JP3213657B2 - Wastewater treatment method and apparatus - Google Patents

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 for purifying sewage containing organic substances and nitrogen compounds in a single tank.

[0002]

2. Description of the Related Art Conventionally, when purifying sewage such as human waste containing organic substances and nitrogen compounds, aerobic bacteria and facultatively anaerobic in an aerobic atmosphere in which dissolved oxygen (DO) is present. An oxidative decomposition process in which anaerobic bacteria and the like are activated by using organic matter contained in sewage as a nutrient source, and oxidatively decompose the organic matter by aerobic bacteria and facultative anaerobic bacteria. Nitrification process in which bacteria and nitric acid oxidize nitrite nitrogen and nitrate nitrogen to oxidized nitrogen, and oxidized nitrate in an anaerobic atmosphere where nutrients are obtained by organic matter or self-decomposition and there is no dissolved oxygen It is necessary to consider a denitrification process in which denitrifying bacteria reduce nitrogen to nitrogen gas by nitric acid respiration.

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

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

[0005] However, Japanese Patent Application Laid-Open No.
No. 95, the method for treating sewage, the dissolved oxygen concentration directly caused by each treatment step, circulating water with respect to the amount of inflow water,
Further, since the indirect management is performed based on the ratio of the returned sludge to the amount of inflow water, the dissolved oxygen concentration in each processing step is likely to fluctuate, and there is a possibility that a good purification treatment cannot be performed. Furthermore, since the purification process 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 flowing into the sewage fluctuates, and the concentration of organic matter in the sewage fluctuates. The oxidative decomposition process could not be performed well, and the balance of organic matter involved in the nitrification and denitrification process fluctuated.
There is a possibility that the purification treatment cannot be performed well. Also, in order to facilitate the management of 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 size of the device is increased and the installation space is increased.

Further, the sewage treatment apparatus described in Japanese Patent Application Laid-Open No. 63-209796 discloses a kinetic constant when environmental factors such as water temperature and pH of sewage are stable, a carbon-based system and a nitrogen-based system. The simulation is performed using the substrate removal rate equation, the growth rate equation for each of the carbon-based and nitrogen-based cells, the mass balance equation relating to the dissolved oxygen concentration, and the mass balance equation for the amount of sludge in the process.

On the other hand, data on the amount of bacterial cells or the rate of nitrification contributing to nitrification in a steady-state process with time are calculated, and a value in which the amount of nitrifying cells or the rate of nitrification is stable is used as a target value. The data is output by the first simulator unit. In addition, the kinetic constant is expressed as a function of the environmental factor, and the kinetic constant according to the environmental factor at each time is used.
Introducing the target value from the first simulator unit, the carbon-based and nitrogen-based substrate removal rate equations, the carbon-based and nitrogen-based cell growth rate equations, the material balance equation related to the dissolved oxygen concentration, and A simulation is performed by calculating using the material balance equation for the amount of sludge in the process.

[0008] Then, by the simulation, an appropriate set value of the control element of the dissolved oxygen concentration at each time point is obtained by the second simulator section, and a mixed solution of the organic wastewater and the activated sludge is aerated in the reaction tank, and the water temperature is adjusted. Even if environmental factors such as pH and the like fluctuate, the amount of nitrifying bacteria or the rate of nitrification is maintained at a target value, and the purification treatment is performed well.

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

The sewage treatment apparatus described in Japanese Patent Application 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. And controlling the air flow regulating valve and the suction valve of the blower, which constitute the aeration device in the nitrification tank, to perform aeration so that the measured dissolved oxygen concentration becomes each corresponding target value.

Further, the oxidation-reduction potential of the denitrification tank is compared with a predetermined oxidation-reduction potential suitable for denitrification, and the nitrification tank is transferred from the nitrification tank to the denitrification tank so that the measured oxidation-reduction potential becomes the set oxidation-reduction potential. To control the amount of circulating water.

In addition, the nitrification efficiency is prevented from lowering due to the shortage of the dissolved oxygen concentration at the inlet portion, and the denitrification efficiency is prevented from lowering due to the introduction of dissolved oxygen into the denitrification tank, so that the purification treatment is performed efficiently and efficiently. .

However, Japanese Patent Application Laid-Open No. 64-5119 discloses this technique.
The apparatus described in Japanese Patent Publication No. 7 controls the amount of circulating water and the state of aeration based on the dissolved oxygen concentration in the nitrification tank and the oxidation-reduction potential indicating the denitrification state of the denitrification tank, and controls the purification treatment in the nitrification / denitrification step. The organic matter is not oxidatively decomposed by monitoring the oxidative decomposition process and controlling the oxidative decomposition process. In addition, the nitrification / denitrification process may not be performed properly due to fluctuations in the balance of organic substances involved in the nitrification / denitrification process. Further, since two units, ie, a nitrification tank and a denitrification tank, are provided, there is a problem that the size of the apparatus is increased and the installation space is increased.

[0014]

As described above, in the method for treating sewage described in Japanese Patent Application Laid-Open No. 61-212395, good purification cannot be performed due to fluctuations in the concentration of dissolved oxygen in each treatment step. There is a danger,
Fluctuations in the amount of organic matter flowing into the sewage and fluctuations in the state of pollution caused by the organic matter make it impossible to perform the oxidative decomposition process satisfactorily. .

In the sewage treatment apparatus described in Japanese Patent Application Laid-Open No. 63-209796, the amount of organic matter flowing into the sewage is changed and the state of contamination by organic matter is controlled in order to control the balance of organic matter based on the nitrification process. , The oxidative decomposition process of organic substances cannot be performed well, the balance of organic substances involved in the nitrification and denitrification steps fluctuates, and there is a possibility that purification treatment cannot be performed well.

Further, in the sewage treatment apparatus described in Japanese Patent Application Laid-Open No. 64-51197, since control for making the oxidative decomposition process of organic matter good is not performed, the amount of inflow of sewage and the state of contamination by organic matter are not controlled. Due to the fluctuation, the organic matter cannot be oxidized and decomposed satisfactorily, and the nitrification / denitrification step may not be performed properly due to the fluctuation of the balance of the organic matter involved in the nitrification / denitrification step.

A method for treating sewage described in JP-A-61-212395 and JP-A-64-511
In the sewage treatment apparatus described in Japanese Patent Publication No. 97-206, a nitrification tank and a denitrification tank are provided, and in the sewage treatment apparatus described in JP-A-63-209796, in order to purify sewage, However, since a separate device such as a denitrification tank is required, there is a problem that the size of the device is increased and the installation space is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a highly reliable sewage system in which oxidative decomposition, nitrification, and denitrification of organic substances are performed in a single tank, and purification is performed easily, efficiently, and reliably. It is an object of the present invention to provide a processing method and an apparatus therefor.

[0019]

According to a first aspect of the present invention, there is provided a method for treating sewage, comprising: measuring a state of contamination of sewage flowing into a reaction tank; measuring a dissolved oxygen concentration of water to be treated in the reaction tank; The contaminated state of the water to be treated at each position in the reaction tank along the direction in which the water to be treated flows, the measurement result of the contamination state of the sewage flowing into the reaction tank, and the measurement result of the dissolved oxygen concentration Based on the organic matter in the water to be treated, various nitrogen compounds and mass balance formula of various microorganisms,
A reaction rate equation for removal of organic substances, conversion of various nitrogen compounds, and growth of various microorganisms, and a production rate equation for organic substances and various nitrogen compounds, respectively, were calculated in the reaction vessel.
An oxidative decomposition step of oxidatively decomposing the organic matter by the microorganism
Nitrification that oxidizes ammonia and ammonia nitrogen to oxidized nitrogen
Aerobic atmosphere where the reaction takes place
Anaerobic atmosphere where the reaction of the denitrification process
The concentration of dissolved oxygen in the water to be treated is controlled so that both occur .

According to a second aspect of the present invention, there is provided a method for treating sewage according to the first aspect, wherein the polluted state of the sewage flowing into the reaction tank is determined by: The measurement is based on at least one of various nitrogen compounds in the sewage.

According to a third aspect of the present invention, there is provided a method for treating sewage according to the first or second aspect, wherein the concentration of dissolved oxygen in the water to be treated is determined by the amount of sewage flowing into the reaction tank, The control is performed based on at least one of an oxygen supply amount to the treated water and a reflux amount of the treated water from a downstream side to an upstream side of the reaction tank.

According to a fourth aspect of the present invention, there is provided a sewage treatment apparatus comprising: a reaction tank having an inflow port into which sewage flows and in which microorganisms inhabit; and an oxygen supply port provided in the reaction tank for supplying oxygen to water to be treated in the reaction tank. A supply unit, a reflux unit provided in the reaction tank for refluxing the water to be treated from a downstream side to an upstream side of the reaction tank, and an inflow adjustment unit for adjusting an inflow amount of sewage flowing through the inlet. A pollution measuring means provided near the inflow port for measuring a pollution state of the incoming sewage, a dissolved oxygen measuring means for measuring a dissolved oxygen concentration of the water to be treated in the reaction tank, and the pollution measuring means and based on the measurement result by at least one of the dissolved oxygen measurement means, said oxygen supply means to control at least one of the inflow adjusting means and the return means, said counter
In the reaction tank, the microorganisms are oxidatively decomposed by the microorganism.
Oxidative decomposition process and conversion of ammoniacal nitrogen to oxidized nitrogen
Aerobic atmosphere where the reaction of the nitrification process
Anaerobic reaction that occurs in the denitrification process of reducing nitrogen to nitrogen gas
Dissolved acid in a state where both
Control means for controlling the element concentration .

[0023]

In the method for treating sewage according to the first aspect, the state of contamination at each position along the flowing direction of the water to be treated in the reaction tank is determined by the state of contamination of the sewage flowing into the reaction tank and the state of contamination of the reaction tank. Based on the dissolved oxygen concentration of the water to be treated in the water, the organic matter in the water to be treated, various nitrogen compounds and the mass balance formula of various microorganisms,
Removal of organics, respectively calculated from the kinetics of the proliferation of conversion and various microorganisms for various nitrogen compounds, the generation kinetics organic and various nitrogen compounds, organic matter by microorganisms
Oxidative decomposition process and oxidative decomposition of ammonia
An aerobic atmosphere in which the nitrification process oxidizes to oxidized nitrogen.
Ambient air and the denitrification process that reduces oxidized nitrogen to nitrogen gas
Both the reaction and the anaerobic atmosphere occur in the reaction tank.
In order to control the concentration of dissolved oxygen in the water to be treated, the oxidative decomposition step of oxidatively decomposing organic substances by microorganisms in one reaction tank, the nitrification step of oxidizing ammonia nitrogen to oxidized nitrogen by microorganisms, and Each of the denitrification steps of reducing oxidized nitrogen to nitrogen gas by microorganisms proceeds well, and sewage is satisfactorily purified.

According to a second aspect of the present invention, there is provided a method for treating sewage according to the first aspect, wherein the polluted state of the sewage flowing into the reaction tank is determined by:
Since the measurement is based on at least one of various nitrogen compounds in the sewage, the contamination state at each position along the flowing direction of the water to be treated in the reaction tank from the contamination state of the sewage flowing into the reaction tank Can be easily calculated, and the purification process of the sewage becomes easy.

According to a third aspect of the present invention, in the treatment method of the first or second aspect, the concentration of dissolved oxygen in the water to be treated in the reaction tank is determined by:
Since the control is performed based on at least one of the oxygen supply amount to the water to be treated in the reaction tank and the reflux amount of the water to be treated from the downstream side to the upstream side of the reaction tank, the purification operation of the sewage is easy,
The oxidative decomposition step of oxidatively decomposing organic substances by microorganisms, the nitrification step of oxidizing ammonia nitrogen to oxidized nitrogen by microorganisms, and the denitrification step of reducing oxidized nitrogen to nitrogen gas by microorganisms are one reaction. Proceeds well and efficiently in the tank,
Sewage is well purified.

According to a fourth aspect of the present invention, there is provided a sewage treatment apparatus for measuring the contamination state of sewage flowing into a reaction tank through an inlet by means of pollution measuring means provided near an inlet of the reaction tank. The dissolved oxygen concentration of the water to be treated in the reaction tank is measured by the oxygen measuring means, and the oxygen supply means for supplying oxygen to the water to be treated is supplied by the control means based on at least one of these results. A microorganism is controlled by controlling at least one of an inflow adjusting means for adjusting the inflow amount and a reflux means for refluxing the water to be treated from a downstream side to an upstream side of the reaction tank.
Oxidative Decomposition Process and Ammonia
The reaction of the nitrification process that oxidizes near nitrogen to oxidized nitrogen
Aerobic atmosphere and reducing oxidized nitrogen to nitrogen gas
Both the reaction tank and the anaerobic atmosphere where the reaction of the denitrification process occurs
An oxidative decomposition process in which the concentration of dissolved oxygen in the water to be treated is controlled to a state generated in the effluent and the sewage is purified, so that the sewage purification treatment operation is easy and organic matter is oxidatively decomposed by microorganisms;
The nitrification step of oxidizing ammonia nitrogen to oxidized nitrogen by microorganisms and the denitrification step of reducing oxidized nitrogen to nitrogen gas by microorganisms proceed efficiently and efficiently in one reaction tank, and sewage becomes good. Purification processing is performed.

[0027]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an apparatus for carrying out a method for treating wastewater according to the present invention.

In FIG. 1, reference numeral 1 denotes a reaction tank. This reaction tank 1 is formed in a cylindrical shape having a volume of, for example, 270 m ³ and a water depth of 10 m, and has a bottom portion 2 protruding downward in a funnel shape at a lower end.
Are formed. And, in the lower part of the reaction tank 1,
An inflow port 4 into which sewage 3, such as human wastewater, containing organic substances and various nitrogen compounds flows, is formed with an opening. The inflow port 4 is provided with contaminants such as sand and gravel, metal pieces, paper, and vinyl in the sewage. Is connected to an inflow pipe 5 led out from a debris removing device (not shown) for separating the water. Furthermore, this inflow pipe 5
Is provided with an electromagnetic valve (not shown) for controlling the flow of the sewage 3 from which contaminants have been removed by the residue removing apparatus into the reaction tank 1. The inflow pipe 5 is provided with a flowmeter (not shown) for measuring the inflow amount of the sewage 3 flowing into the reaction tank 1.

In the reaction tank 1, treated water 3 a, which is a mixed liquid of the sewage 3 flowing into the reaction tank 1 and various microorganisms in the reaction tank 1 from the lower end of the bottom 2 to the upper part of the reaction tank 1. A reflux pipe 7 is connected to the reflux pipe 7. The reflux pipe 7 is provided with a reflux pump and a flow meter (not shown). Further, when the water to be treated 3a 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 of the water to be treated 3a. Is provided with an ejector (not shown) that mixes air into the device.

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

In a substantially intermediate portion of the reaction tank 1, the reaction tank 1 is provided.
Oxygen (DO: Dissolved Oxygen) in the water to be treated 3a
A sensor (not shown) for measuring the concentration of the water is provided, and an outflow pipe 8 for flowing the water to be treated 3a in the intermediate portion out of the reaction tank 1 is connected. And this outflow pipe 8
Is provided with an unillustrated solenoid valve and a flow meter for controlling the outflow amount of the water to be treated 3a.

On the other hand, reference numeral 10 denotes a separation tank, which is provided with a sedimentation section 11 which protrudes downward in a funnel shape at the lower part and has a capacity of 30.
It is formed in a cylindrical shape of m ³ . And this separation tank 10
Outlet pipe 8 connected to reaction tank 1 is connected to the upper part of the tank. At the lower end of the sedimentation section 11 of the separation tank 10, a sludge pipe 12 for returning sludge settled in the sedimentation section 11 to the lower part of the reaction tank 1 is connected. 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 portion of the reaction tank 1 is provided. The return pipe 13 is provided with a return pump and a flow meter (not shown). And
The separation tank 10 has 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. In addition, separation tank 10
Is not limited to a sedimentation type, but may be of any structure such as a membrane separation type for separating sludge by a filtration membrane or a centrifugal separation type.

The apparatus is provided with control means (not shown). The control means controls the state of contamination of the sewage 3 flowing into the reaction tank 1, for example, the amount of the sewage 3 flowing in, and It is possible to input numerical values such as the amount of contaminants flowing into the reaction tank 1 calculated from the concentrations of organic substances and various nitrogen compounds, and a sensor for measuring the dissolved oxygen concentration of the water 3a to be treated in the reaction tank 1 is connected. I have. And the control means,
Based on these various measured values and input values, the opening degree of each solenoid valve and the driving state of the reflux pump, the sludge pump, and the return pump are controlled.

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 via the inflow pipe 5 is collected from the residue removing apparatus, and organic matter in the sewage 3, that is, a biochemical oxygen demand (Biochemical oxygen demand) is obtained.
Oxygen Demand (BOD) and chemical oxygen demand (Ch
Emergency oxygen demand (COD) and the concentration 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, and allows the sewage 3 from the residue removing apparatus to flow into the lower part of the reaction tank 1 from the inflow port 4. The control means closes the solenoid valve when the flow rate of the wastewater 3 reaches a predetermined value.

The treated water 3a into which the sewage 3 has flowed and mixed into the reaction tank 1 is purified by the microorganisms growing in the reaction tank 1, and is returned to the reflux pipe 7 by a reflux pump driven by control means.
To the upper part of the reaction tank 1 while introducing air by an ejector.

Further, the reaction vessel 1 gradually flows downward while being purified by various microorganisms, and a part of the reaction vessel 1 is controlled by the control means so that the opening of the solenoid valve is controlled.
And the remainder is again returned from the bottom of the reactor 1 to the upper portion of the reactor 1 via the reflux pipe 7.

The treated water 3a flowing into the separation tank 10
Sludge suspended in the water to be treated 3a is settled and separated,
The settled sludge is again conveyed to the bottom of the reaction tank 1 through the sludge pipe 12 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 via a return pipe 13 by driving a return pump controlled by a control unit.

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

The control means controls the concentration of the inputted COD, BOD and the concentration of each nitrogen compound, which are in the polluted state of sewage.
The calculation is performed based on the inflow amount of the sewage and the dissolved oxygen concentration of the water to be treated 3a measured by a sensor provided in an intermediate portion of the reaction tank. Then, the denitrifying bacteria dissolve the nitrified oxidized nitrogen in an anaerobic atmosphere in which the dissolved oxygen concentration of the water to be treated 3a for which an appropriate treatment result is obtained, that is, the organic matter in the water to be treated 3a or nutrients obtained by self-decomposition in an anaerobic atmosphere. Denitrification process in which nitric acid is reduced to nitrogen gas by respiration, in aerobic atmosphere with dissolved oxygen concentration, aerobic bacteria and facultative anaerobic bacteria activate 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, ammonia nitrogen is converted to nitrite nitrogen or nitrate by nitrite or nitrate bacteria. The solenoid valves and the pumps are controlled by the flow rate values of the respective flow meters so that the reaction step of the nitrification step of oxidizing nitrogen to oxidized nitrogen proceeds satisfactorily and has a dissolved oxygen concentration at which the sewage 3 is well purified. Control while monitoring.

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

First, in the purification treatment of the sewage 3 containing organic matter and nitrogen compounds, the organic matter contained in the sewage 3 into which aerobic bacteria and facultative anaerobic bacteria flow in an aerobic atmosphere having a dissolved oxygen concentration. Oxidative decomposition process of oxidizing and decomposing organic matter by aerobic bacteria and facultative anaerobic bacteria, etc. in the presence of dissolved oxygen, and converting ammoniacal nitrogen into nitrite by nitrite or nitrate in the presence of dissolved oxygen A nitrification process that oxidizes nitric oxides to oxidized nitrogen or nitrate nitrogen, and a denitrification process in which nitrified oxidized nitrogen is reduced to nitrogen gas by nitric acid respiration in an anaerobic atmosphere with nutrients obtained by organic matter or autolysis. It is necessary to consider the three main reaction steps of the nitriding step.

From this, as shown in the block diagram of FIG. 2, as the state variables, nitrite (B _A1 ), nitrate (B _A2 ), vegetative bacterium (B _H ), hardly degradable Solid organic matter (carbon C _DS , nitrogen N _DS ), easily decomposable solid organic matter (carbon C _S , nitrogen N _S ), hardly decomposable organic matter (carbon C _DD , nitrogen N _DD ), easily decomposable Organic matter (carbon C _D ,
By setting nitrogen N _D ), ammonia nitrogen (N _A ), nitrite nitrogen (N _B1 ), and nitrate nitrogen (N _B2 ), a model of material conversion is created.

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 the values of the half-saturation constants related to nitrification,
It is a value used in the field of sewage treatment.

[0046]

[Table 1]

[Table 2]

[Table 3]

[Table 4] The conversion process of each state variable in FIG. 2 is performed by solubilizing a readily decomposable solid organic substance into a readily decomposable and hardly decomposable soluble organic substance, and producing a readily decomposable soluble organic substance by producing ammoniacal nitrogen. Mineralization and growth of vegetative bacteria, nitrification of ammonia nitrogen and growth of nitrite, nitrification of nitrite and growth of nitrate, reduction of nitrate to nitrite and Denitrification of nitrite nitrogen, removal of organic matter, growth of vegetative bacteria, and autolysis of each bacterium into easily decomposable and hardly decomposable solid organic matter.

Incidentally, the reaction rate of these conversions can be expressed in the range from the 0th-order reaction to the 1st-order reaction depending on the value of the half-saturation constant (Michaelis constant) due to the influence of the substrate involved, and the rate of change is negative. MM type (Mi
chaelis-Menten type).

The solubilization rate (R ₁ mgCOD / l · hr) of the easily degradable solid organic matter is influenced by the MM type and is proportional to the concentration of the allotrophic bacteria. The intake rate (R ₂ mgCOD / lhr), which is the mineralization of soluble organic matter,
The influence of the concentration and the dissolved oxygen concentration was indicated as being proportional to the vegetative bacterium in the MM type.

The nitrite rate (R ₃₁ mgN / l · hr) of ammoniacal nitrogen is affected by the concentration and dissolved oxygen concentration in the MM type and is proportional to the concentration of nitrite. The nitrate rate (R ₃₂ mgN / l · hr) of the agglomerated nitrogen was expressed as being proportional to the nitrate bacterium concentration affected by the concentration and dissolved oxygen concentration in the MM type.

Furthermore, the rate of denitrification of nitrite nitrogen and reduction of nitrate nitrogen to nitrite nitrogen (R ₄₁ , R ₄₂ mgN / l ·
hr), the concentration of nitrite nitrogen or nitrate nitrogen and the concentration of organic matter are affected by the MM type, and the effect of dissolved oxygen can be expressed by a saturated inhibition function. Indicated as proportional.

The rate of self-decomposition of each bacterium into solid organic matter (R5, R61, R62 mg COD / l · hr) is primary for each bacterial concentration, and the dissolved oxygen concentration is affected by the MM type. I took it.

Table 5 shows formulas of the reaction rates in the above steps.

[0053]

[Table 5] On the other hand, taking into account the structure, assumed operating conditions, the above-mentioned respective reaction steps, and the like, the reaction tank 1 is, as shown in FIG.
From the upper part of the aerobic zone (compartment 3), microaerobic zone (compartment 2) and anoxic zone (compartment 1), the volume of each compartment is 88 m ³ , V ₂ as V ₃ respectively.
Virtual partitioned into 94m ³ as 88m ^3, V ₁ as.

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

[0055]

(Equation 1)

[0056]

(Equation 2)

[0057]

(Equation 3) On the other hand, the production rate (F _{i, j} ) related to the state variable i in each section j and the separation tank j is obtained by adding the yield and the conversion ratio to the reaction rates shown in Table 5 in the model of each substance conversion shown in FIG. Shown as multiplied. Table 6 shows some of them.

[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 as follows. ,
It is shown by the material balance formula in each section and the separation tank 10, and this material balance formula is shown in Table 7. In the material balance equation, it is assumed that no material conversion reaction occurs in the separation tank 10.

[0059]

[Table 7] Thus, an oxidative decomposition step of oxidatively decomposing the above-mentioned organic substances with aerobic bacteria or facultative anaerobic bacteria, a nitrification step of oxidizing ammonia nitrogen to oxidized nitrogen with nitrite or nitrate, and The state of treatment in each section of the water to be treated 3a is modeled in consideration of three main reaction steps of a denitrification step in which nitrified oxidized nitrogen is reduced to nitrogen gas by nitric acid respiration by nitric acid respiration.

The concentrations of the organic substances and various nitrogen compounds in the sewage 3 measured in the above formulas 1 to 3, the formulas (16) to (19) in Table 7, and the above examples, ie, the initial conditions, labile soluble organic substances in each compartment and the separation vessel 10 at time t = 0, ammonia nitrogen, as the concentration of the state variable i of each substance such as nitrite nitrogen, for example, C _i shown in Table _{8, 1,} C _{i , 2} , C _{i, 3} , C _{i, 4} , input an arbitrary numerical value other than 0, input the operation values of Q ₁ , Q ₂ , Q ₅ and Q ₆ , and calculated the simulations until the steady state was 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 performed by flowing the sewage 3 into the reaction tank 1 for 23 minutes and stopping the inflow for 37 minutes.
One cycle is defined as 0 minutes, and the inflow rate in this one cycle is set to about 2.5 m ³ / hr. Due to this condition, the hydraulic residence time based on the influent water in the reactor 1 (Hydrauli
c Residence Time (HRT) is 4.5 days.
The sewage 3 flowing in 5 days is retained as the treated water 3a.

Further, the water to be treated 3a in the reaction vessel 1 flows through the reflux pipe 7 at a flow rate of about 27 m ³ / hr, and air is introduced into the reaction vessel 1 by an ejector at a rate of about 1100 to 1300 m ³ / hr. It is driven to return to the top and this
Set to run once every 0 minutes.

Further, the sludge pump is driven so that the sludge settled in the separation tank 10 is conveyed to the bottom of the reaction tank 1 through the sludge pipe 12 at 2.4 m ³ / hr. The return pump is set to drive the sludge floating on the water surface to return to the upper part of the reaction tank 1 at 3.6 m ³ / hr. Thereby, the substantial residence time in the reaction tank 1 is:
1.3 days.

Then, the sewage water 3 is purified under the above-mentioned settings, and the water 3a to be treated 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 performed. The results are shown in Tables 8 and 9 in comparison with the above-mentioned simulation calculation values. Table 10 shows the removal rates in the reaction tank 1 and the separation tank 10 under the above set conditions.
Shown in

The measurement items were 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 Soluble nitrogen, soluble nitrogen oxides such as nitrite nitrogen and nitrate nitrogen, ammonia nitrogen, volatile suspended solids (VSS)
Sewage test methods published in 1984 by the Japan Sewerage Association, and American Public Health
Association (American Public Health Associati
on: APHA), American Water Works
Association (American Water Works Association)
n: AWAWA), Water Pollution Control Federation
Standard Method (STAN) published in the United States as a 16th edition in 1985 at Federation: WPCF.
DARD METHODS).

[0066]

[Table 8]

[Table 9]

[Table 10] Then, as shown in Tables 8 and 9, in the purification treatment under the above settings, the alkalinity of the water 3a to be treated in the reaction tank 1 is 500 mg / l on average (standard deviation 35), and the pH is 6.9.
It is. From these results, it is determined that the influence on the material conversion rate is small. The dissolved oxygen concentration measured by the sensor disposed in the section 2 is about 0.5 mg / l
Met. Furthermore, the total nitrogen (TN: Total Nitrogen) of the sewage 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, ammonia nitrogen (NH ₄ ⁺ -N) is about 27
00mg / 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, solid substances (suspended substances SS: Su
Spend spent solids and volatile suspended solids VSS: Vo
Latile Suspended Solids, etc.) are removed by about 20-35%, and soluble substances are removed by about 90% or more.
In particular, about 95% of soluble nitrogen (SN: Soluble Nitrogen) and soluble biochemical oxygen demand (S-BOD) are removed, and are about 130 and 100 mg / l, respectively, and the sewage 3 is satisfactorily purified. You can see that it has been processed.

Further, the water quality of the purification treatment according to the above setting and the calculated value of the simulation are close to each other, and the respective expressions shown in Tables 1 to 7 and Expressions 1 to 3 which constitute the simulation are expressed as follows. It can be determined that it is well suited for the purification process.

Next, the purification process of the sewage 3 is simulated by using the model of the purification process of the sewage 3 shown in Tables 1 to 7 and Expressions 1 to 3, and the result is shown as follows.
Experiment 2 was performed in comparison with the actual purification treatment of the wastewater 3.

In Experiment 2, the water quality of the inflowed sewage 3 shown in Tables 8 and 9, the volume of each section of the reaction tank 1, the amount of reflux of the sewage 3 and the amount of sediment in the separation tank 10 and the amount of suspended sludge returned. , The dissolved oxygen concentration in each section (0 mg / l in section 1, 0.5 mg / l in section 2 and 1 mg / l in section 3) are shown in Tables 1 to 7 and Equations 1 to 3. Input to the model of the purification process of the water to be treated 3a in each section consisting of each formula,
The calculation was repeated until the water to be treated 3a in each section became a steady state, thereby simulating the purification treatment of the wastewater 3.

Using the apparatus of Experiment 1, purification treatment was performed in the same manner as in Experiment 1, water was collected 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. , One cycle after reaching steady state and one day. The results are shown in FIGS.

The steady state in the simulation is as follows:
During the inflow cycle of the sewage 3, the fluctuation states of the concentrations of ammonia nitrogen, nitrite nitrogen, oxidized nitrogen of nitrate nitrogen, other vegetative bacteria, readily decomposable soluble organic matter, and nitrate bacteria became the same. State. In this steady state, the sludge reaction tank 1 and the separation tank
At 10 the total residence time was about 6 days, the nitric acid spilled out of the system and only the nitrite remained, indicating that nitrite denitrification was dominant in denitrification.

From the results shown in FIG. 3 and FIG. 4, the simulation using the model of the purification process of the wastewater 3 is well approximated, including the actual treatment status of the wastewater 3 and the state variation of the wastewater 3 during the cycle. It can be seen that the sewage 3 can be satisfactorily purified by controlling the operation of the sewage 3 purification based on the model of the sewage 3 purification.

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

From the results shown in FIG. 5 and FIG. 6, when the dissolved oxygen concentration is lowered around the boundary of the dissolved oxygen concentration in the section 2 of about 0.3 to 0.4 mg / l, nitrification becomes less likely to occur. It can be seen that since the amount of nitrate respiration decreases with oxygen respiration, allotrophic bacteria and autotrophic bacteria rapidly decrease and cannot be retained in the system.

As shown in FIG. 7, when the dissolved oxygen concentration rises from the boundary of the dissolved oxygen concentration in the section 2 of about 1 mg / l, the concentrations of nitrite nitrogen and oxidized nitrogen such as nitrate nitrogen increase. However, it can be seen that when the dissolved oxygen concentration decreases, the concentration of ammonia nitrogen and the easily decomposable soluble organic matter increase.

The reason why the ammonia nitrogen is increased is that the amount of oxygen necessary for nitrification is insufficient. Also,
When the dissolved oxygen concentration increases, the oxide nitrogen concentration increases because, in addition to the suppression of denitrification due to dissolved oxygen, the balance between the consumption of organic substances by oxygen respiration and the consumption by nitrate respiration is lost, and the amount of organic substances required for denitrification is reduced. This is due to lack.

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

Next, in Experiment 3, the dissolved oxygen concentration in section 1 was 0 mg / l, the dissolved oxygen concentration in section 2 was 1 mg / l,
Experiment 4 was carried out by setting the dissolved oxygen concentration in section 3 to 2 mg / l, changing the hydraulic residence time in reaction tank 1 and calculating until the water to be treated in each section reached a steady state. Was done. The results are shown in FIGS.

From the results shown in FIG. 8, when 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 much, but the oxidative decomposition of organic matter and It can be seen that the existing amount of heterotrophic bacteria involved in denitrification in the reaction tank 1 decreases as the hydraulic retention time becomes shorter than 6 days.

As shown in FIG. 9, the concentration of easily decomposable soluble organic matter in the sewage 3 flowing out of the reaction tank 1 sharply increases 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 rapidly below 3.6 days. Also, it can be seen that the concentration of ammonia nitrogen increases when the hydraulic retention time is 3 days or less.

Further, from the results shown in FIG. 10, the concentrations of total nitrogen and soluble nitrogen were as follows: the hydraulic retention time was 3.6 days or less, and the chemical oxygen demand (soluble CO
It can be seen that the concentration of D _Cr ) rises below 2.5 days.

In Experiment 4 above, 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 a steady state was reached. Was done. The result is shown in FIG.

From the results shown in FIG. 11, when the dissolved oxygen concentration in the section 2 is 0.65 mg / l or more, the chemical oxygen demand by the readily decomposable soluble organic matter and the concentration of ammonia nitrogen decrease. The easily decomposable soluble organic matter and ammonia nitrogen are removed well, but the concentration of oxidized nitrogen starts to increase. For this reason, 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 similarly to the purification treatment in which the hydraulic retention time is set to 4.5 days. You can see that you can do it. However,
When the hydraulic retention time is 3.6 days, the range of the dissolved oxygen concentration at which good purification treatment of the sewage 3 can be performed becomes extremely narrow.

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

Therefore, the above embodiment is based on the inflow amount of the sewage 3 flowing into the reaction tank 1 and the concentration of the organic matter and each nitrogen compound in the sewage 3, Treatment of the water to be treated 3a comprising a mass balance formula of various nitrogen compounds and various microorganisms, a reaction rate formula of organic matter removal, conversion of various nitrogen compounds and growth of various microorganisms, and a production rate formula 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 water 3a to be treated in the reaction tank 1 is compared with the calculated value of the simulation of the situation model. As a result of simulating the situation model of the treatment of the water to be treated 3a in each section based on the calculated values of the simulation, that is, for example, based on various measured values and input values, the oxidative decomposition process As a dissolved oxygen concentration of the nitrification step and the denitrification step proceeds favorably respectively, sewage 3
Control the inflow, reflux, sludge return, etc.
To purify.

For this reason, in one reaction tank 1, the purification treatment of the sewage 3 containing organic substances and nitrogen compounds, ie,
Denitrification process in which nitrified oxidized nitrogen is reduced to nitrogen gas by nitric acid respiration in an anaerobic atmosphere where organic matter in the treated water 3a or nutrients obtained by self-decomposition and no dissolved oxygen is present, and nitric oxide is breathed by nitric acid. In an aerobic atmosphere where aerobic bacteria exist, 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 bacteria and facultative anaerobic bacteria. There are three main processes: an oxidative decomposition process that decomposes, and a nitrification process that oxidizes ammonia nitrogen to nitrite nitrogen or nitrate nitrogen in the presence of dissolved oxygen. Each can proceed well, and the sewage 3 can be purified well.

Further, since the purification treatment of the wastewater 3 can be performed in one reaction tank 1, the apparatus can be downsized, the installation space can be reduced, the productivity can be improved, the operation cost of the apparatus can be reduced, and the purification operation can be performed. Can be simplified.

Further, only by inputting the measurement results of the concentrations of the organic substances and various nitrogen compounds which are in the polluted state of the inflowing sewage 3, the purification of the sewage 3 is performed almost automatically, and the purification operation can be easily performed. .

In the above embodiment, the biochemical oxygen demand, the chemical oxygen demand, and the concentrations of various nitrogen compounds by the organic matter in the polluted state of the inflowing sewage 3 are measured in advance, and the measurement results are sent to the control means. Although input and purification processing were explained, without using various solenoid valves and flowmeters, the pollution state was measured from the required amount of chemical oxygen, and the inflow, reflux, and sludge return rates were kept constant. A simple type for purifying the sewage 3 or automatically measuring the biochemical oxygen demand, the chemical oxygen demand, and the concentration of various nitrogen compounds by organic substances using a sensor, etc. The amount of organic matter and various nitrogen compounds flowing into the reaction tank 1 is measured as a contaminated state from the inflow amount of the sewage 3, and the operation of the purification process of the sewage 3 is automatically controlled by the control means, thereby purifying the sewage 3. You can do things of automatic that.

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

The wastewater 3 is described using, for example, human wastewater containing organic matter and various nitrogen compounds. However, any wastewater 3 containing any of organic matter and various nitrogen compounds can be used.

[0093]

According to the method for treating sewage according to the first aspect, the state of contamination at each position of the water to be treated in the reaction tank is determined based on the state of contamination of the sewage and the concentration of dissolved oxygen in the water to be treated. hand,
Oxidative decomposition, in which the organic matter is oxidatively decomposed by microorganisms , calculated from the material balance equation, reaction rate equation and production rate equation
Process and nitrate to oxidize ammoniacal nitrogen to oxidized nitrogen
Aerobic atmosphere where the reaction of the
Anaerobic atmosphere in which the reaction of the denitrification process to reduce to elemental gas occurs
In order to control the concentration of dissolved oxygen in the water to be treated so that both occur in the reaction tank, the oxidative decomposition step of oxidatively decomposing organic substances by microorganisms in one reaction tank The nitrification step of oxidizing to nitrogen and the denitrification step of reducing oxidized nitrogen to nitrogen gas by microorganisms can proceed satisfactorily, and sewage can be purified well.

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

According to the method for treating sewage described in claim 3,
3. The treatment method according to claim 1, wherein the dissolved oxygen concentration of the water to be treated is determined based on an inflow amount of the wastewater, an oxygen supply amount to the water to be treated, and a reflux amount of the water to be treated from the downstream side to the upstream side of the reaction tank. , The sewage purification operation can be easily performed, the oxidative decomposition step of oxidatively decomposing organic substances by microorganisms, the nitrification step of oxidizing ammonia nitrogen to oxidized nitrogen by microorganisms, and The denitrification step of reducing nitrocellulose to nitrogen gas by microorganisms can proceed efficiently and efficiently in one reaction tank, and sewage can be satisfactorily purified.

According to the sewage treatment apparatus according to the fourth aspect,
Measure the pollution status of sewage with pollution measurement means,
The dissolved oxygen concentration of the water to be treated in the reaction vessel was measured with a dissolved oxygen measuring means, by the control means on the basis of these results, the oxygen supply means, the inlet adjustment means and recirculation means controls, fine
An oxidative decomposition step of oxidatively decomposing organic matter by living organisms, and
Reaction of nitrification process that oxidizes ammoniacal nitrogen to oxidized nitrogen
Aerobic atmosphere and oxidized nitrogen reduced to nitrogen gas
Reaction with the anaerobic atmosphere where the reaction of the denitrification process
An oxidative decomposition process in which the concentration of dissolved oxygen in the water to be treated is controlled to a state generated in the reaction tank and the sewage is purified. Process for oxidizing nitrogen to oxidized nitrogen with microorganisms and denitrification process for reducing oxidized nitrogen to nitrogen gas with microorganisms can proceed efficiently and efficiently in one reaction tank, and purify sewage well. it can.

[Brief description of the drawings]

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

FIG. 2 is a system explanatory diagram showing a model of substance conversion in a purification treatment step of the wastewater.

FIG. 3 is a graph showing a comparison between a simulation result and an actually measured value in one cycle after the material conversion characteristics of an organic substance and a nitrogen compound reach a steady state.

FIG. 4 is a graph showing a comparison between simulated results and measured values for one day after reaching a steady state in the substance conversion characteristics of the organic substance and the nitrogen compound.

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

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

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

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

FIG. 9 is a graph showing a simulation result when the hydraulic residence time is changed.

FIG. 10 is a graph showing a simulation result when the hydraulic residence time is changed.

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

[Explanation of symbols]

 DESCRIPTION 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 Toshio Yamada 2-9-1, Noribori, Nishi-ku, Osaka-shi, Osaka Inside Ataka Industry Co., Ltd. (56) References JP-A-5-123689 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C02F 3/02 C02F 3/20

Claims (4)

(57) [Claims] 1. A method for measuring the state of contamination of sewage flowing into a reaction tank, measuring the concentration of dissolved oxygen in the water to be treated in the reaction tank, and measuring the concentration of dissolved oxygen in the reaction tank along a direction in which the water to be treated flows. The state of contamination of the water to be treated at each position within, the organic matter in the water to be treated, various nitrogen compounds, based on the measurement result of the state of contamination of the wastewater flowing into the reaction tank and the measurement result of the dissolved oxygen concentration. And the material balance formula of various microorganisms, the removal rate of organic substances, the reaction rate equation of the conversion of various nitrogen compounds and the growth of various microorganisms, and the calculation rate equations of the production rate of organic substances and various nitrogen compounds, respectively, in the reaction vessel, The microorganisms oxidize the organic matter.
Oxidative decomposition process and ammonia nitrogen
An aerobic atmosphere in which the reaction of the nitrification process that oxidizes nitrogen
The reaction of the denitrification process that reduces oxidized nitrogen to nitrogen gas occurs
Wherein the concentration of dissolved oxygen in the water to be treated is controlled in such a state that both the anaerobic atmosphere and the anaerobic atmosphere occur . 2. The method according to claim 1, wherein the polluting state of the sewage flowing into the reaction tank is measured based on at least one of an inflow amount of the sewage, organic matter in the sewage, and various nitrogen compounds in the sewage. The method for treating sewage according to claim 1, wherein: 3. The concentration of dissolved oxygen in the water to be treated is determined based on the amount of wastewater 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 supplied from the downstream to the upstream of the reaction tank. The method according to claim 1, wherein the control is performed based on at least one of a reflux amount of the water to be treated. 4. An inflow port into which sewage flows, and microorganisms are produced.
A reaction tank for breathing, an oxygen supply means provided in the reaction tank for supplying oxygen to the water to be treated in the reaction tank, and the water to be treated provided in the reaction tank from the downstream side to the upstream side of the reaction tank. Reflux means for refluxing, inflow adjustment means for adjusting the amount of inflow of sewage flowing through the inflow port, pollution measurement means provided near the inflow port to measure a pollution state of the inflowing sewage, Dissolved oxygen measuring means for measuring the dissolved oxygen concentration of the water to be treated in the reaction vessel; and the oxygen supply means, the inflow based on the measurement result by at least one of the pollution measuring means and the dissolved oxygen measuring means. At least one of the adjusting means and the reflux means is controlled , and the fine
An oxidative decomposition step of oxidatively decomposing the organic matter by living organisms, and
Nitrification process to oxidize ammonia and ammonia nitrogen to oxidized nitrogen
An aerobic atmosphere in which a reaction occurs, and oxidized nitrogen converted to nitrogen gas
Both in the anaerobic atmosphere where the reaction of the reducing denitrification process occurs
And a control means for controlling the concentration of dissolved oxygen in the water to be treated in a state where water is generated .