JP2000185299A - Method for reducing volume of excessive sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amt. of sludge generated from a waste water treatment equipment in a method for reducing the vol. of excessive sludge by utilizing microorganisms by subjecting sludge to aerobic treatment and subsequently subjecting the same to anaerobic treatment to reduce the amt. of generated sludge with high efficiency. SOLUTION: Excessive sludge is treated with alkali supplied from an alkali supply device 5 to be supplied to a sludge aerobic treatment tank 1 from an excessive sludge inflow port 7. In the sludge aerobic treatment tank 1, temp. is regulated by a temp. regulator 4 and stirring is performed by a stirrer 6 and oxygen is supplied by an oxygen-containing gas supply device 3 and sludge is aerobically treated. The aerobically treated sludge is discharged from a sludge aerobically treated water discharge port 8 and sent to a sludge anaerobic treatment tank 2 from a sludge aerobically treated water inflow port 9. In the sludge anaerobic treatment tank 2, temp. is regulated by a temp. regulator 4 and stirring is performed by a stirrer 6. The sludge subjected to anaerobic treatment is discharged from a sludge anaerobically treated water discharge port 10. By this constitution, excessive sludge can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating excess sludge, which treats excess sludge using microorganisms to reduce or eliminate sludge volume, and a method and apparatus for treating waste water using the same. It is.

[0002]

2. Description of the Related Art A typical method of biological treatment of wastewater is an activated sludge method in which BOD components are decomposed into microorganisms under aerobic conditions, and sedimentation / separation is performed at a later stage. In this method, a part of the settled sludge is returned to the aeration tank, but a part of the sludge needs to be treated as excess sludge after solid-liquid separation in a settling tank or the like.

[0003] Surplus sludge is partly reused as a soil conditioner or compost material, but most is treated as industrial waste. However, due to cost and environmental considerations, methods other than disposal are required. As one of the methods, for example, an anaerobic or aerobic digestion method by an organism is conventionally known. In the anaerobic treatment method, anaerobic microorganisms such as methanogens decompose organic components in sludge to generate methane and carbon dioxide. This method has the advantage that the sludge can be reduced and the energy resources can be recovered at the same time. However, the sludge needs to stay for 10 to 30 days, which causes problems such as an increase in the size of the facility. The aerobic treatment method also requires a long residence time, but has a problem such as a low weight reduction rate, and is hardly used recently.
Further, a method of chemically or physically pretreating the sludge and then anaerobically or aerobically treating the microorganism with a sludge is also being studied. This is a method aimed at shortening the treatment time by the microorganisms at the subsequent stage by forcibly pretreating the sludge. For example, Japanese Patent Application Laid-Open Nos.
Japanese Patent Laid-Open No. 19789 discloses a method of treating sludge cell walls with ozone and then reducing the volume of sludge in an aerobic tank.
Japanese Patent Publication No. 8-76200 is expected to reduce the volume by crushing the cell wall of sludge with ultrasonic waves. In addition, Japanese Unexamined Patent Publication
Japanese Patent No. 8496 discloses an aerobic treatment after adding an alkali or a mineral acid to sludge, treating the sludge under an alkaline condition or an acidic condition. JP-A-4-326998,
Japanese Unexamined Patent Publication No. 5-345200 discloses a method in which a sludge is made alkaline and heated at the same time as a hot alkali treatment is carried out to promote solubilization, followed by anaerobic treatment near neutrality.
Further, JP-A-8-229595 and JP-A-8-243
No. 595 discloses a method of solubilizing sludge by heating.

However, the conventional method using sludge destruction such as ultrasonic waves and ozone requires high equipment and running costs, and the method of adding an acid or alkali requires the cost of chemicals used, equipment and chemicals for neutralization. Further, a more innovative method is desired, for example, a method of heating to a higher temperature raises a problem of an increase in cost for heating.

[0005]

The treatment of sludge generated in wastewater treatment is carried out by landfilling, incineration or the like, but there are many problems in terms of environment, treatment cost and energy. An object of the present invention is to reduce the volume of generated sludge with high efficiency and reduce the amount of generated sludge from wastewater treatment equipment.

[0006]

The object of the present invention is achieved by the following method or apparatus. That is, as a method for reducing excess sludge, "a method for reducing excess sludge using microorganisms, which comprises performing aerobic treatment on sludge and then performing anaerobic treatment on the sludge. "The aerobic and / or anaerobic treatment temperature conditions are 40.
The excess sludge volume reduction method as described above, wherein the temperature is not less than ℃. "A method for reducing excess sludge volume according to any one of the above, characterized by performing an alkali treatment at pH 9 to 13 prior to the aerobic treatment." Performing, a step of solid-liquid separation of the treatment liquid of the wastewater aerobic treatment step, and returning at least a part of the separated sludge in the solid-liquid separation step to the wastewater aerobic treatment step, and at least a part of another part. A wastewater treatment method, comprising: a step of reducing excess volume of the excess sludge; and a step of returning at least a part of water discharged from the excess sludge volume reduction process to the wastewater aerobic treatment step. A wastewater treatment method in which the sludge volume reduction step has the characteristics of the above-mentioned excess sludge volume reduction method. "The excess sludge volume reduction device includes at least an excess sludge inflow port and sludge aerobic treated water. Equipped with discharge port, processing A sludge aerobic treatment tank provided with an oxygen-containing gas supply device in the apparatus, and a sludge anaerobic equipped with at least a sludge aerobic treatment water inlet and a sludge anaerobic treatment water discharge port communicating with an outlet of the sludge aerobic treatment tank An excess sludge volume reducing device having a treatment tank. "," A sludge aerobic treatment tank and a sludge anaerobic treatment tank are provided with a temperature control device for adjusting the temperature to a constant temperature of 40 ° C. or more. The excess sludge volume reduction apparatus described above. ”,“ Upstream of the excess sludge flowing into the sludge aerobic treatment tank, pH 9
The apparatus for reducing excess sludge volume according to any one of the preceding claims, further comprising an apparatus for supplying alkalis of from 13 to 13. ”, As a wastewater treatment device,“ at least a wastewater to be treated, a return sludge inlet, a wastewater aerobic treated water outlet, a wastewater aerobic treatment tank equipped with an oxygen-containing gas supply device, and the wastewater aerobic treated water A solid-liquid separation device having an aerobic treated water inlet, a solid-liquid separated liquid outlet, and a solid-liquid separated sludge outlet, the drain being connected to the outlet, and draining at least a part of the sludge discharged from the solid-liquid separated sludge outlet. A sludge return line for returning to the aerobic treatment tank, and an excess sludge treatment line for introduction to the excess sludge volume reduction device, wherein at least a part of the treated water from the excess sludge treatment device is returned to the drainage aerobic treatment tank A wastewater treatment apparatus having a treated sludge return line, wherein the excess sludge treatment apparatus has any of the above-mentioned features. "

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The outline of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of an apparatus for reducing excess sludge according to the present invention. Excess sludge is alkali-treated by the alkali supply device 5 and supplied to the sludge aerobic treatment tank 1 from the surplus sludge inlet 7. The temperature of the sludge aerobic treatment tank 1 is controlled by the temperature control device 4, the stirring is performed by the stirrer 6, and the oxygen is supplied by the oxygen-containing gas supply device 3,
Sludge is treated aerobically. The sludge treated aerobically is discharged from the sludge aerobic treated water discharge port 8 and sent to the sludge anaerobic treatment tank 2 from the sludge aerobic treated water inlet 9. In the sludge anaerobic treatment tank 2, the temperature is controlled by the temperature control device 4, and stirring is performed by the stirrer 6. The sludge subjected to the anaerobic treatment is discharged from the sludge anaerobic treated water discharge port 10.

FIG. 2 shows an example of the wastewater treatment apparatus according to the present invention. The treated wastewater is supplied from the treated wastewater inlet 14 to the wastewater aerobic treatment tank 11. Drainage aerobic treatment tank 1
In 1, oxygen is supplied by the oxygen-containing gas supply device 3,
Aerobic microbial treatment of the wastewater is performed. The treated water is discharged from the drainage aerobic treated water discharge port 15 and supplied to the solid-liquid separation device 12 from the drainage aerobic treated water inlet 16. The solid-liquid separated liquid is discharged from the solid-liquid separated liquid outlet 17, and the solid-liquid separated sludge is discharged from the solid-liquid separated sludge outlet 18. Part of the discharged sludge is discharged to the drainage aerobic treatment tank 1 through a sludge return line 19.
Returned to 1. Part of the other part is the excess sludge treatment line 20
Is supplied to the excess sludge volume reducing device 13 via the The sludge that has been reduced in volume is returned to the drainage aerobic treatment tank 11 via the treated sludge return line 21. The remaining sludge discharged from the solid-liquid separation sludge discharge port 18 is discharged outside the system as surplus sludge.

The excess sludge volume reduction method can be applied to the excess sludge generated in the wastewater treatment, and the wastewater treatment method using the excess sludge volume reduction method to various wastewaters can be applied.

Surplus sludge mainly refers to returned sludge discharged from sewage treatment plants, night soil treatment plants, and other treatment facilities. However, any other sludge that has a large amount of bacterial cells in the sludge can be used. The present invention is fully applicable. Further, the wastewater treatment method incorporating the present excess sludge treatment method is applicable to municipal sewage, human waste, industrial wastewater, process wastewater containing a large amount of specific substances, and the like.

The sludge aerobic treatment in the present invention refers to supplying oxygen-containing gas to a sludge aerobic treatment tank to aerobically treat microorganisms. As a method of supplying the oxygen-containing gas, a method of supplying air with a blower and ejecting it from a diffuser pipe, a method of supplying air as a gas-liquid two-layer flow like an ejector, or a type of performing ventilation and stirring However, there is no particular limitation. Air is usually used as the oxygen-containing gas, but may be oxygen-enriched air or pure oxygen, and is not particularly limited as long as it contains oxygen. Further, it is desirable that the dissolved oxygen concentration in the sludge aerobic treatment tank is not 0. However, even when the dissolved oxygen concentration is 0 while supplying oxygen due to a high oxygen utilization rate, the sludge aerobic treatment of the present invention is also possible. Included in processing.

[0013] The sludge anaerobic treatment is intended to be treated without supplying oxygen. The anaerobic condition may be a closed processing tank that also prevents oxygen supply from the upper gas phase of the tank, an open processing tank that does not supply oxygen, and the like, but the present invention actively supplies oxygen. There is no particular limitation as long as the method is not performed. In addition, the sludge anaerobic treatment tank usually performs stirring in some form. The stirring is not particularly limited, but may be stirring with a stirrer, bubbling with a gas other than oxygen such as nitrogen gas, or using the flow of inflow water. It does not need to be made, and a gentle stirring state is usually used.

A feature of the present invention is that the excess sludge can be efficiently reduced in volume by subjecting the excess sludge to aerobic treatment and then anaerobic treatment. Another object of the present invention is to reduce the amount of excess sludge generated from a wastewater treatment system by wastewater treatment including a process of performing anaerobic treatment after aerobic treatment of excess sludge.

The details of the mechanism by which excess sludge is reduced in volume by performing anaerobic treatment after sludge aerobic treatment are not clear, but in the preceding sludge aerobic treatment, high-speed treatment of residual organic matter and solubilized matter, especially When the temperature and pH conditions are changed, the solubilization of the sludge progresses due to the change in the conditions, and the environment becomes different from that of the activated sludge tank before the sludge treatment process. It is presumed that the part of the plant dies and the dominant microorganism changes, leading to a reduction in volume. In the latter sludge anaerobic treatment, the oxygen condition is completely different from that in the former aerobic treatment.Therefore, further solubilization and volume reduction such as partial elimination of microorganisms constituting the sludge and decomposition of sludge-derived organic matter by different decomposition cycles are performed. It is estimated that

The effect of the present invention is exhibited even at room temperature. However, by controlling the temperature to 40 ° C. or higher, the activity of microorganisms is activated, and the effect is further enhanced. When the temperature is adjusted, the sludge aerobic treatment tank and the sludge anaerobic treatment tank may be used alone, or both the temperature may be adjusted. The temperature control in the first sludge aerobic treatment tank can be expected to improve the microbial activity by temperature and to solubilize the sludge by temperature, and in the second sludge anaerobic treatment tank, the treatment stability can be measured.

The temperature condition is suitably from 40 ° C. to 80 ° C. Generally, temperature conditions considered to be preferable for the propagation of microorganisms are around room temperature.
It is 30 ° C, and at most 35 ° C. However, in the present invention, high decomposition efficiency is obtained even at a high temperature, which is considered unfavorable for the propagation of microorganisms, that is, at 40 ° C. or higher. Although the details are unknown, it is speculated that at high temperatures, the growth of microorganisms that do not contribute to sludge decomposition is suppressed, and the activity of microorganisms that contribute to sludge decomposition is activated. Further, focusing on the effect of promoting the solubilization of sludge by heat, when the temperature is lower than 40 ° C., it is insufficient. When the temperature is higher than 80 ° C., the energy cost for maintaining the temperature is high and the energy cost is high. The activity of microorganisms that can perform sludge treatment as much as possible becomes difficult. The most efficient in terms of compatibility between the growth of microorganisms and energy cost is that the temperature is 40 to 70 ° C, more preferably 45 to 65 ° C, but if it is set according to the nature of the microorganisms contributing to decomposition. good.

The alkali treatment prior to the aerobic treatment is effective in solubilizing the sludge and specializing the growth conditions of the bacteria in the aerobic treatment. By performing the alkali treatment in the same manner as the temperature, the sludge is solubilized, and easily decomposed microorganisms are eluted. The alkaline condition is preferably 9 to 13.

The method of alkalizing in the present invention includes, but is not limited to, addition of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, sodium hydrogencarbonate and the like. The amount of addition varies depending on the type, temperature and condition of the sludge, but may be an amount capable of achieving pH 9 or more, and may be added in a solid state or an aqueous solution state.

The microorganism to be used is pH 9 or higher and 4
Microorganisms capable of growing at 0 ° C. or higher and capable of using sludge components as nutrient sources are preferred, but are not particularly limited. Microorganisms that can grow under these conditions can be obtained relatively easily from general soil, river water, sludge, etc., unless one or both of the pH and temperature are extremely high. In addition, during the treatment of excess sludge by these microorganisms, the addition of inorganic salts such as potassium phosphate, dipotassium phosphate, magnesium sulfate and ammonium nitrate can sometimes increase the growth, but it is not always necessary. is not.

The present invention is also used for wastewater treatment. "In the method of reducing excess sludge using microorganisms,
A method for reducing excess sludge volume, which comprises subjecting sludge to aerobic treatment followed by anaerobic treatment. Is used in the wastewater treatment, and at least one of a step of performing at least aerobic treatment of the wastewater, a step of solid-liquid separating the treatment liquid of the wastewater aerobic treatment step, and at least one of the separated sludges in the solid-liquid separation step Part is returned to the wastewater aerobic treatment step, having an excess sludge volume reduction step of reducing the volume of at least a part of the other part, at least a part of the wastewater from the excess sludge volume reduction step A wastewater treatment method having a step of returning to a wastewater aerobic treatment step, wherein the excess sludge volume reducing step reduces the volume of excess sludge using microorganisms; Wastewater treatment method, which is a method of reducing excess sludge volume
It is.

In the wastewater treatment process, the activated sludge method is often used. The activated sludge method includes at least an aeration tank as a wastewater aerobic treatment tank and a solid-liquid separation device. As a solid-liquid separation device, sedimentation separation using a sedimentation tank is most widely performed. Other methods using centrifugation and membrane separation are also partially used, and the present invention is not limited to any method. After solid-liquid separation, a method in which a part of the sludge is returned to the aerobic treatment tank of the activated sludge method, and a part of the sludge is withdrawn and treated as excess sludge is widely used. A part or the whole is sent to the excess sludge sludge treatment step, and a part or the whole of the excess sludge treatment step is returned to the activated sludge drainage aerobic treatment tank. At this time, the remaining sludge treatment water may be treated as excess sludge, for example, by performing solid-liquid separation, or may be returned to a treatment tank in the excess sludge treatment step.

The throughput in the excess sludge treatment step is represented by the product of the volume reduction rate and the concentration flow rate. Depending on the properties of the sludge, this throughput is set to the same amount as the excess sludge that has been conventionally disposed. It is also possible to eliminate the amount of excess sludge that is drawn out of the system and disposed of.

[0024]

[Example] (Example 1) Add excess alkali to excess sludge,
The temperature was adjusted to 5 ° C. to perform aerobic and anaerobic two-stage treatment.

Excess sludge collected from a chemical manufacturer's wastewater treatment plant was prepared so that the MLSS became 20,000 mg / l, and 0.3 wt% of sodium hydroxide was added as an alkaline agent to adjust the pH.
Was set to 12 and the sludge was supplied. The feed sludge shown in FIG.
The sludge was supplied to the first sludge aerobic treatment tank at a supply rate of liter / d. The sludge aerobic treatment tank was stirred in a 1-liter capacity treatment tank, air was supplied at 100 ml / min, and the temperature was adjusted to 45 ° C. All of the treated water in the first-stage sludge aerobic treatment tank was supplied to the sludge anaerobic treatment tank. The sludge anaerobic treatment tank had a capacity of 3 liters, was stirred with a stirrer, and was adjusted to a temperature of 45 ° C.

When the MLSS of the excess sludge before the alkali treatment and the treated sludge after the sludge aerobic / anaerobic treatment was measured,
The reduction rates were 20,000 mg / l, 10,600 mg / l and 47%, respectively. Similarly, when TOC was measured in a suspended state,
The reduction rate was 46% at 0,000 mg / l and 5,400 mg / l.

(Comparative Example 1) Alkali was added to excess sludge, and the temperature was adjusted to 45 ° C to perform aerobic single-stage treatment.

Excess sludge collected from a chemical manufacturer's wastewater treatment plant was prepared so that the MLSS was 20,000 mg / l, and 0.3 wt% of sodium hydroxide was added as an alkaline agent to adjust the pH.
Was set to 12 and the sludge was supplied. Feed sludge is 1 liter / d
The sludge was supplied to the aerobic sludge treatment tank at a supply speed of. The aerobic sludge treatment tank is agitated in a 1-liter capacity treatment tank, and air is supplied to 100 ml.
/ min, and the temperature was adjusted to 45 ° C.

When the MLSS of the excess sludge before the alkali treatment and the treated sludge after the sludge aerobic treatment was measured, the reduction rates were 20,000 mg / l, 14,300 mg / l and 29%, respectively.
Also, when the TOC was measured in the same suspended state, it was 10,000 m
g / l, 7,100 mg / l, a decrease of 29%. The MLSS after the alkali treatment was 14,000 mg / l, and slightly increased to 14,300 mg / l after the aerobic treatment, which is considered to be because the alkali-solubilized component changed to cells.

(Comparative Example 2) An alkali was added to excess sludge, and the mixture was adjusted to 45 ° C and subjected to one-stage anaerobic treatment.

Excess sludge collected from a chemical manufacturer's wastewater treatment plant was prepared so that the MLSS was 20,000 mg / l, and 0.3 wt% of sodium hydroxide was added as an alkaline agent to adjust the pH.
Was set to 12 and the sludge was supplied. Feed sludge is 1 liter / d
The sludge was supplied to the anaerobic sludge treatment tank at a supply speed of. The sludge anaerobic treatment tank had a capacity of 3 liters, was stirred with a stirrer, and was adjusted to a temperature of 45 ° C.

When the MLSS of the excess sludge before the alkali treatment and the treated sludge after the sludge anaerobic treatment was measured, the reduction rates were 20,000 mg / l, 13,500 mg / l and 33%, respectively.
Also, when the TOC was measured in the same suspended state, it was 10,000 m
g / l, 7,300 mg / l, a decrease of 27%.

(Comparative Example 3) An alkali was added to excess sludge, and the mixture was adjusted to 45 ° C and subjected to two-stage anaerobic and aerobic treatment.

Excess sludge collected from a wastewater treatment plant of a chemical manufacturer was prepared so that the MLSS was 20,000 mg / l, and 0.3 wt% of sodium hydroxide was added as an alkali agent to obtain a feed sludge. The supplied sludge was supplied to the first-stage sludge anaerobic treatment tank at a supply rate of 1 liter / d. Sludge anaerobic treatment tank capacity 3
Liter and stirred with a stirrer, and the temperature was adjusted to 45 ° C. All of the treated water in the first-stage sludge anaerobic treatment tank was supplied to the sludge aerobic treatment tank. The aerobic sludge treatment tank is stirred in a 1-liter capacity treatment tank, and air is supplied at 100 ml / min.
The temperature was adjusted to 45 ° C.

When the MLSS of the excess sludge before the alkali treatment and the treated sludge after the sludge anaerobic / aerobic treatment was measured,
The reduction rates were 20,000 mg / l, 13,600 mg / l and 32%, respectively. Similarly, when TOC was measured in a suspended state,
The reduction rate was 27% at 0,000 mg / l and 7,200 mg / l.

[0036]

According to the present invention, surplus sludge can be reduced. Further, in the wastewater treatment of the present invention incorporating the present excess sludge treatment, the generation of excess sludge from the wastewater treatment system can be reduced, and depending on the operation method, the generation of excess sludge can be eliminated.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an example of an excess sludge volume reducing device of the present invention.

FIG. 2 is a conceptual diagram of an example of a wastewater treatment device according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 Sludge aerobic treatment tank 2 Sludge anaerobic treatment tank 3 Oxygen-containing gas supply device 4 Temperature control device 5 Alkaline supply device 6 Stirrer 7 Excess sludge inlet 8 Sludge aerobic treated water outlet 9 Sludge aerobic treated water inlet 10 Sludge anaerobic Treated water outlet 11 Wastewater aerobic treatment tank 12 Solid-liquid separator 13 Excess sludge volume reduction device 14 Wastewater inlet for treated water 15 Wastewater aerobic treated water outlet 16 Wastewater aerobic treated water inlet 17 Solid-liquid separated liquid outlet 18 Solid-liquid separation sludge outlet 19 Sludge return line 20 Excess sludge treatment line 21 Treated sludge return line 22 Return sludge inlet

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D059 AA05 BA03 BA11 BA31 BA34 BA48 BA56 BF14 CA22 DA01 DA05 DA08 DA38 EB06

Claims (8)

[Claims] 1. A method for reducing the volume of excess sludge using microorganisms, wherein the sludge is subjected to anaerobic treatment after being subjected to aerobic treatment. 2. The method for reducing excess sludge volume according to claim 1, wherein the temperature condition of the aerobic treatment and / or the anaerobic treatment is 40 ° C. or higher. 3. An alkaline treatment at a pH of 9 to 13 prior to the aerobic treatment.
The excess sludge volume reduction method described in the above. 4. A step of performing aerobic treatment on at least wastewater, a step of solid-liquid separating a treatment liquid in the wastewater aerobic treatment step, and removing at least a part of the separated sludge in the solid-liquid separation step with the wastewater aerobic treatment. It has an excess sludge volume reduction step of returning to the treatment step and reducing the volume of at least a part of the other part, and at least a part of the discharged water from the excess sludge volume reduction step is sent to the wastewater aerobic treatment step. 4. A wastewater treatment method comprising the step of returning the wastewater, wherein the excess sludge volume reduction step has the features of claims 1 to 3. 5. A sludge aerobic treatment tank provided with at least an excess sludge inlet and a sludge aerobic treated water discharge port, and an oxygen-containing gas supply device in a treatment apparatus, and at least a discharge of the sludge aerobic treatment tank. An excess sludge volume reducing device having a sludge anaerobic treatment tank provided with a sludge aerobic treatment water inflow port and a sludge anaerobic treatment water discharge port communicating with an outlet. 6. The excess sludge according to claim 5, further comprising a temperature controller for adjusting the temperature to a constant temperature of 40 ° C. or more in either the sludge aerobic treatment tank or the sludge anaerobic treatment tank. Volume reduction device. 7. An apparatus for supplying alkali to adjust the inflow excess sludge to pH 9 to 13 upstream of the excess sludge inlet provided in the sludge aerobic treatment tank. The excess sludge volume reducing device described in the above. 8. A wastewater aerobic treatment tank provided with at least a treated wastewater inlet, a return sludge inflow, a wastewater aerobic treated water outlet, an oxygen-containing gas supply device, and the wastewater aerobic treated water outlet. A solid-liquid separator having a water inlet, a solid-liquid separation liquid outlet, a solid-liquid separation sludge outlet, and a drainage aerobic treatment of sludge discharged from the solid-liquid separation sludge outlet; Equipped with a sludge return line to return to the tank and a surplus sludge treatment line to be introduced into the excess sludge volume reduction device,
6. A wastewater treatment device having a treated sludge return line for returning at least a part of the treated water from the excess sludge treatment device to the wastewater aerobic treatment tank, wherein the excess sludge treatment device is used.
Wastewater treatment equipment having the characteristics of 1 to 7.