JP2938375B2 - Method and apparatus for preventing excessive aeration of oxidation ditch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing the inflow load to an oxidation ditch (oxidation pond) constituted by an endless circulation flow path comprising a denitrification zone and a nitrification zone. The present invention relates to a method for preventing aeration and an apparatus therefor.

[0002]

2. Description of the Related Art An oxidation ditch, which is one of the methods for biologically purifying sewage, comprises an endless circulation channel in the form of a race track. This circulation channel does not have a clear boundary divided by a partition wall or the like, but is constituted by each region of a denitrification region and a nitrification region as described below.

Since the denitrification zone is furthest from the aeration stirrer and is supplied with sewage from the sewage inlet, the "anaerobic zone" having a dissolved oxygen content of about 1 mg / l (preferably 0.5 mg / l) or less. "
And denitrification (N ₂ gasification) is performed by anaerobic microorganisms.

[0004] The first half of the nitrification region, which is closest to the agitator for aeration, is an "aerobic region" in which the amount of dissolved oxygen is about 1.5 to 2.5 mg / l, and most of organic matter (BOD source) by aerobic microorganisms.
Removal and nitrification of NH ₄ ⁺ (ammoniacal nitrogen).

[0005] The latter half, which is located at an intermediate distance from the aeration stirrer, becomes a "microaerobic zone" in which the amount of dissolved oxygen is about 1 to 1.5 mg / l, and contains NH ₄ ⁺ (ammoniacal nitrogen) NO ₂ ^- (nitrite nitrogen), NO ₃ ^- and oxidation of (nitrate nitrogen) is completed, the amount of dissolved oxygen as described above is 1 mg / l (preferably 0.5mg
/ l) Enter the following denitrification zone, where it is converted to N ₂ and H ₂ O by anaerobic microorganisms and purified.

[0006] Thus, the oxidation ditch is
In addition to the simple aerobic purification of organic substances (BOD source) performed by the standard aeration method, the purification by aerobic nitrification of nitrogen components in parallel and the purification by anaerobic denitrification are performed in parallel. It has the advantage that it can be performed continuously within

For this reason, the oxidation ditch is based on the technique disclosed in Japanese Patent Publication No. 52-6808, and has been improved with some improvements.
It is widely practiced on a scale of 20,000 tons / day.

In Japan, the oxidation ditch method has a residence time of about 24 hours, which is 6 times that of the standard aeration method.
It is installed in areas other than metropolitan areas due to restrictions on the required site area because the water tank capacity increases in proportion to the length of time before and after.

In these areas, the amount of inflow water and inflow contaminants (inflow load) such as nighttime domestic water becomes extremely small. Therefore, when the aeration stirrer is operated normally, dissolved oxygen is reduced. It becomes over-aerated state that is too high. In such an over-aerated state, activated sludge flocs, which are a group of aerobic microorganisms, reduce the amount of viscous secretions that perform flocculating action due to excessive internal respiration of microorganisms, resulting in reduced flocculation. As a result, the separation of activated sludge and supernatant water in the sedimentation tank installed at the next stage of the oxidation ditch greatly deteriorates, and SS (Susus
Suspended as supernatant (pended solid) in the supernatant water, it causes a decrease in water quality including the transparency of the discharged water.

Although it is different from the purpose of preventing the over-aeration state,
It is known to stop and start operation or control the rotation speed of an aeration stirrer based on dissolved oxygen measurements for the purpose of maintaining anaerobicity in a denitrification zone.

[0011] That is, JP-A-62-221498 discloses that the aerator is stopped when the DO value (dissolved oxygen value) in the ditch reaches a set value, and the anaerobic state is maintained for a certain period of time. An operation control method for an oxidation ditch in which the operation of the machine is restarted and the above operation is sequentially repeated is shown.

It is also known to use a submersible propulsion device for the purpose of creating a circulating flow. For example,
No. 28638 (JP-A-61-178095)
In, the continuous flow path is formed by corrosion-resistant pipe,
It is shown that a manhole is provided on the pipe to attach a stirrer and a diffuser, and that a propeller-like rotating body that forms a circulating flow and forms a swirling flow to prevent sedimentation of sludge is used as the stirrer. Have been.

[0013]

However, in the above-mentioned conventional method, the main purpose is to maintain the anaerobic property in the denitrification zone. Of the oxygen supply function and circulating flow forming function that the stirrer has, stopping the aeration stirrer can interrupt the replenishment of DO (dissolved oxygen) and bring it to an anaerobic condition. The function of forming the circulation flow in the oxidation ditch is also interrupted, and the activated sludge precipitates at the bottom of the circulation channel. That is, the method lacks measures to prevent uniform mixing of activated sludge and sewage.

On the other hand, in a pipe-type oxidation ditch disclosed in Japanese Patent Publication No. 1-28638, in which a propulsion device is installed for the purpose of forming a circulating flow, it is assumed that a diffuser is installed as an oxygen supply device. However, since the air diffuser itself cannot form a circulating flow, simultaneous use in combination with a propeller-shaped rotating body as a propulsion device is an essential component. However, this method is essentially different from a general oxidation ditch of the type using an aeration stirrer which originally has both an oxygen supply function and a circulation flow forming function as in the present invention.

In order to prevent the activated sludge floc from becoming finer due to excessive aeration due to excessive oxygen supply at night or the like when the inflow water load is extremely reduced, the supply of oxygen is cut off in principle. That is, the operation of the aeration stirrer must be stopped or decelerated. However, if the aeration stirrer is stopped or decelerated, the circulating flow, which is another function, cannot be formed. If the aeration stirrer is restarted or accelerated based on the measured value of the dissolved oxygen meter during the day when the influent water load returns to normal, the dissolved oxygen amount is normalized, but it has already settled. The uniform mixing of activated sludge and incoming sewage is not easily restored. If such a state is repeated for a long time, it is not possible to prevent the purified water quality from being lowered.

Under such a background, the present invention provides an oxidation ditch for preventing excessive aeration at the time of reducing the load of the inflow water into the oxidation ditch (ie, when the amount of inflow water is extremely reduced at night or the like). It is an object of the present invention to provide a method for preventing over-aeration and an apparatus therefor.

[0017]

According to the method for preventing overoxidation of an oxidation ditch of the present invention, an oxidation ditch (1) comprising an endless circulation flow path comprising a denitrification zone (A) and a nitrification zone (B) is provided. Sewage is introduced from the inlet (2) into the denitrification zone (A) in (A), and the aeration stirrer installed at the beginning of the nitrification zone (B)
Aeration is performed in (3), and the outlet (4) from the end of the nitrification zone (B)
In order to derive the purified water through the process, a dissolved oxygen controller (5) is installed in the nitrification area (B) of the oxidation ditch (1), and a diving propulsion device (6) is installed in the denitrification area (A). Install the agitator for aeration based on the dissolved oxygen measurement value of the dissolved oxygen controller (5).
The operation of (3) is started or stopped, and the operation of the submersible propulsion device (6) is stopped or started.

The apparatus for preventing excessive aeration of the oxidation ditch is provided with a denitrification zone (A) of the oxidation ditch (1) which is constituted by an endless circulation flow path comprising a denitrification zone (A) and a nitrification zone (B). Sewage inlet (2), aeration stirrer (3) at the beginning of nitrification zone (B), and purified water outlet at the end of nitrification zone (B)
In the equipment where (4) was installed, a dissolved oxygen controller (5) was installed in the nitrification zone (B), and a submersible propulsion device (6) was installed in the denitrification zone (A). When the dissolved oxygen measurement value of the total (5) exceeds the upper limit set value, the aeration stirrer (3)
The operation of the submersible propulsion system (6) is started at the same time as the operation of the submersible propulsion system (6) .If the measured dissolved oxygen value falls below the lower limit, the operation of the aeration stirrer (3) is started and the submersible propulsion system (6) is started. A control mechanism (7) for stopping the operation of (6) is provided.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

In the present invention, the denitrification zone (1) of the oxidation ditch (1) composed of an endless circulation flow path composed of a denitrification zone (A) and a nitrification zone (B) is used in accordance with the usual method of oxidation ditch. A) Sewage is introduced from the inlet (2) to the sewage, and purified water is drawn out from the last part of the nitrification zone (B) through the outlet (4). An aeration stirrer (3) is installed at the beginning of the nitrification zone (B) to perform aeration. The oxidation ditch is based on a two-channel one-aerator as shown in FIG. 1 described later, but in some cases, a two-channel two-aerator, a four-channel three aerator, and a multi-channel multi-aerator are used. You can also.

The denitrification zone (A) is an anaerobic zone in which the amount of dissolved oxygen is about 0.2 to 1 mg / l, and denitrification (N ₂ gasification) is performed by anaerobic microorganisms. The dissolved oxygen content in the first half of the nitrification zone (B)
It is an aerobic region of about 1.5 to 2.5 mg / l, and most of organic substances (BOD source) are removed and nitrification of NH ₄ ⁺ (ammonia nitrogen) is performed by aerobic microorganisms. Nitrification zone (B) The latter half is a microaerobic zone with a dissolved oxygen content of 1-1.5 mg / l, NH
₄ ⁺ NO ₂ of (ammonia nitrogen) ^- (nitrite nitrogen), N
O ₃ ^- oxidized to (nitrate nitrogen) is finished, and flows into the de-窒域(A).

In the present invention, a dissolved oxygen controller (5) is installed in the nitrification zone (B) of the oxidation ditch (1). The dissolved oxygen controller (5) can be installed in any position in the aerobic nitrification zone (B), since the control values can be set in the nitrification zone (B). .
This is because the latter half of the nitrification zone (B) is an agitator for aeration that supplies dissolved oxygen in the oxidation ditch.
(3) It is located at an intermediate distance from
This is because it is the most stable area with 1.5 mg / l, and it is easy to set control values.

In the present invention, a submersible propulsion device (6) is installed in the denitrification zone (A), and the aeration stirrer (3) is installed based on the dissolved oxygen measurement value of the dissolved oxygen controller (5). ) Is started or stopped, and the operation of the submersible propulsion device (6) is stopped or started.

In this way, the aeration stirrer (3) is completely stopped at the time when the inflow water load at night has almost disappeared, so that unnecessary supply of dissolved oxygen causing overaeration is not performed. Moreover, since only the necessary circulation flow can be formed, the activated sludge does not settle.

As the above-mentioned submersible propulsion device (6), various types of propulsion devices such as a propeller system, a submersible circulation pump system, and a screw stirrer system with a closed air intake can be used. In particular, a propeller-type propulsion device which does not cause a micronization phenomenon due to the cutting of the activated sludge floc because of its low rotation speed is particularly desirable.

The submersible propulsion device (6) is basically a denitrification zone (A) which requires no supply of oxygen and needs to be anaerobic.
It is installed at an appropriate place. Submerged propulsion device (6) in denitrification zone
Regardless of where installed in (A), only the circulation flow rate is maintained without supplying new dissolved oxygen, but in order to prevent sedimentation of unpurified filth in the incoming sewage, denitrification It is desirable to install a submersible propulsion device (6) immediately before or immediately after the sewage inlet (2) located in the area (A).

In order to start or stop the operation of the aeration stirrer (3) based on the dissolved oxygen measurement value of the dissolved oxygen controller (5) and to stop or start the operation of the submersible propulsion device (6), A control mechanism (7) is provided.

By the control mechanism (7), a dissolved oxygen controller
If the measured dissolved oxygen value in (5) exceeds the upper limit set value, the operation of the aeration stirrer (3) is stopped and the operation of the submersible propulsion device (6) is started, and the measured dissolved oxygen value is increased. When the value falls below the lower limit, the operation of the aeration stirrer (3) is started and the operation of the submersible propulsion device (6) is stopped.

The control mechanism (7) includes a dissolved oxygen controller (5)
The upper limit signal or the lower limit signal, and simultaneously stop the operation of the aeration stirrer (3) and start the operation of the diving propulsion device (6), or stop the operation of the diving propulsion device (6) and perform aeration. The operation of the stirrer (3) may be started.However, in a large oxidation ditch with a long water channel, the circulation flow speed temporarily fluctuates or stops. For example, after the operation of the aeration stirrer (3) is started, the time required for the sewage to go around the ditch (10 to
(About 0 minutes)
It is desirable to provide a delay timer or the like so that the operation of (6) can be stopped and a mechanism that can operate the aeration stirrer (3) and the dive type propulsion device (6) in parallel for a short time.

That is, the control mechanism (7) is a stirrer for aeration.
After sending the operation start command of (3), the operation of the dive propulsion device (6) is stopped at a time interval after it is sent, or after the operation start command of the diving propulsion device (6) is sent, the time difference is set. By sending a command to stop the operation of the aeration stirrer (3), both the aeration stirrer (3) and the submersible propulsion device (6) can be temporarily operated simultaneously.

Next, the operation will be described. In the present invention, the agitator for aeration in the oxidation ditch is used.
If the oxygen supply is not required among the two functions of (3), oxygen supply and circulating flow formation, that is, when the inflow load decreases at night, the dissolved oxygen controller (5) exceeds the upper limit set value. When the condition of excess oxygen occurs, the operation of the aeration stirrer (3) is automatically stopped by the command of the control mechanism (7), the supply of oxygen is cut off, and the operation of the submersible propulsion device (6) starts. I do. As a result, only the circulation flow rate can be maintained without supplying unnecessary oxygen, so that excessive oxidation of the oxidation ditch due to excessive supply of oxygen is prevented, and the quality of the water centered on the purified water SS is reduced. Lowering can be prevented reliably.

[0032]

EXAMPLES The method and apparatus of the present invention will be further described with reference to examples.

EXAMPLES and COMPARATIVE EXAMPLES FIG. 1 is an explanatory view schematically showing an example of a method and an apparatus for preventing excessive oxidation of an oxidation ditch according to the present invention.

(1) is an oxidation ditch,
Sewage is introduced from the inlet (2), and oxygen is supplied and circulating flow is formed by the vertical aeration stirrer (3).
Purified water is derived through (4).

In the latter half of the nitrification zone (B), a dissolved oxygen controller
(5) is installed, and a propeller-type diving propulsion device (6) is installed immediately after the inlet (2).

In the present embodiment, as an index of the water quality maintaining effect of the purified water by preventing over-aeration, a sedimentation tank (not shown) is installed at the next stage of the outlet (4) of the oxidation ditch (1). SS) in the discharge water that is the supernatant water
Was measured and compared.

First, as the method (embodiment) of the present invention, the upper and lower limit set values for control of the dissolved oxygen controller (5) are set to 1.4 mg / l and 1.1 mg / l, respectively, and the aeration in the control mechanism (7) is performed. The simultaneous operation time of the stirrer (3) and the diving propulsion device (6) was set to 10 minutes, the operation was started, and after a test operation period of two months, data was collected for one month, Water was sampled at regular time (9:00 am) and SS was measured.

Subsequently, as a conventional method (comparative example), the control signals from the dissolved oxygen controller (5) and the control mechanism (7) were connected to the aeration stirrer (3) and the diving propulsion device (6). Then, the aeration stirrer (3) was changed to simply operate continuously, operated for one month, and water was taken at a regular time (9:00 am) to measure SS.

Table 1 below shows the results of the SS measurement in the above Examples and Comparative Examples.

[0040]

[Table 1]

As shown in Table 1, during the first month in which the method of the present invention was performed, the SS in the effluent was maintained at less than 20 mg / l (13 to 15 mg / l). Nevertheless, one month after returning to the conventional method of continuously performing the normal operation of the aeration stirrer (3) even at night, the SS in the discharge water had deteriorated to 39 mg / l. This demonstrates the advantages of using the method and apparatus for preventing over-aeration of the oxidation ditch of the present invention.

[0042]

As described in the section of operation, in the present invention, the agitator for aeration in the oxidation ditch is used.
If the oxygen supply is not required among the two functions of (3), oxygen supply and circulating flow formation, that is, when the inflow load decreases at night, the dissolved oxygen controller (5) exceeds the upper limit set value. When the condition of excess oxygen occurs, the operation of the aeration stirrer (3) is automatically stopped by the command of the control mechanism (7), the supply of oxygen is cut off, and the operation of the submersible propulsion device (6) starts. I do. As a result, only the circulation flow rate can be maintained without supplying unnecessary oxygen, so that excessive oxidation of the oxidation ditch due to excessive supply of oxygen is prevented, and the quality of the water centered on the purified water SS is reduced. Lowering can be prevented reliably.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an example of a method and an apparatus for preventing excessive oxidation of an oxidation ditch according to the present invention.

[Explanation of symbols]

(1) ... oxidation ditch, (A) ... denitrification area, (B)
… Nitrification zone, (2)… inlet, (3)… aerator for aeration, (4)…
Outlet, (5) ... dissolved oxygen controller, (6) ... submersible propulsion device, (7) ... control mechanism

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C02F 3/14 C02F 3/12

Claims (4)

(57) [Claims] An oxidation ditch (1) comprising an endless circulation flow path comprising a denitrification zone (A) and a nitrification zone (B).
Sewage is introduced from the inlet (2) into the denitrification zone (A) of the
Aeration is performed with the aeration stirrer (3) installed at the beginning of (B), and the oxidation ditch (1) is used to derive purified water from the nitrification zone (B) through the outlet (4) from the end. A dissolved oxygen controller (5) is installed in the nitrification zone (B), and a submersible propulsion device is installed in the denitrification zone (A).
(6) to start or stop the operation of the aeration stirrer (3) and stop or start the operation of the dive propulsion device (6) based on the dissolved oxygen measurement value of the dissolved oxygen controller (5) A method for preventing excessive oxidation of an oxidation ditch. 2. A dissolved oxygen controller (5) is installed in the latter half of the nitrification zone (B), and a submersible propulsion device (6) is installed immediately before or immediately after the inlet (2). The method for preventing overaeration according to claim 1. 3. An oxidation ditch (1) comprising an endless circulation flow path comprising a denitrification zone (A) and a nitrification zone (B).
Sewage inlet (2) in the denitrification zone (A), aeration stirrer (3) at the beginning of the nitrification zone (B), and purified water outlet (4) at the end of the nitrification zone (B). In the installed facilities, a dissolved oxygen controller (5) was installed in the nitrification zone (B), and a submersible propulsion device (6) was installed in the denitrification zone (A). When the measured dissolved oxygen value exceeds the upper limit set value, the operation of the aeration stirrer (3) is stopped and the operation of the submersible propulsion device (6) is started, and the dissolved oxygen measured value decreases to the lower limit set value. In the case of an oxidation ditch, a control mechanism (7) for starting the operation of the aeration stirrer (3) and stopping the operation of the submersible propulsion device (6) when it falls below is provided. Over-aeration prevention device. 4. A submersible propulsion device having a time lag after the control mechanism (7) issues a command to start operation of the aeration stirrer (3).
By sending the operation stop command of (6), or sending the operation start command of the submersible propulsion device (6) and sending the operation stop command of the aeration stirrer (3) with a time lag, The over-aeration prevention device according to claim 3, characterized in that both the stirrer (3) and the diving propulsion device (6) have a mechanism capable of temporarily operating simultaneously.