JPH1015348A - Treatment of gas containing volatile organohalogen compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further enhance the decomposition efficiency of a volatile organohalogen compd. by uniformly distributing bacteria in a treatment column by passing gas (raw gas) containing a volatile organohalogen compd. through a liquid bed wherein a fluldized bed of a carrier having bacteria supported thereon is formed. SOLUTION: Raw gas containing gaseous volatile organohalogen compd. and a derivative substance is introduced into a treatment tower 1 from an introducing pipe 3. The volatile organaohalogen compds. in the raw gas introduced into the treatment tower 1 becomes bubbles 9 to rise through the fluidlzed bed 6 of a bacteria supported carrier 2 and decomposed in the presence of the derivative substance (nutrient) introduced along with the volatile organaohalogen compd. in the raw gas supported on the carrier 2. The exhaust gas of the treatment tower 1 is discharged to the outside of the system from a discharge pipe 4. The liquid in the treatment tower 1 is circulated from the upper part of the tower to the lower part thereof by circulating pipe 5 and, by this ascending circulating flow,, the bacteria supported carrier 2 is uniformly dispersed to form a fluidized bed 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a gas containing a volatile organic halogen compound, and more particularly, to a method for efficiently treating a gas containing a volatile organic halogen compound such as an organic chlorine compound by utilizing microorganisms. On how to do it.

[0002]

2. Description of the Related Art Groundwater and soil are contaminated with volatile organic halogen compounds such as organic chlorine compounds such as chloromethanes, chloroethylenes and chlorobenzenes.

[0003] The present applicant gasifies volatile organic halogen compounds in groundwater or soil by gas stripping or vacuum extraction, and converts the resulting volatile organic halogen compound-containing gas (raw gas) into natural gas in the presence of an inducer. As a method for safely and efficiently decomposing by microorganisms, as shown in FIG. 2, a treatment tower 12 having a packed bed 11 carrying microorganisms capable of decomposing volatile organic halogen compounds in the presence of an inducer is formed.
The raw gas is introduced together with the gaseous inducer from the pipe 13 and a part of the discharged exhaust gas is used as a processing gas in the pipe 1.
4, a method was proposed in which the remaining portion was circulated and introduced into the lower part of the treatment tower 12 through a pipe 15 in order to uniformly mix the components in the packed bed 11 (JP-A-6-335617). Reference numeral 16 denotes a pipe for introducing the inorganic medium, 17 denotes a spray pipe for spraying the inorganic medium from the top of the tower, and 18 denotes a pipe for circulating the inorganic medium at the bottom of the tower to the top of the tower. According to this method, continuous and efficient processing can be performed by supplying the gaseous inducer together with the raw gas.

On the other hand, as a method of treating groundwater contaminated with volatile organic halogen compounds, there is a method of introducing contaminated water as raw water directly into a fluidized bed treatment tower (JP-A-5-23691, JP-A-7-155792). However, in this case, oxygen is required for the growth of microorganisms and for decomposing the volatile organic halogen compounds, so that pure oxygen or air must be blown separately. Evaporates from water into gas. Therefore, the gas containing the volatile organic halogen compound is further added to the gas described in JP-A-6-3356.
It is necessary to carry out the treatment described in the publication No. 17 or another biological treatment method, or treatment with activated carbon.

Although the method of directly introducing contaminated water into a fluidized-bed treatment tower and treating it does not involve gasification such as air stripping or vacuum extraction, it seems at first glance that the operability is good. However, in practice, it is necessary to treat volatile organic halogen compounds contained in both liquid and gas, so that the operability is poor. On the other hand, if the method is such that volatile organic halogen compounds contained in groundwater or the like are completely transferred into the gas phase by air stripping or the like and the gas is treated as a source gas, oxygen is supplied from the source gas. Therefore, there is no need to separately supply, and only volatile organic halogen compounds in the raw gas are treated, so that operability is also good.

[0006] Even when genetically modified bacteria are used as microorganisms, the method of treating raw gas is advantageous. That is, when a genetically modified bacterium is used, it is feared that the bacterium leaks out of the system and pollutes the environment. As a method for preventing the outflow of recombinant bacteria out of the system, as described in Japanese Patent Application Laid-Open No. 7-46984, a method of providing a sterilizing device such as a sterilizing filter at a gas inlet and a gas outlet of a treatment tower is known. Can be taken. Leakage of the bacteria into the gas is significantly less than leakage of the bacteria into the liquid, so that the outflow of the bacteria can be easily prevented by operating the sterilizing filter.

On the other hand, in the case of a method in which a liquid containing a volatile organic halogen compound is introduced into a fluidized bed treatment tower to treat the liquid, the liquid is sterilized.
The operating pressure increases and the cost increases. Also, the amount of bacteria leaking into the liquid is greater than the amount leaking into the gas,
The clogging of the sterilizing filter is remarkable, and the frequency of replacing the sterilizing filter increases. In the case of treating raw gas, it is necessary to sterilize wastewater generated with the supply of nutrients, but the amount of treatment is limited by the method of introducing contaminated water directly into a fluidized bed treatment tower. Negligible compared to volume.

[0008] Therefore, volatile organic halogen compounds can be used as described in Japanese Patent Application Laid-Open No. H10-163, both in terms of ease of sterilization operation when using genetically modified bacteria and in terms of treatment of exhaust gas generated by the supply of oxygen. As described in 6-335617, it is advantageous to treat as a gas containing volatile organic halogen compounds.

[0009]

The present inventors have analyzed the distribution of microorganisms in a packed bed using the method described in JP-A-6-335617, and found that the distribution of microorganisms has a concentration gradient, The microbial concentration was found to decrease from the bottom to the top. For this reason, the concentration of microorganisms in the upper part of the packed bed is low, and the decomposition of volatile organic halogen compounds is not effectively performed, that is, there is a possibility that the inside of the packed bed is not effectively used as a place where microorganisms grow Was estimated.

Therefore, in such a raw gas processing method, it is considered that there is a possibility that the efficiency of decomposing volatile organic halogen compounds can be further improved by uniformly distributing microorganisms in the processing tower.

[0011] The present invention has been made based on the above-mentioned findings, and when a gas containing a volatile organic halogen compound is passed through a treatment tower holding microorganisms for treatment, the microorganisms in the treatment tower are uniformly dispersed. It is an object of the present invention to provide a method for decomposing a volatile organic halogen compound more efficiently.

[0012]

According to the present invention, there is provided a method for treating a gas containing a volatile organic halogen compound, the method comprising the steps of: A method of treating by contacting a microorganism which can be decomposed below with an inducing substance in the presence of an inducer, characterized in that a raw gas is passed through a liquid layer in which a fluidized bed of a carrier supporting the microorganism is formed.

Since the carrier can stably carry the microorganism, the use of the carrier enables the microorganism to be maintained at a high concentration in the treatment tower, and the treatment can be carried out reliably.

In the present invention, since the carrier carrying the microorganisms is dispersed uniformly, and the raw gas is passed through the fluidized bed which is effectively used as a place where the microorganisms grow, the volatile organic halogen compound can be efficiently removed. Can be disassembled.

That is, the present inventors have conducted the following studies in order to uniformly distribute microorganisms in a treatment tower as a gas reactor.

As a method of uniformly distributing the microorganisms in the treatment tower, fluidization of the carrier can be mentioned. However, a method for fluidizing a carrier in a gas in a gas reactor as described in JP-A-6-335617 is not practical. Therefore, the carrier is placed in the liquid layer, the liquid withdrawn from the upper part of the liquid layer is supplied from the lowermost part of the liquid layer by a pump, and the carrier is floated by giving an upward circulating flow so that the carrier circulates in the treatment tower. A so-called fluidized bed reactor was used. When a gas containing a volatile organic halogen compound was supplied from the lowermost portion of the treatment tower having such a fluidized bed, an increase in decomposition efficiency was observed.

The present invention has been achieved based on the results of such studies.

[0018]

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

FIG. 1 is a system diagram showing a processing apparatus suitable for carrying out the method for processing a gas containing a volatile organic halogen compound of the present invention.

In FIG. 1, reference numeral 1 denotes a treatment tower loaded with a carrier 2 carrying microorganisms. The treatment tower 1 has a raw gas inlet pipe 3 at the bottom and a processing gas discharge pipe at the top. 4 are provided. Reference numeral 5 denotes a circulation pipe for extracting the liquid in the processing tower 1 with the pump P, circulating the liquid into the bottom of the processing tower 1, and introducing the liquid into the processing tower 1 by the circulating liquid flow. Thus, the fluidized bed 6 is formed by floating and flowing the carrier in the column. Reference numeral 7 denotes an inorganic medium introduction pipe, and reference numeral 8 denotes a drain pipe for discharging the liquid in the tower.

In order to treat a gas containing a volatile organic halogen compound in accordance with the method of the present invention using the illustrated apparatus, a raw gas containing a volatile organic halogen compound in a gaseous state and an inducer is introduced into an inlet pipe 3. From the treatment tower 1.

The volatile organic halogen compound in the raw gas introduced into the treatment tower 1 is converted into bubbles 9 to form the microorganism-carrying carrier 2.
During this time, the microorganisms supported on the carrier 2 undergo decomposition treatment in the presence of an inducer (nutrient) introduced together with the volatile organic halogen compound in the raw gas. Then, the exhaust gas of the processing tower 1 is discharged out of the system from the discharge pipe 4 as a processing gas. The liquid in the treatment tower 1 is circulated from the top of the tower to the bottom of the tower by a circulation pipe 5, and a fluid bed 6 in which the microorganism-carrying carriers 2 are uniformly dispersed is formed by the upward circulation. The circulating liquid flow may be at such a speed that the carrier 2 floats to such an extent that it does not flow out of the upper part of the tower, and circulates in the processing tower 1 to be in a fluidized state.
(Height of packed bed during fluidization-height of packed bed) / (filled bed height)
The flow rate is preferably such that the expansion rate represented by × 100% is about 10 to 40%.

In the present invention, the carrier may be in a fluidized bed state in which the carrier particle layer is expanded and expanded,
Further, the carrier particles may form a circulating flow in the treatment tower.

In the present invention, any microorganism capable of decomposing a volatile organic halogen compound in the presence of an inducing substance may be used as the microorganism to be filled in the treatment tower 1. Natural bacteria and other recombinant bacteria can be used. Further, the microorganism may be a single bacterium purely cultured or a mixed bacterium.

The carrier for supporting the microorganisms may be any carrier having a large surface area capable of retaining the microorganisms at a high density, and any carrier capable of smoothly flowing by upward flow. Examples of the material include activated carbon, anthracite, Sand, metal pieces, synthetic resins such as polyurethane and polypropylene can be used.
Those having about 1 to 20 mm are preferable.

The inducer is not particularly limited as long as it can impart a capability of decomposing a microorganism to a volatile organic halogen compound, and is not particularly limited. An aromatic hydrocarbon is desirable, and a volatile substance such as toluene or a non-phenol such as phenol. Volatile materials can be used. When a volatile inducer such as toluene is used, it can be mixed with the raw gas and introduced into the treatment tower as shown in FIG. When a non-volatile inducer is used, as shown in FIG. 3, a separate inducer introduction pipe 10 may be provided and introduced into the treatment tower 1. In addition,
FIG. 3 is different from the device shown in FIG. 1 in that an induction substance introduction pipe 10 is provided, and the other configuration is the same.

As described above, the supply amount of the inducer is appropriately determined so as to obtain a sufficient resolution of the volatile organic halogen compound. For example, when toluene is used as the inducer, It is preferable to supply about 10 to 500 times the volatile organic halogen compound in the raw gas.

In particular, when toluene is used as the inducer, it is preferable to use, as the microorganism, a toluene-assimilating bacterium obtained by performing enrichment culture using toluene as a carbon source from various soils.

The inorganic medium is supplied for the purpose of maintaining the pH in the system and supplying nutrients. The pH in the system is within a pH range in which the ability to decompose by microorganisms is optimally maintained, for example, pH6.
It is preferable to set it to about 5 to 7.5.

In the present invention, examples of the raw gas include a gas containing a volatile organic halogen compound obtained by air stripping or vacuum extraction of groundwater or soil containing a volatile organic halogen compound.

In this case, since the groundwater and the soil contain the volatile organic halogen compound at a low concentration of several ppm, the volatile organic halogen compound in the raw gas obtained from the groundwater and the soil is also very low. It is contained at a low concentration. Therefore, in the treatment tower, in order to efficiently decompose such a low concentration of the volatile organic halogen compound, the microorganism is used so that the microorganism used has a high substrate affinity for the volatile organic halogen compound to be treated. It is important to set processing conditions such as the amount of substance added, gas flow rate, and column capacity.

It is preferable that the gaseous organic halogen compound is supplied directly from the lowermost portion of the processing tower. However, the gaseous organic halogen compound is supplied separately from the processing tower. A mode in which a liquid exchange tower is provided and an organic halogen compound solution can be circulated and supplied into the treatment tower may be used.

When a gas-liquid exchange tower is provided separately from the treatment tower, the gas-organic halogen compound may be supplied as fine bubbles from the bottom of the liquid layer. A gas-liquid exchange column of a so-called gas stripping type may be used in which the gas is filled and the liquid flows from the upper part and the gas is sent from the lower part.

In the above description, the carrier is fluidized by circulating the liquid in the processing tower, but it is also possible to fluidize the carrier by circulating a part of the processing gas.

In the method of the present invention, examples of the volatile organic halogen compound to be treated include organic chlorine compounds such as trichloroethylene, dichloroethylene, and vinyl chloride.

[0036]

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

Example 1 Using the apparatus shown in FIG. 1, trichloroethylene-containing gas was decomposed according to the method of the present invention under the following conditions.

Treatment conditions Treatment tower volume: 1600 cm ³ Carrier: anthracite (particle diameter 0.9 mm), 80
0 cm ³ raw gas flow rate (SV): treatment tower volume against 1L / hr inducer: toluene, Hara supplied from the processing tower bottom with raw gas is mixed so as to be 400ppm in the original gas Gas: trichlorethylene concentration of 16. 2 ppm The liquid drawn by a pump from the upper part of the processing tower was circulated to the lowermost part of the tower, and the carrier was suspended and supplied in an upward flow to the extent that it circulated in the processing tower. The circulation flow rate was 50 L / hr.

The treatment tower is provided with an inorganic medium (RYStanier &ETC; J. Gen. Micro
Biol., p159-p271, standard mineral medium: composition 40
mL / L-1M · (Na ₂ HPO ₄ + KH ₂ PO ₄ )
(PH 6.8), 20 mL / L-Hutner reagent,
1.0 g / L- (NH ₄ ) ₂ SO ₄ ) was supplied at 1 L / day, and the same amount of liquid was discharged.

Microorganisms in the treatment tower were not particularly inoculated and used naturally proliferating microorganisms.

As a result, the concentration of trichlorethylene in the treated gas was 1.1 ppm, and no toluene was detected. The processing efficiency was maintained stably for more than 100 days.

Comparative Example 1 A gas containing trichlorethylene was decomposed under the following conditions using the apparatus shown in FIG.

Processing conditions Processing tower volume: 3140 cm ³ Carrier: peat Raw gas flow rate (SV): 1 L / hr Inducing substance: Toluene, mixed with raw gas at 400 ppm, and supplied from the bottom of processing tower together with raw gas Gas: Trichlorethylene concentration 16.1 ppm In the treatment tower, for the purpose of maintaining pH and supplying nutrients,
100 mL of the same inorganic medium as used in Example 1 was supplied once every 6 hours. The circulation gas flow is 30
L / hr.

The microorganisms in the treatment tower were not particularly inoculated, and used naturally proliferating microorganisms.

As a result, the concentration of trichlorethylene in the processing gas was 6.2 ppm, and no toluene was detected. The processing efficiency was maintained stably for more than 100 days.

Example 2 Using the apparatus shown in FIG. 2, trichloroethylene-containing gas was decomposed under the following conditions according to the present invention.

Treatment conditions Treatment tower volume: 1600 cm ³ Carrier: anthracite (particle diameter 0.9 mm), 80
0 cm ³ raw gas flow rate (SV): 1 L / hr with respect to the processing tower volume Derivative: phenol, phenol 0.52 mg / L
Was supplied from the top of the processing tower at 1 mL / min (carbon load is equivalent to that of toluene in Example 1). Raw gas: Trichlorethylene concentration: 16.3 ppm Other processing conditions were exactly the same as in Example 1.

As a result, the concentration of trichlorethylene in the treated gas was 1.5 ppm, and no phenol was detected from the discharged liquid. The processing efficiency was maintained stably for more than 100 days.

From the above results, it is understood that according to the present invention, volatile organic halogen compounds in the raw gas can be efficiently decomposed and removed.

[0050]

As described above in detail, according to the method for treating a gas containing a volatile organic halogen compound of the present invention, the volatile organic halogen compound contained by treating the gas containing the volatile organic halogen compound is removed. It can be decomposed efficiently.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a processing apparatus suitable for carrying out a method for processing a gas containing a volatile organic halogen compound of the present invention.

FIG. 2 is a system diagram showing a method described in JP-A-6-335617.

FIG. 3 is a system diagram showing a processing apparatus suitable for carrying out the method for processing a gas containing a volatile organic halogen compound of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing tower 2 Carrier 3 Raw gas introduction pipe 4 Processing gas discharge pipe 5 Circulation pipe 6 Fluidized bed 9 Bubbles

Claims (1)

[Claims] 1. A gas containing a volatile organic halogen compound (hereinafter referred to as a raw gas) is brought into contact with a microorganism capable of decomposing the volatile organic halogen compound in the presence of an inducer in the presence of the inducer. A method for treating a gas containing a volatile organic halogen compound, wherein a raw gas is passed through a liquid layer in which a fluidized bed of the carrier carrying the microorganism is formed.