JP3275636B2 - Anaerobic treatment of high-concentration organic wastewater - 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 anaerobic treatment of high-concentration organic wastewater by anaerobic treatment of high-concentration organic wastewater by an upward anaerobic sludge blanket (UASB) method.

[0002]

2. Description of the Related Art As an anaerobic treatment method for organic effluents, solid organic matter and soluble organic matter are put into a digestion tank, and only the soluble organic matter is used instead of the conventional anaerobic digestion method in which digestion is carried out for a long period of time for digestion. A high-load anaerobic treatment method is used in which anaerobic treatment is performed at a high load and a high flow rate. This high-load anaerobic treatment method separates solid organic substances with slow digestion rate and treats them separately.
This is a method in which only a soluble organic substance having a fast digestion rate is processed at a high load by anaerobic processing at a high speed, and the processing can be efficiently performed using a small apparatus.

A typical example of such a high-load anaerobic treatment method is an upward 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 a high speed in an upward flow. Liquid is used for anaerobic treatment. When the treatment is performed in a two-phase system in which the acid generation step and the methane generation step are separated in two stages as described above, a large amount of organic acid-producing bacteria is prevented from being generated in the UASB-type methane fermentation tank. The bulking phenomenon, in which the sedimentation of the granular sludge is degraded, is prevented, thereby enabling a high-load and highly stable treatment.

[0004] When anaerobic treatment is performed in a two-phase system, the pH of the solution in the acid generation tank is lowered due to the generation of organic acids in the acid generation step, which inhibits the activity of acid-producing bacteria and causes acid generation. Speed may decrease. For this reason, an operation of adding an alkali to the water in the acid generation step to maintain the activity of the acid-producing bacteria at a high level is performed. However, a large amount of alkali is required, which causes an increase in cost.

As a method for reducing the amount of alkali to be added, Japanese Patent Publication No. 3-7439 discloses an acid generating tank in which an acid generating solution is used in an amount of 0.5 to 20 times the amount of an organic waste liquid to be treated. The method of returning the item is described in the preceding paragraph. However, the above-mentioned publication does not describe returning the treatment liquid in the methane generation step to the acid generation step in the two-phase UASB method.

[0006] Wat. Res. Vol. 28, No. 2, pp. 475-482
(1994) states that the amount of organic effluent to be treated is 0.1%.
A two-phase UASB method is described in which 5 to 3 times the amount of the processing liquid in the methane generation step is returned to the acid generation tank. However, in this method, the effect of reducing alkali is not so large because the amount of the returned material is small.

In the above conventional method, in the anaerobic treatment method in which the treatment liquid is returned, the HRT of the organic effluent in the acid generation tank (the capacity of the acid effluent tank is reduced to the amount of the organic effluent [the liquid before the return liquid is mixed]. [Treatment liquid] divided by the flow rate (hereinafter sometimes referred to as a drainage-based HRT)). On the other hand, HRT in the acid generating tank Failure to return the treatment liquid is determined by the COD _Cr concentration in the organic effluent, for example COD _Cr concentration 3,00
The standard (liquid temperature 30 to 40 ° C.) is 4 hours for HRT for 0 to 4,000 mg / l, 12 hours for HRT for about 10,000 mg / l, and 24 hours for HRT for about 20,000 mg / l. Has been determined. The reason why the HRT becomes longer as the COD _Cr concentration of the organic effluent becomes higher is that the rate of organic acid production and the growth rate of the acid-producing bacteria are hindered by the pH decrease accompanying the increase of the organic acid concentration in the acid production tank. It is. As described above, in the conventional anaerobic treatment method, the HRT in the acid generation tank is determined by the COD _Cr concentration in the wastewater, and an appropriate HRT according to the treatment method is used.
Has not been considered.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the amount of an alkali for neutralization, to reduce the capacity of an acid generation tank, and to reduce the amount of HRT in an acid generation tank. It is an object of the present invention to propose a method for anaerobic treatment of high-concentration organic effluent, which can efficiently treat effluent by shortening the concentration.

[0009]

According to the present invention, there is provided an acid generating step in which an organic waste liquid is introduced into an acid generating tank, and is contacted with an acid generating bacterium under anaerobic conditions to generate an acid. Introduced into the countercurrent anaerobic sludge blanket type methane fermentation tank, and passed through the sludge blanket consisting of granulated sludge containing methanogens in an upward flow under anaerobic conditions at an ascending linear velocity within a range where granule sludge did not flow out In the anaerobic treatment method including a methane generation step of producing methane by performing a methane generation step, and a return step of returning a part of the processing liquid in the methane generation step to the acid generation step as a return liquid, the COD _Cr concentration of the organic effluent is reduced. 800
0 mg / l or more, the ratio of the amount of the return 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 wastewater, characterized in that:

The organic effluent to be treated as the liquid to be treated in the present invention is 8000 in which the soluble organic matter is COD _Cr.
0 mg / l or more, preferably 8,000 to 40,000
It is a drainage containing mg / l and may contain some solid organic matter. When a large amount of solids is contained, solids and liquids from which solid organic substances have been removed in advance are subjected to treatment.

In the acid generation step of the present invention, the organic effluent is introduced into an acid generation tank, and a part of the treatment liquid in the methane generation step is introduced as a return liquid, whereby the acid generation in the tank is anaerobically performed. It is mixed with bacteria and brought into contact, decomposes organic matter and generates acid. At this time, the ratio of the organic waste liquid and the return liquid to be introduced into the acid generation tank exceeds 3 in the volume ratio of the return liquid / organic waste liquid (the liquid to be treated) (hereinafter, sometimes referred to as the return ratio), The treatment is carried out by adjusting the introduction amount of the organic drainage liquid or the return liquid so as to be preferably 3 to 20. By performing the treatment under the condition that the return ratio exceeds 3, it is possible to greatly reduce the amount of alkali used for neutralization, and to shorten the HRT of the drainage base for efficient treatment as described later. It can be carried out.

In the method of the present invention, the HRT of the organic effluent in the acid generating tank (the effluent-based HRT) is 4 hours or less.
Preferably, it is 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 was inevitably longer as the concentration increased. On the other hand, in the present invention, the drainage-based HRT is shortened as described above. Since the HRT is shortened, the capacity of the acid generation tank can be reduced.

In the method of the present invention, the acid generation rate does not decrease even if the drainage-based HRT is shortened as described above. This is presumed to be due to the following reason. (1) The concentration of the acid-generating bacteria in the acid-generating tank is almost reduced even if the return ratio is increased, because the returned liquid contains organic acid-generating bacteria of the same level as the liquid in the acid-generating tank. 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 increases, so that the inhibition of the acid-producing bacteria is reduced, whereby the activity of the acid-producing bacteria is maintained at a high level.

[0014] In the acid generation step, C in the mixed solution in the acid generation tank is used.
OD _Cr concentration of 2,000 mg / l or less, preferably 1,
It is preferable because the reaction is performed under the condition of 500 to 2,000 mg / l. When the acid generation treatment is performed under such conditions, the HRT based on the waste liquid no longer depends on the _CODCr concentration, and can be efficiently treated with the HRT for 4 hours or less. The pH in the acid generation step is desirably 5 to 7, preferably 5.8 to 6.2. The pH can be adjusted using an alkali such as sodium hydroxide.

The acid-generating solution having undergone the acid-generating step as described above is introduced into a UASB-type methane fermentation tank in which a sludge blanket made of granulated sludge containing methanogens is formed, and is passed upward in flow. Perform the methane generation step. The higher the flow rate of the acid-generating liquid, that is, the higher the ascending linear velocity, the larger the amount of liquid returned can be increased.However, if it is too high, the granular sludge flows out along with the upward flow, The upper limit is limited to the rate at which the granular sludge does not flow. Usually, the upper limit of the ascending 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. The HRT is suitably for 3 to 48 hours, preferably about 4 to 24 hours.

The treatment liquid subjected to the methane generation step as described above is used as an acid generation step such as an acid generation tank or an organic effluent connected to an acid generation tank such that a part of the processing liquid is returned as the return liquid. Return to the introduction route. The remaining part is discharged out of the system as a processing liquid.

[0017]

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

In the methane fermenter 2, a sludge blanket 12 is formed by granule sludge 11 inside,
An acid generation liquid inflow section 13 is provided at a lower portion, and a gas-solid separation plate 14 and a processing liquid overflow section 15 are provided at an upper portion.
The connection path 4 is connected to the acid generation liquid inflow section 13, and the processing liquid discharge path 16 is connected to the processing liquid overflow section 15. The return liquid path 5 branches off from the processing liquid discharge path 16. A gas chamber 18 is formed in the upper part of the methane fermenter 2, and a gas discharge path 19 is connected to the top.

Anaerobic treatment method using the above anaerobic treatment apparatus
The method is as follows: _CrThe concentration is 8000m
g / l or more of the organic effluent is introduced into the acid generating tank 1 and returned.
Liquid returned from the passage 5 and supplied from the alkali supply passage 6
Mixed with the alkali to be supplied and passed through the circulation path 9 by the pump 8.
To maintain the anaerobic state while stirring, to prevent the action of acid-producing bacteria.
Convert more soluble organics to organic acids. Young in the liquid to be treated
If dry SS component is contained, it is anaerobically soluble here
Be transformed into

When performing the acid generation treatment, the flow rate of the return liquid is adjusted so that the return ratio becomes the above value. In addition, H of drainage base
The introduction amount of the liquid to be treated is adjusted or the capacity of the acid generation tank 1 is reduced so that RT is equal to the above time. When the return ratio is increased as in the present invention, the amount of alkali contained in the return liquid (the liquid for the methane generation step) 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 is returned, the acid generation treatment can be performed efficiently even if the HRT is shortened.

The acid generating solution 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 communication line 4 by the pump 7 through the acid product liquid inflow part 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 comes into contact with the granular sludge 11 under anaerobic conditions, whereby the organic acid is anaerobically decomposed by the action of anaerobic microorganisms, particularly methane-producing bacteria, contained in the granular sludge 11 to produce methane and methane. Convert to carbon dioxide. The reaction liquid subjected to methane fermentation is separated into a gas, a liquid, and a solid in a gas-solid separation plate 14, and the separated liquid overflows from a processing liquid overflow section 15 as a processing liquid. The separated solids settle on the sludge blanket 12 as sludge, and the gas rises to the gas chamber 18. If the rising linear velocity of the liquid in the tank rising in the methane fermentation tank 2 is too high, the granular sludge 11 flows out into the processing liquid without being completely separated, so that the rising linear velocity is in the above range.

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

Example 1 An anaerobic treatment was carried out by the anaerobic treatment apparatus shown in FIG. 1 using a synthetic wastewater containing glucose as a main component and having a COD _Cr concentration of 20,000 mg / l as a liquid to be treated. Flow rate of liquid to be treated: 0.6 liter / hr Capacity of acid generation tank: 1.5 liter HRT based on drainage: 2.5 hours Return ratio: 9 pH of liquid in acid generation tank: 6.2 (4% NaOH aqueous solution) Acid generation treatment temperature: 35 ° C Methane fermentation tank capacity: 25 liter Methane fermentation treatment temperature: 35 ° C Anaerobic treatment time: 20 days after completion of startup

As a result of the continuous operation for 20 days, the average sugar concentration of the solution in the acid production tank was 100 mg / l, and it was concluded that the acid production reaction proceeded sufficiently from the viewpoint of preventing bulking of the methane fermentation vessel. At this time, as shown in Table 1, the amount of alkali used was 64 g-NaOH / k per loaded COD _Cr.
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
mg / l, and as shown in Table 1, the concentration of granular sludge in the methane fermentation tank 20 days after the operation decreased from 56,000 mg / l at the start of operation to 32,000 mg / l, Some of them caused an anaerobic bulking phenomenon to flow out into the processing solution, making normal processing impossible.

For this reason, the granule sludge was replaced with new one, and from the viewpoint of preventing bulking, the capacity of the acid generating tank required to maintain the sugar concentration of the liquid in the acid generating tank at 100 mg / l was experimentally determined. However, (Comparative Example 2), return ratio 3
Under the conditions (1) and (2), the required capacity of the acid generating tank was 4.5 liters, 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 of Comparative Example 2, and that the amount of alkali used can be further reduced by increasing the return ratio.

[0029]

As described above, the present invention provides a two-phase UAS
In the anaerobic treatment method by the B method, the CRT is used under the condition that the return ratio exceeds 3 and the HRT based on the drainage is 4 hours or less.
Since OD _Cr concentration was made to process the 8,000 mg / l or more high density organic drainage, reduce the amount of alkali for neutralization, yet efficiently using a small acid formation tank anaerobic Sex treatment can be performed.

[Brief description of the drawings]

FIG. 1 is a system diagram of an anaerobic treatment device of an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Acid production tank 2 Methane fermentation tank 3 Liquid to be treated introduction path 4 Communication path 5 Return liquid path 6 Alkaline supply path 7, 8 Pump 9 Circulation path 11 Granular sludge 12 Sludge blanket 13 Acid generation liquid inflow section 14 Gas solid-liquid separation Plate 15 Treatment liquid overflow 16 Treatment liquid discharge path 18 Gas chamber 19 Gas discharge path

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C02F 3/28

Claims (1)

(57) [Claims] 1. An acid generating step of introducing an organic wastewater into an acid generating tank and contacting it with an acid-producing bacterium under anaerobic conditions to generate an acid, and the acid-generating solution is subjected to an upward anaerobic sludge blanket type methane. Methanogenesis, which is introduced into a fermentation tank and flows upward in an anaerobic manner at an ascending linear velocity that does not allow granule sludge to flow through a sludge blanket consisting of granule sludge containing methanogens. An anaerobic treatment method comprising the step of: returning a part of the treatment liquid of the methane generation step as a return liquid to the acid generation step, wherein the COD _Cr concentration of the organic wastewater is 8,000 mg / l or more. Wherein the ratio of the amount of the return 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 of organic effluent Processing method.