JPH09108689A - Method of controlling intermittent aeration type activated sludge process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the lowering of a phosphorus removing rate in a device equipped with two aeration tanks by adjusting a set value of detected time of an inflection point of a time change curve of ORP in the first aeration tank and based on a difference between the present inflow quantity and the inflow quantity of an inflow quantity pattern at the same time, adding a flocculant to the second aeration tank. SOLUTION: First and second aeration tanks 2a, 2b into which sewage 1 flows and in which organic matter, nitrogen and phosphorus are removed by activated sludge, a final sedimentation basin 4, and a return sludge pump 5 for returning activated sludge to the first aeration tank 2a are provided. Based on outputs of ORP meters 6a, 6b for measuring oxidation-reduction potential in the aeration tanks 2a, 2b, first and second aeration blowers 7a, 7b and first and second agitation pumps 8a, 8b are controlled. An inflow quantity pattern of sewage per day is set in advance, and a difference between the measured value of the inflow quantity from a flow rate measuring device 10 and the inflow quantity of an inflow quantity pattern at the same time is calculated. When the difference exceeds the upper limit value, a flocculant is added to the second aeration tank 2b by an addition pump 1 to remove phosphorus.

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, 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 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 the activated sludge occurs after the exhausted oxygen molecules are exhausted, which leads to the absorption of phosphorus in the subsequent 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 in FIGS. 3 and 4 (a) below.
This will be described with reference to FIG. FIG. 3 shows JP-A-6-5519.
FIG. 4 is a schematic diagram showing a main part configuration for explaining an intermittent aeration method and a control system described in Japanese Patent Publication No. 0, FIG. 3, wherein paths of water and air are indicated by solid arrows, and a control signal system is indicated by dotted arrows. This apparatus is mainly used for the first type in which sewage 1 flows in and organic matter, nitrogen and phosphorus are removed by activated sludge.
It is composed of an aeration tank 2a and a second aeration tank 2b, a final settling tank 4 in which activated sludge is separated by gravity sedimentation to obtain treated water 3, and a returning sludge pump 5 which returns the sedimented activated sludge to the first aeration tank 2a. is there. First aeration tank 2a and second aeration tank 2b
Is about 1: 1, and the total residence time of the treated water is 16 to 32 hours including the final settling tank 4. The control system is a first O that measures the redox potential in the first aeration tank 2a.
RP meter 6a, second ORP meter 6b for measuring redox potential in the second aeration tank 2b, first aeration blower 7a, second aeration blower 7b, first agitation pump 8a based on those values.
Control device 9 for outputting a control signal to the second stirring pump 8b
Consists of

The basic idea of operation control in such a 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, By controlling nitrification and denitrification in the first aeration tank 2a for a certain period of time, the phosphorus release time is ensured, and in the second aeration tank 2b, nitrification and denitrification are performed, and the phosphorus release is controlled while being prevented. One cycle is maintained for a predetermined time, high nitrogen,
To obtain the phosphorus removal rate. A specific method will be described with reference to FIGS. 4A and 4B together with a change in ORP accompanying control. 4 (a) and 4 (b) show that the aeration start time is set to zero at an arbitrary timing during the control.
4 shows changes in ORP with the passage of time, and FIG. 4A is a relational diagram with respect to elapsed time of ORP of the first aeration tank and FIG. 4B is ORP of the second aeration tank.

First, the control method of the first aeration tank 2a will be explained. The aeration time for nitrification and phosphorus absorption is T _e , and the denitrification time is T _f, and the time T _g which is the sum of T _e and T _f is The aeration time T _e is adjusted so as to match the preset time T _gs . Turning now to changes in the ORP of the 1ORP meter 6a, bending point A after denitrification completion has appeared, by measuring the time T _g by detecting A, based on the difference between the T _gs and T _g it is to adjust the aeration time T _e. As a result, as described later, since one cycle is maintained at approximately T _ds time, the phosphorus release time is secured as T _ds −T _gs .

The control method of the second aeration tank 2b will be described.
Letting T _{b be} the aeration time for nitrification and phosphorus absorption, and T _{c be} the stirring time for denitrification to proceed, the time T _d that is the sum of T _b and T _c
As but to match the preset time T _ds, adjust the aeration period T _b, together as one period after the time T _d is finished, the first aeration tank 2a, return simultaneously aerated state second aeration tank 2b Let it. This is done by first 2ORP system detects inflection point B from the change in ORP and 6b measuring the time T _d and adjusts the aeration period T _b on the basis of the difference between the T _ds and T _d. 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.

[0009]

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 under certain specific conditions has the following problems that still have to be solved. One is that the phosphorus removal rate decreases when the organic matter concentration in the inflowing wastewater is low.
This is a phenomenon in which when the concentration of organic substances is low, the amount of released phosphorus decreases in the anaerobic process, resulting in poor phosphorus absorption in the aerobic process.

On the other hand, contrary to the above case, when the organic matter concentration in the inflowing wastewater is extremely high, the amount of phosphorus released increases in the anaerobic process, and as a result, phosphorus is absorbed within the aerobic process time. This is a phenomenon that cannot be done. As described in the prior art, the control method of this method performs the operation of distributing the nitrogen and phosphorus removal steps during one cycle, so it is possible to cope with a certain amount of organic load fluctuation and is good. Excellent treated water quality can be obtained. However, when the fluctuation of the organic matter load is extremely large, 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 intermittent aeration method capable of preventing a reduction in the phosphorus removal rate. It is in.

[0012]

In order to solve the above problems, two methods, method A and method B, were invented. 2 of the present invention
In both methods, the operation of the two-tank intermittent aeration method is performed by using two means in combination as follows. First, in method A, A) a flow meter capable of continuous measurement is installed in the inflow system of the wastewater of the treatment device, and the next process is performed based on the difference between the measured inflow flow rate and a predetermined inflow flow rate. First in
While changing the set value of the detection time of the ORP inflection point of the aeration tank, A) The daily inflow pattern of drainage is set in advance, and the current inflow and the inflow of the inflow pattern at the same time are set. A difference is determined, and when the difference is equal to or more than a predetermined upper limit value, a coagulant that reacts with phosphorus to form a sparingly soluble compound is added to the second aeration tank.

In A, the set value of the detection time of the ORP bending point of the ORP meter of the first aeration tank in the next step is adjusted based on the flow rate measurement value of the flow meter installed in the drainage inflow system up to the previous processing step. To do. That is, when the inflow flow rate in the previous process step is larger than the preset inflow flow rate, the set value of the detection time of the ORP inflection point of the first aeration tank in the next step is increased according to the difference. If it is smaller than the set inflow rate, the set value of the ORP inflection point detection time is decreased.

To explain this meaning, it is known that the release rate of phosphorus varies depending on the amount of organic matter supplied, and tends to increase when the amount of organic matter is large and slow when the amount of organic matter is small. When the amount of organic matter supplied is too large, the amount of phosphorus released becomes too large, and phosphorus cannot be absorbed within the specified aeration time, the phosphorus removal rate decreases, and conversely, when the amount of organic matter supplied is small, the amount of phosphorus released As a result, the 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 phosphorus release amount in the first aeration tank.

It is known that the inflow of wastewater has a high organic matter concentration when the inflow amount is large and is low when the inflow amount is small. Therefore, as described above, when the inflow amount is large,
By increasing the set value of the detection time of the ORP bending point, the phosphorus release time is shortened and the phosphorus release amount is suppressed. Further, when the inflow flow rate is small, the set value of the detection time of the ORP inflection point is reduced to increase the phosphorus release time and increase the phosphorus release amount. In this way, the phosphorus release time is changed by changing the set value of the ORP inflection point detection time, and an appropriate phosphorus release amount is secured.

In A, when a large amount of rainwater is mixed in the drainage such as during rainy weather, the inflow is large, but
Wastewater with low organic matter concentration may flow in. In this case, if the control operation like the method A is performed, the phosphorus removal may be deteriorated. Therefore, in the present invention, a daily inflow pattern is separately set, a difference between the current inflow amount and the inflow amount of the inflow pattern at the same time is obtained, and when the difference is equal to or more than a predetermined upper limit value. It is judged that the above phenomenon is occurring, and the second aeration tank
A flocculant that reacts with phosphorus to form a sparingly soluble compound is added to remove phosphorus.

Next, in the B method, B) a flow meter capable of continuous measurement is installed in the inflow system of the wastewater of the treatment equipment, and the measured value of the inflow rate is equal to or lower than a predetermined lower limit value of the inflow rate. Or when it is above the upper limit value, the aeration time of the first aeration tank in the next process is set to a special value, respectively, and B) the daily inflow pattern of drainage is set in advance and the same as the current inflow A difference from the inflow amount of the time inflow pattern is obtained, and when the difference is equal to or more than a predetermined upper limit value, a coagulant that reacts with phosphorus to form a sparingly soluble compound is added to the second aeration tank.

In B, when the flow rate measurement value of the flow meter installed in the drainage inflow system up to the previous process step is less than or equal to the predetermined lower limit value or more than the upper limit value of the inflow rate,
The set value of the aeration time of the first aeration tank in the next process is set to a special value. For example, when the inflow rate is 100 m ³ / day, the lower limit value of the inflow rate is 30 m ³ /
Day and the upper limit value of 80 m ³ / day, and when it is determined that the upper limit value is exceeded, the set value of the aeration time of the first aeration tank in the next process is set to a predetermined long value. When the value is less than or equal to the lower limit value, the set value of the aeration time of the first aeration tank in the next process is set to a predetermined short value.

To explain this meaning, it is known that the release rate of phosphorus varies depending on the amount of organic matter supplied, and tends to be faster when the amount of organic substance is large and slower when the amount is small. When the amount of organic matter supplied is too large, the amount of phosphorus released becomes too large, and phosphorus cannot be absorbed within the specified aeration time, the phosphorus removal rate decreases, and conversely, when the amount of organic matter supplied is small, the amount of phosphorus released As a result, the 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 phosphorus release amount in the first aeration tank.

It is known that the inflow of wastewater has a high organic matter concentration when the inflow amount is large and is low when the inflow amount is small. Therefore, when the inflow amount exceeds the upper limit value, the phosphorus release amount as described above is generated. It was judged that an excessive phenomenon would occur, and by increasing the set value of the aeration time of the first aeration tank in the next process, the time consumed for nitrification and denitrification was increased, and as a result, the phosphorus release time was reduced. To reduce phosphorus release. Further, when the inflow rate is below the lower limit, it is determined that the phenomenon of weak phosphorus absorption will occur, and by reducing the set value of the aeration time of the first aeration tank in the next step, nitrification and denitrification will be achieved. The consumption time is reduced, the phosphorus release time is secured, and the phosphorus release amount is increased. By performing such processing, the phosphorus release time is changed when the inflow is extreme,
Ensure proper phosphorus release.

In B, when a large amount of rainwater is mixed in the drainage such as in the case of rain, the inflow is large, but
Wastewater with low organic matter concentration may flow in. In such a case, if the control operation like the method B is performed, phosphorus removal may be deteriorated. Therefore, in the present invention, a daily inflow pattern is separately set, a difference between the current inflow amount and the inflow amount of the inflow pattern at the same time is obtained, and when the difference is equal to or more than a predetermined upper limit value. It is judged that the above phenomenon is occurring, and the second aeration tank
A flocculant that reacts with phosphorus to form a sparingly soluble compound is added to remove phosphorus.

By applying the control method and the coagulant addition method according to the above-mentioned method A or method B, the phosphorus removal rate deteriorates when the inflow load fluctuation of wastewater is severe, and the phosphorus removal rate deteriorates in rainy weather. Can be prevented, and stable phosphorus removal can be achieved.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 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 the method A or B of the present invention is applied, and the same symbols as those in FIG. 3 of FIG. Is used, and the handling of arrow lines is the same as in FIG. In FIG. 1, this device is basically the same as the device shown in FIG. 3, except that the flow measuring device 10 and the coagulant addition pump 11 and the coagulant reservoir which can automatically perform continuous measurement are different. It is equipped with 12.

First, the operation control method according to the method A of the present invention using this apparatus is performed by using the following two means in combination. The first of Method A is a flow rate measuring device 1 capable of continuous measurement.
The measurement value Q of inlet flow to be sent to the controller 9 from 0, the inflow rate previously set Q _s, the flow rate in the previous processing step as Q _n-1, when the Q _n-1> Q _s Determines that the phosphorus release rate increases, and increases the set value T _gs of the detection time of the ORP bending point by the first ORP meter 6a in the next step. When Q _n-1 <Q _s , it is determined that the phosphorus release rate decreases, and the set value T of the detection time of the ORP bending point by the first ORP meter 6a in the next step is set.
_{Reduce gs} .

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 as follows (1).
Depends on the formula. T _gs = T _gs0 + K ₁ (Q _n-1 −Q _s ) (1) where T _gs : set value of detection time of first ORP bending point in next process K ₁ : proportional constant Q _n-1 : current Inflow rate in process Q _s : Set value of inflow rate T _gs0 : Set value of detection time of first ORP bending point at inflow rate Q _s T _gs has upper and lower limit set times Change within the range. This calculation can be performed by the controller 9.

The meaning of changing the set value of the ORP bending point detection time will be described. As described in the prior art, 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 ORP inflection point appears in the anaerobic process. Generally, the release rate of phosphorus depends on the supply amount of organic matter, and it is known that the concentration of organic matter is high when the inflow rate is high and low when it is low. When there is a large amount, it can be determined that the phosphorus release rate increases and the phosphorus release amount in the first aeration tank 2a is large. 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, which is also effective for the nitrogen removal.

On the contrary, when the inflow of drainage is small, the first
It can be judged that the amount of phosphorus released in the aeration tank is small. In such a case, the 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 value of the detection time of the ORP inflection point is determined in advance by the average inflow rate,
The set value of the detection time of the ORP bending point of the first aeration tank corresponding to the measured inflow rate can be determined, and as a result, stable nitrogen and phosphorus removal can be achieved. The flow rate measuring device 10 needs to measure at least once per cycle, and in the case of constant measurement, the average value thereof may be used.

The second method A is that when a large amount of rainwater is mixed in the drainage, such as during rainy weather, the drainage having a low organic matter concentration may flow in, although the inflow is large. When such waste water flows in, there is a possibility that stable phosphorus removal cannot be achieved by the first means of Method A. Therefore, using the coagulant addition pump 11 and the coagulant storage tank 12 described above, Addition is performed to prevent deterioration of phosphorus removal. The determination as to whether or not the coagulant is added will be described with reference to FIG.

FIG. 2 is a diagram showing an example of daily inflow rate changes. The inflow pattern of the daily wastewater shown by the dotted line in FIG. 2 is set in advance, and the measured value Q of the inflow rate sent from the flow rate measuring device 10 to the control device 9 is compared with the inflow amount of the inflow amount pattern at the same time. The difference Q _X is calculated and this Q _X
The upper limit value Q _{H of the} difference is set in advance for
When _X> Q _H, determines that a large amount of rainwater into the waste water in rainy weather or the like is mixed, a flocculating agent capable of reacting with phosphorus make compound slightly soluble, with flocculant pump 11, The coagulant storage tank 12 is added to the second aeration tank to remove phosphorus.

This calculation is performed by the control device 9, and a start signal is automatically sent from the control device 9 to the coagulant addition pump 11 based on the determination result. The method of adding a coagulant to the aeration tank for phosphorus removal is known as a commonly performed simultaneous coagulation method.
The type and the like should follow the conditions of the simultaneous agglutination method. The coagulant addition is stopped as follows. The addition of the coagulant is stopped when the difference between the inflow amount pattern and the inflow amount becomes the upper limit value Q _H or less for several hours continuously.

Next, according to the method B of the present invention using this apparatus,
The operation control method is similar to method A, but
This is done by combining the two methods. The first of the B methods allows continuous measurement
Inflow flow from the effective flow rate measuring device 10 to the control device 9
The lower limit value Q of the inflow flow rate with respect to the measured value Q
_L1And the upper limit Q _H1Is set and the previous processing step is
The inflow rate at_n-1As Q_n-1≤Q_L1Became
At this time, the organic matter supply amount becomes insufficient and the phosphorus release amount decreases.
Therefore, it was judged that the phosphorus removal would deteriorate, and
1 Explain the set value of the aeration time of the aeration tank 2a by the conventional technique.
T_eNot the preset T_L1And Q
_n-1≧ Q _H1When the amount of organic matter is excessive, the first aeration tank
If the phosphorus release in 2a becomes excessive and the phosphorus removal deteriorates
Judge and set the aeration time of the first aeration tank 2a in the next process.
T with preset value_H1And Q_L1<Q_n-1<
Q_H1When, the aeration time of the first aeration tank 2a in the next process
The setting value of T is T as described in the prior art._eAnd

Such a lower limit value Q_L1And below that flow rate
Give enough phosphorus release time to secure an appropriate amount of phosphorus release.
Set value T of the aeration time of the first aeration tank 2a_L1, And the upper limit
Value Q _H1And an excess of phosphorus is not released even if the flow rate is higher than that.
The set value of the aeration time of the first aeration tank 2a that gives the gas release time
T_H1If you decide in advance experimentally,
Even in extreme cases, the first aeration tank 2a can release appropriate phosphorus.
The output can be secured, and stable phosphorus removal can be achieved. Ma
T_L1Is smaller than usual and spends nitrogen removal
It will take less time, but generally in such cases nitrogen loading
Since this is also low, this operation does not reduce the nitrogen removal rate.
Absent. T_H1Is higher than usual and is used for nitrogen removal.
Efficient for nitrogen removal as it takes longer to divide
It is a target.

Note that the flow rate measuring device 10 needs to measure at least once per cycle, and in the case of constant measurement, the average value thereof may be used. The second of the B method is that when a large amount of rainwater is mixed in the drainage such as during rainy weather, the drainage with a low organic matter concentration may flow in, even if the inflow is large. When it flows in, stable phosphorus removal may not be achieved by the first means of Method B. Therefore, the coagulant addition pump 11 and the coagulant storage tank 12 described above are used.
Is used to add a coagulant to prevent deterioration of phosphorus removal. The determination as to whether or not the coagulant is added will be described with reference to FIG.

FIG. 2 is a diagram showing an example of daily change of inflow rate. The inflow pattern of the daily drainage shown by the dotted line in FIG. 2 is set in advance, and the measured value Q of the inflow rate sent from the flow rate measuring device 10 to the control device 9 is compared with the inflow amount of the inflow amount pattern at the same time. The difference Q _X is calculated and this Q _X
The upper limit value Q _{H2 of the} difference is set in advance, and Q
_{When X} > Q _H2 , it is determined that a large amount of rainwater is mixed in the wastewater when it rains, and the flocculant that reacts with phosphorus to form a sparingly soluble compound is aggregated using the flocculant addition pump 11. Phosphorus is removed by adding it from the agent storage tank 12 to the second aeration tank 2b.

This calculation is performed by the controller 9, and a start signal is automatically sent from the controller 9 to the coagulant addition pump 11 based on the determination result. The method of adding a coagulant to the aeration tank for phosphorus removal is known as a commonly performed simultaneous coagulation method.
The type and the like should follow the conditions of the simultaneous agglutination method. The coagulant addition is stopped as follows. The addition of the coagulant is stopped when the difference between the inflow pattern and the inflow pattern becomes the upper limit value Q _H2 or less for several hours continuously.

[0037]

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 wastewater is extremely high.
Since the control method of the two-tank intermittent aeration method is such that the nitrogen and phosphorus removal steps are distributed during one cycle,
It is possible to deal with fluctuations in organic matter load to some extent, and good treated water quality can be obtained. However, when the organic load fluctuation is extremely large, the phosphorus removal may be deteriorated.

The two methods A or B of the present invention are made to deal with this problem by using the two means in combination, and have the following advantages. First, the first
In the method, a meter capable of continuously measuring the inflow flow rate is installed in the inflow system of the wastewater of the device in which the two-tank intermittent aeration method is performed, and in the A method, based on the flow rate measurement value of the meter, By changing the set value of the detection time of the ORP inflection point of the first aeration tank and adjusting the phosphorus release time, and in the B method, the measured flow rate of the instrument is below the predetermined lower limit value or above the upper limit value. At this time, control is performed by giving special values to the set values of the aeration time of the first aeration tank.

In the second means, in both the control methods A and B, when the flow rate difference from the set inflow rate pattern exceeds a predetermined value, it reacts with phosphorus in the second aeration tank and is hardly soluble. Add a flocculant to form the compound of. As a result, in the normal case, with the first means, the appropriate amount of phosphorus release in the first aeration tank is secured, the absorption and release of phosphorus proceed in a good state, and a large amount of rainwater is mixed in the drainage. Even in the special case in which the phosphorus is removed by the coagulant by the second means, a high phosphorus removal 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 and coagulant addition method of the present invention is applied.

FIG. 2 is a diagram showing a change in daily inflow in the control method of the present invention, showing an inflow pattern and a measured flow rate.

FIG. 3 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. 4 shows changes in ORP of a first aeration tank and a second aeration tank in a control method of an intermittent aeration method which the present inventors filed,
(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 10 Flow rate measuring device 11 Flocculant addition pump 12 Flocculant storage tank

(72) Inventor Yutaka Mori 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Yasunari Sasaki 1-1, Tanabe-shinden, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji (72) Inventor Akiko Ogura 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (2)

[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 that removes nitrogen and phosphorus in the wastewater while returning it to the tank and extracting it as excess sludge, measure the flow rate of the wastewater flowing into the first aeration tank, Based on the difference with the determined inflow rate, the set value of the detection time of the inflection point of the ORP time change curve in the first aeration tank is adjusted, and the daily inflow pattern of drainage is set in advance. The difference between the inflow rate and the inflow rate of the inflow pattern at the same time is calculated, and when the difference is equal to or greater than the predetermined upper limit value, a flocculant that reacts with phosphorus to form a sparingly soluble compound is added to the second aeration tank. You A method for controlling an intermittent aeration type activated sludge method, which is characterized by the following. 2. 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 that removes nitrogen and phosphorus in the wastewater while returning it to the tank and extracting it as excess sludge, the flow rate of the wastewater flowing into the first aeration tank is measured, and this flow rate measurement value is calculated in advance. When the value is less than the lower limit value or more than the upper limit value, the set value of the aeration time of the first aeration tank is set to a special value, and the daily inflow pattern of drainage is set in advance, and The difference between the inflow rate and the inflow rate at the same time is calculated, and when the difference is equal to or more than a predetermined upper limit, a coagulant that reacts with phosphorus to form a sparingly soluble compound is added to the second aeration tank. When Control method for intermittent aeration type activated sludge process.