JP2000301198A - Volume reducing treatment of sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the vol. of sludge with high efficiency by providing a relatively small-sized equipment easy to operate by subjecting conc. sludge, which is obtained in a sludge concn. process by filtering treatment using a filter membrane, to solubilizing treatment and circulating the treated sludge to a biological treatment process. SOLUTION: A filter membrane type sludge conc. tank 2 having a filter membrane device provided therein is provided in order to perform a sludge concn. process and a solubilizing treatment tank 3 for a solubilizing treatment process is provided. A part of a sludge mixed liquid being low concn. sludge treated in a biological treatment process is supplied to the filter membrane type sludge concn. tank 2 of the sludge concn. process from a sludge mixed liquid supply pipe (c) to be cone. The cone. sludge is supplied to the solubilizing treatment tank 3 of a sludge vol. reducing treatment process from a cone. sludge supply pipe (d) and filtered water transmitted through a filter membrane is discharged as treated water from a filtered water discharge pipe (f). By this constitution, an apparatus can be miniaturized and solubilizing treatment can be efficiently performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sludge volume reduction method for biologically treating organic wastewater to reduce the volume of generated organic sludge (hereinafter simply referred to as sludge).

[0002]

2. Description of the Related Art Conventionally, as a method of treating organic wastewater such as sewage, food wastewater, kitchen wastewater or septic tank sludge, an activated sludge treatment method and a UASB method (upflow anaerobic self-granulating biological bed treatment method) have been known. Biological treatment methods such as fixed-bed catalytic oxidation method and fluidized-bed catalytic oxidation method are used.

[0003] In the activated sludge method, wastewater (hereinafter referred to as raw water) is supplied into a treatment tank in which activated sludge, which is an aerobic microorganism, floats, and is aerated with air, whereby the biological action of the activated sludge is performed. In the UASB method, a fluidized bed is formed with microbial particles obtained by self-granulating anaerobic methanogens, and the raw water flows upward. This is a method in which organic matter in raw water is decomposed by the biological action of methanogens through circulation.

Further, in the fixed-bed catalytic oxidation method, a fixed bed of a biological carrier is provided in a treatment tank, and the air is diffused so that microorganisms adhere to and grow on the surface of the carrier. Is a method of oxidatively decomposing organic matter in raw water by chemical action, and the fluidized bed catalytic oxidation method is a method in which raw water is supplied by filling a liquid in an aerobic biological treatment tank with a biological carrier in a flowable manner. This is a method in which organic matter in raw water is oxidatively decomposed by the biological action of microorganisms adhered and proliferated on the surface of a biological carrier by aeration with air.

[0005] In any of the above biological treatment methods, a large amount of microorganisms proliferated as sludge is generated as biological substances are biologically decomposed. Some of the generated sludge is circulated to the biological treatment process, while the rest is disposed of as excess sludge by an appropriate method. In addition, the surplus sludge amount is 30 to 30 times the organic matter amount (BOD) in raw water introduced into the biological treatment process.
It is said to be 40%. As a method of disposing of the excess sludge, the sludge is concentrated and dehydrated and then disposed of by incineration or landfill, or the volume is reduced by anaerobic digestion treatment.

[0006]

According to the conventional method for disposing of excess sludge, the sludge is concentrated and dewatered and then incinerated or landfilled. The bulk is large because it is as high as 80 wt%,
In the case of requesting disposal from a waste disposal company, the cost of picking up becomes high, and at present, it accounts for much of the cost of wastewater treatment as a whole. Furthermore, in the landfill disposal, the remaining years of the industrial waste landfill are decreasing, and the collection cost is increasing year by year. In addition, incineration disposal requires high fuel consumption due to high water content, increases fuel cost, and requires disposal of exhaust gas and incineration ash.In recent years, incineration itself has become difficult due to dioxin problems. It is a situation that is coming.

In the method of reducing the volume by the anaerobic digestion method, sludge is supplied into a treatment tank in which anaerobic microorganisms such as methane bacteria are suspended, and the anaerobic gas is aerated. It is a method of decomposing organic matter in sludge into methane gas or carbon dioxide gas by the biological action of sexual microorganisms.
It is preferable because methane gas can be effectively used for fuel etc.
The treatment takes time, the facilities such as digestion tanks become excessive, and the amount of sludge finally generated is large, and the disposal involves the above-mentioned problems.

The present invention has been made in view of the above-mentioned problems in the conventional sludge disposal and treatment, and is provided with relatively small and easy operation equipment so as to reduce sludge volume with high efficiency. The purpose of the present invention is to provide a sludge reduction treatment method capable of reducing operating costs and equipment costs, and reducing final disposal costs.

[0009]

In order to achieve the above object, the gist of the present invention is to provide a method according to the first aspect, wherein low-concentration organic sludge is filtered through a filtration membrane to form concentrated sludge and clear water. A sludge concentration step of obtaining the sludge, a solubilization treatment step of solubilizing the sludge by subjecting the concentrated sludge concentrated in the sludge concentration step to high-temperature aerobic biological treatment, and a sludge circulating the solubilized sludge to the biological treatment step This is a sludge volume reduction treatment method comprising a circulation step.

[0010] In the invention according to claim 2, in the sludge reduction treatment method according to claim 1, the biological treatment step is an activated sludge treatment step, and the low-concentration organic sludge is removed from the activated sludge treatment step. The sludge reduction treatment method characterized in that the sludge is a sludge.

[0011] In the invention described in claim 3, the UA
In a wastewater treatment method in which an activated sludge treatment step is provided after the SB treatment step to perform wastewater treatment, a sludge concentration step of filtering the sludge from the activated sludge treatment step with a filtration membrane to obtain concentrated sludge and clarified water; A solubilization treatment step of solubilizing sludge by subjecting the concentrated sludge concentrated in the process and excess self-granulated sludge from the UASB treatment step to high-temperature aerobic biological treatment, and an activated sludge treatment apparatus for treating the solubilized sludge A sludge volume reduction treatment method is provided, wherein a sludge circulation step for circulating the sludge is provided.

In the wastewater treatment method according to the present invention, wherein the wastewater treatment is performed by providing an anaerobic digestion step after the biological treatment step, the sludge from the biological treatment step is filtered through a filtration membrane to form a concentrated sludge. And a solubilization process for solubilizing sludge by high-temperature aerobic biological treatment of concentrated sludge concentrated in the sludge concentration process and circulating sludge from the anaerobic digestion process. It is a sludge volume reduction treatment method characterized by providing a sludge circulation step of circulating the treated sludge to the anaerobic digestion step.

[0013] According to a fifth aspect of the present invention, in the sludge reduction treatment method according to any one of the first to fourth aspects, the MLS of the sludge concentrated in the sludge concentration step is used.
S is in the range of 30,000 to 100,000 mg / L.
The sludge volume reducing method according to any one of claims 1 to 5, wherein the liquid temperature in the solubilizing step is 55 to 80 ° C.

The operation of treating the sludge in the apparatus having the above-mentioned configuration will be described. The sludge concentration step of filtering the low-concentration organic sludge having an MLSS of 1000 to 20,000 mg / L from the activated sludge treatment step through a filtration membrane. Thereby, concentrated sludge and clarified water in which MLSS is concentrated to 30,000 to 100,000 mg / L can be obtained. When the MLSS of the sludge is 30,000 to 100,000 mg / L, the size of the apparatus can be reduced, and the solubilization treatment can be performed efficiently.

The concentrated sludge, the self-granulated sludge from the UASB treatment step and the sludge from the anaerobic digestion treatment step are supplied to the solubilization treatment step, and a liquid temperature of 55 to 80 ° C. and a residence time of 12 to 72 hours. By performing high-temperature aerobic biological treatment and solubilization treatment in a long time, 10 to 40 vol% of sludge is liquefied. By circulating the solubilized sludge to the biological treatment step in the sludge circulation step, the liquefied organic matter is treated again by the biological action, and finally the volume of the sludge is reduced by 20 to 50 vol%, The sludge itself can be settled easily, and the filtration membrane is hardly clogged. Further, by performing the solubilization treatment while maintaining the solution temperature at 55 to 80 ° C,
Activated sludge microorganisms that grow at room temperature can be sterilized, microorganisms that grow at high temperatures can be propagated predominantly, and sludge can be efficiently liquefied.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of an activated sludge treatment apparatus according to one embodiment of the present invention, FIG. 2 is a system diagram of a UASB treatment apparatus according to another embodiment of the present invention, and FIG. 3 is another embodiment of the present invention. FIG. 4 is a system diagram of a sludge concentration step and a solubilization step which are main parts of the present invention.

In FIG. 1, reference numeral 1 denotes activated sludge treatment in a biological treatment step in which activated sludge, which is an aerobic microorganism, floats and is aerated with air to oxidatively decompose organic matter in raw water by the biological action of activated sludge. Activated sludge treatment tank 1
Is a general activated sludge treatment tank, but a fixed bed of biological carriers is provided in the treatment tank, and the air is diffused to adhere and grow microorganisms on the surface of the carrier. In a fixed-bed type contact oxidation treatment tank or an aerobic biological treatment tank that oxidatively decomposes organic matter in raw water, a biological carrier is filled in a flowable manner, and the raw water is supplied and aerated with air. It may be a fluidized-bed contact oxidation treatment tank for oxidatively decomposing organic substances in raw water by the biological action of microorganisms attached to and grown on the surface of the carrier. Further, a nitrification and denitrification treatment tank for biologically nitrifying and denitrifying nitrogen in wastewater may be used. In addition, a filtration membrane device is disposed in the treatment tank 1 to filter sludge and remove treated water. It may be configured to discharge.

2 is a filtration membrane type sludge thickening tank in the sludge thickening step,
Reference numeral 3 denotes a solubilization tank in the solubilization step, which will be described in detail with reference to FIG. A filtration membrane device 5 is provided inside the filtration membrane type sludge concentration tank 2, and the filtration membrane type sludge concentration tank 2 is provided.
May be a tank having an open top surface or a tank having a closed structure, but an open tank having a simple structure is preferable. Further, the filtration membrane device 5 installed therein has a filtration body on the surface of the non-woven fabric formed body, which is a microfiltration having a pore diameter of 0.1 to several μm of cellulose acetate, aromatic polyamide and polysphone. A module formed by adhering a membrane or an ultrafiltration membrane having a molecular weight cut-off of about tens of thousands to several hundreds of thousands, or a dynamic membrane module consisting only of a nonwoven fabric molded article is used. Is preferred.

The filter is preferably in the form of a flat membrane in which a plurality of disc-shaped or rectangular plate-shaped flat membranes are juxtaposed at predetermined intervals in the horizontal direction, but may be cylindrical. It is not limited to. Although not shown, a diffuser for diffusing gas into the liquid passage to be treated is arranged below the filter of the filtration membrane device 5.

The solubilization treatment tank 3 is a treatment tank for solubilizing sludge by subjecting the concentrated sludge concentrated in the sludge concentration step to high-temperature aerobic biological treatment, and is either a tank having an open upper surface or a tank having a closed structure. However, in order to improve the heating effect and the deodorizing effect, a closed tank is preferable.

It is preferable that the solubilization tank 3 has a structure in which the outer surface has a jacket 7 and the tank is heated by circulating steam or hot water inside the jacket 7. May be provided inside or outside for heating. Further, in the solubilization tank 3, a diffuser 6 for blowing air or high-concentration oxygen is provided at a lower portion, and a stirring device 8 is provided at a shaft center. In addition, since the solubilization tank 3 is filled with a biological carrier so as to be capable of flowing and a fluidized bed tank is used, the contact efficiency between oxygen and sludge is increased.
Further solubilization treatment can be performed. As the inoculum, it is preferable to use sludge generated from another same apparatus, but compost sludge can also be used.

FIG. 2 shows the formation of a fluidized bed with microbial particles obtained by self-granulating anaerobic methane-producing bacteria. UASB treatment tank 1 of UASB treatment process for decomposing
0, and the activated sludge treatment tank 1 in the activated sludge treatment step
a is provided, and FIG. 3 supplies excess sludge generated in a biological treatment process or the like to a treatment tank in which anaerobic microorganisms such as methane bacteria are suspended and aerated with an anaerobic gas. An anaerobic digestion tank 11 in an anaerobic digestion step for decomposing organic matter in sludge into methane gas, carbon dioxide gas or the like by the biological action of anaerobic microorganisms is provided.

The method for treating organic waste water by the above-structured apparatus will be described in detail below. In the method in which the activated sludge treatment tank 1 is provided as the biological treatment step in FIG. 1, the raw water of the organic wastewater supplied to the activated sludge treatment tank 1 from the raw water supply pipe a is the activated sludge which is an aerobic microorganism. By floating and aerating with air, organic matter in raw water is oxidatively decomposed by the biological action of activated sludge. M in this activated sludge treatment
LSS is generally 1000-20,000 mg / L.

The sludge mixture, which is a low-concentration sludge treated in the biological treatment step, is passed through a sludge mixture discharge pipe b to a subsequent settling tank 4.
However, a part of the sludge is supplied to the filtration membrane type sludge thickening tank 2 in the sludge thickening step from the sludge mixed liquid supply pipe c, and the sludge is concentrated. The MLS of the concentrated sludge that has been subjected to the concentration treatment
S is 30,000 to 100,000 mg / L, the concentrated sludge is supplied from the concentrated sludge supply pipe d to the solubilization tank 3 in the sludge volume reduction step, and the filtered water that has passed through the filtration membrane is treated water as filtered water discharge pipe. It is discharged out of the system from f. When the MLSS of the sludge is 30,000 to 100,000 mg / L, the size of the apparatus can be reduced, and the solubilization treatment can be performed efficiently.

The sludge mixture supplied to the sedimentation tank 4 is subjected to sedimentation and separation of the sludge, the supernatant water is discharged as treated water from the treated water discharge pipe h to the outside of the system, and the settled sludge is the sludge concentration in the activated sludge treatment tank 1. Is circulated from the settling sludge supply pipe g in order to maintain In addition, instead of the sludge mixture supplied to the filtration membrane type sludge concentration tank 2, a branch pipe is provided in the settling sludge supply pipe g, and the branch pipe is connected to the filtration membrane type sludge concentration tank 2 to activate the activated sludge treatment tank. A part of the settled sludge which is the low concentration sludge circulated in 1 may be supplied.

The concentrated sludge supplied to the solubilization tank 3 is
The liquid temperature is maintained at 55 to 80 ° C and the residence time is 12 to 72.
As time passes, solubilization is performed by the biological oxidizing action of the hot aerobic organism. Thereby, 10 to 40 vol of sludge
% Is liquefied and the solubilized sludge is circulated from the solubilized sludge supply pipe e in the sludge circulation step to the activated sludge treatment tank 1, whereby the liquefied organic matter is again treated by biological action, and finally In addition, the volume of the sludge is reduced by 20 to 50 vol%, and the sludge itself is liable to settle and the filtration membrane is hardly clogged. In addition, the liquid temperature is 55-8
By performing the solubilization treatment while maintaining the temperature at 0 ° C., the activated sludge microorganisms that grow at room temperature can be sterilized, and the microorganisms that grow at high temperatures can be propagated predominantly, and the sludge can be efficiently liquefied.

In a wastewater treatment method in which an activated sludge treatment tank 1a is provided downstream of the UASB treatment tank 10 shown in FIG. 2, the sludge from the activated sludge treatment tank 1a is transferred to a filtration membrane type sludge concentration tank 2 in a sludge concentration step. The supplied sludge is concentrated, and the concentrated concentrated sludge and the excess self-granulated sludge from the UASB treatment step are supplied to the solubilization treatment tank 3 in the sludge volume reduction treatment step, and are filtered through the filtration membrane. Water is discharged out of the system as treated water. The concentrated sludge supplied to the solubilization tank 3 is
The sludge is solubilized by the biological oxidizing action of the high-temperature aerobic organism to liquefy 10 to 40 vol% of the sludge, and the solubilized sludge is liquefied by circulating from the sludge circulation step to the activated sludge treatment tank 1a. The organic matter is again treated by biological action, finally reducing the volume of the sludge by 20 to 50 vol%.

In the wastewater treatment method in which an anaerobic digestion tank 11 for anaerobic digestion treatment of the excess sludge generated in the biological treatment step shown in FIG. 3 is provided and the wastewater is treated, the excess sludge which is a low-concentration sludge from the biological treatment step is used. Is supplied to the filtration membrane type sludge thickening tank 2 in the sludge thickening step, and the sludge is concentrated. The concentrated thickened sludge and the circulated sludge from the anaerobic digestion tank 11 in the anaerobic digestion step are treated in the sludge volume reduction processing step. The filtered water supplied to the solubilization treatment tank 3 and permeating the filtration membrane is discharged out of the system as treated water. The concentrated sludge supplied to the solubilization tank 3 is solubilized by the biological oxidizing action of a high-temperature aerobic organism, 10 to 40 vol% of the sludge is liquefied, and the solubilized sludge is removed from the sludge circulation process. By circulating through the anaerobic digestion tank 11, the liquefied organic matter is again treated by biological action, and finally, the volume of the sludge is reduced by 20 to 50 vol%.

The sludge concentration step and the solubilization step will be described in more detail with reference to FIG. The sludge supplied to the sludge thickening tank 2 is filtered by a filtration membrane reduced in pressure by a filtration membrane device 5 provided inside the sludge thickening tank 2, and the filtered water that has passed through the filtration membrane is discharged as filtered water as treated water. The concentrated sludge discharged from the pipe f to the outside of the system and concentrated on the non-permeate side is supplied from the concentrated sludge supply pipe d to the solubilization treatment tank 3 in the sludge reduction treatment step.

The concentrated sludge supplied to the solubilization tank 3 is
The treatment tank is heated by flowing steam or hot water through the jacket 7 and is stirred by the stirrer 8, and air or high-concentration oxygen is supplied from the diffuser 6, and the liquid temperature becomes 55 to 80 ° C. It is retained and solubilized by the biological oxidative action of a hot aerobic organism with a residence time of 12 to 72 hours. Excess gas is exhausted from the exhaust pipe j. As a result, 10 to 40 vol% of the sludge is liquefied, and the solubilized sludge is liquefied by circulating from the solubilized sludge supply pipe e in the sludge circulation step to the activated sludge treatment tank 1 in the biological treatment step. The organic matter is treated again by a biological action, and finally, the volume of the sludge is reduced by 20 to 50 vol%, and the sludge itself can easily be settled and the filtration membrane can be hardly clogged.

An example in which organic wastewater is treated using the sludge volume reduction treatment method according to one embodiment of the present invention will be described in detail below.

Example 1 Using the apparatus shown in FIG. 1, food-based organic wastewater (BOD: 1,400 mg / L) was supplied to an activated sludge treatment tank for treatment, and the MLSS was 1,000 to 20,000 m2.
g / L sludge mixed solution is supplied to a sludge concentration tank, and MLS
A concentrated sludge in which S was concentrated to 40,000 to 60,000 mg / L was obtained. The concentrated sludge was supplied to a solubilization tank and solubilized at a liquid temperature of 60 ° C. for 24 hours. As a result, 10 to 40 vol% of the sludge was liquefied. As a result of circulating the solubilized sludge to the activated sludge treatment tank and performing biological treatment again, finally, 20 to 50 vol% of the sludge is reduced in volume,
Excess sludge pulled out from the settling tank hardly occurred. The treated water, which is the supernatant of the sedimentation tank, has a BOD of 10 mg /
L or less.

[0033]

The present invention is a method which has a high effect of reducing sludge volume by adding equipment of relatively small size and easy operation, and has a low operation cost and equipment cost, and a final disposal cost. This is a sludge volume reduction treatment method that can be reduced in cost.
In the invention as set forth in claim 1, the concentrated sludge is obtained by filtration treatment with a filtration membrane in the sludge concentration step, the concentrated sludge is solubilized, and the sludge is circulated to the biological treatment step.
The volume can be reduced by 50 vol%.

According to the second aspect of the present invention, in the sludge volume reducing method according to the first aspect, the biological treatment step is an activated sludge treatment step, and the low-concentration organic sludge is sludge from the activated sludge treatment step. Due to this, surplus sludge discharged from the activated sludge treatment step can be almost eliminated.

According to the third aspect of the present invention, the UAS
In a wastewater treatment method in which an activated sludge treatment step is provided after the B treatment step, the sludge in the activated sludge treatment step is filtered through a filtration membrane in the sludge concentration step to obtain concentrated sludge, and the concentrated sludge is subjected to UASB treatment. The excess self-granulated sludge from the process is solubilized and circulated to the biological treatment process, so that 20 to 50 vol% of the sludge can be reduced in volume.

According to a fourth aspect of the present invention, there is provided a wastewater treatment method in which an anaerobic digestion step is provided after the biological treatment step to perform wastewater treatment, wherein the sludge in the activated sludge treatment step is filtered through a filtration membrane in the sludge concentration step. To obtain a concentrated sludge, solubilize the concentrated sludge and the circulating sludge from the anaerobic digestion step, and circulate to the biological treatment step to obtain 20 to 50 v of the sludge.
ol% can be reduced.

According to a fifth aspect of the present invention, in the sludge reduction treatment method according to any one of the first to fourth aspects, the MLSS of the sludge concentrated in the sludge concentration step is 30 or less.
When the concentration is 000 to 100,000 mg / L, the apparatus can be downsized, and the solubilization treatment can be performed efficiently.

In the invention according to claim 6, in the sludge volume reducing method according to any one of claims 1 to 5, the liquid temperature in the solubilization step is 55 to 80 ° C. Thereby, the device can be downsized and the solubilization process can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a system diagram of an activated sludge treatment apparatus according to an embodiment of the present invention.

FIG. 2 is a system diagram of a UASB processing apparatus according to another embodiment of the present invention.

FIG. 3 is a system diagram of an anaerobic digestion treatment apparatus according to another embodiment of the present invention.

FIG. 4 is a system diagram of a sludge concentration step and a solubilization step which are main parts of the present invention.

[Explanation of symbols]

 1: activated sludge treatment tank 2: filtration membrane type sludge concentration tank 3: solubilization treatment tank 4: sedimentation tank 5: filtration membrane device 6: diffuser means 7: jacket 8: stirrer 10: UASB treatment tank 11: anaerobic digestion Tank

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) C02F 11/04 C02F 11/04 Z 11/12 11/12 EF term (reference) 4D006 GA06 GA07 HA21 HA41 HA95 JA57Z KA01 KA12 KA43 KA72 KB22 KB23 MA02 MA03 MA06 MA16 MA22 MB02 MB05 MC18 MC54 PA02 PB20 PB70 PC64 4D028 AB03 BA00 BB02 BC17 BC18 BD11 BD16 BD17 CA00 4D040 BB05 BB13 BB14 BB23 BB54 BB57 A03BA03 BA03 A03BA03 BA03 BA03 A03BA03 BA03 A02BA03

Claims (6)

[Claims] 1. A sludge concentration step in which low-concentration organic sludge is filtered through a filtration membrane to obtain concentrated sludge and clarified water, and the concentrated sludge concentrated in the sludge concentration step is subjected to high-temperature aerobic biological treatment to enable sludge. A sludge reduction treatment method comprising a solubilization treatment step of solubilizing treatment and a sludge circulation step of circulating the solubilized sludge to a biological treatment step. 2. The biological treatment step is an activated sludge treatment step,
The sludge reduction treatment method according to claim 1, wherein the low-concentration organic sludge is sludge from an activated sludge treatment step. 3. A wastewater treatment method in which an activated sludge treatment step is provided after the UASB treatment step to perform wastewater treatment, wherein the sludge from the activated sludge treatment step is filtered through a filtration membrane to obtain concentrated sludge and clear water. And a solubilization treatment step of solubilizing the sludge by subjecting the concentrated sludge concentrated in the sludge concentration step and excess self-granulated sludge from the UASB treatment step to high-temperature aerobic biological treatment, and solubilized sludge. A sludge circulation step of circulating the sludge into an activated sludge treatment apparatus. 4. A wastewater treatment method in which an anaerobic digestion step is provided after the biological treatment step to perform wastewater treatment, wherein the sludge from the biological treatment step is filtered through a filtration membrane to obtain concentrated sludge and clear water. And a solubilization treatment step of solubilizing the sludge by subjecting the concentrated sludge concentrated in the sludge concentration step and the circulating sludge from the anaerobic digestion step to high-temperature aerobic biological treatment, and anaerobic digestion of the solubilized sludge. A sludge volume reduction treatment method comprising a sludge circulation step for circulating the sludge. 5. MLSS of sludge concentrated in a sludge concentration step
Is 30,000 to 100,000 mg / L.
The sludge volume reduction treatment method according to claim 4. 6. The sludge reduction treatment method according to claim 1, wherein the liquid temperature in the solubilization treatment step is 55 to 80 ° C.