water is mixed with the pollutants at a
concentration higher than the standard for waste water.
[0055] Pollutants to Be Treated
[0056] Pollutants to be treated may include organochlorine
compounds such as chloroethylene, 1,1-dichloroethylene,
cis-1,2-dichloroethylene, trans-1,2-dichloroethylene,
trichloroethylene, tetrachloroethylene, chloromethane,
dichloromethane and trichloromethane.
[0057] Untreated Water Serving as Source for Functional Water
[0058] The untreated water may be any water so long as any
substance that may adsorb chlorine gas does not stand included or
any substance that may react with chlorine gas without irradiation
by light does not stand dissolved. Where polluted underground water
is purified, the underground water itself may be used as the
untreated water so that the quantity of waste water can further be
reduced. Since, however, there is a problem that the pollutants
having dissolved therein may evaporate as a result of the rise of
water temperature at the time of electrolysis to contaminate the
air surrounding the system, it is preferable to add sodium
hypochlorite or the like without relying on the electrolysis.
[0059] Functional Water (I) and (II) and Air That Contains Chlorine
Formed Therefrom
[0060] With regard to the mixing proportion of gaseous pollutants
and the air that contains chlorine, in the decomposition treatment
tank, it may preferably be so regulated that the chlorine
concentration in the air is from 5 ppm to 1,000 ppm. Especially
when the chlorine concentration is from 20 ppm to 500 ppm, and
further from 80 ppm to 300 ppm, which may differ depending on the
concentration of the substance to be treated, the substance to be
treated can be decomposed with an especially remarkable
efficiency.
[0061] In the present invention, the functional water is brought
into contact with the air to generate the air that contains
chlorine that is necessary for the decomposition. The part where
the functional water is subjected to aeration, which is one of
preferred methods of contact, functions as a feeder of chlorine
basically necessary for the decomposition. The gas-phase reaction,
which takes place subsequently in the decomposition treatment tank,
is the principal site of the decomposition reaction. Hence, in the
case where the generation of chlorine and the decomposition
reaction are unified, as shown in FIG. 1 or 3, the proportion of
the gas-phase portion to the liquid-phase portion has a great
influence on the decomposition power. More specifically, the
quantity of chlorine that can be fed increases with an increase in
the volume of the functional water, but the gas-phase portion
decreases and the reaction zone of decomposition also decreases.
Conversely, the site of the reaction increases with an increase in
the gas-phase portion and the decomposition reaction proceeds
quickly, but the feed of chlorine decreases because of a decrease
in the liquid-phase portion. There are various factors that affect
this process, such as the rate of aeration and the feed speed of
functional water. In the case where the formation of the air that
contains chlorine and the decomposition reaction region (reaction
region) are unified, as shown in FIG. 1 or 3, the liquid-phase
portion in the treatment tank may be from 5% to 30%, and preferably
from 10% to 20%. Also, in the case where they are not unified, as
shown in FIG. 2, the proportion of the volume of the tank in which
the air that contains chlorine is formed to the volume of the tank
in which the decomposition reaction is carried out may also
preferably be approximately from 1:2 to 1:9.
[0062] Here, the functional water (I) and (II) serving as the
source from which the air that contains chlorine is fed refer to,
e.g., water having properties such that its hydrogen ions are at a
concentration (pH value) from 1 to 4, and preferably from 2 to 3,
and dissolved chlorine is at a concentration from 5 mg/L to 150
mg/L, and preferably from 30 mg/L to 120 mg/L.
[0063] Such functional water, in particular functional water (II),
which is the regenerated functional water, can be obtained by
dissolving an electrolyte such as sodium chloride or potassium
chloride in the untreated water and electrolyzing this water in a
water tank having a pair of electrodes, being obtained in the
vicinity of the anode thereof. Here, the electrolyte in the
untreated water before electrolysis may preferably be at a
concentration of, in the case of, e.g., sodium chloride, from 20
mg/L to 2,000 mg/L, and more preferably from 200 mg/L to 1,000
mg/L.
[0064] Here, in the case where the diaphragm is provided between a
pair of electrodes, the acidic water formed in the vicinity of the
anode can be prevented from being mixed with the alkaline water
formed in the vicinity of the cathode.
[0065] As the diaphragm, preferably usable is, e.g., an
ion-exchange membrane. Then, as a means for obtaining such
functional water, any commercially available generator for strongly
acidic electrolytic water may be used, as exemplified by OASIS
BIOHALF (trade name; manufactured by Asahi Glass Engineering Co.,
Ltd.) and Strong Electrolytic Water Generator Model FW-200 (trade
name; manufactured by Amano K. K.).
[0066] Functional water formed from a system having no diaphragm
may also be used as the functional water described above. For
example, it is functional water having the dissolved chlorine
concentration from 2 mg/L to 100 mg/L, preferably from 20 mg/L to
80 mg/L, and having a pH from 4 to 10, preferably from 5 to 8.
[0067] The functional water having the above properties may be
obtained not only by electrolysis, but may also be prepared by
dissolving various reagents in the untreated water. For example, it
may be prepared by dissolving 0.001 mol/L to 0.1 mol/L of
hydrochloric acid, 0.005 mol/L to 0.02 mol/L of sodium chloride and
0.0001 mol/L to 0.01 mol/L of sodium hypochlorite. The functional
water thus prepared is used as functional water put previously in
the decomposition treatment tank as the functional water (I) at the
time of the start of the decomposition, or used when the
underground water that contains pollutants is converted to
functional water and supplied to the decomposition treatment
tank.
[0068] Functional water having a pH of 4 or above may also be
obtained not only by electrolysis, but may also be prepared by
dissolving various reagents in the untreated water. For example, it
may be prepared by dissolving 0.001 mol/L to 0.1 mol/L of
hydrochloric acid, 0.001 mol/L to 0.1 mol/L of sodium hydroxide and
0.0001 mol/L to 0.01 mol/L of sodium hypochlorite. Alternatively,
it may also be prepared by dissolving only a hypochlorite, e.g.,
0.0001 mol/L to 0.01 mol/L of sodium hypochlorite. Functional water
having a pH of 4.0 or below and having the dissolved chlorine
concentration from 2 mg/L to 2,000 mg/L may also be prepared using
the hydrochloric acid and hypochlorite.
[0069] In place of the hydrochloric acid, other inorganic acid or
organic acid may be used. As the inorganic acid, usable are, e.g.,
hydrofluoric acid, sulfuric acid, phosphoric acid and boric acid.
As the organic acid, e.g., acetic acid, formic acid, malic acid,
citric acid and oxalic acid maybe used. The functional water may
also be produced using, e.g., N.sub.3C.sub.3O.sub.3NaCl.sub.2,
commercially available as a weak acidic water generating powder
(e.g.,trade name: Kino-san 21X; available from Clean Chemical K.
K). The functional water prepared using such chemicals also has the
ability to decompose organochlorine compounds under irradiation by
light like the functional water obtained by electrolysis, though
having a difference in decomposition power as is apparent from the
Examples. Here, the untreated water may include city water, river
water and sea water. These types of water usually have a pH in the
range from 6 to 8 and the dissolved chlorine concentration of, at
most, less than 1 mg/L. Such untreated water does not have the
above ability to decompose pollutants as a matter of course.
[0070] The chlorine necessary for the decomposition can be
generated from all of these types of water, and any of these and
the treatment target gas may be mixed, followed by irradiation by
light so as to be used in the present invention, which dec.omposes
the treatment target pollutants.
[0071] Light Irradiation Means
[0072] As a light irradiation means usable in the present
invention, light have a wavelength, e.g., from 300 to 500 nm is
preferred, and the use of light from 350 to 450 nm is more
preferred. Also, as light irradiation intensity for the functional
water and treatment target, in the case of, e.g., a light source
having a peak around 360 nm, decomposition sufficient for practical
use proceeds at an intensity of hundreds of .mu.W/cm.sup.2
(measured between 300 nm and 400 nm). Stated specifically, the
irradiation may be performed in an amount of light from 10
.mu.W/cm.sup.2 to 10 mW/cm.sup.2, and preferably from 50
.mu.W/cm.sup.2 to 5 mW/cm.sup.2.
[0073] Then, as a light source of such light, natural light (e.g.,
sunlight) or artificial light (e.g., a mercury lamp, a black light
and a color fluorescent lamp) may be used.
[0074] In the present invention, it is unnecessary to use
ultraviolet light of about 250 nm or shorter wavelength. Hence, it
is also neither necessary to provide any safety device so that
human bodies are not affected, nor is it necessary to construct the
decomposition treatment tank using quartz glass through which the
ultraviolet light can readily pass. Thus, the system can be set up
at a low cost.
[0075] Means for Generating Air That Contains Chlorine
[0076] As a means for generating the air that contains chlorine,
any device may be used that brings the functional water and the air
into contact with each other, e.g., which sends the air to the
surface of the functional water. In order to improve efficiency, it
is more advantageous to use a device that can ensure a large
gas-liquid contact area. As a means for ensuring such a large
contact area, preferred are a means for jetting the functional
water in the air in the form of droplets and a means for aerating
the functional water.
[0077] These devices may be made of any materials, so long as they
are not corroded by the treatment target and chlorine. For example,
usable are a porous diffusion plate made of sintered glass, porous
ceramic, sintered SUS316 stainless steel or a net woven with
fibrous SUS316 stainless steel, and a sparger nozzle shower head
made of pipes of glass, ceramic or SUS316 stainless steel.
EXAMPLES
[0078] The present invention is described below in greater detail
by the following Examples. These Examples by no means limit the
present invention.
Example 1
[0079] Batch operation of a single-unit type decomposition
treatment tank, without a diaphragm:
[0080] The same decomposition system as the system shown in FIG. 1,
but having the storage tank 110 removed therefrom, was made ready
for use. The electrolytic cell 102 was so set up as to be able to
electrolyze about 50 ml of water through a platinum electrode.
[0081] First, the functional water (I) was prepared in the
following way using the electrolytic cell 102.
[0082] The electrolyte concentration of water containing sodium
chloride as an electrolyte, the electrolysis electric-current
value, the electrolysis time and so forth were changed in variety,
and the pH of the resultant acidic functional water obtained on the
anode side was measured with a pH meter (TCX-90i). The
concentration of dissolved chlorine was also measured with a
simplified reflection photometer (trade name: RQ flex; manufactured
by Merck & Co., Inc.; test paper: Reflectoquant chlorine test
paper).
[0083] As a result of this measurement, it was ascertained that the
pH of this functional water changed from 4.0 to 10.0 and the
concentration of dissolved chlorine from 2 mg/L to 70 mg/L,
depending on the concentration of sodium chloride (standard
concentration: 1,000 mg/L), the electrolysis electric-current
value, the electrolysis time and so forth.
[0084] Accordingly, as the functional water (I) used in the present
Example, functional water having a pH of 7.9 and having the
dissolved chlorine concentration of 15 mg/L was used. This
functional water (I) was water obtained by putting 50 mL of
distilled water in the electrolytic cell 102, and adding thereto
from the electrolyte solution feed unit 105 2 mL of an aqueous
sodium chloride solution having a concentration of 20% (250 g/L) to
form an aqueous solution of about 1,000 mg/L of sodium chloride,
followed by electrolysis for 12 minutes. Next, 50 mL of the
functional water (I) was put into a 500 mL volume decomposition
treatment tank 101 made of glass.
[0085] In an experiment conducted previously, this functional water
(I) was put into the decomposition treatment tank 101, shown in
FIG. 1, and air was sent to the aeration means 107 at a flow rate
of 300 mL/min. by means of an air pump. Here, the concentration of
chlorine in the gaseous phase portion in the decomposition
treatment tank 101 was measured with a detecting tube (manufactured
by GASTEC CORPORATION K. K., No. 8H) several times. As a result,
this concentration was in the range from 80 ppm to 300 ppm, but
gradually decreased.
[0086] The gaseous phase portion of this decomposition treatment
tank 101 was irradiated by light by means of a black light
fluorescent lamp (trade name: FL10BLB; manufactured by Toshiba
Corporation; 10 W), which is the light irradiation means 106. This
irradiation was made using an amount of light from 0.4 to 0.7
mW/cm.sup.2.
[0087] Simultaneously with the irradiation by light, air containing
TCE and PCE at a concentration of 100 ppm imitated polluted air
vacuum-extracted from polluted soil formed using a permeator
(manufactured by GASTEC CORPORATION K. K.) was sent at a flow rate
of 300 mL/min. from the aeration means 107 provided at the bottom
of the decomposition treatment tank 101.
[0088] For 30 minutes after this system began to operate, the
concentration of TCE and PCE in the air exhausted from the
decomposition treatment tank 101 was periodically checked by
sampling using a gas-tight syringe. The concentration of TCE and
PCE was measured by gas chromatography (using GC-14B, trade name;
manufactured by Shimadzu Corporation and having an FID detector;
column: DB-624, available from J & W K. K.). However, neither
of these compounds was always detectable. The concentration of TCE
and PCE in the functional water was also measured in the same way
after the treatment was completed, but neither compound was
detectable. This showed that the TCE and PCE were decomposable.
[0089] Next, all functional water waste liquor at the bottom of the
decomposition treatment tank 101 was completely removed and
returned to the electrolytic cell 102 through the functional water
waste liquor flow-back pipe 109 to effect electrolysis again for 12
minutes. As a result, functional water (II) having a pH of 2.3 and
having the dissolved chlorine in a concentration of 27 mg/L was
formed.
[0090] This functional water (II) was poured into the decomposition
treatment tank 101, where the black light fluorescent lamp was
again turned on, and simultaneously aerated with the air containing
TCE and PCE. In this treatment, too, the concentration of chlorine
in the gaseous phase portion in the decomposition treatment tank
101 and the concentration of TCE and PCE in the exhaust air were
periodically measured, but neither compound was always
detectable.
[0091] This operation was carried out five times or more, but the
TCE and PCE was included in the exhaust air only starting on the
6th operation. Accordingly, the decomposition was stopped, and the
functional water was fed back to the decomposition treatment tank
101. Then, after 2 mL of an aqueous sodium chloride solution were
added from the electrolyte solution feed unit 105, the electrolysis
was again carried out for 12 minutes. Thereafter, the functional
water formed was again supplied to the decomposition treatment tank
101, followed by aeration under irradiation by light from the lamp.
As a result, the TCE and PCE were not detectable.
[0092] From this fact, it has been ascertained that the electrolyte
may be added once in every five operations when the functional
water waste liquor is returned batch-wise, whereby the TCE and PCE
can be continuously decomposed while the functional water waste
liquor having been aerated is electrolyzed and regenerated into the
functional water (II), which is again utilized as the feed source
of the air that contains chlorine.
Example 2
[0093] Continuous operation of single-unit type decomposition
treatment tank without a diaphragm:
[0094] The same decomposition system as the system shown in FIG. 1,
but having the storage tank 110 removed therefrom was made ready
for use.
[0095] 50 mL of functional water (I) formed in the same manner as
in Example 1 was put into the decomposition treatment tank 101.
Subsequently, 50 mL of an aqueous sodium chloride solution having a
concentration of 1,000 mg/L were put into the electrolytic cell 102
to effect electrolysis, during which the functional water was
supplied from the electrolytic cell 102 at a flow rate of 2 mL/min.
by means of a pump. Also, the aerated functional water waste liquor
was drained off at the same rate so as to be completely returned to
the electrolytic cell 102 and so that the quantity of the
functional water in the decomposition treatment tank 101 and
electrolytic cell 102 was constant.
[0096] In an experiment made previously, air was sent to the
aeration means 107 at a flow rate of 300 mL/min. by means of an air
pump while the functional water was circulated between the
decomposition treatment tank 101 and the electrolytic cell 102.
Here, the concentration of chlorine in the gaseous phase portion in
the decomposition treatment tank 101 was measured with a detecting
tube (manufactured by GASTEC CORPORATION K. K., No. 8H) several
times. As a result, the concentration was in the range from 80 ppm
to 300 ppm at the beginning, but gradually increased.
[0097] This decomposition treatment tank 101 was irradiated by
light from a black light fluorescent lamp and, simultaneously, the
air containing TCE and PCE at a concentration of 100 ppm was sent
at a flow rate of 300 mL/min., in the same manner as in Example
1.
[0098] For about 4 hours after this system began to be operate, the
concentration of TCE and PCE in the air exhausted from the
decomposition treatment tank 101 was periodically checked by
sampling using a gas-tight syringe, and the concentration of TCE
and PCE was measured in the same manner as in Example 1. However,
neither compound was always detectable. This showed that the TCE
and PCE were decomposable only by again electrolyzing the
functional water waste liquor into the functional water (II)
followed by aeration when the functional water is circulated five
times through the system.
[0099] After that, however, the TCE and PCE was detectable in the
exhaust air. Accordingly, 4 mL of an aqueous sodium chloride
solution were gradually added to the electrolytic cell 102 from the
electrolyte solution feed unit 105 over a period of about 30
minutes. As a result, the TCE and PCE became undetectable.
[0100] From this fact, it has been ascertained that the electrolyte
may be added every time the water in the system is circulated five
times when the functional water waste liquor is continuously
returned. Whereby, the TCE and PCE can be continuously decomposed
while the functional water waste liquor, having been aerated, is
electrolyzed and regenerated into the functional water (II), which
is again utilized as the feed source of the air that contains
chlorine.
Example 3
[0101] Batch operation of separation type decomposition treatment
tank without a diaphragm:
[0102] Using the same decomposition system as the system shown in
FIG. 1, except that the functional water aeration tank 201 was
separate from the decomposition treatment tank 101, an experiment
was conducted in the same manner as in Example 1. Here, the
functional water aeration tank 201 was 70 mL in volume, and 50 mL
of functional water was put into it. Also, the decomposition
treatment tank 101 was 450 mL in volume.
[0103] As a result, entirely the same results as those in Example 1
were obtained.
[0104] From this fact, it has been ascertained that even when the
functional water aeration tank 201 is separate from the
decomposition treatment tank 101, the electrolyte may be added
every time the water in the system is circulated five times when
the functional water waste liquor is returned batch-wise. Whereby,
the TCE and PCE can be continuously decomposed while the functional
water waste liquor, having been aerated, is electrolyzed and
regenerated into the functional water (II), which is again utilized
as the feed source of the air that contains chlorine.
Example 4
[0105] Batch operation of aeration type decomposition treatment
tank using air not containing any pollutants without a
diaphragm:
[0106] Using the same decomposition system as the system shown in
FIG. 1, except that the polluted air from the permeator was
directly sent to the decomposition treatment tank 101 and 300
mL/min. of the air not containing any pollutants was sent to the
aeration means 107 provided at the bottom of the decomposition
treatment tank 101, at a flow rate of 300 mL/min. by means of an
air pump, an experiment was conducted in the same manner as in
Example 1.
[0107] As a result, entirely the same results as those in Example 1
were obtained.
[0108] From this fact, it has been ascertained that even when the
functional water is aerated with the air not containing any
pollutants to form the air that contains chlorine, which is then
mixed with pollutants in the decomposition treatment tank 101, the
electrolyte may be added every time the water in the system is
circulated five times when the functional water waste liquor is
returned batch-wise. Whereby, the TCE and PCE can be continuously
decomposed while the functional water waste liquor, having been
aerated, is electrolyzed and regenerated into the functional water
(II), which is again utilized as the feed source of the air that
contains chlorine.
Example 5
[0109] Batch operation of single-unit type decomposition treatment
tank with a diaphragm:
[0110] An experiment was conducted using a system in which, as
shown in FIG. 3, the diaphragm 111 was attached to the electrolytic
cell 102 and the alkaline-water pipe 112 was provided on the
cathode side.
[0111] In the same manner as in Example 1, the electrolyte
concentration of water containing sodium chloride as an
electrolyte, the electrolysis electric-current value, the
electrolysis time and so forth were changed in variety, and the pH
and the concentration of the dissolved chlorine of the resultant
acidic functional water obtained on the anode side were measured
with a pH meter (TCX-90i).
[0112] As a result of this measurement, it was ascertained that the
pH of this functional water changed from 1.0 to 4.0 and the
concentration of dissolved chlorine from 5 mg/L to 150 mg/L,
depending on the concentration of sodium chloride (standard
concentration: 1,000 mg/L), the electrolysis electric-current
value, the electrolysis time and so forth.
[0113] Accordingly, as the functional water (I) used in the present
Example, functional water having a pH of 2.1 and having a dissolved
chlorine concentration of 60 mg/L was used. This functional water
(I) was 50 mL of acidic electrolytic water obtained on the side of
the anode 104 by putting 100 mL of distilled water in the
electrolytic cell 102 and adding thereto from the electrolyte
solution feed unit 105 4 mL of an aqueous sodium chloride solution
having a concentration of 20% (250 g/L), to form an aqueous
solution of about 1,000 ML of sodium chloride, followed by
electrolysis for 12 minutes.
[0114] This functional water (I) was supplied to the decomposition
treatment tank 101 in the same manner as in Example 1, and an
experiment was made in the same manner as in Example 1, except that
the concentration of the air containing TCE and PCE was doubled to
200 ppm. With regard to the functional water waste liquor, it was
neutralized in the functional water waste liquor flow-back pipe 109
by supplying from the alkaline-water pipe 112 50 mL of alkaline
water formed on the side of the cathode of the electrolytic cell
102, thereafter temporarily stored in the storage tank 110 and then
returned to the electrolytic cell 102. Here, the pH of the
functional water waste liquor having not been neutralized was 2.3.
After neutralization, it was 6.8.
[0115] As a result, entirely the same results as those in Example 1
were obtained.
[0116] From this fact, it has been ascertained that even when the
functional water formed in the electrolytic cell having a diaphragm
is used, the electrolyte may be added every time the water in the
system is circulated five times when the functional water waste
liquor is returned batch-wise. Whereby, the TCE and PCE can be
continuously decomposed while the functional water waste liquor,
having been aerated, is electrolyzed and regenerated into the
functional water (II), which is again utilized as the feed source
of the air that contains chlorine.
Example 6
[0117] Batch operation of single-unit type decomposition treatment
tank, using functional water with a hypochlorite:
[0118] An experiment was conducted in the same manner as in Example
5, except that 50 mL of functional water (I) formed by adding
hydrochloric acid, sodium chloride and sodium hypochlorite were put
into the decomposition treatment tank 101 at the time the
experiment was started.
[0119] The functional water (I) was prepared by adding to distilled
water the hydrochloric acid, sodium chloride and sodium
hypochlorite so as to be at concentrations of 0.006 mol/L, 0.01
mol/L and 0.002 mol/L, respectively. Here, the functional water (I)
had a pH of 2.3 and had the dissolved chlorine concentration of 110
mg/L.
[0120] This functional water (I) was supplied to the decomposition
treatment tank 101 in the same manner as in Example 5, and an
experiment was conducted in the same manner as in Example 5, except
that sodium chloride was added to the returned functional-water
waste liquor from the electrolyte solution feed unit 105 so as to
be at a concentration of 1,000 mg/L and thereafter the electrolysis
was carried out.
[0121] As a result, quite the same results as those in Example 1
were obtained, except that the TCE and PCE were detectable in the
exhaust air when the functional water (II) formed after the
functional water waste liquor was returned seven times to effect
electrolysis repeatedly was used.
[0122] From this fact, it has been ascertained that even when the
functional water with a hypochlorite is used, the electrolyte may
be added every time the water in the system is electrolyzed six
times to regenerate the functional water (II). Whereby, the TCE and
PCE can be continuously decomposed, while the aerated functional
water waste liquor is electrolyzed and regenerated into the
functional water (II), which is again utilized as the feed source
of the air that contains chlorine.
* * * * *