JP2001347296A - Method and apparatus for treating sludge, and method and apparatus for treating sewage by utilizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic sewage treatment apparatus capable of reducing the generation sludge at a low running cost and having a miniaturized solubilizing tank. SOLUTION: The organic sewage treatment apparatus is equipped with a biological treatment system (5) for biologically treating sewage (4), a solid-liquid separator (6) for subjecting sewage after biological treatment to solid-liquid separation treatment to obtain treated water and return sludge, a means for obtaining drawn sludge (11) from a part of the return sludge, an alkali treatment tank (1) for treating the drawn sludge with alkali, a biological solubilizing tank (3) for biologically solubilzing sludge after alkali treatment under an anaerobic, oxygen-free or microaerophilic condition and a sludge return means (13) for returning solubilized sludge to the biological treatment system.

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 solubilizing sludge generated in a biological treatment process of organic wastewater.
The present invention relates to a method and an apparatus for treating organic wastewater capable of reducing the volume of generated wastewater.

[0002]

2. Description of the Related Art A large amount of sludge is generated from a biological treatment process such as an activated sludge method for organic wastewater such as sewage, and the treatment and disposal of this sludge is presently the biggest problem. Conventionally, these sludges are added to a dehydration aid, dehydrated by a dehydrator, and then disposed of by landfill or incineration. However, in the case of landfill disposal, there is a problem in that disposal costs increase due to a decrease in disposal sites. In addition, in the case of incineration, large-scale incineration involves problems such as the burden on the incinerator and the disposal of incineration ash.

Conventionally, an anaerobic digestion (methane fermentation) method has been known as a method for reducing the volume of excess sludge, but this method requires a long residence time, and the tank becomes large. . In addition, since the volume reduction effect is not so large, the digested sludge remaining after digestion had to be dewatered and disposed.

Various methods have been proposed for reducing the volume of sludge. For example, Japanese Patent Application Laid-Open No. 9-253684 discloses a method in which drawn sludge is solubilized in an anaerobic fermentation step.
A method is described in which the sludge is returned to the activated sludge system to suppress the amount of sludge generated. JP-A-11-90493 discloses digestion with an enzyme produced from a thermophilic aerobic bacterium,
A method is described in which the inside of a solubilization tank is set to a temperature at which both heat denaturation can be promoted, sludge is solubilized therein, and then returned to an aeration tank to reduce the volume of excess sludge.

[0005] Japanese Patent Application Laid-Open No. 7-116865 describes a method in which cell walls of sludge are destroyed and solubilized by adding ozone, and then the volume of sludge is reduced in an aerobic tank. In Japanese Patent No. 2132622, the solubilization is promoted by applying a hot alkali treatment, and then the sludge is reduced by returning the sludge to an aeration tank.

[0006]

However, among the conventional methods described above, in the solubilization of sludge only by anaerobic fermentation treatment (Japanese Patent Application Laid-Open No. 9-253684), it is necessary to obtain a sufficient solubilization rate. A long residence time is necessary, and the enlargement of the solubilization tank is inevitable.

[0007] In the solubilization of sludge by enzymes produced by high-temperature aerobic bacteria (JP-A-11-90493), running costs are reduced due to heating costs and aeration costs for maintaining aerobic conditions. Increase.

Further, in the case of solubilization of sludge by ozone oxidation (Japanese Patent Laid-Open No. Hei 7-116865), there is a risk of foaming trouble in an ozone oxidation tank, and necessity of ozone treatment is required. In addition, since the cost of the ozone generator and the ozone addition is high, the initial cost is high and the running cost is increased.

Furthermore, in the solubilization by heating alkali treatment (Japanese Patent No. 2132622), a large amount of a drug is required, so that the cost of the drug is high, and the cost for heating is also required, so that the running cost is increased.

As described above, none of the methods can reduce the volume of sludge at low running cost without increasing the size of the solubilization tank.

Therefore, the present invention provides a method for efficiently solubilizing sludge generated in a biological treatment process of organic wastewater at a low running cost while enabling the solubilization tank to be downsized. It is an object of the present invention to provide a method for treating organic wastewater that can significantly reduce the amount of generated sludge by utilizing the same.

Further, the present invention provides a sludge solubilization apparatus capable of reducing the size of a tank at a low running cost and an organic wastewater treatment apparatus capable of remarkably reducing the amount of generated sludge using the apparatus. The purpose is to:

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a step of subjecting sludge generated in a biological treatment step of sewage to alkali treatment, and the step of subjecting the sludge after the alkali treatment to anaerobic or non-analytical treatment. And a step of biologically solubilizing under oxygen or microaerobic conditions.

The present invention also provides a step of biologically treating the sewage, a step of solid-liquid separating the sewage after the biological treatment to obtain treated water and return sludge, and a step of extracting sludge from a part of the return sludge. Process, a process of alkali-treating the extracted sludge, and immediately sludge the alkali-treated sludge,
A method for treating sewage, comprising the steps of: biologically solubilizing and decomposing under oxygen-free or microaerobic conditions; and returning the solubilized sludge to the biological treatment system.

Preferably, the step of treating the sludge with an alkali is carried out at a pH of less than 9.

Preferably, the sludge is concentrated prior to the alkali treatment of the extracted sludge.

Further, the present invention provides an alkali treatment tank for treating sludge generated in a biological treatment process of wastewater with an alkali, and an alkali treatment tank connected to the alkali treatment tank, wherein the sludge after the alkali treatment is anaerobically, oxygen-free, or slightly alkaline. And a biological solubilization tank that biologically solubilizes under air conditions.

Still further, the present invention provides a biological treatment system for biologically treating wastewater, a solid-liquid separation device for solid-liquid separating the wastewater after the biological treatment to obtain treated water and returned sludge, Means for obtaining extracted sludge from a part of the sludge, an alkali treatment tank for alkali-treating the extracted sludge, and an organism for solubilizing the alkali-treated sludge biologically under anaerobic, oxygen-free or microaerobic conditions. The present invention provides a wastewater treatment apparatus comprising a chemical solubilization tank and sludge return means for returning the solubilized sludge to a biological treatment system.

In the processing apparatus of the present invention, it is preferable that the alkaline processing tank is an extrusion flow type processing tank.

Further, it is preferable that the biological solubilization tank is an extrusion flow type treatment tank.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method and an apparatus for treating sludge of the present invention, and a method and an apparatus for treating organic wastewater using the same will be described with reference to the drawings.

An example of the sludge solubilizing apparatus according to the present invention is as follows.
As shown in FIG.

In the illustrated processing apparatus, sludge is introduced into the alkaline processing tank 1. In the alkali treatment tank 1,
The sludge is subjected to an alkali treatment by adding a small amount of the alkali agent 2, and is kept for a predetermined time. By this treatment, various microbial cell components constituting the sludge are reformed into a form susceptible to biological degradation.

Examples of the alkali agent for the alkali treatment include, but are not limited to, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like. .

The amount of the alkaline agent required here can be appropriately determined according to the type, concentration, state and the like of the sludge. In the method of the present invention, since the sludge after the alkali treatment is biologically solubilized in the subsequent stage, compared with the case where the sludge is solubilized only by the alkali treatment, it is possible to reduce the amount of the alkali agent to a small amount. Become. In this case, the pH in the alkali treatment tank 1 may be less than 9,
You don't have to. However, for efficient solubilization, the pH is preferably 7 or more, and 8 or more.
More preferably, it is the above. Therefore, in the present invention, it is preferable that the pH in the alkali treatment tank 1 be 8 or more and less than 9. As a result, the cost of chemicals can be reduced as compared with the conventional case where alkali treatment is performed at a high pH.

The alkali treatment may be performed while heating, but is preferably performed at room temperature. In the present invention, a sufficient effect can be obtained even at room temperature, so that heating costs are not required. The alkali treatment tank 1 can be of a complete mixing type or an extrusion flow type.
In particular, the extrusion flow method is preferable because more efficient processing such as further cost reduction by reducing the alkali agent and downsizing of the tank by shortening the residence time can be expected.

The sludge after the alkali treatment is subsequently led to the biological solubilization tank 3, where the solubilization proceeds further under the anaerobic, oxygen-free or microaerobic conditions by the action of the sludge solubilizing bacteria.

When the sludge after the alkali treatment is exposed to aerobic conditions, there is a possibility that the alkali-solubilized component may be re-sludged. In order to avoid this, it is desired that the sludge after the alkali treatment be introduced into the biological solubilization tank 3 without contact with air.

Here, the solubilization of sludge in the biological solubilization tank 3 will be described in detail.

Microorganisms involved in the solubilization of sludge in the biological solubilization tank 3 include proteins and carbohydrates which are main components of sludge at normal temperature, normal pressure, anaerobic, anoxic or microaerobic conditions. Microorganisms that can secrete proteases or amylase that decomposes and can use sludge components as a nutrient source are suitable, but not particularly limited.

Since the sludge is pretreated with an alkali, the cells in the sludge are destroyed and the intracellular solution is eluted, so that the solubilization rate in the biological solubilization tank 3 is significantly higher than that of the conventional method. To improve. Thereby, the residence time in the solubilization tank can be reduced, and the tank volume of the biological solubilization tank 3 can be reduced.

As described above, in the present invention, the solubilization of sludge in the biological solubilization tank 3 is performed under anaerobic, oxygen-free or microaerobic conditions, so that aeration is not required.
Thus, the sludge can be treated without any special additional facilities, but a simple stirrer may be installed to increase the reactivity. Even when a stirrer is installed, the cost can be kept much lower than the aeration cost. Further, in the present invention, a sufficient effect can be obtained even at room temperature, so that heating is not required, so that a very simple and low running cost process can be constructed as compared with the conventional method.

From the alkaline treatment tank 1 to the biological solubilization tank 3
The alkaline treatment liquid that has flowed into the solubilization tank 3 is neutralized to near neutrality by performing the treatment under anaerobic, oxygen-free or slightly aerobic conditions. Therefore, in the present invention, an acid or the like for neutralizing the processing solution is not required,
No chemical cost for neutralization is required.

The biological solubilization tank 3 may be of a complete mixing type, but by using an extrusion flow type, a pH gradient can be formed in the solubilization tank. Since the sludge immediately after flowing into the solubilization tank maintains a high pH, more efficient solubilization can be expected, and the cost of chemicals can be further reduced.

An organic sludge treatment method and treatment apparatus of the present invention utilizing the above-described sludge solubilization method will be described below with reference to the drawings.

FIG. 2 shows an example of an organic sludge treatment apparatus according to the present invention.

In the illustrated treatment apparatus, the organic sewage 4 is first introduced into the biological treatment tank 5, subjected to biological treatment for a predetermined time, and then introduced into the sedimentation tank 6. Here, sludge is separated to obtain clear treated water 7. As the biological treatment method, an activated sludge method, a rotating disk method, a sprinkling filter method, a dipping filter method, and the like can be adopted, but are not limited thereto.

Most of the settled separated sludge 8 after solid-liquid separation is
The sludge is returned from the sludge return line 10 to the biological treatment tank 5. On the other hand, sludge 1 pulled out from sludge return line 10
1 is introduced into the sludge concentrating means 12, and after being concentrated to a predetermined concentration, is led to the above-mentioned sludge solubilizer.

The sludge 13 solubilized by the above-mentioned sludge solubilizer is returned to the return line 10 and returned to the biological treatment tank 5.
To be biologically treated again. As a result, the organic matter in the solubilized sludge is removed by aerobic biodegradation in the biological treatment tank 5, and the amount of excess sludge 9 discharged is significantly reduced.

As shown in the processing apparatus shown in the figure, it is preferable that the extracted sludge 11 be concentrated by a concentrator 12 such as a centrifugal separator before the sludge 11 is introduced into the alkali treatment tank 1 to reduce the amount of liquid. . Thereby, the amount of the alkali agent required to maintain the inside of the alkali treatment tank 1 at a predetermined pH can be reduced. Therefore, the alkali cost can be further reduced. Further, the decrease in the total amount of the treated sludge leads to further miniaturization of the alkali treatment tank 1 and the biological solubilization tank 3.

[0041]

Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited thereto.

Example 1 First, surplus sludge collected from a sewage treatment plant was degassed with nitrogen and sealed in a container, and microorganisms having the ability to decompose sludge under anaerobic, oxygen-free or microaerobic conditions were used. Enrichment culture was performed.

The sludge-solubilizing bacteria were obtained from the concentrated culture solution obtained by examining the sludge degradability in a sterilized sludge supernatant medium. These treatments were performed at normal temperature and normal pressure under anaerobic conditions.

Next, the excess sludge is reduced to about 10 g / L by MLSS.
, And sodium hydroxide as an alkali agent was added thereto, followed by stirring for one day to carry out an alkali treatment. The pH of the sludge after the treatment was about 8.5.

Thereafter, 20 ml of the sludge after the alkali treatment and 20 ml of the pure culture solution of the above-mentioned sludge-solubilizing bacteria were mixed,
The flask was charged into a 50-ml baffled flask. Further, after the upper space was replaced with nitrogen, the container was sealed and sealed at 20 ° C. and 1 ° C.
The plate was shaken at 00 rpm for 3 days. After processing, MLSS
Was measured and compared with the initial MLSS and expressed as a solubilization ratio.

As a comparative example, sludge adjusted to have an MLSS of about 10 g / L was prepared without adding an alkali agent.
Stirred for days. Trying to solubilize the sludge by the same procedure as in the above-mentioned Example, except that 20 ml of this medium was used instead of the pure culture solution of the sludge-solubilizing bacteria, and this was mixed with 20 ml of the sludge-solubilizing bacteria culture medium. Was.

Table 1 below shows the solubilization ratio of sludge in Examples and Comparative Examples together with treatment conditions.

[0048]

[Table 1]

As shown in Table 1, in the method of the present invention in which the treatment is performed by adding an alkali agent and a sludge solubilizing bacterium,
A high solubilization rate of at least four times that of the comparative example could be obtained in a relatively short processing time. On the other hand, in a comparative example performed without adding an alkali agent and a sludge solubilizing bacterium, 4
In a short treatment time of days, the sludge hardly solubilized.

(Example 2) A continuous treatment test of the present invention was performed on surplus sludge. FIG. 3 shows the configuration of the apparatus used here.

In the illustrated device, the volume is 400 ml.
The sludge solubilizer is constituted by the cylindrical alkaline treatment tank 1 of the above and the biological solubilization tank 3 of the same type and the same volume. Using such an apparatus, only mechanical stirring was performed without aeration at normal temperature and normal pressure while keeping all treatment tanks sealed. As the test sludge, surplus sludge 14 collected from a sewage treatment plant was used, adjusted to an MLSS of about 10 g / L, and stored at 4 ° C. This sludge was continuously supplied to the alkali treatment tank 1 by the sludge transport pump 15 at regular intervals so as to have a residence time of 6 hours.

The alkali treatment tank 1 was controlled with sodium hydroxide 2 so that the pH was maintained at 8.5 by a pH controller 16. A part of the sludge treated in the alkali treatment tank 1 was withdrawn by the sludge transport pump 21 and flowed into the biological solubilization tank 3, while the remaining sludge overflowed. By comparing the MLSS of the outflow sludge 20 with the MLSS of the test sludge 14, the sludge solubilization rate of the alkali treatment tank 1 was calculated.

The pH of the biological solubilization tank 3 was not adjusted, and the operation was performed with the residence time set to 3 days. At the beginning of the experiment, 5 ml of the culture concentrate of the sludge-solubilizing bacteria obtained in Example 1 was added to the biological solubilization tank 3. In the biological solubilization tank 3, as in the case of the alkali treatment tank, sludge overflowed and the water level was maintained.

The sludge solubilization rate in the biological solubilization tank was determined by comparing the MLSS of the sludge 23 flowing out with the MLSS of the sludge 20 flowing out of the alkali treatment tank. In addition, the MLSS of the sludge 23 is replaced with the MLS of the test sludge 14.
By comparing with S, the sludge solubilization rate of the entire system was determined.

Comparative Example 1 was carried out in the same system as described above, except that the pH of the alkaline treatment tank 1 was set to 7 and the biological solubilization tank 3 was not inoculated with sludge solubilizing bacteria. And Further, the same experiment was performed in a system in which the pH of the alkaline treatment tank 1 was set to 7 and the biological solubilizing tank 3 was inoculated with sludge solubilizing bacteria.

The results obtained are summarized in Table 2 below.

[0057]

[Table 2]

As shown in Table 2, in the present invention in which the alkali treatment and the biological treatment with the sludge-solubilizing bacteria were performed, the solubilization rate nearly four times as high as that of the untreated comparative example 1 was obtained. In addition, comparing the example with the comparative example 2, the biological solubilization tank of the example was twice or more as large as the comparative example 2 even though the sludge solubilizing bacteria were all inoculated. A solubilization rate has been obtained. In the present invention, it is considered that the pretreatment with an alkali is performed, so that the sludge is modified by the treatment into a property that is susceptible to decomposition by the enzyme of the sludge solubilizing bacteria.

(Example 3) A treatment test was conducted on sewage by the following method to compare the present invention with the conventional technology. The biological treatment tank 5 was activated sludge treatment.

Method A: Processed according to the method of the present invention shown in FIG.

Method B: The sludge was solubilized only by the anaerobic fermentation treatment shown in FIG. In the apparatus shown in FIG. 4, the sludge solubilization device including the sludge concentration means 12, the alkali treatment tank 1, and the biological solubilization tank 3 is provided only in the biological solubilization tank 3 which performs treatment by anaerobic fermentation. Except for the replacement, it is the same as that shown in FIG.

Method C: The sludge was solubilized by the enzyme produced by the high-temperature aerobic bacteria shown in FIG. FIG.
Is an aeration device for maintaining aerobic conditions in the biological solubilization tank 3 except for the alkali treatment tank 1;
The apparatus is the same as the apparatus shown in FIG. 2 except that a heating means for setting a high temperature condition is provided.

Method D: Treatment was carried out by the method of solubilizing sludge by ozone oxidation shown in FIG. The apparatus shown in FIG. 6 includes a sludge solubilization device including a sludge concentration means 12, an alkali treatment tank 1, and a biological solubilization tank 3, which is connected to an ozone generator 24.
It is the same as that shown in FIG. 2 except that it was replaced with an ozone treatment tank 25.

Method E: Treatment was carried out by solubilization by a heated alkali treatment shown in FIG. The apparatus shown in FIG. 7 is the same as that shown in FIG. 2 except that a heating means is provided in the alkali treatment tank 1 except for the biological solubilization tank 3.

Method F: Processing was performed by the conventional method shown in FIG. The apparatus shown in FIG. 8 is the same as that shown in FIG. 2 except that a step for solubilizing sludge is not provided.

Table 3 below shows the sewage quality. In addition, each method was tested on a scale of a treated water volume of 120 L / d.

[0067]

[Table 3]

The results are shown in Table 4 below. The initial cost, running cost, and solubilization tank volume were compared with the result of the present invention (method A) as 1. Regarding the amount of sludge generated, the amount of sludge generated by the conventional method was compared with one.

[0069]

[Table 4]

As shown in Table 4, according to the method of the present invention, it was possible to operate at very low running cost and in a small solubilization tank volume without generating excess sludge.

[0071]

As described above, according to the present invention, a sludge treatment method capable of efficiently solubilizing sludge at a low running cost while enabling the solubilization tank to be downsized, There is provided a method for treating organic sewage that can significantly reduce the amount of generated sludge using this method. Further, according to the present invention, the amount of generated sludge can be remarkably reduced at a low running cost, and the sludge treatment apparatus which has achieved the downsizing of the solubilization tank, and the amount of generated sludge is significantly reduced by using this apparatus. An apparatus for treating organic wastewater is provided.

According to the present invention, sludge can be efficiently solubilized without using complicated operations and equipment, so that the treatment time can be reduced and the size of the solubilization equipment can be reduced accordingly. In addition, the solubilization of sludge by microorganisms not only can reduce the cost of chemicals for alkali treatment, but also eliminates the need for chemicals for neutralization, leading to cost reduction. In the alkali treatment, treatment at room temperature is sufficient, and heating cost is not required.

Further, since the biological solubilization and decomposition of sludge is carried out under normal temperature, normal pressure, anaerobic, oxygen-free or microaerobic conditions, heating and aeration are not required, and operation at a low running cost is possible. Becomes The sludge solubilized in this way is
By returning the sludge to the biological treatment system, the generation of excess sludge can be significantly reduced, and the conventional sludge dewatering process, sludge incineration process, etc. can be significantly reduced in scale, and in some cases, such a process becomes unnecessary. .

The present invention is extremely effective for treating sludge generated from a biological treatment process of organic wastewater such as sewage, and has great industrial value.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of the present invention.

FIG. 2 is a diagram for explaining another example of the present invention.

FIG. 3 is a diagram illustrating an example of a continuous test according to the present invention.

FIG. 4 is a diagram for explaining a method of solubilizing sludge using only an anaerobic fermentation treatment.

FIG. 5 is a diagram for explaining a method of solubilizing sludge using an enzyme produced by a thermophilic aerobic bacterium.

FIG. 6 is a diagram for explaining a method of solubilizing sludge by ozone oxidation.

FIG. 7 is a diagram for explaining a method of solubilizing sludge by a heated alkali treatment.

FIG. 8 is a diagram for explaining a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Alkaline treatment tank 2 ... Alkaline agent 3 ... Biological solubilization tank 4 ... Inflow organic sewage 5 ... Biological treatment tank 6 ... Solid-liquid separation means 7 ... Treated water 8 ... Sedimentation separation sludge 9 ... Surplus sludge 10 ... Return Sludge 11: Sludge withdrawn from the returned sludge line 12: Sludge concentrating means 13: Solubilized sludge 14 ... Test sludge 15: Sludge transport pump 16 ... pH controller 17 ... pH sensor 18 ... Alkaline liquid pump 19 ... Alkaline treatment tank solenoid valve 20 ... Sludge flowing out of alkali treatment tank 21 ... Sludge transport pump 22 ... Solenoid valve in biological solubilization tank 23 ... Sludge outflow in biological solubilization tank 24 ... Ozone generator 25 ... Ozone treatment tank

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Yasuko Yao, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Toshiaki Inventor Bureau 1-1-2, Marunouchi, Chiyoda-ku, Tokyo, Japan (72) Inventor: Jun Miyata 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (8)

[Claims] 1. A step of subjecting sludge generated in a biological treatment step of wastewater to alkali treatment, and a step of immediately biologically solubilizing the sludge after the alkali treatment under anaerobic, oxygen-free or microaerobic conditions. And a method for treating sludge. 2. a step of biologically treating the wastewater, a step of solid-liquid separating the wastewater after the biological treatment to obtain treated water and return sludge, and a step of extracting sludge from a part of the return sludge to obtain sludge. An alkali treatment of the extracted sludge; a biologically solubilized decomposition of the sludge after the alkali treatment immediately under anaerobic, oxygen-free or microaerobic conditions; and And returning the wastewater to a treatment system. 3. The method for treating sludge according to claim 1, wherein the step of treating with alkali is carried out at a pH of less than 9. 4. The method according to claim 2, further comprising a step of concentrating the sludge prior to the alkali treatment of the extracted sludge. 5. An alkali treatment tank for alkali-treating sludge generated in a biological treatment process of sewage, and an alkali treatment tank connected to the alkali treatment tank, wherein the sludge after the alkali treatment is subjected to anaerobic, oxygen-free or microaerobic conditions. And a biological solubilizer for biologically solubilizing the sludge. 6. A biological treatment system for biologically treating sewage, a solid-liquid separation device for solid-liquid separation of the biologically treated sewage to obtain treated water and returned sludge, and extracting from a part of the returned sludge. Means for obtaining sludge, an alkali treatment tank for treating the extracted sludge with an alkali, and a biological solubilization tank for biologically solubilizing the sludge after the alkali treatment under anaerobic, oxygen-free or microaerobic conditions. And a sludge return means for returning the solubilized sludge to a biological treatment system. 7. The sludge treatment apparatus according to claim 5, wherein the alkaline treatment tank is an extrusion flow treatment tank. 8. The sludge treatment apparatus according to claim 5, wherein the biological solubilization tank is an extrusion flow treatment tank, or the sludge treatment apparatus according to claim 6 or 7.