JPH08141552A - Method for treating nitrogen in wastewater - Google Patents

Abstract

PURPOSE: To provide a method for treating nitrogen in wastewater which removes ammonia having poison contained in wastewater without retarding biological nitration and conducts stable biological nitration-denitrification. CONSTITUTION: In a method for treating nitrogen in wastewater 1 containing ammonia-type nitrogen and oxidized nitrogen, after the wastewater 1 being treated 2 physicochemically by ammonia stripping, the residual oxidized nitrogen is denitrified 6 biologically. A steam stripping method, an air stripping method, etc., are applicable to the ammonia stripping treatment, and a known activated sludge method, etc., can be used optionally in the biological denitrification.

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.

[0003]

DISCLOSURE OF THE INVENTION The present invention is a nitrogen of wastewater capable of performing stable biological nitrification denitrification by removing toxic ammonia contained in the wastewater without inhibiting biological nitrification. It is an object to provide a processing method.

[0004]

In order to solve the above-mentioned problems, in the present invention, in a method for treating nitrogen of wastewater containing ammoniacal nitrogen and oxidized nitrogen, the wastewater is physicochemically stripped with ammonia. After the treatment, the residual oxidized nitrogen is biologically denitrified, which is a method for treating wastewater with nitrogen.

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 ammonia stripping step 2 to dissipate ammonia. The exhaust gas 3 containing the diffused ammonia flows into the ammonia removing 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 ammonia stripping step 2, any of known techniques such as a steam stripping method, an air stripping method, and a vacuum degassing method can be used, but the higher the pH of the liquid in the step 2, the higher the removal rate of ammonia. It is advisable to add an alkaline agent when the pH in step 2 is near neutral or lower. The structure of the step 2 may be either a scrubber type in which the liquid in the step 2 is dropped from the upper part of the column to bring the gas into countercurrent contact, or an aeration type in which the gas is directly blown into the liquid in the step 2. Wastewater 1
It may be selected by conducting an experiment with a pilot plant or the like depending on the conditions such as the pH and other properties, the nitrogen concentration, the target removal rate, the presence or absence of excess steam, and the like.

Oxidized nitrogen remaining in the effluent 5 from the ammonia stripping step 2 is denitrified in a biological denitrification step 6 under anaerobic conditions and then discharged as treated water 7. It In the denitrification step 6, a known denitrification method or denitrification apparatus such as an activated sludge system, a fixed bed system or a fluidized bed system filled with a biologically-adhesive carrier or an entrapping biological carrier can be used. When the ammonia-removed water does not contain sufficient organic matter (oxidized nitrogen reducing substance) for denitrification, it is advisable to add a reducing agent such as methanol 8. For example, the amount of methanol added is preferably about 2.5 times that of oxidized nitrogen. In the step 4 of removing the ammonia gas in the exhaust gas 3 from the ammonia stripping step 2, 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.

[0007]

The method of the present invention is suitable for treating wastewater having a high ammonia concentration and a high pH. Under high pH conditions, ammonia stripping can be easily performed without adding an alkaline agent, which is economical, and by removing high-concentration ammonia, the biological step of the next step can be performed. It can be expected to alleviate the inhibition of the denitrification reaction by free ammonia in the denitrification process. Since ammonia is an alkaline substance, the ammonia stripping-treated water has a lower pH as well as a lower ammonia concentration. Therefore, as shown in the following equation, the ammonia-removed water has a free ammonia concentration significantly lower than that of the waste water, so that a smooth biological reaction can be expected as described above. NH ₄ ⁺ + OH ^- ⇔ NH ₃ ↑ + H ₂ O

[0008]

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 the flow configuration diagram shown in FIG.
In FIG. 2, wastewater 1 is an ammonia stripping tank 2
Ammonia is diffused by the air 11 that is introduced into the air and is supplied through the air diffuser 10. The exhaust gas 3 containing the diffused ammonia flows into the ammonia absorption tower 4. In the tower 4, the ammonia in the exhaust gas 3 is absorbed and removed by sulfuric acid, and then introduced into a deodorizing step 12 using activated carbon as a deodorant in order to further remove residual odorous components, and is emitted into the atmosphere as a treated gas 13.

Outflow water 5 from the ammonia stripping tank 2
Is introduced into the denitrification tank 15 under anaerobic conditions together with the sludge 14 returned from the settling tank 18, and the oxidized nitrogen contained in the outflow water 5 is the coexisting BOD component or the methanol 8 added from the outside. Is used as a reducing agent to be decomposed into nitrogen gas by denitrifying bacteria. In the denitrification treated water 16 from the denitrification tank 15, BOD components or methanol remaining in the aeration step 17 are oxidatively decomposed under aerobic conditions,
Solid-liquid separation is carried out in the settling tank 18, the separated solid denitrifying bacteria are returned to the denitrifying tank 15 as return sludge 14, and the separated water is discharged as treated water 7. A stirrer 19 for stirring is provided in the denitrification tank 15, and the gas 20 generated by the denitrification is introduced into the deodorizing step 12.

Next, the results of carrying out the present invention based on the flow of FIG. 2 will be described. The implementation conditions are shown below. Tank volume, ammonia stripping tank: 4.0 m ³ , denitrification tank: 1.6 m ³ , aeration tank: 0.3 m ³ , precipitation tank: 0.5 m ³ , ammonia absorption tower (scrubber type): 0.2 m ³ , Deodorizing step (filling with activated carbon): 0.2 m ³ ,

Flow rate, amount of treated wastewater: 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: 0.5 ml / min, denitrification tank MLSS : 5000 mg / liter, the ammonia-stripping tank was automatically injected with caustic soda solution by an injection pump linked with a pH meter in order to maintain the pH at 8.9. Sulfuric acid was added to the denitrification tank to maintain the pH at 8.5.

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 concentration of free ammonia harmful to denitrifying bacteria can be reduced by removing ammonia prior to denitrification.

[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: Ammonia stripping step, 3: Exhaust gas, 4: Ammonia removal step, 5: Outflow water, 6: Denitrification step, 7: Treated water, 8: Methanol, 10: Air diffuser, 1
1: Air, 12: Deodorizing step, 13: Treated gas, 14: Return sludge, 15: Denitrifying tank, 16: Denitrifying treated water, 17: Aeration step, 18: Settling tank, 19: Stirrer, 20: Denitrifying gas

Claims (1)

[Claims] 1. A method for treating nitrogen of wastewater containing ammoniacal nitrogen and oxidized nitrogen, wherein the wastewater is physicochemically subjected to ammonia stripping treatment, and then residual oxidized nitrogen is biologically removed. A method for treating wastewater with nitrogen, characterized by nitrifying.