JPH05317880A - Treatment of waste water containing ammonia or organic nitrogen compound - Google Patents

Abstract

(57) [Summary] [Objective] Nitrogen is efficiently removed from wastewater containing ammoniacal or organic nitrogen compounds by a simple operation by one-step aerobic treatment. [Structure] Introducing an organic wastewater containing an ammoniacal or organic nitrogen compound into an organic acid fermentation tank 1 and anaerobically performing an organic acid fermentation treatment to decompose the organic nitrogen compound into ammoniacal nitrogen, and Organic matter is decomposed to produce organic acid. The organic acid fermentation liquid 4 is introduced into the denitrification tank 2, aerated so as to maintain an aerobic state with a dissolved oxygen concentration of 0.5 mg / l or less, and biologically denitrified.

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 which removes nitrogen from wastewater containing ammoniacal or organic nitrogen compounds by biological denitrification.

[0002]

2. Description of the Related Art As a method for treating wastewater containing ammoniacal or organic nitrogen compounds, there is a biological nitrification denitrification treatment method. This method uses activated sludge for COD in wastewater,
Along with decomposing the BOD component, the organic nitrogen compound is converted to ammonia nitrogen, and the ammonia nitrogen is nitrified (oxidized) into nitrite or nitrate nitrogen by nitrifying bacteria, and then denitrified (reduced) by denitrifying bacteria. Is the way.

In such a conventional biological nitrification denitrification treatment method, nitrification is performed by nitrosomonas, which oxidizes ammoniacal nitrogen to nitrite nitrogen, and nitrobacter, which oxidizes nitrite nitrogen to nitrate nitrogen. Is carried out by autotrophic bacteria (also called inorganic trophic bacteria and autotrophic bacteria), and denitrification is carried out by heterotrophic bacteria.

The conventional forms of biological nitrifying and denitrifying treatment can be roughly classified into the following three methods. 1) Method of performing nitrification and denitrification in separate tanks 2) Method of dividing one tank with a biofilter, etc., nitrification at the bottom and denitrification at the top 3) Performing in one tank A method of alternately performing aerobic treatment (nitrification) and anaerobic treatment (denitrification) by dividing them

However, in the above methods 1) and 2), it is necessary to separately provide a nitrification tank (aerobic tank) and a denitrification tank (anaerobic tank), which causes a problem that the apparatus and operation become complicated. .. In addition, there is a problem that the nitrification liquid needs to be circulated to the denitrification tank in order to use the organic substance for denitrification. Further, in the method of 3) above, only one tank is required, but since aerobic treatment and anaerobic treatment are alternately performed by dividing the time, aeration must be performed intermittently, and in order to increase the nitrogen removal rate. Has a problem that raw water can be introduced only during anaerobic treatment. As described above, the conventional biological nitrification denitrification treatment method has a problem that nitrogen cannot be removed efficiently by a simple operation.

On the other hand, Japanese Patent Laid-Open No. 61-185398 discloses that
A method is described in which an organic acid fermentation liquor is subjected to membrane separation and then the separated liquor is added to a biological nitrification denitrification treatment. However, this method is applied to the conventional biological nitrification and denitrification method consisting of a combination of aerobic treatment and anaerobic treatment, and the acid fermentation of sludge as a hydrogen donor in the denitrification process by the aerobic treatment. It is only disclosed that a liquid is used, and the wastewater is dissolved in the presence of an organic acid so that the dissolved oxygen concentration is 0.5 m.
Aeration and biological denitrification to maintain aerobic conditions below g / l are not disclosed.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide an ammoniacal or organic nitrogen compound capable of efficiently removing nitrogen with a simple operation by a single aerobic treatment. It is to propose a method for treating wastewater containing water.

[0008]

The present invention is the following method for treating wastewater containing ammoniacal or organic nitrogen compounds. (1) Waste water containing ammoniacal or organic nitrogen compounds is dissolved in the presence of an organic acid to a dissolved oxygen concentration of 0.5 mg / l.
A method for treating wastewater containing ammoniacal or organic nitrogen compounds, which comprises aerating so as to maintain the following aerobic condition and biologically denitrifying. (2) Wastewater containing ammoniacal or organic nitrogen compounds is subjected to organic acid fermentation treatment to produce organic acid, and then aerated so as to maintain an aerobic state with a dissolved oxygen concentration of 0.5 mg / l or less. , A method for treating wastewater containing ammoniacal or organic nitrogen compounds, characterized by biologically denitrifying.

The wastewater to be treated by the method of claim 1 of the present invention is a wastewater containing an ammoniacal or organic nitrogen compound, and may contain other organic substances and other components. However, in the method of claim 1, the organic nitrogen compound is decomposed into ammonia, nitrite or nitrate nitrogen by aeration and denitrified, but the organic nitrogen compound is previously removed by a method such as activated sludge treatment. After decomposition, it is preferably subjected to the treatment of the present invention. The wastewater to be treated by the method of claim 2 of the present invention is an organic wastewater containing an ammoniacal or organic nitrogen compound, and may contain other organic substances and other components.

In the method of claim 1, acetic acid is the most suitable as the kind of organic acid to be present during aeration, but other organic acids such as butyric acid and propionic acid may be used. The organic acid may be added to the waste water, may be added to the denitrification tank, and waste water containing such an organic acid may be mixed. The concentration of the organic acid in the waste water is usually up to 2%, preferably 1000 to 5000 mg / l.

Aeration is performed using an oxygen-containing gas such as air, and the dissolved oxygen concentration at that time is 0.5 mg / l or less,
Aeration is preferably performed so as to maintain the aerobic state at the lower limit of detection to 0.2 mg / l. Dissolved oxygen concentration is 0.5 mg / l
When it exceeds, the concentration of nitrous acid and nitric acid remaining in the treated water increases, and the concentration of ammonia gradually increases accordingly, and finally the nitrogen removal is substantially stopped. The lower limit of the dissolved oxygen concentration can be near the boundary where the dissolved oxygen concentration can or cannot be detected. Even at the lowest measurable concentration of dissolved oxygen concentration, for example, a concentration of about 0.07 mg / l, denitrification proceeds efficiently. In the present invention, aeration using an oxygen-containing gas, denitrification is performed by maintaining an aerobic state, the dissolved oxygen concentration may be zero due to the convenience of the operation, if it is a short time It is possible to return to normal.

In the present invention, denitrification proceeds along with the decomposition of organic acid. Therefore, the higher the organic substance (acid) load is, the better the nitrogen removal efficiency will be in the range where solid-liquid separation is not adversely affected. Generally, the BOD sludge load as a whole of the biological denitrification treatment is 0.1 kg-BOD / MLSS · day or more,
Preferably 0.1 to 0.2 kg-BOD / MLSS · d
ay is desirable. The BOD sludge load as a whole of the conventional biological nitrification denitrification treatment is usually 0.05 kg-BOD /
Since it is less than or equal to MLSS · day, the BO in the present invention
D Sludge load is quite high. Also, as other conditions,
Normal temperature is 10 to 40 ° C, preferably 15 to 35 ° C, p
H is preferably 6 to 9, more preferably 6.5 to 7.5. Aeration is preferably performed continuously.

In the case of wastewater containing no microorganisms, the target microorganisms can be grown by inoculating activated sludge or digested sludge first and culturing under the above conditions, and then the sludge is returned. Then, if aeration is performed, the process continues. By performing aeration under such conditions, denitrification can be efficiently performed aerobically in one tank. At this time, the organic nitrogen compounds in the wastewater are decomposed, the produced ammoniacal nitrogen is oxidized to nitrite or nitrate nitrogen, and is further reduced to nitrogen gas by microorganisms and biologically denitrified and removed. It In addition, BOD components such as organic acids in the wastewater are also removed at the same time.

The low dissolved oxygen concentration condition as described above in the present invention is too low as the concentration for nitrifying bacteria such as nitrosomonas and nitrosobacter which are the dominant species in the conventional nitrification reaction. Although it is inferior, in the present invention, denitrification is efficiently carried out aerobically and aerobically. In the presence of organic acids,
It is presumed that heterotrophic bacteria different from autotrophic bacteria such as nitrosomonas and nitrosobacter become the dominant species, and this organic acid heterotrophic bacterium is involved in biological denitrification.

Although the mechanism of denitrification in the present invention is not clear, the organic acid heterotrophic bacterium requires an organic acid when reducing nitrite or nitrate nitrogen, and at this time, the ammoniacal nitrogen is nitrite Or it is presumed to be nitrified to nitrate nitrogen. The denitrification reaction does not occur even if an organic substance such as glucose, protein, or peptone is used instead of the organic acid. This is presumably because the organic acid heterotrophic bacterium cannot grow as a dominant species in the presence of an organic substance other than the organic acid, and therefore nitrification does not proceed.

The method according to the second aspect of the present invention is to carry out an organic acid fermentation treatment in order to generate the organic acid in the above reaction from wastewater. The organic acid fermentation process in this process can be performed under the same conditions as the acid fermentation process in the conventional anaerobic process (methane fermentation), but it is preferable to perform it so that acetic acid is produced in a large amount.

Organic nitrogen compounds in the wastewater are decomposed into ammonia; organic acids such as formic acid, acetic acid, butyric acid, propionic acid and the like; alcohols such as ethanol and the like by the organic acid fermentation treatment. Organic acid is also formic acid,
Decomposes into organic acids such as acetic acid, butyric acid and propionic acid; alcohols such as ethanol.

The organic acid fermentation can be carried out by installing an organic acid fermentation tank, maintaining the raw water storage tank anaerobic, or lengthening the residence time of the first settling tank, usually at a temperature of 10 to 10. It is carried out at 40 ° C, preferably 15 to 35 ° C.

After the organic acid fermentation treatment to produce the organic acid, the waste water is aerated so as to maintain the aerobic state in which the dissolved oxygen concentration is 0.5 mg / l or less, as in the method of claim 1. Biologically denitrifying.

[0020]

EXAMPLES Next, examples of the present invention will be described. Figure 1
FIG. 3 is a flow chart showing a method for treating wastewater according to an embodiment of the present invention. In the figure, 1 is an organic acid fermentation tank, 2 is a denitrification tank, and 3 is a solid-liquid separation tank.

In the treatment method, first, organic raw water (wastewater) containing an ammoniacal or organic nitrogen compound is introduced into the organic acid fermentation tank 1 to anaerobically perform the organic acid fermentation treatment. In this step, the organic nitrogen compound is decomposed into ammonia nitrogen, and other organic substances are decomposed to generate an organic acid.

The acid fermentation liquor 4 obtained by the organic acid fermentation treatment is the denitrification tank 2
Then, the air 6 is diffused from the diffuser tube 5 to be aerated, and the dissolved oxygen concentration is maintained in an aerobic state of 0.5 mg / l or less. By aeration, undegraded organic nitrogen compounds are decomposed, ammoniacal nitrogen is oxidized to nitrite or nitrate nitrogen, biologically denitrified by heterotrophic bacteria, and BOD components such as other organic acids. Are also removed at the same time.
The denitrification liquid 7 subjected to the denitrification is introduced into the solid-liquid separation tank 3 and is subjected to solid-liquid separation. The separated water is discharged outside the system as treated water. Part of the precipitate is returned to the denitrification tank 2 as return sludge 8, and the rest is discharged outside the system as excess sludge 9.

The above treatment is carried out by the method of claim 2, but when the organic acid is obtained from other steps, the organic acid is added to the denitrification tank 2 by the method of claim 1 and the same as above. The aeration process may be performed on.

Example 1 The organic wastewater was treated according to the flow of FIG. That is, glucose 10000 mg / l, NH ₄ Cl 5
A waste water A containing 000 mg / l and KH ₂ PO ₄ 500 mg / l and a waste water B containing MgSO ₄ .7H ₂ O 500 mg / l and CaCl ₂ .2H ₂ O 500 mg / l were separately pumped in equal amounts. Was sent to the organic acid fermenter 1 and was used as raw water for the organic acid fermentation treatment. The treatment was carried out by controlling the residence time to be 2 days, pH 6.0, BOD sludge load of 3.5 kg-BOD / liter-tank / day, and temperature of 30 ° C.

The acid fermentation broth 4 treated in the organic acid fermentation tank 1 is introduced into the denitrification tank 2, and while continuously aerating the air 6 from the air diffuser 5, the dissolved oxygen concentration is 0.4 mg / l, the residence time is 2 days. ,
Biological denitrification was performed by controlling the pH to 6.8 and the temperature to 30 ° C. MLSS at this time is 11500 mg / l
Met. The quality of the treated water treated in this way is T
OC 47 mg / l, ammoniacal nitrogen (NH ₄ -N)
35 mg / l, nitrite nitrogen (NO ₂ -N) 17mg /
l, was nitrate nitrogen _{(NO 3 -N) 2.2mg / l} .

Comparative Example 1 The same raw water as in Example 1 was directly introduced into the denitrification tank 2 without performing the organic acid fermentation treatment, and the dissolved oxygen concentration was 0.4 mg /
It was aerated and biologically denitrified while being maintained at 1. M
As a result of keeping the LSS at 12000 mg / l, the water quality of the treated water was TOC lowered to 52 mg / l, but ammoniacal nitrogen remained at 1210 mg / l. Nitrate nitrogen was not detected, and the amount of nitrite nitrogen was very small.

Comparative Example 2 After the same treatment as in Example 1, the dissolved oxygen concentration was gradually increased. As a result, the dissolved oxygen concentration was 0.7 mg /
When the operation was continued for 1 month at 1 liter, nitrite nitrogen and nitrate nitrogen in the treated water gradually increased to 160 mg / l nitrite nitrogen and 230 mg / l nitrate nitrogen. In addition, ammoniacal nitrogen was 130 mg / l.
When the operation was continued for a further month, ammoniacal nitrogen in treated water was 850 mg / l and nitrite nitrogen was 26 mg / l.
1 and nitrate nitrogen became 77 mg / l.

Example 2 In Example 1, acetic acid was added instead of glucose, and aeration was directly carried out without performing organic acid fermentation to perform biological denitrification. As a result, the quality of treated water was
Was almost the same as.

[0029]

As described above, according to the present invention, wastewater containing an ammoniacal or organic nitrogen compound is dissolved in the presence of an organic acid or after an organic acid fermentation treatment to generate an organic acid. Aeration was performed to maintain an aerobic state with an oxygen concentration of 0.5 mg / l or less, and biological denitrification treatment was performed. Can be removed.

[Brief description of drawings]

FIG. 1 is a flowchart showing a processing method of an embodiment.

[Explanation of symbols]

 1 Organic acid fermentation tank 2 Denitrification tank 3 Solid-liquid separation tank 4 Acid fermentation liquid 5 Air diffuser 6 Air 7 Denitrification liquid 8 Return sludge 9 Excess sludge

Claims (2)

[Claims] 1. A waste water containing an ammoniacal or organic nitrogen compound is dissolved in an organic acid in the presence of a dissolved oxygen concentration of 0.5.
A method for treating wastewater containing ammoniacal or organic nitrogen compounds, which comprises aerating so as to maintain an aerobic state of not more than mg / l and performing biological denitrification. 2. A wastewater containing an ammoniacal or organic nitrogen compound is subjected to an organic acid fermentation treatment to produce an organic acid, and then the aerobic state in which the dissolved oxygen concentration is 0.5 mg / l or less is maintained. A method for treating wastewater containing ammoniacal or organic nitrogen compounds, which comprises aeration and biological denitrification.