JP2005131451A - Nitrification method for ammonia nitrogen-containing wastewater - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which can efficiently treat nitrite-type nitrification at a low cost without requiring an extra additive and treatment process. <P>SOLUTION: A nitrification tank is divided into two tanks, a first notification tank 1 and a second nitrification tank 2. The flow direction of ammonia nitrogen-containing wastewater is alternately changed in the direction from the first nitrification tank 1 to the second nitrification tank 2 and the direction from the second nitrification tank 2 to the first nitrification tank 1 so that the concentration of free ammonia in water to be treated, in one nitrification tank on the upstream side, is made to be equal to or more than the concentration inhibiting the activities of nitrite-oxidizing bacteria and that residual ammonia nitrogen is converted into nitrous acid in the other nitrification tank on the downstream side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a biological treatment method of ammonia nitrogen, and more particularly to a method of biologically removing high concentration ammoniacal nitrogen contained in waste water.

  Ammonia nitrogen contained in sewage, manure, industrial wastewater, etc. is considered to cause a decrease in dissolved oxygen and eutrophication in closed waters such as lakes and inner bays where it is discharged. Conventionally, as a nitrogen removal technique for removing nitrogen components from these wastewaters, biological nitrification / denitrification treatment using microorganisms has been performed. Biological nitrification and denitrification treatment uses ammonia oxidizing power and nitrite oxidizing power of nitrifying bacteria, which are autotrophic bacteria, to convert ammonia nitrogen in wastewater through nitrite nitrogen in an aerobic state. Oxidizes to neutral nitrogen. Thereafter, ammonia nitrogen in the wastewater is removed by reducing nitrate nitrogen to nitrogen gas in an anaerobic state using the organic matter in the wastewater as an electron donor by the action of denitrifying bacteria which are heterotrophic bacteria.

  Biological nitrification using these microorganisms generally involves ammonia being oxidized to nitric acid through nitrite by an oxidative action jointly performed by ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. If this activity is suppressed, the oxidation rate of nitrous acid decreases, and nitrous acid accumulates in the liquid to be treated. The former is called nitrate-type nitrification, and the latter is called nitrite-type nitrification.

  The nitrification reaction and the subsequent denitrification process are as shown in the following equation.

NH ₄ ⁺ + 3 / 2O ₂ → NO ₂ ⁻ + H ₂ O + 2H ⁺ (1)
^{_{NO 2 - +1/2 · O 2 →}} NO 3 - (2)
2NO ₂ ⁻ + 6H → N ₂ + 2H ₂ O + 2OH ⁻ (3)
2NO ₃ ⁻ + 10H → N ₂ + 4H ₂ O + 2OH ⁻ (4)
As described above, the nitrification / denitrification reaction is divided into two types, nitrite-type nitrification-denitrification and nitrate-type nitrification-denitrification, and one of them proceeds with priority depending on the operating conditions. The former keeps oxidation of ammonia nitrogen (NH ₄ -N) at the stage of nitrite nitrogen (NO ₂ -N) in the formula (1), which is denitrified by denitrifying bacteria as shown in formula (3). Nitrogen. In the latter, the oxidation of ammonia nitrogen is nitrified to the stage of nitrate nitrogen (NO ₃ -N) in formula (2) via formula (1) and then denitrified as in formula (4). . When these two methods are compared, the former nitrite-type nitrification denitrification can reduce the amount of aeration during the nitrification reaction, significantly reduce the operating power cost of the blower, and reduce the amount of electrons in the denitrification process. The addition amount of organic substances such as methanol as a donor can also be reduced. Furthermore, since it is not necessary to react to nitrate nitrogen, the time required for the nitrification reaction can be shortened. Thus, although there are many advantages for nitrite type nitrification, it is not easy to stably maintain the nitrite type nitrification process. Thus, the following methods have been proposed as related to nitrite type nitrification technology.

  For example, Patent Document 1 proposes an activated sludge treatment method that prioritizes nitrite type nitrification by maintaining the dissolved oxygen concentration in the aeration tank at a predetermined concentration (conventional method 1).

  Patent Document 2 proposes an ammonia-containing wastewater treatment method in which a medium for ammonia-oxidizing bacteria and an inhibitor of nitrite-oxidizing bacteria are added to activated sludge (conventional method 2).

  Patent Document 3 proposes a biological treatment method for ammonia nitrogen in which a nitrite type nitrification reaction is carried out by maintaining the ammonia nitrogen concentration in the nitrification tank at 250 to 550 mg / L ( Conventional method 3).

  Furthermore, in Patent Document 4, the aeration air volume is adjusted so that the dissolved oxygen concentration in the nitrification tank is 1.5 mg / L or less, and the ammonia oxidizing bacteria are in the form of granules or a microbial membrane formed on the surface of the carrier. There has been proposed a nitrification method of ammonia nitrogen-containing water retained in a nitrification tank in the form of (Method 4).

  In Patent Document 5, a concentration gradient is provided so that the dissolved oxygen concentration in the nitrification tank is 6 mg / L at the maximum and 0 mg / L at the minimum, and the time during which the dissolved oxygen concentration is 0 to 0.5 mg / L is nitrified. There has been proposed a nitrification method for waste water that provides a gradient in the dissolved oxygen concentration in the nitrification tank so that the raw water retention time in the tank is 25 to 50% (conventional method 5).

Patent Document 6 proposes a biological treatment method for wastewater containing high ammonia that utilizes the difference in growth rate between ammonia-oxidizing bacteria and nitrite-oxidizing bacteria (conventional method 6).
Japanese Patent Laid-Open No. 4-122498 JP 2001-170684 A JP 2000-61494 A JP 2003-24987 A JP 2003-33787 A European Patent No. 826639

  According to the conventional method 1, it is possible to preferentially advance the ammonia oxidation reaction over the nitrite oxidation reaction that is required to have a higher oxidation level by keeping the dissolved oxygen concentration low. When the concentration is lowered, the ammonia oxidation reaction itself is delayed.

  In addition, as in the conventional method 2, the addition of an inhibitor of nitrite oxidizing bacteria requires the cost of adding the inhibitor, and if the inhibitor remains in the treated water, it may adversely affect other organisms due to its toxicity. There is.

  Further, in the conventional method 3, ammonia nitrogen tends to remain at a high concentration in the treated water, so that a subsequent treatment step is necessary.

  Furthermore, in the conventional method 4, it is necessary to familiarize and maintain the granule, which is complicated.

  In the conventional method 5, the ammonia oxidation reaction is delayed in the region where the dissolved oxygen concentration is kept low.

  Further, since the conventional method 6 is a chemostat operation, it is difficult to keep the sludge concentration high, and the treatment is unstable.

  The present invention has been made in view of such problems of the prior art, and its object is to eliminate the need for extra additives and processing steps, and to efficiently perform nitrite type nitrification at low cost. It is to provide a method that can be performed.

  In order to achieve the above object, the present invention divides the nitrification tank into two tanks, a first nitrification tank and a second nitrification tank, and determines the concentration of free ammonia in one nitrification tank located upstream from the nitrite oxidizing bacteria. The direction in which the ammonia nitrogen-containing wastewater is circulated while the remaining ammonia nitrogen is nitrified in the other nitrification tank located on the downstream side is the direction from the first nitrification tank to the second nitrification tank. Or the direction from the second nitrification tank to the first nitrification tank is alternately changed, so that the first nitrification tank and the second nitrification tank periodically have high ammonia loads. Nitrification is performed, and an environment in which the activity of nitrite-oxidizing bacteria is inhibited is formed. The nitrification tank that once became nitrite type due to high ammonia load has the property of maintaining the nitrite type for a certain period even if the ammonia concentration in the tank decreases. In the nitrification tank on the downstream side, nitric acid is not substantially produced even if the concentration of free ammonia falls below the concentration that inhibits the activity of nitrite oxidizing bacteria. For the above reasons, a high nitritation rate can be realized without leaving ammonia nitrogen in the treated water at a high concentration. Incidentally, from the above principle, it is preferable that the sludge in the downstream nitrification tank is in a state in which the activity of the nitrite oxidizing bacteria is suppressed at the start of operation.

The present invention has the following effects.
(1) According to the first aspect of the present invention, the activity of nitrite-oxidizing bacteria is always maintained in the nitrification tank from the upstream side to the downstream side without requiring extra additives and processing steps and without increasing the cost. Is suppressed, and the nitrite type nitrification process can be carried out reliably.
(2) According to the second and third aspects of the invention, more preferable operating conditions for nitrite nitrification can be provided.
(3) According to the invention described in claim 4, the amount of ammonia-oxidizing bacteria in the first nitrification tank and the second nitrification tank can be maintained at a high concentration, and it is possible to cope with load fluctuations and high loads of raw water. .
(4) According to the invention described in claim 5, ammonia nitrogen in the raw water is rapidly oxidized to nitrous acid.
(6) According to the invention described in claim 6, it is possible to accurately detect the change timing of the flow direction of the ammoniacal nitrogen-containing wastewater, and the optimum operation method of the process according to claim 1 is efficiently executed. be able to.

  Since the growth of nitrite-oxidizing bacteria is inhibited when the concentration of free ammonia increases, ammonia nitrogen is stopped by the oxidation of nitrite nitrogen by ammonia-oxidizing bacteria. For this purpose, the concentration of free ammonia in the nitrification tank located on the upstream side is preferably 10 mg / L or more, and more preferably 20 mg / L or more.

  Moreover, in order to implement | achieve the more preferable operating condition of nitrite type nitrification, it is preferable that the pH in a 1st nitrification tank and a 2nd nitrification tank is 7-9, and temperature is 25-40 degreeC, More preferably, the pH is 7.5 to 9, and the temperature is 30 to 40 ° C.

In this specification, “ammonia nitrogen” refers to the sum of “NH ₄ ⁺ ” and “NH ₃ ” represented by the following formula, and “free ammonia” refers to “NH ₃ ” represented by the following formula.

遊離アンモニアの濃度はアンモニア性窒素濃度を測定することにより、下記式により計算した。

The concentration of free ammonia was calculated by the following equation by measuring the ammoniacal nitrogen concentration.

第一硝化槽および第二硝化槽がアンモニア酸化細菌の担持担体を備えていることが好ましい。第一硝化槽および第二硝化槽のアンモニア酸化細菌の菌体量を高濃度に保持し、原水の負荷変動や高負荷に対応することができるからである。担体の材質としては、ポリプロピレン、ポリウレタン、セルロース、ポリエステル、ポリビニルアルコール、ポリエチレングリコール系樹脂、アクリル系樹脂、アクリルアミド系樹脂、オレフィン系樹脂、スチレン系樹脂、ポリエーテル等の有機高分子化合物からなる、内部に網目構造を有するプラスチック担体、スポンジ担体、繊維状担体、不織布、ゲル担体、その他に多孔性無機高分子化合物、活性炭などが挙げられる。担体の比重は０．８〜１．５、細孔の孔径は１０〜１０００μｍ、空隙率は３０〜９０％、比表面積は５００〜１００００ｍ²／ｍ³、粒径は１〜２０mmのものが好ましい。

The first nitrification tank and the second nitrification tank are preferably provided with a carrier for supporting ammonia-oxidizing bacteria. This is because the amount of the ammonia-oxidizing bacteria in the first nitrification tank and the second nitrification tank can be maintained at a high concentration, and it is possible to cope with load fluctuations and high loads of raw water. The material of the carrier is made of an organic polymer compound such as polypropylene, polyurethane, cellulose, polyester, polyvinyl alcohol, polyethylene glycol resin, acrylic resin, acrylamide resin, olefin resin, styrene resin, or polyether. In addition, a plastic carrier having a network structure, a sponge carrier, a fibrous carrier, a nonwoven fabric, a gel carrier, a porous inorganic polymer compound, activated carbon, and the like can be given. The specific gravity of the support is preferably 0.8 to 1.5, the pore diameter is 10 to 1000 μm, the porosity is 30 to 90%, the specific surface area is 500 to 10,000 m ² / m ³ , and the particle diameter is preferably 1 to 20 mm. .

  The dissolved oxygen concentration in the first nitrification tank and the second nitrification tank is preferably 2 mg / L or more. This is because ammonia nitrogen in the raw water is rapidly oxidized to nitrous acid. For that purpose, the dissolved oxygen concentration is more preferably 4 mg / L or more.

  The concentration of nitric acid in the nitrification tank located downstream is measured, and the direction in which the ammonia-containing nitrogen-containing waste water is circulated is determined from the first nitrification tank toward the second nitrification tank or the second, depending on the measured concentration of nitric acid. It is preferable to alternately change any of the directions from the nitrification tank toward the first nitrification tank. This is due to the following reason.

  Since the growth of nitrite oxidizing bacteria is inhibited by high ammonia nitrogen load, nitrite type nitrification can be preferentially advanced if the nitrification tank is made high ammonia nitrogen load. However, when the ammonia concentration of the water to be treated in the nitrification tank is high, the water to be treated discharged from the nitrification tank contains a high concentration of ammoniacal nitrogen. Since ammonia nitrogen is discharged as it is, a separate ammonia removal step is required.

  Therefore, according to the present invention, the nitrification tank is divided into two tanks, a first nitrification tank and a second nitrification tank, and the free ammonia concentration in the nitrification tank located upstream is a concentration that inhibits the activity of nitrite oxidizing bacteria. By doing so, nitrification of ammonia nitrogen is prevented in the upstream nitrification tank, nitric acid is not substantially generated in the upstream nitrification tank, and a part of the ammonia nitrogen is converted to nitrous acid, and the downstream side Ammonia nitrogen remaining in the nitrification tank is nitrified.

  In addition, the direction in which the ammonia-containing nitrogen-containing wastewater is circulated is alternately changed to either the direction from the first nitrification tank to the second nitrification tank or the direction from the second nitrification tank to the first nitrification tank. Therefore, nitrification with a high ammonia load is periodically performed in the first nitrification tank and the second nitrification tank, and the nitrite-oxidizing bacteria always lose activity in both tanks. Therefore, even if the free ammonia concentration in the downstream nitrification tank is below the concentration that inhibits the growth of nitrite-oxidizing bacteria, the nitrite-oxidizing bacteria do not immediately recover their activity in the downstream nitrification tank. Since nitrite production by bacteria occurs preferentially, nitric acid production is substantially less likely to occur.

  In this way, in the upstream nitrification tank, a part of the ammonia nitrogen is converted to nitrous acid, and in the downstream nitrification tank, the remaining ammonia nitrogen is converted to nitrous acid, hardly generating nitric acid. The nitric acid type nitrification process can be carried out reliably and efficiently.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram of an apparatus suitable for carrying out the nitrification method for ammonia nitrogen-containing waste water of the present invention.

  In FIG. 1, 1 is a 1st nitrification tank, 2 is a 2nd nitrification tank, and switches the direction which distribute | circulates waste_water | drain like FIG.1 (a) (b) periodically. In FIG. 1A, since the first nitrification tank 1 is located on the upstream side and the second nitrification tank 2 is located on the downstream side, free ammonia in the water to be treated in the first nitrification tank 1 located on the upstream side. The concentration is made higher than the concentration that inhibits the activity of nitrite-oxidizing bacteria, and residual ammoniacal nitrogen is nitrified in the second nitrification tank 2 located on the downstream side.

  In FIG. 1 (a), for example, the operating condition of the first nitrification tank 1 is that the concentration of free ammonia in the tank is 20 mg / liter that inhibits the activity of nitrite oxidizing bacteria, and the pH of the water to be treated is 8.1. By setting the temperature of the water to be treated to 35 ° C. and the dissolved oxygen concentration to 5 mg / liter, the ammonia-containing nitrogen-containing wastewater flowing into the first nitrification tank 1 Is inhibited, and a part of ammonia nitrogen is converted into nitrite by the carrier 3 holding ammonia oxidizing bacteria.

  Next, the water to be treated flows into the second nitrification tank 2. For example, the operating condition of the second nitrification tank 2 is that the pH in the tank is 8.1, the temperature is 35 ° C., and the dissolved oxygen concentration is 5 mg / liter. It is made nitrite by oxidizing bacteria 3.

  The above-mentioned free ammonia concentration, pH, water temperature and dissolved oxygen concentration can of course be selected from numerical values other than those described above, and the nitrite type nitrification process is performed according to the properties of the water to be treated. It is possible to select the necessary operating conditions.

  Although the concentration of ammoniacal nitrogen in the second nitrification tank 2 on the downstream side is low, the nitrite-oxidizing bacteria have lost activity due to the periodic switching operation in the flow direction of the waste water. Therefore, even if the concentration of free ammonia in the second nitrification tank 2 on the downstream side is a concentration that inhibits the growth of nitrite-oxidizing bacteria, nitric acid is hardly generated in the second nitrification tank 2 on the downstream side.

  However, as the time passes, the nitrite-oxidizing bacteria regain activity in the downstream second nitrification tank 2 where the ammonia concentration is low, so that nitric acid is generated. As shown in FIG. If the flow direction of the ammonia nitrogen-containing waste water is changed from the second nitrification tank 2 to the first nitrification tank 1, the second nitrification tank 2 is located on the upstream side, and the first nitrification tank 1 is on the downstream side. Will be located.

  For example, the operating conditions of the upstream second nitrification tank 2 are: the concentration of free ammonia in the tank is 20 mg / liter which inhibits the growth of nitrite-oxidizing bacteria, the pH is 8.1, the temperature is 35 ° C., and dissolved. The operating condition of the first nitrification tank 1 on the downstream side is 5 mg / liter, and the pH in the tank is 8.1, the temperature is 35 ° C., and the dissolved oxygen concentration is 5 mg / liter. In the second nitrification tank 2, the growth of nitrite oxidizing bacteria is inhibited in the second nitrification tank 2, and a part of the ammonia nitrogen is converted to nitrite by the carrier 3 holding the ammonia oxidizing bacteria. Is done.

  In the first nitrification tank 1 on the downstream side, residual ammonia nitrogen in the water to be treated is converted into nitrous acid by the ammonia oxidizing bacteria 3. Further, in the first nitrification tank 1 on the downstream side, the activity of the nitrite oxidizing bacteria is inhibited due to the above high ammonia concentration operation, and the production of nitric acid hardly occurs for a certain period.

  The operating conditions of the nitrification tank in this case are also numerical values other than the above-mentioned free ammonia concentration, pH, water temperature and dissolved oxygen concentration according to the properties of the water to be treated in order to execute the nitrite type nitrification process. Of course you can choose.

  In this way, the nitrification tank is divided into two tanks, the first nitrification tank 1 and the second nitrification tank 2, and the concentration of free ammonia in one nitrification tank located upstream is the concentration that inhibits the activity of nitrite oxidizing bacteria. The direction in which the ammonia nitrogen-containing wastewater is circulated while the residual ammonia nitrogen is converted to nitrous acid in the other nitrification tank located on the downstream side is the direction from the first nitrification tank 1 to the second nitrification tank 2 By alternately changing one of the directions from the two nitrification tanks 2 to the first nitrification tank 1, the activity of the nitrite oxidizing bacteria is inhibited in any one of the nitrification tanks located upstream, and the downstream The nitric acid concentration in one of the nitrification tanks located on the side is kept below a certain level. In this manner, nitric acid is hardly generated in both the upstream and downstream nitrification tanks, and the nitrite type nitrification process can be executed reliably and efficiently.

  The change timing of the flow direction of the ammonia-containing nitrogen-containing wastewater can be, for example, a stage where the nitrate nitrogen concentration in the nitrification tank located on the downstream side exceeds 20 mg / liter.

  FIG. 2 is a schematic layout showing an example in which a nitrification device and a denitrification device are combined. In FIG. 2 (a), the ammonia-containing nitrogen-containing wastewater is passed from the path 4 to the denitrification tank 5 so that the first nitrification tank 1 is on the upstream side and the second nitrification tank 2 is on the downstream side. In the second nitrification tank 2, a part of the water to be treated in which most of the nitrogenous nitrogen is nitritized is sent to the denitrification tank 5 via the path 6 and denitrified. The remaining treated water is discharged from the path 8.

  Then, when the concentration of nitric acid in the second nitrification tank 2 on the downstream side becomes equal to or higher than a certain concentration after the lapse of a certain period of time, the ammonia-containing nitrogen-containing waste water flows upstream from the second nitrification tank 2 as shown in FIG. The flow direction is changed so that the first nitrification tank 1 is on the downstream side. In FIG. 2 (b), in the first nitrification tank 1 located on the downstream side, a part of the water to be treated in which most of the ammonia nitrogen has been nitritized is sent to the denitrification tank 5 via the route 9, and denitrified. Is done. The remaining treated water is discharged from the path 11.

  FIG. 3 is a schematic layout diagram showing another example in which a nitrification apparatus and a denitrification apparatus are combined. FIG. 2 is a diagram showing an example in which the nitrification device and the denitrification device are separately installed, while FIG. 3 is a diagram showing an example in which the nitrification device and the denitrification device are arranged close to each other in the same tank. In FIG. 3A, the ammonia nitrogen-containing wastewater that has flowed into the denitrification tank 5 from the path 12 passes from the first nitrification tank 1 on the upstream side to the second nitrification tank 2 on the downstream side, and a part of the wastewater is denitrification tank 5. Will be returned. The remaining waste water is discharged from the path 13.

  Then, after a certain period of time, when the concentration of nitric acid in the second nitrification tank 2 on the downstream side becomes a certain concentration or more, as shown in FIG. The flow direction is changed so that the first nitrification tank 1 is on the downstream side. In FIG. 3B, the ammonia nitrogen-containing wastewater that has flowed into the denitrification tank 5 from the path 12 passes from the second nitrification tank 2 on the upstream side to the second nitrification tank 1 on the downstream side, and a part of the wastewater is denitrification tank 5. Will be returned. The remainder of the waste water is discharged from the path 14.

Next, FIG. 4 shows the relationship between the “free ammonia concentration” and the “NO ₃ —N and NO _X —N concentration” in the ammoniacal nitrogen-containing waste water. “NO _X -N” means the sum of “NO ₃ -N” and “NO ₂ -N”. In FIG. 4, the symbol “◯” indicates “NO ₃ -N”, and the symbol “ “ _X ” indicates “NO _X -N”. As is apparent from FIG. 4, the concentration of NO ₃ —N decreases as the free ammonia concentration increases, and the situation where the activity of nitrite oxidizing bacteria is inhibited in the nitrification tank can be read. That is, the activity of nitrite oxidizing bacteria is greatly reduced by setting the free ammonia concentration to 20 mg / liter, and the activity of nitrite oxidizing bacteria is almost completely stopped by setting the free ammonia concentration to 40 mg / liter or more. I understand that However, if the free ammonia concentration in the nitrification tank is kept higher than necessary, ammonia nitrogen may remain without being nitrified in the downstream nitrification tank. It is preferable to set the concentration of free ammonia in the upstream nitrification tank so as not to exceed the nitrification capacity of the downstream nitrification tank.

  Next, the water quality obtained when the ammonia nitrogen-containing wastewater is nitrified by the method of the present invention will be described.

  The schematic configuration of an apparatus to which the method of the present invention is applied is as shown in FIG. 1, and the first nitrification tank 1 and the second nitrification tank 2 are each composed of a 4-liter square tank made of transparent vinyl chloride resin.

Then, as shown in FIG. 5, artificial ammonia nitrogen-containing waste water having an ammonia nitrogen (NH ₄ —N) concentration of 870 mg / liter is transferred from the first nitrification tank 1 to the second nitrification tank 2 at 6 liter / liter. I went through the day. At that time, the inside of the first nitrification tank and the second nitrification tank was set to pH 8.1, the temperature was set to 35 ° C., and the dissolved oxygen concentration was set to 5 mg / liter. Reference numeral 15 denotes a bacteria-supporting carrier made of a nonwoven fabric. The NH ₄ -N concentration in the first nitrification tank 1 on the second day after the start of the introduction of the ammonia-containing wastewater is 260 mg / liter, the NO ₂ -N concentration is 610 mg / liter, and the NO ₃ -N concentration is 2.6 mg / liter. The NH ₄ —N concentration in the second nitrification tank 2 was 7.8 mg / liter, the NO ₂ —N concentration was 850 mg / liter, and the NO ₃ —N concentration was 9.4 mg / liter. The NH ₄ -N concentration in the first nitrification tank 1 is kept around 200 mg / liter, and nitric acid is hardly produced in the first nitrification tank, but the NO ₃ -N concentration in the second nitrification tank is time-lapsed. One month after the start of the introduction of the ammoniacal nitrogen-containing wastewater, the NO ₃ —N concentration became 21 mg / liter. Therefore, in order to prevent further recovery of the activity of the nitrite oxidizing bacteria in the second nitrification tank, the flow direction of the ammoniacal nitrogen-containing wastewater was changed from the second nitrification tank 2 to the first nitrification tank 1. . At that time, the inside of the first nitrification tank and the second nitrification tank was set to pH 8.1, the temperature was set to 35 ° C., and the dissolved oxygen concentration was set to 5 mg / liter. As a result, the NH ₄ -N concentration in the second nitrification tank 2 on the second day after changing the flow direction is 400 mg / liter, the NO ₂ -N concentration is 460 mg / liter, and the NO ₃ -N concentration is 8.4 mg / liter. In the first nitrification tank 1, the NH ₄ —N concentration was 15 mg / liter, the NO ₂ —N concentration was 840 mg / liter, and the NO ₃ —N concentration was 12 mg / liter.

  Thus, by changing the flow direction of the ammoniacal nitrogen-containing wastewater, it was possible to suppress the generation of nitric acid and preferentially generate nitrous acid.

  INDUSTRIAL APPLICABILITY The present invention can be applied to an apparatus that efficiently nitrites ammoniated nitrogen-containing wastewater with little nitrification.

It is a conceptual diagram of the apparatus suitable for implementing the nitrification method of the ammonia nitrogen containing waste_water | drain of this invention. 1 is a schematic layout view of an embodiment of an apparatus suitable for carrying out the nitrification method for ammonia nitrogen-containing waste water and the subsequent denitrification method of the present invention. FIG. It is a schematic arrangement view of another embodiment of an apparatus suitable for carrying out the nitrification method for ammonia nitrogen-containing waste water and the subsequent denitrification method of the present invention. It is a diagram showing the relationship between the "free ammonia concentration" of ammonium nitrogen-containing wastewater as "NO ₃ -N and NO _X -N concentration". It is a schematic block diagram of the further another Example of the apparatus suitable for implementing the nitrification method of ammonia nitrogen containing waste_water | drain of this invention.

Explanation of symbols

1 First nitrification tank 2 Second nitrification tank 5 Denitrification tank 15 Bacterial carrier

Claims (6)

  A method of supplying wastewater containing ammonia nitrogen to a nitrification tank and aeration in the presence of ammonia-oxidizing bacteria to nitrify the nitrification tank into two tanks, a first nitrification tank and a second nitrification tank The concentration of free ammonia in one nitrification tank located upstream is higher than the concentration that inhibits the activity of nitrite-oxidizing bacteria, while the remaining ammonia nitrogen is nitrified in the other nitrification tank located downstream, The direction in which the nitrogen-containing wastewater is circulated is characterized by alternately changing either the direction from the first nitrification tank to the second nitrification tank or the direction from the second nitrification tank to the first nitrification tank. A method for nitrifying wastewater containing ammonia nitrogen. The method for nitrifying ammonia-containing nitrogen-containing wastewater according to claim 1, wherein the concentration of free ammonia in the nitrification tank located on the upstream side is 10 mg / L or more. The method for nitrifying ammonia nitrogen-containing wastewater according to claim 1 or 2, wherein the pH in the first nitrification tank and the second nitrification tank is 7 or more and the temperature is 25 ° C or more. The method for nitrifying ammonia-containing nitrogen-containing wastewater according to claim 1, 2 or 3, wherein the first nitrification tank and the second nitrification tank are provided with a carrier for holding cells. The method for nitrifying ammonia nitrogen-containing wastewater according to claim 1, wherein the dissolved oxygen concentration in the first nitrification tank and the second nitrification tank is 2 mg / L or more. The nitric acid concentration in the nitrification tank located downstream is measured, and the direction in which the ammoniacal nitrogen-containing wastewater is circulated is changed according to the measured nitric acid concentration. The nitrification method of the ammonia nitrogen containing waste_water | drain of description.

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