JP2806495B2 - Excess sludge treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating excess sludge, and more particularly to a method for digesting excess sludge in an anaerobic digestion tank.

[0002]

2. Description of the Related Art Biological treatment of wastewater containing organic matter is roughly classified into aerobic treatment such as activated sludge method and anaerobic treatment such as methane fermentation method. The required excess sludge is generated. Most of the excess sludge is microbial cells that have grown by ingesting organic matter in the wastewater to be treated, and the method of disposal is generally landfilling, incineration, or composting. However, there are problems in terms of environmental impact and disposal costs. In recent years, excess sludge has been reduced in anaerobic digesters before disposal.

In an anaerobic digestion tank, organic matter in excess sludge is first hydrolyzed by a hydrolytic bacterium, then decomposed to an organic acid by an acid-producing bacterium, and finally decomposed mainly to methane gas by a methane-producing bacterium to form sludge solids. Weight loss is performed. The method of treating in an anaerobic digestion tank is a space-saving and energy-saving treatment method that does not require oxygen supply because an organic substance is decomposed in an anaerobic state and does not require an oxygen supply device for aeration. Further, energy can be recovered from methane gas generated as a final product, which is economically excellent.

[0004]

However, the above-described treatment method in the anaerobic digestion tank has a problem that the digestion rate is low and the digestibility is low because the microorganisms in the excess sludge are hardly decomposed. For example, when processing excess sludge generated in an urban sewage treatment plant in an anaerobic digestion tank, the digestibility of organic matter is only about 30% even if one month is spent. This causes problems such as the necessity of a large anaerobic digestion tank.

In order to solve these problems, there has been proposed an anaerobic digestion method of surplus sludge in which excess sludge to be treated is subjected to a wet medium stirring type mill treatment prior to digestion treatment in an anaerobic digestion tank (Japanese Patent Publication No. Hei 9-222). No. 4-15040). The wet medium agitation milling process is to rotate the stirring disk inserted in the cylindrical container at high speed, vigorously agitate the small balls and beads in the container,
Grinding is performed by the shear frictional force generated between the beads. Anaerobic treatment by grinding excess sludge by wet media stirring mill treatment (hereinafter referred to as wet bead mill treatment) until microbial cell walls of microorganisms are destroyed, and elute or disperse intracellular components in colloidal form. The digestibility in the digester is about 1.
It can be improved about 5 times.

However, even when the wet bead mill treatment is performed, a large amount of undestructed microorganisms remains in the excess sludge.
In the subsequent anaerobic treatment, a sufficient amount of sludge solid matter may not be achieved. In order to further reduce excess sludge, a method of treating excess sludge having a higher digestibility has been required.

Accordingly, an object of the present invention is to provide a method for treating excess sludge having a high digestibility and a high digestion rate.

[0008]

Referring to the embodiment of FIG. 1, the method for treating excess sludge according to the present invention is a method for digesting excess sludge in an anaerobic digestion tank 1 in which anaerobic digestion of excess sludge is performed. Prior to digestion in the tank 1, it is ground by a stone mill type pulverizer 2 having a pulverizing section between opposing surfaces of a pair of non-porous whetstones 2a and 2b moving relatively. Here, the millstone-type crusher 2 has a pair of non-porous whetstones 2a and 2b opposed to each other, moves the opposing surfaces of the whetstone 2a and the whetstone 2b relative to each other, and places an excess in the opposing gap between the moving opposing surfaces. It is made by passing sludge and grinding. Preferably, the two opposing surfaces of the pair of grindstones 2a and 2b are slid while being substantially in contact with each other, and excess sludge is passed through a minute gap between the opposing sliding surfaces to grind.

The present invention can be applied to excess sludge generated by biological treatment such as aerobic treatment and anaerobic treatment, and if necessary, ultrasonic treatment, alkali treatment, Heat treatment or chemical treatment or a combination thereof can be performed. The anaerobic digestion treatment after grinding the excess sludge can be performed by any method belonging to the prior art, and is not limited to the type of anaerobic microorganism used, the temperature and days of digestion treatment, the type of anaerobic digestion tank, and the like. .

[0010]

The grinding stone of the conventional mill-type crusher has about 40% of pores. For example, the grinding stone may be broken or broken due to expansion of gas in the pores due to frictional heat at the time of grinding.
On the other hand, the non-porous grindstones 2a and 2b used in the present invention have few pores, so that the possibility of breakage due to frictional heat or the like is extremely small. Therefore, the distance between the opposing surfaces of the grinding wheels 2a and 2b (hereinafter, sometimes referred to as clearance) is close to 0 mm, that is, the grinding wheels 2a and / or 2b are substantially in contact with each other.
Can be slid. In the case of a grindstone with pores, there is a concern that microorganisms in the excess sludge to be treated enter the pores and proliferate and contaminate the crusher, but in the case of non-porous grindstones 2a and 2b, contamination by such microorganisms is avoided. . Non-porous whetstone
2a and 2b can be made of, for example, ceramics, and non-porous whetstones called ceramic grinders belong to a known technique.

The millstone type pulverizer 2 shown in FIG. 1 has a pair of disc-shaped non-porous whetstones 2a facing each other with an adjustable gap therebetween.
An inlet pipe 12 is provided to penetrate from one side of the grinding wheel 2a to the other side, and the other grinding wheel 2b is rotationally driven while facing the other side of the grinding wheel 2a. The excess sludge introduced into the mill crusher 2 is sent to the opposing gap between the two grindstones 2a and 2b via the inlet pipe 12, and the sent excess sludge is separated by the centrifugal force caused by the rotation of the grindstone 2b. To the periphery. During the passage from the center of the opposing gap to the periphery, the excess sludge is centrifuged,
It is crushed by impact force, shearing force, etc., and most microorganisms in surplus sludge are crushed to mere organic matter which can be subject to decomposition of anaerobic microorganisms. In the wet bead mill treatment in which the microorganisms are crushed by the shear frictional force between the beads, considerable microorganisms that do not collide with the beads remain, whereas in the mill crusher 2, the microorganisms in the excess sludge cause the opposed gap between the two whetstones 2a and 2b to pass. Since it always passes for a certain period of time, the microbial cell wall can be highly destroyed as compared with the wet bead mill treatment. The shape of the grindstones 2a and 2b is not limited to the disk shape in the illustrated example, and the surplus sludge may be ground by driving the grindstone 2a or both grindstones 2a and 2b instead of driving the grindstone 2b. Reference numeral 13 in the figure denotes a feed groove for moving excess sludge smoothly while crushing it.

The curves connecting the white squares in the graphs of FIGS. 2 (A) to 2 (C) are curves of excess sludge generated in a standard municipal sewage treatment plant using a stone mill type pulverizer 2 and then grinding sludge. The figure shows the gas generation rate, the integrated gas amount, and the COD removal rate with respect to the elapsed time when a liter was enclosed in an anaerobic digestion tank 1 having a capacity of 3 liters together with 1.5 liters of seed sludge and digested. As a stone mill type pulverizer 2, a stone mill type grinder pulverizer PARABOY-MINI manufactured by Masuko Sangyo Co., Ltd. was used, and pulverization was performed under the condition that the clearance between both whetstones was 0 mm. For comparison, the same amount of sludge was digested without being ground by the millstone type pulverizer 2, and the results are shown as curves connecting black triangle points in each graph. As can be seen from each graph, when the excess sludge was ground with the millstone crusher 2, the digestibility was increased to about 4 times as compared with the case without the treatment, and the gas generation rate was shortened after the start of the digestion treatment. It was confirmed that the peak reached.

[0013] Further, instead of the mortar-type crusher 2, the same amount of sludge is dried and mortar-treated in a mortar or EIGE.
The digestion treatment was performed by performing a wet bead mill treatment with a wet crushing and dispersing machine M-250 manufactured by R Company, and the results are shown in each graph of FIG. 2 as a curve connecting black square points and a curve connecting white circle points.
It was confirmed that the crushing treatment by the stone mortar crusher 2 can achieve a digestibility more than twice that of the mortar treatment and the wet bead mill treatment.

Thus, the object of the present invention, that is, the provision of the "method of treating excess sludge having a high digestion rate and a high digestion rate" can be achieved.

[0015]

FIG. 3 shows an embodiment in which excess sludge generated in anaerobic treatment of high-concentration organic wastewater such as kitchen waste is treated by the treatment method of the present invention. The high-concentration organic wastewater is sent to the anaerobic digestion tank 1 through the wastewater pipe 6 and is brought into contact with anaerobic microorganisms for a predetermined time to decompose organic substances. To the aeration tank 4 via
The organic matter in the digestive juice is further decomposed by the aerobic microorganism. The processing liquid in which organic substances are decomposed in the aeration tank 4 is sent to the sedimentation separation tank 5, and solids in the processing liquid are settled and separated as a precipitate, and the supernatant is discharged from the processing water pipe 8 to the outside of the processing system. The separated solids, ie, excess sludge, are sent to the millstone crusher 2 via the return pipe 10 and ground, and then returned to the anaerobic digestion tank 1 for digestion. By repeating this cycle, it is possible to construct a high-concentration organic wastewater treatment system that hardly emits excess sludge that may cause environmental pollution.

Between the sedimentation separation tank 5 and the mill crusher 4,
A pretreatment tank (not shown) for performing ultrasonic treatment, alkali treatment, heat treatment, or chemical treatment on excess sludge can be provided. By such pretreatment, it is expected that the digestibility of excess sludge after pulverization by the millstone type pulverizer 2 is further increased.

The methane gas generated in the anaerobic digestion tank 1 is stored in the methane gas holder 3 through the gas pipe 11, and the energy of the methane gas is used for heating the anaerobic digestion tank 1, the driving force of the aerator in the aeration tank 3, and And / or can be used as a driving force for the grindstone 2a or 2b of the millstone crusher 2. By utilizing methane gas energy generated in the wastewater treatment system, energy supply from outside the treatment system can be minimized or unnecessary, and energy saving of the wastewater treatment system can be achieved.

[0018]

As described in detail above, the method for treating excess sludge according to the present invention involves the following remarkable effects because excess sludge is digested in an anaerobic digestion tank after being ground by a millstone-type pulverizer. To play.

(1) The digestibility of the excess sludge in the anaerobic digestion tank is about 4 times that in the case where the sludge crushing treatment is not performed before the digestion treatment, and about 2 times that in the case where the wet bead mill treatment is performed. Can be raised to a degree. (2) Since the digestibility peaks in a short time after the start of the digestion treatment, the desired excess sludge can be reduced in a short time. (3) Since the digestion rate is high and the digestion rate is high, sufficient reduction of excess sludge can be achieved even in a small anaerobic digestion tank.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is a graph showing experimental results of the present invention.

FIG. 3 is an explanatory diagram of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anaerobic digestion tank 2 Stone mill crusher 2a, 2b Whetstone 3 Methane gas holder 4 Aeration tank 5 Sedimentation separation tank 6 Wastewater pipe 7 Digestion liquid pipe 8 Processing liquid pipe 9 Processing water pipe 10 Return pipe 11 Gas pipe 12 Feed pipe 13 Send groove.

Continued on the front page (72) Inventor Kosaku Osato 2-9-1-1, Tobita-Shi, Chofu-shi, Tokyo Kashima Construction Co., Ltd. Technical Research Institute (72) Inventor Yui Hatano 2-9-1-1, Tobita-Shi, Tobita, Chofu-shi, Tokyo Shika Kashima Construction Co., Ltd. (72) Inventor Nahoko Kobayashi Nahako 2-19-1, Tobita-shi, Tokyo No. Kashima Construction Co., Ltd. Technical Research Institute (56) Reference JP-A-2-211299 (JP, A) JP-A-1-99696 (JP, A) JP-A-63-224798 (JP, A) JP 5-228459 (JP, A) Japanese Utility Model Showa 62-62840 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) C02F 11/00-11/20 B02C 7/12

Claims (4)

(57) [Claims] In a treatment method for digesting surplus sludge in an anaerobic digestion tank, before the excess sludge is digested in the anaerobic digestion tank, a crushing section is provided between opposing surfaces of a pair of relatively non-porous whetstones that move relatively. Of excess sludge ground by a millstone mill. 2. The processing method according to claim 1, wherein said pair of whetstones are slid while being substantially brought into contact with each other, and said excess sludge is passed through a minute gap between said two opposing surfaces. A method for treating surplus sludge that has been ground. 3. The method for treating excess sludge according to claim 1, wherein ultrasonic treatment, alkali treatment, heat treatment, chemical treatment or a combination thereof is performed before grinding the excess sludge. 4. The processing method according to claim 1, 2 or 3,
A method for treating excess sludge, wherein energy of methane gas generated in the digestion treatment is recovered and used for driving a grindstone of the millstone crusher.