JP3277628B2 - Biological abnormality detection method for aeration tank - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the biological treatment of wastewater by the activated sludge method, in which existing measuring instruments (dissolved oxygen meter, air flow meter, flow meter) installed in an aeration tank are program-controlled. And a method for detecting a biological abnormality in an aeration tank, wherein the method detects a harmful substance such as cyan in wastewater.

[0002]

BACKGROUND OF THE INVENTION The present invention relates to automatic control of an aeration tank (aeration tank) for purifying sewage by an activated sludge method and automatic warning of a biological abnormality caused by contamination of harmful substances such as cyanide during operation. In order to clarify the role of the aeration tank in the treatment, an outline of the wastewater treatment currently being implemented will be described with reference to FIG.

[0003] As shown in this figure, wastewater collected in a sand basin is first sent to a sedimentation basin after large trash and sand are removed there, and after relatively sedimentable sediment is settled, the supernatant water is removed. It is sent to the aeration tank and treated by the activated sludge method, which is a biological wastewater treatment method using microorganisms.

[0004] As described above, the self-cleaning action of microorganisms operating in a natural environment is performed by an aeration tank (aeration tank).
It is controlled and managed artificially. The activated sludge method, which is widely used for treating municipal sewage and various organic industrial wastewaters,
It applies oxidative decomposition of organic matter in wastewater by aerobic microorganisms.

In this method, the supply of oxygen is extremely important for promoting biochemical reactions such as the oxidation of organic substances by microorganisms, the growth of microorganisms, and the autooxidation of organic substances. Governs the success or failure of

In practice, as shown in FIG. 10, air is blown into an aeration tank using a blower and circulated in the aeration tank, thereby supplying oxygen to aerobic microorganisms and promoting its biochemical reaction. Wastewater treatment efficiently.

[0007] Wastewater inflow and blowing (oxygen supply)
Is measured by a flow meter and an air flow meter, respectively, and the dissolved oxygen amount in the aeration tank is measured by a dissolved oxygen meter.

[0008] The wastewater flowing into the aeration tank only removes inhomogeneous substances such as garbage, but does not treat pollutants contained in the wastewater. Further, since the wastewater treatment is an open system, harmful substances such as cyanide are mixed into the aeration tank and act as inhibitors of microorganisms in the aeration tank.

In particular, even a very small amount of cyanogen completely inhibits the biochemical reaction of cyanogen-sensitive microorganisms, and stops oxidative decomposition of organic substances contained in wastewater during aeration.

[0010]

As described above, cyanide acts as an inhibitor of the oxidative decomposition of organic substances by aerobic microorganisms, and only reduces the wastewater treatment capacity by the activated sludge method (referred to as biological treatment abnormality). Alternatively, cyanide, as represented by hydrogen cyanide, sodium cyanide, and potassium cyanide, is extremely toxic, and great care must be taken in testing for the escape of cyanide into the natural environment.

Conventional cyan detection involves a method of generating a potential corresponding to the cyan ion concentration using an ion electrode, which is an electrochemical sensor, to measure free cyanide in water, or a method of decomposing a cyano complex by irradiation with ultraviolet light. Although a method of measuring cyan using an ion electrode is used, there is a problem that the measurement of cyan is hindered by the presence of coexisting ions.

Further, since the ion electrode is characterized by selectively responding to a specific ion in the solution, a commercially available cyan detection device applying the principle of the ion electrode is a dedicated device for only cyan detection, There is a problem that there is no other function.

Further, since the detection accuracy of a commercially available cyan detector is high and the detection accuracy depends on the presence or absence of inspection, maintenance inspections such as replenishment of reagents and sensitivity calibration have to be performed at intervals of two weeks, and running costs are low. However, the current situation is that the number of introduction to sewage treatment plants is small.

Generally, there is no method for detecting cyan in a processing plant where no cyan detecting device is installed, and it is an important issue to overcome this.

The present invention has been made in view of the above problems, and provides a method for detecting an abnormality in biological treatment of an aeration tank caused by a harmful substance such as cyan without using a conventional cyan detection device. It is in.

[0016]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that when performing aeration treatment of the water to be treated by the activated sludge method in the aeration tank, In the biological abnormality detection method of the aeration tank for detecting biological abnormality, the constant control of the dissolved oxygen concentration in the aeration tank is performed by increasing or decreasing the oxygen supply amount to the aeration tank according to the increase or decrease of the inflow of the water to be treated. Setting a first threshold value for a decreasing rate of the oxygen supply amount in the aeration tank and a second threshold value for an increasing rate of the dissolved oxygen concentration in the aeration tank; When the rate of decrease is greater than the threshold value and the rate of increase in the dissolved oxygen concentration exceeds the threshold value, it is determined that a biological abnormality has occurred in the aeration tank. Biological abnormality detection method in the tank To provide.

According to a second aspect of the present invention, there is provided a method for detecting a biological abnormality in an aeration tank, wherein the biological abnormality in the aeration tank is detected when performing the aeration treatment by the activated sludge method for the water to be treated in the aeration tank. A constant oxygen supply amount control to the aeration tank is performed, and a first threshold value and a second threshold value are set for an increase rate and a decrease rate of the flow rate of the water to be treated into the aeration tank, respectively. Setting a third threshold value and a fourth threshold value larger than the third threshold value with respect to the increasing rate of the dissolved oxygen concentration in the aeration tank;
When the rate of increase in the inflow of the water to be treated into the aeration tank exceeds the first threshold, and when the rate of increase of the dissolved oxygen concentration in the aeration tank exceeds the third threshold ,
And the rate of decrease in the inflow of the water to be treated into the aeration tank exceeds the second threshold, and the rate of increase of the dissolved oxygen concentration in the aeration tank exceeds the fourth threshold. A method for detecting a biological abnormality in the aeration tank, wherein it is determined that a biological abnormality has occurred in the aeration tank.

[0018]

Generally, in the biological treatment of wastewater by the activated sludge method, harmful substances such as cyanide act as inhibitors of the oxidative decomposition of organic substances by aerobic microorganisms. As a result, the wastewater treatment capacity by the activated sludge method is reduced. Dissolved oxygen consumption by aerial microorganisms is reduced.

In particular, when harmful substances such as cyanide flow under the condition that the wastewater inflow rate and the oxygen supply rate per unit time are constant, the dissolved oxygen consumption by the aerobic microorganisms decreases.
The dissolved oxygen concentration per unit time increases rapidly. By detecting this phenomenon, it is possible to detect harmful substances such as cyan and to warn of an abnormal biological treatment.

Further, by controlling the concentration of dissolved oxygen at a constant amount of wastewater inflow per unit time, it is possible to reduce the amount of dissolved oxygen consumed by aerobic microorganisms when a harmful substance such as cyan flows. A control mechanism is provided to reduce the amount of oxygen supplied from the blower in response to detect harmful substances such as cyanide from the increase in dissolved oxygen concentration, the increase in oxygen concentration, and the decrease in oxygen supply per unit time. , Can be alerted to biological treatment abnormalities.

Further, the supply amount of oxygen per unit time is controlled to be constant, so that the amount of change in the inflow amount of wastewater per unit time and the dissolved oxygen consumption of aerobic microorganisms generated when harmful substances such as cyan flow in. From the amount of change in the dissolved oxygen concentration per unit time due to the decrease in the amount, detect harmful substances such as cyan,
A biological treatment abnormality can be warned.

It is also possible to improve the reliability of detection of biological treatment abnormality by introducing a circuit that does not warn of biological treatment abnormality when precipitation is not confirmed or during inspection.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings, but the present invention is not limited to the following embodiments.

In this embodiment, the operation of the aeration tank is controlled by: (1) a mechanism for controlling the amount of wastewater inflow per unit time and a blowing rate (oxygen supply rate); and (2) a mechanism for controlling the concentration of dissolved oxygen. (3) A mechanism for controlling the air blowing amount (oxygen supply amount) to be constant by performing a program control to detect a harmful substance such as cyan contained in the wastewater and warn of the biological treatment abnormality caused thereby.

(1) Constant control of wastewater inflow and oxygen supply per unit time First, the supernatant wastewater of the sedimentation basin is flowed into the aeration tank at a certain flow rate. Here, it is assumed that the treated water treated by the activated sludge method is not drained from the aeration tank when the wastewater is flowing. Therefore, the amount V of wastewater in the aeration tank increases with time. Oxygen is supplied by blowing air to an aeration tank by a blower. The dissolved oxygen concentration in the aeration tank is measured at any time with a dissolved oxygen meter.

The supply amount of oxygen per unit time from the blower is S liter / hour, the consumption amount of oxygen per unit time by aerobic microorganisms is C liter / hour, and the amount of wastewater flowing into the aeration tank per unit time. Is V: liter / hour, the dissolved oxygen concentration DO in the aeration tank at a certain time T is
In simple terms, it can be expressed by Equation 1.

[0027]

DO = (ST-CT) / VT = (SC) / V = (S / V) (1-C / S) As shown in FIG. 1, oxygen per unit time from the blower When the supply amount S and the wastewater inflow amount V per unit time into the aeration tank are controlled to be constant, respectively, the value of S / V becomes a constant A, and the dissolved oxygen concentration in the aeration tank becomes Expression 2.

[0028]

DO = A (1−C / S) Therefore, when the aeration tank is operating normally, the dissolved oxygen concentration in the aeration tank depends on C / S.

When harmful substances such as cyanide are mixed in the aeration tank, they become inhibitors of the oxidative decomposition of organic substances by the aerobic microorganisms, reduce the wastewater treatment capacity by the activated sludge method, and reduce per unit time by the aerobic microorganisms. Oxygen consumption C
Decreases to C ′.

This is because the C / S value is reduced, and the dissolved oxygen concentration in the aeration tank increases from the time when harmful substances such as cyanide are mixed in the aeration tank. As shown in FIG. The straight line has an inclination of an angle θ ₁ (differential coefficient) with respect to the positive direction of the time axis, and the dissolved oxygen concentration increases simultaneously with the incorporation of harmful substances such as cyan.

Therefore, at the time when the dissolved oxygen concentration increases, biological abnormality detection by harmful substances such as cyan can be performed using the dissolved oxygen meter.

The abnormalities in biological treatment due to the contamination of harmful substances such as cyan as described above are determined by using a conventional measuring instrument such as a dissolved oxygen meter or an air flow meter to control the concentration of dissolved oxygen to a constant value. By calculation,
FIG. 3 shows a flowchart of the detection.

The sequence control by constant control of the wastewater inflow amount and the oxygen supply amount per unit time is as follows.

(1) The amount of wastewater inflow per unit time is set.

(2) Set the amount of oxygen supply per unit time.

(3) Set the time to be measured by the dissolved oxygen meter.

(4) If the amount of increase in dissolved oxygen concentration per unit time θ ₁ is 1 mg / l or more, the process proceeds to the next step. Otherwise, give feedback.

(5) At the time of inspection and when rainfall is not detected for 10 minutes or more by the rain detector, the above detection is not performed. Otherwise proceed to the next.

(6) An alarm for abnormal biological treatment is issued.

By the constant control of the wastewater inflow rate and the oxygen supply rate per unit time, it is possible to detect harmful substances such as cyan by using an existing dissolved oxygen meter and to warn of biological treatment abnormality.

Further, at the time of inspection, a circuit for preventing a malfunction when temporarily increasing the air flow rate to prevent clogging of the diffuser plate is introduced, and when no precipitation is confirmed, there is no inflow of cyan. By eliminating the need, the reliability of detection of harmful substances such as cyanide and the warning of abnormal biological treatment has been improved.

(2) Dissolved oxygen concentration constant control Dissolved oxygen concentration constant control is a treatment of wastewater by the activated sludge process while maintaining the dissolved oxygen concentration in the aeration tank at a constant level, by biological treatment caused by the inflow of harmful substances such as cyanide. This is to detect an abnormality. Also in this case, the inflow of wastewater per unit time is assumed to be constant.

When harmful substances such as cyan are mixed in the aeration tank,
When the oxygen consumption C per unit time by the aerobic microorganisms decreases to C ′, the C / S value decreases, and as is apparent from Equation 2, the dissolved oxygen concentration forms with respect to the positive direction of the time axis. increases at the corner θ ₁ of the slope.

In order to keep the concentration of dissolved oxygen in the aeration tank constant, control is performed so as to reduce the oxygen supply amount S per unit time from the blower, which has been controlled so far, to S '. As shown in FIG. 4, immediately after the blast volume, resulting a positive direction and angle theta ₂ of the negative slope of the time axis, the blowing rate is reduced at the same time as the mixing of hazardous substances cyan like.

By this operation, the dissolved oxygen concentration DO 'in the aeration tank is expressed by Equation 3 when S' / V is A '.

[0046]

DO ′ = A ′ (1−C ′ / S ′) where DO before harmful substance mixing and D by the above operation.
In order to make O ′ equal, the blowing amount is controlled as shown in Expression 4.

[0047]

S ′ = S−C + C ′ = S− (C−C ′) = S−ΔC Unit time due to aerobic microorganisms as time elapses after harmful substances such as cyan began to enter the aeration tank. The reduction amount ΔC of the oxygen consumption per unit increases, and as a result, control is performed so as to reduce the oxygen blowing amount. This control mechanism is provided with a minimum value of the oxygen supply amount by the blower.

Abnormalities in biological treatment caused by the contamination of harmful substances such as cyan as described above are controlled to a constant dissolved oxygen concentration using existing measuring instruments such as a dissolved oxygen meter and an air flow meter, and the sequence calculation of the programmable controller PC is performed. Is shown in FIG.

The sequence control by the constant control of the dissolved oxygen concentration is as follows.

(1) Set the time to be measured by the dissolved oxygen meter.

(2) If the increase amount θ ₁ of the dissolved oxygen concentration per unit time is 1 mg / l or more, the process proceeds to the next step. Otherwise, give feedback.

(3) The dissolved oxygen concentration per unit time is θ
₁ If you increase takes control so that the oxygen supply amount per unit time from the blower theta ₂ decreases. If the amount of decrease θ _{2 in the} amount of air blow per unit time is 100 m ³ / h or more, the process proceeds to the next step. Otherwise, give feedback.

(4) If the amount of increase in the dissolved oxygen concentration per unit time θ ₁ is 1 mg / l or more and the amount of decrease in the amount of air blow per unit time θ ₂ is 100 m ³ / h or more, proceed to the next step. move on.

(5) The amount of oxygen supplied by the blower reaches the minimum value, and the amount of decrease θ _{2 in the} amount of air blow per unit time is 10
If it is 0 m ³ / h or more, proceed to the next stage.

(6) When the increasing amount θ ₁ of the dissolved oxygen concentration per unit time is 1 mg / l or more and the decreasing amount θ ₂ of the blowing amount per unit time is 100 m ³ / h or more, or If the supply amount has reached the minimum value and the amount of decrease θ _{2 in the} amount of air blown per unit time is 100 m ³ / h or more, the process proceeds to the next step.

(7) If the constant control of the dissolved oxygen concentration becomes impossible under the conditions of (6), the process proceeds to the next stage.

(8) At the time of inspection and when rainfall is not detected for 10 minutes or more with the rain detector, the above detection is not performed. Otherwise proceed to the next.

(9) In the cases of (7) and (8), a warning of the biological treatment abnormality is issued.

In the constant control of the dissolved oxygen concentration, harmful substances such as cyanide can be detected using an existing dissolved oxygen meter and an air flow meter, and a biological treatment abnormality can be warned. Furthermore, a circuit has been introduced to prevent malfunctions when temporarily increasing the air flow to prevent clogging of the diffuser plate during inspection, and if precipitation is not confirmed, there is no inflow of cyanide, so detection is unnecessary. As a result, the reliability of detection of harmful substances such as cyanide and the warning of abnormal biological treatment has been improved.

(3) Constant control of air flow (oxygen supply amount) Constant control of air flow (oxygen supply amount) is achieved by inflow of harmful substances such as cyan while keeping the oxygen amount supplied from the blower to the aeration tank constant. To detect abnormal biological treatment.

In the constant control of dissolved oxygen, the amount of wastewater flowing into the aeration tank is fixed. However, even when the amount of wastewater changes with time, by controlling the blowing amount to be constant, cyan cyanide can be obtained as follows. Biological treatment abnormalities caused by the inflow of harmful substances such as harmful substances can be detected.

As shown in FIG. 6, when the amount t of wastewater flowing into the aeration tank per unit time fluctuates with time, assuming that the oxygen amount S supplied from the blower to the aeration tank is constant, the processing is started. At time T, the dissolved oxygen concentration and the amount of change when the aeration tank is operating normally, and the increase and decrease thereof are expressed by the following formula (5).
It is represented by Equations 6 and 7.

[0063]

OD = (ST-CT) ÷ ΣV (t) dt

[0064]

ΔOD = {{(S−C) T ₂ ÷ ΣV (t) dt} − {(S−C) T ₁ ÷ ΣV (t) dt}} ÷ (T ₂ −T ₁ )

[0065]

DOD = a−b {V (T) T} Therefore, as is apparent from Equation 7 (where a and b are constants), the concentration of dissolved oxygen decreases as the inflow rate of wastewater per unit time increases. As the amount of wastewater flowing in per unit time decreases, the dissolved oxygen concentration increases.

A harmful substance such as cyan flows into the aeration tank,
When the oxygen consumption C per unit time by the aerobic microorganisms decreases to C ′, the dissolved oxygen concentration increases rapidly under the condition that the wastewater inflow and the oxygen supply are constant.

When a harmful substance such as cyan flows into the aeration tank when the flow rate of wastewater per unit time changes while the oxygen supply rate is constant, as shown in FIG. Assuming that V (t), the change amount ΔV (t) of the inflow amount of wastewater per unit time is expressed by Expression 8, and the change amount ΔOD of the dissolved oxygen concentration per unit time is expressed by Expression 9.

[0068]

ΔV (t) = θ ₁ , θ ₃ = {V (t ₂ ) −V (t ₁ )} (T ₂ −T ₁ )

[0069]

ΔOD = θ ₂ , θ ₄ = {{(S−C ′) T ₂ ÷ ΣV (t) dt} − {(S−C) T ₁ ÷ ΣV (t) dt}} ÷ (T ₂ -T ₁ ) Here, as shown in FIG. 7, the increase amount of wastewater inflow per unit time is θ ₁ , the decrease amount is θ ₃ , and the increase amount of dissolved oxygen concentration per unit time is θ and ₂ and θ _4.

Under constant control of the air flow rate (oxygen supply rate), abnormalities in biological treatment due to the inflow of harmful substances such as cyan can be determined by the sequence measurement of the programmable controller PC using existing measuring instruments such as a dissolved oxygen meter and a flow meter. Is shown in FIG.

The successive control in the constant air blowing (oxygen supply) control is as follows.

(1) Set the time to be measured by the dissolved oxygen meter.

(2) If the increase θ ₁ of wastewater inflow per unit time is 1000 m ³ / h or more, the process proceeds to the next step. Otherwise, give feedback.

(3) If the increase amount θ ₂ of the dissolved oxygen concentration per unit time is 1 mg / l or more, the process proceeds to the next step. Otherwise, give feedback.

(4) If the increase θ ₁ of the wastewater per unit time is 1000 m ³ / h or more and the increase θ ₂ of the dissolved oxygen concentration per unit time is 1 mg / l or more, the process proceeds to the next step.

(5) If the waste water inflow reduction amount θ ₃ per unit time is not less than 1000 m ³ / h, the process proceeds to the next step. Otherwise, give feedback.

(6) If the increase amount θ ₄ of the dissolved oxygen concentration per unit time is 2 to 3 mg / l or more, the process proceeds to the next step. Otherwise, give feedback.

(7) If the amount of decrease θ ₃ of wastewater per unit time is not less than 1000 m ³ / h and the amount of increase θ ₄ of dissolved oxygen concentration per unit time is not less than ₂ to 3 mg / l, proceed to the next step. move on.

(8) The oxygen supply amount by the blower is controlled to be constant, and the above measurement is not performed at the time of inspection. Otherwise proceed to the next.

(9) If (4) and (8) are satisfied, go to the next step.

(10) If (7) and (8) are satisfied, proceed to the next step.

(11) When (9) and (10) are satisfied,
An alarm is issued for biological treatment abnormality.

When the inflow of wastewater increases, the dissolved oxygen concentration generally decreases at a constant air flow, but the dissolved oxygen concentration increases due to a decrease in the dissolved oxygen consumption of microorganisms due to the inflow of harmful substances such as cyanide. (2) ~
Detected in (4).

When the inflow of wastewater decreases, the dissolved oxygen concentration generally increases at a constant blowing rate, but the dissolved oxygen concentration decreases due to a decrease in the dissolved oxygen consumption of microorganisms due to the inflow of harmful substances such as cyanide. The increase is detected in (5) to (7).

In the constant control of the blown air amount (oxygen supply amount), harmful substances such as cyan can be detected using an existing dissolved oxygen meter and an air flow meter, and a biological treatment abnormality can be alerted. In addition, a circuit to prevent malfunctions when temporarily increasing the air flow rate to prevent clogging of the diffuser plate during inspection has been introduced.If no precipitation is confirmed, no detection is necessary because there is no inflow of cyanide. As a result, the reliability of the detection of harmful substances such as cyanide and the warning of abnormal biological treatment has been improved.

As described above, in the biological treatment of wastewater by the activated sludge method, only existing measuring instruments such as a dissolved oxygen meter, a flow meter and an air flow meter installed in an aeration tank are used.
The biological abnormality of the aeration tank can be detected by controlling these programs.

[0087]

As described above, according to the present invention, the following various effects can be obtained.

(1) Even if a dedicated cyan detector is not installed, harmful substances such as cyan contained in wastewater can be used by using existing measuring instruments (dissolved oxygen meter, flow meter, air flow meter). Substance can be detected.

(2) A biological treatment abnormality caused by a harmful substance such as cyan contained in the wastewater can be detected by flowing a certain amount of wastewater per unit time into the aeration tank and controlling the concentration of dissolved oxygen to be constant.

(3) Even if the amount of wastewater flowing into the aeration tank per unit time changes, harmful substances such as cyanide contained in the wastewater can be brought about by controlling the oxygen supply amount to the aeration tank to be constant. Biological treatment abnormality can be detected.

(4) When no precipitation is confirmed or when an alarm is not issued for biological treatment abnormality during inspection, the reliability of abnormality detection can be improved.

(5) All operations are automatically controlled by the sequence calculation of the programmable controller PC, so that the operation of the sewage treatment plant can be efficiently performed.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram of a dissolved oxygen concentration under a wastewater inflow rate and a blowing rate constant control condition.

FIG. 2 is a characteristic diagram of a dissolved oxygen concentration per unit time with respect to an operation time when a harmful substance such as cyan flows under a control condition of a constant wastewater inflow rate and a blowing rate.

FIG. 3 is a flowchart showing control under a constant wastewater inflow and airflow control condition.

FIG. 4 is a characteristic diagram showing a dissolved oxygen concentration per unit time with respect to an operation time when a harmful substance such as cyan flows in under a dissolved oxygen concentration constant control condition.

FIG. 5 is a flowchart showing control under the condition of a constant dissolved oxygen concentration.

FIG. 6 is a characteristic diagram showing a flow rate of wastewater and a concentration of dissolved oxygen with respect to an operation time under a constant airflow control condition.

FIG. 7 is a characteristic diagram showing a change in an inflow amount of wastewater and a dissolved oxygen concentration with respect to an operation time when a harmful substance such as cyan flows in under a constant airflow control condition.

FIG. 8 is a flowchart showing control under a constant air volume control condition.

FIG. 9 is an explanatory view of a conventional wastewater treatment method.

FIG. 10 is an explanatory diagram of an aeration tank.

Claims (2)

(57) [Claims] 1. A method for detecting biological anomalies in an aeration tank for detecting biological anomalies in the aeration tank when performing an aeration process by an activated sludge method for the water to be treated in the aeration tank. The dissolved oxygen concentration in the aeration tank is controlled to be constant by increasing or decreasing the oxygen supply amount to the aeration tank in accordance with the increase or decrease in the amount. The first control is performed with respect to the decrease rate of the oxygen supply amount in the aeration tank. A threshold value, a second threshold value is set for the increase rate of the dissolved oxygen concentration, and a decrease rate of the oxygen supply amount is larger than the threshold value;
And a biological abnormality detection method for an aeration tank, wherein it is determined that a biological abnormality has occurred in the aeration tank when an increase rate of the dissolved oxygen concentration exceeds the threshold value. 2. A method for detecting biological anomalies in an aeration tank when performing aeration treatment by an activated sludge method in an aeration tank for a water to be treated, comprising the steps of: A constant supply amount control is performed, and a first threshold value and a second threshold value are set for an increase rate and a decrease rate of the inflow amount of the treatment target water into the aeration tank, respectively. A third threshold value and a fourth threshold value that is larger than the third threshold value with respect to the increase rate of the dissolved oxygen concentration in the aeration tank, When the rate of increase of the inflow exceeds the first threshold and the rate of increase of the dissolved oxygen concentration in the aeration tank exceeds the third threshold,
And the rate of decrease in the inflow of the water to be treated into the aeration tank exceeds the second threshold, and the rate of increase in the concentration of dissolved oxygen in the aeration tank exceeds the fourth threshold. A biological abnormality detection method for an aeration tank, wherein it is determined that a biological abnormality has occurred in each of the aeration tanks.