JPH09155384A - Anaerobic treatment process for organic discharge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the volume of sludge while controlling the deterioration of the treated water quality by extracting the specified amount of mixed liquid or concentrated liquid in an anaerobic treatment tank, heating the extracted sludge at the specified temperature and then transferring the sludge to the anaerobic treatment tank. SOLUTION: Organic discharge or sludge is introduced from a line 4 for liquid to be treated into an anaerobic treatment tank 1, and mixed with returned sludge from a return sludge line 5 and biological sludge in the anaerobic treatment tank 1, and the anaerobic treatment is carried out. A part of the mixed liquid is introduced into a membrane separation device 2 by a pump 12, and the membrane separation is carried out by a separating membrane 13, and permeated liquid 14 thus prepared is discharged from a treated liquid line 16, and a part of concentrate 15, namely 1/15 or less of total keeping sludge amount of the anaerobic treatment tank 1 per day is discharged from a concentrate discharge line 17 and introduced into a heat treatment tank 3, while a part of the whole of a remaining part is returned from the return sludge line 5 into the anerobic treatment tank 1. The concentrate 15 is heated at the temperature of 60-100 deg.C or under for 30 minutes or more by a heater 21 in a heating tank 3 to modify the quality of sludge, and then the sludge is returned from a sludge line 23 into the anaerobic treatment tank 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for anaerobically treating an organic waste liquid by anaerobically treating the organic waste liquid and reducing the volume of sludge produced by heat treatment.

[0002]

2. Description of the Related Art In a method of aerobically treating organic waste liquid in the presence of activated sludge, a large amount of surplus activated sludge which is hardly dehydrated is produced. A large amount of excess digested sludge is also produced by a method of anaerobically treating the organic waste liquid in the presence of anaerobic sludge. In order to reduce the volume of such excess sludge, a method of aerobically or anaerobically digesting excess sludge has been used.
In the aerobic digestion, the excess sludge is simply aerated in a digestion tank to digest it, and the aerated sludge is separated into solid and liquid to return the separated sludge to the digestion tank. In anaerobic digestion, excess sludge is put into a digestion tank and digested by the action of anaerobic bacteria.

[0003] Such a digestion method digests by utilizing the action of aerobic or anaerobic organisms. However, since excess sludge itself is biologically stable through biological treatment, sludge is reduced. There is a limit to the volume of the sludge, usually 30
Only ４０40% is reduced in volume.

In order to improve such a point, Japanese Patent Publication No.
No. 61994 describes a method for treating organic wastewater in which excess sludge is solubilized at a pH of 2.5 or lower at a temperature of 50 ° C. or higher and then returned to an aeration tank. In addition, JP-A 1-224
No. 100 is anaerobic digested sludge at 100-180 ℃
It describes a method for treating organic sludge in which this heat-treated sludge is returned to the anaerobic digestion tank after being heat-treated.

[0005]

However, although it is possible to reduce the volume of sludge by such a conventional method, since the conditions for solubilization treatment are severe at high temperatures, hardly biodegradable organic substances are produced. There is a problem that the chromaticity and COD of the treatment liquid are increased and the quality of the treated water is deteriorated, and moreover, a device having high heat resistance and pressure resistance is required, which consumes a large amount of energy and is costly.

In order to solve the above problems, the object of the present invention is to prevent the deterioration of treated water quality, and further, by heating at low temperature, reduce the volume of sludge at low cost. It is to propose a processing method.

[0007]

According to the present invention, an organic effluent is anaerobically treated in the anaerobic treatment tank in the presence of biological sludge containing anaerobic microorganisms, and an anaerobic treatment tank is introduced per day. Anaerobic equivalent to twice the amount of sludge (solid content) in the organic effluent and equivalent to 1/15 or less (solid content) of the total amount of sludge in the anaerobic treatment tank per day. A heat treatment step of extracting the mixed solution or the concentrated solution in the treatment tank, heat-treating the drawn sludge at a temperature of 60 to less than 100 ° C. for 30 minutes or more, and then transferring it to the anaerobic treatment tank. Anaerobic treatment method for sexual drainage.

The organic waste liquid to be treated in the present invention is a waste liquid (including sludge) containing an organic substance to be treated by anaerobic treatment, but it is a biodegradable organic substance, an inorganic substance, cellulose, paper. , Cotton, wool cloth, solid matter in human waste, etc. may be contained. Such organic effluents include sewage, sewage first sludge, night soil, septic tank sludge, food factory effluent, beer waste yeast and other industrial effluents, excess sludge generated when treating these effluents, etc. Can be given.

Examples of the anaerobic treatment process for anaerobically treating such organic waste liquid include an anaerobic digestion method and a high load anaerobic treatment method. The treatment conditions of the anaerobic treatment are not particularly limited, and the usual anaerobic biological treatment conditions can be adopted. For example, the MLSS concentration in the anaerobic treatment tank is 5,000 to 100,
000 mg / l, preferably 30,000-60,000
0 mg / l, anaerobic treatment temperature 30-38 ° C or 45-6
Anaerobic treatment can be performed under the condition of 0 ° C. Since the present invention includes a heat treatment step, if the anaerobic treatment tank is sufficiently kept warm, the temperature of 45 to 60 ° C can be maintained without heating.

In the present invention, a part of the biological sludge is extracted from the treatment system in such anaerobic treatment, and this extracted sludge is heat-treated. When removing the biological sludge, the concentrated solution concentrated by the concentrator may be withdrawn, or the mixed solution may be withdrawn from the anaerobic treatment tank, but the heat treatment can be performed in a treatment tank with a small capacity. In addition, the former is preferable because it requires less heating energy. As a concentrator,
Known devices such as a precipitation device, a centrifugal separator, and a membrane separator can be used. Among these, the centrifugal separator and the membrane separator are preferable because the sludge can be highly concentrated and the amount of the sludge to be heat-treated can be easily adjusted to a predetermined amount of 2 times or more and 1/15 or less of the above.

The amount of drawn-out sludge to be heat-treated is at least twice as much as the sludge in the organic effluent introduced into the anaerobic treatment tank (hereinafter sometimes referred to as input sludge), preferably 2.5 times.
To 4 times the amount (solid content weight) and 1/15 or less of the total amount of sludge in the anaerobic treatment tank per day, preferably 1
/ 15 to 1/50 (solid content weight). The amount of drawn sludge to be heat-treated is the amount per day. By setting the amount of sludge to be heat-treated at least twice as much as the amount of input sludge, it is possible to increase the volume reduction of sludge in the entire treatment system. Also, by setting the amount of sludge held in the anaerobic treatment tank to 1/15 or less, the anaerobic treatment can be performed in a state where the sludge activity of the entire anaerobic treatment tank is maintained high.

The heat treatment condition is that the treatment temperature is 60 to 10
It is lower than 0 ° C, preferably 90 to 95 ° C. The treatment time is related to the treatment temperature, and is 30 minutes or longer when the treatment temperature is 90 ° C or higher and lower than 100 ° C, preferably 40 to 60 minutes, and 30 minutes or longer when the treatment temperature is 60 ° C or higher and lower than 90 ° C.
It is preferably 60 to 120 minutes. The heat treatment can be performed continuously or batchwise.
When the process is carried out continuously, the above processing time is the residence time.

It is difficult to reduce the volume of living organisms in sludge because they are not assimilated by other organisms. However, when they die by heat treatment, they are assimilated by other living organisms and can be reduced in volume. Becomes In this case, it is not necessary to completely solubilize the sludge by heat treatment. The sludge is reformed by the heat treatment as described above, and by further anaerobically treating the reformed sludge, digestion is promoted and the solid content of the sludge is decomposed,
Liquefaction, which reduces excess sludge volume. The anaerobic treatment of the heat-treated sludge can be carried out by returning (circulating) it to the anaerobic treatment tank of the treatment system from which the sludge has been extracted, or by introducing it into the anaerobic treatment tank of another treatment system.

The heat treatment temperature in the present invention is 60 to 10
The temperature is lower than 0 ° C, which is lower than the heating temperature for conventional solubilization treatment, but even when heat treatment is performed at such a relatively low temperature, organisms die, so the digestive action in the anaerobic treatment tank is promoted. To be done. For example, when a sludge having the same amount as the input sludge is heat-treated, the digestibility is about 70%. Although the digestibility of 70% is smaller than that when the solubilization treatment is performed at a temperature of 100 ° C. or higher, in the method of the present invention, the amount of sludge to be heat-treated is increased and is twice or more the input sludge amount. Digestibility of almost 100% can be achieved. Here, the digestibility is the rate at which the organic solid content of the input sludge is decomposed by anaerobic treatment (digestion), and the digestibility is 1
00% means that excess sludge is not generated from the anaerobic treatment system.

In the method of the present invention, since the heat treatment is carried out at a low temperature of 60 to less than 100 ° C., it is possible to suppress the formation of the biodegradable component. Moreover, it is possible to use a device having lower heat resistance and pressure resistance than the conventional one, and it is possible to reduce energy consumption and suppress odor.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. 1 and 2 are system diagrams showing an anaerobic treatment apparatus according to different embodiments, FIG. 1 is an example of heat treatment of concentrated sludge in which an anaerobic treatment liquid is concentrated by a concentrator, and FIG. 2 is an anaerobic treatment tank. The example which heat-processes the mixed liquid of is shown.

In FIG. 1, 1 is an anaerobic treatment tank, 2 is a membrane separator, and 3 is a heat treatment tank. In the treatment method by the treatment apparatus of FIG. 1, the organic sludge or sludge is introduced into the anaerobic treatment tank 1 from the liquid passage 4 to be treated, and the returned sludge and organisms in the anaerobic treatment tank 1 are returned through the return sludge passage 5. Anaerobic treatment is performed while mixing with sludge and gently stirring with a stirrer 6. As a result, the organic matter in the liquid to be treated is decomposed by the acid-producing bacterium and the methane-fermenting bacterium. The digestion gas containing the produced methane gas is discharged from the exhaust gas passage 7.

A part of the mixed solution in the anaerobic treatment tank 1 is connected to the communication path 1.
It is taken out of the apparatus 1, is pressurized by the pump 12, is guided to the membrane separation device 2, and is separated by the separation membrane 13. Thereby, the permeated liquid 14 and the concentrated liquid 15 are separated. The permeated liquid 14 is discharged as a processing liquid from the processing liquid passage 16 to the outside of the system. Part of the concentrated liquid 15 is taken out from the concentrated liquid take-out path 17 and introduced into the heat treatment tank 3, and part or all of the remaining part is returned from the return sludge path 5 to the anaerobic treatment tank 1. When excess sludge is generated, it is discharged from the excess sludge discharge path 18 to the outside of the system.

In the heat treatment tank 3, the concentrated liquid 15 is fed to the heater 2
It is heated by 1 and heat-treated while being gently stirred by the stirrer 22. This reforms the sludge. The heat-treated sludge is returned from the heat-treated sludge passage 23 to the anaerobic treatment tank 1,
Treat anaerobically. As a result, the solid content modified by the heat treatment is digested, and the excess sludge generated from the treatment system is reduced in volume.

In the treatment method using the apparatus shown in FIG. 2, a part of the mixed liquid in the anaerobic treatment tank 1 is drawn as drawn sludge from the sludge drawing passage 24, and the drawn sludge is introduced into the heat treatment tank 3 for heat treatment. . Other operations are the same as those in FIG.

Although the membrane separator 2 is used as the concentrating device in FIGS. 1 and 2, other concentrating devices such as a precipitation device and a centrifuge can be used. Further, in FIG. 1, the returning of the sludge from the returning sludge passage 5 can be omitted.

[0022]

【Example】

Comparative Example 1 A 6 liter anaerobic treatment tank was heated to 37 ° C., sewage anaerobic digestion sludge was concentrated to 20,000 mg / l, and 3 liter was added. Next, 100 ml of a mixed sludge of surplus sludge of sewage and surplus sludge of first sludge: first sludge = 1: 1 was added every day, and anaerobic treatment was performed. This MLSS concentration is 12,000 to 17,
It was 000 mg / l. In addition, Saturday was added on Friday and Sunday was added on Monday. Also, although the anaerobic treatment liquid corresponding to the amount of inflow water was discharged, the sludge was not returned from the concentrator. After one month, the MLSS concentration in the anaerobic treatment tank was 8,200 mg / l. The processing conditions and results are summarized in Table 1.

Comparative Example 2 Following Comparative Example 1, the mixed solution in the anaerobic treatment tank was treated with 200 times a day.
After withdrawing ml, the mixture was heat-treated in a heat treatment tank at 95 ° C. for 30 minutes and then returned to the anaerobic treatment tank. No sludge was returned from the concentrator. When this operation was continued for one month, the MLSS concentration in the anaerobic treatment tank was 5,500 mg / l.
Dropped and stabilized. The processing conditions and results are summarized in Table 1.

Example 1 Following Comparative Example 2, 200 ml of the anaerobic treatment liquid was centrifuged per day, 100 ml of the supernatant was discarded, and the remaining whole amount was returned to the anaerobic treatment tank. Other operations were performed in the same manner as in Comparative Example 2. When this operation was continued for 6 months, M in the anaerobic treatment tank
The LSS concentration was stable at 28,000 to 32,000 mg / l, and discharge of sludge out of the system became unnecessary. The processing conditions and results are summarized in Table 1.

Example 2 The amount of the mixed solution to be heat treated was 200 ml / day to 60 ml.
Was carried out in the same manner as in Example 1 except that the date was changed. The MLSS concentration in the anaerobic treatment tank is 48,000 to 52,000.
It became 0 mg / l. It remained stable for 3 months in this state. Moreover, it was not necessary to discharge sludge out of the system. The processing conditions and results are summarized in Table 1.

Comparative Example 3 The amount of the mixed solution to be heat-treated is 200 ml / day to 40 ml.
Was carried out in the same manner as in Example 1 except that the date was changed. As a result, the MLSS concentration in the anaerobic treatment tank gradually increased,
It did not reach a certain value. The processing conditions and results are summarized in Table 1.

Comparative Example 4 In Comparative Example 3, the MLSS concentration in the anaerobic treatment tank was 5
The sludge was returned to the anaerobic treatment tank from the centrifugal separator so as to have a concentration of 10,000 mg / l. As a result, 0.2 per day
g of excess sludge (dry weight) was generated. The processing conditions and results are summarized in Table 1.

Comparative Example 5 The amount of the mixed solution to be heat treated was changed to 300 ml / day, and the sludge was returned from the centrifugal separator so that the MLSS concentration in the anaerobic treatment tank became 10,000 mg / l. Others were the same as in Comparative Example 3. As a result, 0.3 per day
g of excess sludge (dry weight) was generated. The processing conditions and results are summarized in Table 1.

[0029]

[Table 1]

From the results shown in Table 1, even when the heating temperature is a low temperature of less than 100 ° C., the amount of heat-treated sludge with respect to the amount of sludge input is 2 or more, and the amount of heat-treated sludge with respect to all the sludge retained in the anaerobic treatment tank is It can be seen that a digestibility of 100% can be achieved when the ratio is 1/15 or less. On the other hand, when the amount of sludge to be heat treated is out of the above range, the digestibility is low.

[0031]

EFFECTS OF THE INVENTION In the method for treating organic waste liquid of the present invention, heat treatment of sludge is performed at a low temperature and under specific conditions, so that the quality of treated water such as an increase in chromaticity and COD is deteriorated. It is possible to suppress and reduce the volume of sludge. Also,
Since the heat treatment is performed at a low temperature, the energy consumption can be reduced, and it is not necessary to use a device having high heat resistance and pressure resistance, and thus the treatment can be performed at low cost.

[Brief description of the drawings]

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

FIG. 2 is a system diagram showing an anaerobic treatment apparatus according to another embodiment of the present invention.

[Explanation of symbols]

 1 Anaerobic treatment tank 2 Membrane separation device 3 Heat treatment tank 4 Liquid passage for treatment 5 Return sludge passage 6, 22 Stirrer 7 Exhaust gas passage 11 Communication passage 12 Pump 13 Separation membrane 14 Permeate 15 Concentrated liquid 16 Treated liquid passage 17 Concentrated liquid Extraction path 18 Excess sludge extraction path 21 Heater 23 Heat treatment sludge path 24 Sludge extraction path

Claims (1)

[Claims] 1. An anaerobic treatment step of anaerobically treating organic effluent in the presence of biological sludge containing anaerobic microorganisms in an anaerobic treatment tank, and sludge in the organic effluent introduced into the anaerobic treatment tank per day. Mixture or concentration in the anaerobic treatment tank which is more than twice the amount (solid content weight) and is equivalent to 1/15 or less (solid content weight) of the total amount of sludge in the anaerobic treatment tank per day. The liquid is drawn out, and the drawn sludge is kept at a temperature below 60 to 100 ° C for 3
A method of anaerobic treatment of organic waste liquid, comprising a heat treatment step of carrying out a heat treatment for 0 minutes or more and then transferring it to an anaerobic treatment tank.