JP2003326297A - Nitrification method for waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out a high-efficiency and low-cost nitrification method due to the finding that a nitrous acid type nitrification process can be stably performed from an acclimatizing stage with relatively low ammonia nitrogen concentration to a normal operation stage with high concentration. <P>SOLUTION: In the nitrification method for waste water by bringing waste water containing ammonia nitrogen into contact with nitrifying bacteria in a nitrification tank 12 under aerobic conditions to produce oxidized nitrogen, the pH of the waste water in the nitrification tank 12 is controlled to the range from 7.5 to 9.5 when the concentration of ammonia nitrogen in the waste water is 40 to 1,000 mg/l. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nitrification treatment method for wastewater, and more particularly to a nitrification treatment technology for wastewater containing a high concentration of ammoniacal nitrogen.

[0002]

2. Description of the Related Art In order to nitrify ammoniacal nitrogen in waste water, it is common to use a biological treatment method using bacteria called nitrifying bacteria. For nitrifying bacteria, ammoniacal nitrogen (NH ₄ -N) is added to nitrite nitrogen (NO ₂ -N)
There are ammonia-oxidizing bacteria that convert into nitrous acid and nitrite-oxidizing bacteria that convert nitrite nitrogen into nitrate nitrogen (NO ₃ -N). And, when nitrification is performed under aerobic conditions in the pH of wastewater such as sewage treatment, there are always both ammonia-oxidizing bacteria and nitrite-oxidizing bacteria,
A so-called nitric acid-type nitrification treatment in which ammoniacal nitrogen is oxidized to nitrate nitrogen is performed.

In general, oxidizing oxygen to nitrite nitrogen consumes less oxygen than oxidizing to nitrate nitrogen. Therefore, the amount of aeration to be aerated in the nitrification tank can be reduced, and the nitrification treatment can be followed. The amount of organic substances added can be reduced in the denitrification treatment that is usually provided.

Therefore, if a so-called nitrite type nitrification treatment that surely stops the nitrification reaction up to nitrite nitrogen, a low-cost nitrification treatment process can be constructed. In addition, nitric acid nitrification treatment is performed with ammonia nitrogen →
Whereas the nitrite nitrogen → nitric acid nitrogen requires two oxidation steps, the nitrite type nitrification requires only one step of ammonia nitrogen → nitrite nitrogen, so nitrification efficiency is high. Can be improved.

Here, looking at the types of ammonia-oxidizing bacteria that convert ammoniacal nitrogen to nitrite nitrogen,
With respect to ammonia nitrogen, which is a substrate (energy supply source) of ammonia-oxidizing bacteria, it exhibits the maximum ammonia oxidation activity under conditions where the ammonia nitrogen concentration is relatively low, such as sewage, and for example, the ammonia nitrogen concentration is 1000 to 20.
In the high concentration condition such as 00 mg / L, the type which is inhibited by the substrate itself and the higher the ammonia nitrogen concentration is, the more the ammonia oxidation activity is increased. For example, in the high concentration condition where the ammonia nitrogen concentration is about 2000 mg / L, It is known that there are several types that exhibit a fast ammonia oxidation rate. The former ammonia-oxidizing bacteria will be referred to as low-concentration ammonia-compatible bacteria, and the latter ammonia-oxidizing bacteria will be referred to as high-concentration ammonia-compatible bacteria. In addition, high-concentration ammonia-compatible bacteria have a high oxidation treatment rate per unit cell under high-concentration conditions, so by constructing a nitrification tank that uses a biota mainly composed of high-concentration ammonia-compatible bacteria, The nitrification treatment efficiency can be improved.

However, the ammonia nitrogen concentration at the beginning of the operation is 1000 mg / L, for example, during the acclimatization operation of the nitrification tank.
Under the following relatively low concentration conditions, low concentration ammonia-corresponding bacteria also proliferate remarkably during the acclimation process. As a result, the residual ammoniacal nitrogen concentration in the treated water decreases due to the low-concentration ammonia-compatible bacteria, but the ammoniacal nitrogen concentration is 1000 m
There is a problem that a high nitrification treatment rate cannot always be obtained when the normal operation in a high concentration region of g / L or more is performed and the high-concentration ammonia-corresponding bacteria do not sufficiently proliferate and are small. Moreover, once it is said that the highly active biota in which high-concentration ammonia-compatible bacteria predominantly propagate, the nitrification reaction is stopped by nitrite nitrogen, but in many cases,
There is a problem that nitrate nitrogen starts to be generated with the lapse of time, and the nitric acid-type nitrification reaction is finally changed.

[0007]

As described above, in order to carry out a low-cost nitrite type nitrification treatment method using a high-concentration ammonia-compatible bacterium of the types of ammonia-oxidizing bacteria,
Ammonia nitrogen concentration can be predominantly propagated even in acclimatization operation at a relatively low concentration of less than 1000 mg / L, and the ammonia nitrogen concentration is 1
Even after shifting to normal operation with a high concentration of 000 mg / L or more, it is necessary to establish technically so that the nitrite type nitrification treatment can be stably maintained.

The present invention has been made in view of the above circumstances, and in nitrification treatment of wastewater containing a high concentration of ammonia nitrogen, the ammonia nitrogen concentration is relatively high from the acclimation operation to a high concentration. It is an object of the present invention to provide a wastewater nitrification treatment method capable of performing a highly efficient and low-cost nitrification treatment method, since the nitrite-type nitrification treatment can be stably performed until normal operation.

[0009]

In order to achieve the above-mentioned object, the present invention produces wastewater containing ammoniacal nitrogen and nitrifying bacteria in a nitrification tank under aerobic conditions to produce oxidative nitrogen. In the wastewater nitrification treatment method, when the concentration of ammonia nitrogen in the wastewater is 40 to 1000 mg / L, the pH of the wastewater in the nitrification tank is controlled to be in the range of 7.5 to 9.5. Characterize.

According to the present invention, in the nitrification treatment, when the concentration of ammonia nitrogen in the wastewater is 40 to 1000 mg / L, the pH of the wastewater in the nitrification tank is adjusted to be in the range of 7.5 to 9.5. Since it is controlled, the ammonia-rich nitrogen-containing bacteria can be dominated by high-concentration ammonia-compatible bacteria even during acclimatization operation at a relatively low ammonia-nitrogen concentration of less than 1000 mg / L, and the ammoniacal nitrogen concentration is 1000 mg / L or more. The nitrite type nitrification treatment can be stably maintained even after shifting to normal operation with high concentration. Since the concentration of ammonia nitrogen of 40 to 1000 mg / L substantially corresponds to the concentration of ammonia nitrogen at the time of acclimatization operation before shifting to normal operation, the present invention provides that the concentration of ammonia nitrogen is 1000.
When treating wastewater of mg / L or more, nitrite type nitrification treatment of high efficiency and low cost is performed, so that it is extremely effective as an operating condition particularly during acclimatization operation.

When the concentration of ammonia nitrogen in the waste water is 40 to 1000 mg / L, the pH of the waste water in the nitrification tank is
Explaining the reason why control is performed so as to be in the range of 7.5 to 9.5, ammonia that is measured as ammoniacal nitrogen includes ammonia in the form of ions and free ammonia. The substrate of ammonia-oxidizing bacteria is free ammonia (NH ₃ ) that is not in the ionic form, and the abundance ratio of ionic form of ammonia and free ammonia changes with pH. Free ammonia also inhibits the activity of nitrite-oxidizing bacteria that oxidize nitrite nitrogen to nitrate nitrogen. Therefore, if the abundance ratio of free ammonia can be intentionally increased, the bacteria compatible with high-concentration ammonia can be dominantly propagated and the nitrite type nitrification treatment can be stably performed.

From this point of view, the inventor diligently studied a technique for intentionally increasing the abundance ratio of free ammonia, and as a result, the concentration of ammonia nitrogen in the waste water was 40 to 1000 m.
When it is g / L, the pH of the wastewater in the nitrification tank is 7.5 to 9.5.
It has been found that by controlling the alkali side in the range of 1, the amount of free ammonia can be increased and the control of stopping the oxidation of ammonia nitrogen by nitrite nitrogen can be performed. In this case, if the pH of the wastewater is less than 7.5, the alkalinity is too weak and the effect of increasing the abundance ratio of free ammonia does not occur, and if the pH is more than 9.5, the alkalinity is too strong and the nitrifying bacteria become It loses activity or dies. When the ammonia nitrogen concentration of wastewater in the nitrification tank is less than 40 mg / L, p
Even if H is controlled to 7.5 to 9.5, the absolute amount of free ammonia is insufficient and the bacteria compatible with low-concentration ammonia dominate, so that the nitrite-type nitrification reaction cannot be reliably performed. On the other hand, when the concentration of ammonia nitrogen in the waste water exceeds 1000 mg / L, the absolute amount of free ammonia is sufficient, and the effect of controlling the pH to 7.5 to 9.5 becomes small. Therefore, when the pH of the wastewater in the nitrification tank is controlled to the alkaline side in the range of 7.5 to 9.5, the abundance ratio of free ammonia is effectively increased to predominantly propagate high-concentration ammonia-corresponding bacteria. The concentration of ammoniacal nitrogen that can contribute to nitric acid type nitrification reaction is 40 to 1000 mg /
It is in the range of L.

According to claim 2 of the present invention, in claim 1,
When nitrate nitrogen is detected in the type of oxidized nitrogen produced, the pH of the wastewater in the nitrification tank is adjusted to 7.5 to 9.5.
In this range, the pH value is set to be higher than the pH value when the nitrate nitrogen is detected. Therefore, even if the nitric acid nitrification treatment is started, it can be returned to the nitrite nitrification treatment again. In this case, after returning to the nitrite type nitrification treatment, even if the pH value in which nitrate nitrogen is detected is returned, it does not return to the nitric acid type nitrification treatment. Therefore, when nitrate nitrogen is detected in the types of oxidized nitrogen produced, p
It is preferable to raise H.

According to a third aspect of the present invention, a plurality of nitrification tanks are provided in series, and the pH of the wastewater in the nitrification tanks is gradually reduced from the upstream nitrification tank to the downstream nitrification tank. In addition to controlling the above, the nitrification treatment method satisfying claim 1 or 2 is performed in at least the most upstream nitrification tank, so that the total nitrification reaction rate in each nitrification tank can be increased.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the method for nitrifying waste water according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram of a nitrification treatment apparatus 10 of a first embodiment to which the wastewater nitrification treatment method of the present invention is applied.

As shown in FIG. 1, wastewater containing ammoniacal nitrogen flows into the nitrification tank 12 and is nitrified under aerobic conditions. The ammonia nitrogen concentration of the inflowing waste water is in the range of 40 to 1000 mg / L.

In the nitrification tank 12, a plurality of corrugated plate-like adhering and fixing plates 14, 14 for adhering and holding nitrifying bacteria are submerged and arranged. At the start of operation, activated sludge in wastewater is adhered and fixed to the adhering and fixing plate 14. Start acclimation by attaching and increase the concentration of nitrifying bacteria. The means for holding the nitrifying bacteria is not limited to the attachment fixing plate 14, and a carrier in which activated sludge or purely cultured nitrifying bacteria are entrapped and immobilized is used as in the second embodiment described later. You may make it throw in in the nitrification tank 12. In the case of a carrier, it is preferable to provide a carrier outflow preventing mechanism such as a screen at the outlet of the nitrification tank 12.

An air diffuser 15 connected to the blower 13 is provided at the bottom of the nitrification tank 12, and the air is aerated from the air diffuser 15 to form the inside of the nitrification tank 12 under an aerobic condition.

Above the nitrification tank 12, an alkali tank 16 for storing an alkaline liquid for adjusting the pH of the wastewater in the nitrification tank 12 is provided, and an addition amount adjusting valve 20 is provided in the middle of the addition pipe 18. A pH meter 22 for measuring the pH of wastewater is provided in the nitrification tank 12, and the addition amount of the alkaline liquid from the addition amount adjusting valve 20 is adjusted based on the pH meter 22. The pH value of the wastewater in the nitrification tank 12 is adjusted to the range of 7.5 to 9.5. For example, control is performed on the basis of pH 8.5, which is the median value of pH 7.5 to 9.5, and when the pH is lower than 8.5, the alkaline solution is added from the alkaline tank 16 to return the pH to 8.5. Control.

Further, in the nitrification tank 12, there is provided a detector 17 for detecting at least nitrate nitrogen among the oxidizing nitrogen produced by oxidizing ammonia nitrogen, and the detector 17 detects nitrate nitrogen. When detected, the pH of the wastewater in the nitrification tank 12 is temporarily increased from the pH value when nitrate nitrogen is detected in the range of 7.5 to 9.5 from the addition amount adjusting valve 20. Adjust the amount of alkaline solution added.
When controlling the pH to 8.5 with the pH meter 22, the detector 1
When nitrate nitrogen is detected in 7, the pH is temporarily controlled to pH 9.0, for example.

FIG. 2 shows a wastewater nitrification treatment method of the present invention using the nitrification treatment apparatus 10 of the first embodiment configured as described above.
00 mg / L was nitrified at pH 8.5.
In the case of the present invention, ammoniacal nitrogen (NH
_{The 4} -N) concentration decreased sharply from the start of operation to about 30 days, and thereafter, the NH ₄ -N concentration remained stable at about 100 mg / L. Along with this, nitrite nitrogen (NO ₂ -N) is generated, and the NO ₂ -N concentration increases in inverse proportion to the decrease of the NH ₄ -N concentration, and about 400 mg / It was stable at about L. Start operation 1 for nitrate nitrogen (NO ₃ -N)
No production was observed even after 50 days. This result is
The concentration of ammonia nitrogen in the wastewater is 40-1000mg /
When L, the pH of the wastewater in the nitrification tank 12 is 7.5 to 9.5.
Similar results can be obtained when control is performed within the range. This means that high-concentration ammonia-compatible bacteria predominantly propagate in the nitrification tank by carrying out the wastewater nitrification treatment method of the present invention. In particular, when nitrifying a high concentration of ammonia nitrogen having a concentration of 1000 mg / L or more in wastewater, the concentration of ammonia nitrogen in the acclimation operation is approximately 40 to 1000 mg / l.
At L, high-concentration ammonia-compatible bacteria can be dominated and proliferated, so that a transition to steady operation at a high concentration of 1000 mg / L or more can be smoothly performed.

FIG. 3 shows that the same nitrification treatment apparatus 10 is used.
Waste water having an ammoniacal nitrogen concentration of 00 mg / L has a pH of 7.
It is a comparative example in which nitrification treatment was performed at 0. In the case of the comparative example, the NH ₄ -N concentration in the treated water continues to decrease until about 45 days from the start of operation and becomes lower than that of the present invention, and the NO ₂ -N concentration increases in inverse proportion to this. . But no
_The NO ₂ -N concentration began to decrease and the NO ₃ -N concentration began to increase from the 45th day after the start of operation when the ₂ -N concentration reached its peak. And about 120 days after the start of operation, NO _2-
The N concentration and the NO ₃ -N concentration were reversed, and the nitrification reaction in the nitrification tank was almost completely transferred to the nitric acid type nitrification reaction on the 150th day after the start of operation. This means that outside the pH range of the present invention, low-concentration ammonia-corresponding bacteria and nitrite-oxidizing bacteria predominantly propagate in the nitrification tank with the passage of time after the start of operation. ing.

FIG. 4 is a block diagram of the nitrification treatment apparatus 30 of the second embodiment to which the wastewater nitrification treatment method of the present invention is applied, and shows a case where the treatment tanks are provided in multiple stages to perform multistage nitrification treatment.

As shown in FIG. 4, the wastewater containing ammoniacal nitrogen first flows into the first nitrification tank 32 to undergo the first-stage nitrification treatment under aerobic conditions, and then the second nitrification tank 34.
And is subjected to a second nitrification treatment under aerobic conditions. In this case, in the first nitrification tank 32, when the concentration of ammoniacal nitrogen in the waste water is 40 to 1000 mg / L,
A nitrification treatment method is performed in which the pH of the wastewater in the nitrification tank 32 is controlled to be in the range of 7.5 to 9.5.

Diffuser tubes 40 and 42 connected to blowers 36 and 38 are provided at the bottoms of the nitrification tanks 32 and 34, respectively, and by aerating air from the diffuser tubes 40 and 42, the nitrification tanks are respectively aerated. Aerobic conditions are formed within 32,34.

Into each of the nitrification tanks 32 and 34, a carrier 44 in which activated sludge and purely cultured nitrifying bacteria are entrapped and immobilized,
A carrier outflow prevention mechanism such as a screen (not shown) is provided at the outlets of the nitrification tanks 32 and 34.

Above the first nitrification tank 32, the first nitrification tank 3 is provided.
No. 1 in which the alkaline liquid for adjusting the pH of the wastewater in 2 was stored
An alkali tank 46 is provided, and an addition amount adjustment valve 48 is provided in the middle of the addition pipe 47. First nitrification tank 32
A pH meter 50 for measuring the pH of the wastewater in the first nitrification tank 32 is provided therein, and the addition amount of the alkaline liquid from the addition amount adjusting valve 48 is adjusted based on the pH meter 50. As a result, the pH of the wastewater in the first nitrification tank 32 is controlled to be in the range of 7.5 to 9.5. Here, the first nitrification tank 3
The pH of the wastewater in 2 will be controlled to 8.0.

A second alkali tank 52 for adding an alkaline solution and an acid tank 54 for adding an acid solution are provided above the inside of the second nitrification tank 34, and the addition amount is provided in each of the addition pipes 56, 58. Adjustment valves 60, 62 are provided. In the second nitrification tank 34, the wastewater p in the second nitrification tank 34
A pH meter 64 for measuring H is provided, and the addition amount of the alkaline liquid or the acid liquid from the addition amount adjusting valves 60 and 62 is adjusted based on the pH meter 64. As a result, the pH value of the wastewater in the second nitrification tank 34 is controlled to be lower than the pH value of the wastewater in the first nitrification tank 32. Here, the pH value of the second nitrification tank 34 is controlled to be 7.0.

Further, in the first nitrification tank 32, as in the first embodiment, there is a detector 66 for detecting at least nitrate nitrogen among the oxidizing nitrogen produced by oxidizing ammonia nitrogen. The data of the detector 66 provided is connected to the addition amount adjusting valve 48 of the first alkali tank 46.

FIG. 5 shows the results of carrying out the nitrification treatment method of waste water of the present invention using the nitrification treatment apparatus 30 of the second embodiment configured as described above. As a result, when the ammonia nitrogen concentration in the wastewater is 40 to 1000 mg / L,
It is a multi-stage system consisting of two nitrification tanks 32 and 34, and the first nitrification tank 32 is operated under the operating conditions in which high-concentration ammonia-compatible bacteria having a pH of 8.0 dominately propagate, and the second nitrification tank 34 has a low concentration of 7.0. It was possible to increase the nitrification reaction rate of the entire nitrification treatment apparatus 30 by setting the operating conditions in which the ammonia-compatible bacteria proliferate predominantly.

Looking at the behavior of the NH ₄ -N concentration, NO ₂ -N concentration and NO ₃ -N concentration in the first nitrification tank 32, as shown in FIG. Three
The NH ₄ -N concentration of the wastewater in 2 dropped sharply, and the NH ₄ -N concentration reached the minimum of about 100 mg / L at about the 50th day, and then stabilized. Along with this, NO ₂ -N is generated, and the NO ₂ -N concentration increases in inverse proportion to the decrease of the NH ₄ -N concentration. About 50 m after the start of operation, about 400 m
It was stable at about g / L. About 60 days after the start of operation, the NO ₂ -N concentration decreased at some rate, and the NO ₃ -N concentration increased accordingly, and nitric acid-type nitrification reaction was temporarily recognized. The pH value is temporarily adjusted to 8.0 by adding an alkaline solution from the first alkaline tank 46 of the first treatment tank 32.
It was possible to return to the nitrite type nitrification reaction again by increasing the temperature from 1 to 8.5. As a result, when nitrate nitrogen is detected in the type of oxidative nitrogen produced and the nitrification reaction of nitric acid type is about to be changed, the pH of the wastewater in the first nitrification tank 32 is set to 7.5 to 9. By temporarily increasing the pH value when nitrate nitrogen is detected in the range of 5, the nitrite type nitrification reaction can be restored.

[0033]

As described above, according to the nitrification treatment method of wastewater according to the present invention, in the nitrification treatment of wastewater containing a high concentration of ammonia nitrogen, the acclimation with a relatively low concentration of ammonia nitrogen is carried out. Since the nitrite type nitrification treatment can be stably performed from the time of operation to the normal operation with high concentration, a highly efficient and low cost nitrification treatment method can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a nitrification treatment apparatus according to a first embodiment to which a wastewater nitrification treatment method of the present invention is applied.

FIG. 2 shows the NH ₄ -N concentration and NO ₂ in the nitrification tank when the present invention is carried out in the nitrification treatment apparatus of the first embodiment.
-Graph showing behavior of N concentration and NO ₃ -N concentration

FIG. 3 shows the NH ₄ -N concentration and NO ₂ in the nitrification tank when a comparative example is carried out in the nitrification treatment apparatus of the first embodiment.
-Graph showing behavior of N concentration and NO ₃ -N concentration

FIG. 4 is a configuration diagram of a nitrification treatment apparatus of a second embodiment to which the wastewater nitrification treatment method of the present invention is applied.

FIG. 5 shows a first nitrification treatment apparatus according to a second embodiment.
NH ₄ -N concentration, NO ₂ -N concentration and NO ₃ in the treatment tank
-Graph showing behavior of N concentration

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Nitrification processing apparatus of 1st Embodiment, 12 ... Nitrification tank, 13 ... Blower, 14 ... Adhesion fixing plate, 15 ... Diffuser plate tube, 16 ... Alkaline tank, 17, 66 ... Detector, 18
… Addition pipe, 20… Addition amount adjusting valve, 22… pH meter,
30 ... Nitrification treatment apparatus of the second embodiment, 32 ... First nitrification tank, 34 ... Second nitrification tank, 36, 38 ... Blower, 40,
42 ... Air diffuser, 44 ... Carrier, 46 ... First alkali tank, 48, 60 ... Addition amount adjusting valve, 50, 64 ... pH
Total, 52 ... Second alkaline tank, 54 ... Acid tank

Claims (3)

[Claims] 1. A method for nitrifying wastewater, wherein wastewater containing ammoniacal nitrogen and nitrifying bacteria are contacted in a nitrification tank under aerobic conditions to produce oxidative nitrogen, the concentration of ammoniacal nitrogen in the wastewater. Is 40 to 1000 m
When it is g / L, the pH of the wastewater in the nitrification tank is 7.5.
A method for nitrifying waste water, which is controlled to fall within a range of 9.5. 2. When nitrate nitrogen is detected in the kind of generated oxidizing nitrogen, waste water p in the nitrification tank is detected.
The method for nitrifying waste water according to claim 1, wherein H is set to a value in the range of 7.5 to 9.5, which is higher than the pH value when the nitrate nitrogen is detected. 3. A plurality of nitrification tanks in which a carrier on which nitrifying bacteria are fixed are introduced, and the pH of the wastewater in the nitrification tank is gradually reduced from the upstream nitrification tank to the downstream nitrification tank. A nitrification treatment method for wastewater, characterized in that the pH of the nitrification tank is controlled, and at least the most upstream nitrification tank is subjected to the nitrification treatment method satisfying claim 1 or 2.