JP3180174B2 - Biological denitration method for exhaust gas containing nitrogen oxides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for the biological denitration of exhaust gas containing less than 10 ppm of dilute nitrogen oxides, for example, exhaust gas containing nitrogen oxides for removing nitrogen oxides from gas in automobile tunnels.

[0002]

2. Description of the Related Art A conventional biological denitration method for nitrogen oxide-containing exhaust gas is disclosed in Japanese Patent Application Laid-Open No. 52-120963,
Japanese Unexamined Patent Publication (Kokai) No. 52-129677 discloses that an exhaust gas containing nitrogen oxides is first contacted with ozone (O ₃ ) to convert nitrogen oxides into NO.
_The exhaust gas is oxidized to an oxidation degree of ₂ or more, and then the exhaust gas is supplied to an absorption tower, absorbed by an absorbing solution, and then brought into contact with a mixed solution containing a denitrifying bacterium and a hydrogen donor to thereby form a nitrogen gas. Are described.

[0003] In addition, an aqueous solution of sodium thiosulfate is used as an absorbent, and microorganisms (Tiobacillus deniterificant: T
Hitherto, a method of biologically performing denitration using an absorption tower containing oyster shells on which immobilized Hiobacillus denitrificans is immobilized is already known.

[0004]

When nitrogen oxides contained in exhaust gas are oxidized to NO ₂ or a nitrogen form having an oxidation degree higher than NO ₂ , there is a problem in that use of ozone increases costs.

[0005] Further, in the biological denitration method using an aqueous sodium thiosulfate solution as an absorbent and a oyster shell as a filler, there is a problem of clogging and durability of the oyster shell used as the filler. In addition, as a bacterium that performs denitrification, Thiobacillus deniterificant is used in an integrated culture, but there are problems such as an increase in cost, such as mass culture of the bacterium.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a method for biologically denitrifying an exhaust gas containing nitrogen oxides using nitrifying bacteria and denitrifying bacteria in a biologically stable and low-cost manner. I will provide a.

[0007]

SUMMARY OF THE INVENTION The present invention provides a method for biologically removing nitrogen oxides in an exhaust gas, the method comprising contacting the exhaust gas with an aqueous solution of sodium thiosulfate in an absorption tower to remove the nitrogen oxides in the exhaust gas. After being absorbed in an aqueous solution of sodium thiosulfate and oxidized by microorganisms supported on an immobilization carrier in an absorption tower, the aqueous solution of sodium thiosulfate is allowed to flow into a fixed-bed reactor, and to a saddle-type ceramic in the fixed-bed reactor. A biological denitration method for a nitrogen oxide-containing exhaust gas, which comprises removing nitrogen oxides oxidized by microorganisms carried by the microorganisms.

[0008]

[Function] Various activated microorganisms inhabit sewage activated sludge and nitrite oxidizing nitrogen oxides (Nitrosomo
nas) and nitric acid bacteria (Nitrobactor), and a small number of bacteria that denitrify using hydrogen ions generated during oxidation of reducing sulfur compounds (eg, sulfur, thiosulfate, etc.). Exists.

Therefore, the nitrite bacteria, nitrate bacteria and Thiobacillus deniterificant are inhabited in an appropriate environment (oxidation-reduction potential: OPR, pH, substrate, etc.), and are proliferated in large quantities at low cost from sewage activated sludge. It is possible to do.

That is, the absorbing solution of nitrogen oxides in the exhaust gas is an aqueous solution of sodium thiosulfate, and the nitric acid bacteria and the nitric acid bacteria living in the absorption tower are oxidized to nitrogen oxides of NO ₃ ⁺ or more. By contacting the absorption solution containing nitrogen oxides with the thiobacillus denite refinant cultured in large quantities from a sewage treatment plant, denitrification can be performed using hydrogen ions generated when thiosulfuric acid is oxidized. It is.

[0011] In addition, the literature "Lawrence, AW: Autotrophic
Denitrification Using Sulfur Electron Donors, U.
S.EPA-600 / 2-78-113 (1978), Bisogni, JJJr., Driscol
l, CTJr .: Denitrification Using Thiosulfate and S
ulfide, J. En. Eng., ASCE, 103, 593 (1977)], the stoichiometric formula for sulfur denitrification when thiosulfate ion is used as the electron donor is given by the following formula (1).

[0012]

[Number 1] ^{_{0.844S 2 O 3 2 · + NO}} 3 · +0.347 CO 2 + 0.0865 HCO 3 · +0.0865 NH 4 + +0.434 H 2 O → 0.0865 C 5 H 7 O 2 N + 0.5 N 2 ^{_{+ 1.689 SO 4 2 · + 0.697}} H + ...... (1)

The nitrogen oxides that have not been sufficiently reduced to nitrogen gas in the absorption tower are cultivated in large quantities from the sewage activated sludge in the same manner as described above, which inhabits a fixed-bed reactor filled with saddle-type ceramics connected to the absorption tower.・ It is completely reduced to nitrogen gas by denite refinant.
The fixed bed reactor is kept anaerobic in order to grow Thiobacillus deniterificants.

On the basis of this idea, denitration from exhaust gas containing nitrogen oxides is performed. That is, Tables 1 and 2 filled in an absorption tower 1 and a fixed-bed reactor 2 as shown in FIG.
The sewage activated sludge is put into a fixed bed type reactor 2 for immobilizing the sewage activated sludge on a saddle-type ceramic immobilization carrier showing examples of its physical properties and component compositions.
Circulating the sewage activated sludge using the circulation pump 10 for about a day,
Immobilize.

[0015]

[Table 1]

[0016]

[Table 2]

After the circulating liquid becomes transparent and the sewage activated sludge is fixed, a small amount of sodium thiosulfate and an aqueous solution containing ammoniacal nitrogen are mixed into the circulating liquid, and the oxidation-reduction potential of the fixed-bed reactor 2 ( ORP) is -150 to -20
The control is performed using the ORP sensor 3, the ORP control device 4, the pH sensor 5, and the pH control device 6 so that 0 mV (vs. Ag / AgCl) and the pH are 6.5 to 7.5. The concentration of the aqueous solution of sodium thiosulfate is preferably adjusted to 100 to 500 mg / liter.

When the pH deviates from the set value, an acid or alkali is added by an acid / alkali supply pump 7,
Control to be within the control range. When the ORP becomes lower than the set value, the ORP is raised by operating the blower 9 to aerate the air.

When the circulation is continued for several days in this way, an aerobic part due to oxygen in the exhaust gas and an anaerobic part where oxygen is not sufficiently reached by the immobilized carrier and microorganisms are formed in the absorption tower 1. And the absorption tower 1
Nitrite and nitrate grow in an atmosphere near aerobic conditions, and Thiobacillus deniterificant grows preferentially in an atmosphere near anaerobic conditions in an absorption tower.
In the anaerobic atmosphere of the fixed-bed reactor 2, Thiobacillus denite refinant grows preferentially, and the nitrogen concentration in the circulating fluid is almost below the detection limit (detection tube:
0.04 ppm or less).

After acclimation of the microorganism by the above method, exhaust gas containing about 10 ppm of nitrogen oxides is aerated so that the space velocity (SV) of the absorption tower becomes about 50 h ^-1 . When the concentration of nitrogen oxides in the exhaust gas in the absorption tower outlet becomes less than the detection limit, increasing increments of about 50h ^-1 to SV, a maximum SV is at about 400h ^-1, nitrogen oxides in the exhaust gas in the absorption tower outlet The concentration of the substance is below the detection limit.

[0021]

EXAMPLE As an example 1, activated sludge of sewage was introduced into an absorption tower 1.
Further, the activated sludge was introduced into the fixed-bed reactor such that the amount of the activated sludge cells became 1 g / liter with respect to the amount of the immobilized carrier of the fixed-bed reactor 2 and circulated for about one day.

After the circulating liquid becomes transparent and the sewage activated sludge is fixed, sodium thiosulfate and ammonium nitrogen are added to the circulating liquid at a concentration of 200 mg / liter, 1
0 mg / liter was added. At this time, the oxidation-reduction potential (ORP) of the fixed-bed reactor was -150 m
V (vs. Ag / AgCl), OR so that the pH is about 7.0
P sensor 3, ORP controller 4, pH sensor 5, p
Control was performed using the H control device 6.

That is, when the pH deviates from the set value, the acid
An acid or an alkali was added by an alkali supply pump 7, and controlled to be within a control range. When the ORP became lower than the set value, the ORP was raised by operating the blower 9 and aerating the air.

Thereafter, circulation was continued for several days, and when the concentrations of sodium thiosulfate and ammonia nitrogen fell below the initial concentrations, they were added again to maintain the initial concentrations.

After the end of the seven-day acclimatization period, the exhaust gas containing 3 ppm of nitrogen oxides is discharged at the space velocity (S
V) was ventilated to 50 h ^-1 . The concentration of nitrogen oxides in the exhaust gas at the outlet of the absorption tower fell below the detection limit after 2 days (detection tube: 0.04 ppm or less). The concentration of sodium thiosulfate in the circulating fluid is 100 to 200 m
g / liter.

Further, as a result of increasing the SV by 50 h ^-1 at a time, the maximum SV was 400 h ^-1 and the concentration of nitrogen oxides in the exhaust gas at the outlet of the absorption tower was lower than the detection limit.

In Example 2, as in Example 1, activated sludge of sewage was immobilized so that the amount of activated sludge cells was 1 g / liter with respect to the amount of immobilized carrier in the absorption tower 1 and the fixed bed reactor 2. It was placed in a bed reactor and circulated for about one day.

After the activated sludge is immobilized on the immobilization carrier,
Exhaust gas containing 3 ppm of nitrogen oxides was aerated so that the space velocity (SV) of the absorption tower was 50 h ^-1 without acclimation with sodium thiosulfate and ammoniacal nitrogen.

At this time, the oxidation-reduction potential (ORP) of the fixed bed reactor was -150 mV (vs. Ag / AgCl), pH
Was controlled using the ORP sensor 3, the ORP controller 4, the pH sensor 5, and the pH controller 6 so as to be about 7.0.

That is, when the pH deviates from the set value, the acid
An acid or an alkali was added by an alkali supply pump 7, and controlled to be within a control range. When the ORP became lower than the set value, the ORP was raised by operating the blower 9 and aerating the air. The concentration of sodium thiosulfate in the circulating fluid was 100 to 2 as in Example 1.
It was adjusted to be 00 mg / liter.

The concentration of nitrogen oxides in the exhaust gas at the outlet of the absorption tower gradually decreased, and became lower than the detection limit after 20 days.

Further, as a result of raising the SV by 50 h ^-1 , the maximum SV was 400 h ^-1 , and the concentration of nitrogen oxides in the exhaust gas at the outlet of the absorption tower was lower than the detection limit.

[0033]

As described above, according to the present invention, the exhaust gas is brought into contact with the aqueous solution of sodium thiosulfate in the absorption tower to absorb the nitrogen oxides, oxidized by the microorganisms carried in the tower, and further oxidized. This is a method in which a nitrogen oxide-containing exhaust gas can be treated at low cost and with high efficiency by flowing an aqueous solution into a fixed-bed reactor and removing nitrogen oxides oxidized by microorganisms supported in the reactor. Exhaust gas containing less than 10 ppm of diluted nitrogen oxides,
For example, nitrogen oxides can be treated biologically stably and at low cost from exhaust gas and the like in an automobile tunnel.

[Brief description of the drawings]

FIG. 1 is a block connection diagram showing an example of a nitrogen oxide-containing exhaust gas treatment apparatus suitable for performing a denitration method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Absorption tower 2 Fixed-bed type reactor 3 ORP sensor 4 ORP controller 5 pH sensor 6 pH controller 7 Acid / alkali addition pump 8,9 Blower 10 Circulation pump 11 Gas flow meter 12 Air diffuser

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C02F 3/34 ZAB B01D 53/34 ZAB // C12M 1/00 (72) Inventor Kiyoshi Aridome 20-1 Shintomi, Futtsu-shi, Chiba New Japan-made Inside the Technology Development Division of Steel Corporation (72) Inventor Osamu Miki 20-1 Shintomi, Futtsu City, Chiba Prefecture Inside the Technology Development Division of Nippon Steel Corporation (72) Hideaki Yabe 20-1 Shintomi, Futtsu City, Chiba Prefecture New Nippon Steel Corporation Technology Development Division (56) References Table 5-56 362 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 53/56 B01D 53/14 102 B01D 53/34 ZAB B01D 53/77 C02F 3/34 101 C02F 3/34 ZAB

Claims (1)

(57) [Claims] In a method for biologically removing nitrogen oxides in an exhaust gas, the exhaust gas is brought into contact with an aqueous solution of sodium thiosulfate in an absorption tower, and the nitrogen oxides in the exhaust gas are absorbed by the aqueous solution of sodium thiosulfate. After being oxidized by the microorganisms supported on the immobilization carrier in the absorption tower, the aqueous solution of sodium thiosulfate was allowed to flow into the fixed-bed reactor, and nitrogen oxidized by the microorganisms supported on the saddle-type ceramics in the fixed-bed reactor. A biological denitration method for exhaust gas containing nitrogen oxides, comprising removing oxides.