JPH09108694A - Method of assuming mixed state of nitrification/ denitrification reaction tank by activated sludge process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove organic materials and nitrogen with high efficiency by performing optimization treatment of parameters by the measured value of tracer concentration, the number of models used for examination and an equation expressing models and comparing parameters obtained every model to determine a model having optimum reversely mixed quantity. SOLUTION: In a circulation type activated sludge process, anaerobic tanks 1a, 1b for performing denitrification of feed water, aerobic tanks 2a-2c for performing nitrification and a sedimentation tank 7 for performing solid-liquid separation are included. In a controller to which the measured value of tracer concentration measured by a tracer method, the number of models used for examination and an equation expressing models are inputted during operation, optimization is repeatedly per-formed until the convergence range of parameters becomes a set value or less. Next, when the optimization is finished for all models, parameters obtained every model are compared, and in consideration of a sum of squares of residuals to the measured value and consistency of parameters and models and the like, a model having optimum parameters is determined to assume the mixed state of a reaction tank.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating a mixed state of a biological reaction tank in an apparatus for highly efficiently removing organic matter and nitrogen in raw water by using a nitrification / denitrification reaction by an activated sludge method.

[0002]

2. Description of the Related Art Various methods have conventionally been proposed for efficiently removing organic matter in wastewater such as sewage and removing nitrogen and phosphorus which are considered to be the causative agents of eutrophication in closed water areas. . Furthermore, it is expected that the removal rate of nitrogen will be increased in recent years, and regulations on nitrogen will be tightened.Therefore, it is thought that the number of facilities adopting advanced treatment processes that can remove this will increase. To be

Although physicochemical methods and biological methods have been proposed as means for removing nitrogen and phosphorus in wastewater, physicochemical methods are not widely used because of the high cost. For example, a phosphorus removal method which has been put into practical use as a physicochemical method includes a coagulation precipitation method and a crystallization method, but this method has a drawback in terms of cost and maintenance.

As a method for biologically removing nitrogen and phosphorus simultaneously, a circulation type nitrification denitrification method and an oxidation ditch method are drawing attention as a modified method of the conventional activated sludge method. In the circulating nitrification denitrification method, for example, as shown in FIG. 13, the biological reaction tanks are anaerobic tanks 1a and 1b in which dissolved oxygen (hereinafter abbreviated as DO) does not exist and a plurality of aerobic tanks 2 in which DO exists.
a, 2b, 2c, and the anaerobic tanks 1a, 1b are used to agitate the inflowing raw water 3 by an agitation mechanism 10 under anoxic conditions to denitrify by denitrifying bacteria in the activated sludge,
Next, the air diffuser 4 arranged inside the aerobic tanks 2a, 2b, 2c
By supplying air from the blower 5, oxidative decomposition of organic matter by activated sludge and nitrification of ammonia by nitrifying bacteria are performed in the presence of oxygen by aeration.

Then, the nitrification solution in the last-stage aerobic tank 2c is fed into the anaerobic tank 1a by using the nitrification solution circulation pump 6, whereby the denitrification effect of the anaerobic tanks 1a and 1b is promoted.

The denitrifying bacterium is a bacterium that reduces N0 ₂ -N and N0 ₃ -N to N ₂ by respiration of nitric acid under anaerobic conditions. Reference numeral 7 denotes a final settling basin, and the supernatant of the final settling basin 7 is discharged as treated water 11 after passing through a disinfection tank or the like not shown in the figure, and a part of sludge settled in the final settling basin 7. Is returned to the anaerobic tank 1a by the sludge return pump 8, and other sludge is sent from the excess sludge drawing pump 9 to an excess sludge treatment device (not shown) for treatment.

[0007] By using such a circulating nitrification denitrification method, an effect comparable to the organic matter removal effect achieved by a normal standard activated sludge method can be obtained, and nitrogen and phosphorus removal rates higher than those of the activated sludge method. Is achieved.

On the other hand, the oxidation / ditch method is a type of activated sludge method, and has a simple system configuration as a treatment method in a small-scale sewage treatment plant, the construction cost and maintenance cost are low, and the treated water quality is stable. Known for doing In this oxidation-ditch method (hereinafter abbreviated as OD method), raw water 3 is introduced into an elliptical pool-like biological reaction tank 15 which is an endless water channel having an appropriate water depth as shown in FIG. The partition 16 is used to create a planar circulation flow, and the mechanical aeration stirrer 17, 17 such as a rotor is used to circulate the raw water 3 as shown by the arrow A while mixing with the activated sludge for treatment. Supply the required oxygen. 7 is a final sedimentation tank, and the supernatant of this final sedimentation tank 7 is treated water 11
Part of the sludge settled in the final settling basin 7 is returned to the biological reaction tank 15 via a pipe 18.
Mechanical aeration stirrer 17 is 1 or 2 per bioreactor
It is customary to use four or four units.

In the OD method, the aeration time for the inflowing raw water 3 is increased to about 24 to 48 hours to allow a reaction to have a margin, and at the same time, the hydraulic retention time (HRT) is longer than that of the standard activated sludge method. It is characterized in that both volume load and sludge load are operated low by setting and increasing the activated sludge suspended matter (MLSS). Therefore, it has the advantages that it is resistant to fluctuations in inflow load and that the amount of sludge generated is small, and because it is relatively easy to maintain and manage, the number of small-scale sewage treatment plants is increasing.

The nitrogen removal reaction in such a circulation type nitrification / denitrification reaction tank is roughly classified into a nitrification reaction and a denitrification reaction, but both reactions are susceptible to dissolved oxygen (DO). In the nitrification reaction, it is important to control the aerobic state at the inlet of the aerobic tank, and in the anaerobic tank, the anaerobic state at the outlet adjacent to the downstream aerobic tank. Anaerobic and aerobic conditions are completely maintained by providing a partition wall that separates both adjacent reaction tanks, but if there is no partition wall that completely separates both reaction tanks, back mixing (or back mixing) is performed from the downstream reaction tank. Occurs, the movement of the mixed liquid between the both reaction tanks occurs, so that the influence of the DO becomes considerably large.

For example, as shown in the schematic view of FIG. 7, the inflow amount (= apparent flow rate) into the biological reaction tank 1 is Q ₀ (m ³ / m)
in) and the back mixing amount from the (n + 1) th tank to the nth tank is b (m ³ / min), the nth tank to the [n + 1] th tank
Since the apparent flow rate into the tank is Q ₀ , the actual outflow Q from the n-th tank to the [n + 1] -th tank is [Q ₀ + b] (m ³ /
min).

Therefore, when the back mixing amount b increases, the outflow amount Q to the adjacent tanks also increases, and the actual mixing state of the adjacent reaction tanks changes greatly. Therefore, in the anaerobic tank in the biological reaction tank without a partition, DO increases with the phenomenon of bringing in DO from the downstream aerobic tank due to back mixing,
Therefore, denitrification inhibition may occur, or nitrification rate limiting may occur with the decrease of DO due to the outflow of the mixed solution having low DO from the upstream anaerobic tank. Therefore, it is important to always understand the mixed state of the reaction tanks by checking the amount of back mixing between the reaction tanks.

On the other hand, in the bioreaction tank, the liquids are mixed by aeration by the air supplied from the blower 5 or a combination of agitation and aeration. At this time, the liquid is mixed at the corners around the bottom wall of the bioreaction tank. In some cases, the dead space indicated by d in FIG. In this dead space d, the liquid is not sufficiently mixed and is stagnant, so that the reaction does not occur in the dead space d and the reaction proceeds only in the remaining portion.

If the rotation speed of the stirrer is insufficient or the amount of air during aeration is insufficient, the dead space d becomes large and a reaction occurs with respect to the actual volume of the reaction tank. Since the volume of the dead space may be considerably reduced, it is important to understand the volume of the dead space d in order to improve the control accuracy of the operation amount.

The tracer method is mentioned as a method for investigating the mixed state in the reaction tank (see the sewage test method). In this tracer method, an aqueous solution in which a tracer substance is dissolved is put into the inlet of a biological reaction tank, and the mixture is sampled in a reaction tank whose mixed state is desired to be checked over time, and the concentration of the tracer substance in the sample is analyzed. In this method, each parameter of the model is determined so as to match the obtained analysis value of the tracer concentration.

For example, as a method for testing the mixing characteristics of the aeration tank based on the above sewage test method, an aqueous solution of sodium chloride is instantaneously added to the inlet of the aeration tank so that the amount of chlorine ions in the mixed solution is about twice or more the amount. After the introduction, some time after the introduction, the mixed solution at the outlet of the aeration tank is sampled at a proper time interval and measured at a constant time interval until the chloride ion concentration becomes steady. During the tracer test, the amount of sewage flowing into the aeration tank, the amount of returned sludge and the amount of air are kept constant.

In the example of FIG. 7, the calculation interval is 1 (min), and the tracer concentration of the n-th tank after the time t (min) is C
Assuming that the tracer concentration of the n-th tank after _n (t) and time t + 1 (min) is C _n (t + 1), t + 1 (m
The tracer concentration C _n (t + 1) after (in) is represented by the following difference equation.

C _n (t + 1) = {C _n-1 (t) · Q + C _n (t) · (V · (1-d) −Q−b) + C _{n + 1} (t) · b} / {V・ (1-d)} (1) where C _n-1 (t): Tracer concentration in the (n-1) th tank after t (min) V: nth Tank volume C _{n + 1} (t): Tracer concentration in the (n + 1) th tank after t (min) Q: Flow rate of raw water (m ³ / min) (actual outflow from upstream tank to downstream tank) b : Backmixing amount (m ³ / min) d: Dead space ratio (-) For all reaction tanks, enter difference equations such as equation (1), enter Q, b, and d, and set t to 1 (min ), The change with time of the calculated value of the tracer concentration of each tank can be obtained.

On the other hand, nitrogen removal in the OD method is carried out by dissolving oxygen (hereinafter D) in the flow direction in the reaction tank 15 which is an endless water channel.
It can be carried out by providing a concentration gradient of O) to partially create an anaerobic / aerobic state and causing a denitrification / nitrification reaction.
It is important to keep the sludge mixing state uniform while maintaining the concentration gradient of.

When the water quality simulation is carried out by the OD method, as shown in FIG. 9, the complete mixing tank 15a (first
Tank), 15b (k-th tank), 15c (k-th tank), 15
The reaction model is constructed by considering a model in which d (k + 1st tank) and 15e (final tank) are connected by the circulation path 20,
It is important to know how many complete mixing tanks it will consist of. In addition, in the nitrification reaction, it is necessary to maintain sufficient DO for nitrification, and in the denitrification reaction, it is necessary to maintain an anaerobic state.

However, when the rotational speed of the stirrer in the reaction vessel by the OD method is low and the flow rate is low, back mixing from the downstream shown by arrow E in the figure occurs, so that the influence of DO may increase. There is. That is, in the anaerobic part, the DO is brought in by the reverse mixing from the downstream aerobic part to increase the DO and denitrification inhibition occurs, and in the aerobic part, the DO decreases due to the inflow of the low-DO mixed liquid from the upstream anaerobic part. A nitrification rate-controlling occurs. Therefore, it is important to understand the mixing state by examining the amount of back mixing between the complete mixing tanks.

Also in the case of the OD method, as in the case of the circulation type nitrification denitrification method, a dead space indicated by d may occur at the corners around the side wall of the biological reaction tank 15, and the reaction occurs in this dead space d. It does not happen and the reaction proceeds only in the remaining part. In particular, when the rotation speed of the stirrer is insufficient or the amount of air at the time of aeration is insufficient, the dead space d becomes large, and the volume in which the reaction takes place is considerably smaller than the actual volume of the reaction tank. Therefore, it is important to know the volume of the dead space d.

In the tracer test of the OD method, an aqueous solution in which a tracer substance is dissolved is charged into the inlet of the biological reaction tank 15,
As described above, the mixed solution is sampled in a reaction tank whose mixed state is to be examined over time, the concentration of the tracer substance is analyzed, and each parameter of the model is determined so as to match the analyzed value.

In the example of the model consisting of n perfect mixing tanks shown in FIG. 9, the calculation interval is 1 (min) and the time t (m
in) the kth tank tracer concentration is C _k (t), and the time t + 1 (min) is the kth tank tracer concentration is C
Assuming that the tracer concentration in the final settling tank 7 after _k (t + 1), t (min) is C _{n + 1} (t), t + 1 (m
The tracer concentration C _k (t + 1) after (in) is represented by the following difference equation.

When k = 1, C _k (t + 1) = {C _{n + 1} (t) Q _r + C _n (t)  (Sv-b- (Q ₀ + Q _r )) + C _k (t ) ・ (V ・ (1-d) -S ・ v) + C _{k + 1} (t) ・ b} / {V ・ (1-d)} ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (2) 1 < When k <n, C _k (t + 1) = {C _k-1 (t) · S · v + C _k (t) · (V · (1-d) −S · v−b) + C _{k + 1} (t ) · B} / {V · (1-d)} ···· (3) When k = n, C _k (t + 1) = {C _k−1 (t) · S · v + C _k ( t) · (V · (1 -d) -b - (S · v-b- (Q 0 + Q r)) - (Q 0 + Q r)} / {V · (1-d)} ···· (4) where _{C k-1 (t):} t (min) after the (k-1) tank of tracer concentration _{C k (t): t (} min) after the first (k) tank tracer concentration _{C k + 1 (t):} t (min) after the (k + 1) tank Racer concentration V: the k tank volume Q _0: flow rate of the inflow raw water _{^{(m 3 / min) Q r}} : return sludge flow rate from the final sedimentation basin (m ³ / min) b: backmixing amount (m ³ / min) d: dead space ratio (-) s: mixed solution cross-sectional area in OD (m ³ ) v: flow rate in OD (m / min) For all reaction tanks, a difference equation such as equations (2) to (4) is used. Vertically input Q, b, d, and for t, 1 (mi
By performing the calculation for each n), the change with time of the calculated value of the tracer concentration in each tank can be obtained.

[0026]

The mixed state of the bioreactor by the activated sludge method should be modeled so as to match the measured values of the concentration of the tracer substance obtained by the tracer method for some mixing models as described above. The actual situation is that the amount of reverse mixing b and the dead space ratio d as parameters of are determined by a trial and error method. However, in the circulation type nitrification denitrification method or OD method in which an anaerobic tank and an aerobic tank exist, the mixing state differs depending on the stirring of the reaction tank and the presence or absence of aeration (anaerobic state or aerobic state). Therefore, it may take a long time to determine the parameter, or the accuracy of the obtained parameter may decrease.

Further, since the dead space indicated by d is likely to occur at the corner portion around the bottom wall of the biological reaction tank, the liquid is not mixed in the dead space d and becomes a stagnation state so that the reaction does not occur. In consideration of the fact that the volume in which the reaction takes place becomes considerably smaller than the actual volume of the biological reaction tank, the above parameters must be determined in order to improve the control accuracy of the manipulated variable.

Therefore, the present invention estimates the mixing state of the biological reaction tank in the control of the nitrification / denitrification reaction tank by such an activated sludge method, and considers the back mixing amount and the dead space ratio to mix the biological reaction tank. It is an object of the present invention to provide a mixed state estimation method capable of determining a model having optimal parameters from mixed models representing states in a short time.

[0029]

In order to achieve the above-mentioned object, the present invention comprises a step of denitrifying raw water with denitrifying bacteria in an anaerobic tank, and a step of nitrifying with nitrifying bacteria in an aerobic tank,
In the treatment by the nitrification / denitrification reaction tank by the circulation type activated sludge method including the step of separating the solid-liquid in the settling tank and discharging the supernatant as treated water, the actual measurement value of the tracer concentration measured by the tracer method and examination According to the number of models used in the above and the equations representing the models, the parameter is optimized until the convergence range of the amount of backmixing in which the mixed solution moves from the downstream reaction tank to the upstream reaction tank becomes less than or equal to a preset value. The nitrification / denitrification reaction by the activated sludge method, in which the model with the optimum amount of backmixing is determined by comparing the parameters obtained for each model after performing the optimization process and optimizing for all models. A method for estimating a mixed state of a tank is provided.

According to the second aspect, the measured value of the tracer concentration measured by the tracer method, the number of models used for the study, and the equation representing the model are used to move the mixed solution from the downstream reaction tank to the upstream reaction tank as a parameter. The amount of backmixing and the dead space ratio in the biological reaction tank are optimized, and the actual value of the tracer concentration is calculated as the residual sum of squares of the calculated value, or the convergence range of the conversion rate becomes less than or equal to the preset value. The nitrification / denitrification reaction tank by the activated sludge method, in which the parameters obtained for each model are compared with each other to determine the model having the optimum amount of back-mixing A mixed state estimation method is provided.

As a nitrification / denitrification reaction tank by the activated sludge method, raw water is introduced into a biological reaction tank consisting of an endless water channel, and a mechanical device is provided in a circulation flow formed in a flat shape by using partition walls. When using the oxidation ditch method in which raw water is mixed with activated sludge while aeration is performed by an aeration stirrer, a model in which multiple complete mixing tanks are connected to a biological reaction tank by a circulation path is used. Then, the mixed state of the nitrification / denitrification reaction tank is estimated in the same manner as described above.

In order to ensure consistency between the above parameters and the model, the amount of backmixing between the anaerobic tanks is smaller than the amount of backmixing between the anaerobic tank and the aerobic tank, and the biological reaction tank in which the rotation speed of the agitator is large. The dead space ratio of is smaller than the dead space ratio of the bioreactor with small rotation speed.

According to such a method for estimating the mixed state of the reaction tank, it becomes possible to constantly grasp the mixed state of the reaction tank from the amount of back mixing and dead space ratio between the reaction tanks as parameters, and the amount of back mixed can be calculated. The change in the actual mixing state of the reaction tanks due to the increase in the outflow amount to the adjacent tanks as the size increases, or the DO due to the back mixing from the aerobic tank downstream to the anaerobic tank in the biological reaction tank without a partition wall It is possible to perform operation control such as inhibition of denitrification due to the phenomenon of bringing in NO, or elimination of nitrification rate limiting due to decrease in DO due to outflow of the mixed solution from the upstream anaerobic tank.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Various embodiments of a method and apparatus for estimating a mixed state of a nitrification / denitrification reaction tank by an activated sludge method according to the present invention will be described below with reference to the drawings. Will be described in detail with the same reference numerals.

FIG. 1 is a flow chart showing an example of an actual measurement operation for estimating a mixed model of a biological reaction tank by the circulation type nitrification denitrification method. First, the operation is started in step 100 and the tracer method is used in step 101. Enter the measured value (change over time) of the measured tracer concentration. Next, in step 102, the number (n) of models used for examination is input, and in step 103, an equation representing the model is input. Then, in steps 104 and 105, the parameters are optimized until the convergence range of the parameters becomes equal to or less than a preset value. The conversion is repeated, and the parameter obtained in step 106 is stored in the parameter variable.

When the optimization is completed for all the models, the parameters obtained for each model are compared in steps 107 and 108, and the residual sum of squares with the measured value, the consistency between the parameters and the model, etc. are considered. Then step 109
Determine the model with the optimal parameters in step 11
The operation ends with 0.

The consistency between the parameters and the model means, for example, that the amount of backmixing between the anaerobic tanks is smaller than the amount of backmixing between the anaerobic tank and the aerobic tank, and the deadness of the biological reaction tank in which the rotation speed of the agitator is large. The space ratio is based on data such as being smaller than the dead space ratio of a biological reaction tank with a small rotation speed.

In the present embodiment, both cases where the dead space d is generated at the corners around the bottom wall of the biological reaction tank and when the dead space d is not generated will be considered. Since the input model equation is a nonlinear difference equation, the nonlinear simplex method is used to optimize the parameters in each model.

2 to 6 show five examples of the reverse mixing model in the mixing tanks of the anaerobic tank and the aerobic tank. As a parameter indicating the back mixing, the ratio of the back mixing amount and the inflow amount to the biological reaction tank, that is, the inflow ratio is used. Further, the dead space ratio indicated by d is different for each tank.

The example of FIG. 2 is a case where the reverse mixing ratio from the aerobic tank to the anaerobic tank constituting the biological reaction tank 1 is uniform (b0), and the example of FIG. Depending on the aeration state of the tank, it is divided into 4 types, anaerobic tank ⇔ anaerobic tank (b0), anaerobic tank ⇔ aerobic tank (b1), aerobic tank ⇔ anaerobic tank (b2), aerobic tank ⇔ aerobic tank (b3). It is an example.

In the example of FIG. 4, the anaerobic tank ⇔ anaerobic tank (b0), anaerobic tank ⇔ depending on the aeration state of the reaction tanks having the reverse mixing ratios adjacent to each other.
In this example, there are three aerobic tanks (b1) and aerobic tanks ⇔ aerobic tanks (b2). In this case, it is considered that the anaerobic tank ⇔ aerobic tank and the aerobic tank ⇔ anaerobic tank have the same reverse mixing state.

The example of FIG. 5 is a case where the reverse mixing ratios between the reaction tanks are different (b0, b1, b2, b3, b4, b5, b6), and the example of FIG. This is the case where back mixing (b0) due to stirring occurs in mixing between air tanks, and back mixing (b1) due to stirring and air lift effect occurs in mixing between the anaerobic tank and aerobic tank. In this case, the air lift effect occurs in the aerobic tank, but the air lift effect between the adjacent aerobic tanks is canceled, so only the reverse mixing by stirring is performed.

Next, referring to FIG. 8, the biological reaction tank 1 by the OD method
A measurement operation example for estimating the mixed model of No. 5 will be described. First, the operation starts in step 200, and then step 201
Enter the measured value (change with time) of the tracer concentration measured by the tracer method. Next, in steps 202 and 203, the parameters are repeatedly optimized until the convergence range of the parameters becomes equal to or smaller than a preset value, the parameters obtained in step 204 are stored and stored, and the operation ends in step 205. Since the equations representing the model are nonlinear difference equations, the nonlinear simplex method is used to optimize the parameters in each model.

This OD method is basically set to be carried out at low load operation, but generally the load is further reduced at the initial stage of operation start until the planned water quantity is reached. It takes a considerable amount of time. When the stirring operation is continuously performed as described above, the DO concentration becomes high and the state of over-aeration tends to occur, sludge dispersion and sludge sedimentation separability in the final sedimentation basin 7 are deteriorated, and the treated water quality is deteriorated. Fear occurs. Further, since the DO concentration becomes higher as a whole, the denitrification reaction that requires an anaerobic state is less likely to occur, so that the nitrogen removal rate also decreases.

In response to the above, there is also a means for carrying out intermittent aeration by stopping the stirring operation at a certain time zone.
Such an intermittent aeration means has a problem that the processing efficiency differs depending on the setting of the aeration / stopping time ratio or the total time of one cycle, and the dead space ratio increases.

10 to 12 show three examples of reaction models involving back mixing by the OD method. The example in FIG.
As shown in FIG. 14, the biological reaction tank 15 by the OD method.
Has an elliptical shape, and has an inlet 3a and an outlet 3b for the raw water 3.
Is a reaction model diagram in the case where is on the opposite side of the long axis of the reaction tank 15 and the reverse mixing ratio is uniform b. In this example, the raw water in the complete mixing tank 15e (final tank) passes through the circulation path 15
The raw water in the complete mixing tank 15c (k-th tank) which has been circulated back to the a (first tank) and reacted for a predetermined time is the final settling basin 7
And the supernatant water is discharged as treated water 11 and a part of the sludge settled in the final settling basin 7 is returned to the raw water 3 as return sludge Q _r .

In the example of FIG. 11, the biological reaction tank 15 has an elliptical shape, and the inlet 3a and outlet 3b of the raw water 3 are the reaction tank 1.
5, the outlet 3b is located immediately before the inlet 3a, and the reverse mixing ratio is uniform b. The reaction model in this example is the same as that described in FIG. 9, and the raw water in the complete mixing tank 15e (final tank) is returned to 15a (first tank) and circulated, and the complete mixing tank is reacted for a predetermined time. The raw water in 15e (final tank) is sent to the final settling basin 7 and the supernatant water is discharged as treated water 11. A part of the sludge settled in the final settling basin 7 is returned sludge Q _{r into the} raw water 3 as raw water. It has been returned.

In the example of FIG. 12, the bioreactor is horseshoe-shaped,
This is the case where the inflow port 3a and the outflow port 3b of the raw water 3 are on the opposite sides of the long axis of the reaction tank 15 and the reverse mixing ratio is uniform b. Four aeration stirrers 17 are used for one biological reaction tank. The reaction model in this example is the same as that in FIG. 10, and the raw water in the complete mixing tank 15e (final tank) returns to 15a (first tank) and circulates, and the complete mixing tank 15 is reacted for a predetermined time.
The raw water in c (tank k) is sent to the final settling basin 7, the supernatant water is discharged as treated water 11, and part of the sludge settled in the final settling basin 7 is returned sludge Q _r in the raw water 3 Have been sent back to.

[0049]

As described in detail above, according to the method for estimating the mixed state of the nitrification / denitrification reaction tank by the activated sludge method according to the present invention, the operation of the reaction tank including the anaerobic tank and the aerobic tank is operated. Even if the mixing state differs depending on the state, it becomes possible to grasp the mixing state of the reaction tank from the back mixing amount between each reaction tank, and when the back mixing amount becomes large, the outflow amount to the adjacent tank increases. Due to changes in the mixing state, DO from the aerobic tank downstream to the anaerobic tank in the biological reaction tank without partition walls
It is possible to perform operation control in which denitrification is inhibited due to the phenomenon of bringing in nitrogen, or nitrification rate limiting due to a decrease in DO due to the outflow of the mixed solution from the upstream anaerobic tank is eliminated.

In addition, not only the amount of backmixing between the reaction tanks as a parameter but also the dead space ratio generated in the bottom wall of the biological reaction tank, which depends on the rotation speed of the agitator, is taken into consideration. The accuracy of estimation is high because the change in state, inhibition of denitrification, and the decrease phenomenon of DO due to the outflow of the mixed solution are grasped. In particular, even if the expected number of parameters increases, it takes a long time to determine the parameters. No longer needed
Further, there is a feature that the obtained parameters have high accuracy, and a model having optimum parameters can be determined in a short time from the mixing models representing the mixed state of the reaction tank.

[Brief description of the drawings]

FIG. 1 is a flow chart showing an example of measurement operation for estimating a mixed model of a nitrification / denitrification reaction tank by the activated sludge method according to the present embodiment.

FIG. 2 is a schematic diagram showing an example of a reverse mixing model in a mixing tank of an anaerobic tank and an aerobic tank.

FIG. 3 is a schematic diagram showing another example of a reverse mixing model in a mixing tank of an anaerobic tank and an aerobic tank.

FIG. 4 is a schematic diagram showing another example of a reverse mixing model in a mixing tank of an anaerobic tank and an aerobic tank.

FIG. 5 is a schematic diagram showing another example of a reverse mixing model in a mixing tank of an anaerobic tank and an aerobic tank.

FIG. 6 is a schematic diagram showing another example of a reverse mixing model in a mixing tank of an anaerobic tank and an aerobic tank.

FIG. 7 is a schematic diagram showing a relationship between inflow and outflow of raw water into a reaction tank and back mixing.

FIG. 8 is a flowchart illustrating an example of measurement operation for estimating a mixing model of a biological reaction tank by the OD method.

FIG. 9 is a reaction model diagram in the case where the biological reaction tank according to the OD method is elliptical, the raw water inlet and outlet are on the same side, the outlet is located immediately before the inlet, and the reverse mixing ratio is uniform.

FIG. 10 is a reaction model diagram according to the OD method in the case where the biological reaction tank is elliptical, the raw water inlet and outlet are on opposite sides, and the reverse mixing ratio is uniform.

FIG. 11 is a schematic diagram when the biological reaction tank by the OD method is elliptical, the raw water inlet and outlet are on the same side, and the outlet is located immediately before the inlet.

FIG. 12 is a schematic diagram when the biological reaction tank by the OD method is horseshoe-shaped and the raw water inlet and outlet are on opposite sides.

FIG. 13 is a schematic diagram showing an example of a circulating nitrification denitrification method.

FIG. 14 is a schematic diagram showing an example of the oxidation / ditch method.

[Explanation of symbols]

 1a, 1b ... anaerobic tank 2a, 2b, 2c ... aerobic tank 4 ... aeration pipe 5 ... blower 6 ... nitrification liquid circulation pump 7 ... final sedimentation tank 8 ... sludge return pump 9 ... excess sludge extraction pump 10 ... stirring mechanism 11 ... Treated water 15 ... Biological reaction tank 16 ... Partition wall 17 ... Mechanical aeration agitator 20 ... Circulation path

Claims (4)

[Claims] 1. A step of denitrifying raw water with denitrifying bacteria in an anaerobic tank, and a step of nitrifying with nitrifying bacteria in an aerobic tank.
In the treatment by the nitrification / denitrification reaction tank by the circulation type activated sludge method, which includes the step of separating the solid-liquid in the settling tank and discharging the supernatant as treated water, the measured value of the tracer concentration measured by the tracer method and examination According to the number of models used in the above and the equations representing the models, the parameter is optimized until the convergence range of the amount of backmixing in which the mixed solution moves from the downstream reaction tank to the upstream reaction tank becomes less than or equal to a preset value. The nitrification and denitrification by the activated sludge method is characterized in that the model having the optimum backmixing amount is determined by comparing the parameters obtained for each model after performing the optimization process and optimizing for all models. A method for estimating the mixed state of a nitrogen reaction tank. 2. A step of denitrifying raw water with denitrifying bacteria in an anaerobic tank, and a step of nitrifying with nitrifying bacteria in an aerobic tank.
In the treatment by the nitrification / denitrification reaction tank by the circulation type activated sludge method, which includes the step of separating the solid-liquid in the settling tank and discharging the supernatant as treated water, the measured value of the tracer concentration measured by the tracer method and examination Based on the number of models used for the model and the equations representing the models, the tracer is optimized by optimizing the dead space ratio in the biological reaction tank and the amount of backmixing that moves the mixed solution from the downstream reaction tank to the upstream reaction tank as parameters. It was calculated for each model after continuing to optimize the measured value of the concentration until the sum of squared residuals of the calculated value or the convergence range of the conversion rate was less than or equal to a preset value. A method for estimating the mixed state of a nitrification / denitrification reaction tank by the activated sludge method, which compares parameters and determines a model having an optimum backmixing amount. 3. Raw water is introduced into a biological reaction tank consisting of an endless water channel, and is accompanied by aeration by a mechanical aeration stirrer provided in a circulating flow formed in a flat shape by using partition walls. In the water treatment equipment by the oxidation-ditch method, which mixes with activated sludge while circulating, the biological reaction tank is a model in which a plurality of complete mixing tanks are connected by a circulation path, and the tracer concentration measured by the tracer method. Based on the measured value of, the number of models used in the study, and the equations representing the models, the convergence range of the amount of backmixing in which the mixed solution moves from the downstream reaction tank to the upstream reaction tank is set as a parameter or less as a parameter. The parameters are optimized until all the parameters are reached, and the parameters obtained for each model are compared and then optimized. Mixed state estimation method of nitrification and denitrification reactor by activated sludge process, characterized in that to determine the model with a reverse mixing amount. 4. In order to make the parameters consistent with the model, the amount of backmixing between the anaerobic tanks is smaller than the amount of backmixing between the anaerobic tank and the aerobic tank, and an organism with a large agitator rotation speed. The method for estimating the mixed state of a nitrification / denitrification reaction tank by the activated sludge method according to claim 1 or 2, wherein a factor that the dead space ratio of the reaction tank is smaller than the dead space ratio of the biological reaction tank having a small rotation speed.