JPH09131595A - Control method for intermittent exposure type activated sludge method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the degradation in a phosphorus removal rate by a novel control method as the phosphorus removal rate degrades when the org. matter concn. in flowing-in waste water is extremely low or high in a biological treatment method for removing nitrogen and phosphorus from sewage and living waste water. SOLUTION: This control method for intermittent exposure type activated sludge method comprises first admitting the waste water into a first aeration tank in which a first ORP meter is installed, then admitting the waste water into a second aeration tank in which a second ORP meter is installed and subjecting the waste water to aerating and stirring in these two aeration tanks. The treated water is thereafter released from the final settling basin. The settled sludge is returned to the aeration tanks and is withdrawn as excess sludge, by which the nitrogen and phosphorus in the waste water are removed. The aeration time Te in the first aeration tank and the denitrification time Tf based on the detection of the ORP inflection point of the first ORP meter are measured and a DN ratio Tf/Te is determined. The set time for nitrification, denitrification and phosphorus release in the first aeration tank is controlled from this value, by which the adequate phosphorus release quantity is assured and the degradation in the phosphorus removal rate is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for biologically treating sewage and domestic wastewater, and more particularly to a method for controlling a process for removing nitrogen and phosphorus in wastewater.

[0002]

2. Description of the Related Art The treatment of sewage and domestic wastewater mainly involves the removal of organic substances, and biological treatment represented by the activated sludge method has been generally used. However, in recent years, eutrophication has become a major problem in closed water bodies such as lakes and marshes, and it has become important to remove nitrogen and phosphorus which cause this problem. Therefore, a treatment method capable of removing nitrogen and phosphorus in addition to organic substances has been developed as an improved method of the activated sludge method, and typical methods include the A ₂ O method (anaerobic-anoxic-aerobic method) and the batch method. Activated sludge method, intermittent aeration type activated sludge method (hereinafter, abbreviated as intermittent aeration method) and the like. In these methods, microorganisms are alternately subjected to aerobic and anaerobic conditions to remove organic matter, nitrogen and phosphorus.

Here, the principle of sewage treatment for removing nitrogen and phosphorus will be briefly described. Organic matter in the sewage becomes food for microorganisms constituting the activated sludge and is decomposed and removed. Nitrogen is oxidized from NH ₄ —N (ammonia nitrogen) to NO ₃ —N (nitrate nitrogen) under the aerobic condition by the action of nitrifying bacteria, and then NO ₃ by the action of the denitrifying bacteria under anaerobic conditions. -N is removed is reduced to N ₂ (nitrogen gas). The relationship between nitrification and denitrification is summarized as follows. Reaction Nitrogen morphological change Reaction conditions Microbial nitrification reaction Ammonium nitrogen → Nitrate nitrogen Aerobic (with dissolved oxygen) Nitrifying bacteria Denitrification reaction Nitrate nitrogen → Nitrogen gas Anaerobic (without dissolved oxygen) Denitrifying bacteria Phosphorus aeration tank operation By altering the conditions alternately between aerobic and anaerobic, activated sludge having the property of accumulating a large amount of phosphorus in cells is produced, and the activated sludge is removed by using this activated sludge. That is, this activated sludge has the property of releasing phosphorus under anaerobic conditions and absorbing phosphorus under aerobic conditions, so it absorbs phosphorus under aerobic conditions, and the activated sludge that has absorbed a large amount of phosphorus as surplus sludge. Dephosphorization is performed by removing from the treatment system. This relationship can be organized as follows. Phosphorus concentration in the reaction tank Reaction condition Phosphorus removal Phosphorus release increase Anaerobic (no dissolved oxygen) -Phosphorus absorption decreased aerobic (dissolved oxygen) Activated sludge withdrawal In this way, nitrogen and phosphorus removal are aerobic and anaerobic. Although the conditions are essential, strictly speaking, the anaerobic conditions for denitrification and the anaerobic conditions for dephosphorization are different, and in the intermittent aeration method, denitrification is completed and NO ₃ -N is caused in the tank. The release of phosphorus from activated sludge occurs after the elimination of oxygen molecules, which leads to the absorption of phosphorus in the next aeration process.

The intermittent aeration method is a method that has attracted attention because the ratio of aerobic conditions and anaerobic conditions can be set in terms of time, and it can be applied to existing facilities relatively easily. As a method to greatly improve the intermittent aeration method,
An apparatus provided with a first aeration tank into which waste water flows and a second aeration tank connected in series to the first aeration tank, and a final settling tank after that, and a control method therefor (hereinafter referred to as "2"). Japanese Patent Application Laid-Open No. 6-55190 discloses a tank type intermittent aeration method.

The outline is shown below in FIG. 1 and FIG.
This will be described with reference to FIG. FIG. 1 is Japanese Unexamined Patent Publication No. 6-5519.
It is a schematic diagram which shows the principal part structure for demonstrating the intermittent aeration method and control system of Unexamined-Japanese-Patent No. 0, and the path | route of water and air is shown by the solid line arrow in FIG. This device is mainly used for removing organic matter, nitrogen and phosphorus by activated sludge.
An aeration tank 2a and a second aeration tank 2b, a final sedimentation basin 4 from which activated sludge is separated by gravity sedimentation to obtain treated water 3, and a return sludge pump 5 for returning the settled activated sludge to the first aeration tank 2a. I have. First aeration tank 2a and second aeration tank 2
The volume ratio of b is about 1: 1, and the total residence time of the treated water is 16 to 32 hours including the final sedimentation basin 4. The control system performs a first measurement for measuring the oxidation-reduction potential in the first aeration tank 2a.
The first aeration blower 7a, the second aeration blower 7b, the first ORP meter 6a, the second ORP meter 6b for measuring the redox potential in the second aeration tank 2b, and the first aeration blower 7a, the second aeration blower 7b, based on the measured values of 6a and 6b.
It comprises a stirring pump 8a and a control device 9 for controlling the second stirring pump 8b.

The basic idea of operation control in this system is to use two aeration tanks, a first aeration tank into which waste water flows and a second aeration tank connected in series to the first aeration tank.
Both aeration tanks control aeration and agitation in the same cycle.
In the first aeration tank 2a, nitrification and denitrification are performed for a certain period of time, and the remaining time is secured as the phosphorus release time. Also, the second
In the aeration tank 2b, nitrification and denitrification are maintained for one cycle time to prevent phosphorus release. By this control method, a high nitrogen and phosphorus removal rate can be obtained.

[0007] Next, a concrete method will be described with reference to ORP accompanying control.
With reference to FIG. 2A and FIG. 2 (a) and 2 (b) show changes in ORP with the passage of time, with the aeration start time being a zero point at an arbitrary timing during execution of control, and FIG. The ORP of the first aeration tank, (b) is a relationship diagram with respect to the elapsed time of each ORP of the second aeration tank.

First, the control method of the first aeration tank 2a will be described. An aeration time for nitrification and phosphorus absorption is Te, a denitrification time is Tf, and a time Tg which is a sum of Te and Tf is a preset time Tgs. The aeration time Te is adjusted so as to coincide with Looking at the change in the ORP of the first ORP meter 6a, the inflection point A appears after the end of denitrification, the time Tg is measured by detecting A, and the aeration time Te is calculated based on the difference between Tgs and Tg. To adjust. As a result, since one cycle is maintained at about Tds time as described later, the phosphorus release time is secured as Tds-Tgs.

The control method of the second aeration tank 2b is such that the aeration time for nitrification and phosphorus absorption is Tb, the stirring time for denitrification to be TC, and the time Td which is the sum of Tb and TC is a preset time. The aeration time Tb is adjusted so as to match Tds, and at the same time, assuming that one cycle is completed after the time Td, the first aeration tank 2a and the second aeration tank 2b are simultaneously returned to the aeration state. This is performed by detecting the bending point B from the change of the ORP of the second ORP system 6b, measuring the time Td, and adjusting the aeration time Tb based on the difference between Tds and Td. As a result, since the aeration state is established immediately after the denitrification is completed, phosphorus is not released in the second aeration tank 2b, and a high nitrogen and phosphorus removal rate is obtained.

[0010]

As described above, the present inventors have described the two-tank intermittent aeration method described in Japanese Patent Application Laid-Open No. 6-55190. However, the biological dephosphorization method including this method has the following problems that must be solved. One is that the phosphorus removal rate decreases when the organic matter concentration in the inflowing wastewater is low. This is because when the organic matter concentration is low, the amount of phosphorus released decreases in the anaerobic process,
As a result, it is a phenomenon that phosphorus absorption becomes poor in the aerobic process. On the other hand, contrary to the above case, when the concentration of organic substances in the inflowing wastewater is extremely high, the amount of phosphorus released increases in the anaerobic process, and as a result, phosphorus cannot be completely absorbed within the aerobic process time. It is a phenomenon. As described in the prior art, the control method of this method performs the operation in which the nitrogen and phosphorus removal steps are distributed during one cycle, so it is possible to cope with a certain amount of organic matter load fluctuation and is good. Excellent treated water quality can be obtained. However, when the organic load fluctuation is extremely large, phosphorus removal may be deteriorated.

The present invention has been made to improve the above-mentioned points, and an object thereof is to provide a method for controlling a sewage treatment process by a two-tank intermittent aeration method capable of preventing a reduction in phosphorus removal rate. Especially.

[0012]

In order to solve the above problems, according to the present invention, the operation of the two-tank intermittent aeration method is carried out in accordance with the increase or decrease of the organic matter concentration of the inflowing water in the first aeration tank for removing nitrogen and phosphorus. This is done by changing the time allocation of. Specific method, DN ratio of aeration time for the current step in the first aeration tank (T _e) and the inter-de窒時 _{(T f) R n = T} f /
T _e is calculated, and based on this DN ratio, the first O
The set value of the ORP bending point detection time T _{gs (n + 1)} of the RP meter is adjusted. For example, when the aeration time of the first aeration tank is 30 minutes and the denitrification time is 25 minutes, the DN ratio R _n = 25/30 = 0.83.
And this 0.83 and a preset DN ratio R ₀
= 1.0, and the first in the next step depending on the difference.
Setting value of ORP inflection point detection time T _{gs (n + 1)}
To increase. When the measured value R _n of the DN ratio in the current process is larger than the set value R ₀ , the ORP of the first ORP meter is detected.
Decrease the setting value of the bending point detection time. This method is 2
In the tank-type intermittent aeration method, as described in the section of the prior art, phosphorus is released in the first aeration tank, but the release rate of phosphorus varies depending on the amount of organic matter supplied, When the amount of organic matter is large, it tends to be fast, and when it is small, it tends to be slow. Therefore, when the organic substance supply amount is too large, the phosphorus release amount becomes too large, phosphorus cannot be absorbed in a predetermined aeration time, and the phosphorus removal rate decreases. In addition, when the amount of organic matter supplied is small, the amount of released phosphorus becomes small, and as a result, the absorption of phosphorus becomes weak and the phosphorus removal rate decreases. That is, in order to perform stable phosphorus removal, it is important to secure an appropriate phosphorus release amount in the first aeration tank. Here, the above-mentioned DN ratio is calculated by the present inventors from Japanese Patent Laid-Open No. 6-262197.
Since it is an index described in Japanese Patent Publication No. Gazette and is an effective index for judging changes in the amount of inflowing organic matter, D in the present process
When the N ratio R _n is smaller than the set DN ratio R ₀ (the amount of supplied organic matter is large), the OR of the first ORP meter in the next step
By increasing the set value T _{gs (n + 1)} of the P inflection point detection time, the phosphorus release time is shortened and the phosphorus release amount is suppressed. When the DN ratio R _n of the current process is larger than the set DN ratio R ₀ (the amount of organic matter supplied is small), the first OR
By decreasing the set value T _{gs (n + 1)} of the ORP inflection point detection time of the P meter, the phosphorus release time is increased and the phosphorus release amount is increased. Thus, by changing the set value T _gs of the ORP bending point detection time of the first ORP meter,
The phosphorus release time is changed to ensure an appropriate phosphorus release amount.

According to the above operating method, it is possible to prevent the deterioration of the phosphorus removal rate that occurs when the organic matter load fluctuation of the inflowing raw water is severe, and it is possible to perform stable phosphorus removal.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. The device and control system for the two-tank intermittent aeration method to which the method of the present invention is applied have the same configuration as the schematic diagram shown in FIG. 1, and therefore, illustration thereof is omitted here, and FIG. 1 and FIG. 2 are referred to again. Explain. Although the method of the present invention uses the DN ratio as a control index, a detailed description of this DN ratio is given in Japanese Patent Laid-Open No. 6-262 by the present inventors.
Since it is described in Japanese Patent Publication No. 197, it is omitted.

In the present process, the first aeration tank 2a has a predetermined time (T
_e ) After performing aeration, the process proceeds to the stirring step, and the first ORP
The denitrification time (T _f ) is measured based on the detection of the ORP bending point A of the total 6a to obtain R _n = T _f / T _e, and the DN ratio R ₀ is set in advance for this R, When the DN ratio in the current treatment step is R _n , it is determined that the phosphorus release amount increases when R _n <R ₀ , and the first treatment step of the next treatment step is performed.
Setting value T of the detection time of the ORP bending point A of the ORP meter 6a
_{Increase gs (n + 1)} . When R _n > R ₀ , it is determined that the phosphorus release amount decreases, and the set value T _{gs (n + 1)} of the detection time of the ORP bending point A of the first ORP meter 6a in the next processing step is reduced. Specifically, the method of adjusting the set value T _gs of the detection time of the ORP bending point of the first ORP meter 6a is based on the following formula (1). T _{gs (n + 1)} = T _gs0 + K (R ₀ −R _n ) (1) where T _{gs (n + 1)} : Set value of first ORP meter bending point detection time in the next process K: Proportional constant R _n: DN ratio R ₀ in the current process: the default value for DN ratio T _gs0: the first detection time of the ORP meter inflection point default value T _gs when the DN ratio R ₀ upper and lower limit of A set time is set and the value is changed within that range. Such calculation is performed by the controller 9.

The reason why the set value T _gs of the detection time of the first ORP bending point is changed will be described. As described above, in the first aeration tank of the two-tank intermittent aeration method, phosphorus is absorbed in the aerobic process and phosphorus is released after the first ORP inflection point appears in the anaerobic process. It is generally known that the release rate of phosphorus depends on the supply amount of organic matter, and that the release rate is high when the supply rate of organic matter is large and slow when it is small. Further, the DN ratio is small when the organic substance supply amount is large, and becomes large when the organic substance supply amount is small. Therefore, for example, when the DN ratio is small, the organic substance supply amount is large and the phosphorus release rate is high. It can be determined that the amount of phosphorus released increases in the first aeration tank 2a. If this release amount is too large, phosphorus cannot be completely absorbed within the aerobic process time of the first aeration tank and the second aeration tank, phosphorus remains in the treated water, and the treated water quality deteriorates. Therefore, by increasing the set value of the detection time of the ORP bending point of the first aeration tank, the release time of phosphorus is shortened and the release amount is suppressed. At this time, the time allotted to the nitrogen removal increases, so that the nitrogen removal is also efficient.

On the contrary, when the DN ratio is large, it can be judged that the phosphorus release amount in the first aeration tank is small. In such a case,
Absorption of phosphorus in the aerobic process becomes poor and the quality of treated water deteriorates. Therefore, by reducing the set value of the detection time of the ORP inflection point of the first aeration tank, the release time of phosphorus is increased, the amount of phosphorus released is increased, and poor phosphorus absorption is prevented. At this time, since the set value of the detection time of the ORP inflection point of the first aeration tank is made small, the time spent for nitrogen removal is reduced, but in such a case, generally, the nitrogen load is also low, so this operation removes nitrogen. It doesn't get worse. Therefore, if the set values of the DN ratio at the average organic load and the detection time of the first ORP inflection point are determined in advance, the O of the first aeration tank corresponding to the DN ratio is determined.
The set value for the detection time of the RP inflection point can be determined, and as a result, stable nitrogen and phosphorus removal can be achieved.

[0018]

In the biological dephosphorization method, there is a problem that the phosphorus removal rate decreases when the organic matter concentration in the inflowing wastewater is low or when the organic matter concentration in the inflowing wastewater is extremely high.
The control method of the 2-tank intermittent aeration method is such that the nitrogen and phosphorus removal steps are distributed during one cycle, so it is possible to cope with a certain amount of organic matter load fluctuation, and the treated water quality is good. Is obtained. However, when the organic load fluctuation is extremely large, the phosphorus removal may be deteriorated.
The method of the present invention has been made to address this problem and has the following advantages.

The set value of the ORP inflection point detection time of the first ORP meter is adjusted based on the DN ratio which is the ratio of the aeration time and the denitrification time in the first aeration tank. As a result, an appropriate amount of phosphorus release is always secured in the first aeration tank, the phosphorus absorption and release proceed in a good state, and a high phosphorus removal rate can be maintained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a main configuration of a sewage treatment apparatus to which a control method of an intermittent aeration method applied by the present inventors is applied.

FIG. 2 shows changes in ORP of the first aeration tank and the second aeration tank in the control method of the intermittent aeration method which the present inventors applied for,
(A) ORP of the first aeration tank, (b) O of the second aeration tank
Relationship diagram for each lapse of time of RP

[Explanation of symbols]

 1 Sewage 2a First aeration tank 2b Second aeration tank 3 Treated water 4 Final sedimentation tank 5 Return sludge pump 6a 1st ORP meter 6b 2nd ORP meter 7a 1st aeration blower 7b 2nd aeration blower 8a 1st stirring pump 8b 2nd agitation Pump 9 Control device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yutaka Mori, 1-1 Tanabe Shinden, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Fuji Electric Co., Ltd. (72) Yasunari Sasaki, 1 Nitta, Tanabe-Kawasaki, Kawasaki-shi, Kanagawa No. 1 in Fuji Electric Co., Ltd. (72) Inventor Akiko Ogura No. 1 Shinden Tanabe, Kawasaki-ku, Kawasaki-shi, Kanagawa Inside Fuji Electric Co., Ltd.

Claims (1)

[Claims] A first aeration tank provided with a first ORP meter;
A second aeration tank provided with a second ORP meter connected in series to the first aeration tank and draining water into the first aeration tank;
After performing treatment by alternately repeating the aerobic state in which aeration is performed in the two aeration tanks and the anaerobic state in which aeration is stopped and stirring is performed, the treated water is discharged from the final settling tank, and the settled sludge is aerated. In the control method of the intermittent aeration type activated sludge method of removing nitrogen and phosphorus in wastewater while returning to the tank and surplus sludge, a predetermined time (T
e) After performing aeration, the process proceeds to the stirring step, and the first ORP
The denitrification time (Tf) is measured based on the detection of the ORP bending point of the meter to obtain Tf / Te (DN ratio), and the ORP bending point detection time of the first ORP meter is set based on the DN ratio. A method for controlling an intermittently aerated activated sludge method, which is characterized by adjusting a value.