JPH0788490A - Method and apparatus for treating waste water - Google Patents

Abstract

PURPOSE:To improve purification efficiency and reliability by a method in which the degree of contamination at each position along the flow of water to be treated in a reaction tank is calculated by given expressions on the basis of the contamination condition of the inflow waste water and the concentration of the dissolved oxygen in the water to be treated in the tank to control the concentration of dissolved oxygen. CONSTITUTION:The flow rate Q1 of waste water 3 flowing into a reaction tank 1 from a residual removing apparatus through an inflow pipe 5, the concentration C10 of organic substances and various kinds of nitrogen compounds in the waste water 3 are measured to input the values into a control means. The control means to which the concentration of dissolved oxygen of the water 3a to be treated existing in the reaction tank 1 which is measured in the intermediate part of the reaction tank 1 is input calculates the contamination condition of the water to be treated by applying the measurement results to the material balance expression of organic substances, nitrogen compounds, and microorganisms in the water 3a to be treated, the reaction rate expressions of the removal of the organic substances, the conversion of the nitrogen compounds, and the propagation of the microorganisms, and the generation rate expressions of the organic substances and the nitrogen compounds. The results are compared with the calculated values of the simulation of a status model to control the inflow amount Q1, the reflux amount Q2, the sludge return amounts Q5, Q6, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating sewage which purifies sewage containing organic substances and nitrogen compounds in a single tank.

[0002]

2. Description of the Related Art Conventionally, when purifying sewage containing organic matter, nitrogen compounds, etc., such as human waste, in an aerobic atmosphere in which dissolved oxygen (DO) is present, aerobic bacteria and facultative anaerobes are present. Oxidative decomposition process in which sexual bacteria activate organic substances contained in sewage as nutrient sources and oxidize and decompose organic substances with aerobic and facultative anaerobic bacteria. Nitrification process in which bacteria or nitric acid bacteria oxidize nitrite nitrogen or nitrate nitrogen to oxidized nitrogen, and in an anaerobic atmosphere where nutrients are obtained by organic substances or self-decomposition and dissolved oxygen does not exist It is necessary to consider the denitrification process in which nitrogen denitrifying bacteria reduce nitrogen to nitrogen gas by respiration of nitric acid.

Therefore, the processing steps in different atmospheres,
It is necessary to understand and control the complicated relationship between the transfer of sewage between each treatment process and the increase and decrease of organic matter, various nitrogen compounds and various bacteria. Therefore, the relationship between the dissolved oxygen concentration and the amount of organic matter, various nitrogen compounds, and various bacteria in each step is calculated by various mathematical expressions and grasped, and a method for automatically controlling the purification treatment based on the calculated results, for example, JP-A-61-212395, JP-A-63-209796, and JP-A-6-26
The configuration described in Japanese Patent Publication No. 4-51197 is known.

The method for treating sewage described in Japanese Patent Laid-Open No. 61-212395 discloses a method of inflowing sewage into an anaerobic denitrification tank, total nitrogen concentration in sewage, and sludge returned from the separation tank to the denitrification tank. And the concentration of activated sludge in circulating water from the aerobic nitrification tank to the denitrification tank. Further, using these as control factors, the ratio of circulating water to inflow water, and
Calculate the ratio of returned sludge to inflow water. Then, the amount of circulating water and the amount of sludge to be returned are controlled based on these calculated values, and biological denitrification of the wastewater is carried out fully automatically and efficiently for purification treatment.

However, this Japanese Patent Laid-Open No. 61-2123
The method for treating sewage described in Japanese Patent Publication No. 95 discloses the dissolved oxygen concentration directly attributable to each treatment step as
Further, since the indirect management is performed based on the ratio of the returned sludge to the inflow water amount, the dissolved oxygen concentration in each treatment process tends to fluctuate, and there is a possibility that good purification treatment cannot be performed. Furthermore, because the purification treatment is controlled based on the amount of circulating water and the amount of returned sludge in the circulation of the nitrification / denitrification process, the amount of organic matter in the inflowing wastewater varies, and the concentration of pollution caused by the organic matter in the wastewater varies. The oxidative decomposition process cannot be performed well, and the balance of organic substances involved in the nitrification and denitrification process changes.
There is a possibility that the purification process cannot be performed properly. Further, in order to easily control the dissolved oxygen concentration, each treatment step is performed using two reaction tanks, an aerobic nitrification tank and an anaerobic denitrification tank,
There is a problem that the device becomes large and the installation space is enlarged.

Further, the wastewater treatment apparatus described in JP-A-63-209796 discloses a kinetic constant, a carbon type and a nitrogen type when environmental factors such as the temperature and pH of the wastewater are stable. The simulation is performed by using the substrate removal rate equation, the carbon-based and nitrogen-based cell growth rate equations, the mass balance equation related to the dissolved oxygen concentration, and the mass balance equation for the amount of sludge in the process.

On the other hand, the time-dependent change data of the bacterial cell amount or nitrification rate that contributes to nitrification in the steady-state process is calculated by using this, and the stable value of the nitrifying bacterial cell volume or nitrification rate is used as the target value. It is output by the first simulator section. In addition, the dynamic constant is expressed as a function of the environmental factor, and the dynamic constant corresponding to the environmental factor at each time point is used,
Introducing the target value from the first simulator part, carbon-based and nitrogen-based substrate removal rate equations, carbon-based and nitrogen-based cell growth rate equations, mass balance equations related to dissolved oxygen concentration, and A simulation is performed by calculating the amount of sludge in the process using a mass balance formula.

Then, by this simulation, an appropriate set value of the control element for the dissolved oxygen concentration at each time point is obtained in the second simulator section, and the mixed solution of the organic sewage and the activated sludge is aerated in the reaction tank to obtain the water temperature. Even if environmental factors such as pH and pH fluctuate, the amount of nitrifying bacteria or the nitrification rate is maintained at the target value and the purification treatment is performed well.

However, this Japanese Patent Laid-Open No. 63-2097
The apparatus described in Japanese Patent Laid-Open No. 96 keeps the amount of nitrifying bacteria or the nitrification rate constant and allows the nitrification step to proceed efficiently and satisfactorily. Therefore, in order to purify the sewage, an apparatus for performing the denitrification step after this nitrification step is required. For this reason, the device for purifying the sewage becomes large,
There is a problem that the installation space increases and the operation of the purification process becomes complicated.

The sewage treatment apparatus described in Japanese Patent Laid-Open No. 64-51197 measures the dissolved oxygen concentration at the inlet, middle and outlet of the nitrification tank, and sets the respective preset target values. In comparison with the above, the air volume control valve and the suction valve of the blower that configure the aeration device in the nitrification tank are controlled and aerated so that the measured dissolved oxygen concentrations reach the corresponding target values.

Further, the redox potential of the denitrification tank is compared with a preset redox potential suitable for denitrification so that the measured redox potential becomes the set redox potential from the nitrification tank to the denitrification tank. Control the amount of circulating water.

The nitrification efficiency is prevented from lowering due to the insufficient dissolved oxygen concentration at the inlet, and the denitrification efficiency is prevented from lowering due to the introduction of dissolved oxygen into the denitrification tank for efficient and satisfactory purification treatment. .

However, this Japanese Patent Laid-Open No. 64-5119
Since the apparatus described in Japanese Patent Publication No. 7 controls the amount of circulating water and the aeration state based on the dissolved oxygen concentration in the nitrification tank and the redox potential indicating the denitrification state in the denitrification tank, the purification treatment in the nitrification / denitrification process is controlled. Since the oxidative decomposition process of organic substances is not monitored and control is not performed to perform the oxidative decomposition process satisfactorily, it is possible to oxidize and decompose organic substances satisfactorily due to changes in the inflow of sewage and the pollution state due to organic substances. In addition, there is a risk that the nitrification / denitrification process will not be performed well due to fluctuations in the balance of organic substances involved in the nitrification / denitrification process. Further, since two nitrification tanks and denitrification tanks are provided, there is a problem that the apparatus becomes large and the installation space expands.

[0014]

As described above, in the method for treating sewage described in JP-A-61-212395, a satisfactory purification treatment cannot be performed due to the fluctuation of the dissolved oxygen concentration in each treatment step. There is a possibility that
Due to fluctuations in the amount of organic matter in the inflowing wastewater and changes in the pollution state due to organic matter, the oxidative decomposition process may not be performed well, and the balance of organic substances involved in the nitrification / denitrification process may fluctuate, which may prevent good purification treatment. .

Further, in the wastewater treatment apparatus described in Japanese Patent Laid-Open No. 63-209796, since the balance of organic matter is managed based on the nitrification process, the fluctuation of the amount of organic matter in the inflowing wastewater and the state of contamination by the organic matter. Due to the fluctuation of the above, the oxidative decomposition process of the organic matter cannot be performed well, the balance of the organic matter involved in the nitrification / denitrification process varies, and there is a possibility that the purification treatment cannot be performed satisfactorily.

Further, in the wastewater treatment apparatus described in Japanese Patent Laid-Open No. 64-51197, control is not performed to favorably perform the oxidative decomposition step of organic matter, so that the inflow amount of wastewater and the state of contamination by organic matter can be prevented. Due to the fluctuation, the organic matter cannot be oxidatively decomposed well, and the balance of the organic matter involved in the nitrification / denitrification step may fluctuate, so that the nitrification / denitrification step may not be performed well.

A method for treating sewage described in JP-A-61-212395 and JP-A-64-511.
The sewage treatment apparatus described in Japanese Patent Publication No. 97 is provided with two nitrification tanks and denitrification tanks. With the sewage treatment apparatus described in Japanese Patent Application Laid-Open No. 63-209796, in order to purify sewage, Since a device such as a denitrification tank is required separately, there is a problem that the device becomes large and the installation space expands.

The present invention has been made in view of the above-mentioned problems, and is highly reliable sewage which is easily and efficiently and surely purified by causing oxidative decomposition, nitrification and denitrification of organic substances in a single tank. It is an object of the present invention to provide a processing method and a device therefor.

[0019]

According to a first aspect of the present invention, there is provided a method for treating sewage, wherein the sewage contaminated state flowing into the reaction tank is measured, and the dissolved oxygen concentration of the water to be treated in the reaction tank is measured. The polluted state of the treated water at each position in the reaction tank along the direction in which the treated water flows, the measurement result of the polluted state of the wastewater flowing into the reaction tank and the measurement result of the dissolved oxygen concentration Based on, and the material balance equation of the organic matter in the water to be treated, various nitrogen compounds and various microorganisms,
The dissolved oxygen concentration is controlled by calculating from the reaction rate equations of removal of organic matter, conversion of various nitrogen compounds and growth of various microorganisms, and the production rate equations of organic matter and various nitrogen compounds, respectively.

According to a second aspect of the present invention, there is provided a wastewater treatment method according to the first aspect, wherein the state of pollution of the wastewater flowing into the reaction tank is determined by the inflow amount of the wastewater and the organic matter in the wastewater. The measurement is based on at least one of various nitrogen compounds in the waste water.

The method for treating sewage according to claim 3 is the same as the treatment method according to claim 1 or 2, wherein the dissolved oxygen concentration of the water to be treated is determined by the inflow amount of the sewage flowing into the reaction tank, The control is performed based on at least one of the oxygen supply amount to the treated water and the reflux amount of the treated water from the downstream side to the upstream side of the reaction tank.

According to a fourth aspect of the present invention, there is provided an apparatus for treating sewage, comprising: a reaction tank having an inflow port for sewage; and an oxygen supply means provided in the reaction tank for supplying oxygen to the water to be treated in the reaction tank. A recirculation means provided in this reaction tank for recirculating the water to be treated from a downstream side to an upstream side of the reaction tank; an inflow adjusting means for adjusting an inflow amount of waste water flowing in through the inflow port; and the inflow port A pollution measuring means for measuring the polluted state of the inflowing sewage, a dissolved oxygen measuring means for measuring the dissolved oxygen concentration of the water to be treated in the reaction tank, the pollution measuring means and the dissolved oxygen. The control means controls at least one of the oxygen supply means, the inflow adjustment means, and the reflux means based on the measurement result by at least one of the measurement means.

[0023]

The method for treating wastewater according to claim 1, wherein the pollution state at each position along the flowing direction of the water to be treated in the reaction tank is determined by the pollution state of the wastewater flowing into the reaction tank and the reaction tank. Based on the dissolved oxygen concentration of the water to be treated in the organic matter in the water to be treated, various nitrogen compounds and mass balance equations of various microorganisms,
One reaction to control the dissolved oxygen concentration of the water to be treated by calculating from the reaction rate equations for removal of organic substances, conversion of various nitrogen compounds and growth of various microorganisms, and the production rate equations for organic substances and various nitrogen compounds In the tank, there are an oxidative decomposition step in which organic matter is oxidatively decomposed by microorganisms, a nitrification step in which ammonia nitrogen is oxidized by microorganisms into oxidized nitrogen, and a denitrification step in which oxidized nitrogen is reduced by microorganisms into nitrogen gas. Good progress and good purification of wastewater.

According to a second aspect of the present invention, there is provided the wastewater treatment method according to the first aspect, wherein the state of pollution of the wastewater flowing into the reaction tank is determined by the inflow amount of the wastewater and the organic matter in the wastewater.
Since it is measured based on at least one of various nitrogen compounds in the wastewater, the pollution status at each position along the flowing direction of the treated water in the reaction tank from the pollution status of the wastewater flowing into the reaction tank Can be easily calculated, and sewage can be easily purified.

The method for treating wastewater according to claim 3 is the method for treating wastewater according to claim 1 or 2, wherein the dissolved oxygen concentration of the water to be treated in the reaction tank is determined by the inflow amount of the wastewater flowing into the reaction tank,
Since the control is performed based on at least one of the amount of oxygen supplied to the water to be treated in the reaction tank and the amount of reflux of the water to be treated from the downstream side to the upstream side of the reaction tank, the purification treatment operation of the wastewater is easy,
One reaction is an oxidative decomposition process in which microorganisms oxidize and decompose, a nitrification process in which ammonia nitrogen is oxidized into oxidized nitrogen by microorganisms, and a denitrification process in which oxidized nitrogen is reduced to nitrogen gas by microorganisms. Good progress in the tank,
Sewage is purified well.

In the sewage treatment apparatus according to a fourth aspect of the present invention, the pollution measuring means provided in the vicinity of the inflow port of the reaction tank measures the state of pollution of the sewage flowing into the reaction tank through the inflow port and dissolves it. The dissolved oxygen concentration of the water to be treated in the reaction tank is measured by the oxygen measuring means, and the control means based on at least one of these results, the oxygen supply means for supplying oxygen to the water to be treated, the sewage. At least one of the inflow adjusting means for adjusting the inflow amount and the reflux means for refluxing the treated water from the downstream side to the upstream side of the reaction tank is controlled to control the dissolved oxygen concentration of the sewage in the treated water. Since sewage is purified, the sewage purification operation is easy, and the oxidative decomposition step in which organic matter is oxidatively decomposed by microorganisms, the nitrification step in which ammonia nitrogen is oxidized by microorganisms into oxidized nitrogen, and the oxidized nitrogen are With microorganisms Denitrification step of reducing the hydrogen gas proceeds well better efficiency in one reaction vessel, sewage is satisfactorily purification treatment.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of an embodiment of an apparatus for carrying out the wastewater treatment method of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 is a reaction tank, and this reaction tank 1 is formed in a cylindrical shape having a volume of 270 m ³ and a water depth of 10 m, for example, and a bottom portion 2 protruding downward in a funnel shape is formed at a lower end thereof.
Are formed. And, in the lower part of this reaction tank 1,
An inflow port 4 is formed to allow inflow of sewage 3 containing organic matter and various nitrogen compounds, such as human waste water, and foreign substances such as sand and gravel in sewage, metal pieces, paper and vinyl are formed in the inflow port 4. Is connected to an inflow pipe 5 derived from a residue removal device (not shown) that separates. Furthermore, this inflow pipe 5
Is provided with a solenoid valve (not shown) for controlling the inflow of the wastewater 3 from which contaminants have been removed by the residue removal device into the reaction tank 1. Further, the inflow pipe 5 is provided with a flow meter (not shown) for measuring the inflow amount of the dirty water 3 flowing into the reaction tank 1.

Then, in the reaction tank 1, treated water 3a which is a mixed liquid of waste water 3 flowing into the reaction tank 1 from the lower end of the bottom 2 to the upper part of the reaction tank 1 and various microorganisms in the reaction tank 1 Is connected to a reflux pipe 7, and the reflux pipe 7 is provided with a reflux pump and a flow meter (not shown). Further, when the water 3a to be treated flows into the reaction tank 1, air is sucked into the upper part of the reflux pipe 7 by the negative pressure generated by the flow-through of the water 3a to be treated. An ejector (not shown) for mixing air in is provided.

The various microorganisms in the reaction tank 1 can be obtained by culturing in the reaction tank 1 or returning sludge from the separation tank 10 described later.

Further, the reaction tank 1 is provided at a substantially middle portion of the reaction tank 1.
Oxygen (DO: Dissolved Oxygen) of treated water 3a inside
A sensor (not shown) for measuring the concentration of the water is provided, and an outflow pipe 8 for outflowing the treated water 3a in the intermediate portion to the outside of the reaction tank 1 is connected. And this outflow pipe 8
Is provided with a solenoid valve and a flow meter (not shown) that control the outflow amount of the water 3a to be treated.

On the other hand, 10 is a separation tank, and this separation tank 10 is provided with a settling section 11 projecting downward in a funnel shape at the bottom and has a volume of 30.
It is formed in a cylindrical shape of m ³ . And this separation tank 10
The outflow pipe 8 connected to the reaction tank 1 is connected to the upper part of the. A sludge pipe 12 for returning the sludge settled in the settling unit 11 to the lower portion of the reaction tank 1 is connected to the lower end of the settling unit 11 of the separation tank 10, and the sludge pipe 12 and a flow meter (not shown) are connected to the sludge pipe 12. Is provided. Furthermore, in this separation tank 10,
A return pipe 13 for returning the sludge floating on the water surface in the separation tank 10 to the upper part of the reaction tank 1 is provided, and the return pipe 13 is provided with a return pump and a flow meter (not shown). And
The separation tank 10 is formed with a discharge port 14 for discharging the purified supernatant as treated water.

The reaction tank 1 and the separation tank 10 are formed so that the water volume does not change. Furthermore, the separation tank 10
Is not limited to the sedimentation type, and may have any structure such as a membrane separation type in which sludge is separated by a filtration membrane or a centrifugal separation type.

Further, this apparatus is provided with a control means (not shown), which controls the polluted state of the sewage 3 flowing into the reaction tank 1, for example, the amount of the sewage 3 flowing in and the amount of the sewage 3 in the sewage 3. Numerical values such as the amount of pollutants flowing into the reaction tank 1 calculated from the concentrations of organic substances and various nitrogen compounds can be input, and a sensor for measuring the dissolved oxygen concentration of the treated water 3a in the reaction tank 1 is connected. There is. And the control means
The opening degree of each solenoid valve and the driving states of the reflux pump, the sludge pump and the return pump are controlled based on these various measured values and input values.

Next, the operation of this apparatus will be described for the treatment of sewage.

First, a small amount of sewage 3 flowing into the reaction tank 1 through the inflow pipe 5 is collected from the decontamination device, and the organic matter in the sewage 3, that is, the biochemical oxygen demand (Biochemical oxygen demand) (Biochemical
Oxygen Demand: BOD) and chemical oxygen demand (Ch
Emical Oxygen Demand (COD) and the concentrations of various nitrogen compounds are measured, and the measurement results are input to the control means. Then, the control means opens the electromagnetic valve of the inflow pipe 5 to a predetermined opening degree, and causes the dirty water 3 from the residue removing device to flow into the lower portion of the reaction tank 1 from the inflow port 4. The control means closes the solenoid valve when the flow rate of the dirty water 3 reaches a predetermined level.

Then, the treated water 3a in which the wastewater 3 flows into the reaction tank 1 and is mixed is purified by the microorganisms growing in the reaction tank 1, and the reflux pipe 7 is driven by the reflux pump driven by the control means.
Is introduced to the upper part of the reaction tank 1 while introducing air by an ejector.

Further, the reaction tank 1 is gradually purified by various microorganisms and gradually flows to the lower part, and a part of the reaction tank 1 is separated from the outlet pipe 8 opened by the opening of the solenoid valve being controlled by the control means.
And the rest recirculates from the bottom of the reaction tank 1 to the upper part of the reaction tank 1 via the reflux pipe 7.

Then, the treated water 3a flowing into the separation tank 10
Sludge floating in this treated water 3a is separated and separated,
The sludge that has settled is transported to the bottom of the reaction tank 1 through the sludge pipe 12 again by driving the sludge pump controlled by the control means. The sludge floating on the water surface of the separation tank 10 is returned to the upper part of the reaction tank 1 through the return pipe 13 by driving the return pump controlled by the control means.

Then, the treated water in the purified separation tank 10 is discharged through the discharge port 14.

The control means controls the concentration of input COD, BOD and each nitrogen compound, which is the polluted state of the sewage,
It is calculated based on the inflow amount of sewage and the dissolved oxygen concentration of the water to be treated 3a measured by a sensor provided in the middle part of the reaction tank. Then, the dissolved oxygen concentration of the water to be treated 3a for which an appropriate treatment result is obtained, that is, the organic substances in the water to be treated 3a or the nutrients obtained by self-decomposition in an anaerobic atmosphere to denitrify the nitrified oxidized nitrogen. Denitrification process of reducing to nitrogen gas by respiration of nitric acid, aerobic bacterium and facultative anaerobic bacterium in the aerobic atmosphere where dissolved oxygen concentration exists activates the remaining organic matter in the treated water 3a as a nutrient source. , An oxidative decomposition process in which this organic matter is oxidatively decomposed by aerobic bacteria or facultative anaerobic bacteria, and in the presence of dissolved oxygen, ammoniacal nitrogen is converted into nitrite nitrogen or nitrate by nitrite bacteria or nitric acid bacteria. The flow rate of each solenoid valve and each pump should be adjusted so that the reaction process of the nitrification process, which oxidizes nitrogen to nitrogen, progresses satisfactorily and the sewage 3 has a dissolved oxygen concentration that is satisfactorily purified. Control while monitoring.

Next, the operation of the above embodiment will be described.

First, in the purification treatment of the sewage 3 containing the organic matter and the nitrogen compound, the organic matter contained in the sewage 3 into which the aerobic bacteria and facultative anaerobic bacteria flow in the aerobic atmosphere in which the dissolved oxygen concentration exists. Oxidative decomposition process that activates as a nutrient source and oxidatively decomposes organic matter with aerobic bacteria and facultative anaerobic bacteria.In the presence of dissolved oxygen, ammonia nitrogen is converted into nitrite nitrogen by nitrite bacteria and nitric acid bacteria. And nitrification process of oxidizing nitric acid to oxidized nitrogen, and denitrifying bacteria that reduce nitrified oxidized nitrogen to nitrogen gas by respiration of nitric acid in an anaerobic atmosphere with nutrients obtained by organic substances or autolysis. It is necessary to consider the three main reaction processes of the nitrification process.

From this fact, as shown in the block diagram of FIG. 2, as the state variables, nitrite bacteria (B _A1 ), nitric acid bacteria (B _A2 ), allotrophic bacteria (B _H ), persistent biodegradability Solid organic matter (carbon C _DS , nitrogen N _DS ), easily decomposable solid organic matter (carbon C _S , nitrogen N _S ), hardly decomposable soluble organic matter (carbon C _DD , nitrogen N _DD ), easily decomposable solubility Organic matter (carbon C _D ,
_A model of material conversion is created by setting nitrogen N _D ), ammonia nitrogen (NA), nitrite nitrogen (N _B1 ), and nitrate nitrogen (N _B2 ).

The coefficients of each substance conversion shown in FIG. 2 are shown in Tables 1 to 4. The values shown in Tables 1 to 4 are, except for the value of the half-saturation constant related to nitrification,
It is a value used in the field of sewage treatment.

[0046]

[Table 1]

[Table 2]

[Table 3]

[Table 4] Further, the conversion process of each state variable in FIG. 2 is performed by solubilizing easily decomposable solid organic matter into easily decomposable and hardly decomposable soluble organic matter, and easily decomposable soluble organic matter as production of ammonia nitrogen. Mineralization and growth of allotrophic bacteria, nitration of ammoniacal nitrogen and nitrite growth, nitration of nitrite nitrogen and growth of nitrites, reduction of nitrate nitrogen to nitrite nitrogen and Denitrification of nitrite nitrogen, removal of organic substances and growth of allotrophic bacteria, and self-decomposition of each bacterium into easily and persistently degradable solid organic substances.

The reaction rates of these conversions can be displayed in the range of the 0th-order reaction to the 1st-order reaction depending on the value of the half-saturation constant (Michaelis constant), and the rate of change becomes negative. MM type (Mi
chaelis-Menten type).

The solubilization rate (R ₁ mgCOD / l · hr) of the easily decomposable solid organic matter is affected by the MM type in that concentration and is proportional to the concentration of allotrophic bacteria. Intake rate (R ₂ mgCOD / l · hr), which is the mineralization of soluble organic matter, is
The effect of the concentration and the dissolved oxygen concentration was shown as MM type and proportional to allotrophic bacteria.

Further, the rate of nitrite nitration of ammonia nitrogen (R ₃₁ mgN / l · hr) is affected by the concentration and the dissolved oxygen concentration in MM type and is proportional to the concentration of nitrite bacteria. The nitrification rate (R ₃₂ mgN / l · hr) of natural nitrogen was expressed as being affected by the concentration and the dissolved oxygen concentration in MM type and being proportional to the nitric acid bacterium concentration.

Further, the rate of denitrification of nitrite nitrogen and reduction of nitrate nitrogen to nitrite nitrogen (R ₄₁ , R ₄₂ mgN / l.
hr) is influenced by the MM type in the concentration of nitrite nitrogen or nitrate nitrogen and the concentration of organic matter, respectively, and the effect of dissolved oxygen can be expressed by a saturation type inhibition function, Displayed as proportional.

The autolysis rate (R5, R61, R62mgCOD / l · hr) of each bacterium into a solid organic substance is primary for each bacterium concentration, and the dissolved oxygen concentration is affected by the MM type. I decided to receive it.

Table 5 shows the mathematical formulas for the reaction rates in the above steps.

[0053]

[Table 5] On the other hand, in consideration of the structure of the reaction tank 1, the assumed operating conditions, the above reaction steps, etc., as shown in FIG.
From the upper part to the aerobic zone (compartment 3), the microaerobic zone (compartment 2) and the anoxic zone (compartment 1), the volume of each compartment is 88 m ³ and V ₂ as V ₃ respectively.
Is virtually divided into 88 m ³ and V _{1 into} 94 m ³ .

Assuming that the compartments and the separation tank 10 are completely mixed, the water balance equations in the compartments and the separation tank 10 can be displayed as shown in Expressions 1 to 3. Note that Q _k in each equation is the water amount (m ³ / hr) at each place shown in FIG.
The value of Q _{k on} the right side of each equation is actually measured by each flow meter.

[0055]

[Formula 1]

[0056]

[Formula 2]

[0057]

[Formula 3] On the other hand, the production rate (F _{i, j} ) related to the state variable i in each compartment j and the separation tank j is calculated by adding the yield and the conversion rate to the reaction rate shown in Table 5 in the model of each substance conversion shown in FIG. Shown as multiplied. A part thereof is shown in Table 6.

[0058]

[Table 6] Then, the temporal variation of the concentration (C _{i, j} ) of the state variable i of each substance such as easily decomposable soluble organic matter, ammonia nitrogen, and nitrite nitrogen in each section j of the reaction tank 1 and the separation tank j is ,
It is shown by the mass balance formula in each compartment and the separation tank 10. The mass balance formula is shown in Table 7. In the mass balance equation, it is assumed that no substance conversion reaction has occurred in the separation tank 10.

[0059]

[Table 7] Thus, the oxidative decomposition step of oxidatively decomposing the above-mentioned organic matter with aerobic bacteria or facultative anaerobic bacteria, the nitrification step of oxidizing ammonia nitrogen into oxidized nitrogen with nitrite bacteria or nitric acid bacteria, and, Considering the three main reaction steps of the denitrification step in which the denitrifying bacteria reduce the nitrified oxidized nitrogen to nitrogen gas by respiration of nitric acid, the situation of the treatment in each section of the treated water 3a is modeled.

Then, the concentrations of the organic substances and various nitrogen compounds in the wastewater 3 measured in the above formulas 1 to 3 and the formulas (16) to (19) in Table 7 and the above-mentioned examples are set as initial conditions, that is, As the concentration of the state variable i of each substance such as easily decomposable soluble organic matter, ammoniacal nitrogen, and nitrite nitrogen in each compartment and the separation tank 10 at time t = 0, for example, C _{i, 1} and C _i shown in Table 8 are shown. _{, 2} , C _{i, 3} , C _{i, 4} input any numerical value other than 0, input operation values of Q ₁ , Q ₂ , Q ₅ and Q ₆ and calculate until the steady state is reached. Table 9 shows the calculated values.

On the other hand, in the above embodiment, as the control by the control means, the purifying operation of the sewage 3 is made to flow the sewage 3 into the reaction tank 1 for 23 minutes, and the inflow is stopped for 37 minutes.
One minute is set to 0 minute, and the inflow rate in this one cycle is set to about 2.5 m ³ / hr. Due to this condition, the hydraulic retention time (Hydrauli) based on the inflow water in the reaction tank 1
c Residence Time: HRT) is 4.5 days.
Sewage water 3 flowing in in 5 days is retained as treated water 3a.

Further, the water to be treated 3a in the reaction tank 1 is passed through the reflux pipe 7 by a reflux pump at a flow rate of about 27 m ³ / hr, and air is introduced by an ejector at about 1100 to 1300 m ³ / hr. Drive it to reflux to the top, and this reflux is 1
Set to do once every 0 minutes.

Further, the sludge pump is driven so as to convey the precipitated sludge in the separation tank 10 at 2.4 m ³ / hr to the bottom of the reaction tank 1 through the sludge pipe 12, and the separation tank 10 It is set to drive the return pump so that the sludge floating on the water surface is returned to the upper part of the reaction tank 1 at 3.6 m ³ / hr. As a result, the substantial residence time in the reaction tank 1 is
It will be 1.3 days.

Then, the sewage 3 is purified under the above settings, the treated water 3a is sampled at each point of the reaction tank 1 and the separation tank 10, and the substance conversion characteristics of organic substances and nitrogen compounds are inspected.
Experiment 1 was conducted. The results are shown in Tables 8 to 9 in comparison with the above simulation calculation values. In addition, the removal rates in the reaction tank 1 and the separation tank 10 under the above set conditions are shown in Table 10.
Shown in.

The measurement items are dissolved oxygen (DO: Diss
olved Oxygen), pH, alkalinity, total and soluble chemical oxygen demand (COD _Cr ) measured in potassium dichromate, total and soluble biochemical oxygen demand (BOD), total and Soluble Nitrogen, Soluble Nitrite Nitrogen and Nitrate Oxidized Nitrogen, Ammonia Nitrogen, Volatile Suspended Solids (VSS)
Sewage test method published by the Japan Sewer Association in 1984 and American Public Health
Association (American Public Health Associati
on: APHA), American Water Works
Association (American Water Works Associatio
n: AWWA), Water Pollution Control Federation
Standard Method (STAN) published in the United States as the 16th edition in 1985 by the Federation: WPCF).
DARD METHODS).

[0066]

[Table 8]

[Table 9]

[Table 10] Then, as shown in Tables 8 and 9, in the purification treatment with the above settings, the alkalinity of the water 3a to be treated in the reaction tank 1 is 500 (standard deviation 35) mg / l on average, and the pH is 6.9.
Is. From these results, it is judged that the influence on the substance conversion rate is small. Further, the dissolved oxygen concentration measured by the sensor arranged in the section 2 is about 0.5 mg / l.
Met. Furthermore, the total nitrogen (TN: Total Nitrogen) of the wastewater 3 flowing into the reaction tank 1 is about 3450 mg / l, and the total chemical oxygen demand (T (Total) -COD _Cr ) is about 1550.
0 mg / l, ammoniacal nitrogen (NH ₄ ⁺ -N) is about 27
00 mg / l, soluble chemical oxygen demand (S (Soluble)
-COD _Cr ) is about 5530 mg / l.

Further, as shown in Table 10, in the reaction tank 1 and the separation tank 10, the solid matter-related (suspended material SS: Su
spended Solids and volatile floating substances VSS: Vo
Latile Suspended Solids, etc.) are removed by about 20 to 35%, and soluble substances are removed by about 90% or more.
In particular, soluble nitrogen (SN: Soluble Nitrogen) and soluble biochemical oxygen demand (S-BOD) are removed by about 95%, which are about 130 and 100 mg / l, respectively, and sewage 3 is well purified. You can see that it is being processed.

Further, the water quality of the purification treatment by the above settings and the calculated value of the simulation are close to each other, and the equations shown in Tables 1 to 7 and Equations 1 to 3 constituting the simulation are the same as those of the sewage 3. It can be judged that it is well suited for purification treatment.

Next, the purification treatment of the sewage 3 was simulated with the model of the purification treatment of the sewage 3 made up of the equations shown in Tables 1 to 7 and Equations 1 to 3, and the results are
Experiment 2 was carried out in comparison with the actual purification treatment of sewage 3.

In this experiment 2, the water quality of the inflowing sewage 3 shown in Tables 8 and 9, the volume of each section of the reaction tank 1, the recirculation amount of the sewage 3 and the returning amount of the sedimentation and floating sludge in the separation tank 10 were measured. The dissolved oxygen concentration in each compartment (0 mg / l for compartment 1, 0.5 mg / l for compartment 2, 1 mg / l for compartment 3) is shown in Tables 1 to 7 and Equations 1 to 3 Input to the model of purification treatment of the treated water 3a in each section consisting of each equation,
The calculation was repeated until the treated water 3a in each section became a steady state, and the purification treatment of the sewage 3 was simulated.

Further, using the apparatus of Experiment 1, purification treatment was carried out by the same operation as in Experiment 1, water was sampled at each point of the reaction tank 1 and the separation tank 10, and the substance conversion characteristics of organic substances and nitrogen compounds were examined. , And compared with simulated results for one cycle and one day after reaching a steady state. The results are shown in FIGS. 3 and 4.

The steady state in the simulation is
During the inflow cycle of sewage 3, the fluctuation conditions of the concentrations of ammonia nitrogen, nitrite nitrogen and oxidized nitrogen of nitrate nitrogen, allotrophic bacteria, easily decomposable soluble organic matter, nitric acid bacteria became the same. State. Further, in this steady state, the sludge reaction tank 1 and separation tank were operated under the operating conditions of Experiment 2.
The total residence time at 10 was about 6 days, and it was found that nitric acid bacteria flowed out from the system, only nitrite bacteria remained, and denitrification was predominantly nitrite denitrification.

From the results shown in FIGS. 3 and 4, the simulation by the model of the purification treatment of the sewage 3 gives a good approximation including the actual treatment state of the sewage 3 and the state variation of the sewage 3 during the cycle. It is understood that the sewage 3 can be satisfactorily purified by controlling the operation of the sewage 3 purification process based on the model of the sewage 3 purification process.

Next, in a simulated test in Experiment 2, the dissolved oxygen concentration in compartment 1 was 0 mg / l, the dissolved oxygen concentration in compartment 2 was 0.5 mg / l, and the dissolved oxygen concentration in compartment 3 was 1 mg / l.
The dissolved oxygen concentration in compartment 1 is set to 0 mg / l, the dissolved oxygen concentration in compartment 2 is changed, the dissolved oxygen concentration in compartment 3 is set to twice the dissolved oxygen concentration in compartment 2, and calculation is performed until a steady state is reached. Experiment 3 was performed. The results are shown in FIGS. The hydraulic retention time in the reaction tank 1 was set to 4.5 days, which is the condition for the actual purification treatment operation.

From the results shown in FIGS. 5 and 6, when the dissolved oxygen concentration in the compartment 2 is about 0.3 to 0.4 mg / l and the dissolved oxygen concentration is lowered, nitrification hardly occurs. It can be seen that since the amount of respiration of nitric acid is reduced together with the respiration of oxygen, the amount of autotrophic bacteria and autotrophic bacteria is rapidly reduced and cannot be retained in the system.

Further, as shown in FIG. 7, when the dissolved oxygen concentration rises when the dissolved oxygen concentration in section 2 is about 1 mg / l, the concentration of oxidized nitrogen such as nitrite nitrogen and nitrate nitrogen increases. However, it is understood that when the dissolved oxygen concentration decreases, the concentration of ammonia nitrogen and the easily decomposable soluble organic substance increase.

The reason why ammonia nitrogen increases is that the amount of oxygen required for nitrification is insufficient. Also,
When the dissolved oxygen concentration rises, the oxidized nitrogen concentration rises because, in addition to suppressing denitrification by dissolved oxygen, the balance between the consumption of organic substances by oxygen respiration and the consumption by nitric acid respiration is disturbed, and the amount of organic substances required for denitrification is increased. This is because there will be a shortage.

Therefore, it can be judged that it is appropriate to purify the sewage 3 so that the dissolved oxygen concentration in the compartment 2 becomes 0.5 to 1.5 mg / l.

Next, in Experiment 3, the dissolved oxygen concentration in compartment 1 was 0 mg / l and the dissolved oxygen concentration in compartment 2 was 1 mg / l.
The dissolved oxygen concentration in the compartment 3 was set to 2 mg / l, the hydraulic retention time in the reaction tank 1 was changed, and the water to be treated in each compartment was calculated and simulated until it reached a steady state, and Experiment 4 was performed. I went. The results are shown in FIGS. 8 to 10.

From the results shown in FIG. 8, if the hydraulic retention time is longer than 2 days, the existing amount of autotrophic bacteria involved in nitrification in the reaction tank 1 does not change so much, but oxidative decomposition of organic matter and It can be seen that the existing amount of allotrophic bacteria involved in denitrification in the reaction tank 1 decreases as the hydraulic retention time becomes shorter than 6 days.

Further, as shown in FIG. 9, the concentration of the easily decomposable soluble organic matter in the sewage 3 flowing out from the reaction tank 1 sharply rises when the hydraulic retention time is shorter than 3 days. further,
The concentration of oxidized nitrogen increases when the hydraulic retention time is shorter than 4.5 days, and increases sharply after 3.6 days or less. Also, it can be seen that the concentration of ammoniacal nitrogen increases when the hydraulic retention time becomes 3 days or less.

Further, from the results shown in FIG. 10, the concentrations of total nitrogen and soluble nitrogen were such that the hydraulic retention time was 3.6 days or less, the chemical oxygen demand of soluble organic matter (soluble CO 2
It can be seen that the concentration of D _Cr ) increases after 2.5 days.

In Experiment 4, the hydraulic retention time was set to 3.6 days, the dissolved oxygen concentration was changed in the same manner as in Experiment 3, and the calculation was performed until the steady state was calculated and simulated. I went. The result is shown in FIG.

From the results shown in FIG. 11, when the dissolved oxygen concentration in the compartment 2 is 0.65 mg / l or more, the chemical oxygen demand due to the easily decomposable soluble organic matter and the concentration of ammonia nitrogen decrease. , Easily decomposable soluble organic matter and ammonia nitrogen are well removed, but the concentration of oxidized nitrogen begins to rise. Therefore, by setting the dissolved oxygen concentration in the section 2 to about 0.65 to 0.7 mg / l, a good purification treatment can be performed as well as the purification treatment in which the hydraulic retention time is set to 4.5 days. You know what you can do. However,
When the hydraulic retention time is 3.6 days, the range of dissolved oxygen concentration at which good purification treatment of sewage 3 can be performed becomes extremely narrow.

That is, by setting the hydraulic retention time to 4.5 days, it can be judged that stable treatment can be performed with a margin.

Therefore, in the above-mentioned embodiment, the organic matter in the treated water 3a in the reaction tank 1 is determined from the inflow amount of the wastewater 3 flowing into the reaction tank 1 and the concentrations of the organic matter and the nitrogen compounds in the wastewater 3. Treatment of treated water 3a consisting of mass balance equations of various nitrogen compounds and various microorganisms, reaction rate equations for removal of organic substances, conversion of various nitrogen compounds and growth of various microorganisms, and rate equations for production of organic substances and various nitrogen compounds The situation model is executed in each section of the reaction tank 1, and the result of calculating the dissolved oxygen concentration of the treated water 3a in the reaction tank 1 is compared with the calculation value of the simulation of the situation model to continuously calculate the situation model. As along with the calculated value of the simulation, that is, based on, for example, various measured values and input values, as a result of simulating the situation model of the treatment of the treated water 3a in each section, the oxidation decomposition step As a dissolved oxygen concentration of the nitrification step and the denitrification step proceeds favorably respectively, sewage 3
The amount of sewage is controlled by controlling the inflow rate, recirculation rate, sludge return rate, etc.
Purify.

Therefore, in one reaction tank 1, the purification treatment of the sewage 3 containing the organic matter and the nitrogen compound, that is,
In the anaerobic atmosphere where nutrients are obtained by organic substances or self-decomposition in treated water 3a and dissolved oxygen does not exist, the denitrification process in which the denitrifying bacteria reduce nitrified oxidized nitrogen to nitrogen gas by respiration of nitric acid, dissolved oxygen In an aerobic atmosphere in which water is present, aerobic bacteria and facultative anaerobic bacteria activate the remaining organic matter in the treated water 3a as a nutrient source and oxidize the organic matter with aerobic and facultative anaerobic bacteria. The three main steps are the oxidative decomposition step of decomposing and the nitrification step of oxidizing ammonia nitrogen into nitrite nitrogen and oxidized nitrogen of nitrate nitrogen in the presence of dissolved oxygen by nitrite bacteria and nitric acid bacteria. Each can proceed satisfactorily, and the sewage 3 can be satisfactorily purified.

Further, since the wastewater 3 can be purified by one reaction tank 1, the apparatus can be downsized, the installation space can be reduced, the manufacturability can be improved, the operating cost of the apparatus can be reduced, and the purification operation can be performed. Can be simplified.

Further, by simply inputting the measurement results of the concentrations of organic substances and various nitrogen compounds in the polluted state of the inflowing wastewater 3, the purification processing of the wastewater 3 is performed almost automatically, and the purification processing operation can be facilitated. .

In the above embodiment, the biochemical oxygen demand, the chemical oxygen demand, and the concentration of various nitrogen compounds due to the organic matter, which is the polluted state of the inflowing sewage 3, are measured in advance, and the measurement result is used as the control means. I explained the input and purification process, but without using various solenoid valves and flow meters, I measured the pollution state from the chemical oxygen demand, and made the inflow rate, reflux rate, sludge return rate constant, A simple type for purifying the sewage 3, a biochemical oxygen demand by an organic substance, a chemical oxygen demand and the concentration of various nitrogen compounds are automatically measured by a sensor, etc., and the measurement result and the inflow sewage 3 The amount of organic substances, various nitrogen compounds, etc. flowing into the reaction tank 1 is measured as a polluted state from the inflow amount of the sewage 3, and the control means automatically controls the operation of the purification treatment of the sewage 3 to purify the sewage 3. You can do things of automatic that.

Further, the dissolved oxygen concentration of the treated water 3a was measured by the sensor provided in the middle of the reaction tank 1 in the section 2 for explanation, but the sensor is reacted along the flowing direction of the treated water 3a. A plurality of tanks are provided in the tank 1, and a plurality of virtual compartments are provided corresponding to the respective compartments. Based on the dissolved oxygen concentration of each, a status model of the purification treatment of the water 3a to be treated in each compartment is executed, and the compartments are provided in each compartment. The dissolved oxygen concentration may be adjusted with an aeration device. Further, one sensor may be moved to measure the dissolved oxygen concentration at each position of the reaction tank 1 to control the operation of purifying the sewage 3.

Further, as the sewage 3, the explanation has been made by using, for example, human waste water containing an organic substance and various nitrogen compounds, but any sewage 3 containing either an organic substance or various nitrogen compounds can be targeted.

[0093]

According to the method for treating sewage according to the first aspect of the present invention, the state of pollution at each position of the water to be treated in the reaction tank is based on the state of contamination of the sewage and the dissolved oxygen concentration of the water to be treated. hand,
In order to control the dissolved oxygen concentration of the water to be treated, it is calculated from the mass balance equation, reaction rate equation and production rate equation, respectively.
In one reaction tank, an oxidative decomposition process in which microorganisms oxidize and decompose, a nitrification process in which ammonia nitrogen is oxidized by microorganisms into oxidized nitrogen, and a denitrification process in which oxidized nitrogen is reduced by microorganisms into nitrogen gas. Can proceed satisfactorily, and sewage can be satisfactorily purified.

According to the sewage treatment method of claim 2,
The method for treating wastewater according to claim 1, wherein the polluted state of the wastewater flowing into the reaction tank is measured based on the inflow amount of the wastewater, the organic matter in the wastewater, and various nitrogen compounds in the wastewater. The pollution state at each position along the flowing direction of the treated water in the reaction tank can be easily calculated from the pollution state of the inflowing wastewater, and the wastewater can be easily purified.

According to the sewage treatment method of claim 3,
The treatment method according to claim 1 or 2, wherein the dissolved oxygen concentration of the water to be treated is defined as the inflow amount of sewage, the oxygen supply amount to the water to be treated, and the reflux amount of the water to be treated from the downstream side to the upstream side of the reaction tank. Since it is controlled based on the above, the purification treatment operation of wastewater can be easily performed, and the oxidative decomposition step in which organic matter is oxidized and decomposed by microorganisms, the nitrification step in which ammonia nitrogen is oxidized by microorganisms into oxidized nitrogen, and the oxidized nitrogen The denitrification step of reducing methane to nitrogen gas with microorganisms can be effectively and efficiently progressed in one reaction tank, and sewage can be satisfactorily purified.

According to the wastewater treatment apparatus of the fourth aspect,
While measuring the pollution status of sewage with pollution measuring means,
The dissolved oxygen measuring means measures the dissolved oxygen concentration of the water to be treated in the reaction tank, and the control means controls the oxygen supply means, the inflow adjusting means and the reflux means on the basis of these results to control the treated water. Since the concentration of dissolved oxygen is controlled and sewage is purified, sewage can be easily purified, and an oxidative decomposition process in which organic matter is oxidatively decomposed by microorganisms, nitrification in which ammonia nitrogen is oxidized by microorganisms into oxidized nitrogen The process and the denitrification process of reducing oxidized nitrogen to nitrogen gas by microorganisms are 1
The two reaction tanks can proceed satisfactorily and efficiently, and sewage can be satisfactorily purified.

[Brief description of drawings]

FIG. 1 is a system explanatory view showing the configuration of an embodiment of an apparatus for carrying out the wastewater treatment method of the present invention.

FIG. 2 is a system explanatory view showing a model of substance conversion in the same sewage purification process.

FIG. 3 is a graph showing a comparison between a simulation result and an actual measurement value in one cycle after reaching the steady state of the substance conversion characteristics of organic substances and nitrogen compounds.

FIG. 4 is a graph showing a comparison between a simulation result and a measured value for one day after reaching a steady state of the substance conversion characteristics of organic substances and nitrogen compounds.

FIG. 5 is a graph showing a simulation result in which the dissolved oxygen concentration in the same section 2 is changed.

FIG. 6 is a graph showing a simulation result in which the dissolved oxygen concentration in the same section 2 is changed.

FIG. 7 is a graph showing a simulation result in which the dissolved oxygen concentration in the same section 2 is changed.

FIG. 8 is a graph showing a simulation result in which the hydraulic retention time is changed.

FIG. 9 is a graph showing a simulation result in which the hydraulic retention time is changed.

FIG. 10 is a graph showing a simulation result in which the hydraulic retention time is changed.

FIG. 11 is a graph showing a simulation result in which the dissolved oxygen concentration in the same section 2 is changed.

[Explanation of symbols]

 1 Reaction Tank 3 Sewage 3a Treated Water 4 Inlet 5 Inflow Pipe 7 Reflux Pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Tsuno 2-8-14, Kinugawa, Otsu City, Shiga Prefecture (72) Inventor Toshio Yamada 2-9, Sellobori, Nishi-ku, Osaka City, Osaka Prefecture Ataka Industrial Co., Ltd.

Claims (4)

[Claims] 1. The reaction tank along the direction in which the water to be treated flows, by measuring the polluted state of sewage flowing into the reaction tank and measuring the dissolved oxygen concentration of the water to be treated in the reaction tank. The polluted state of the treated water at each position in the, based on the measurement result of the polluted state of the sewage flowing into the reaction tank and the measurement result of the dissolved oxygen concentration, organic matter in the treated water, various nitrogen compounds And a mass balance equation of various microorganisms, a reaction rate equation for removal of organic matter, conversion of various nitrogen compounds and growth of various microorganisms, and a production rate equation of organic matter and various nitrogen compounds, respectively, to dissolve the treated water A method for treating sewage, which comprises controlling the oxygen concentration. 2. A polluted state of sewage flowing into a reaction tank is measured based on at least one of an inflow amount of the sewage, an organic matter in the sewage, and various nitrogen compounds in the sewage. The method for treating sewage according to claim 1, which is characterized in that. 3. The dissolved oxygen concentration of the water to be treated is determined by the inflow amount of sewage flowing into the reaction tank, the amount of oxygen supplied to the water to be treated in the reaction tank, and the amount of oxygen from the downstream side to the upstream side of the reaction tank. The method for treating sewage according to claim 1 or 2, wherein the control is performed based on at least one of the reflux amounts of the water to be treated. 4. A reaction tank having an inflow port for inflowing sewage, oxygen supply means provided in the reaction tank for supplying oxygen to the water to be treated in the reaction tank, and the reaction tank provided in the reaction tank. Recirculation means for recirculating the water to be treated from the downstream side to the upstream side, inflow adjusting means for adjusting the inflow amount of sewage flowing in through the inflow port, and the inflowing sewage provided in the vicinity of the inflow port Pollution measuring means for measuring the pollution state of, the dissolved oxygen measuring means for measuring the dissolved oxygen concentration of the water to be treated in the reaction tank, the measurement by at least one of the pollution measuring means and the dissolved oxygen measuring means A sewage treatment apparatus comprising: a control unit that controls at least one of the oxygen supply unit, the inflow adjustment unit, and the reflux unit based on the result.