JPH08257588A - Anaerobic treatment of organic wastewater - Google Patents

Abstract

(57) [Abstract] [Purpose] When the organic effluent is separated into an acid production step and a methane production step and subjected to anaerobic treatment, the amount of alkali used for pH adjustment is reduced, and by simple operation, In addition, organic substances are stably removed at low cost. [Structure] The liquid to be treated 6 is introduced into the acid production tank 1 to generate an acid, then introduced into the decarbonation tank 2, aerated with air to decarbonate, and then introduced into the pH adjustment tank 3. After the alkali 22 is added to adjust the pH, methane is produced in the methane production tank 4. At this time, the flow rate of the liquid to be treated 6 is measured by the flow meter 15, and the blower 12 is controlled according to the value to prevent excessive aeration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anaerobic treatment method for treating an organic effluent by separating it into an acid producing step and a methane producing step, and more specifically, an anaerobic method suitable for treatment when the treatment load varies. The present invention relates to a sex processing method.

[0002]

2. Description of the Related Art As a method for treating organic waste liquid, there is an anaerobic treatment method for treating in an acid producing step and a methane producing step. Recently, the anaerobic treatment technology is significantly different from the conventional anaerobic digestion of human waste and sludge, and is progressing toward high load and high efficiency. In addition, the treatment system is being converted from the conventional one-phase system (mixed system of acid production reaction and methane production reaction) to a two-phase system in which the acid production process and the methane production process are separated in order to enable stable treatment. .

However, in such a two-phase process, the amount of alkali used for adjusting the pH of the reaction tank increases. When operating with a low load set in the conventional one-phase system, organic acids such as acetic acid, propionic acid, and lactic acid generated in the acid formation reaction are immediately decomposed by the methanation reaction, so in normal operation The organic acid does not remain in the reaction tank, and therefore it is not necessary to neutralize the liquid in the reaction tank.

However, when the methane production process is operated under a high load in the two-phase system, the concentration of organic acid in the liquid flowing into the methane production process is high. Contact with generated sludge. Since the optimum pH of the methanogenic sludge is 6 to 8, even an organic acid that is easily decomposed into the methanogenic sludge will result in a decrease in the activity of the methanogenic sludge at a low pH.

Therefore, normally, an alkali such as sodium hydroxide is injected to adjust the pH to around 6 immediately before flowing into the methane production tank, but the amount of alkali used is large and the treatment cost is increased.

In order to improve such points, a part of the treated liquid flowing out from the methane production process is returned to the acid production process, and the liquid inside the acid production tank is aerated with air to decarbonate it. An anaerobic treatment method for drainage has been proposed (JP-A-5-277486). However, in this method, when the processing load of the organic waste liquid is reduced or the load is stopped, the reducing substance concentration in the liquid in the tank of the acid generation tank is lowered,
It becomes relatively over-aerated and the dissolved oxygen concentration increases,
For this reason, the activity of acid-producing bacteria and methanogenic bacteria is reduced, and stable treatment tends to be impossible.

[0007]

DISCLOSURE OF THE INVENTION An object of the present invention is to reduce the amount of alkali used in a method of anaerobic treatment by returning the treatment liquid of the methane production process to the acid production process, and further, a simple operation. Therefore, it is to propose an anaerobic treatment method of organic waste liquid capable of stably removing organic matter at low cost.

[0008]

According to the present invention, an acid producing step of producing an acid by contacting an organic waste liquid with an acid producing bacterium, and aeration of the acid producing solution obtained in this acid producing step to decarboxylate Deoxidation step, a decarboxylation solution decarboxylated in this decarboxylation step is contacted with methanogenic bacteria to produce methane, and a part of the treatment liquid flowing out from this methanation step is an acid production step. In the method for anaerobic treatment of organic waste liquid, which includes a returning step of returning to the above step, the aeration amount in the decarboxylation step is adjusted according to the fluctuation of the processing load amount of the organic waste liquid or the fluctuation of the pH of the acid generation liquid. An anaerobic treatment method for an organic waste liquid, which is characterized in that

The organic effluent to be treated in the present invention may be any organic effluent containing an organic substance and capable of anaerobic treatment, such as CODcr 1000 to 30000 mg.
It is preferably about 1 / l, but higher or lower concentrations can be treated. Examples of such organic effluent include food factory effluent, paper pulp factory effluent and other industrial effluents, sewage, night soil, sludge, and effluents obtained by treating these.

In the anaerobic treatment method of the present invention, the acid production step and the methane production step are performed separately. In the acid production step, the organic waste liquid is introduced into the acid production tank and brought into contact with the acid producing bacteria to produce acid.

In the present invention, the acid-generating liquid obtained in the acid-generating step
Aerate and decarbonate. In this case, change the load of the organic drainage.
Aeration amount is adjusted according to the fluctuation of the pH of the acid generating solution
It Fluctuations in the treatment load are due to the organic emissions introduced into the acid production tank.
By detecting the flow rate of the liquid with a flow meter, or
It can be understood from the ON / OFF status of the pump. And
If the processing load decreases or becomes zero, change the aeration amount.
Reduce or stop aeration. In addition, the processing load increases
If added, restart aeration or increase the amount of aeration. Was
However, the upper limit of the amount of aeration gives a decarboxylation effect by aeration.
This is the upper limit, and is not necessarily proportional to the increase in processing load.
Yes. Specifically, depending on the fluctuation of the processing load, the acid generation liquid
1m³0 to 50m³Aerate air in the range of / hr
It 50m ³Decarburization beyond aeration even if it exceeds a / hr
Acid effect is small, but on the contrary, dissolved oxygen concentration or redox potential
Increase, leading to a decrease in the activity of acid-producing bacteria and methanogenic bacteria.
It is not preferable.

In the present invention, instead of adjusting the aeration amount according to the fluctuation of the processing load amount, the aeration amount can be adjusted according to the fluctuation of the pH of the acid generating solution. The fluctuation of the pH of the acid generating liquid can be grasped by the pH detection device, and when the pH approaches or becomes higher than a predetermined value, the aeration amount is reduced or stopped. When the pH becomes lower than the predetermined value, the aeration is restarted or the aeration amount is increased.

The adjustment of the aeration amount according to the fluctuation of the processing load amount and the adjustment of the aeration amount according to the fluctuation of the pH of the acid generating solution are substantially the same operations. That is, when the load is large, a large amount of organic acid is generated and the pH is lowered, and when the load is small, only a small amount of organic acid is generated.
The H drop is small. For this reason, if a large amount of aeration is performed when the load is large and the pH is lowered, decarboxylation occurs, so the amount of alkali used for neutralization is reduced. In this case, oxygen dissolved by aeration is removed by the reducing substance in the liquid. When the load is small and the pH does not drop, the reducing substance is also small, so the amount of aeration is reduced or stopped to prevent excessive aeration.

It is also possible to measure the dissolved oxygen concentration or the redox potential of the liquid to be decarboxylated and adjust the aeration amount according to the fluctuation of these values. It is not realistic because the equipment cost and maintenance cost are high.

Aeration can be carried out in an acid production tank,
Alternatively, a decarbonation tank may be provided separately from the acid generation tank, and the acid generation liquid may be partially introduced into the decarbonation tank. In the former case, the cost is most advantageous, and in the latter case, the influence of aeration on the activity of the acid-producing bacterium can be eliminated, whereby the acid-producing reaction can be carried out most stably.

By adjusting the amount of aeration and decarbonating as described above, over-aeration is prevented, whereby the activity of anaerobic microorganisms, acid-producing bacteria and methanogenic bacteria, is prevented from decreasing, and stable. It is possible to remove organic substances. Moreover, the amount of alkali used for pH adjustment can be reduced by decarboxylation. That is, the alkali for pH adjustment is
In addition to neutralizing the organic acid generated in the acid formation reaction, it is also consumed for neutralizing the carbonic acid dissolved in the liquid. Therefore, by removing carbonic acid by aeration, the amount of alkali for pH adjustment can be reduced. In this case, the aeration removes the carbonic acid brought in by returning the treatment liquid flowing out from the methane production process and the carbonic acid produced by the organic acid production reaction in the acid production tank, thereby reducing the consumption of alkali.

Exhaust gas containing odor is generated by performing aeration, but normally the acid generating tank is completely sealed structure and the generated odor gas is deodorized. Therefore, new aeration is required. However, there is no problem in terms of odor control. Also in the case of the decarbonation tank, the problem of odor does not occur by adopting a completely closed structure and performing the same deodorizing treatment.

The decarbonated solution after decarboxylation is introduced into a methane producing tank after undergoing a pH adjusting step and brought into contact with methanogenic bacteria to produce methane. The tank load of this methane production process is 5
It is preferred that the CODcr / m ³ d is about 15 kg and the residence time is 5 to 72 hours. In the present invention, the aeration amount is adjusted as described above to prevent overaeration, so that the activity of the methanogen is maintained high and the methanogenic reaction proceeds stably.

A part of the treatment liquid flowing out from the methane production process, that is, the anaerobic treatment liquid is returned to the acid production process. The anaerobic treatment liquid contains the alkaline component added in the pH adjusting step. By returning this, it becomes possible to prevent a decrease in pH in the acid production tank. The flow rate of the treatment liquid returned to the acid production step is appropriately 20 to 100% by volume of the amount of water of the liquid to be treated flowing into the acid production step. Naturally, the greater the return flow rate, the higher the effect of preventing pH decrease.
Also, by returning the anaerobic treatment liquid to the acid generation step,
Organic acid-producing bacteria that flow out into the treatment liquid are constantly supplied to the acid-producing step. By supplying this bacterium, the acid production reaction is stabilized, and it becomes possible to carry out the treatment corresponding to the water amount and load fluctuation.

[0020]

Embodiments of the present invention will be described below. FIG. 1 and FIG. 2 are flow charts showing anaerobic treatment methods of different embodiments, FIG. 1 is an example of adjusting the aeration amount according to the fluctuation of the treatment load amount, and FIG. An example is shown in which the aeration amount is adjusted according to the fluctuation. In FIG.
1 is an acid production tank, 2 is a decarbonation tank, 3 is a pH adjusting tank, 4 is U
It is an ASB type methane production tank.

In the treatment method according to the flow of FIG. 1, the liquid feed pump 5 is driven to introduce the liquid 6 to be treated into the acid-producing tank 1, and the mixture is mixed with the acid-producing bacteria in the tank while being stirred by the stirrer 7 to anaerobically The acid generation step of sexual treatment is performed. A part of the acid generation liquid 11 is introduced into the decarbonation tank 2, and air is sent from the blower 12 to the air diffuser 13 for aeration to perform decarbonation. The exhaust gas 14 is introduced into a deodorizing device (not shown) to deodorize.

At this time, the flow rate of the liquid to be treated 6 is measured by the flow meter 15
Detected and output this value to the controller 16. In accordance with this value, the control device 16 calculates an aeration air amount such that the dissolved oxygen concentration or the oxidation-reduction potential of the tank liquid in the decarbonation tank 2 does not rise, and outputs this signal to the blower 12 to diffuse air. The amount of air aerated from the device 13 is adjusted. That is, when the flow rate of the liquid 6 to be treated becomes smaller than the predetermined value or becomes zero, the aeration air amount is reduced or adjusted to zero. Further, when the introduction of the liquid to be treated 6 is restarted or the flow rate is increased, the aeration is restarted or the aeration air amount is increased. By decarbonating in this way, pH
The amount of alkali to be added in the adjusting tank 3 can be reduced, and even if the treatment load amount of the liquid to be treated 6 varies, the methane production process of the subsequent process can be stably performed. Further, since the acid generation step and the decarboxylation step are performed in separate tanks, aeration does not adversely affect the acid generation reaction, and the acid generation reaction is stably performed.

The decarbonated solution 21 is introduced into the pH adjusting tank 3 and an alkali (for example, sodium hydroxide) 22 is added to adjust the pH.
adjust. At this time, the pH of the solution in the pH adjusting tank 3 is adjusted to p
The H detection device 23 detects the pH value and outputs the pH value to the control device 16. The control device 16 calculates the amount of alkali to be added from this pH value, and the valve 2
A control signal is output to No. 4 to adjust the amount of alkali added. The pH adjustment range is preferably pH 6 to 8, which is considered suitable for the activity of methanogens. In this case, since the liquid to which the alkali 22 is added has been decarbonated, the addition amount of the alkali can be small.

The pH adjusting liquid 25 is UAS by the pump 26.
It is continuously supplied to the bottom of the B-type methane production tank 4 and methane-fermented by the methanogenic bacteria in the granulated sludge 27. A part of the treatment liquid 28 treated in the methane production process is returned to the acid production tank 1 as a return liquid 30 by the circulation pump 29, and the rest is discharged outside the system. The digestion gas (methane gas) 31 generated in the methane production process is sent to a gas storage tank (not shown). In this case, since the amount of aerated air in the decarbonation tank 2 is adjusted and the anaerobic property is maintained, the activity of the methanogen in the methanogenesis tank 4 is maintained high, and thereby stable methane production is performed. .

It is also possible to omit the decarbonation tank 2 and carry out the decarbonation treatment in the acid production tank 1. Even in this case, since the aeration air amount is adjusted according to the fluctuation of the processing load amount, a stable acid generation reaction is performed. Further, as the methane production tank 4, other than the UASB type can be adopted. Further, instead of measuring the flow rate of the liquid 6 to be treated, the aeration can be turned on / off according to ON / OFF of the liquid supply pump 5.

In the processing method according to the flow of FIG. 2, the pH of the solution in the acid production tank 1 is detected by the pH detection device 32,
The amount of air aerated from the air diffuser 13 is adjusted based on this pH value. Specifically, when the difference between the detected pH value and the pH setting value in the pH adjusting tank 3 is within 0.5, it is preferable to reduce or stop the aeration amount. When the pH difference is larger than 0.5, it is preferable to restart aeration or increase the aeration amount. Other operations are the same as in the case of FIG. Also, omitting the pH detection device 32 of the acid production tank 1,
Aeration can be adjusted only by the pH detection device 23 of the pH adjustment tank 3. That is, the aeration can be reduced or stopped when the indicated value of the pH detection device 23 exceeds the set value.

Example 1 According to the flow of FIG. 1, synthetic effluent containing glucose as a main component (CODcr concentration 4000 mg / l) was anaerobically treated. Acid production tank 1, decarbonation tank 2, pH adjustment tank 3, UAS
The capacity of B type methane production tank 4 is 7.2 lite.
r, 0.7 liter, 0.5 liter, and 25 liter.
The liquid in each tank was 35 ° C., the pH setting value in the pH adjusting tank 3 was 6, and the flow rate of the returning liquid 30 was 3 liter / hr.

To clarify the effect when the load is stopped, 1
The liquid to be treated 6 is repeatedly supplied and stopped every other day, and the liquid to be treated 6 is
The continuous operation was carried out for 60 days including the supply date and the stop date. The flow rate of the liquid to be treated 6 on the supply day was 3 liter / hr. The amount of aeration air in the decarbonation tank 2 was 3.5 liter-air / hr when the liquid feed pump 5 was operating, and the aeration was stopped when the liquid feed pump 5 was stopped. Solubility COD of treated liquid 28 (effluent of methane production tank) during the last 10 days of operation
The cr concentration and pH are shown in Table 1.

Example 2 According to the flow of FIG. 2, the same anaerobic treatment of synthetic wastewater as in Example 1 was performed for 60 days. The aeration air amount in the decarbonation tank 2 is 3.5 liter-air / hr when the pH of the liquid in the acid generation tank 1 is 5.5 or less, and 2 when the pH is 5.5 to 6.
Aeration was stopped when liter-air / hr and pH exceeded 6. The results are shown in Table 1.

Comparative Example 1 Anaerobic treatment was carried out in the same manner as in Example 1. However, even when the load was stopped, decarbonation aeration was continued at 3.5 liter-air / hr. The results are shown in Table 1.

[0031]

[Table 1] Note) Measurement result of effluent of methane production tank (treatment liquid) Average value during the last 10 days of operation

As is apparent from Table 1, Examples 1 and 2 had good treatment results. On the other hand, in Comparative Example 1, the soluble CODcr concentration of the treatment liquid was high, and the removal rate of organic pollutants was low. In order to clarify the cause of this, after the test was completed, the activity of the methanogenic bacteria (acetic acid-utilizing methane generation rate) of the granule sludge 27 in the methane production tank 4 was measured by a batch experiment. Moreover, the methanogenic activity of the comparative example was clearly lower than that of the example. It is presumed that this is because the liquid containing dissolved oxygen flows into the methanogen tank 4 due to over-aeration when the load is stopped, and the methanogen that is an absolute anaerobic bacterium is inhibited. It is considered that the organic acid remained in the treatment liquid 28 due to the decrease in the activity of the methanogen and the concentration of soluble CODcr increased.

[0033]

[Table 2] * 1 Generation rate of acetic acid-utilizing methane after the end of the test

In Comparative Example 1, since the organic acid concentration in the returned liquid 30 returned to the acid production tank 1 was high, as shown in Table 3, the alkali consumption was also higher than that in each Example. it was high. That is, it was shown that if the amount of aeration in the decarbonation tank 2 is not properly controlled, the alkali reduction, which is the purpose of decarbonation, may not be achieved. For reference, the anaerobic treatment was carried out in the same manner as in Example 1 except that no decarbonation aeration was performed in the decarbonation tank 2.
Alkali consumption (addition amount) is 173 kg-NaOH /
It was ton CODcr.

[0035]

[Table 3] Note) Average value during the last 10 days of operation

[0036]

As described above, according to the anaerobic treatment method of the present invention, fluctuations in the treatment load of organic waste liquid or p
Since the amount of aeration is adjusted according to the fluctuation of H to prevent over-aeration, it is possible to reduce the amount of alkali used for pH adjustment, and with a simple operation and at a low cost, stable organic substances can be obtained. Can be removed.

[Brief description of drawings]

FIG. 1 is a flowchart showing a processing method according to an embodiment.

FIG. 2 is a flowchart showing a processing method of another embodiment.

[Explanation of symbols]

 1 Acid generation tank 2 Decarbonation tank 3 pH adjustment tank 4 Methane generation tank 5 Feed pump 6 Liquid to be treated 7 Stirrer 11 Acid generation liquid 12 Blower 13 Diffuser 14 Exhaust gas 15 Flowmeter 16 Controller 21 Decarbonation liquid 22 Alkali 23, 32 pH detector 24 Valve 25 pH adjusting liquid 26 Pump 27 Granule sludge 28 Treatment liquid 29 Circulating pump 30 Return liquid 31 Digestion gas

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[Procedure amendment]

[Submission date] March 30, 1995

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Fig. 2]

FIG.

Claims (1)

[Claims] 1. An acid producing step of producing an acid by contacting an organic waste liquid with an acid producing bacterium, a decarboxylation step of aerating and decarbonating the acid producing solution obtained in this acid producing step, Includes a methane production step of contacting the decarboxylated liquid decarboxylated in the carbonation step with a methanogenic bacterium to produce methane, and a return step of returning a part of the treatment liquid flowing out from the methane production step to the acid production step In the method for anaerobic treatment of organic wastewater, the organic wastewater characterized by adjusting the aeration amount in the decarboxylation step according to the fluctuation of the processing load of the organic wastewater or the fluctuation of the pH of the acid generation liquid. Liquid anaerobic treatment method.