JPH0568849A - Method and device for desulfurizing digestion gas - Google Patents

Abstract

PURPOSE:To desulfurize a digestion gas generated by anaerobic digestion at a low cost and with high efficiency, to obtain a treated gas having a high content of methane, to make hydrogen sulfide harmless and to discharge the harmless gas along with a processing soln. CONSTITUTION:The digestion gas generated in an anaerobic digester 1 is brought into contact with a liq. mixture in an aerobic oxidation device 2 or a processing soln. in an absorber 3 to absorb the hydrogen sulfide in the digeastion gas, the liq. absorbent is aerobically oxidized in the oxidation device 2, and the hydrogen sulfide is oxidized and desulfurized.

Description

Detailed Description of the Invention

[0001]

The present invention relates to sewage, night soil, industrial wastewater,
The present invention relates to a method and an apparatus for desulfurizing digestive gas for removing hydrogen sulfide from digestive gas generated by anaerobic microbial digestion of organic substances such as sludge and dust.

[0002]

BACKGROUND ART Anaerobic microbial digestion (hereinafter sometimes referred to as anaerobic digestion) and a method for treating organic substances such as wastewater such as sewage, night soil, industrial wastewater, and solid waste such as sludge and garbage, and Aerobic microbial oxidation (hereinafter sometimes referred to as aerobic oxidation) is performed. In the anaerobic digestion, digestive gas (biogas) is generated by methane fermentation. In addition to methane, the digestive gas contains gases such as carbon dioxide and hydrogen sulfide. Such digestive gas is usually used effectively as fuel for boilers or incinerators for the purpose of recovering energy, but from the viewpoint of preventing corrosion of incinerators and preventing air pollution, before use for combustion. Hydrogen sulfide is removed (desulfurization). Digestion gas usually contains about 0.05 to 2 v / v% hydrogen sulfide, but this concentration varies depending on the concentration of sulfate ion in wastewater or waste subjected to methane fermentation treatment.

Conventionally, as a method for desulfurizing digested gas, there are a water cleaning method of cleaning gas with water, a chemical cleaning method of cleaning gas with chemicals, a method of decomposing hydrogen sulfide by microorganisms, and the like.

Of these methods, the water washing method is a method in which a digestion gas is brought into contact with a washing liquid, and hydrogen sulfide in the gas is absorbed by the washing liquid to desulfurize the gas. However, in the conventional water washing method, the absorption efficiency is poor, and in order to obtain a high desulfurization rate, a large amount of washing liquid is required, and the waste liquid that has absorbed hydrogen sulfide needs to be treated by adding an iron salt or the like. However, there is a problem that it is difficult to treat the generated sludge.

The chemical cleaning method is a method in which an absorbent such as alkali, for example, sodium hydroxide is used in place of the cleaning liquid, and hydrogen sulfide is absorbed in this absorbent to desulfurize. In this method, since it reacts with a chemical to desulfurize, a large amount of digestion gas is treated, or the treatment cost is high when hydrogen sulfide has a high concentration. Further, since carbon dioxide contained in the digestive gas is also absorbed by the absorbent, an absorbent more than that required for absorbing hydrogen sulfide is required. Further, there is a problem that it is difficult to treat the waste liquid that has absorbed hydrogen sulfide.

[0006] As a method of utilizing microorganisms, there is a method of decomposing hydrogen sulfide by aerating digestion gas through a biological desulfurization tower filled with a packing material layer to which microorganisms that oxidize and decompose hydrogen sulfide adhere. 2-26615).

This method is an excellent method in that hydrogen sulfide can be selectively decomposed and removed efficiently, and no new waste liquid is generated with desulfurization, but the digestion gas does not contain oxygen. Therefore, it is necessary to supply the air or oxygen gas required for oxidizing hydrogen sulfide to the biological desulfurization tower together with the digestion gas. For this reason, air or oxygen gas remains in the digestive gas and carbon dioxide is also produced, which lowers the content rate of methane gas, which is the main component of the digestive gas, and reduces the utility value.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems, in order to solve the above problems, the methane gas content is not reduced, the cost is low, the efficiency is high, and the desulfurization can be performed at a high desulfurization rate. Therefore, it is an object of the present invention to propose a method and an apparatus for desulfurizing digestion gas that does not generate new waste liquid.

[0009]

The present invention provides the following digestion gas desulfurization method and apparatus. (1) A digestive gas generated by anaerobic microbial digestion of an organic substance is brought into contact with a cleaning liquid consisting of a mixed liquid or a treatment liquid in aerobic microbial oxidation of an organic substance, and hydrogen sulfide in the digestive gas is replaced with the cleaning liquid. A method for desulfurizing a digestive gas, comprising: an absorption step of absorbing the absorption solution obtained by the above step; and an oxidation step of oxidizing the absorbed liquid obtained in the absorption step by aerobic microorganisms to oxidize the absorbed hydrogen sulfide. (2) In an anaerobic digestion facility that digests organic substances by anaerobic microorganisms to generate digestive gas, an aerobic oxidizer that decomposes organic substances by aerobic microbial oxidation of organic substances, and the anaerobic digestion facility The generated digestive gas is brought into contact with a cleaning liquid composed of a mixed liquid or a treatment liquid in the aerobic oxidation device to absorb hydrogen sulfide in the digestive gas into the cleaning liquid, and the absorption from the anaerobic digestion facility. A gas supply path for supplying a digestive gas to the apparatus, a liquid supply path for supplying a mixed solution or a processing solution from the aerobic oxidation apparatus to the absorption apparatus, and an absorption solution returned from the absorption apparatus to the aerobic oxidation apparatus A desulfurization apparatus for digestive gas, comprising a return liquid passage.

The digestive gas to be treated in the present invention is generated by methane fermentation during anaerobic digestion of wastewater such as sewage, night soil, industrial wastewater and organic substances such as sludge and solid waste such as garbage. It is a digestive gas that does. Such digestive gas usually contains gases such as carbon dioxide and hydrogen sulfide in addition to methane gas. The above-mentioned digestive gas is generally generated by anaerobic digestion in an anaerobic digester, but it may also be generated by anaerobic digestion in an anaerobic digester other than the anaerobic digester such as a garbage landfill. Anaerobic digestion is performed by utilizing the action of anaerobic microorganisms by keeping the organic substance that is the object to be treated in an anaerobic state, and can be used for any anaerobic type such as packed bed type, fluidized bed type, sludge blanket type, etc. It can be processed by a digester.

In the present invention, in the absorbing step, the digestive gas is brought into contact with the cleaning liquid so that hydrogen sulfide in the digestive gas is absorbed by the cleaning liquid. As the cleaning liquid, a mixed liquid or a treatment liquid for aerobic oxidation of an organic substance is used. The organic substance that performs aerobic oxidation is often the digestive liquid (treatment liquid) of anaerobic digestion, but it may be the same organic substance as the object to be treated of anaerobic digestion, or another organic substance. Good.

In these cases, the digestive liquid of the anaerobic digestion facility is introduced into the aerobic oxidation device to perform aerobic oxidation, and the mixed solution or treatment liquid is sent to the absorption device as a cleaning liquid, and the anaerobic digestion facility is used. Although it is generally contacted with digestive gas supplied from the subject, the target of anaerobic digestion and the target of aerobic oxidation may be different. Further, in a system in which the anaerobic digestive liquid is discharged as it is to a sewer or the like, a part of the anaerobic digestive liquid can be aerobically oxidized in order to carry out the desulfurization of the present invention. In this case, the amount of anaerobic digestive fluid that performs aerobic oxidation is
It may be in the range necessary for the oxidation step of desulfurization.

The aerobic oxidation is a treatment for keeping an organic substance as an object to be treated in an aerobic state and oxidatively decomposing the organic substance by utilizing the action of aerobic microorganisms. The activated sludge method and the spray filter method are used. The treatment can be carried out by a treatment method using any aerobic oxidizer such as an immersion type fixed bed method, a fluidized bed method or a rotating disk method.

The mixed liquid in the aerobic oxidation used as the cleaning liquid is a mixed liquid in which the liquid to be treated during the aerobic oxidation is mixed with sludge containing aerobic microorganisms (activated sludge). Is a treatment liquid obtained by finishing aerobic oxidation and separating sludge.

As a cleaning liquid, the use of a mixed liquid has a higher hydrogen sulfide absorption efficiency and a higher desulfurization rate. It is speculated that this is due to adsorption by sludge or ingestion by aerobic microorganisms, but it is not clear. If the absorption device with the highest gas-liquid contact efficiency is used, the absorption efficiency of the treatment liquid will be high and the desulfurization rate will be high.

The absorbing device used in the absorbing step may be any one capable of efficiently bringing the digestive gas and the cleaning liquid into gas-liquid contact with each other, such as an aeration tank, a packed tower, a spray tower, and a scrubber.
Any form can be used. The conditions for passing digestion gas to the absorber are usually a space velocity (SV) of 5 to 50.
hr ^-1, preferably 10～20Hr ^-1, liquid passing condition of the cleaning liquid is usually residence time (HRT) is 2-20 minutes, preferably desirably 5-10 minutes.

By making gas-liquid contact in the absorption device, hydrogen sulfide in the digestion gas is absorbed by the cleaning liquid to obtain an absorption liquid. At this time, carbon dioxide and other impurities in the digested gas are also absorbed by the cleaning liquid, and a processed gas having a high methane concentration is obtained. When the mixed solution is used as the cleaning solution, when hydrogen sulfide is absorbed by the mixed solution, it is considered that adsorption by sludge or ingestion by microorganisms occurs. The higher the pH of the cleaning liquid, the higher the absorption efficiency of hydrogen sulfide, but generally the pH
It is preferably 7-9.

Since the organic matter is decomposed by aeration and the carbon dioxide is stripped in the mixed solution or treatment solution of the aerobic oxidizer, both alkalinity and pH are higher than those of the anaerobic digestion solution. p
H is usually 7-9. Therefore, the mixed solution or the treatment solution can be used as it is as a cleaning solution without adjusting the pH, but when the pH is low, an alkali may be added.

The absorption liquid which has absorbed hydrogen sulfide in the absorption step is returned to the aerobic oxidation device in the oxidation step for aerobic oxidation, and the hydrogen sulfide is oxidized by the action of aerobic microorganisms. At this time, other impurities absorbed in the absorption step are also treated. For example, carbon dioxide is stripped and organic matter is decomposed.

Aerobic microorganisms in the aerobic oxidizer are:
Mainly bacteria that aerobically decompose organic matter,
Since sludge contains sulfur-oxidizing bacteria such as Thiobacillus, Thiotrix and Begiatoa,
Due to the oxidizing action, hydrogen sulfide is oxidized to sulfate ions or elemental sulfur to render it harmless.

Oxidation of hydrogen sulfide produces sulfate ions, which lowers the pH of the mixed solution or treatment solution. Usually, without adjusting the pH, the mixed solution or the treatment solution can be directly sent to the absorption step to absorb hydrogen sulfide, but if the amount of hydrogen sulfide is large, the amount of sulfate ions produced is also large. When is less than 7, it is preferable to maintain the pH at 7-9 by adding an alkali such as sodium hydroxide. Even in this case, the amount of alkali used is
Less than the chemical cleaning method.

The mixed liquid obtained by decomposing organic substances by aerobic oxidation and oxidizing hydrogen sulfide is subjected to solid-liquid separation to remove solids, and the separated liquid is discharged as a treatment liquid. The necessary amount of separated sludge is returned to the aerobic oxidizer, and excess sludge is discharged to the outside of the system. During this time, part of the mixed solution or the processing solution is sent to the absorption device as a cleaning solution.

[0023]

EXAMPLES The present invention will be described below with reference to examples. Figure 1
FIG. 2 is a system diagram showing a digestion gas desulfurization apparatus according to another embodiment. In the figure, 1 is an anaerobic digester, 2
Is an aerobic oxidizer, and 3 is an absorber.

The anaerobic digester 1 comprises a closed tank,
A biomass 4 containing anaerobic microorganisms such as a sludge blanket and a fluidized bed is formed. An object introduction passage 5 communicates with the lower part of the anaerobic digester 1, an anaerobic digestion liquid transfer passage 6 communicates with the aerobic oxidizer 2 via a pump P ₁ from the upper part, and a gas supply passage 7 from the top. Communicates with the bottom of the absorber 3.

The aerobic oxidizer 2 comprises an aerobic oxidizer 8 and a solid-liquid separator 9. An anaerobic digestion liquid transfer passage 6 and a return liquid passage 10 are connected to the upper part of the aerobic oxidation part 8, and an air diffuser pipe 11 is provided in the lower part thereof, and an air supply passage 12 is connected thereto. The treatment liquid discharge path 13 is connected to the solid-liquid separation section 9.

The absorption device 3 is internally provided with the cleaning liquid 14 in FIG.
Is stored, and the filling layer 15 is formed in FIG. The gas supply passage 7 and the return liquid passage 10 are connected to the lower portion of the absorber 3, and the gas discharge passage 16 and the liquid passage 17 are connected to the upper portion. The liquid feed passage 17 is connected to the aerobic oxidation section 8 of the aerobic oxidation device 2 in FIG. 1 and the treatment liquid discharge passage 13 in FIG. 2 via a pump P ₂ .

The desulfurization method of the above-mentioned digestion gas desulfurization apparatus is as follows. First, an anaerobic digester 1 is introduced with an object to be treated consisting of an organic substance such as sewage, human waste, drainage, etc. from the object introduction path 5 and brought into anaerobic contact with the biomass 4 in an upward flow. Methane fermentation and acid fermentation are performed by the action of the sex microorganisms, and organic substances are decomposed. The digestion gas generated by this anaerobic digestion is supplied to the absorber 3 from the gas supply passage 7, and the anaerobic digestion liquid is transferred from the anaerobic digestion liquid transfer passage 6 to the aerobic oxidation device 2 by the pump P ₁ .

In the aerobic oxidizer 2, the liquid to be treated flowing in from the anaerobic digestion liquid transfer passage 6 is mixed with activated sludge in the aerobic oxidizer 8, and an oxygen-containing gas such as air is supplied from the air supply passage 12. Then, air is diffused from the air diffuser 11 to perform aerobic oxidation. In this aerobic oxidation, organic substances are decomposed by the action of aerobic microorganisms contained in activated sludge. Then, a part of the mixed liquid in the aerobic oxidation unit 8 enters the solid-liquid separation unit 9 and is solid-liquid separated, and the separated liquid is discharged from the processing liquid discharge passage 13 as a processing liquid. Part of the separated activated sludge is returned to the aerobic oxidation section 8, and the excess sludge is discharged to the outside of the system.

In the absorption step, desulfurization of digestive gas is carried out by first removing a part of the mixed liquid from the aerobic oxidation part 8 of the aerobic oxidation device 2 in FIG. Each of the parts is sent to the upper part of the absorption device 3 by the pump P ₂ through the liquid supply path 17, and in FIG.
2 and sprayed on the packed bed 15 in FIG. Then, the digestive gas supplied from the gas supply path 7 is passed upward through the cleaning liquid 14 or the packed bed 15 to make gas-liquid contact, and hydrogen sulfide, carbon dioxide, and other water-soluble components in the digestive gas are removed from the cleaning liquid 14 Absorb it.

The cleaning liquid 14 has a good absorption efficiency of hydrogen sulfide, carbon dioxide and the like, since carbon dioxide is removed and the pH is 7 to 9 in both cases of the mixed liquid and the treatment liquid. The digested gas from which hydrogen sulfide, carbon dioxide, etc. have been removed by gas-liquid contact is treated as a process gas with a high methane concentration,
Emitted from 6. The cleaning liquid 14 that has absorbed hydrogen sulfide, carbon dioxide, etc. is returned to the aerobic oxidation device 2 through the return liquid passage 10 as an absorbing liquid.

The absorption liquid returned to the aerobic oxidizer 2 is
As an oxidation step, activated sludge is mixed in the aerobic oxidation part 8 and undergoes aerobic oxidation. Then, due to the action of aerobic microorganisms, hydrogen sulfide and other oxidizable substances in the absorbing solution are microbially oxidized and rendered harmless. Carbon dioxide is stripped and removed by aeration. When sulfate ions are generated by the oxidation of hydrogen sulfide and the pH is lowered too much, alkali is injected into the aerobic oxidation section 8 to adjust the pH.

The above-mentioned oxidation step for desulfurization is carried out at the same time as the aerobic oxidation for removing organic matters, and the detoxified processing solution can be discharged as it is from the processing solution discharge passage 13.

In the above embodiment, the anaerobic digester 1 is used.
Although the anaerobic digestion liquid of 1. is aerobically oxidized in the aerobic oxidation device 2, when the anaerobic digestion liquid is discharged as it is to sewage or the like, a mixed liquid or treatment liquid of another aerobic oxidation device such as wastewater. Can be used as the cleaning liquid 14, and the absorbing liquid can be returned.

It is also possible to desulfurize digestive gas generated from a waste disposal site, a composting facility or the like. In these cases, a mixed liquid or treatment liquid of aerobic oxidation such as leachate is used as the cleaning liquid 14
Can be used as

The test examples will be described below. Test Example 1 A desulfurization test of a digestion gas generated by anaerobic digestion of corn starch wastewater was conducted by a method according to FIG. However, the packed bed 15 of the absorber 3 is omitted. That is, a 5-liter activated sludge aeration tank was used as the aerobic oxidizer 2, a 500 ml washing bottle was used as the absorber 3, and the treatment liquid of the aerobic oxidizer 2 was sent as the washing liquid 14, and the treatment liquid was continuously supplied for 10 days under the following conditions. A desulfurization test was conducted.

Composition of digestion gas: methane about 80% by volume, carbon dioxide about 20% by volume, hydrogen sulfide about 5000 ppm Cleaning solution: treatment solution, pH 7.4 Absorption condition: cleaning solution flow rate: about 50 ml / min, digestion gas flow rate: 100 ml / min Aerobic oxidation conditions: liquid to be treated; anaerobic digestion liquid of corn starch wastewater, BOD ₅ about 100 mg / l, pH 7.2, residence time; 24 hours, addition of alkali; none

During the continuous desulfurization test, 2 in the morning and in the evening.
The concentration of hydrogen sulfide in the treated gas was measured. Stable desulfurization occurred during the 10 day test period. The results are as follows. The numerical values are average values. Hydrogen sulfide concentration in digested gas: 5030ppm Hydrogen sulfide concentration in treated gas: 670ppm Hydrogen sulfide removal rate: 86.7% MLSS in activated sludge aeration tank: 3400mg / l SO ₄ ^2- concentration in treated liquid: 2.5 mg / l SO ₄ ^2- concentration in cleaning solution (treatment solution): 920 mg / l

Test Example 2 A desulfurization test of a digestion gas was conducted by a method according to FIG. However, in the aerobic oxidation apparatus 2, another synthetic wastewater was aerobically oxidized. That is, 5000m as aerobic oxidizer 2
1 of activated sludge aeration tank, 500 ml of washing bottle as the absorption device 3, the mixed liquid in the aerobic oxidation device 2 was fed as the washing liquid 14, and the continuous desulfurization test was conducted for about 10 days under the following conditions. ..

Composition of digestion gas: same as in Test Example 1 Cleaning solution: mixed solution, pH 7.5 Absorption condition: cleaning solution flow rate; 100 ml / min, cleaning solution retention time (MRT); about 5 minutes, digestion gas flow rate; 15
0 ml / min, digestive gas space velocity (SV); 18 hr
^-1 Aerobic oxidation conditions: liquid to be treated; BOD ₅ about 50 mg / l synthetic wastewater, pH 7.2, flow rate of liquid to be treated; 2000 ml
/ Day, addition of alkali; sodium hydroxide at pH 7.
Add to 5

During the continuous desulfurization test, 2 in the morning and in the evening.
The concentration of hydrogen sulfide in the treated gas was measured. About 10
Stable desulfurization occurred during the day-long test period.
The results are as follows. The numerical values are average values. Hydrogen sulfide concentration in digested gas: about 5000ppm Hydrogen sulfide concentration in treated gas: 250ppm Hydrogen sulfide removal rate: about 95% SO ₄ ^2- concentration: Most of absorbed hydrogen sulfide is oxidized to SO ₄ ^2- Was

Comparative Example 1 A desulfurization test was conducted under the following conditions, using a 500 ml washing bottle as the absorber 3 and tap water as the washing liquid.

Composition of digestion gas: same as in Test Example 1 Cleaning solution: Tap water, pH about 7 Absorption condition: Flow rate of cleaning solution: 0 to 150 ml / mi
n, digestion gas flow rate; 100 ml / min

Thirty minutes after keeping the flow rate of the cleaning liquid flowing through the absorber 3 constant, the concentration of hydrogen sulfide in the treated gas was measured. As a result, when the flow rate of the cleaning liquid is made to be considerably large and made to be approximately the same as the flow rate of the digestion gas, the removal rate of hydrogen sulfide is about 80%, and when the flow rate of the cleaning liquid is less than this, it is about 75%. The removal rate of hydrogen sulfide was low as compared with Test Examples 1 and 2.

[0044]

According to the present invention, the digestive gas is brought into contact with the mixed solution or treatment solution for aerobic oxidation to absorb hydrogen sulfide, and this is oxidized by aerobic microbial oxidation. Desulfurization at low cost and high desulfurization rate,
This makes it possible to obtain a processing gas having a high methane content, detoxify hydrogen sulfide, and discharge it together with the processing liquid.

[Brief description of drawings]

FIG. 1 is a system diagram showing a digestion gas desulfurization apparatus of an example.

FIG. 2 is a system diagram showing a digestion gas desulfurization device of another embodiment.

[Explanation of symbols]

 1 Anaerobic digester 2 Aerobic oxidizer 3 Absorber 4 Biomass 5 Material introduction passage 6 Anaerobic digestion liquid transfer passage 7 Gas supply passage 8 Aerobic oxidation portion 9 Solid-liquid separation portion 10 Return liquid passage 11 Air diffuser 12 Air supply passage 13 Treatment liquid discharge passage 14 Cleaning liquid 15 Packed bed 16 Gas discharge passage 17 Liquid supply passage

Claims (2)

[Claims] 1. A digestive gas generated by anaerobic microbial digestion of an organic substance is brought into contact with a cleaning liquid consisting of a mixed liquid or a treatment liquid for aerobic microbial oxidation of an organic substance,
An absorption step of absorbing hydrogen sulfide in the digestion gas into the cleaning liquid, and an oxidation step of oxidizing the absorbed hydrogen sulfide by oxidizing the absorption liquid obtained in the absorption step by aerobic microorganisms. And the method of desulfurizing digestive gas. 2. An anaerobic digestion facility that digests organic substances by anaerobic microorganisms to generate digestive gas, an aerobic oxidizer that decomposes organic substances by aerobic microbial oxidation of organic substances, and the anaerobic digestion. A digestion gas generated in the facility is brought into contact with a cleaning liquid composed of a mixed liquid or a treatment liquid in the aerobic oxidation device, and an absorption device for absorbing hydrogen sulfide in the digestive gas into the cleaning liquid, and from the anaerobic digestion facility. A gas supply path for supplying digestive gas to the absorption device, a liquid supply path for supplying a mixed solution or a treatment liquid from the aerobic oxidation device to the absorption device, and an absorption liquid from the absorption device to the aerobic oxidation device. A digestion gas desulfurization apparatus having a return liquid passage for returning the digestion gas.