JP2002172399A - Denitrification treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biological nitrification and denitrification treatment method enabling the stable removal of nitrogen and capable of sufficiently reducing the volume of a reaction tank required in a denitrification process. SOLUTION: Raw water from raw water piping 1 in introduced into a nitrification tank 10 while it receives the addition of a pH controller from adding piping 2 to be subjected to nitrite type nitrification and the treated water is introduced into a USB type denitrification tank 20. A granular sludge bed 21 is formed in the denitrification tank 20 and the treated water from the denitrification tank 20 is aerobically treated in a re-aeration tank 30 to decompose residual organic matter and the aerobically treated water is subjected to solid-liquid separation treatment in a sedimentation basin 40. The outflow water of the nitrification tank 10 is subjected to solid-liquid separation treatment and only water may be introduced into the denitrification tank 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for biologically denitrifying wastewater containing ammoniacal nitrogen,
In particular, the present invention relates to a denitrification treatment method having a nitrification step and a denitrification step. More specifically, the subsequent denitrification step is preferably performed in an upward sludge bed (USB: Upflow Sludge Blanke).
The present invention relates to a denitrification treatment method performed by a biological denitrification device of the type t).

[0002]

2. Description of the Related Art As a method of treating wastewater containing ammoniacal nitrogen, the ammoniacal nitrogen is biologically nitrified into nitrous acid or nitric acid, and then this nitrous acid or nitric acid is biologically reduced and denitrified. Biological denitrification treatment methods are well known.

In the nitrification step, the amount of oxygen required in the nitrification step and the amount of hydrogen donors such as methanol required in the subsequent denitrification step are reduced by stopping at the stage where the ammonia nitrogen is nitrified into nitrite. I can do it.

As a method of controlling the nitrification step to nitrite-type nitrification, the concentration of dissolved oxygen and pH in a nitrification tank are controlled (Japanese Patent Application Laid-Open Nos. 53-70551 and 59-92096).
Microbial inhibition by ammonia, nitrous acid and sulfide (JP-A-60-212294, JP-A-2-1986)
95, JP-A-4-161299).
In addition, the inside of the nitrification tank is maintained at a higher temperature of 30 to 40 ° C., which is more suitable for the growth of ammonia oxidizing bacteria than nitrite oxidizing bacteria, and sludge is not returned. The residence time is 0.5 to 2.5 days. There is also a method of maintaining nitrite-type nitrification by preferentially growing ammonia-oxidizing bacteria by maintaining the degree to be as short as possible (The SHARON process: a inn
Ovative Methods for Nitro
gen removal from ammonium
-Rich waste water / Wat. Sc
i. Tech. Vol. 37 No. 9 pp135-
142 1998). Here, nitrite-type nitrification refers to nitrite nitrogen that accounts for 50% or more of the oxidized nitrogen (nitrite nitrogen and nitrate nitrogen) generated in the nitrification step.

[0005] All of these nitrite-type nitrification methods limit the activity or growth of nitrite-oxidizing bacteria, and cause a difference between the ammonia oxidation activity and the nitrite oxidation activity in the nitrification tank, and as a result, they are essentially intermediate products. It leaves some nitrous acid. In the case of performing nitrite-type nitrification in this way, the water to be treated is wastewater containing a high concentration of ammonia of 100 to 3,000 mg-N / L in order to make the ammonia oxidation activity higher than the nitrite oxidation activity. There are many.

[0006]

As described above, in nitrite type nitrification, since the treatment target is wastewater containing high concentration of ammonia, the nitrification treatment water contains high concentration of oxidized nitrogen, There is a problem that a large-capacity denitrification tank is required in order to perform the denitrification treatment in the denitrification step.

An object of the present invention is to provide a denitrification treatment method capable of performing this denitrification step in a small-capacity denitrification tank.

[0008]

The denitrification treatment method of the present invention comprises a step of biologically nitrifying ammoniacal nitrogen in wastewater into nitrogen oxides, and a step of biologically reducing the nitrogen oxides. Denitrification method having a step of denitrification, wherein the nitrification step is performed in a nitrification tank of nitrite type nitrification, and the denitrification step is performed in a denitrification tank filled with denitrifying bacteria granules. It is characterized by the following.

In the present invention, the nitrification step is of the nitrite type, and the amount of oxygen required in the nitrification step and the amount of hydrogen donor required in the subsequent denitrification step can be reduced.

The denitrification step is carried out by a denitrification tank filled with denitrifying bacteria granules, preferably a USB type biological denitrification apparatus filled with granules, so that the denitrification tank can have a small capacity. .

In this USB type biological denitrification apparatus,
Without using a carrier for denitrifying bacteria, a sludge bed of granules in which the denitrifying bacteria were agglomerated in high concentration was formed in the reaction tower, and nitrite-nitrified water was introduced from the lower part of the reaction tower to form the granules. To decompose nitrate nitrogen and nitrite nitrogen in the nitrifying and nitrifying water, and remove the denitrifying water from the solid-liquid separation section at the top of the reaction tower. Since the USB type denitrification treatment tank has a sludge bed in which denitrifying bacteria are coagulated at a high concentration, the denitrification treatment can be performed at a high load.

If the SS concentration in the inflow water into the USB type denitrification tank is high, the maintenance of granules in the denitrification tank may become unstable. That is, the granules flow out due to the SS in the inflow water, the SS precipitates and the granules flow out, or the granules are destroyed by the SS.

Therefore, in the present invention, it is desirable to subject the nitrite-type nitrification-treated water to a solid-liquid separation treatment and feed only the separated water to the denitrification step.

In the denitrification treatment step of the USB system, an organic substance (normally methanol) necessary for the denitrification reaction is injected into the raw water (nitrified water) as in the ordinary denitrification treatment step. In order to complete the process quickly, the organic material is injected in excess of the theoretically necessary amount of organic matter, usually about 1.2 times the theoretical amount (about 3 times the N concentration).

In the denitrification reaction tower, the organic matter injected into the raw water is consumed in an amount corresponding to the amount of denitrified nitrite nitrogen. Because of the injection, surplus organic substances not consumed by the denitrification reaction remain in the denitrification treatment water, and BO
D, COD is high, and the water cannot be discharged as it is. Therefore, in the present invention, an aerobic biological treatment step such as a re-aeration tank is provided after the denitrification reaction step in order to remove organic substances such as methanol which are not removed by the denitrification reaction. Is preferred.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a system diagram showing a biological denitrification apparatus for performing a denitrification treatment method according to an embodiment of the present invention.

This biological denitrification apparatus includes a nitrification tank 10, a denitrification tank 20, a re-aeration tank 30, and a sedimentation tank 40.

Raw water (drainage containing ammoniacal nitrogen) is introduced into the nitrification tank 10 through a raw water pipe 1. The raw water pipe 1 is connected to a pipe 2 for adding a pH adjuster and a pipe 43 for returning sludge from the sedimentation tank 40. This nitrification tank 1
An air diffuser 11 for blowing an oxygen-containing gas such as air into the tank is provided at the bottom of the chamber. In this nitrification tank 10, nitrite-type nitrification mainly proceeds, but nitrate-type nitrification also partially progresses.

In the nitrification tank 10, nitrification-treated water mainly subjected to nitrite-type nitrification passes through a pipe 12 and, on the way, receives an organic substance such as methanol (hydrogen donor) from a pipe 13, and receives a USB. It is fed to the lower part of the denitrification tank 20 of the type. The denitrification tank 20 is composed of a vertically long reaction tower. The lower part has a conical portion whose diameter is reduced downward, and the upper part has a cylindrical shape. Piping 1
The organic wastewater containing nitrite nitrogen from Step 2 is introduced into the tower from the lower part of the denitrification tank 20 and flows upward in the tower, and the treated water is taken out from the upper part of the tower via a take-out pipe 22, It is sent to the re-aeration tank 30. In addition, a part of the treated water is
Or may be circulated through the raw water piping 1.

Inside the denitrification tank 20, a granular sludge bed 21 is formed. Granule sludge bed 2
1 usually occupies 40 to 60% of the reaction tower volume.

The denitrification-treated water fed into the re-aeration tank 30 is aerated by an oxygen-containing gas such as air blown by a diffuser 31 to aerobically decompose residual organic matter.

The water from which the organic matter has been decomposed in the re-aeration tank 30 is sent from a pipe 32 to a sedimentation tank 40, the supernatant water is taken out as treated water from a pipe 41, and the settled sludge is withdrawn from a pipe 42. Then, a part of the sludge is returned to the nitrification tank 10 and the re-aeration tank 30 via the return pipes 43 and 44.

FIG. 2 shows that the effluent from the nitrification tank 10 of FIG. 1 is introduced into the sedimentation basin 15 via the pipe 16 to be separated into solid and liquid, and only the separated liquid is fed from the pipe 12 to the denitrification tank 20 It is something to do. A pipe 13 for adding an organic substance is connected to the pipe 12. The settled sludge in the sedimentation basin 15 is returned to the nitrification tank 10 via the return pipe 17.
The return sludge from the sedimentation tank 40 is returned to the return pipe 44
Is returned only to the re-aeration tank 30 via the 2 are the same as those in FIG. 1, and the same reference numerals indicate the same parts.

In the biological denitrification apparatus of the present invention, the raw water to be denitrified preferably has an ammonia nitrogen concentration of 100 to 3000 mg-N / L.

It should be noted that the PO ₄ -P concentration is 0.1% with respect to the raw water.
If necessary, phosphoric acid, phosphate, or the like is added as P in an amount of about 0.5 to 1% of the added amount of methanol so that the concentration becomes 5 to 30 mg-P / L.

Since the pH is lowered by nitrification, a pH adjuster is added to the raw water as shown in FIGS.
Preferably, the pH within 0 is maintained between 6.0 and 7.0.
The pH adjusting agent may be directly added to the nitrification tank 10 instead of from the pipe 1.

In the nitrification tank 10, the N load is 0.5 to 4 kg.
−N / m ³ . d, especially 0.5 to 2 kg / m ³ . d is preferred. The hydraulic retention time HRT is preferably 2 hours to 2 days, and the water temperature is preferably 15 to 40 ° C, particularly preferably 25 to 37 ° C.

The N load of the denitrification tank 20 is 2 to 10 kg-N /
m³・ D especially 5 to 10 kg-N / m ³-D is preferred.
The sludge bed ratio in the denitrification tank 20 is 20-70%, especially 40-70%.
60% is preferred. The sludge concentration in this sludge bed is 20,000 to 1
It is preferable that the amount is from 10,000 to 60,000 mg / L. Through
As for water conditions, HRT is preferably 1 to 8 hr, particularly 1.5 to 4 hr.
Preferably, the LV is 0.5 to 10 m / hr, particularly 2 to 6 m / h.
r is preferred. The pH is 6.5-9.0, especially 7.0-8.0.
0 is preferable, and the water temperature is 15 to 35 ° C, particularly 20 to 30 ° C.
preferable.

The amount of the hydrogen donor such as methanol added from the pipe 13 to the pipe 12 is determined by the amount of NO _X −
N is preferably 2 to 3 times the amount of N.

[0030]

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

Example 1 Using the apparatus shown in FIG. 1, 10 mg of yeast extract was added to tap water.
/ L, _NH 4 Cl to _{500mg-N / L, H 3} PO 4 to 10 mg-P / L become as in Synthesis drainage (25 ℃, pH6.5) was prepared by adding flowing at 4.2 L / hr Then, processing was performed for 55 days (of which, 15 days were a start-up period). The nitrification tank 10 having a capacity of 20 L contains 40 sponge carriers.
In addition to the volume% addition, nitrification denitrification sludge from a human waste treatment plant was introduced as seed sludge. The sludge concentration in the nitrification tank 10 is 1,20
It was 0 mg / L. Denitrification tank 20 consisting of a cylindrical reaction tower
Has a diameter of 12 cm, a length of a straight body portion of 85 cm, a height of a conical portion at a lower portion of the reaction tower of 12 cm, and a volume of 10 L. The amount of methanol added from the pipe 13 is 1,000 mg
/ L.

In this denitrification tank 20, granular sludge obtained from a USB denitrification treatment tank of pickling effluent of stainless steel was fed as seed sludge to 50% of the tower height from the lower part of the denitrification tank. The sludge concentration in the granular sludge bed 21 is 350,000.
It was 0 mg / L.

During this time, the sludge bed 21 formed by the granules
Sludge was appropriately pulled out so that the interface of did not exceed a height of 65% from the lower part of the denitrification tank 20.

4 days after the elapse of 15 days required for starting the apparatus
The average value of the water quality when the treatment was performed by continuously passing water for 0 days was as follows. Outflow water of the nitrification tank 10 NH ₄ -N concentration: 20 mg-N / L NO ₂ -N concentration: 400 mg-N / L NO ₃ -N concentration: 80 mg-N / L Outflow water NO _X -N concentration of the denitrification tank 20 : 1 mg-N / L or less Removal rate of total nitrogen (total of NH ₄ -N and NO _X -N):
96% or more

Comparative Example 1 Instead of the USB type denitrification tank 20 of FIG. 1, a floating sludge type denitrification tank (capacity: 10 L), (MLSS concentration: 4000 mg /
Except that L) was installed, the same operation was performed by the nitrification denitrification treatment apparatus of the same configuration.

As a result, the quality of the water discharged from the denitrification tank had a high NO _X -N concentration as follows. NO _X -N concentration: 375 mg-N / L Total nitrogen removal rate: 21%

COMPARATIVE EXAMPLE 2 A nitrification denitrification treatment apparatus of the same configuration except that a floating sludge denitrification tank (50 L, MLSS concentration: 4,000 mg / L) was installed instead of the USB type denitrification tank 20 of FIG. As a result, the water quality of the denitrification tank effluent was as low as NO _X -N concentration as follows: NO _X -N concentration: 1 mg-N / L or less Total nitrogen removal rate: 96% or more

As is clear from the comparison between Example 1 and Comparative Examples 1 and 2, in Comparative Example 1 in which the denitrification tank had the same volume as in Example 1, the denitrification was extremely insufficient. To achieve the same level of denitrification efficiency, a denitrification reaction tank volume about 5 times that of Example 1 is required as in Comparative Example 2. That is, according to the first embodiment, treated water having the same high quality can be obtained by using a denitrification tank having a volume about 1/5 of that of the comparative example 2.

Example 2 A nitrification and denitrification treatment apparatus equipped with a sedimentation basin 15 as shown in FIG. 2 was used.
The operation was performed under the same conditions as in Example 1. Start-up operation
Later, when the device was operated under the above conditions for 60 days, in Example 1,
Granules flow along with the suspended sludge flowing from the
And the sludge bed ratio in the tank gradually decreased. 45 days later
37%, NO in treated water_XSo that -N remains
became. The sludge bed ratio in the tank on the 60th day was 32%.
NO of water _X-N concentration is 75mgN / L, TN removal rate is
It was 81%. On the other hand, in the second embodiment,
Gradually increased from 50% to 65% on days 25 and 52
When it reaches, up to 50% granule becomes excess sludge
However, throughout the operation period, NO
_X-N concentration is 1mgN / L or less, total nitrogen removal rate is 96%
That was all.

As described above, it was recognized that the nitrification and denitrification treatment operation could be stably continued for a long time by installing the sedimentation basin 15.

[0041]

As described above, according to the present invention, there is provided a biological nitrification and denitrification treatment method which enables stable nitrogen removal and requires a small reactor volume in the denitrification step. .

[Brief description of the drawings]

FIG. 1 is a system diagram of a biological denitrification device used in a denitrification treatment method according to an embodiment.

FIG. 2 is a system diagram of a biological denitrification device used in the denitrification treatment method according to the embodiment.

[Explanation of symbols]

 Reference Signs List 10 nitrification tank 15 sedimentation tank 20 denitrification tank 30 re-aeration tank 40 sedimentation tank

Claims (2)

[Claims] 1. A denitrification treatment method comprising the steps of biologically nitrifying ammoniacal nitrogen in wastewater into nitrogen oxides and biologically reducing and denitrifying said nitrogen oxides. A denitrification treatment method, wherein the nitrification step is performed in a nitrification tank of nitrite type nitrification, and the denitrification step is performed in a denitrification tank filled with denitrifying bacteria granules. 2. The denitrification treatment method according to claim 1, wherein the effluent of the nitrification step is separated into sludge and water, and only the separated water is sent to the denitrification step.