JPH08141596A - Nitrogen treatment method for waste water containing ammonia nitrogen and oxide nitrogen - Google Patents

Abstract

PURPOSE: To stably treat waste water containing ammonia nitrogen and oxide nitrogen in such a state that the action of nitrifying bacteria is suppressed. CONSTITUTION: In a method for treating nitrogen of waste water 1 containing ammonia nitrogen and oxide nitrogen, oxide nitrogen in the waste water 1 is biologically denitrified and the waste water is subjected to ammonia stripping treatment. A known activated sludge system can be utilized in biological denitrification and a steam stripping method or an air stripping method can be utilized in ammonia stripping treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater with nitrogen, and more particularly to a method for treating nitrogen contained in wastewater which is difficult to be biologically nitrified with wastewater containing ammoniacal nitrogen and oxidized nitrogen.

[0002]

2. Description of the Related Art Nitrogen treatment of waste water has been conventionally conducted by biological nitrification denitrification method, ammonia stripping method, chlorine oxidation method,
Although the adsorption method and the like are known, the biological nitrification denitrification method is mostly used because the method used does not cause secondary pollution, is easy to maintain and manage, and the treatment cost is relatively low. However, in the biological nitrification denitrification method, ammonia is finally treated to nitrogen gas by nitrifying bacteria that nitrify to nitrate ions and denitrifying bacteria that reduce and decompose nitrate ions to nitrogen gas. By the way, since nitrifying bacteria are more susceptible to changes in environmental conditions such as pH and toxic substances than denitrifying bacteria, one of the biggest problems is that the waste water that can be treated is limited.

For this reason, conventionally, no effective treatment method has been known for wastewater containing both ammonia and nitric acid and oxidized nitrogen such as nitrous acid. For example, a high concentration of oxidized nitrogen causes wastewater to be in an acidic state, but under such conditions, neutralization with a chemical agent or JP-A-3-229695.
As disclosed in Japanese Patent Laid-Open Publication No. 2004-163, there is no choice but to adopt a method such as using a special microorganism, which is not always practical.

[0004]

DISCLOSURE OF THE INVENTION In view of the above-mentioned prior art, the present invention provides nitrogen capable of stably treating wastewater containing ammoniacal nitrogen and oxidized nitrogen even when the action of nitrifying bacteria is suppressed. It is an object to provide a processing method.

[0005]

In order to solve the above-mentioned problems, the present invention provides a method for treating nitrogen in wastewater containing ammoniacal nitrogen and oxidized nitrogen, in which the oxidized nitrogen in the wastewater is biologically treated. The nitrogen treatment method for waste water is characterized in that the waste water is subjected to ammonia stripping treatment after being denitrified.

Next, the present invention will be described in detail with reference to FIG. 1 showing a basic flow. In Figure 1, wastewater that inhibits or significantly delays the biological nitrification reaction 1
Is introduced into the biological denitrification step 2 under anaerobic conditions, and after the oxidized nitrogen in the wastewater 1 is denitrified, it is introduced into the ammonia stripping step 4. The wastewater 1 that inhibits the biological nitrification reaction is a wastewater containing a cyanide compound such as thiocyan and cyan, a heavy metal such as nickel and mercury, and a high concentration of salts. In the denitrification step 2, a known denitrification method or denitrification apparatus such as an activated sludge system, a fixed bed system or a fluidized bed system packed with a biofouling carrier or a bioentrapping carrier can be used. When the wastewater 1 does not contain sufficient organic matter (oxidized nitrogen reducing substance) for denitrification, a reducing agent such as methanol 8 may be added. For example, the amount of methanol added is preferably about 2.5 times that of oxidized nitrogen.

In the denitrification process outflow water 3 introduced into the ammonia stripping process 4, ammonia is diffused in this process 4, and the exhaust gas 6 flows into the ammonia removal process 7.
In the ammonia stripping step 4, any of known techniques such as a steam stripping method, an air stripping method, and a vacuum degassing method can be used. However, the higher the pH of the liquid in the step 4, the higher the removal rate of ammonia. When the pH in 4 is below neutral, it is advisable to add an alkaline agent. Step 4
As for the structure of (3), either a scrubber type in which the liquid in step 4 is dropped from the upper part of the tower and countercurrently contacting the gas or an aeration type in which gas is blown directly into the liquid in step 4 can be adopted. Those methods and structures are the characteristics of wastewater 1, nitrogen concentration, target removal rate,
It may be selected by conducting an experiment with a pilot plant or the like depending on conditions such as the presence or absence of excess steam. As the step 7 of removing the ammonia gas in the exhaust gas 6, known techniques such as absorption by an acid such as sulfuric acid or phosphoric acid and oxidative decomposition by a catalyst can be used. A solution obtained by absorbing ammonia in sulfuric acid or phosphoric acid becomes ammonium sulfate or phosphorus, which is effective as a fertilizer.

[0008]

The present invention does not use the action of nitrifying bacteria but treats only oxidized nitrogen with denitrifying bacteria and removes the residual ammoniacal nitrogen by stripping. The method of the present invention is suitable for treating wastewater having a high concentration of oxidized nitrogen. This is because the pH rises due to the generation of hydroxide ions by the denitrification reaction as shown in the following formula (1), but the high p
Under H condition, ammonia ions are transferred to free ammonia (ammonia gas) as shown in the formula (2), so that ammonia stripping can be easily performed economically. 2NO ₃ ⁻ + 5H ₂ → N ₂ + 2OH ⁻ + 4H ₂ O (1) NH ₄ ⁺ + OH ⁻ ⇔ NH ₃ + H ₂ O (2)

[0009]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited thereto. First Embodiment The present invention will be described based on a specific flow configuration diagram shown in FIG. In FIG. 2, the wastewater 1 is introduced into the denitrification tank 11 under anaerobic conditions together with the returned sludge 10 from the settling tank 14, and the oxidized nitrogen contained in the wastewater 1 is added from the coexisting BOD component or from the outside. It is decomposed into nitrogen gas by denitrifying bacteria using methanol 8 or the like as a reducing agent. A stirrer 16 for stirring is provided in the denitrification tank 11, and the gas 24 generated by the denitrification is introduced into the deodorizing step 17.

The denitrifying water 12 denitrified in the denitrification tank 11 undergoes oxidative decomposition of the BOD component or methanol remaining in the aeration step 13 under aerobic conditions, and solid-liquid separation is carried out in the settling tank 14 for denitrifying bacteria to return sludge. The separated water is returned to the denitrification tank 11, and the separated water is introduced into the ammonia stripping step 4 as denitrification treated water (oxidized nitrogen, BOD removed water) 15. In the ammonia stripping process 4 liquid, ammonia is diffused by the air 19 supplied through the air diffuser 18, and the exhaust gas 20 flows into the ammonia absorption tower 21. In the tower 21, the ammonia in the exhaust gas 20 is absorbed and removed by sulfuric acid, and then, in order to further remove the remaining odorous components, it is introduced into a deodorizing step 17 using activated carbon as a deodorant and is emitted to the atmosphere as a treated gas 22. . Outflow water from the ammonia stripping tank 4 is discharged as treated water 23 from which both oxidized nitrogen and ammonia nitrogen have been removed.

Next, the results of carrying out the present invention based on the flow diagram of FIG. 2 will be described. The implementation conditions are shown below. Tank volume, denitrification tank: 1.6 m ³ , aeration tank: 0.3 m ³ , precipitation tank: 0.5 m ³ , ammonia stripping tank: 4.0 m ³ , ammonia absorption tower (scrubber type): 0.2 m ³ , Deodorizing step (filling with activated carbon): 0.2 m ³ , flow rate, wastewater treatment amount: 1 m ³ / day, amount of returned sludge: 1 m ³ / day, amount of air for ammonia stripping: 3000 m ³ / day, 100% methanol injection amount: 1.3 ml / min, denitrification tank MLSS: 5200 mg / liter, the ammonia stripping tank was automatically injected with a caustic soda solution by an injection pump linked with a pH meter in order to maintain the pH at 8.9.

Table 1 shows the quality of treated water as an implementation result.

[Table 1] Unit: mg / liter except pH

[0013]

EFFECTS OF THE INVENTION According to the present invention which rationally utilizes a physicochemical method and a biological method, the following effects can be obtained in the denitrification treatment of wastewater containing a mixture of ammonia nitrogen and oxidized nitrogen. You can (1) Nitrogen can be completely removed even in wastewater that inhibits or delays the nitrification reaction by nitrifying bacteria. (2) The ammonia stripping process inflow water p is denitrified prior to the ammonia stripping process.
Since H can be increased, the amount of the pH adjusting alkali agent added can be small, and ammonia stripping can be economically performed.

[Brief description of drawings]

FIG. 1 is a basic flow configuration diagram for explaining a processing method of the present invention.

FIG. 2 is a specific flow configuration diagram used in an embodiment of the present invention.

[Explanation of symbols]

1: Waste water, 2: Denitrification process, 3: Denitrification process effluent, 4: Ammonia stripping process, 5: Treated water, 6: Exhaust gas, 7: Ammonia removal process, 8: Methanol, 10:
Return sludge, 11: denitrification tank, 12: denitrification water, 13: aeration process, 14: sedimentation tank, 15: denitrification treated water, 16: stirrer,
17: Deodorizing step, 18: Air diffuser, 19: Air, 20: Exhaust gas, 21: Ammonia absorption tower, 23: Treated water

Claims (1)

[Claims] 1. A method of treating nitrogen in wastewater containing ammoniacal nitrogen and oxidized nitrogen, wherein biological nitrogen is removed from the oxidized nitrogen in the wastewater, and then the wastewater is subjected to ammonia stripping treatment. A method for treating wastewater with nitrogen, comprising: