U.S. patent application number 12/382334 was filed with the patent office on 2009-07-23 for process and apparatus for producing entrapping immobilization pellets.
This patent application is currently assigned to HITACHI PLANT TECHNOLOGIES, LTD.. Invention is credited to Naoki Abe, Koutarou Aoyama, Hiroyoshi Emori, Takayuki Kouno, Tatsuo Sumino.
Application Number | 20090184048 12/382334 |
Document ID | / |
Family ID | 36829722 |
Filed Date | 2009-07-23 |
United States Patent
Application |
20090184048 |
Kind Code |
A1 |
Abe; Naoki ; et al. |
July 23, 2009 |
Process and apparatus for producing entrapping immobilization
pellets
Abstract
A large amount of entrapping immobilization pellets with highly
stable quality are produced inexpensively by high-speed treatment.
There is provided a process for producing entrapping immobilization
pellets in which microorganisms are entrapped and immobilized in an
immobilizing agent, the process comprising polymerizing a mixture
containing the microorganisms and a solution of the immobilizing
agent in a forming frame into a gel to prepare a pellet block.
Inventors: |
Abe; Naoki; (Chiyoda-ku,
JP) ; Aoyama; Koutarou; (Chiyoda-ku, JP) ;
Sumino; Tatsuo; (Chiyoda-ku, JP) ; Emori;
Hiroyoshi; (Chiyoda-ku, JP) ; Kouno; Takayuki;
(Matsudo-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
HITACHI PLANT TECHNOLOGIES,
LTD.
Tokyo
JP
|
Family ID: |
36829722 |
Appl. No.: |
12/382334 |
Filed: |
March 13, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11445189 |
Jun 2, 2006 |
|
|
|
12382334 |
|
|
|
|
Current U.S.
Class: |
210/502.1 ;
435/182 |
Current CPC
Class: |
C02F 3/108 20130101;
C02F 3/348 20130101; Y02W 10/10 20150501; C12N 11/04 20130101; C12N
11/08 20130101; Y02W 10/15 20150501 |
Class at
Publication: |
210/502.1 ;
435/182 |
International
Class: |
B01D 39/02 20060101
B01D039/02; C12N 11/04 20060101 C12N011/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2005 |
JP |
2005-166045 |
Claims
1. Entrapping immobilization pellets produced by an apparatus for
producing entrapping immobilization pellets, the apparatus
comprising at least one forming frame in which a mixture containing
microorganisms and an immobilizing agent solution is polymerized
into a gel to prepare a pellet block.
2. A wastewater treatment equipment in which wastewater is treated
with the entrapping immobilization pellets according to claim 1.
Description
[0001] This is a Division of application Ser. No. 11/445,189 filed
Jun. 2, 2006, which claims the benefit of Japanese Patent
Application No. 2005-166045 filed Jun. 6, 2005. The disclosures of
the prior applications are hereby incorporated by reference herein
in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a process and an apparatus
for producing entrapping immobilization pellets, entrapping
immobilization pellets, and wastewater treatment equipment using
the pellets. More particularly, the present invention relates to a
process and an apparatus for producing entrapping immobilization
pellets suitable for nitrification promoting advanced sewage
treatment process in the field of wastewater treatment or the
like.
[0004] 2. Description of the Related Art
[0005] Nitrifying bacteria in activated sludge used for wastewater
treatment grow slower than common bacteria. In particular, in
winter during which water temperatures are low, such bacteria have
only a small number of bacterial cells and thus exhibit
significantly reduced nitrification activity. This tendency also
applies to microorganisms having the same properties as in
nitrifying bacteria. In this situation, there has been made an
attempt to improve nitrification performance by attaching activated
sludge containing nitrifying bacteria to the surface of an
attachment material such as quartz sand, activated carbon, or
plastic to increase the concentration of nitrifying bacteria (see
"Water treatment by microorganism immobilization method: Pellet
immobilization method, entrapping immobilization method,
biologically activated carbon method," published by NTS Inc. in
2000). However, attachment immobilization pellets in which
microorganisms are attached to an attachment material have a
drawback in that the concentration of nitrifying bacteria cannot be
sufficiently increased because the attached microorganisms are
released from the material, or microorganisms differing from
nitrifying bacteria as target microorganisms are attached to the
pellets. Accordingly, wastewater has been treated at high speed
with increased nitrification activity by producing entrapping
immobilization pellets in which useful microorganisms such as
nitrifying bacteria are immobilized in an immobilizing agent, and
packing a wastewater treatment tank with the entrapping
immobilization pellets to increase the concentration of nitrifying
bacteria.
[0006] Entrapping immobilization pellets are produced by tube
forming, dropping granulation, sheet forming or the like. Tube
forming is a method comprising injecting a mixture of
microorganisms with a polymer material into a vinyl tube with a
diameter of several millimeters to polymerize and extrude the
mixture, and cutting the mixture into cylindrical pellets with a
certain length. This method can provide pellets with high form
accuracy, but is not suitable for mass production. Dropping
granulation is a method comprising dropping a mixture of
microorganisms with a polymer material into a separate liquid to
produce spherical pellets. This method allows easy mass production,
but has a drawback in that the produced pellets have various
particle sizes.
[0007] As a device for solving these problems, Japanese Patent
Application Laid-Open No. 2003-235553 discloses sheet forming
comprising forming a mixture of microorganisms with a polymer
material into a sheet, and finely cutting the sheet to produce
rectangular pellets. In the sheet forming, as shown in FIG. 11, a
raw material or chemical is cast into a space between belt
conveyors 26, 28 by a stirring and extrusion unit 20, and is formed
into a continuous sheet in the space between the belt conveyors.
Then, the sheet is cut into lattices with a rotary blade 36 at
certain intervals in the widthwise direction. Next, the
lattice-shaped pellet block is cut into pellets 46 having a certain
length using a guillotine cutting unit 38. This method can easily
automate a granulation apparatus and provide a high form accuracy,
and is thus assumed to be most suitable for mass granulation.
SUMMARY OF THE INVENTION
[0008] However, it is generally assumed that gel polymerization is
preferably carried out in an atmosphere of an inert gas such as
nitrogen, because oxygen in the air is reacted with a radical to
inhibit curing. When a gel is prepared for electrophoresis in a
laboratory, in order to prevent a gel solution from coming into
contact with air and thereby oxidizing or inhibiting polymerization
of the solution, a space between two plates or above the gel is
charged with n-butyl alcohol to carry out polymerization or the
like (see websites on the SDS-PAGE experimental method). However,
since entrapping immobilization pellets are produced in a large
amount, it is difficult in terms of cost to carry out the
polymerization in an oxygen-free atmosphere as described above.
[0009] The sheet forming of Japanese Patent Application Laid-Open
No. 2003-235553 has also a drawback in that polymerization is not
stable and the pellets have reduced strength because the mixture
has a large interface area in contact with air. Another drawback is
that an unpolymerized substance remains on the sheet surface in
contact with oxygen, and the unpolymerized substance is discharged
as COD when the pellets are used for wastewater treatment. Since
the formed sheet has unstable quality as described above, when
wastewater treatment equipment is packed with entrapping
immobilization pellets, the entrapping immobilization pellets
cannot sufficiently exhibit their wastewater treatment performance
in many cases.
[0010] The present invention has been achieved in view of such
circumstances. An object of the present invention is to provide a
process and an apparatus for producing entrapping immobilization
pellets which can produce a large amount of entrapping
immobilization pellets having highly stable quality inexpensively
by high-speed treatment, entrapping immobilization pellets, and
wastewater treatment equipment using the pellets.
[0011] According to a first aspect of the present invention, to
attain the aforementioned object, there is provided a process for
producing entrapping immobilization pellets in which microorganisms
are entrapped and immobilized in an immobilizing agent, the process
comprising polymerizing a mixture containing the microorganisms and
a solution of the immobilizing agent in a forming frame into a gel
to prepare a pellet block.
[0012] The present inventors have found that, in conventional sheet
forming, the polymerization rate and the polymerization state
differ between parts in contact with air and parts not in contact
with air during gel polymerization, and thus the products have
significantly different qualities. Specifically, the present
inventors have found that, in conventional sheet forming, the
mixture has a large area in contact with air, in particular,
unpolymerized parts tend to appear on the surface of the mixture in
contact with air, and the resulting pellets have different
qualities.
[0013] The present invention reduces the interface of the mixture
in contact with oxygen in the air by polymerization in the forming
frame, and thus can produce entrapping immobilization pellets with
highly stable quality. By employing a plurality of the forming
frames, a large amount of entrapping immobilization pellets can be
produced inexpensively at high speed. Further, since it is not
necessary to replace the atmosphere in the polymerization step with
a large volume of an inert gas, the production cost can be
considerably reduced. The oxygen concentration in the forming frame
may be further reduced by replacement with an inert gas.
[0014] In the first aspect, the forming frame is preferably made of
a material that does not reduce activity of microorganisms, a
material that does not inhibit polymerization reaction of the
mixture, or a structure and a material in which oxygen or the like
that inhibits polymerization reaction is hardly included.
Specifically, a material that does not inhibit polymerization
reaction of the mixture and has low wettability with the pellet
block is preferable. For example, vinyl chloride, SUS, and an
acrylic resin are more preferable. The pellet block polymerized in
the forming frame having low wettability as described above can be
smoothly removed from the forming frame with its shape maintained.
In order to reduce the contact interface with oxygen, the forming
frame preferably has a structure that can be closed with a lid or
the like, or a structure having a small opening area for the
mixture (corresponding to the bottom area) during polymerization,
in particular. The shape of the forming frame (shape of the pellet
block) is preferably a cuboid or cube from the viewpoint of
handling, yield, and the like, but is not limited thereto. The
shape may be a cylinder or the like. The pellet block refers to a
pellet mass to be cut into substantially cubic entrapping
immobilization pellets.
[0015] According to a second aspect of the present invention, there
is provided the process for producing entrapping immobilization
pellets according to the first aspect, wherein the pellet block has
a deformation ratio of 50% or more. In the second aspect, the
pellet deformation ratio is represented by the formula 1.
Pellet deformation ratio(%)=(H0-H1)/H0.times.100 (Formula 1)
[0016] H0: Initial pellet thickness before compression, H1: Pellet
thickness immediately before breakdown of pellet gel
[0017] A deformation ratio of 50% in the second aspect means that
the pellet block can be compressed to 50% of the initial thickness
of entrapping immobilization pellets, and is broken down if further
compressed.
[0018] When forming a pellet block using a forming frame, it is
difficult to remove the block from the forming frame, resulting in
a decrease in production efficiency. As a result of extensive
studies in this situation for a technique of easily removing a
pellet, the present inventors have found that the time for removing
a pellet block largely depends on the deformation ratio of the
pellet block. Specifically, a pellet having a small deformation
ratio is attached to the forming frame and is set too much. Thus,
the wall resistance between the forming frame and the pellet block
is increased, making it difficult to remove the block from the
frame. Further, a pellet having a too small deformation ratio is
highly fragile (neither plastic nor ductile), and thus tends to be
broken down even by a little external force.
[0019] In the second aspect, since the pellet has a deformation
ratio of 50% or more, the pellet can be easily removed from the
forming frame. When the pellet has a deformation ratio of 70% or
more, the pellet can be more easily removed, favorably. As a result
of extensive studies for controlling the deformation ratio of the
pellet, the present inventors have found that a deformation ratio
of 50% or more can be achieved using, as an immobilizing agent, a
prepolymer having a molecular weight of 1,000 to 13,000 at a
concentration per pellet of 3 to 10 mass %.
[0020] According to a third aspect of the present invention, there
is provided the process for producing entrapping immobilization
pellets according to the first or second aspect, wherein the
mixture is heated to or maintained at a predetermined temperature
during polymerization of the mixture.
[0021] As described above, when the mixture is polymerized in the
forming frame, the mixture can be heated to or maintained at an
appropriate temperature. Accordingly, in the reaction frame, the
polymerization reaction rate can be controlled, and the reaction
can be uniformly carried out.
[0022] According to a fourth aspect of the present invention, there
is provided the process for producing entrapping immobilization
pellets according to any one of the first to third aspects, wherein
the mixture is polymerized for 10 to 60 minutes at a temperature of
the forming frame of 20 to 30.degree. C.
[0023] The polymerization temperature is a factor that affects the
pellet strength and the polymerization rate. When the
polymerization temperature is 20.degree. C. or higher, the pellet
strength is high in a substantially stable manner, and the
polymerization rate is also high. However, when the polymerization
temperature is higher than 30.degree. C., the pellet strength and
the polymerization rate almost do not change. On the other hand,
when the polymerization temperature is lower than 20.degree. C.,
the pellet strength is considerably reduced, and the polymerization
rate is also reduced. Accordingly, the polymerization temperature
is preferably 20.degree. C. or higher, and more preferably 20 to
30.degree. C.
[0024] When the polymerization time is longer than 60 minutes, the
mixture is completely gelled, the forming frame has strong wall
resistance, and thus the gel cannot be removed. On the other hand,
when the time is shorter than 10 minutes, the mixture is
insufficiently gelled, and it is thus difficult to remove the gel
as a block. Accordingly, the present inventors have found that the
block can be easily removed from the forming frame when polymerized
at a polymerization temperature of 20 to 30.degree. C. for a
polymerization time of 10 to 60 minutes, although the appropriate
polymerization time varies according to the polymerization
temperature. With the polymerization temperature and the
polymerization time of the present invention as described above,
polymerization can be carried out for a short time to form a pellet
block having an appropriate pellet strength.
[0025] According to a fifth aspect of the present invention, there
is provided the process for producing entrapping immobilization
pellets according to any one of the first to fourth aspects,
further comprising: after preparing the pellet block in the forming
frame, injecting a gas or liquid into the forming frame to remove
the pellet block.
[0026] Depending on the material of the forming frame or the
strength of the pellet block, it is difficult to remove the pellet
block from the forming frame, disadvantageously, for example, a
part of the pellet block remains in the forming frame. Thus, in the
fifth aspect, by pressurizing an inside of the forming frame or
injecting a liquid such as water into the frame to improve slip
properties, the pellet block can be easily removed without damages.
The removal time can also be reduced.
[0027] According to a sixth aspect of the present invention, there
is provided the process for producing entrapping immobilization
pellets according to any one of the first to fifth aspects, further
comprising: cutting the pellet block into lattices while fixing a
periphery of the pellet block; and then cutting the lattice-shaped
pellet block substantially into cubes to provide pellets.
[0028] In the sixth aspect, the pellet block is first cut into
lattices with, for example, lattice-shaped cutting blades, and then
is cut perpendicular to the longitudinal direction with a rotary
cutting blade. Thus, a large amount of uniform and substantially
cubic pellets that have excellent form accuracy can be produced by
high-speed treatment. Since the pellet block is cut while fixed,
the pellet block is not deformed by pressure from the cutting
blade. Accordingly, the pellet block can be cut into pellets with a
uniform size without deformation of the cutting surfaces.
[0029] According to a seventh aspect of the present invention,
there is provided the process for producing entrapping
immobilization pellets according to any one of the first to sixth
aspects, further comprising: controlling a transport speed of the
pellet block and a speed of cutting the lattice-shaped pellet block
substantially into cubes, so that the entrapping immobilization
pellets after cutting are substantially cubes.
[0030] The general problem is that, when pellets not having a
uniform shape are put into a wastewater treatment tank and used,
the pellets clog a screen for preventing discharge of pellets or
are discharged from the screen. Accordingly, pellets with a stable
shape are required. In the seventh aspect, when the pellet block is
cut while transporting the pellet block, the transport speed of the
pellet block and the cutting speed of the lattice-shaped pellet
block (corresponding to the rotation speed of the rotary cutting
blade, for example) are controlled so that the resulting pellets
are substantially cubes with a uniform size. Thus, a large amount
of entrapping immobilization pellets having a stable shape can be
produced.
[0031] According to an eighth aspect of the present invention,
there is provided an apparatus for producing entrapping
immobilization pellets, comprising at least one forming frame in
which a mixture containing microorganisms and an immobilizing agent
solution is polymerized into a gel to prepare a pellet block.
[0032] In the eighth aspect, the present invention is embodied as
an apparatus in which a mixture containing microorganisms and an
immobilizing agent solution is polymerized in at least one forming
frame. The present invention reduces the interface of the mixture
in contact with oxygen in the air by polymerization in the forming
frame, and thus can prevent generation of an unpolymerized part.
Accordingly, entrapping immobilization pellets with highly stable
quality can be produced. By employing a plurality of the forming
frames, a large amount of entrapping immobilization pellets can be
produced inexpensively at high speed.
[0033] According to a ninth aspect of the present invention, there
is provided the apparatus for producing entrapping immobilization
pellets according to the eighth aspect, wherein the forming frame
comprises a heating device.
[0034] By providing the heating device in the forming frame as
described above, the mixture can be heated to or maintained at an
appropriate temperature to carry out polymerization. Accordingly,
in the reaction frame, the polymerization reaction rate can be
controlled, and the reaction can be uniformly carried out.
[0035] According to a tenth aspect of the present invention, there
is provided the apparatus for producing entrapping immobilization
pellets according to the eighth or ninth aspect, further
comprising: an extrusion device which extrudes the pellet block
from the forming frame, wherein the extrusion device comprises at
least one of an inclination device of inclining the forming frame
and a pressurizing device of pressurizing an inside of the forming
frame.
[0036] Depending on the material of the forming frame or the
strength of the pellet block, it is difficult to remove the pellet
block from the forming frame, disadvantageously, for example, a
part of the pellet block remains in the forming frame. Thus, in the
tenth aspect, by pressurizing the inside of the forming frame or
injecting a liquid such as water into the frame to improve slip
properties, the pellet block can be easily removed without damages.
Accordingly, the removal time can be reduced.
[0037] According to an eleventh aspect of the present invention,
there is provided the apparatus for producing entrapping
immobilization pellets according to any one of the eighth to tenth
aspects, further comprising lattice-shaped cutting blades of
cutting the pellet block into lattices; and a rotary cutting blade
of cutting the pellet block cut into lattices substantially into
cubes, the blade provided downstream of the lattice-shaped cutting
blades.
[0038] In the eleventh aspect, the pellet block is first cut into
lattices, and then is cut perpendicular to the longitudinal
direction with the rotary cutting blade. Thus, a large amount of
uniform and substantially cubic pellets that have excellent form
accuracy can be produced by high-speed treatment. Since the pellet
block is cut while fixed, the pellet block can be left undeformed
by pressure from the cutting blade.
[0039] According to a twelfth aspect of the present invention,
there is provided the apparatus for producing entrapping
immobilization pellets according to any one of the eighth to
eleventh aspects, further comprising: a control device which
controls a transport speed of the pellet block and a rotation speed
of the rotary cutting blade, so that the entrapping immobilization
pellets after cutting are substantially cubes.
[0040] The problem is that, when pellets not having a uniform shape
are put into a wastewater treatment tank and used, the pellets clog
a screen for preventing discharge of pellets or are discharged from
the screen. Accordingly, pellets with a stable shape are required.
In the twelfth aspect, when the pellet block is cut while
transporting the pellet block, the pellet block is first cut into
lattices with the lattice-shaped cutting blades while transporting
the block. Next, the lattice-shaped pellet block is cut into blocks
of entrapping immobilization pellets at certain intervals
perpendicular to the longitudinal direction with the rotary cutting
blade. In cutting the pellet block, by controlling the transport
speed of the pellet block and the rotation speed of the rotary
cutting blade, a large amount of substantially cubic entrapping
immobilization pellets can be produced in a stable manner.
[0041] According to a thirteenth aspect of the present invention,
there is provided the apparatus for producing entrapping
immobilization pellets according to any one of the eighth to
twelfth aspects, wherein the microorganisms are bacteria contained
in activated sludge. Since activated sludge containing target
microorganisms (such as nitrifying bacteria) as described above is
used in a wastewater treatment process, a relatively large amount
of microorganisms are available inexpensively.
[0042] According to a fourteenth aspect of the present invention,
there is provided the apparatus for producing entrapping
immobilization pellets according to any one of the eighth to
thirteenth aspects, wherein the forming frame is substantially a
cuboid or cube.
[0043] The entrapping immobilization pellets used in the present
inventions are substantially cubes excellent in terms of stirring
and flowability in a wastewater treatment tank. In the fourteenth
aspect, since the shape of the pellet block is a cuboid or cube, a
large amount of uniform and cubic entrapping immobilization pellets
can be efficiently produced.
[0044] According to a fifteenth aspect of the present invention,
there is provided the apparatus for producing entrapping
immobilization pellets according to the fourteenth aspect, wherein
the forming frame has a ratio V/S of the volume V to the bottom
area S of 10 to 100.
[0045] In the fifteenth aspect, the shape of the forming frame is
specified. By providing the pellet block with a shape defined by
the present invention, the contact interface with oxygen
(corresponding to the bottom area part) can be reduced, and the
resistance when removing the block from the forming frame can also
be reduced. Accordingly, entrapping immobilization pellets with
highly stable quality can be efficiently produced. The shape of the
forming frame is preferably a cuboid, a cube or the like, but is
not limited thereto. The shape may be a cylinder or the like.
[0046] According to a sixteenth aspect of the present invention,
there is provided entrapping immobilization pellets produced by the
apparatus for producing entrapping immobilization pellets according
to any one of the eighth to fifteenth aspects.
[0047] The entrapping immobilization pellets according to the
sixteenth aspect are produced using the apparatus for producing
entrapping immobilization pellets of the present invention. Thus,
uniform and cubic entrapping immobilization pellets with highly
stable quality can be obtained.
[0048] According to a seventeenth aspect of the present invention,
there is provided a wastewater treatment equipment in which
wastewater is treated with the entrapping immobilization pellets
according to the sixteenth aspect.
[0049] According to the seventeenth aspect, entrapping
immobilization pellets produced using the production apparatus of
the present invention are put into a wastewater treatment tank to
carry out wastewater treatment. Thus, microorganisms can be packed
with the wastewater treatment tank at a high concentration, and
wastewater can be efficiently treated.
[0050] As described above, the present invention can produce a
large amount of entrapping immobilization pellets with highly
stable quality inexpensively by high-speed treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] FIG. 1 is a plan view showing an entire configuration of the
apparatus for producing entrapping immobilization pellets to which
the present invention is applied;
[0052] FIG. 2 is an oblique view showing the forming frame
according to an embodiment of the present invention;
[0053] FIG. 3 is a side view showing the cutting unit according to
an embodiment of the present invention;
[0054] FIG. 4 is a graph showing the relation between the V/S ratio
and the pellet strength in an example of the present invention;
[0055] FIG. 5 is a graph showing the relation between the V/S ratio
and the removal time in an example of the present invention;
[0056] FIG. 6 is a graph showing the relation between the pellet
deformation ratio and the removal time in an example of the present
invention;
[0057] FIG. 7 is a graph showing the relation between the
prepolymer molecular weight and the pellet deformation ratio in an
example of the present invention;
[0058] FIG. 8 is a graph showing the relation between the
prepolymer concentration and the pellet deformation ratio in an
example of the present invention;
[0059] FIG. 9 is a graph showing the relation between the
polymerization time and the removal time in an example of the
present invention;
[0060] FIG. 10 is a graph showing the relation between the
polymerization temperature and the pellet strength in an example of
the present invention; and
[0061] FIG. 11 is a view showing a configuration of a conventional
apparatus for producing entrapping immobilization pellets.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0062] Preferred embodiments of the process and the apparatus for
producing entrapping immobilization pellets, the entrapping
immobilization pellets, and the wastewater treatment equipment
using the pellets of the present invention will be described below
with reference to the accompanying drawings.
[0063] FIG. 1 is a view showing an entire configuration of the
production apparatus of the present invention. As shown in FIG. 1,
the production apparatus 10 is configured to comprise a raw
material mixing section 1, a pellet block preparation section 2,
and a pellet block cutting section 3 as main components.
[0064] The raw material mixing section 1 comprises, as main
components, a raw material tank 12 in which a raw material is
stored, chemical tanks 14, 22 in which chemicals are stored, and a
stirring and extrusion unit 20 in which the raw material is mixed
with the chemicals.
[0065] In the raw material tank 12, microorganisms (activated
sludge) as a raw material are stored. In the chemical tank 14, a
chemical such as an immobilizing agent solution is stored. In the
chemical tank 22, a chemical such as a polymerization initiator is
stored.
[0066] Pumps 16, 18, 24 are driving devices of introducing the raw
material in the raw material tank 12, the chemical in the chemical
tank 14, and the chemical in the chemical tank 22 into the stirring
and extrusion unit 20, respectively, and are provided between the
stirring and extrusion unit 20 and the raw material tank 12, the
chemical tank 14, and the chemical tank 22, respectively. Thus, a
mixture as a raw material for producing entrapping immobilization
pellets can be prepared in the stirring and extrusion unit 20 and
extruded into a forming frame 52.
[0067] Microorganisms to be immobilized are bacteria contained in
activated sludge, which are complex microorganisms comprising
nitrifying bacteria, denitrifying bacteria, and anaerobic
ammonium-oxidizing bacteria. In order to increase the initial
immobilizing concentration of the target microorganisms, the
activated sludge concentration is preferably 10,000 to 40,000
mg-ss/L. Pure microorganisms such as microcystis decomposing
bacteria, PCB decomposing bacteria, dioxin decomposing bacteria,
and environmental hormone decomposing bacteria can also be
used.
[0068] Examples of immobilizing agent prepolymers and crosslinking
agents that can be used in the present invention include the
following compounds:
monomethacrylates such as polyethylene glycol monomethacrylate,
polyprene glycol monomethacrylate, polypropylene glycol
monomethacrylate, methoxydiethylene glycol methacrylate,
methoxypolyethylene glycol methacrylate, methacryloyloxyethyl
hydrogen phthalate, methacryloyloxyethyl hydrogen succinate,
3-chloro-2-hydroxypropyl methacrylate, stearyl methacrylate,
2-hydroxy methacrylate, and ethyl methacrylate; monoacrylates such
as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, isobutyl
acrylate, t-butyl acrylate, isooctyl acrylate, lauryl acrylate,
stearyl acrylate, isobornyl acrylate, cyclohexyl acrylate,
methoxytriethylene glycol acrylate, 2-ethoxyethyl acrylate,
tetrahydrofurfuryl acrylate, phenoxyethyl acrylate,
nonylphenoxypolyethylene glycol acrylate, nonylphenoxypolypropylene
glycol acrylate, silicon-modified acrylate, polypropylene glycol
monoacrylate, phenoxyethyl acrylate, phenoxydiethylene glycol
acrylate, phenoxypolyethylene glycol acrylate, methoxypolyethylene
glycol acrylate, acryloyloxyethyl hydrogen succinate, and lauryl
acrylate; dimethacrylates such as 1,3-butylene glycol
dimethacrylate, 1,4-butanediol dimethacrylate, ethylene glycol
dimethacrylate, diethylene glycol dimethacrylate, triethylene
glycol dimethacrylate, polyethylene glycol dimethacrylate, butylene
glycol dimethacrylate, hexanediol dimethacrylate, neopentyl glycol
dimethacrylate, polyprene glycol dimethacrylate,
2-hydroxy-1,3-dimethacryloxypropane,
2,2-bis-4-methacryloxyethoxyphenylpropane,
3,2-bis-4-methacryloxydiethoxyphenylpropane, and
2,2-bis-4-methacryloxypolyethoxyphenylpropane; diacrylates such as
ethoxylated neopentyl glycol diacrylate, polyethylene glycol
diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate,
tripropylene glycol diacrylate, polypropylene glycol diacrylate,
2,2-bis-4-acryloxyethoxyphenylpropane,
2-hydroxy-1-acryloxy-3-methacryloxypropane; trimethacrylates such
as trimethylolpropane trimethacrylate; triacrylates such as
trimethylolpropane triacylate, pentaerythritol triacylate,
trimethylolpropane EO-added triacylate, glycerol PO-added
triacylate, and ethoxylated trimethylolpropane triacylate;
tetraacrylates such as pentaerythritol tetraacrylate, ethoxylated
pentaerythritol tetraacrylate, propoxylated pentaerythritol
tetraacrylate, and ditrimethylolpropane tetraacrylate; urethane
acrylates such as urethane acrylate, urethane dimethyl acrylate,
and urethane trimethyl acrylate; and other compounds such as
acrylamide, acrylic acid, and dimethylacrylamide.
[0069] The polymerization in the present invention is most
appropriately radical polymerization using potassium persulfate,
but may be polymerization using ultraviolet rays or electron beams
or redox polymerization. In polymerization using potassium
persulfate, it is preferable to add 0.001 to 0.25 mass % of
potassium persulfate and 0.001 to 0.5 mass % of a polymerization
initiator. As the polymerization initiator,
.beta.-dimethylaminopropionitrile,
N,N,N',N'-tetramethylethylenediamine, sodium sulfite, or the like
is preferable.
[0070] The pellet block preparation section 2 comprises the forming
frame 52 of producing a pellet block 60 by polymerizing the
mixture, a heating device 53 of heating the forming frame 52, a
transfer stage 54 of transporting the forming frame 52, and a
removal device 56 of removing the pellet block 60 as main
components.
[0071] The forming frame 52 is in the shape of a container in which
the mixture is polymerized while reducing contact with oxygen. A
plurality of the forming frames 52 are arranged on the transfer
stage 54, and a predetermined amount of the mixture is introduced
into each of the forming frames 52.
[0072] The material for the forming frame 52 is preferably a
material that does not inhibit polymerization reaction of the
mixture and has low wettability with the pellet block 60. For
example, vinyl chloride, SUS, an acrylic resin, or the like is more
preferable. The size of the forming frame 52 is preferably about 1
to 10 L in terms of removability and productivity.
[0073] The forming frame 52 preferably has a shape to have a ratio
V/S of the volume V of the forming frame 52 to the bottom area S of
the forming frame 52 of 10 to 100. By providing the pellet block
with such a shape, the contact interface with oxygen (corresponding
to the bottom area part) can be reduced, and the resistance when
removing the block from the forming frame can also be reduced.
Accordingly, entrapping immobilization pellets with highly stable
quality can be efficiently produced. The shape of the forming frame
52 is preferably a cuboid or cube from the viewpoint of handling
and yield, but is not limited thereto. The shape may be a cylinder
or the like. In order to suppress contact with oxygen during
polymerization, the forming frame preferably has a structure that
can be closed with a lid 57 (see FIG. 2) or the like or a
vertically long structure with a small opening surface.
[0074] The heating device 53 is provided in the forming frame 52.
Thus, the mixture can be heated to or maintained at a temperature
appropriate for polymerization reaction in the forming frame 52.
Accordingly, the polymerization reaction rate of the mixture can be
increased, and the pellet block 60 can be produced in a short
time.
[0075] Specific examples of the heating device 53 include various
heaters, but other devices that can maintain the mixture in the
forming frame 52 at a predetermined temperature are also
possible.
[0076] FIG. 2 is a schematic view of the forming frame 52 with an
injection pipe 56 mounted. As shown in FIG. 2, the injection pipe
56 is communicated with the bottom of the forming frame 52 via a
joint 55. When removing the pellet block 60, the forming frame 52
is inclined at about 45.degree., and air or water is injected into
the forming frame 52 from the injection pipe 56 at a predetermined
pressure (about 0.1 MPa) to pressurize the inside. The pellet block
60 is thus extruded from the forming frame 52. The injection pipe
56 may be provided on the forming frame 52, or may be mounted from
the outside. The bottom of the forming frame 52 may be formed with
a valve or a plug, for example, so that the frame can be
communicated with the injection pipe 56 except when preparing the
pellet block 60.
[0077] The pellet block 60 may be removed by a method of inclining
the forming frame 52 and injecting an inert gas (such as nitrogen
gas or air) or a liquid (such as water) into the forming frame 52
at a predetermined pressure, or by a method of opening a plug (not
shown) provided on the bottom of the forming frame 52 and making
the pressure on the bottom of the forming frame atmospheric.
Alternatively, the pellet block 60 may be removed by injecting a
liquid that can reduce wettability between the forming frame 52 and
the pellet block 60 into the forming frame 52 to improve slip
properties of the pellet block 60. After removing the pellet block
60, the forming frame 52 is used for polymerizing the mixture
again.
[0078] The pellet block cutting section 3 includes a cutting unit
58 comprising a transport device 62 and an extrusion board 64 which
transport the pellet block 60 while fixing, a fixing stage 65 of
fixing the pellet block 60, lattice-shaped cutting blades 66A, 66B,
and a rotary cutting blade 68 as main components. FIG. 3A is a side
view showing the cutting unit 58, and FIG. 3B is a plan view
corresponding to FIG. 3A.
[0079] The fixing stage 65 has a shape of a groove in which the
pellet block 60 is fixed when cutting the pellet block 60. The
groove has almost the same width as in the pellet block 60, and the
pellet block 60 is placed in the groove. The lattice-shaped cutting
blades 66A, 66B are provided on the top of the groove. The pellet
block 60 is transported through the fixing stage 65 to the
lattice-shaped cutting blades 66A, 66B by the extrusion board
64.
[0080] The extrusion board 64 extrudes the pellet block 60 into the
lattice-shaped cutting blades 66A, 66B at a predetermined speed. As
shown in FIG. 3A, the extrusion board 64 is configured to be
movable by the transport device 62 such as a ball screw mechanism
or a cylinder mechanism which can control the transport speed, for
example.
[0081] The lattice-shaped cutting blades 66A, 66B are formed by
providing a plurality of cutting blades at predetermined intervals
in the shape of lattices. In the lattice-shaped cutting blades 66A,
66B in FIGS. 3A and 3B, cutting blades lattice-shaped in the
crosswise direction (A-A' direction) are combined with cutting
blades lattice-shaped in the longitudinal direction (B-B'
direction). As the lattice-shaped cutting blades 66A, 66B, wire
saws or cutter blades arranged in the shape of lattices can be
used. In the present embodiment, in order to produce 3 mm-square
cubic entrapping immobilization pellets 70, lattice-shaped cutting
blades provided at intervals of about 3 mm each are preferable. The
pellet block 60 is cut into about 3 mm-narrow lattices with the
lattice-shaped cutting blades 66A, 66B.
[0082] The rotary cutting blade 68 cuts the pellet block 60 with
about 3 mm-narrow lattices perpendicular to the transport direction
at a predetermined rotation speed.
[0083] A thin cutting blade having a thickness of 1 mm, for
example, is used for the lattice-shaped cutting blades 66A, 66B or
the rotary cutting blade 68.
[0084] Thus, the pellet block 60 is cut into lattices in the fixing
stage 65, while the block is transported by the transport device 62
at a predetermined transport speed. The lattices are then cut into
3 mm-square cubes with the rotary cutting blade 68.
[0085] Next, the process for producing entrapping immobilization
pellets using the production apparatus 10 in FIG. 1 will be
described.
[0086] First, a raw material in the raw material tank 12 (such as
activated sludge) and a chemical in the chemical tank 14 (such as
an immobilizing agent solution) are mixed and fed into the stirring
and extrusion unit 20 by driving the pumps 16, 18. Then, the
mixture fed into the stirring and extrusion unit 20 is mixed with a
chemical (such as a polymerization initiator) fed thereinto from
the other chemical tank 22 by the pump 24, followed by stirring.
The mixture is extruded into the forming frame 52 arranged on the
transport stage 54 running (raw material mixing section 1).
[0087] Then, the mixture is polymerized into a gel in the forming
frame 52 heated to or maintained at 20 to 30.degree. C. In this
case, the mixture contains an immobilizing agent, water, activated
sludge, a polymerization initiator, a polymerization accelerator,
and the like. Polymerization reaction proceeds for 10 to 60 minutes
to produce a gelled pellet block 60. Thereafter, the forming frame
is inclined at about 45.degree.. At the same time, the removal
device 56 is mounted on the bottom of the forming frame 52, and air
is injected into the forming frame 52 at a pressure of about 0.1
MPa. Thus, the gelled pellet block 60 is smoothly removed from the
forming frame 52 while maintaining the formed shape in the forming
frame 52 (pellet block preparation section 2).
[0088] Next, the pellet block 60 removed from the forming frame 52
is transported to the cutting unit 58 and stored in the fixing
stage 65. The pellet block 60 is cut into about 3 mm-wide lattices
with the lattice-shaped cutting blades 66A, 66B, while being
transported by the transport device 62 and the extrusion board 64,
and then the lattices are cut substantially into cubes with the
rotary cutting blade 68. 3 mm-square cubic entrapping
immobilization pellets 70 are thus produced (pellet block cutting
section 3).
[0089] As described above, the process for producing entrapping
immobilization pellets of the present invention carries out
polymerization in the forming frame in order to reduce the contact
interface with air, and accordingly can produce a pellet block with
highly stable quality inexpensively. By cutting the pellet block
with the lattice-shaped cutting blades and the rotary cutting blade
while fixing, a large amount of uniform and substantially cubic
pellets can be produced at high speed.
EXAMPLES
[0090] Examples of the present invention will be described below.
However, the present invention is not limited to the examples.
[0091] 1) The relation between the type of forming method and the
amount of COD eluted, 2) the V/S ratio as a shape condition of the
forming frame, 3) the pellet deformation ratio, 4) prepolymer
properties (molecular weight and concentration), and 5)
polymerization conditions (polymerization time and temperature)
were examined using the production apparatus 10 of the present
invention shown in FIG. 1. As the pellet materials, those of FIG. 1
were mainly used.
TABLE-US-00001 TABLE 1 Type of material Content Activated sludge
MLSS 30000 mg/L Number of nitrifying bacteria 5 .times. 10.sup.6
cells/mL Immobilizing agent Polyethylene glycol dimethacrylate
Polymerization initiator Potassium persulfate: 0.025 mass %
Polymerization accelerator N,N,N',N'-tetramethylethylenediamine:
0.05 mass %
1) The Relation Between the Type of Forming Method and the Amount
of COD Eluted
[0092] Entrapping immobilization pellets (hereinafter referred to
as "pellets") were prepared using the process and the apparatus for
producing entrapping immobilization pellets of the present
invention under the following conditions. First, a prepolymer
having a molecular weight of 9,000 as an immobilizing agent was
dissolved in water at a prepolymer concentration per pellet of 10
mass % to prepare an immobilizing agent solution. Next, the
immobilizing agent solution and activated sludge in Table 1 were
put into a 4 L-volume forming frame 52 having a V/S ratio of 40 to
prepare a mixture, and then a polymerization initiator and a
polymerization accelerator in Table 1 were added to the mixture.
The mixture was polymerized at a polymerization temperature of
20.degree. C. for a polymerization time of 30 minutes to prepare a
pellet block. The pellet block was cut into 3 mm-square cubes to
prepare pellets (pellets produced by the block forming of the
present invention).
[0093] Further, pellets were prepared by conventional sheet forming
under the same conditions except for the forming method (pellets
produced by conventional sheet forming).
[0094] The pellet strengths of the pellets prepared by the
respective forming methods were measured and compared. Using a
rheometer, the pellet strengths were measured as a compression
force per unit area when compressing entrapping immobilization
pellets with a certain force to break the pellet gel (meaning that,
when the pellet strength is 7 kg/cm.sup.2, the pellets are broken
down by applying pressure above the compression force). Next, the
pellets were added to 425 mL of tap water at a true volume ratio of
15% to provide 500 mL of a mixture, which was then stirred with a
stirrer in a beaker for 30 minutes. Then, the COD concentrations
were measured for the pellets prepared by the respective forming
methods using a method of measuring the oxygen demand by potassium
permanganate at 100.degree. C. in accordance with JIS K 0102 to
calculate the amounts of COD eluted (unit: 1 mg/L).
TABLE-US-00002 TABLE 2 Item Block forming Sheet forming Compression
strength (kg/cm.sup.2) 7.3 4.1 Amount of COD eluted (mg/L) 180
720
[0095] As is clear from Table 2, the block forming attained a
compression strength about 1.8 times of that attained by the
conventional sheet forming, and polymerization was carried out well
by the block forming. As shown in Table 2, the block forming of the
present invention only attained a considerably small amount of COD
eluted about 1/4 of that attained by the conventional sheet
forming. Therefore, it was found that unpolymerized parts of the
pellets can be reduced by the block forming of the present
invention.
2) The V/S Ratio as a Shape Condition of the Forming Frame
[0096] The shape condition of the forming frame which can reduce
the contact interface with oxygen and allows easy removal from the
forming frame was examined. A pellet block was prepared in the same
manner as in 1). The pellet strength was measured by the same
method as in 1). The removal time was defined as a period during
which the forming frame was inclined at about 45.degree. in the
horizontal direction after polymerization, air was injected into
the bottom of the forming frame at a pressure of 0.1 MPa, and the
pellet block was removed.
[0097] According to the relation between the V/S ratio and the
pellet strength (compression strength) in the forming frame in FIG.
4, when the V/S ratio was less than 10, the interface in contact
with oxygen in the forming frame during polymerization had a large
area, and the pellet strength tended to be reduced. On the other
hand, it was found that the pellet strength was high almost in a
stable manner at a V/S ratio of 10 or more. According to the
relation between the V/S ratio and the removal time in FIG. 5, when
the V/S ratio was more than 100, the forming frame had wall
resistance increased, making it difficult to remove the pellet
block from the forming frame. Therefore, it was found that a V/S
ratio of 10 to 100 is an appropriate condition in which
polymerization can be carried out well and the pellet block can be
easily removed.
3) Pellet Deformation Ratio
[0098] Next, the relation between removability from the forming
frame and the pellet deformation ratio was examined. A pellet block
was prepared in the same manner as in 1). Using a rheometer, the
pellet deformation ratio was calculated as a ratio of the pellet
thickness immediately before breakdown of entrapping immobilization
pellets by compressing the pellets with a certain force to the
initial pellet thickness. The removal time was defined as a period
during which the forming frame was inclined at about 45.degree. in
the horizontal direction after polymerization for 30 minutes, air
was injected into the bottom of the forming frame at a pressure of
0.1 MPa, and the pellet block was removed.
[0099] As is clear from FIG. 6, the removal time was considerably
reduced at a pellet deformation ratio of 50% or more, and the
pellet block could be removed in a short time almost certain at a
pellet deformation ratio of 70% or more. Accordingly, it was found
that the pellet block is hard and fragile at a deformation ratio of
less than 50%, and thus it takes a long time to remove the pellet
block and the production efficiency is decreased.
[0100] Therefore, it was found that the pellet deformation ratio is
preferably 50% or more, and more preferably 70% or more.
4) Prepolymer Properties (Molecular Weight and Concentration)
[0101] It was found in 2) that the pellet deformation ratio is
related with the prepolymer molecular weight and concentration of
the immobilizing agent. Then, the relation between the prepolymer
molecular weight and concentration and the pellet deformation ratio
was examined. A pellet block was prepared on conditions that the
prepolymer molecular weight was 500 to 20,000 and the prepolymer
concentration was 0 to 20 mass %, using a polymerization initiator
and a polymerization accelerator in Table 1 at a polymerization
temperature of 20.degree. C. for a polymerization time of 30
minutes. Using a rheometer, the pellet deformation ratio was
calculated as a ratio of the pellet thickness immediately before
breakdown of entrapping immobilization pellets by compressing the
pellets with a certain force to the initial pellet thickness.
[0102] As is clear from FIG. 7, when the prepolymer concentration
was 10 mass %, the pellet deformation ratio was 50% or more and the
pellet block could be easily removed if the prepolymer molecular
weight was 1,000 to 13,000, and the pellet deformation ratio was
70% or more and the pellet block could be more easily removed if
the prepolymer molecular weight was 4,000 to 12,000.
[0103] As is clear from FIG. 8, when the prepolymer molecular
weight was 9,000, the pellet deformation ratio was 50% or more and
the pellet block could be easily removed if the prepolymer
concentration was 2.5 to 11 mass %, and the pellet deformation
ratio was 70% or more and the pellet block could be more easily
removed if the prepolymer concentration was 3 to 10 mass %.
5) Examination on Polymerization Conditions (Polymerization Time
and Temperature)
[0104] Polymerization conditions having an influence on the pellet
strength were examined. A pellet block was prepared from a
prepolymer having a molecular weight of 9,000 and a polymerization
initiator and a polymerization accelerator in Table 1 at a
polymerization temperature of 20.degree. C. for a polymerization
time of 10 to 70 minutes to examine the influence by the
polymerization time. Then, the removal time was measured by the
same method as in 3).
[0105] As shown in FIG. 9, when the polymerization time was shorter
than 10 minutes, polymerization was insufficient and the pellet
block could not be removed. When the polymerization time was 60
minutes or longer, it took a long time to remove the pellet block.
When the polymerization time was 80 minutes or longer, the pellet
block could not be removed. Therefore, when the polymerization time
is 10 to 60 minutes, polymerization can be sufficiently carried
out, and the removal time can be reduced.
[0106] Further, a pellet block was prepared using a prepolymer
having the same molecular weight at a polymerization temperature of
5 to 40.degree. C. for a polymerization time of 30 minutes to
examine the influence by the polymerization temperature. Then, the
pellet strength was measured by the same method as in 1).
[0107] As shown in FIG. 10, it was found that, when the
polymerization temperature was 20.degree. C. or higher, the pellet
strength was high almost in a stable manner. On the other hand,
when the polymerization temperature was lower than 20.degree. C.,
the pellet strength was considerably reduced as the temperature was
lowered. In particular, when the temperature was 10.degree. C. or
lower, polymerization was insufficient. Even when the
polymerization temperature was higher than 30.degree. C., the
pellet strength almost did not change. Therefore, it was found that
the polymerization temperature is preferably 20.degree. C. or more,
and more preferably 20 to 30.degree. C. when using an immobilizing
agent having a molecular weight of 9,000.
[0108] As described above, since the area of the contact interface
with oxygen is reduced during polymerization by applying the
present invention, a large amount of entrapping immobilization
pellets with highly stable quality can be produced inexpensively by
high-speed treatment.
* * * * *