U.S. patent application number 10/320277 was filed with the patent office on 2004-01-08 for method and apparatus for treating sludge, and method and apparatus for treating wastewater utilizing the same.
This patent application is currently assigned to JFE ENGINEERING CORPORATION. Invention is credited to Miyata, Jun, Miyazawa, Kunio, Tsubone, Toshiaki, Yamaguchi, Toyoshi, Yao, Yasuko, Yomura, Yoshinori.
Application Number | 20040004038 10/320277 |
Document ID | / |
Family ID | 30002345 |
Filed Date | 2004-01-08 |
United States Patent
Application |
20040004038 |
Kind Code |
A1 |
Yamaguchi, Toyoshi ; et
al. |
January 8, 2004 |
Method and apparatus for treating sludge, and method and apparatus
for treating wastewater utilizing the same
Abstract
Provided are a method and an apparatus for treating organic
wastewater and sludge, which remarkably reduce the generated amount
of sludge at much lower running cost, and which get the size
smaller the capacity of the solubilization tank. The method and
apparatus for treating sludge has: an biological treatment system,
which applies biological treatment to wastewater, a solid-liquid
separation unit for separating a solid from a liquid in the
wastewater after treating the biologically, to obtain a treated
wastewater and a returned sludge. And the apparatus has means for
obtaining a withdrawn sludge from a part of the returned sludge, an
alkali-treatment tank, which applies alkali-treatment to the
withdrawn sludge. The apparatus, also, has a biological
solubilization tank, which solubilizes the sludge after treating
the alkali-treatment under an anaerobic, anoxic, or microaerophilic
condition, and a means for returning sludge to recycle the
solubilized sludge to the biological treatment system.
Inventors: |
Yamaguchi, Toyoshi;
(Kawasaki, JP) ; Miyazawa, Kunio; (Sakura, JP)
; Yao, Yasuko; (Tokyo, JP) ; Tsubone,
Toshiaki; (Tokyo, JP) ; Miyata, Jun;
(Yokohama, JP) ; Yomura, Yoshinori; (Kawasaki,
JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
JFE ENGINEERING CORPORATION
TOKYO
JP
|
Family ID: |
30002345 |
Appl. No.: |
10/320277 |
Filed: |
December 16, 2002 |
Current U.S.
Class: |
210/623 |
Current CPC
Class: |
C02F 2209/06 20130101;
Y02W 10/10 20150501; C02F 1/66 20130101; C02F 3/286 20130101; C02F
11/02 20130101; Y02W 10/15 20150501; C02F 3/1221 20130101; Y02W
10/27 20150501; C02F 3/30 20130101; C02F 11/04 20130101; Y02W 10/20
20150501 |
Class at
Publication: |
210/623 |
International
Class: |
C02F 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2002 |
JP |
2002-195085 |
Oct 28, 2002 |
JP |
2002-312939 |
Claims
What is claimed is:
1. A method for treating a sludge comprising the steps of: treating
a wastewater biologically to generate a sludge; treating the sludge
by an alkali-treatment; and solubilizing the treated sludge by the
alkali-treatment, biologically, under an anaerobic, an anoxic, or a
microaerophilic condition.
2. A method for treating a wastewater comprising the steps of:
treating a wastewater biologically; separating a solid from a
liquid in the wastewater treated biologically, to obtain a treated
wastewater and a returned sludge; withdrawing the sludge from a
part of the returned sludge to obtain a withdrawn sludge; and
treating the withdrawn sludge by an alkali-treatment; and
solubilizing and decomposing the withdrawn sludge, biologically,
under an anaerobic, an anoxic, or a microaerophilic condition.
3. The method according to claim 1, wherein a pH value is less than
9 during treating the sludge by the alkali-treatment.
4. The method according to claim 2, wherein a pH value is less than
9 during treating the sludge by the alkali-treatment.
5. The method according to claim 2, further comprising the step of
thickening the sludge before treating the withdrawn sludge by the
alkali-treatment.
6. An apparatus for treating a sludge comprising: an
alkali-treatment tank for treating a sludge by an alkali-treatment,
generated in the biologically treated wastewater; and a biological
solubilization tank, located at downstream side of the
alkali-treatment tank, connected with the alkali-treatment tank via
a passage, to biologically solubilize the sludge after treating the
sludge by the alkali-treatment under an anaerobic, an anoxic, or a
microaerophilic condition.
7. An apparatus for treating a wastewater comprising: a biological
treatment system to treat a wastewater biologically; a solid-liquid
separation unit, located at downstream side of the biological
treatment system, connected with the biological treatment system
via a passage, to separate the biologically treated wastewater in
the biological treatment system and to obtain the treated
wastewater and the returned sludge. a sludge thickening device for
obtaining a withdrawn sludge from a part of the returned sludge; an
alkali-treatment tank to treat the withdrawn sludge by the
alkali-treatment; a biological solubilization tank to biologically
solubilize the sludge after treating the sludge by the
alkali-treatment, under an anaerobic, an anoxic, or a
microaerophilic condition; and means for returning the solubilized
sludge for recycling the solubilized sludge into the biological
treatment system.
8. The apparatus according to claim 6, wherein the alkali-treatment
tank is a tank of plug flow type.
9. The apparatus according to according to claim 7, wherein the
alkali-treatment tank is a tank of plug flow type.
10. The apparatus according to claim 6, wherein the biological
solubilization tank is a tank of plug flow type.
11. The apparatus according to claim 7, wherein the biological
solubilization tank is a tank of plug flow type.
12. A method for treating a sludge comprising the steps of:
treating a wastewater biologically to generate the sludge; and
treating the sludge by an alkali-treatment, by intermittently
adding the alkali to the sludge at a determined interval.
13. The method according to claim 12, further comprising the step
of solubilizing a sludge biologically after treating the sludge by
the alkali-treatment, under an anaerobic, an anoxic, or a
microaerophilic condition.
14. The method according to claim 12, wherein a retention time of
the sludge in the alkali-treatment step is held from for 3 hours to
for 24 hours and the retention time of the sludge in the biological
solubilization step is held from for 1 day to for 3 days.
15. The method according to claim 13 further comprising the step
of: treating the sludge by the alkali-treatment under the normal
temperature and the normal pressure; and solubilizing the sludge
biologically, under the normal temperature and the normal
pressure.
16. The method according to claim 14 further comprising treating
the sludge by alkali-treatment under the normal temperature and the
normal pressure; solubilizing the sludge biologically, under the
normal temperature and the normal pressure.
17. An apparatus for treating a sludge comprising: an
alkali-treatment tank for intermittently adding the alkali at a
determined interval to the sludge generated by treating a
wastewater biologically, and for treating the sludge by the alkali
with holding a retention time of from for 3 hours to for 24 hours;
a biological solubilization tank for solubilizing biologically the
treated sludge by the alkali-treatment, at a normal temperature and
a pressure in an anaerobic, an anoxic, or a microaerophilic
condition, with the retention time of from for 1 day to for 3 days,
wherein the biological solubilization tank being located at
downstream side of the alkali-treatment tank and being connected
with the alkali-treatment tank via a passage; and means for
transporting at least a part of the alkali-treated sludge into the
biological solubilization tank.
18. A method for treating a wastewater comprising: treating a
wastewater biologically in a biological treatment system;
separating a solid from a liquid after treating the wastewater
biologically, to obtain a treated wastewater and a returned sludge,
and to obtain a withdrawn sludge from a part of the returned
sludge; treating the withdrawn sludge in an alkali-treatment, by
intermittently adding the alkali at a determined interval, with
holding a retention time after adding the alkali from for 3 hours
to for 24 hours; solubilizing the alkali-treated sludge
biologically at the normal temperature and the pressure in an
anaerobic, an anoxic, or a microaerophilic atmosphere, with holding
a retention time after adding alkali, from for 1 day to 3 days; and
returning the solubilized sludge to the biological treatment
system.
19. An apparatus for treating a wastewater comprising: means for
treating a wastewater biologically in a biological treatment
system; means for separating a solid from a liquid in the
biologically treated wastewater, to obtain a treated wastewater and
a returned sludge; means for obtaining a withdrawn sludge from a
part of the returned sludge; means for treating the withdrawn
sludge by intermittently adding an alkali at a determined interval,
with holding a retention time after adding the alkali from for 3
hours to for 24 hours; means for biologically solubilizing the
withdrawn sludge immediately after the alkali-treatment, wherein
the biological solubilization is achieved at the normal temperature
and the pressure in an anaerobic, an anoxic, or a microaerophilic
atmosphere, with holding a retention time after adding the alkali
from for 1 day to 3 days; and means for returning the solubilized
sludge to the biological treatment system.
20. A method for treating a wastewater comprising the steps of:
treating a wastewater biologically; separating a solid from a
liquid in the biologically treated wastewater to obtain a treated
wastewater and a returned sludge; treating a part of the return
sludge by an alkali-treatment, within a range of pH value from 9 to
12.5; solubilizing the sludge biologically immediately after
treating the sludge by the alkali-treatment, in an anaerobic, an
anoxic, or a microaerophilic condition; and returning the
solubilized sludge to the biological treatment system.
21. The method according to claim 20 further comprising the step of
thickening the sludge before treating the sludge by the
alkali-treatment.
22. An apparatus for treating a wastewater comprising: a biological
treatment tank to treat a wastewater biologically; a solid-liquid
separation unit to separate the wastewater discharged from the
biological treatment tank to obtain a treated wastewater and a
returned sludge; an alkali-treatment tank to treat a part of the
returned sludge by the alkali within a range of pH value from 9 to
12.5; a biological solubilization tank, connected to the
alkali-treatment tank, to biologically solubilize the sludge
discharged from the alkali-treatment tank under an anaerobic,
anoxic, or microaerophilic condition; and means for returning the
sludge discharged from the biological solubilization tank to the
biological treatment tank, to recycle the sludge.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for solubilizing
sludge generated from a biological treatment process for organic
wastewater and an apparatus thereof. Specifically, the present
invention relates to a method and an apparatus for treating sludge,
which suppresses the generation of excess sludge by solubilizing,
in order to make it possible to reduce the generated amount of the
sludge, and also relates to a method and an apparatus for treating
wastewater thereof.
BACKGROUND OF THE INVENTION
[0002] From biological treatment process such as activated sludge
process, there generate a large amount of sludge, where organic
wastewater such as sewage is dealt with. And today, it is the most
serious problem how to treat and dispose the sludge.
Conventionally, the sludge has been dewatered through a dehydrator
by adding a dewatering assistant, then has been disposed by
landfill or by incineration. However, in case of disposing sludge
as landfill, there occurs a problem of significant increase in
disposal cost, owing to the shortage in available landfill area. In
case of incinerating sludge, there occur several problems, which
are, overloading to the incinerator and how to dispose ash after
incineration. Accordingly, the above-mentioned problems give users
a lot of burden.
[0003] An aerobic digestion (methane fermentation) process is known
to the world as one of a method for reducing the volume of sludge.
The process, however, needs a long retention time so that the size
and capacity of a tank becomes gigantic. In addition, the effect,
which is given by reducing the sludge, is not so high, even in the
gigantic tank. Above all, the digested sludge, which is left after
the digestion treatment, cannot help dewatering, before disposal
treatment.
[0004] Various processes have been presented to reduce the volume
of sludge, up to now. For example, Japanese Patent Laid-Open No.
H9-253684 discloses a process to reduce the volume of generated
sludge by solubilizing the withdrawn sludge in the anaerobic
fermentation step, followed by recycling the fermented withdrawn
sludge to the activated sludge system. Furthermore, there is a
proposed technology to reduce the volume of generated excess
sludge, which is applied to the wastewater-treatment technology.
This technology conducts the steps of: withdrawing a part of the
returned sludge; applying alkali-treatment to the withdrawn and
returned sludge by adding an alkali; applying biological treatment
to the alkali-treated sludge under an anaerobic, anoxic, or
microaerophilic condition; and recycling the biologically-treated
sludge to the biological treatment step such as aeration tank.
[0005] According to these conventional technologies, however,
solubilizing the sludge merely by the anaerobic fermentation
treatment needs a long retention time for attaining sufficient
solubilized ratio, which inevitably increases the size of the
solubilization tank. For example, in case that enzymes produced by
thermophilic aerobic bacteria solubilize the sludge, the running
cost increases, which is the heating cost and the running cost for
running on the aeration in order to maintain the aerobic
condition.
[0006] As for the solubilization of sludge by ozone oxidation,
foaming trouble in the ozone oxidation tank may occur. And the
treatment system for emitting ozone is required. Furthermore, the
investment cost to install an ozonizer and the running cost to add
ozone is high. So, the initial investment cost increase to a great
degree simultaneously with increasing running cost. With regard to
the solubilization by hot-alkali-treatment process, a large amount
of chemicals are required, which invites cost-increase for the
chemicals and the heating. This results in increasing the running
cost.
[0007] As mentioned above, without applying a large scale of the
solubilization tank and with the low running cost, no conventional
technologies can achieve the volume reduction of sludge.
SUMMARY OF THE INVENTION
[0008] In order to solve the above-described problems, the present
invention provides the methods and apparatuses, as follows.
[0009] First, a method for treating a sludge comprising the steps
of:
[0010] treating a wastewater biologically to generate a sludge;
[0011] treating the sludge by an alkali-treatment; and
[0012] solubilizing the alkali-treated sludge biologically, under
an anaerobic, an anoxic, or a microaerophilic condition.
[0013] Second, a method for treating a wastewater comprising the
steps of:
[0014] treating a wastewater biologically;
[0015] separating a solid from a liquid in the wastewater treated
biologically, to obtain a treated wastewater and a returned
sludge;
[0016] withdrawing the sludge from a part of the returned sludge to
obtain a withdrawn sludge; and
[0017] treating the withdrawn sludge by an alkali-treatment;
and
[0018] solubilizing and decomposing the withdrawn sludge,
biologically, under an anaerobic, anoxic, or a microaerophilic
condition.
[0019] (Note: In the above-mentioned description, there exists an
expression of `treating a wastewater biologically`. In this
expression, a wastewater means flowing into a method and an
apparatus of the present invention, and then, the wastewater is
dealt with (treated) in the method and the apparatus. There, also,
exists an expression of `to obtain a treated wastewater`. In this
expression, `a treated wastewater` mainly means the wastewater
after having been dealt with (having been treated with) in the
method and the apparatus of the present invention. In the
specification, there are found the expressions of `a treated
wastewater`, or `the quality of the treated wastewater`. These are
mainly defined as `after having treated in the method and the
apparatus for treating the sludge and the wastewater of the present
invention.)
[0020] Third, an apparatus for treating a sludge comprising:
[0021] an alkali-treatment tank for treating a sludge by an
alkali-teratment, generated in the biologically treated wastewater;
and
[0022] a biological solubilization tank, located at downstream side
of the alkali-treatment tank, connected with the alkali-treatment
tank via a passage, to biologically solubilize the sludge after
treating the sludge by the alkali-treatment under an anaerobic, an
anoxic, or a microaerophilic condition.
[0023] Fourth, an apparatus for treating a wastewater
comprising:
[0024] a biological treatment system to treat a wastewater
biologically;
[0025] a solid-liquid separation unit, located at downstream side
of the biological treatment system, connected with the biological
treatment system via a passage, to separate the biologically
treated wastewater in the biological treatment system and to obtain
the treated wastewater and the returned sludge.
[0026] means for obtaining a withdrawn sludge from a part of the
returned sludge;
[0027] an alkali-treatment tank to treat the withdrawn sludge by
the alkali-treatment;
[0028] a biological solubilization tank to biologically solubilize
the sludge after treating the sludge by the alkali-treatment, under
an anaerobic, an anoxic, or a microaerophilic condition; and
[0029] a sludge returning passage for recycling the solubilized
sludge into the biological treatment system.
[0030] Fifth, a method for treating a sludge comprising the steps
of:
[0031] treating a wastewater biologically to generate the sludge;
and
[0032] treating the sludge by an alkali-treatment, by
intermittently adding the alkali to the sludge at a determined
interval.
[0033] Six, an apparatus for treating a sludge comprising:
[0034] an alkali-treatment tank for intermittently adding the
alkali at a determined interval to the sludge generated by treating
a wastewater biologically, and for treating the sludge by the
alkali-treatment with holding a retention time of from for 3 hours
to for 24 hours;
[0035] a biological solubilization tank for solubilizing
biologically the treated sludge by the alkali, at a normal
temperature and a pressure in an anaerobic, anoxic, or
microaerophilic condition, with the retention time of from for 1
day to for 3 days, wherein the biological solubilization tank being
located at downstream side of the alkali-treatment tank and being
connected with the alkali-treatment tank via a passage; and
[0036] means for transporting at least a part of the alkali-treated
sludge into the biological solubilization tank.
[0037] Seventh, a method for treating a wastewater comprising:
[0038] treating a wastewater biologically in a biological treatment
system;
[0039] separating a solid from a liquid after treating the
wastewater biologically, to obtain a treated wastewater and a
returned sludge, and to obtain a withdrawn sludge from a part of
the returned sludge;
[0040] treating the withdrawn sludge by intermittently adding
alkali at a determined interval, with holding a retention time
after adding the alkali from for 3 hours to for 24 hours;
[0041] solubilizing the alkali-treated sludge biologically at a
normal temperature and a pressure in an anaerobic, anoxic, or
microaerophilic atmosphere, with holding a retention time after
adding alkali from for 1 day to 3 days; and
[0042] returning the solubilized sludge to the biological treatment
system.
[0043] Eighth, an apparatus for treating a wastewater
comprising:
[0044] means for treating a wastewater biologically in a biological
treatment system;
[0045] means for separating a solid from a liquid in the
biologically treated wastewater, to obtain a treated wastewater and
a returned sludge;
[0046] means for obtaining a withdrawn sludge from a part of the
returned sludge;
[0047] means for treating the withdrawn sludge by intermittently
adding an alkali at a determined interval, with holding a retention
time after adding the alkali from for 3 hours to for 24 hours;
[0048] means for solubilizing the treated sludge by the
alkali-treatment biologically solubilization treatment to the
sludge after treating the alkali-treatment at a normal temperature
and a pressure in an anaerobic, anoxic, or microaerophilic
atmosphere, with holding a retention time after adding alkali from
for 1 day to 3 days; and
[0049] means for returning the solubilized sludge to the biological
treatment system.
[0050] Ninth, a method for treating a wastewater comprising the
steps of:
[0051] treating a wastewater biologically;
[0052] separating a solid from a liquid in the biologically treated
wastewater to obtain a treated wastewater and a returned
sludge;
[0053] treating a part of the return sludge by an alkali-treatment,
within a range of pH value from 9 to 12.5;
[0054] solubilizing the sludge biologically immediately after
treating the sludge by the alkali, in an anaerobic, anoxic, or
microaerophilic condition; and
[0055] returning the solubilized sludge to the biological treatment
system.
[0056] Tenth, an apparatus for treating a wastewater
comprising:
[0057] a biological treatment tank to treat a wastewater
biologically;
[0058] a solid-liquid separation unit to separate the wastewater
discharged from the biological treatment tank to obtain a treated
wastewater and a returned sludge;
[0059] an alkali-treatment tank to treat a part of the returned
sludge by the alkali within a range of pH value from 9 to 12.5;
[0060] a biological solubilization tank, connected to the
alkali-treatment tank, to biologically solubilize the sludge
discharged from the alkali-treatment tank under an anaerobic,
anoxic, or microaerophilic condition; and
[0061] means for returning the sludge discharged from the
biological solubilization tank to the biological treatment tank, to
recycle the sludge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] FIG. 1 shows an example of the Embodiment 1 according to the
present invention.
[0063] FIG. 2 shows another example of the Embodiment 1 according
to the present invention.
[0064] FIG. 3 shows an example of continuous testing according to
the Embodiment 1 of the present invention.
[0065] FIG. 4 shows an example of solubilized sludge solely by the
anaerobic fermentation treatment according to the Embodiment 1 of
the present invention.
[0066] FIG. 5 shows an example of solubilized sludge by enzymes
produced by thermophilic aerobic bacteria according to the
Embodiment 1 of the present invention.
[0067] FIG. 6 shows an example of solubilized sludge by ozone
oxidation according to the Embodiment 1 of the present
invention.
[0068] FIG. 7 shows an example of solubilized sludge by
hot-alkali-treatment according to the Embodiment 1 of the present
invention.
[0069] FIG. 8 shows an example of conventional process.
[0070] FIG. 9 is a block diagram showing outline of the wastewater
treatment apparatus according to the Embodiment 2 of the present
invention.
[0071] FIG. 10 is an outline of an apparatus used in continuous
treatment testing according to the Embodiment 2 of the present
invention.
[0072] FIG. 11 is a characteristic curve showing the change in MLSS
with time during alkali-treatment according to the Embodiment 2 of
the present invention.
[0073] FIG. 12 is a characteristic curve showing the change in pH
with time during alkali-treatment according to the Embodiment 2 of
the present invention.
[0074] FIG. 13 shows an example of an embodiment according to the
Embodiment 3 of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0075] Embodiment 1
[0076] The method and the apparatus for treating a sludge, and the
method, the apparatus for treating organic wastewater, and those
for utilizing hereof according to the Embodiment 1, are described
below, referring to the drawings.
[0077] FIG. 1 shows one example of a device for solubilizing
sludge, according the Embodiment 1.
[0078] According to the treatment device given in the drawing, the
sludge is introduced into an alkali-treatment tank 1. Inside of the
alkali-treatment tank 1, the sludge is treated by alkali by way of
adding a slight amount of alkali 2, while the sludge being held for
a predetermined period. Through the alkali-treatment, a various
kinds of components, which are constituted as one of the
microorganism's cells, to generate the sludge, are improved to be
various structures that are easily biologically decomposed.
[0079] Examples of alkali, which are added to conduct the
alkali-treatment, are sodium hydroxide, potassium hydroxide,
calcium hydroxide, magnesium hydroxide, sodium carbonate, and
sodium hydrogencarbonate. However, the applicable alkali is not
limited to those examples.
[0080] The necessary additive amount of alkali depends on,
respectively, which means, the kind, the concentration, the
condition, the state, and the like of the sludge. According to the
Embodiment 1, the sludge after treated by alkali is biologically
solubilized in a later stage. Accordingly, compared with
solubilizing sludge solely by alkali-treatment, the Embodiment 1
consumes less amount of alkali. In that case, pH within the
alkali-treatment tank 1 may be less than 9 of pH value, and higher
pH is not required. Nevertheless, for solubilizing efficiently, 7
of pH value or higher is preferable, and 8 of pH value or higher is
more preferable. Therefore, according to the Embodiment 1, the pH
in the alkali-treatment tank 1 is preferably within a range from 8
or more to 9 or less. By this way, the Embodiment 1 can invite cost
reduction of chemicals, compared with the conventional
alkali-treatment methods, which are conducted at a high range of
the pH value.
[0081] The alkali-treatment is preferably carried out at normal
temperature. Heating is not always necessary for the
alkali-treatment. Embodiment 1 shows that the alkali-treatment at
normal temperature attains a satisfactory effect to need no heating
cost. The alkali-treatment tank 1 may be complete mixing type or
plug-flow type. Particularly, in case of adopting the plug-flow
type, it can be attained that reducing the amount of alkali reduces
the further amount of cost. In addition, it can be attained that
the size of tank is got to be smaller by the reason of shortening
the retention time. So, the plug-flow type is preferable and
expected to bring more efficient treatment. After being treated by
alkali, the sludge is introduced into a biological solubilization
tank 3, where further solubilized process goes on by the sludge
solubilized bacteria's action. The process is achieved under an
anaerobic, anoxic, or microaerophilic condition.
[0082] With regard to the sludge after being treated by alkali,
there is a possibility that the alkali-solubilizable components
become sludge again, when they are exposed to an aerobic
environment. In order to avoid the phenomenon, it is preferable
that the sludge treated by alkali is introduced into the biological
solubilization tank 3, without getting touch with the air.
[0083] Solublizating the sludge in the biological solubilization
tank 3 is described in detail, as follows.
[0084] As one of microorganisms influencing on solubilizing the
sludge in the biological solubilization tank 3, the following
microorganisms are preferable. That's to say, there are preferable
microorganisms, which secrete protease and amylase for decomposing
proteins and carbohydrates, (Note: the proteins and the
carbohydrates are major components of the sludge.), under the
condition of the normal temperature and pressure, an anaerobic, an
anoxic, or a microaerophilic environment. Additionally speaking,
they can utilize the component of the sludge as nutrients. However,
the microorganisms are not specifically limited to those given
above.
[0085] The sludge is treated by alkali on a preliminary treatment
stage. As the result of it, there occur the destruction of
bacterial cells and the elution of intracellular fluid. The
solubilizing rate in the biological solubilization tank 3
enormously increases compared with the conventional processes.
Owing to the increased solubilizing rate, the retention time in the
solubilization tank can be held to be shorter. And, by that reason,
it can be attained to get the capacity of the biological
solubilization tank 3 to be smaller.
[0086] As described above, according to the Embodiment 1,
solubilizing the sludge is performed in the biological
solubilization tank 3, under an anaerobic, anoxic, or
microaerophilic condition. Consequently, no aeration is needed.
Therefore, there is nothing special for the additional device to
treat the sludge. However, in order to increase the reactivity of
the sludge, a simple agitator may be installed. Even in case of
installing the agitator, the installation cost can be reduced,
compared with the installation cost for the aerator. Furthermore,
according to the Embodiment 1, the satisfactory effect is attained,
even at the normal temperature, so that no heating is required.
Accordingly, compared with the conventional processes, the
Embodiment 1 can provide a much simpler and lower running cost
process.
[0087] The alkaline liquid is treated in the solubilization tank 3
under an anaerobic, anoxic, or microaerophilic condition.
Afterwards, the alkaline liquid, which has been introduced into the
biological solubilization tank 3 from the alkali-treatment tank 1,
is neutralized to the neighborhood at the neutral of pH value.
Consequently, the Embodiment 1 needs no acid or the like to
neutralize the treated liquid and it needs no chemicals cost for
neutralization.
[0088] The biological solubilization tank 3 may be the complete
mixing type. However, the plug-flow type can create a pH gradient
inside of the solubilization tank. Since the sludge, which has been
introduced immediately into the solubilization tank, keeps a high
pH, the further efficient solubilization can be expected and the
further low chemicals cost can be attained.
[0089] The method and the apparatus for treating organic sludge
utilizing the above-described solubilizing sludge process according
to the Embodiment 1 are explained in more detail, in accordance
with the drawing.
[0090] FIG. 2 shows an example of organic sludge treatment device,
according to the Embodiment 1.
[0091] In the treatment device shown in FIG. 2, organic wastewater
4 is introduced into a biological treatment tank 5, where the
wastewater 4 is subjected to biological treatment for a
predetermined period. After that, the wastewater 4 is introduced
into a precipitating tank 6, where the sludge is separated to
obtain a clear treated wastewater 7. The biological treatment
process may be activated sludge process, rotary biological contact
process, watering biofilter-bed process, submerged biofilter-bed
process. However, the biological treatment process is not limited
to the above-given ones.
[0092] Most part of the precipitated sludge 8 after the
solid-liquid separation treatment is recycled to the biological
treatment tank 5 from sludge returned line 10. On the other hand,
sludge 11 withdrawn from the sludge returned line 10 is introduced
into a sludge thickening device 12, where the sludge 11 is
concentrated to a predetermined concentration, then the sludge 11
is introduced into the above-described sludge solubilization
device.
[0093] Sludge 13, which is treated to be solubilized in the sludge
solubilization device, is returned to the returns line 10 to
recycle to the biological treatment tank 5 for achieving again the
biological treatment. As a result, the organic in the sludge, which
has been solubilized, are removed by aerobic biological
decomposition in the biological treatment tank 5. Consequently, the
discharged amounts of the excess sludge 9 decreases remarkably.
[0094] As shown in the treatment device given in the Figure, before
the withdrawn sludge 11 is introduced into the alkali-treatment
tank 1, it is preferred that the withdrawn sludge 11 has been
concentrated by a concentrator 12 such as a centrifugal separator,
in order to reduce the amount of the liquid. Such a preliminary
treatment brings out the reduction of the amount of alkali for
maintaining the pH in the alkali-treatment tank 1, to a certain
degree. And, the alkali cost is further reduced. Reducing the total
amount of the treated sludge makes it possible to get the size of
the alkali-treatment tank 1 to be smaller and the size of the
biological solubilization tank 3, to the further smaller
EXAMPLES
[0095] The Embodiment 1 is further described in more detail,
showing the concrete examples, as follows. However, the Embodiment
1, is not limited to this example.
Example 1
[0096] Excess sludge, which had been extracted from a sewage
treatment plant, was deaerated by nitrogen. And then, the excess
sludge treated in this way, was transported and packed into a
sealed container. In the container, enriching the culture of
microorganisms was achieved, making use of the microorganism's
ability, which is the ability to decompose the sludge under an
anaerobic, anoxic, or microaerophilic condition.
[0097] The enriched cultural liquid, which had been obtained in the
above-mentioned way, was analyzed in a sterilized sludge
supernatant culture medium, in order to determine the power for
decomposing the sludge. As the result of it, the solubilized
bacteria in the sludge were obtained. The above-mentioned treatment
was achieved at the normal temperature and the pressure, under an
anaerobic condition.
[0098] As the next step, the excess sludge was adjusted to contain
approximately 10 g/L of MLSS (activated sludge concentration).
Sodium hydroxide as the alkali was added to the sludge, where the
alkali-treatment was achieved by mixing and agitating for one day.
After treating the sludge, the pH value of the sludge was
approximately 8.5.
[0099] Afterwards, the 20 ml of sludge obtained by the
alkali-treatment and the 20 ml of pure cultured fluid of the
above-described sludge solubilized bacteria were mixed together.
The mixture was poured into the flask with baffle, whose capacity
is 50 ml. After filling the upper space in the flask with nitrogen,
the flask was sealed. And, the contents were treated by shaking
them at 20.degree. C., 100 rpm and for 3 days. After treating in
such a way, MLSS of the mixture was measured and the percentage of
the solubilized amount was derived and determined, in comparison
with the initial MLSS.
[0100] As one of the Comparative Example, the sludge, which was
adjusted to approximately 10 .mu.L of MLSS, was agitated f or one
day, without adding alkali. Instead of the pure cultured fluid of
solubilized bacteria in the sludge, 20 ml of sterilized medium for
culturing solubilized bacteria was used to mix with 20 ml of the
alkali-treated sludge. Except the Comparative Example as mentioned
above, solubilizing the sludge was achieved as the same procedure
with the other mentioned example as mentioned above.
[0101] The percentage of the solubilized sludge in the Example 1
and in the Comparative Example is given in Table 1, along with the
treatment conditions.
1 TABLE 1 Solubilized Treatment condition percentage (%) Example
Alkali-treatment + Solubilized bacteria 34 adding treatment for
sludge Comparative Without adding alkali and sludge 8 Example
solubilized bacteria
[0102] As shown in Table 1, the Embodiment 1, which treats by way
of adding alkali and sludge solubilized bacteria, the following
result was attained. That's to say, it is the high solubilized
percentage, which means, more than four times that of the
Comparative Example, within a relatively short treatment period. To
the contrary, the Comparative Example, which did not add alkali and
sludge solubilized bacteria, did not solubilize almost of the
sludge within a short period such as 4-day treatment.
Example 2
[0103] Concerning the excess sludge, a continuous treatment testing
according to the Embodiment 1 was achieved. FIG. 3 shows the system
configuration of the device, which was used in the Example 2.
[0104] In FIG. 2, the sludge solubilization device has a
cylindrical alkali-treatment tank 1, whose capacity is 400 ml. In
addition, a biological solubilization tank 3 has the same shape and
the same capacity with those of the alkali-treatment tank 1. Merely
the mechanical agitation was achieved, without aeration under the
condition of the normal temperature and pressure, while both of
treatment tanks were kept in sealed state. As the testing piece of
the sludge, excess sludge 14 was used, which was extracted from a
sewage treatment plant, and which was adjusted to approximately 10
g/L of MLSS, to be stored at 4.degree. C. The sludge was
successively supplied into the alkali-treatment tank 1, by
operating a sludge transfer pump 15, at a regular interval, for
keeping the retention time of 6 hours.
[0105] The pH value in the alkali-treatment tank 1 was controlled
at 8.5, by using sodium hydroxide 2, and by using a pH controller
16. A part of the treated sludge in the alkali-treatment tank 1,
was withdrawn by a sludge transfer pump 21, and was fed into the
biological solubilization tank 3, while the rested sludge was
overflowed to be discharged. In comparison with the MLSS of the
overflowed sludge 20 and the MLSS of tested sludge 14, the
percentage of the solubilized sludge in the alkali-treatment tank 1
was derived.
[0106] There was no chance to adjust pH in the biological
solubilization tank 3. The operation was carried out, determining
the retention time of 3 days. The 5-ml of concentrated cultured
fluid, which contained the sludge solubilized bacteria, was added
to the biological solubilization tank 3. The cultured fluid had
previously been was prepared in Example 1 at the beginning stage of
the experiment. Concerning the biological solubilization tank 3,
the similar treatment with the alkali-treatment tank was proceeded,
which was, overflowing the sludge to keep the liquid level.
[0107] The MLSS of the effluent sludge 23 was compared with the
MLSS of the effluent sludge 20 of the alkali-treatment tank to
derive the percentage of the solubilized sludge in the biological
solubilization tank. In comparison with the MLSS of sludge 23 and
the MLSS of testing sludge 23, the percentage of the solubilized
sludge for the total system was determined.
[0108] An experiment as the Comparative Example 1 was given with
the similar system mentioned above, except that the pH value in the
alkali-treatment tank 1 was set to 7, and except that the
biological solubilization tank 3 did not receive sludge solubilized
bacteria. Similar experiment as the Comparative Example 2 was
given, while setting the pH value in the alkali-treatment tank 1 to
be value 7, and adding the sludge solubilized bacteria into the
biological solubilization tank 3.
[0109] The obtained results are summarized in Table 2.
2 TABLE 2 Comparative Comparative Example Example 1 Example 2 The
pH set level in alkali- 8.5 7 7 treatment tank Addition of sludge
solubilized Added Not added Added bacteria into biological
solubili- zation tank Sludge solubilization percentage 15.1 3.8 3.5
in alkali-treatment tank (%) Sludge solubilization percentage 19.2
5.3 8.1 in biological solubilization tank (%) Sludge solubilization
percentage 34.3 9.1 11.6 of total system (%)
[0110] As shown in Table 2, the Embodiment 1, which applies the
alkali-treatment and the biological treatment by sludge solubilized
bacteria, attained that the percentage of solubilization is around
four times the percentage of the Comparative Example 1 without
being treated. When the Example is compared with the Comparative
Example 2, the biological solubilization tank showed in the Example
attained two times or more the percentage of solubilization than
that showed in the Comparative Example 2. But, in both cases, the
sludge-solubilized bacteria are applied to be added. Since the
Embodiment 1 applied preliminarily the alkali-treatment, the sludge
was presumably improved to be characteristics, which is easy to be
decomposed by the enzymes of the sludge solubilized bacteria.
Example 3
[0111] Making use of sewage, a treatment testing was achieved by
the following procedure. Looking into in detail, the Embodiment 1
and the conventional technology were compared with each other. In
the embodiment, it made it a rule that the activated sludge process
operated the biological treatment tank 5.
[0112] Method A: The treatment was achieved by the Embodiment 1
shown in FIG. 2.
[0113] Method B: The treatment was achieved by the sludge
solubilization solely, by the anaerobic fermentation treatment
shown in FIG. 4. The device shown in FIG. 4 is the same with that
of FIG. 2. Different is that the sludge solubilization device
consisting of the sludge thickening device 12, the alkali-treatment
tank 1, and the biological solubilization tank 3 is replaced merely
with biological solubilization tank 3 for treating by anaerobic
fermentation.
[0114] Method C: The treatment was achieved by the sludge
solubilization process, shown in FIG. 5, using enzymes produced
from the thermophilic aerobic bacteria. The device shown in FIG. 5
is the same with FIG. 2. Different points from FIG. 2 are that the
alkali-treatment tank 1 was eliminated, that an aerator, which
maintains the aerobic condition in the biological solubilization
tank 3 are added, and that a heating means to establish a high
temperature state were added.
[0115] Method D: The treatment was achieved by the sludge
solubilization process by ozone oxidation, shown in FIG. 6. The
device shown in FIG. 6 is as the same as that of FIG. 2. Different
configuration is that the sludge solubilization device, which
consists of the sludge thickening device 12, the alkali-treatment
tank 1 and the biological solubilization tank 3, is replaced with
an ozonizer 24 and an ozone treatment tank 25.
[0116] Method E: The treatment was achieved by the solubilization
by hot-alkali-treatment. The device shown in FIG. 7 is the same
with that of FIG. 2, except that the biological solubilization tank
3 was eliminated and except that the heating means was added into
the alkali-treatment tank 1.
[0117] Method F: The treatment was achieved by the conventional
process shown in FIG. 8. The device shown in FIG. 8 is the same
with that of FIG. 2, except that the sludge solubilization step is
not applied.
[0118] Table 3 shows the quality of sewage tested. The testing was
carried out at a throughput of 120 L/d, in any of the method.
3 TABLE 3 Water temperature 20-25.degree. C. SS 90-110 mg/L BOD
120-135 mg/L
[0119] Table 4 shows the results. Additionally speaking, the
initial cost, the running cost, and the capacity of the
solubilization tank are compared with mutually on the basis of the
Embodiment 1 (Method A) as unity.
[0120] The quality of generated sludge was compared with, on the
basis of the conventional method as unity.
4 TABLE 4 A B C D E F Initial cost 1 0.9 1.4 2.4 0.85 0 Running
cost 1 0.9 1.8 2.2 3 3.1 Solubilization 1 4.0 1.3 0.9 0.03 -- tank
capacity Generated 0 0.5 0 0 0.3 1 sludge
[0121] As shown in Table 4, the Embodiment 1 process makes it
possible to operate the treatment system at much lower running cost
with a small capacity of solubilization tank, and without
generating excess sludge.
[0122] As described above, the Embodiment 1 reduces the capacity of
solubilization tank, and provides a sludge treatment method, which
can efficiently solubilize the sludge at low running cost, and an
organic wastewater treatment method, which can significantly reduce
the generated sludge by making use of the sludge treatment method.
Furthermore, the Embodiment 1 can significantly reduce the
generated sludge at low running cost, and provides a sludge
treatment apparatus for minimizing the solubilization tank
capacity, and an organic wastewater treatment apparatus, which can
reduce the generated sludge remarkably, by making use of the sludge
treatment apparatus.
[0123] The Embodiment 1 makes it possible to solubilize efficiently
the sludge without applying complex operation and facilities.
Consequently, it becomes available that treating period is shorter
and that the accompanied solubilization device is got to be smaller
size.
[0124] Furthermore, by applying the sludge solubilization treatment
using microorganisms, the chemicals cost for alkali-treatment
reduces, and no chemical agent for neutralization is required to
reduce the cost. The alkali-treatment is satisfactorily done at the
normal temperature, so that no heating cost is necessary.
[0125] Furthermore, solubilized decomposing the sludge biologically
is carried out at the normal temperature and pressure under an
anaerobic, anoxic, or microaerophilic condition. No heating and
aeration are necessary. Thus, the operation can be done at the
lower running cost. Recycling thus solubilized sludge into the
biological treatment system brings up that the generated excess
sludge are decreased to a big deal, which invites reducing the
number of the conventional sludge dewatering step and the sludge
incineration step. So, in some case, such steps are not
required.
[0126] The Embodiment 1 is extremely effective in treating the
sludge generated from biological treatment process of organic
wastewater such as sewage. The value for the industrial use is very
high.
[0127] Embodiment 2
[0128] The Embodiment 2 is described in detail, as follows.
[0129] The term "solubilizing sludge" in the specification defines
a general concept, which includes, various substances in the sludge
to the substances of low molecular weight, which converts organic
substances to inorganic substances, which destructs bacterial
cells, and which elutes intracellular fluid, and the like.
[0130] According to the sludge treatment process of Embodiment 2,
the sludge is solubilized and improved to be a different quality,
by adding intermittently an alkali at a predetermined interval.
[0131] In the conventional processes, a method using pH control is
used as one of the regular alkali-treatment. From this point of
view, the inventors of the present invention have found out that
the treatment capacity is different and the treatment capacity
depends on the concentration of the treated sludge. That's to say,
in accordance with decreasing the activated sludge concentration
(MLSS), the consumption of chemicals, which is used to cancel the
buffer action of the sludge, increases, compared with the consumed
amount of chemicals used to solubilize the sludge. As a result of
it, even when the added amount of chemicals per unit dry sludge is
the same one, the lower concentration of the activated sludge
cannot solubilize and improve the sludge to a satisfactory
degree.
[0132] Judging from the above stand point of view, the Embodiment 2
tried and attained to solve the above-mentioned problems, by way of
adding a predetermined amount of alkali intermittently at a
predetermined interval. The way is independent of pH value, without
keeping the continuous control of pH. Immediately after adding
alkali, the pH value in the alkali-treatment tank becomes very
high. Thus, the consumed amount of alkali for canceling the buffer
action reduces, which results in consuming the alkali efficiently
to enhance solubilizing and improving the sludge. Afterwards,
adding alkali is not taken place for a certain period, until adding
alkali is taken place on the next time. Consequently, the pH value
in the alkali-treatment tank decreases, and the solubilized
percentage also decreases. However, totally, in case of being
compared with the continuous control of pH value, using the same
consumed amount of alkali, the effect, which is invited by the
solubiled sludge and by the improved sludge, drastically
increases.
[0133] A preferred range of activated sludge concentration (MLSS)
of the sludge, which is subjected to the solubilization treatment
according to the Embodiment 2, is 60 g/L or less and more
preferably from 20 to 1 g/L.
[0134] Preferably, the range of interval for adding alkali is
fallen within from 0.5 to 48 hours. If the interval for adding
alkali is less than 0.5 hour, the advantageous effect cannot be
obtained, compared with the continuous control method. Contrarily,
if the interval for adding alkali exceeds 48 hours, the added
amount per once becomes excessive, and in spite that solubilization
is saturated by alkali, there increases a useless consumption of
alkali. Consequently, the intervals for adding alkali are
preferably from fallen within the range from 0.5 to 48 hours, more
preferably fallen within the range from 8 to 36 hours, and the most
preferably fallen within the range from 12 to 24 hours.
[0135] As examples of alkali for adding the alkali-treatment
process, are sodium hydroxide, potassium hydroxide, calcium
hydroxide, magnesium hydroxide, sodium carbonate, and sodium
hydrogencarbonate. However, the adequate alkali is not limited to
those examples.
[0136] The required and added amount of alkali per once is
determined to be an appropriate one, depending on the kind, the
concentration, the condition, and the like, of the applicable
sludge. According to the Embodiment, which means substitution
method, the sludge after having been treated by alkali is
biologically solubilized on a later stage. By that reason, compared
with the case of solubilizing the sludge just by alkali-treatment,
it makes it possible to suppress the consumed amount of alkali, to
less degree.
[0137] The alkali-treatment may be achieved under the heated
environment or pressurized environment. However, the
alkali-treatment attains the satisfactory result, even under the
condition of the normal temperature and pressure. In this case,
there is required no cost for heating and pressurization. The term
"normal temperature" referred herein is defined to be fallen within
the temperature range from 5.degree. C. to 35.degree. C.,
preferably from 15.degree. C. to 30.degree. C. The term "normal
pressure" referred herein is defined to be the atmospheric
pressure.
[0138] According to the Embodiment, the alkali-treatments tank,
where the alkali-treatment is carried out by irregular operation.
So, the characteristic of the effluent sludge, which is flowed out
from the alkali-treatment tank, varies, depending on the passing
time. Nevertheless, the characteristics of the sludge at the exit
of the biological solubilization tank, which is the exit of the
final solubilization system, can be kept to be a definite one,
regardless of the passing time. Because, on a succeeding stage, the
sludge after the alkali-treatment is treated to be solubilized in
the biological solubilization tank, where it takes a long retention
time of the sludge. From time to time, when the sludge, which has
been solubilized biologically by alkali-treatment, the variation of
the sludge has a possibility to influence on the waste disposal
facility to get worse. But, by the above-mentioned way in the
sludge treatment method, such an anxiety can be removed.
[0139] A method for treating wastewater and an apparatus for
treating the same by making use of the above-mentioned method for
the sludge, are described as follows, referring to the drawing.
FIG. 9 shows an example of wastewater treatment apparatus according
to the Embodiment 2.
[0140] One example of the apparatus for treating wastewater is
shown in FIG. 9.
[0141] The apparatus for treating the wastewater has a biological
treatment tank 105, a precipitating tank 106, an alkali-treatment
tank 101, and a biological solubilization tank 103. The wastewater
is brought from the source of wastewater (not shown). And, the
wastewater is introduced into the biological treatment tank 105, by
way of a line 104. The wastewater is subjected to biological
treatment in the biological treatment tank 105 for a predetermined
period, then is transported into a precipitating tank 106. The
wastewater has the characteristics of an organic one. The
precipitating tank 106 separates sludge from liquid to be clear
treated wastewater. The treated wastewater is discharged from the
precipitating tank 106 via a passage 107. As the biological
treatment process of the embodiment, activated sludge process,
rotary biological contacts process, percolation filter-bed process
and submerged biofilter-bed process. However, the biological
treatment process is not limited into the above-given ones. Most
part of the precipitated sludge 108 after the solid-liquid
separation treatment is recycled into the biological treatment tank
105 from a sludge return passage 110. On the other hand, the sludge
111, which has been withdrawn from the sludge return line 110, is
introduced into the alkali-treatment tank 101 of the solubilization
sludge device. The solubilization sludge device is described in
FIG. 1 of the Embodiment 1, where the sludge 111 is treated as
described before.
[0142] In the solubilizing sludge device, the sludge 112, which has
been treated to be solubilized in the alkali-treatment tank 101 and
in the biological solubilization tank 103, is returned back trough
the return passage 110. And then, the sludge is introduced into the
biological treatment tank 105, again, for recycling and treating
again biologically. As a result of this procedure, the organic in
the sludge, which was solubilized, are removed by decomposing
aerobically and biologically, and by converting to inorganic in the
biological treatment tank 105. Thus, the discharged amount of
excess sludge from the precipitating tank 106 via a passage 109
decreases remarkably.
[0143] The Embodiment 2, referring to examples, are described in
detail, below. However, the Embodiment is not limited to these
examples.
Example 4
[0144] Treating excess sludge continuously is explained below,
which is related to Embodiment 2, in accordance with FIG. 10.
[0145] FIG. 10 shows a continuous treatment device used in the
continuous treatment test. The continuous treatment device has the
cylindrical alkali-treatment tank 101, which has a capacity of 40
ml, and the biological solubilization tank 103, which has the same
capacity. Both of the alkali-treatment tank 101 and the biological
solubilization tank 103 are kept to be sealed and packed at the
normal temperature and pressure, and are agitated merely by
mechanical agitator, without using aeration. The testing sludge was
excess sludge extracted from a sewage treatment plant, which was
stored in an excess sludge tank 113, while adjusting the MLSS to
approximately 20 g/L at 4.degree. C. The sludge was successively
introduced into the alkali-treatment tank 101 by a sludge transfer
pump 114 at a predetermined interval, so as the retention time of
the sludge are held to be 6 hours.
[0146] Sodium hydroxide (4% concentration) stored in an alkali
storage device 102 as the alkali was introduced into the
alkali-treatment tank 101 by an alkali transfer pump 117 by a
predetermined amount once every 24 hours. The every added amount of
alkali was determined to be the same amount of the added sodium
hydroxide as the amount of a period of 24 hours under the condition
that the pH value detected by a pH sensor 116 was kept to be 8.5 by
a pH controller 115. That is to say, the consumed amount of alkali
during treating the alkali by the pH control is arranged to be the
same amount as the added amount of alkali per unit amount of dry
sludge. The retention time (HRT) in the alkali-treatment tank 101
was held to be for 6 hours.
[0147] Partial treated sludge was withdrawn from the
alkali-treatment tank 101 by using a sludge transfer pump 120, in
order to introduce to the biological solubilization tank 103. On
the contrary, the other rested part of the treated sludge was
overflowed to be discharged from the alkali-treatment tank 101,
using an alkali-treatment tank solenoid valve 118.
[0148] In the biological solubilization tank 103, solubilization
was treated, by using the sludge-solubilized bacteria, for 3 days
duration as the retention time (HRT). In the same way with in the
alkali-treatment tank 101, the biological solubilization tank 103
was kept and controlled to be an adequate water level, by way of
overflowing the sludge from the alkali-treatment tank, making use
of using a solenoid valve, located in the biological solubilization
tank 121.
[0149] The MLSS of effluent sludge 119, which has been overflowed
from the alkali-treatment tank 101, varies as the time passes, and
depends on the passing time. By that reason, the sludge was
extracted at a regular interval to determine the MLSS.
Simultaneously with the above-mentioned extraction, the value of pH
was measured. The results are shown in FIG. 11 and FIG. 12. The
vertical axis of FIG. 11 is MLSS (g/L), and the horizontal axis
thereof is time (hour). The vertical axis of FIG. 12 is pH value,
and the horizontal axis thereof is time (hour).
[0150] After a single cycle (24 hours) of alkali-treatment was
completed, MLSS values were plotted to derive formula, then were
integrated and averaged. By comparing the averaged MLSS value with
the MLSS of testing sample, the percentage of the solubilized
sludge in the alkali-treatment tank 101 was calculated. The result
is given in Table 5.
[0151] The MLSS of effluent sludge 122, which had been overflowed
from the biological solubilization tank 103, was compared with the
MLSS of effluent sludge 119. And, the percentage of the solubilized
sludge in the biological solubilization tank was determined. By
comparing the result with the MLSS of the testing sludge, the
percentage of the solubilized sludge as the total system was
determined. The result is also given in Table 5.
Comparative Example 1
[0152] The MLSS of testing sludge was adjusted to approximately 40
g/L. Sodium hydroxide was added to the sludge so that the pH
detected by a pH sensor 116 in the alkali-treatment tank 101 can be
to be kept on 8.5 by a pH controller 115. Other conditions were the
same with those in the Example. Thus, the testing sludge was
continuously treated.
[0153] Similar with the Example 4, the MLSS of the effluent sludge
119 was compared with the MLSS of the testing sludge 113, the
percentage of solubilized sludge in the alkali-treatment tank 101
was calculated. By comparing the MLSS of the effluent sludge 122
with the MLSS of the effluent sludge 119, the percentage of
solubilized sludge in the biological solubilization tank was
determined. Also, by comparing with the MLSS of the testing sludge
113, the percentage of the solubilized sludge in the total system
was determined. The results are also given to Table 5.
Comparative Example 2
[0154] Continuous treatment was achieved as the same as the
Comparative. Example 1 was given below, except that the MLSS of
testing sludge was adjusted to about 20 g/L. And then, each
solubilized percentage of the sludge was determined. The result is
given also in Table 5.
5 TABLE 5 Solubilization percentage Example/ Sludge Added alkali
Alkali- Biological Comparative concentration Method of alkali
(g-NaOH/g- treatment solubilization Example (g/L) addition sludge)
tank tank Total Example 1 20 Intermittent 0.052 22.8 10.1 32.9
addition at every 24 hours Comparative 40 pH (8.5) 0.052 21.5 10.9
32.4 Example 1 continuous control Comparative 20 pH (8.5) 0.052
14.6 6.2 20.8 Example 2 continuous control
[0155] Example 4 shows adding alkali intermittently. In the
Example, the solubilization percentage value of 22.8% for
alkali-treatment and the solubilization percentage value of 10.1%
for microorganisms treatment are added, to summarize the total
solubulized percentage value of the sludge 32.
[0156] Furthermore, as shown in FIG. 11 and FIG. 12, the pH value
in the initial stage of adding alkali was 11 or more. And MLSS in
that stage was approximately 11 g/L. At this time, the
solubilization percentage reached to approximately 50%. After that,
MLSS gradually increased, while pH reduced to the neighborhood
point of neutral. And then, at the time of 12 hours later, MLSS
arrived at the pH value 7. The phenomena proved that adding alkali
intermittently suppresses the excessive consumed alkali, owing to
the concentrated progress of solubilization immediately after
adding alkali, which results in obtain the high solubilization
percentage, totally.
[0157] The Comparative Example 1, which adopted approximately 40
g/L of MLSS for the testing sludge, gave 21.5% of alkali-treatment
solubilization percentage, 10.9% of microorganisms treatment
solubilization percentage, to be summarized as the total value,
which means, 32.4% of solubilization percentage of the sludge.
[0158] On the other hand, the Comparative Example 2 adopted
approximately 20 g/L of MLSS for the testing sludge. In this case,
the solubilization percentage in the alkali-treatment was reduced
to the degree of 14.6%, the solubilization percentage in the
microorganisms treatment reduced to the degree of 6.2%, to be
summarized as the total reduced value, 20.8%. The reason why such a
reduction can be obtained is thought presumably, as follows. That's
to say; the lower concentration value of the treated sludge is, the
higher the consumed amount of alkali, which is used for canceling
the buffer action of sludge in the alkali-treatment tank.
Consequently, it fails to solubilize the sludge sufficiently and to
improve efficiently the sludge.
[0159] By comparing the Example 4 with the Comparative Examples 1
and 2, it was confirmed that treating the sludge by intermittent
addition of alkali invites an efficient process for reducing the
volume of the sludge. From another aspect of view, it attains a
stable and efficient solubilizing percentage of the sludge,
independent of the sludge concentration value.
[0160] As described above, the Embodiment 2 provides a method for
treating a sludge, which is not influenced by the sludge
concentration and, which in a stable way and efficiently,
solubilizes the sludge by adding intermittently into the
alkali-treatment tank. And the Embodiment provides a method for
treating wastewater, which makes use of the method for treating
sludge, in order to reduce the generated amount of sludge
remarkably. Furthermore, the Embodiment 2 provides an apparatus for
treating sludge. In the apparatus, the sludge is efficiently
solubilized. And, the apparatus for treating wastewater makes use
of the apparatus for treating the sludge, invite the reduction of
the generated amount of the sludge, to a great extent.
[0161] Since the Embodiment obtains an efficient solubilization
method for the sludge, which is independent of the sludge
concentration. The method and the apparatus enable us to create a
realistic process for solubilizing the sludge, from both viewpoints
of the running cost and the stability in treating. When the sludge
solubilized in such a way is recycled to the biological treatment
system, the generated amount of the excess sludge can be minimized.
This embodiment makes it unnecessary to maintain the conventional
sludge dewatering step, the sludge incineration step, and the like,
or else, which can also, minimize the facility scale of these
steps. The Embodiment is extremely effective for treating the
sludge generated from the biological treatment process for
wastewater such as sewage. Therefore, the Embodiment brings the
society a lot of the industrial value.
[0162] As described in detail above, the Embodiment provides a
treating method for solubilizing sludge, which solubilizes the
sludge generated from an biological treatment process of
wastewater, at high efficiency and at lower running cost, and an
apparatus thereof. The embodiment, furthermore, provides a method
for treating wastewater, in which, by utilizing the sludge
treatment method and apparatus to significantly reduce the
generated amount of the sludge, and an apparatus thereof.
[0163] Embodiment 3
[0164] FIG. 13 shows an example of the Embodiment 3. The wastewater
treatment device comprises a wastewater treatment system and a
sludge treatment system. The wastewater treatment system has an
aeration tank 210, which is an biological treatment tank to treat
wastewater under an aerobic condition, and a solid-liquid separator
211, which receives the wastewater from the aeration tank 210 to
precipitate the sludge, thus separating the treated wastewater and
the returned sludge. The aeration tank 210 has a diffuser 212 for
blowing fine air bubbles into the aeration tank. A returned sludge
passage 213 is prepared to recycle the sludge to the aeration tank
210, where the sludge has been obtained by solid-liquid separation
treatment.
[0165] The sludge treatment system has a sludge-thickening unit
220. This system concentrates the sludge discharged from the
solid-liquid separator 211, an alkali-treatment tank 221, which
applies alkali-treatment to the concentrated sludge discharged from
the sludge thickening unit 220 by adding alkali thereto. And this
system has a solubilization tank 222, which applies biological
treatment to the sludge discharged from the alkali-treatment tank
221 in order to solubilize and in order to decompose in the tanks.
The solubilization tank 222 is kept in an anaerobic, anoxic, or
microaerophilic condition by agitating mildly. The system has an
alkali-feed unit 223, a pH meter 224, and a solubilized sludge
returned passage 225, which recycles the solubilized sludge to the
aeration tank 210.
[0166] The apparatus according to the Embodiment is not limited to
the device configuration shown in FIG. 13. For example, the
wastewater treatment system adopts the aeration tank 210, such as
the biological treatment tank, which is assuming the activated
sludge process. For instance, not only the activated sludge process
but several devices may be applied to, which are, wastewater
treatment using oxidation ditch process, rotary biological contact
process, percolation filter-bed process, submerged biofilter-bed
process, or the like.
[0167] Preferable alkali, which is fed to the alkali-treatment tank
221, is the alkali, whose characteristic has high solubility, such
as sodium hydroxide, potassium hydroxide, and sodium carbonate.
[0168] Treating the wastewater, which is achieved by the
above-mentioned configuration of devices, is carried out, as
follows. Wastewater after removing a large size of solid and sand,
which have comparatively high specific gravity, is introduced into
the aeration tank 210. And then, the wastewater is subjected to
biological treatment. Simultaneously with this treatment, a great
deal of amount of returned sludge is introduced into the aeration
tank 210 via the returned sludge passage 213. The wastewater after
being treated biologically becomes clean. And, the clean wastewater
is fed into the solid-liquid separator 211, altogether with the
sludge. In the solid-liquid separator 211, two sorts of layers are
formed. One is supernatant layer, the other is sludge layer. The
supernatant is discharged as the treated wastewater. On the other
hand, the precipitated sludge is recycled to the aeration tank 210
via the returned sludge passage 213.
[0169] In regard with the returned sludge, some parts of the
returned sludge are withdrawn from the returned sludge passage 213
to enter the sludge thickening unit 220, where the sludge is
concentrated. The concentrated sludge is fed into the
alkali-treatment tank 221. An alkali is added from the alkali feed
unit 223 to the alkali-treatment tank 221 in order to adjust the pH
within the range from 9 to 12.5, preferably within the range from
9.5 to 11. The alkali-added sludge undergoes the alkali-treatment
for approximately from 3 to 24 hours with agitating. Through the
alkali-treatment, the components of the sludge is destroyed to
become soluble substances.
[0170] The sludge discharged from the alkali-treatment tank 221 is
fed into the solubilization tank 222, where the sludge is kept
under the condition of an anaerobic, anoxic, or microaerophilic for
approximately for from 1 to 3 days. During treating in the
solubilization tank 222, the soluble substances generated in the
alkali-treatment tank 221 are further decomposed by the biological
treatment. As the result of it, the treated substances become to
have low molecular weight chemical compounds, such as organic
acids. Consequently, the pH value usually reduces to the degree of
from 7 to 8.
[0171] The sludge discharged from the solubilization tank 222 is
recycled into the aeration tank 210, via the solubilized sludge
returned passage 225. In the aeration tank 210, where the
solubilized sludge is recycled back and entered into, the BOD
components in the entered wastewater are decomposed, and the BOD
components in the solubilized sludge, which has been reduced in the
molecular weight, are also decomposed. At that time, if high
molecular weight substances (i.e. substances difficult to
decompose) exist in the solubilized sludge, these substances are
discharged, together with the treated wastewater without being
decomposed, which will result in degrading the quality of the
treated wastewater. However, if, treating sludge is achieved under
the above-given conditions, the molecular weight of sludge is fully
kept on reducing. And most of the components in the solubilized
sludge are completely decomposed to another substances, which is,
carbon dioxide and water (and nitrogen, in case of treating
denitrification). By that reason, the amount of solubilized sludge
components, which has been discharged together with the treated
wastewater, reduces remarkably. In the end, such a reduction
suppresses the degraded degree of the quality, which is related to
the treated wastewater.
[0172] As described above, the sufficient solubilization and
decomposition invite the sludge treatment system the result that
almost of no excess sludge is generated, or else, there generates
just the least amount. In addition, decomposing BOD components is
enhanced in the wastewater treatment system, so, the quality of the
treated wastewater is improved to a big deal, compared with the
conventional technology, which concerns with the way to reduce the
volume of the sludge.
Example 5
[0173] A wastewater treatment device, which has a similar
configuration with FIG. 13, was made use of for treating the
sewage, which was extracted from a sewage treatment facility. The
temperature of the treated wastewater was fallen within a range
from 20.degree. C. to 25C. Flow SS was within a range from 90 to
110 mg/L and BOD was within a range from 150 to 185 mg/L. The
alkali-treatment tank and the solubilization tank had a sealed
structure. In this case, the sludge was just agitated mechanically,
without any of aeration.
[0174] (Condition of the Wastewater Treatment System)
[0175] The amount of the returned sludge: 0.5 times as much as the
amount of the treated wastewater.
[0176] (Conditions of the Sludge Treatment System)
[0177] Condition for treating in the alkali-treatment tank
[0178] the withdrawn amount of the sludge: one fifth of the amount
of the returned sludge.
[0179] Alkali agent used: NaOH
[0180] the determined pH value: 9.3, 10.5
[0181] Retention time: for 6 hours
[0182] Condition for treating in the solubilization tank
[0183] Retention time: for 2.5 days
[0184] The result, which was achieved under the above-mentioned
conditions, is shown in Table 6, as follow.
Comparative Example 3
[0185] In the Comparative Example, the same wastewater treatment
apparatus was used. In this case, the pH value in the
alkali-treatment tank was determined to be lower than value 9. The
treatment conditions were as the same as those in the Example,
except that the pH value in the alkali-treatment tank is determined
to be 8.5. The result is given also in Table 6, together with the
results of the examples.
6 TABLE 6 Comparative Example Example 1 Example 2 pH in
alkali-treatment tank 8.5 9.3 10.5 Solubilizing sludge percentage
(%) 32.3 36.8 39.6 s-BOD of solubilized sludge 485 932 1960 COD of
treated wastewater 25.4 15.2 8.5 Ratio of running cost 1 1.12
1.32
[0186] In Table 6, the ratio of the running cost means that the
electric cost and the chemicals cost are summarized totally in the
Examples, and that the each ratio in the Examples is based on the
basis of the cost of the Comparative Example as unity, whose value
is 1. The reason why the running costs increase in the Examples
depends on the rising of the aeration power, which has resulted by
the increase in the aeration tank load. In this case, the rising of
the amount of the consumed chemicals cost (alkali, etc) causes the
rising of the aeration power.
[0187] Table 6 shows that the percentage of the solubilized sludge
rate increases from the value of more than pH 9 in the
alkali-treatment tank. From more than pH 9, the increasing degree
of the solubilizing ratio becomes higher, depending on the
increasing degree of pH value. Simultaneously with the increasing
of solubilizing ratio, the value of the soluble BOD rises in the
solubilized sludge, and the value of the COD descends in the
treated wastewater. Accordingly, it is important that the generated
amount of the excess sludge is suppressed, and it is important that
the quality of the treated wastewater is improved to be closer at
the quality of the treated wastewater, which has been discharged
from a wastewater treatment device. (Note: In this case, the waste
treatment device has no sludge treatment system for solubilizing
the sludge). In order to achieve the above-mentioned objects, the
pH value in the alkali-treatment tank is required to be kept to the
degree of more than value 9.
[0188] According to the Embodiment, the generated amount of the
excess sludge reduces. And, the quality of the treated wastewater
is improved. As the result of it, the quality of the treated
wastewater can approach much closer to the quality of the treated
wastewater discharged from a wastewater treatment device, which has
no sludge treatment system.
* * * * *