JP2002079034A - Biological desulfurization method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an amount of alkali for adjusting pH and a volume of an oxidation tank by enhancing the treatment performance in a method for feeding hydrogen sulfide-containing gas into a gas-liquid contact tower and removing hydrogen sulfide in the gas with an absorbing liquid and transferring the absorbing liquid absorbed hydrogen sulfide into the oxidation tank to aerobically oxidize and decompose the sulfide by microorganisms. SOLUTION: A biological desulfurization method consists of an absorbing process for introducing the hydrogen sulfide-containing gas into the gas-liquid contact tower to bring the same into contact with the absorbing liquid to absorb hydrogen sulfide in the raw gas by the absorbing liquid and an oxidation process for aerobically oxidizing and decomposing the absorbing liquid, obtained in the absorbing process, by microorganisms supported on a carrier. A biological desulfurization apparatus is equipped with the gas-liquid contact tower 2 for bringing the hydrogen sulfide- containing gas into contact with the absorbing liquid, the oxidation tank 4 receiving the absorbing liquid discharged from the gas-liquid contact tower 2 and holding the carrier 8 for oxidizing and decomposing sulfide in the absorbing liquid and equipped with an aeration means 7, and a means 15 for circulating and supplying a part of the treated water discharged from the oxidation tank 4 to the gas-liquid contact tower 2 as the absorbing liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for biological desulfurization of hydrogen sulfide-containing gas, and more particularly, to the method produced by anaerobic digestion of organic substances such as sewage, human waste, industrial wastewater, sludge, and garbage. The present invention relates to a biological desulfurization method and a biological desulfurization device for efficiently removing hydrogen sulfide from digestive gas containing hydrogen sulfide.

[0002]

2. Description of the Related Art Conventionally, wastewater such as sewage, human waste, industrial wastewater,
Alternatively, as a method for treating organic substances such as solid waste such as sludge and garbage, there is an anaerobic microorganism digestion (anaerobic digestion) method.
Digestion gas (biogas) containing methane generated by methane fermentation in anaerobic digestion is usually effectively used as fuel for boilers and incinerators for the purpose of energy recovery.

However, since digested gas contains carbon dioxide, hydrogen sulfide, and the like, in addition to methane, when effectively used as fuel for boilers and incinerators, corrosion and damage to equipment and the like occur. It is necessary to remove (desulfurize) hydrogen sulfide contained for the purpose of preventing air pollution.

As a method for desulfurizing digestive gas, Japanese Patent Laid-Open No.
No. 8849 discloses a method in which a digestive gas is introduced into a gas-liquid contact tower and brought into contact with an absorbent to absorb hydrogen sulfide in the digestive gas into the absorbent and absorb hydrogen sulfide discharged from the gas-liquid contact tower. A method has been proposed in which a liquid is aerobically oxidized and decomposed by microorganisms in an oxidation tank.

This method is excellent in desulfurization efficiency and does not generate waste liquid due to desulfurization. In particular, the gas-liquid contact efficiency is increased by filling the gas-liquid contact tower with a filler, thereby further improving the efficiency. Desulfurization can be performed.

[0006]

However, the method described in Japanese Patent Application Laid-Open No. 5-68849 has the following problems. That is, when the gas-liquid contact tower is filled with the filler, the gas-liquid contact efficiency can be improved.
The pH of the discharged absorbent decreases, and the sulfur load of the oxidation tank also increases. In response to the decrease in the pH of the absorbing solution, when the amount of water supplied to the oxidation tank is increased, the capacity of the oxidation tank for securing the residence time is increased, or the sulfur-oxidizing bacteria flow out and the oxidative decomposition efficiency is reduced. There is a problem, and when alkali is added to the absorbing solution to lower the pH, there is a problem that the amount of alkali used increases. In addition, a sedimentation basin and sludge return means are required to collect the sulfur-oxidizing bacteria that have flowed out.

The present invention solves the above-mentioned conventional problems, and introduces a hydrogen sulfide-containing gas into a gas-liquid contact tower to bring the gas into contact with an absorbing solution to absorb and remove hydrogen sulfide in the gas, thereby absorbing the hydrogen sulfide. In the method of introducing a liquid into an oxidation tank and aerobically oxidizing and decomposing sulfides in the liquid by using microorganisms, the processing capacity of the oxidation tank is improved, the amount of alkali used for pH adjustment is reduced, and the capacity of the oxidation tank is reduced. It is an object of the present invention to provide a biological desulfurization method capable of reducing the amount of biodesulfurization.

[0008]

According to the biological desulfurization method of the present invention, a raw gas containing hydrogen sulfide is introduced into a gas-liquid contact tower,
An absorption step of causing the absorption liquid to absorb hydrogen sulfide in the raw gas by contact with the absorption liquid; and an oxidation step of aerobically oxidatively decomposing the absorption liquid discharged from the absorption step by microorganisms supported on a carrier. It is characterized by comprising.

In this biological desulfurization method, it is preferable to use biologically treated water of organic wastewater as the absorbing liquid.

[0010] The biological desulfurization apparatus of the present invention comprises a gas-liquid contact tower for bringing a raw gas containing hydrogen sulfide into contact with an absorbing solution, and an absorbing solution discharged from the gas-liquid contact tower. An oxidation tank holding a carrier that oxidatively decomposes sulfide, and having an aeration unit, and a unit that circulates and supplies a part of the treated water discharged from the oxidation tank to the gas-liquid contact tower as an absorption liquid. It is characterized by becoming.

In the present invention, a microorganism (sulfur oxidizing bacterium) for oxidative decomposition of sulfide in the absorbing solution is carried on a carrier in an oxidation tank. For this reason, it becomes possible to keep sulfur oxidizing bacteria at a high concentration in the oxidation tank, and it is possible to increase the processing capacity of the oxidation tank and increase the tank load. Since the sulfur oxidizing bacteria are held in the carrier and can be prevented from flowing out together with the oxidized tank treated water, the amount of inflow and outflow water in the oxidized tank can be increased, so that a large amount of makeup water can be introduced into the oxidized tank. It is possible to reduce the amount of alkali used for adjusting the pH of the treatment water in the oxidation tank returned to the gas-liquid contact tower as the absorbent. Since the sulfur oxidizing bacteria are held at a high concentration in the carrier, the residence time in the oxidation tank can be shortened, and the capacity of the oxidation tank can be reduced. No sedimentation basin is required because there is no problem of sulfur oxidizing bacteria flowing out. The operation and effect described above are achieved.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a biological desulfurization method and a biological desulfurization apparatus according to the present invention.

In the figure, reference numeral 1 denotes an anaerobic digestion tank,
Raw water such as sewage and human waste is introduced. The anaerobic digestion gas generated in the methane fermentation digestion tank 1 is introduced into the gas-liquid contact tower 2 from the pipe 12, part of the digestion liquid pump P ₁
Is supplied to the oxidation tank 4 from a pipe 13 having The gas-liquid contact tower 2 is a packed tower in which a packed layer of the packing material 3 is formed, and the digestive gas introduced from the bottom of the tower and the absorbing liquid sprinkled from the top of the tower are brought into countercurrent contact.

The gas passing conditions of the digestion gas into the gas-liquid contact tower 2 are usually space velocity (SV) of 5 to 100 hr ^-1 , preferably 10 to 20 hr ^-1 , and the flow of the absorbing liquid is usually 10 to 100% by volume, preferably 4
It is desirable that the water flow rate be 0 to 80% by volume.

By gas-liquid contact in the gas-liquid contact tower 2,
Hydrogen sulfide in the digestion gas is absorbed in the absorbing solution. At the same time, carbon dioxide and other impurities in the digestion gas are also absorbed in the absorbing solution. The processing gas having a high methane concentration from which hydrogen sulfide or the like has been removed by gas-liquid contact is supplied from a pipe 14 to a use place such as a boiler or an incinerator.

As the absorbing liquid of the gas-liquid contact tower 2, the higher the pH, the higher the efficiency of hydrogen sulfide absorption.
9 are used. In this embodiment, as the absorbing liquid,
Processing solution from the oxidation tank 4 will be described later, it is introduced from the pipe 15 with a pump P _2. This treatment liquid has a high alkalinity because hydrogen sulfide absorbed in the oxidation tank 4 and organic substances brought in from makeup water described later are decomposed and carbon dioxide is stripped by aeration. pH 7-9. Therefore, the treatment liquid in the oxidation tank 4 has a pH
The solution can be used as it is without adjustment, but if the pH is low, an alkali such as sodium hydroxide may be added as needed.

The absorption liquid that has absorbed hydrogen sulfide in the gas-liquid contact tower 2 is supplied from the pipe 16 to the oxidation tank 4.

The oxidizing tank 4 has an aerobic oxidizing section 5 for aerobically oxidizing organic substances and hydrogen sulfide in the water to be treated by microorganisms, and a solid-liquid separating section 6. The aerobic oxidizing section 5 is provided with a diffuser 7. And a microorganism-carrying carrier 8 is charged.

In the aerobic oxidizing section 5, the digestion treatment liquid flowing from the anaerobic digestion tank 1 is treated by microorganisms carried on a carrier.
Under aeration, it undergoes aerobic oxidation and decomposes organic substances contained therein.
Further, the absorptive liquid flowing from the gas-liquid contact tower 2 also oxidizes the contained hydrogen sulfide and other oxidizable substances by aerobic oxidation in the aerobic oxidizing section 5, and the hydrogen sulfide is oxidized to sulfate ions. Carbon dioxide is removed by air stripping by aeration.

That is, the aerobic microorganisms in the oxidation tank 4 are:
Some bacteria aerobically decompose organic matter, but the sludge supported on the carrier is mainly composed of sulfur oxidizing bacteria such as genus Thiobacillus, Thiotrix and Vegiatoa. Hydrogen is oxidized to sulfate ions and elemental sulfur.

Since the oxidation of hydrogen sulfide generates sulfate ions, the pH of the treated water in the oxidation tank 4 decreases. As described above, the treated water in the oxidation tank 4 can be sent directly to the absorption step to absorb hydrogen sulfide without adjusting the pH, but when the amount of hydrogen sulfide is large, the amount of sulfate ion generated is large. When the pH is lower than 9, the pH is adjusted by adding an alkali.

The carrier of the aerobic oxidizing section 5 is not particularly limited, but a porous sintered material, plastic, coke, sponge, or the like, which can easily carry microorganisms, has a large surface area, and has good water permeability is suitable. is there. The size of the carrier material is not particularly limited, but is generally 2 to 20 mm in diameter and 2 to 40 mm in height in the form of a column or a cylinder, or 2 to 30 mm × 2 to 30 mm × 2 in terms of handleability and the like. ~
It is preferably a lump of 30 mm. The amount of the carrier is 5 to 50% by volume based on the volume of the aerobic oxidizing section 5.
It is preferable to set the degree. The treated water in the aerobic oxidizing section 5 is discharged through the solid-liquid separating section 6, a part of the water is introduced into the gas-liquid contact tower through the pipe 15 as an absorbent, and the remainder is discharged out of the system through the pipe 17.

In the oxidation tank 4, the microorganisms are supported on the carrier 8, so that the cells can be maintained at a high concentration.
The efficiency of aerobic oxidative decomposition can be increased, and the residence time can be significantly reduced as compared with the conventional method. The residence time (HRT) of the oxidation tank 4 varies depending on the properties of the raw gas and raw water and other processing conditions, but is usually about 2 to 15 hours.

In the biological desulfurization apparatus shown in FIG. 1, the digestion solution from the anaerobic digestion tank 1 is aerobically oxidized in the oxidation tank 4, but this digestion treatment solution is discharged as it is without aerobic oxidation. In some cases.

In FIG. 1, the water treated in the oxidizing tank 4 is introduced into the gas-liquid contact tower 2 as an absorbing solution. However, the digesting solution in the anaerobic digesting tank 1 may be used as the absorbing solution. The digestion treatment liquid has higher alkalinity than the activated sludge treated water, which is advantageous in replenishment of alkalinity.However, from the viewpoint of preventing clogging of the filler due to the high SS concentration, it is necessary to take measures such as washing. Required.

When the activated sludge treated water in the oxidizing tank 4 is used as the absorbing solution, alkali can be replenished with the alkalinity of the activated sludge treated water, and a buffering action against a decrease in the pH of the absorbing solution can be obtained. Further, when the SS concentration is several mg / L to 30 mg / L.
Since it is as low as mg / L, clogging of the filler in the gas-liquid contact tower 2 can be prevented. Further, there is an effect that the supply of the minimum nutrients (nitrogen, phosphorus, minerals, etc.) to the sulfur-oxidizing bacteria can be complemented. On the other hand, if it is a digestion solution,
Since the alkalinity is higher than such activated sludge treated water (secondary treated water), a greater buffering effect can be obtained against a decrease in pH.

In the case where the digestion solution is discharged out of the system as it is and the oxidative decomposition in the oxidizing tank 4 is not performed, wastewater from another process may be introduced into the oxidizing tank 4.

Further, in the biological desulfurization apparatus shown in FIG. 1, the gas-liquid contact tower 2 is filled with the filler 3, but this filler is not always required and may be omitted. However, filling the filler 3 is preferable because the gas-liquid contact efficiency can be increased and the desulfurization efficiency can be increased. As the filler 3, a known plastic or metal material generally used for gas-liquid contact can be used. In order to prevent the filler 3 from being clogged, the gas-liquid contact tower 2 is filled. Microorganisms are not adhered to the material, and when microorganisms are generated, they are washed and removed so that sulfur oxidation hardly occurs in the gas-liquid contact tower 2.

The raw gas containing hydrogen sulfide to be treated in the present invention is used for anaerobic digestion of organic substances such as wastewater such as sewage, human waste, industrial wastewater and solid waste such as sludge and garbage. And digestive gas generated by methane fermentation, as well as odorous gas generated from garbage disposal sites, composting facilities, and the like.

[0031]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 A desulfurization test was performed on digested gas of the following concentration generated by anaerobic digestion of wastewater of beer production having the following quality using the biological desulfurization apparatus shown in FIG. [Beer brewery waste water _{quality] BOD: 2000mg / L COD Cr} : 3300mg / L SS: 1000mg / L [ digestion gas _{concentration] H 2 S: 2000ppm CH 4} : about 80 vol% CO _2: 20 vol%

The specifications and processing conditions of each part are as follows.
You. [Anaerobic digestion tank] Raw water introduction amount: 9000 L / hr Capacity: 32 m³  [Gas-liquid contact tower] Capacity: 400L Filler: Net ring (registered by Dainippon Plastics Co., Ltd.)
Trademark) Filler filling amount: 250 L Absorbent pH: 7.0-7.5 Absorbent flow: 4500 L / hr Digestion gas flow: 8000 NL / hr (SV: 20 hr)
^-1[Oxidation tank] Aerobic oxidation part capacity: 2000 L Carrier (3 × 3 × 3 mm sponge) input amount: 600 L MLSS of aerobic oxidation part: 620 mg / L Aeration amount: 10,000 NL / hr Residence time (HRT): 8 hr Solid-liquid separation unit capacity: 400 L Amount of treated water discharged out of the system: 300 L / hr

As a result, the following properties are obtained as the anaerobic digestion liquid, the processing gas from the gas-liquid contact tower 2 and the processing water from the oxidation tank 4, and the residence time in the oxidation tank 4 is reduced to increase the efficiency. Processing was done. [Anaerobic digestion solution] pH: 7.2 BOD: 90mg / L SS: 120mg / L [ process _{gas] H 2 S: 80ppm (H} 2 S removal rate: 96%) [water oxidation basin replenisher] SO ₄ ^2- : 25.5 mg / L sulfide: 1 mg / L or less [Treatment water (absorbent before gas-liquid contact)] SO ₄ ^2- : 235 mg / L Sulfide: 1 mg / L or less

Comparative Example 1 A treatment was performed under the same conditions as in Example 1 except that the carrier was not charged into the oxidation tank. As a result, the MLSS of the oxidation tank was 128 mg / L, and the residence time was insufficient, so that the water quality of the treatment liquid was reduced as described below. [Treated water] SO ₄ ²⁻ : 52.8 mg / L Sulfide: 38.6 mg / L

[0036]

As described in detail above, according to the biological desulfurization method and the biological desulfurization apparatus of the present invention, a hydrogen sulfide-containing gas is introduced into a gas-liquid contact tower and brought into contact with an absorbing solution to reduce hydrogen sulfide in the gas. In the method of absorbing and removing and absorbing the hydrogen sulfide, the absorbing solution is introduced into the oxidation tank, and the sulfide in the liquid is aerobically oxidized and decomposed by microorganisms.
It is possible to reduce the amount of alkali used for adjustment and the capacity of the oxidation tank.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a biological desulfurization method and a biological desulfurization device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anaerobic digestion tank 2 Gas-liquid contact tower 3 Filler 4 Oxidation tank 5 Aerobic oxidation part 6 Solid-liquid separation part 7 Air diffuser 8 Carrier

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C02F 3/30 C02F 3/30 B 3/34 3/34 Z F term (Reference) 4D003 AA14 AB02 BA02 CA08 EA14 EA19 EA21 EA25 FA05 FA06 4D020 AA04 BA23 BB03 BC05 BC06 CB08 CD03 DB05 DB07 DB08 4D040 BB42 BB82 DD03 DD16 DD31

Claims (3)

[Claims] 1. An absorption step in which a raw gas containing hydrogen sulfide is introduced into a gas-liquid contact tower and brought into contact with an absorbing liquid to absorb the hydrogen sulfide in the raw gas into the absorbing liquid, and discharged from the absorbing step. An oxidizing step of aerobically oxidatively decomposing the absorbing liquid by microorganisms supported on a carrier. 2. The biological desulfurization method according to claim 1, wherein biologically treated water of organic wastewater is supplied to the absorption step as an absorbing liquid. 3. A gas-liquid contact tower for bringing a raw gas containing hydrogen sulfide into contact with an absorbing solution, and an absorbing solution discharged from the gas-liquid contact tower are introduced to oxidize and decompose sulfides in the absorbing solution. An oxidation tank holding a carrier and having aeration means, and a means for circulating and supplying a part of the treated water discharged from the oxidation tank to the gas-liquid contact tower as an absorption liquid. Biological desulfurization equipment.