JPH05228485A - Nitration liquid circulation control of aerobic anaerobic active sludge method - Google Patents

Abstract

PURPOSE:To accelerate a denitrification reaction speed, and at the same time, optimize nitration liquid circulation control in a nitration liquid circulation method by which, to return a nitration liquid in a last stage aerobic tank used in an aerobic/anaerobic active sludge process to a front stage aerobic tank for circulatory denitrification. CONSTITUTION:A circulation control valve 7b is provided in the last stage tank of an aerobic tank 2, and a circulation control valve 7b and a respiration speed gauge 8 are installed in the aerobic tank 2 one stage before or after the last stage tank. A nitration liquid circulation control part 9 interprets the degree of nitration in accordance with the measurement value of the respiration speed gauge 8. For example, if the nitration is sufficient, the part 9 closes the valve 7a and, at the same time, opens the valve 7b. On the other hand, if the nitration is insufficient, the part 9 closes the valve 7b, and at the same time, opens the valve 7a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrification solution circulation control method in a denitrification reaction of an anaerobic aerobic activated sludge method.

[0002]

2. Description of the Related Art Removal of nutrient salts such as nitrogen and phosphorus is an important problem for sewage treatment plants that discharge treated water into closed water areas such as inner bays and lakes. Most of the current sewage treatment plants use a treatment method called activated sludge method. However, although this method is excellent in removing organic pollutants, it has a drawback that it can hardly remove nutrient salts. Therefore, from the front of the aeration tank, which is the main reaction tank of the activated sludge method,
The so-called anaerobic aerobic activated sludge method, in which the aeration of a reaction tank having a volume of about ⅓ to ½ is stopped to make an anaerobic state, is attracting attention because it is effective in removing nutrients.

Nitrogen components in waste water are generally oxidized to nitric nitrogen by nitrifying bacteria in activated sludge under aerobic conditions in which oxygen is dissolved. In the standard activated sludge method, only a small amount of inflowing nitrogen is removed by bacterial growth, and most of it is oxidized to nitrate nitrogen as described above, or is released in the form of ammonia nitrogen by suppressing the oxidation. It Therefore, the removal of nitrogen is at most 20 to 30%.

To biologically remove this nitrogen, FIG.
The aeration tank of the standard activated sludge aeration tank is stopped in the anaerobic state as shown in the above, and the nitrate nitrogen generated in the latter stage is returned to this anaerobic tank, where it is contacted with the organic matter in the inflowing wastewater to denitrify. A so-called nitrification solution circulation method is often adopted. In FIG. 2, 1 is an anaerobic tank, 2 is an aerobic tank, 3 is a final settling tank, 4 is return sludge, 5 is excess sludge, and 6 is a circulating nitrification solution.

Nitrification is an autotrophic bacterium Nitro
somonas turns ammonia into nitrous acid, Nitrob
It is a reaction in which acter oxidizes nitrous acid to nitric acid, and can be expressed by the following equations (1) and (2). NH ₄ ⁺ +1.5 O ₂ → NO ₂ ⁻ + H ₂ O + 2H ⁺ …… (1) NO ₂ ⁻ +0.5 O ₂ → NO ₃ ⁻ …… (2) Moreover, the denitrification reaction is nitrite or nitric acid by denitrifying bacteria. Can be expressed by the following equations (3) and (4). ^{_{2NO 3 - + 2H 2 → 2NO}} 2 - + 2H 2 O ...... (3) 2NO 2 - + 3H 2 → N 2 ↑ + 2OH - + 2H 2 O ...... (4) (3), (4) H 2 of formula in the waste water It is supplied by the decomposition of organic substances.

[0006]

THE INVENTION Problems to be Solved] However denitrification anaerobic aerobic activated sludge method which is currently done nitrification of NO ₃ ^- to mold by increasing the air volume is the reaction time or take longer for a method that performs the There was a problem that I had to do it. Theoretically, if the above nitrification reaction is stopped by the formula (1) and the denitrification reaction is carried out only by the formula (4), the reaction time will be shortened,
The amount of air blow can also be reduced. However, since nitrous acid exists in the outflow water from the aerobic tank, there arises a problem that the environment of the discharge destination is deteriorated. In addition, it is difficult to set conditions for stable generation of nitrous acid due to changes in inflow water quality and inflow.

The present invention has been made in view of the above points, and an object thereof is to provide a nitrification solution circulation control method in an anaerobic aerobic activated sludge method which can accelerate the denitrification reaction rate and can perform optimal nitrification solution circulation. To provide.

[0008]

According to the present invention, of the aeration tanks divided into a plurality of tanks of the anaerobic aerobic activated sludge method, the anterior tank is placed in an anaerobic state and the nitrification solution in the final tank is placed in the anaerobic anterior tank. In the nitrification solution circulation method, in which the nitrification solution is returned to the organic substance of the inflowing water and is denitrified, the first extraction port for returning the nitrification solution from the final aerobic tank to the previous anaerobic tank, and the final nitrification solution 2nd to return from the aerobic tank of the previous stage to the anaerobic tank of the previous stage
And a respiration velocimeter for a process installed in the aerobic tank several stages before the last stage, the first retrieving port, the first retrieving port according to the measurement value of the respiration rate meter, Two
It is characterized by controlling the circulation amount of the nitrification liquid that is returned from the outlet of the to the anaerobic tank in the previous stage.

[0009]

[Function] When the nitrification is performed sufficiently, the nitrogen in the vicinity of the second outlet (aerobic tank several stages before the final stage) becomes a mixture of nitrous acid and nitric acid, and the first outlet (final stage Nitrogen in the vicinity of the aerobic tank) is in the form of nitric acid. The degree of such nitrification is measured by a respiration rate meter, and the circulation amount of nitrification liquid is controlled according to the measured value.

That is, when nitrification is sufficiently performed and ammonia nitrogen is almost removed at the second outlet, the circulation from the first outlet is stopped and the second outlet is stopped.
Circulate only from the outlet. On the other hand, when nitrification is insufficient, the circulation from the second outlet is stopped, and the circulation is performed only from the first outlet.

By such circulation control, the denitrification rate can be increased, and an unstable anaerobic state due to excessive nitrification can be prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1, the same parts as those in FIG. 2 are designated by the same reference numerals. The conventional method was to circulate the nitrification solution from the last stage of the aerobic tank as shown in FIG. 2, but in the present invention, in addition to this, a circulation outlet is provided from the upstream side of the first or second stage.

That is, a circulation control valve 7a is provided at the final stage of the aerobic tank 2, and the aerobic tank 2 is located one stage upstream from the final stage.
A circulation control valve 7b is provided in the. Further, in the aerobic tank 2 located one step upstream of the final step, the respiration rate (ATU
Providing a -r _r) a total of 8. 9 is a nitrification solution circulation control unit,
To what extent the valves 7a and 7b are opened is determined according to the measurement value of the respiration rate meter 8. The valve opening control unit 10 controls the opening of each of the circulation control valves 7a and 7b in accordance with the control output of the control unit 9.

When the nitrification is sufficiently performed, the nitrogen is in the form of a mixture of nitrous acid and nitric acid in the vicinity of the upstream outlet (circulation control valve 7b), and the final stage outlet (circulation control valve 7a) is entirely of nitric acid type. Becomes

The degree of nitrification can be determined by collecting water and measuring the concentrations of ammonia nitrogen and nitrate nitrogen by manual analysis. However, the respiratory rate (Nit-r) for removal of ammonia nitrogen on-line is used. _r ) A more responsive decision can be made by using a measuring instrument. Then, the correlation between the manual analysis value of the ammonia nitrogen concentration and the respiration rate is obtained in advance, and the degree of nitrification is judged by the measured value of the respiration rate which changes from moment to moment. Take control.

That is, when the nitrification is sufficiently performed and most of the ammonia nitrogen is removed at the upstream outlet (circulation control valve 7b), the circulation from the valve 7a is stopped, and the circulation is at the upstream outlet. (Circulation control valve 7b)
If the nitrification is insufficient, conversely, circulation is performed only from the final stage outlet (circulation control valve 7a).

[0017]

As described above, according to the present invention, the first outlet for returning the nitrification solution from the final aerobic tank to the preceding anaerobic tank, and the nitrification solution several steps before the final step. A second take-out port for returning from the aerobic tank of the first stage to the anaerobic tank of the previous stage, and a respiration rate meter for a process installed in the aerobic tank of several stages before the final stage, Since the circulation amount of the nitrification solution returned from the first and second outlets to the anaerobic tank in the previous stage is controlled according to the measured value of, the following excellent effects can be obtained.

(1) Nitrogen-type denitrification can be performed by providing an outlet for the circulation of the nitrification solution on the upstream side (second outlet) in addition to the conventional aeration tank outlet (first outlet). Therefore, the denitrification reaction speed becomes faster.

(2) If the nitrification progresses too much, the circulated nitrification solution may destabilize the anaerobic state and hinder the denitrification reaction. In such a case, from the upstream outlet (second outlet). Circulating can keep anaerobic condition.

(3) Since the degree of nitrification can be judged almost in real time by using the respiration rate meter, the nitrification solution circulation system can be optimized.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing an embodiment of the present invention.

FIG. 2 is a system configuration diagram showing a conventional anaerobic / aerobic activated sludge method.

[Explanation of symbols]

1 ... Anaerobic tank, 2 ... Aerobic tank, 3 ... Final settling tank, 4 ... Return sludge, 5 ... Excess sludge, 6 ... Nitrification liquid, 7a, 7b ... Circulation control valve, 8 ... Respirometer, 9 ... Nitrification liquid Circulation control unit, 10
… Valve opening controller.

Claims (1)

[Claims] 1. An aeration tank divided into a plurality of tanks in the anaerobic aerobic activated sludge method, the former tank is put into an anaerobic state, and the nitrification solution in the final tank is returned to the former tank in the anaerobic state, and the inflow water is converted into organic matter. In the nitrification solution circulation method in which contact and denitrification are performed, the first outlet for returning the nitrification solution from the final aerobic tank to the previous anaerobic tank, and the nitrification solution several steps prior to the final stage A second outlet for returning from the tank to the anaerobic tank in the previous stage, and a respiration rate meter for the process installed in the aerobic tank several stages before the final stage are provided, and the measurement value of the respiration rate meter is provided. In accordance with the above, the method for controlling the circulation of nitrification liquid in the anaerobic aerobic activated sludge method, which comprises controlling the circulation amount of the nitrification liquid returned from the first outlet and the second outlet to the anaerobic tank in the previous stage.