JPH08197083A - Method for controlling intermittently-aerated activated sludge process - Google Patents

Abstract

PURPOSE: To prevent the lowering of the phosphorus removal rate in a two-tank intermittent aeration method by adjusting the set detecting time of a first ORP (oxidation-reduction potential) crooked point of a succeeding cycle based on the absolute value of the value measured by a first ORP meter when one cycle of treating stage is finished. CONSTITUTION: As for the measured ORP value sent from a first ORP meter 6a, the absolute value of the measured ORP value when one cycle of treating stage is finished is calculated by a controller 9. The absoulte value of the measured ORP value is preset for the absolute value. When the absolute value of the measured ORP value in the preceding treating stage is larger than the set absolute value, the discharge of phosphorus is judged to be increased, and the set detecting time of the first ORP crooked point of the succeeding cycle is prolonged. Conversely, when the discharge is judged to be decreased, the detecting time of the ORP crooked point is shortened. Consequently, nitrogen and phosphorus are stably removed even when the load is widely fluctuated.

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 Sewage and domestic wastewater are mainly treated to remove organic substances, and a biological treatment method represented by an activated sludge method has been generally used. However, in recent years, eutrophication has become a major problem in closed water areas such as lakes and marshes, and the removal of nitrogen and phosphorus, which cause this, has become important. for that reason,
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. Typical methods include the A ₂ O method (anaerobic-anoxic-aerobic method) and batch 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 the purpose of removing nitrogen and phosphorus will be briefly described. Organic matter in the sewage is decomposed and removed as food for the microorganisms that make up the activated sludge. Nitrogen oxidizes NH ₄ —N (ammoniacal nitrogen) to NO ₃ —N (nitrate nitrogen) under the aerobic condition by the action of nitrifying bacteria, and then NO under the anaerobic condition by the action of denitrifying bacteria. _3- N is reduced to N ₂ (nitrogen gas) and removed. The relationship between nitrification and denitrification can be summarized as follows.

Reaction nitrogen morphological change Reaction conditions Microorganism Nitrification reaction Ammonium nitrogen → Nitrate nitrogen Aerobic (with dissolved oxygen) Nitrifying bacteria Denitrification reaction Nitric acid nitrogen → Nitrogen gas Anaerobic (without dissolved oxygen) Denitrifying bacteria Phosphorus is aerated By alternately changing the operating conditions of the tank to aerobic or anaerobic, activated sludge having a property of accumulating a large amount of phosphorus in the cell is produced, and the activated sludge is removed by utilizing this activated sludge. That is, since this activated sludge has the property of releasing phosphorus under anaerobic conditions and absorbing phosphorus under aerobic conditions, it absorbs phosphorus under aerobic conditions, and the activated sludge that has absorbed a large amount of phosphorus is treated as excess sludge. Dephosphorization is performed by removing it from the processing system. This relationship can be organized as follows.

Phosphorus concentration in the reaction tank Reaction conditions Phosphorus removal Phosphorus release Increase Anaerobic (No dissolved oxygen) -Phosphorus absorption Decrease Aerobic (Dissolved oxygen) Activated sludge extraction In this way, in the removal of nitrogen and phosphorus, Two conditions, aerobic and anaerobic, are indispensable. Strictly speaking, the anaerobic condition for denitrification and the anaerobic condition for dephosphorization are different. Release of phosphorus from the activated sludge occurs after the elimination of oxygen molecules due to NO ₃ —N in the interior, which leads to absorption of phosphorus in the subsequent aeration step.

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 can be applied to existing facilities relatively easily. As a method to greatly improve the intermittent aeration method,
An apparatus equipped 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 at the subsequent stage, and its control method (hereinafter A two-tank intermittent aeration method is disclosed in JP-A-6-55190.

The outline is shown in FIGS. 4 and 5 (a) below.
This will be described with reference to (b). FIG. 4 shows JP-A-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 of water and air is represented by the solid line arrow in FIG. 4, and a control signal system is represented by the dotted line arrow. This device is mainly equipped with a first aeration tank 2a and a second aeration tank 2b in which sewage 1 flows in and organic matter, nitrogen and phosphorus are removed by activated sludge, and activated sludge is separated by gravity sedimentation to obtain treated water 3. It comprises a final settling tank 4 and a returning sludge pump 5 for returning the settled activated sludge to the first aeration tank 2a. 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 including the final settling tank 4 is 16 to 32 hours. The control system measures the redox potential in the first aeration tank 2a.
ORP meter 6a, a second ORP meter 6b for measuring the redox potential in the second aeration tank 2b, and a first aeration blower 7a, a second aeration blower 7b, and a first stirring pump 8a based on these ORP values. , And a control device 9 for outputting a control signal to the second stirring pump 8b.

The basic idea of operation control in such an apparatus system is that two aeration tanks, a first aeration tank 2a into which waste water flows and a second aeration tank 2b connected in series to the first aeration tank, are provided. By controlling nitrification and denitrification in the first aeration tank 2a for a certain period of time, the phosphorus release time is secured, and in the second aeration tank 2b, nitrification and denitrification are performed, and the phosphorus release is controlled while being prevented. It is to maintain one cycle for a predetermined time and obtain a high nitrogen and phosphorus removal rate. A specific method will be described with reference to FIGS. 5A and 5B together with a change in ORP due to control. FIGS. 5 (a) and 5 (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. 1 ORP of aeration tank 2a, FIG. 5 (b)
[Fig. 3] is a relational diagram with respect to each time passage of ORP of the second aeration tank 2b.

First, a method of controlling the first aeration tank 2a will be described. The aeration time for nitrification and phosphorus absorption is T _e ,
The denitrification time is T _f, and the aeration time T _e is adjusted so that the time T _g, which is the sum of T _e and T _f , matches the preset time T _gs . Here, the ORP of the first ORP total 6a
The bending point A appears after the end of denitrification, the time T _g is measured by detecting the bending point A, and the aeration time T _e is adjusted based on the difference between T _gs and T _g. To do. As a result, since one cycle is maintained at about T _ds time as described later, the phosphorus release time is secured as T _ds −T _gs .

The control method of the second aeration tank 2b is as follows.
is there. The aeration time for nitrification and phosphorus absorption is T_b, Denitrification
The stirring time to progress is T_CAnd T_bAnd T_CWhen is the sum of
Interval T _dIs a preset time T_dsTo match
Aeration time T_bAnd adjust the time T_dOne more cycle
Assuming the end, the first aeration tank 2a and the second aeration tank 2b are
Sometimes it returns to aeration. This is the second ORP system 6
The bending point B is detected from the change in ORP of b, and the time T_dMeasure
Set, T_dsAnd T_dAeration time T based on the difference between_bAdjust
By doing. As a result, as soon as denitrification is completed,
As a result of the aeration, the phosphorus in the second aeration tank 2b
High release rate of nitrogen and phosphorus without being released
It

[0011]

However, the biological dephosphorization method still has the following problems to be solved. One is that the phosphorus removal rate decreases when the concentration of organic matter in the inflowing raw water is low. this is,
When the organic matter concentration is low, the amount of phosphorus released decreases in the anaerobic process, resulting in poor phosphorus absorption in the aerobic process. Therefore, for example, when the sewage contains a large amount of rainwater, a phenomenon occurs in which the concentration of organic substances decreases and the phosphorus removal rate also decreases. The other is that, contrary to the above case, the phosphorus removal rate decreases when the organic matter concentration in the inflowing raw water is extremely high. This is a phenomenon that occurs when the concentration of organic substances 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. As described above, the control method of this system performs the operation of distributing the nitrogen and phosphorus removal steps during one cycle of the treatment step, so that the organic matter load fluctuation of the inflowing sewage is normally prevented. It is possible to deal with it, and good treated water quality can be obtained. However, when the organic load fluctuation is extremely large as described above, the phosphorus removal rate may deteriorate.

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

[0013]

In order to solve the above problems, the operation of the two-tank type intermittent aeration method of the present invention is performed as follows. The first method is the first OR installed in the first aeration tank.
The absolute value of the measured value at the end of one cycle of the P meter,
The difference between the predetermined ORP value and the absolute value is calculated, and based on the difference, the O of the first ORP meter in the next cycle is determined.
The set value of the RP bending point detection time is changed.

The second method is the first method installed in the first aeration tank.
Difference between the ORP value of the ORP meter at the time of detecting the ORP bending point and the ORP value at the end of the current cycle (ΔORP)
Then, based on the difference between the ΔORP and a predetermined ΔORP, the O of the first ORP meter in the next cycle is taken.
The set value of the RP bending point detection time is changed. The third method is to obtain the absolute value of the measured value of the first ORP meter installed in the first aeration tank at the end of one cycle, and if the absolute value is less than or equal to a predetermined absolute value, After detecting the ORP bending point of the ORP meter of No. 1, an organic substance is added to the first aeration tank.

The fourth method, like the second method, is ΔOR.
P is calculated, and when ΔORP is less than or equal to a predetermined value,
After detecting the ORP bending point of the first ORP meter in the next cycle, an organic substance is added to the first aeration tank. The fifth method is
When the absolute value of the measured value at the end of one cycle of the first ORP meter installed in the first aeration tank is obtained, and the absolute value is equal to or more than the upper limit or the lower limit of the predetermined absolute value, the second aeration tank A flocculant that reacts with phosphorus to form a sparingly soluble compound is added to.

The sixth method, like the second method, is ΔOR.
When P is determined and ΔORP is equal to or higher than a predetermined upper limit value or lower than a predetermined lower limit value, a flocculant which reacts with phosphorus to form a sparingly soluble compound is added to the second aeration tank.

[0017]

The first method of the present invention is the ORP at the end of one cycle of the first ORP meter installed in the first aeration tank.
The set value of the first ORP inflection point detection time of the first aeration tank in the next cycle is adjusted based on the absolute value of the measured value.
For example, the O of the first ORP meter at the end of one cycle
When the absolute value of the RP measured value is 150 mV, it is compared with the preset absolute value of ORP of 200 mV, and the set value of the ORP bending point detection time of the first aeration tank in the next cycle is reduced according to the difference. If it is larger than the set absolute value of ORP, the set value of the ORP bending point detection time is increased. In the control of the first aeration tank according to the present invention, first, aeration is performed for a predetermined time, and then the process proceeds to a stirring process. In this stirring process, first, the denitrification reaction proceeds, and after the denitrification reaction ends, phosphorus is removed. Release is done. The release rate of phosphorus varies depending on the amount of the organic substance supplied, and tends to increase when the amount of the organic substance is large and slow when the amount of the organic substance is small. Therefore, when the supply amount of the organic matter is too large, the release amount of phosphorus becomes excessively large, the phosphorus cannot be absorbed in a predetermined aeration time, and the phosphorus removal rate decreases. Further, when the supply amount of organic matter is small, the release amount of 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 amount of phosphorus released in the first aeration tank. Further, the measurement value of the ORP meter is an index for judging the release amount of phosphorus, and the lower the ORP value, the higher the release amount of phosphorus. Therefore, as described above, the first OR at the end of one cycle
When the absolute value of the ORP value of the P meter is larger than the set value, the set value of the ORP inflection point detection time is increased to shorten the phosphorus release time and suppress the phosphorus release amount.
When the absolute value of the ORP value is smaller than the set value, the set value of the ORP inflection point detection time is set to be small to increase the phosphorus release time and increase the phosphorus release amount. In this way, by changing the set value of the ORP inflection point detection time, the phosphorus release time is changed, and an appropriate phosphorus release amount is secured.

In the second method of the present invention, the set value of the ORP bending point detection time of the first aeration tank in the next cycle is adjusted by using the measurement value of the first ORP meter installed in the first aeration tank. This is almost the same as the first method, but the method of calculating the set value of the ORP bending point detection time is different from the first method. That is, the difference between the ORP value at the time of detecting the ORP bending point of the first ORP meter and the ORP value at the end point of the current cycle is obtained, and the set value of the ORP bending point detection time is changed based on the difference.

The third method of the present invention is the O 2 at the end of one cycle of the first ORP meter installed in the first aeration tank.
The absolute value of the RP measurement value is obtained. For example, when the value is 50 mV, it is compared with a predetermined lower limit threshold value 100 mV of the absolute value, and it is determined that it is less than or equal to the threshold value. After detecting the ORP inflection point of the ORP meter, the organic substance is added to the first aeration tank. When the absolute value of the ORP measurement value at the end of one cycle is small, as described in the first method, it can be determined that the phosphorus release amount is small and the organic substance supply amount is insufficient. Therefore, the ORP of the limit condition that the supply amount of organic substances does not become insufficient
By determining the absolute value of the value from the past operation record and setting it as a threshold value, it is possible to determine that the organic substance is added below the threshold value and not added above the threshold value. The fourth method is basically the same as the third method, except that the first method is the same as the first method.
The difference between the ORP value of the ORP meter at the time of detecting the ORP bending point and the ORP value at the end of the current cycle is used.

In the fifth method of the present invention, O at the end of one cycle of the first ORP meter installed in the first aeration tank
Obtain the absolute value of the RP measurement value, for example, the value is 50 mV
At this time, this is compared with a predetermined absolute lower limit threshold value of 100 mV and an upper limit threshold value of 300 mV, and it is determined that it is less than or equal to the lower limit value, and reacts with phosphorus in the second aeration tank in the next cycle. Then, a flocculant which forms a sparingly soluble compound is added. The same applies when the value is equal to or higher than the upper limit threshold.
When the absolute value of the ORP measurement value at the end of one cycle is small, it can be determined that the amount of released phosphorus is small and the phosphorus removal rate decreases, and when the absolute value of the ORP measurement value at the end of one cycle is large. It can be judged that the amount of released phosphorus becomes excessive and the phosphorus removal rate decreases. Therefore, the OR of the marginal conditions that does not deteriorate the phosphorus removal
The absolute value of the P value is calculated from the past operation results, and the P value is set as the upper limit and the lower limit of the threshold value. It can be determined that it is not necessary to add a coagulant within the threshold range.

The sixth method of the present invention is basically the same as the fifth method, except that when the addition or non-addition of the coagulant is determined, the ORP bending point of the first ORP meter is detected. ORP
The difference between the value and the ORP value at the end of the current cycle. According to the above control method, it is possible to prevent the deterioration of the phosphorus removal rate that occurs when the fluctuation of the inflow load of raw water is severe, and it is possible to perform stable phosphorus removal.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. First, the first method of the present invention will be described. First
The device and control system of the two-tank intermittent aeration method to which the method of (3) is applied have the same configuration as the schematic diagram shown in FIG. 5, so the illustration of the device and ORP change diagram is omitted here,
It will be described with reference to FIGS. 4 and 5 again.

In the first method, the absolute value O of the ORP measurement value at the end of one cycle of the processing step is calculated for the ORP measurement value sent from the first ORP meter 6a to the control device 9, and this O The absolute value O _s of the ORP measurement value is set in advance for the value, and the absolute value of the ORP measurement value at the end of one cycle in the previous processing step is set to O _n-1 , and O _n-1 > O _s. When it is, it is judged that the phosphorus release amount increases, and point A in FIG.
Set as first ORP inflection point] detection time set value T _gs is increased. When O _n-1 <O _s , it is determined that the phosphorus release amount decreases, and the set value T _gs of the first ORP bending point detection time in the next step is reduced. Specifically, the method of adjusting the set value T _gs of the first ORP bending point detection time is based on the following equation (1).

T _gs = T _gs0 + K ₁ (O _n-1 −O _s ) (1) where T _gs : Set value of _first ORP bending point detection time in next process K ₁ : Proportional constant O _n-1 : ORP absolute value O _s at the end of one cycle in the current process: Set value of ORP absolute value at the end of one cycle T _gs0 : First ORP inflection point detection time at the ORP absolute value O _s at the end of one cycle The setting value T _gs of is set with an upper limit and a lower limit setting time, and is changed within that range. This calculation can be performed by the controller 9.

Here, 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, the first aeration tank 2a used in the two-tank type intermittent aeration method
Then, phosphorus absorption is performed in the aerobic process and the first in the anaerobic process.
After detecting the ORP inflection point of, the release of phosphorus is performed. In general, it is known that the lower the ORP value in the anaerobic state is, the higher the phosphorus release amount is, and the higher the ORP value is, the lower the ORP value is. If it is also low and the absolute value is high, it can be determined that the phosphorus release amount in the first aeration tank 2a is large. If this amount of release is too large, the released phosphorus cannot be completely absorbed within the time of the aerobic process of the first aeration tank 2a and the second aeration tank 2b, and phosphorus remains in the treated water, resulting in a treated water quality. Getting worse. Therefore, by increasing the set value of the ORP bending point detection time of the first aeration tank 2a, the phosphorus release time is shortened and the release amount is suppressed. At this time, the time allotted to the removal of nitrogen becomes long, so that the removal of nitrogen is also efficient.

On the contrary, the OR at the end of one cycle
If the P value is higher than normal and lower in absolute value, the first
It can be determined that the amount of phosphorus released in the aeration tank 2a is small. In such a case, absorption of phosphorus in the aerobic process becomes poor, and the quality of treated water deteriorates. Therefore, by decreasing the set value of the detection time of the first ORP inflection point of the first aeration tank 2a, the release time of phosphorus is increased and the amount of phosphorus release is increased to prevent poor phosphorus absorption. To do. In this case, since the set value of the detection time of the first ORP inflection point of the first aeration tank 2a is made small, the time spent for nitrogen removal is reduced, but generally, such a phenomenon occurs when the organic load of raw water is low. Since this occurs, the nitrogen load is also low at this time, so the nitrogen removal rate does not decrease due to this operation.

Therefore, if the ORP absolute value at the end of one cycle under the average load condition and the set value of the first ORP bending point detection time are determined in advance, the measured ORP of the first ORP meter is determined. First aeration tank 2a corresponding to the value
The setting value of the ORP inflection point detection time can be determined, and as a result, stable nitrogen and phosphorus removal can be achieved. Also, the ORP value itself may be used instead of the absolute value of the ORP value, and this is merely a numerical treatment that can be handled in the same manner as the methods described above.

Next, the second method of the present invention will be described. Second
Is basically the same as the first method, and the first O
Only the index used for the calculation of the set value of the RP bending point detection time is different, and therefore only this point will be described. Second
In the method described above, regarding the ORP measurement value sent from the first ORP meter 6a to the control device 9, the ORP value at the time when the first ORP inflection point of the current processing cycle is detected and the ORP value at the end of the current cycle. And the difference (ΔORP) with
This ΔORP is used to adjust the set value of the first ORP bending point detection time in the next cycle.

Specifically, the method of adjusting the set value T _gs of the first ORP bending point detection time is based on the following equation (2). T _gs = T _gs1 + K ₂ (ΔORP _n-1 −ΔORP _s ) (2) where T _gs : set value of first ORP bending point detection time in next process K ₂ : proportional constant ΔORP _n-1 : current process At the time of detection of bending point in
Value and the ORP value at the end of the cycle ΔORP _s : Set value of the difference between the ORP value at the time of detecting the inflection point and the ORP value at the end of the cycle T _gs1 : The first ORP inflection point detection time at the time of ΔORP _s The setting value T _gs of is set with an upper limit and a lower limit setting time, and is changed within that range. This calculation is performed by the controller 9.

That is, it can be determined that the phosphorus release amount is large when ΔORP is larger than usual and the phosphorus release amount is small when ΔORP is smaller than usual. FIG.
The data obtained in the continuous control experiments conducted so far by the present inventors using the apparatus shown in FIG. 4 using prepared sewage obtained by mixing human waste, cafeteria drainage, soap water, tap water, sodium acetate, etc. Is a graph in which the vertical axis plots the increase of the PO4-P concentration in the first aeration tank 2a due to phosphorus release, and the horizontal axis plots ΔORP. It can be seen from FIG. 1 that the greater ΔORP is, the more phosphorus is released, and the smaller ΔORP is, the less phosphorus is released.

Next, the third method of the present invention will be described. Figure 2
[Fig. 3] is a schematic diagram showing a main configuration of a device and a control system of a two-tank type intermittent aeration method to which a third method is applied. 2 that are common to those in FIG. 4 are denoted by the same reference numerals, and the handling of arrow lines is also the same as in FIG. In FIG. 2, this device is basically the same as the device shown in FIG. 4, but is different in that an organic material addition pump 10 and an organic material storage tank 11 are provided.

In the third method, for the ORP measurement value sent from the first ORP meter 6a to the controller 9, the absolute value O of the ORP measurement value at the end of one cycle of the processing step is calculated, and this O value is calculated. On the other hand, the lower limit value O _L of the absolute value of the ORP measurement value is set in advance, and the absolute value of the ORP measurement value at the end point of one cycle in the previous processing step is set to O _n-1 , and O _n-1 < When it becomes O _L , it is judged that the phosphorus release amount is small and the supply amount of organic matter is insufficient, and from the next cycle, the first OR of the first ORP meter is determined.
After detecting the P bending point, the organic substance is added to the first aeration tank 2a using the organic substance addition pump 10. The addition amount can be determined by experimentally obtaining the normal organic load and the organic load at the lower limit value O _L in advance.

This calculation is carried out by the controller 9, and based on the result of the judgment, the controller 9 causes the organic substance addition pump 10 to operate.
Then, the start signal is automatically sent. As the organic substance to be added, it is preferable to use biodegradable organic substances such as saccharides that are easily ingested by acetic acid and microorganisms and can obtain a relatively high phosphorus release rate. Stopping the addition of organic substances is performed as follows. Upper limit O _H of the absolute value of the advance ORP measurements
Is set, and when the upper limit value is continuously exceeded several times, the addition of the organic substance is stopped from the next processing cycle.

In the third method, the organic substance is added to the first aeration tank 2a, but the organic substance is added to the second aeration tank 2a.
Since it is also decomposed and removed in b, the organic matter concentration in the treated water does not increase. Therefore, the absolute value of the ORP measurement value at the end of one cycle when the minimum amount of organic substances required for proper phosphorus release is supplied is experimentally determined as the lower limit value O _L in advance to complete one cycle. The organic substance injection timing can be determined from the absolute value of the ORP measurement value at that time, and as a result, the reduction of the phosphorus removal rate can be prevented.

Next, the fourth method of the present invention will be described. Fourth
The method is basically the same as the third method, but the ORP of the current treatment cycle is used to judge the addition or non-addition of organic substances.
The only difference is that the difference (ΔORP) between the ORP value at the time of detecting the bending point and the ORP value at the end of the cycle is used. Further, ΔORP is as described in the explanation of the second method.

Next, the fifth method of the present invention will be described. FIG.
[Fig. 6] is a schematic diagram showing a main part configuration of an apparatus and a control system of a two-tank type intermittent aeration method to which a fifth method is applied. 2 that are common to FIG. 2 are denoted by the same reference numerals, and the handling of arrow lines is also the same as in FIG. In FIG. 3, this device is basically the same as the device shown in FIG. 2, except that the coagulant addition pump 12 and the coagulant reservoir tank are installed without the organic substance addition pump 10 and the organic substance reservoir tank 11. 13 is equipped.

In the fifth method, with respect to the ORP measurement value sent from the first ORP meter 6a to the controller 9, the absolute value O of the ORP measurement value at the end of one cycle of the processing step is calculated, and this O respect, may be set the lower limit value O _L and the upper limit value O _H of the absolute value of the advance ORP measurements, respectively, the absolute value of the ORP measurements at the end of one cycle time of the previous processing steps as O _n-1 , O _n-1 <O
When _L or O _n-1> O _H, in the case of O _n-1 <O _L,
Phosphorus emission is reduced organic material supply amount is insufficient, determines that the phosphorus removal is deteriorated, in the case of O _n-1> O _H, phosphorous emissions excessive organic matter supply amount becomes excessive, phosphorus removal is worsened Then, from the next cycle, the aggregating agent adding pump 12 is used to change the aggregating agent that reacts with phosphorus to form a sparingly soluble compound.
Is added to the second aeration tank 2b from the flocculant storage tank 13 to remove phosphorus.

This calculation is performed by the controller 9, and a start signal is automatically sent from the controller 9 to the coagulant addition pump 12 based on the determination result. The method of adding the coagulant to the aeration tank for removing phosphorus is known as a commonly-used coagulation method. Therefore, the addition amount, type, etc. of the coagulant follow the conditions of the coagulation method. Is good. Stopping the addition of the coagulant is performed as follows. The absolute value of the ORP measurements at the end of one cycle time of the processing steps, the upper and lower limit values O _H consecutively several times, when it returns to a range between O _L, and stops the addition of the agent from the next cycle .

Therefore, the coagulant injection timing can be determined from the absolute value of the ORP measurement value at the end of one cycle, and as a result, the phosphorus removal rate can be prevented from decreasing. Next, a sixth method of the present invention will be described. The sixth method is basically the same as the fifth method, except that the addition or non-addition of the coagulant is determined by determining the ORP value at the ORP inflection point detection point of the current treatment cycle and the ORP value at the end point of the cycle. Difference from the value (ΔOR
The only difference is that P) is used. Further, ΔORP is as described in the explanation of the second method.

[0040]

EFFECT OF THE INVENTION In the biological dephosphorization method, there is a problem that the phosphorus removal rate decreases when the organic matter concentration in the inflowing raw water is low or when the organic matter concentration in the inflowing raw water is extremely high. Since the control method of the intermittent aeration method operates so as to distribute the nitrogen and phosphorus removal steps during one cycle of the treatment cycle, it is possible to cope with the fluctuation of the organic matter load of the sewage that normally flows in. Good quality of treated water can be obtained. However, when the organic load fluctuation as described above 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 first method of the present invention is based on the absolute value of the measured value at the end of one cycle of the first ORP meter installed in the first aeration tank, and the set value for the first ORP bending point detection time. To regulate the phosphorus release time. In the second method, based on the difference between the ORP measurement value of the first ORP meter at the time of detecting the ORP bending point and the ORP measurement value of the first ORP meter at the end of the current cycle, O
The set value of the RP inflection point detection time is changed to adjust the phosphorus release time.

As a result, in the first and second methods, an appropriate amount of phosphorus release in the first aeration tank is always secured, absorption and release of phosphorus proceed in good condition, and a high phosphorus removal rate is achieved. Can be maintained. In the third method of the present invention, the absolute value of the measured value at the end of one cycle of the first ORP meter installed in the first aeration tank is determined, and if the absolute value is equal to or less than a predetermined value, the organic substance is supplied. After determining that the amount is insufficient and detecting the ORP bending point of the first ORP meter,
Add organics to the aeration tank. In the fourth method, the first O
Obtain the difference between the ORP measurement value of the RP meter at the time of detecting the ORP bending point and the ORP measurement value of the first ORP meter at the end of the current cycle. If the difference is less than a predetermined value, add an organic substance. To do.

As a result, in the third and fourth methods, since sufficient organic matter is supplied to release phosphorus, the release and absorption of phosphorus proceed in a good state, and a high phosphorus removal rate can be maintained. it can. The fifth method of the present invention is to obtain the absolute value of the measured value at the end of one cycle of the first ORP meter installed in the first aeration tank, and if the absolute value is less than or equal to the predetermined lower limit value or more than the upper limit value. If present, a flocculant that reacts with phosphorus to form a sparingly soluble compound is added to the second aeration tank. In the sixth method, the difference between the ORP measurement value of the first ORP meter at the time of detecting the ORP bending point and the ORP measurement value of the first ORP meter at the end of the current cycle is calculated, and the difference is predetermined. If it is below the lower limit or above the upper limit, a flocculant is added.

As a result, in the fifth and sixth methods, since phosphorus is removed by adding the coagulant, a high phosphorus removal rate can be maintained as in the first to fourth methods. As described above, according to the method of the present invention, stable phosphorus removal can be performed without affecting the nitrogen removal even when the organic matter load fluctuation of the inflowing sewage is large.

[Brief description of drawings]

FIG. 1 is the first of the present invention by ΔORP and phosphorus release.
The graph which shows the relationship of PO4-P concentration increase of the aeration tank

FIG. 2 is a schematic diagram showing a main configuration of a sewage treatment apparatus to which a third control method of the present invention is applied.

FIG. 3 is a schematic diagram showing a main configuration of a sewage treatment apparatus to which a fifth control method of the present invention is applied.

FIG. 4 is a schematic diagram showing a configuration of main parts of a sewage treatment apparatus to which the control method of the intermittent aeration method applied by the present inventors is applied.

FIG. 5 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) is ORP of the first aeration tank, (b) is O of the second aeration tank
Relationship diagram of RP with time

[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 First ORP meter 6b Second ORP meter 7a First aeration blower 7b Second aeration blower 8a First stirring pump 8b Second stirring pump 9 Control device 10 Acetic acid addition pump 11 Acetic acid storage tank 12 Flocculant addition pump 13 Flocculant storage tank

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

Claims (6)

[Claims] 1. A first aeration tank provided with a first ORP meter,
A second aeration tank, which is connected in series to the first aeration tank and has a second ORP meter installed, is provided with the waste water flowing into the first aeration tank,
After performing treatment by alternately repeating the aerobic state where aeration is performed in the two aeration tanks and the anaerobic state where 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 that removes nitrogen and phosphorus in wastewater while returning to the tank and removing excess sludge, the absolute value of the measurement value of the first ORP meter at the end of one cycle of the treatment process Based on the above, a control method for an intermittent aeration type activated sludge method, which comprises adjusting a set value of a detection time of an ORP inflection point of a first ORP meter. 2. A first aeration tank provided with a first ORP meter,
A second aeration tank, which is connected in series to the first aeration tank and has a second ORP meter installed, is provided with the waste water flowing into the first aeration tank,
After performing treatment by alternately repeating the aerobic state where aeration is performed in the two aeration tanks and the anaerobic state where 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 that removes nitrogen and phosphorus in wastewater while returning to the tank and removing excess sludge, the ORP measurement value at the time of detecting the ORP bending point of the first ORP meter and the current treatment Control of the intermittent aeration type activated sludge method characterized by adjusting the set value of the ORP inflection point detection time of the first ORP meter based on the difference from the ORP measured value of the first ORP meter at the end of the cycle Method. 3. A first aeration tank provided with a first ORP meter,
A second aeration tank, which is connected in series to the first aeration tank and has a second ORP meter installed, is provided with the waste water flowing into the first aeration tank,
After performing treatment by alternately repeating the aerobic state where aeration is performed in the two aeration tanks and the anaerobic state where 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 removing excess sludge, the absolute value of the measurement value of the first ORP meter at the end of one cycle of the treatment process Seeking,
When this absolute value is less than or equal to a predetermined value, the first OR
A method for controlling an intermittent aeration type activated sludge method, which comprises adding an organic substance to a first aeration tank after detecting an ORP bending point of a P meter. 4. A first aeration tank provided with a first ORP meter,
A second aeration tank, which is connected in series to the first aeration tank and has a second ORP meter installed, is provided with the waste water flowing into the first aeration tank,
After performing treatment by alternately repeating the aerobic state where aeration is performed in the two aeration tanks and the anaerobic state where 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 that removes nitrogen and phosphorus in wastewater while returning to the tank and removing excess sludge, the ORP measurement value at the time of detecting the ORP bending point of the first ORP meter and the current treatment The difference from the ORP measurement value of the first ORP meter at the end of the cycle is calculated, and when the difference is less than or equal to a predetermined value, the first O
A method for controlling an intermittent aeration type activated sludge method, which comprises adding an organic substance to a first aeration tank after detecting an ORP bending point of an RP meter. 5. A first aeration tank equipped with a first ORP meter,
A second aeration tank, which is connected in series to the first aeration tank and has a second ORP meter installed, is provided with the waste water flowing into the first aeration tank,
After performing treatment by alternately repeating the aerobic state where aeration is performed in the two aeration tanks and the anaerobic state where 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 removing excess sludge, the absolute value of the measurement value of the first ORP meter at the end of one cycle of the treatment process Seeking,
Control of the intermittent aeration type activated sludge method characterized by adding a flocculant which reacts with phosphorus to form a sparingly soluble compound in the second aeration tank when the absolute value is below a predetermined lower limit or above a predetermined upper limit Method. 6. A first aeration tank provided with a first ORP meter,
A second aeration tank, which is connected in series to the first aeration tank and has a second ORP meter installed, is provided with the waste water flowing into the first aeration tank,
After performing treatment by alternately repeating the aerobic state where aeration is performed in the two aeration tanks and the anaerobic state where 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 that removes nitrogen and phosphorus in wastewater while returning to the tank and removing excess sludge, the ORP measurement value at the time of detecting the ORP bending point of the first ORP meter and the current treatment The difference from the ORP measurement value of the first ORP meter at the end of the cycle is determined, and when the difference is less than or equal to a predetermined lower limit value or more than an upper limit value, it reacts with phosphorus in the second aeration tank to form a poorly soluble compound. A control method for an intermittent aeration type activated sludge method, which is characterized by adding a flocculating agent.