JPH091178A - Anaerobic treatment of high-concentration organic waste liquid - Google Patents

Abstract

PURPOSE: To make efficient treatment by lessening the amt. of an alkali for neutralization and shortening the HRT in an acid forming vessel at the time of subjecting a high-concn. org. waste liquid to an anaerobic treatment by an upflow anaerobic sludge blanket (UASB) method. CONSTITUTION: The org. waste liquid having a CODcr concn. of >=8000mg/l from a liquid-to-be-treated introducing path 3 is introduced into an acid forming vessel 1 where the waste liquid is mixed with the return liquid returned from a return path 5 and the alkali supplied from an alkali supplying path 6 and is subjected to an acid forming treatment. At this time, the return liquid flow rate is so adjusted that the volumetric ratio of the liquid to be treated/the return liquid exceeds 3. The introducing amt. of the liquid to be treated is so adjusted that the HRT (the volume of the acid forming vessel/the flow rate of the liquid to be treated) of the liquid to be treated in the acid forming vessel 1 attains <=4 hours. The acid forming liquid is introduced into the lower part of a methane fermentation vessel 2 and is passed through a sludge blanket 12 in upward current flow, by which the liquid is subjected to methane fermentation. The treated liquid is partly returned as the return liquid into the acid forming vessel 1 and the balance thereof is discharged as the treated liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for anaerobic treatment of high-concentration organic waste liquid by anaerobic treatment of the high-concentration organic waste liquid by an upflow anaerobic sludge blanket (UASB) method.

[0002]

2. Description of the Related Art As a method for anaerobic treatment of organic waste liquid, solid organic matter and soluble organic matter are put into a digestion tank and retained for a long time for digestion. Instead of the conventional anaerobic digestion method, only soluble organic matter is dissolved. A high-load anaerobic treatment method for treating anaerobically with a high load and a high flow rate is performed. This high-load anaerobic treatment method separates solid organic matter with a slow digestion rate and treats it separately,
This is a method in which only a soluble organic substance having a high digestion rate is treated at high speed with a high load by an anaerobic treatment, and the treatment can be efficiently performed using a small apparatus.

A typical example of such a high-load anaerobic treatment method is an upflow anaerobic sludge blanket (UA).
SB) method. In the UASB method, the acid generation step and the methane generation step are usually performed in separate treatment tanks, and the acid generation liquid is passed through a UASB-type methane fermentation tank having a sludge blanket made of granulated sludge at high speed in an upward flow. Liquid is anaerobically treated. When the treatment is carried out in a two-phase system in which the acid production step and the methane production step are separated into two stages in this way, a large amount of organic acid-producing bacteria in the UASB-type methane fermentation tank is prevented from occurring. The bulking phenomenon that deteriorates the settling property of the granule sludge in the above step is prevented, which enables high-load and highly stable treatment.

When the anaerobic treatment is carried out by the two-phase method, the pH of the solution in the acid producing tank is lowered because an organic acid is produced in the acid producing step, which inhibits the activity of the acid producing bacterium to produce the acid. It may slow down. For this reason, an operation of adding an alkali to the water in the acid-producing step to maintain the activity of the acid-producing bacterium at a high level is performed, but a large amount of alkali is required, which causes a high cost.

As a method of reducing the amount of alkali to be added, Japanese Patent Publication No. 3-7439 discloses that an acid generating solution is added in an amount of 0.5 to 20 times the amount of the organic waste liquid to be treated. The method of returning to the previous stage is described. However, the above publication does not describe returning the treatment liquid of the methane production step to the acid production step in the two-phase UASB method.

Also, Wat. Res. Vol.28, No.2, pp.475-482
(1994), the amount of organic waste liquid to be treated was 0.
A two-phase UASB method is described in which 5 to 3 times the amount of the treatment liquid in the methane production process is returned to the acid production tank. However, with this method, the amount of returned products is small, so the effect of reducing alkali is not so great.

By the way, in the above-mentioned conventional method, in the anaerobic treatment method for returning the treatment liquid, the HRT of the organic waste liquid in the acid generation tank (the capacity of the acid generation tank is adjusted to the organic waste liquid [return liquid before mixing) Treatment liquid] A value obtained by dividing by a flow rate, which may be referred to as a drainage-based HRT in the following), has not been reported as an appropriate value. On the other hand, the HRT in the acid generation tank when the treatment liquid is not returned is determined by the COD _Cr concentration in the organic waste liquid, for example, the COD _Cr concentration is 3,000.
HRT 4 hours in the case of 0 to 4,000 mg / l, HRT 12 hours in the case of approximately 10,000 mg / l, HRT 24 hours in the case of approximately 20,000 mg / l as a guideline (liquid temperature 30 to 40 ° C) It has been decided. The reason why the HRT becomes longer as the COD _Cr concentration of the organic waste liquid becomes higher is that the organic acid production rate and the growth rate of the acid-producing bacterium are inhibited by the pH decrease accompanying the increase of the organic acid concentration in the acid production tank. Is. As described above, in the conventional anaerobic treatment method, the HRT in the acid production tank is determined by the COD _Cr concentration in the effluent, and the HRT suitable for the treatment method is determined.
Has not been examined.

[0008]

DISCLOSURE OF THE INVENTION An object of the present invention is to reduce the amount of alkali added for neutralization, to reduce the capacity of the acid generation tank, and to reduce the HRT in the acid generation tank. It is an object of the present invention to propose an anaerobic treatment method for high-concentration organic wastewater which can be treated efficiently by shortening the temperature.

[0009]

According to the present invention, an organic effluent is introduced into an acid-producing tank and brought into contact with an acid-producing bacterium under anaerobic conditions to produce an acid. Introduced into a countercurrent anaerobic sludge blanket-type methane fermenter, a sludge blanket consisting of granule sludge containing methanogens is passed anaerobically under upward flow at an increasing linear velocity within the range where granule sludge does not flow out. In the anaerobic treatment method including a methane production step for producing methane to produce methane and a return step for returning a part of the treated solution of the methane production step to the acid production step as a return solution, the COD _Cr concentration of the organic waste liquid is 800
0 mg / l or more, the ratio of the amount of the returned liquid to the amount of the organic waste liquid introduced into the acid generation tank exceeds 3, and the HRT of the organic waste liquid in the acid generation tank is 4 hours or less. An anaerobic treatment method for high-concentration organic drainage, which is characterized in that

The organic waste liquid to be treated as the liquid to be treated in the present invention is a soluble organic substance in the form of COD _Cr of 8,000.
0 mg / l or more, preferably 8,000 to 40,000
It is a waste liquid containing mg / l, and may contain some solid organic matter. When a large amount of solid content is contained, solid organic matter is removed in advance by solid-liquid separation, and the solid organic matter is subjected to treatment.

In the acid production step of the present invention, the organic waste liquid is introduced into the acid production tank, and a part of the treated liquid in the methane production step is introduced as a return liquid to generate acid in the tank under anaerobic conditions. It is mixed with bacteria and brought into contact with it to decompose organic substances and generate acids. At this time, the ratio of the organic effluent introduced into the acid production tank and the returned liquid exceeds 3 in the volume ratio of the returned liquid / organic effluent (treatment liquid) (hereinafter sometimes referred to as the return ratio), The amount of the organic drainage liquid or the return liquid introduced is preferably adjusted so as to be 3 to 20 for the treatment. By treating under a condition that the return ratio exceeds 3, it is possible to greatly reduce the amount of alkali used for neutralization, and to shorten the drainage-based HRT as described later for efficient treatment. It can be carried out.

In the method of the present invention, the HRT of the organic waste liquid in the acid generation tank (HRT based on the waste liquid) is 4 hours or less,
It is preferably 2.5 to 4 hours. In the conventional method, when returning the return fluid to the acid generating tank, due to the use of acid production tank of equal or greater volume as compared with the case of not returning, the drainage base HRT's drainage COD _Cr It became longer as the concentration increased. On the other hand, in the present invention, as described above, the drainage-based HRT is shortened for processing. Since the HRT becomes short, the capacity of the acid production tank can be reduced.

The method of the present invention does not reduce the acid production rate by the above-described shortening of the drainage-based HRT. It is presumed that this is due to the following reasons. (1) Since the returned solution contains almost the same amount of organic acid-producing bacteria as the solution in the acid-producing tank, the concentration of acid-producing bacteria in the acid-producing tank is almost reduced even if the return ratio is increased. do not do. (2) Since the return ratio is large, the dilution ratio of the acid concentration in the acid generation tank increases and the pH rises, and the inhibition of acid-producing bacteria is reduced, whereby the activity of acid-producing bacteria is maintained high.

The acid production step is carried out by adding C to the mixed solution in the acid production tank.
The OD _Cr concentration is 2,000 mg / l or less, preferably 1,
It is preferable to carry out under the condition of 500 to 2,000 mg / l. When the acid generation treatment is performed under such conditions, the effluent-based HRT can no longer depend on the COD _Cr concentration and can be efficiently treated by the HRT for 4 hours or less. Further, it is desirable that the pH of the acid generation step is 5 to 7, preferably 5.8 to 6.2. The pH can be adjusted using an alkali such as sodium hydroxide.

The acid-producing solution that has been subjected to the acid-producing step as described above is introduced into a UASB-type methane fermentation tank in which a sludge blanket composed of granulated sludge containing methanogens is formed, and passed through in an upward flow. Perform the methane production process. It is possible to increase the amount of liquid to be returned as the flow rate of the acid generating liquid, that is, the higher the linear velocity of rising, is, but if it becomes too fast, the granule sludge will flow out along with the upward flow, The upper limit is limited to the speed at which granule sludge does not flow out. Usually, the upper limit of the rising linear velocity is about 2 m / hr. Therefore, the rising linear velocity of the UASB type methane fermentation tank is 0.5 to 2 m / hr, preferably 1 to 1.5 m / hr.
Is appropriate. Further, HRT is suitable for 3 to 48 hours, preferably 4 to 24 hours.

The treated liquid which has been subjected to the methane production process in this way is an organic waste liquid which is communicated to the acid production process such as an acid production tank or an acid production tank so that a part of the treated liquid is used as a return liquid and the return ratio is the same. Return to the introduction route. The rest is discharged as a processing liquid out of the system.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a system diagram showing the anaerobic treatment apparatus of the embodiment. In the figure, 1 is an acid production tank and 2 is a UASB type methane fermentation tank. The acid production tank 1 is configured to introduce an effluent containing a soluble organic substance from the liquid to be treated introduction path 3 and maintain it in an anaerobic state to perform organic acid fermentation. In the acid production tank 1, in addition to the liquid to be treated introduction passage 3, a communication passage 4 for communicating with the methane fermentation tank 2, a return liquid passage 5 and an alkali supply passage 6
Is connected. A pump 7 is provided in the communication path 4. Further, the acid generation tank 1 is provided with a circulation path 9 having a pump 8 for stirring.

In the methane fermentation tank 2, a sludge blanket 12 is formed by granule sludge 11 inside,
The acid generating liquid inflow portion 13 is provided in the lower portion, and the gas solid-liquid separation plate 14 and the processing liquid overflow portion 15 are provided in the upper portion.
The connecting passage 4 is connected to the acid generating liquid inflow portion 13, and the processing liquid discharge passage 16 is connected to the processing liquid overflow portion 15. The return liquid passage 5 is branched from the treatment liquid discharge passage 16. A gas chamber 18 is formed in the upper part of the methane fermentation tank 2, and a gas discharge path 19 is connected to the top.

Anaerobic treatment method using the above anaerobic treatment apparatus
The method is COD from the liquid introduction path 3 to be treated. _CrConcentration is 8000m
Introduce an organic waste liquid of g / l or more into the acid generator tank 1 and return it
Return liquid returned from line 5 and alkali supply line 6
It is mixed with the alkali to be supplied, and pumped through circulation circuit 9.
To maintain the anaerobic state while stirring, and to the action of acid-producing bacteria.
Convert more soluble organics to organic acids. Young in the liquid to be treated
If it contains dried SS components, it is anaerobically soluble here.
Be transformed into

When performing the acid generation treatment, the flow rate of the returning liquid is adjusted so that the returning ratio becomes the above value. Also, drainage-based H
The amount of the liquid to be treated introduced is adjusted or the capacity of the acid generation tank 1 is reduced so that the RT becomes the time. When the return ratio is increased as in the present invention, the alkali component contained in the return liquid (methane treatment process liquid) is supplied to the acid generation tank 1 in such a large amount, so that the amount of alkali added can be reduced, and As the pH rises and a large amount of acid-producing bacteria are returned, the acid-producing treatment can be efficiently performed even if the HRT is shortened.

The acid-generating liquid that has been subjected to the acid-generating treatment in the acid-generating tank 1 is
It is introduced into the lower part of the methane fermentation tank 2 from the connecting path 4 by the pump 7 through the acid generation liquid inflow portion 13, and is passed through the sludge blanket 12 in an upward flow as a methane generation step. At this time, the acid-generating liquid contacts the granulated sludge 11 under anaerobic condition, and the organic acid is decomposed anaerobically by the action of the anaerobic microorganisms contained in the granulated sludge 11, in particular, methane-producing methane. Convert to carbon dioxide. The methane-fermented reaction liquid is separated into gas, liquid and solid by the gas solid-liquid separation plate 14, and the separated liquid overflows from the processing liquid overflow section 15 as a processing liquid. The separated solids settle as sludge on the sludge blanket 12, and the gas rises to the gas chamber 18. If the rising linear velocity of the in-tank liquid rising in the methane fermentation tank 2 is too high, the granulated sludge 11 is not completely separated and flows into the treatment liquid, so the rising linear velocity is within the above range.

A part of the treatment liquid is returned as a return liquid from the return liquid passage 5 to the acid production tank 1, and the rest is discharged from the treatment liquid discharge passage 16. Product gas such as methane gas generated in the methane fermentation tank 2 is collected in the gas chamber 18 and discharged from the gas discharge passage 19.

Example 1 The anaerobic treatment apparatus shown in FIG. 1 was used to perform anaerobic treatment under the following conditions using synthetic waste water containing glucose as a main component and having a COD _Cr concentration of 20,000 mg / l as a liquid to be treated. Liquid to be treated flow rate: 0.6 liter / hr Acid production tank capacity: 1.5 liter Effluent-based HRT: 2.5 hours Return ratio: 9 Acid production tank liquid pH: 6.2 (4% NaOH aqueous solution) Acid production treatment temperature: 35 ° C Methane fermentation tank capacity: 25 liter Methane fermentation treatment temperature: 35 ° C Anaerobic treatment time: 20 days after completion of start-up

As a result of continuous operation for 20 days, the average sugar concentration in the liquid in the acid production tank was 100 mg / l, and it could be concluded that the acid production reaction proceeded sufficiently from the viewpoint of preventing bulking of the methane fermentation tank. As shown in Table 1, the amount of alkali used at this time was 64 g-NaOH / k per load COD _Cr.
It was g-COD. The results are summarized in Table 1.

Comparative Examples 1 and 2 Processing was performed in the same manner as in Example 1 except that the return ratio was set to 3 (Comparative Example 1). As a result, the sugar concentration in the acid production tank was 500.
As shown in Table 1, the concentration of granule sludge in the methane fermentation tank after 20 days of operation decreased from 56,000 mg / l at the start of operation to 32,000 mg / l, and sludge was exceeded. An anaerobic bulking phenomenon, in which part of the water was released into the processing solution, caused normal processing to become impossible.

Therefore, by replacing the granulated sludge with a new one, from the viewpoint of preventing bulking, the acid production tank capacity necessary to keep the sugar concentration in the acid production tank liquid at 100 mg / l was experimentally determined. However (Comparative Example 2), return ratio 3
The acid generator tank capacity required under the conditions was 4.5 liter, which was three times as large as that of Example 1. Table 1 shows the results.

[0027]

[Table 1]

From the results shown in Table 1, it can be seen that the amount of alkali used in Example 1 is 26% smaller than that in Comparative Example 2, and the amount of alkali used can be further reduced by increasing the return ratio.

[0029]

As described above, the present invention is a two-phase UAS.
In the anaerobic treatment method by the B method, the return ratio exceeds 3, and the drain-based HRT is 4 hours or less, C
Since high-concentration organic wastewater with an OD _Cr concentration of 8,000 mg / l or more is treated, the amount of alkali for neutralization is reduced, and a small acid generation tank is used to efficiently and anaerobically Can be sexually processed.

[Brief description of the drawings]

FIG. 1 is a system diagram of an anaerobic treatment apparatus according to an embodiment.

[Explanation of symbols]

 1 acid production tank 2 methane fermentation tank 3 treated liquid introduction passage 4 connecting passage 5 return liquid passage 6 alkali supply passage 7, 8 pump 9 circulation passage 11 granule sludge 12 sludge blanket 13 acid production liquid inlet 14 gas solid-liquid separation Plate 15 Processing liquid overflow 16 Processing liquid discharge path 18 Gas chamber 19 Gas discharge path

Claims (1)

[Claims] 1. An acid generation step of introducing an organic waste liquid into an acid generation tank and contacting it with an acid-producing bacterium under anaerobic conditions to generate an acid, and an acid-generating solution being an upflow anaerobic sludge blanket type methane. Introduced into a fermenter, sludge blanket consisting of granulated sludge containing methanogenic bacteria is passed anaerobically in an upward flow at an increasing linear velocity within the range where granulated sludge does not flow out to produce methane. In an anaerobic treatment method including a process and a return process in which a part of the treatment liquid of the methane production process is returned to the acid production process as a return liquid, the COD _Cr concentration of the organic waste liquid is 8,000 mg / l or more. The ratio of the amount of the returned liquid to the amount of the organic waste liquid introduced into the acid generation tank exceeds 3, and the HRT of the organic waste liquid in the acid generation tank is 4 hours or less. Anaerobic concentration organic waste Processing method.