JPH07299495A - Nitrification accelerating method for activated sludge circulation modulating method and method for predicting nitrification rate - Google Patents

Abstract

PURPOSE:To provide a nitrification accelerating method of an activated sludge circulation modifying method which enhances the denitrification effect in anaerobic tank by accelerating nitrification in aerobic tanks and a method for predicting nitrification rates. CONSTITUTION:This activated sludge circulation modifying method treatment includes a stage for denitrifying raw water 3 in the anaerobic tank 1, a stage for nitrification this water in the aerobic tanks 2a to 2c and a stage for subjecting the water to sepn. of solid from liquid in a final settling basin 7 and releasing the supernatant liquid as treated water 11. While a flow meter 15 for the raw water 3 to be admitted into the anaeration tanks 1a to 1b is disposed, an ATU-Rr meter 16 is installed at the upstream part of the aerobic tanks 2a to 2c. This nitrification accelerating method comprises estimating the nitrification rates in the aerobic tanks 2a to 2c from the oxygen consumption and dissolved oxygen quantity based on the nitrification reaction and executing DO control 20 so as to permit SRT control 21 for the purpose of assuring the target nitrification rates according to these values and the inflow rate of the raw water 3. This method for predicting the nitrification rates comprises predicting the nitrification rate in the nitrifying vessels in accordance with the SRT control based on the prediction of the water temp. and nitrification reaction model equation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for promoting nitrification during operation and a method for predicting nitrification rate in an apparatus for highly efficiently removing organic matter and nitrogen in wastewater by using a modified anaerobic-aerobic activated sludge circulation method. The present invention relates to a method for keeping the activity of nitrifying bacteria high by predicting changes in water temperature and performing optimal SRT control.

[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. . Particularly in recent years, it has been required to increase the removal rate of nitrogen, and it is expected that regulations on nitrogen will become stricter.Therefore, it is thought that the number of facilities that employ advanced treatment processes that can remove this will increase. To be

As a biological biological method for simultaneously removing nitrogen and phosphorus, the anaerobic-aerobic activated sludge method has attracted attention as a modification of the conventional activated sludge method. This anaerobic-aerobic activated sludge method is, for example, as shown in FIG. 9, a biological reaction tank is a anaerobic tank 1a, 1b in which dissolved oxygen (hereinafter abbreviated as DO) does not exist, and a plurality of stages of aerobic cells in which DO exists. The anaerobic tanks 1a, 1b are divided into tanks 2a, 2b, 2c, and the anaerobic tanks 1a, 1b are used to agitate the inflowing raw water 3 with an agitation mechanism 10 to denitrify bacteria by denitrifying bacteria in the activated sludge. Aerobic tank 2a, 2
By supplying air from the blower 5 to the air diffusing pipe 4 arranged inside b and 2c, 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 nitrifying solution in the last-stage aerobic tank 2c is fed into the anaerobic tank 1a by using the nitrifying solution circulating pump 6, whereby the denitrifying effect of the anaerobic tanks 1a and 1b is promoted.

The above-mentioned denitrifying bacterium refers to a bacterium that reduces N0 ₂ -N and N0 ₃ -N to N ₂ and NO ₂ by respiration of nitric acid under anaerobic conditions. Also, phosphorus in raw water is anaerobic tanks 1a and 1b.
It is released inside and is taken in and removed by the activated sludge in the aerobic tanks 2a, 2b and 2c. 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.

On the other hand, in order to accelerate the nitrification reaction, SRT (sludge retention time) control is generally adopted in which the concentration of activated sludge in the nitrification tank is increased to reduce the amount of excess sludge drawn out so that nitrifying bacteria are not discharged to the outside of the system. ing.

By using such an anaerobic-aerobic activated sludge treatment method, an effect comparable to the organic matter removal effect achieved by the usual standard activated sludge method can be obtained, and nitrogen and phosphorus are more effective than the activated sludge method. A high removal rate is achieved.

[0007]

However, in the case of such a conventional anaerobic-aerobic activated sludge treatment method, it is difficult to establish an efficient operation control method, and in particular, by estimating the nitrification rate in the aerobic tank. There has been a problem that it is difficult to carry out control to secure a target nitrification rate to improve nitrification efficiency, and thereby to enhance the denitrification effect in the anaerobic tank. Further, the SRT control that is generally adopted to increase the nitrification rate may not be able to be properly controlled when the water temperature changes rapidly, and there is a problem that a stable nitrification reaction cannot be maintained.

That is, the operation mode in the anaerobic-aerobic activated sludge method can be roughly classified into a denitrification reaction in the anaerobic tanks 1a and 1b and a nitrification reaction in the aerobic tanks 2a, 2b and 2c. The latter, that is, the nitrification reaction, is the rate-determining reaction. In particular, in order to remove nitrogen efficiently by the anaerobic-aerobic activated sludge treatment method, it is required to maintain denitrification in the anaerobic tank and nitrification in the aerobic tank under the optimum operating conditions, and the nitrogen removing step. Is highly influenced by the nitrification process, so that the nitrification reaction must be performed well in order to perform good nitrogen removal.

This nitrification reaction is caused by nitrifying bacteria, and it is known that the activity of this nitrifying bacteria is easily affected by subtle changes in pH, water temperature and the like. or,
In order to take sufficient aeration time, it is necessary to make the volume of the biological reaction tank 2-3 times larger than in the case of the standard activated sludge method, and it is used under conditions where it is difficult to secure land for urban areas. There is a problem that it is difficult.

On the other hand, in the activated sludge process, the nitrogen component in the raw water is decomposed into ammoniacal nitrogen. This ammoniacal nitrogen is oxidized to nitrate nitrogen under the presence of nitrifying bacteria and in the condition of rich dissolved oxygen. At the sewage treatment plant, it is an important issue in operation management whether the nitrogen component remains ammoniacal or is oxidized to nitrate nitrogen before being discharged depending on the characteristics of the treatment plant and the conditions of the discharge destination. . Especially when nitrite nitrogen is present in the treated water, COD of the treated water
(Chemical oxygen demand) requires a large amount of oxidant, and the DO of the treated water discharge destination decreases, which damages the biota of the discharge destination. There is a fear of being lost. Therefore, nitrite nitrogen in the treated water must be removed as much as possible, but for that purpose, after aeration treatment with multiple aeration tanks,
Since the denitrification process must be performed by the denitrification tank, the number of facilities must be increased and the processing time becomes long.

Therefore, if it is important to discharge the environment of the water area of the discharge destination, it is preferable to discharge it as nitrate nitrogen, but since this nitrification reaction is slower than that of general BOD oxidizing bacteria, it is affected by water temperature and load fluctuation. Instability tends to occur and complete nitrification is difficult. Since this incomplete nitrification reaction raises the BOD (biochemical oxygen demand) of the treated water and the COD, the operation for promoting nitrification must be passive.

Further, in the case of the circulation method in which nitrogen is removed in order to prevent eutrophication in the water area of the discharge destination, it is an absolute condition to promote nitrification. Thus, promotion of nitrification of nitrogen components is an important factor in sewage treatment.

As one means for promoting the nitrification reaction,
As described above, the SRT that increases the concentration of activated sludge and reduces the amount of excess sludge drawn so that nitrifying bacteria are not discharged to the outside of the system.
(Sludge retention time) control is generally adopted. However, increasing the excess sludge concentration may reduce the solid-liquid separation efficiency in the settling basin and increase the concentration of suspended solids in the effluent, which naturally limits the SRT control. Especially in winter when the water temperature decreases, the activity of nitrifying bacteria also decreases,
It is difficult to maintain a proper nitrification reaction even if the concentration of activated sludge is increased to the limit.

In the ordinary SRT control, the operator of the sewage treatment plant manually operates the SRT in consideration of the daily water temperature, the concentration of sludge and suspended solids in the aerobic tank, and the solid-liquid separation efficiency in the sedimentation basin.
Are operating. However, since the SRT control requires a certain period of time until the effect is exerted, it is often impossible to take appropriate measures only by operating the SRT when the water temperature changes abruptly.

The incomplete nitrification reaction caused by such various factors causes the BOD and COD of the treated water to rise, and the nitrification reaction may be completely stopped when the water temperature further decreases. In order to stabilize the nitrification reaction, clarify the factors that affect nitrification, understand the current progress of nitrification, and predict how the nitrification reaction will proceed in response to expected changes. is important. However, since the influencing factors and the kinetic constants of the nitrification reaction change depending on the characteristics of the treatment plant and the properties of the raw water that flows in, there are no known examples of mathematical models of the nitrification reaction used in actual operation. Is the actual situation.

Therefore, the present invention solves the problems of such anaerobic-aerobic activated sludge treatment and prevents the reduction of nitrification reaction due to the DO concentration in a plurality of aerobic tanks.
As a result, a method for predicting nitrification rate in nitrification reaction using time-series water quality analysis values and measured values in a model formula of nitrogen component and a method for promoting nitrification in a modified activated sludge circulation method that can enhance denitrification reaction in an anaerobic tank, It is an object of the present invention to provide a method for keeping the activity of nitrifying bacteria high by predicting changes in water temperature and performing optimal SRT control.

[0017]

In order to achieve the above object, the present invention performs a step of denitrifying raw water with denitrifying bacteria in an anaerobic tank, and nitrifying with nitrifying bacteria in a plurality of aerobic tanks. In a modified activated sludge circulation process including a step and a step of solid-liquid separating in a settling tank and discharging a supernatant as treated water, a raw water flow meter flowing into the anaerobic tank is provided,
At the upstream of the multi-stage aerobic tank, a measuring instrument for the value obtained by subtracting the oxygen consumption rate associated with the nitrification reaction from the total oxygen consumption rate was attached.
Estimate the nitrification rate in the aerobic tank from the oxygen consumption and dissolved oxygen based on the nitrification reaction, and enable SRT control to secure the target nitrification rate according to the value and the inflow of raw water. Thus, there is provided a nitrification accelerating method for performing DO control for controlling the blower flow rate of a blower to an aerobic tank.

Further, the change in the water temperature in the treatment plant is predicted from the past data, and when the decrease in the water temperature is predicted, the set value of the SRT is increased so as to match the time, while the increase in the water temperature is predicted. In such a case, the control is performed so that the SRT set value is lowered so as to suit the time, so that the SRT control is adapted to the transition of the water temperature and appropriate SRT control corresponding to the rapid change of the water temperature. A method for promoting nitrification is provided.

Further, according to claim 4, the optimization is performed in which the specific growth rate is calculated based on the analysis value and the measured value of nitrogen, and the nitrification rate and the amount of nitrifying bacteria are calculated from the obtained specific growth rate and the activated sludge concentration value. After this optimization process, the prediction conditions such as the prediction of water temperature change based on past data and the prediction of load fluctuation are input after this optimization process, and the calculation is performed to predict the nitrification rate based on the nitrification reaction model formula. A method for predicting nitrification rate in a modified sludge circulation method is provided.

[0020]

[Operation] According to the method for promoting nitrification in the modified activated sludge circulation method, raw water is denitrified in an anaerobic tank or under anaerobic conditions, and aeration in an aerobic tank or under aerobic conditions and nitrification based on the effects of nitrifying bacteria On the other hand, the oxygen consumption rate [Nt-Rr] and [DO] involved in the nitrification reaction in the upstream aerobic tank are measured, and the above-mentioned [Nt-Rr] value accompanying the nitrification of the activated sludge in the aerobic tank The actual nitrification rate of the activated sludge is estimated from the [DO] value and the inflow rate of the raw water, and the DO control for controlling the blower air flow of the blower enables the SRT control to secure the target nitrification rate. Be implemented.

At the time of the above, by predicting the change in the water temperature and controlling so as to increase or decrease the set value of the SRT so as to be suitable for the time, it is suitable for the rapid change in the water temperature after the present time. It becomes possible to carry out SRT control.

Further, according to the method for predicting nitrification rate in the modified activated sludge circulation method, the specific growth rate is calculated based on DO, pH and water temperature, and the nitrification rate and nitrifying bacteria are calculated based on this specific growth rate value and MLSS value. The amount is calculated, and the prediction conditions such as the prediction of the water temperature change based on the past data and the load change prediction are input, and the prediction is calculated based on the model formula. Then, the calculated predicted value and the target value are compared and the DO
Or, the coping method regarding the SRT is set, and it becomes possible to shift to an appropriate coping operation.

As a result, a decrease in nitrification efficiency due to fluctuations in the inflow load or the amount of water is prevented, and the nitrification reaction of the aerobic tank as a whole based on the activity of nitrifying bacteria in the aerobic tank is promoted. The effect of improving the removal rate is obtained.

[0024]

Example Since the nitrification reaction occurs due to the growth of nitrifying bacteria in the activated sludge, even if the concentration of the activated sludge is increased, this reaction does not occur unless the nitrifying bacteria are present in the sludge. Therefore, in order to increase the nitrification rate, it is more effective to increase the ratio of nitrifying bacteria in the activated sludge than to increase the activated sludge concentration. Since nitrification reaction and BOD removal occur at the same time in sewage treatment, if nitrifying bacteria grow, BOD-utilizing bacteria that occupy most of the activated sludge also grow. These activated sludges undergo a decomposition reaction at the same time as they proliferate, and the difference between this proliferation and decomposition is the increased amount of sludge.

From the mission of sewage treatment, it is not possible to reduce the BOD removal rate, so it is not possible to suppress the growth of BOD-assimilating bacteria, but if the decomposition reaction is promoted, the nitrification rate in the activated sludge should be increased. Is possible. It is known that this autolysis reaction increases as SRT and sludge age increase, but other factors have not been clarified. Therefore, the effect on the decomposition rate of nitrifying bacteria and BOD-assimilating bacteria is investigated, and the condition that the decomposition rate of BOD-assimilating bacteria is increased under the condition that the decomposition rate of nitrifying bacteria is not decreased, and the difference in the decomposition rates is used. It is possible to increase the efficiency of the nitrification reaction.

Therefore, in this embodiment, first, as a preliminary experiment, three sets of reaction devices each having the DO control device shown in FIG. 3 were used, and the effect of changing the set value of DO was investigated. 22 in the figure
Is a thermostatic chamber, and a reaction chamber 23 is arranged in the thermostatic chamber 22. The reaction chamber 23 is provided with an air diffuser 4 for dispersing the air sent from the blower 5 and a stirring mechanism 23. 24 is a DO meter and 25 is a controller, and on / off control of the blower 5 is performed based on the output signal of the controller 25. 27 is a pump for discharging the supernatant from the reaction tank 23, and 28 is a pump for extracting excess sludge.

Then, the effect of the change in the set value of DO with respect to the inflow water 26 into the reaction tank 23 was examined. In the experiment, the initial MLSS (Activated Sludge Float) value was the same as the volume load and sludge extraction amount, and the DO was "1.0" and "3.0", respectively.
The batch culture was carried out for 1 month by setting it to "6.0". Then finally MLSS is 1900, 1800, 155
It became 0, and it was found that the higher the DO setting value, the lower the MLSS.

Next, all the DO set values were set to "3.0" under the same conditions as above, and the concentration of nitrate nitrogen was measured every hour after the loading was started to examine the nitrification rate. As a result, there was no difference in the amount of nitric acid produced in each series, and the nitrification rate per unit sludge (mg-N / g-ss · h) was "2.9".
It became "3.3" and "3.5", and it was found that the higher the DO setting value, the higher the nitrification rate. This indicates that the higher the DO, the faster the decomposition rate of BOD-assimilating bacteria, but that the decomposition rate of nitrifying bacteria is not affected. Therefore, by increasing the DO set value, the proportion of nitrifying bacteria in the activated sludge can be increased.

Utilizing the above results, an apparatus was realized in which the nitrification reaction was enhanced and the volume of the biological reaction tank was reduced. This will be described with reference to FIG.

In FIG. 1, 1a and 1b are anaerobic tanks into which raw water 3 flows, 2a, 2b and 2c are a plurality of aerobic tanks for nitrification, and the anaerobic tanks 1a and 1b and aerobic tank 2a are shown. , 2
The same biological reaction tanks as b and 2c are divided by a partition plate 13 and divided.

The anaerobic tanks 1a, 1b have a stirring mechanism 10,
10, air diffusers 4, 4 and 4 as an air blowing mechanism are arranged in the aerobic tanks 2a, 2b and 2c, and a blower for supplying air to the air diffusers 4, 4 and 4 to the outside. 5 are deployed. 6 is a nitrification solution circulation pump.

Reference numeral 7 is a final sedimentation pond, and this final sedimentation pond 7
A stirring mechanism 14 is provided in the. Reference numeral 8 is a sludge return pump for returning a part of the sludge to the anaerobic tank 1a, and reference numeral 9 is a surplus sludge drawing pump for sending another sludge to a surplus sludge treatment device (not shown). A timer is usually attached to the excess sludge removal pump, and the excess sludge removal pump is set to perform a removal operation of the excess sludge at every predetermined time.

In this embodiment, the flow meter 15 for measuring the inflow rate of the raw water 3 into the anaerobic tank 1a is provided in the preceding stage of the anaerobic tank 1a.
ATU-Rr meter 1 is installed in the aerobic tank 2a.
6 is attached. The inflow amount of the raw water 3 measured by the flow meter 15 and the [Nt-Rr] value 17 and the [DO] value 18 calculated based on the value measured by the ATU-Rr meter 16 are input to the control system 19. It has been entered. Then, based on the set value output from the control system 19, the DO
The control 20 and the SRT control 21 are implemented.

The basic operation of such a device is as follows. As shown in FIG. 1, first, raw water 3 is anaerobic tanks 1a, 1
The inflow amount when flowing into b is measured by the flow meter 15, and this measured value is input to the control system 19. Anaerobic tank 1a, based on the stirring action and the action of denitrifying bacteria agitation mechanism 10, 10 in the water at _{1b, NO 3 -N, NO 2} -
Reduction of N ions to N ₂ , that is, denitrification, is performed.

Next, the raw water 3 flows into the aerobic tanks 2a, 2b, 2c, and aeration is performed by aeration from the diffuser pipes 4, 4, 4 as the blower 5 is driven, and based on the action of nitrifying bacteria. Ammoniacal nitrogen NH ₄ -N NO ₂ -N or N
Oxidation to O ₃ -N, that is, nitrification is performed.

[0036] Thus nitrification reaction is oxidation of ammonium nitrogen by nitrifying bacteria, nitrification rate can be expressed as an increase rate of decreasing speed or NO _X -N ammoniacal nitrogen _{(NO 2 -N + NO 3 -N} ) .

The other denitrification reaction can be expressed as 2NO ₃ ⁻ +5 (H ₂ ) → N ₂ ↑ + 2OH ⁻ + 2H ₂ O.

During the above operation, the inflow rate of the raw water 3 is measured by the flow meter 15 and the oxygen consumption rates [Nt-Rr] 17 and [DO] 18 involved in the nitrification reaction are measured by the ATU-Rr meter 16. , Aerobic tanks 2a, 2b, 2 based on the values of [Nt-Rr] 17 and [DO] 18
The DO control 20 that controls the air flow rate of the blower 5 with respect to c is performed, and the SRT control 21 that controls the operation of the excess sludge extraction pump 9 to reduce the outflow amount of nitrifying bacteria is performed. In other words, the control system 1
9 is a blower 5 for the aerobic tanks 2a, 2b, 2c so as to enable SRT control for ensuring a target nitrification rate according to the inflow rate of the raw water 3 and the nitrification rate in the aerobic tank 2a. The feature of the present embodiment is that the DO control for controlling the air flow rate is performed.

As a concrete control example, when the [Nt-Rr] value becomes smaller than the lower limit value due to, for example, a change in water temperature, a command for increasing the DO set value is output so that the [Nt-Rr] value becomes high. To do. At this time, if the DO value is sufficiently high, raise the pH setting value with the DO setting value left unchanged [N
[t-Rr] value is increased and the set value of SRT is lowered to carry out operation control to reduce the outflow amount of nitrifying bacteria. SR
The T control is a method of increasing the sludge concentration so as to accelerate the nitrification reaction so that nitrifying bacteria are not discharged to the outside of the system, and the excess sludge withdrawal amount is reduced.

During the above operation, the nitrification solution in the aerobic tank 2c is fed into the anaerobic tank 1a by using the nitrification solution circulation pump 6, so that the denitrification effect in the anaerobic tank is promoted. Particularly, phosphorus in the wastewater is released in the anaerobic tank, and is taken into and removed by the activated sludge in the aerobic tank.

A part of the sludge settled in the final settling basin 7 is returned to the anaerobic tank 1a by the sludge return pump 8, and the other sludge is sent to the excess sludge treatment device by the excess sludge drawing pump 9 for treatment. The supernatant of the final sedimentation tank 7 is treated water 1
It is discharged after passing through a disinfection tank (not shown) as No. 1.

The above ATU-Rr meter 16 is used to monitor the progress of the nitrification reaction in the aerobic tank 2. That is, oxygen utilization rate
(Or respiration rate, hereinafter abbreviated as Rr) includes the amount of oxygen consumed during oxidative decomposition of organic matter, the amount of oxygen consumed for endogenous respiration of activated sludge, and the amount of oxygen consumed for nitrification reaction. Be done.

This value is expressed as a respiratory rate due to removal of organic substances and endogenous respiration, that is, a value obtained by subtracting the oxygen consumption rate associated with the nitrification reaction from the total oxygen consumption rate. Therefore, the progress of the nitrification reaction is based on the difference (ATU-Rr) between Rr and Rr measured by adding N-allylthiourea (chemical formula C ₄ H ₈ N ₂ S, hereinafter abbreviated as ATU), which is a nitrification inhibitor. You can ask.

When the difference is [Nt-Rr], [Nt-Rr] = [Rr]-[ATU-Rr] (1) That is, [Nt-Rr] represents the amount of oxygen consumption associated with the nitrification reaction, so that it can be determined that the nitrification reaction is slow when the value is small and the nitrification reaction is fast when the value is large.

The values measured by these measuring devices are input to the control system 19, the ideal nitrification rate is calculated from the volume of the aerobic tank and the hydraulic retention time, and the activated sludge in the aerobic tank 2 is calculated. [Nt-Rr] 17, [DO] associated with nitrification
18 is used to estimate the actual nitrification rate of activated sludge.

[Nt-R in the above equation (1)
When the value of r] is small and the nitrification reaction must be enhanced, the amount of sludge returned from the final settling tank 7 to the anaerobic tank 1 by the sludge return pump 8 is increased to increase the MLSS which is the activated sludge suspended matter, and By controlling the excess sludge drawing pump 9, the SRT, which is the sludge retention time, is adjusted, and the aerobic tank 2
In the case where the nitrification by means of nitrogen is carried out smoothly, the amount of the nitrification solution returned from the aerobic tank 2 to the anaerobic tank 1 based on the action of the nitrification solution circulation pump 6 is increased to increase the circulation ratio of the solution. The removal rate can be increased. In particular, it is a feature of the present embodiment that the stable nitrogen removal is performed by preventing the nitrification failure due to the water temperature drop or the load change.

[Nt-Rr] when the load is low at night.
Since the value of is also extremely small, the amount of aeration in the aerobic tank can be reduced and the circulation amount of nitrification liquid can be reduced.
Optimal operation control can be performed by maintaining the SS concentration high and increasing the DO consumption of the anaerobic tanks 1a and 1b.

Next, an actual example of control in the control system 19 will be described based on the flow chart of FIG. First, control starts in step 100, and in step 101, the inflow load amount related to nitrogen is measured. This inflow load is calculated from the concentration of Kjeldahl nitrogen or total nitrogen and the inflow of the raw water 3.

Next, at step 102, the required nitrification rate, that is,
The nitrification rate R (mg-N / g-ss-h) for completing the nitrification reaction at the end of the nitrification tank with respect to the inflow load is calculated.

R = (TN × Q) / (MLSS × V) (2) where TN: total inflow nitrogen concentration (mg / l), Q = inflow water amount (l / h) MLSS: concentration of suspended matter in activated sludge, V: volume of nitrification tank (l) In step 103, the nitrification rate and the respiration rate [Nt-Rr] required for nitrification, which have been investigated in advance, are converted into the nitrification reaction corresponding to R. Based on this, the respiration rate is calculated, the lower limit value for control is set in step 104, and the actual [Nt-Rr] value is measured in step 105.

Then, in step 106, it is judged whether or not the measured value is above the set lower limit value, and if YES, it is judged in step 107 whether or not there is a new load amount measurement. If there is a measurement, the process returns to step 101, and if not, the process returns to step 105 to measure the next [Nt-Rr] value.

If NO at step 106, that is, if the measured value is less than or equal to the lower limit value, the required SRT is estimated at step 108. Required here SRT = 1 / μ (μ:
Specific growth rate, 1 / d). Further, in step 109, MLSS is estimated. And in step 110 M
Determine if LSS is within administrative limits.

If YES in step 110, that is, if MLSS is within the limit value, this SRT set value is output in step 111, and if NO in step 110, that is, MLSS exceeds the limit value, in step 112. The DO set value is calculated, the DO set value is output in step 113, and the process proceeds to step 111.

In FIG. 1, most of the ammoniacal nitrogen contained in the raw water 3 such as sewage passes through the anaerobic tanks 1a and 1b as it is. Therefore, ATU-Rr
In the most upstream part of the aerobic tanks 2a, 2b, 2c in which the total 16 is installed, nitrification rate limiting due to the decrease of ammonia nitrogen does not occur. It is also known that [Nt-Rr] becomes constant when the water temperature is constant and ammonia nitrogen is present at 3 (mg / l) or more. Therefore, by installing the ATU-Rr meter as described above and measuring [Nt-Rr], the change in nitrification activity can be directly detected.

Next, the nitrification reaction model will be described below. The specific growth rate μ of the nitrifying bacteria is expressed by the following equation.

Μ = μ _max · [exp (θ (t−15))] · [1−0.833 (7.2−pH)] · [DO / (DO + Kdo)] (3) where μ: specific growth Velocity (l / day), μ _max = Maximum specific velocity (1 / day) θ: Temperature coefficient (-), Kdo: Saturation constant (mg / l), DO: Dissolved oxygen (mg / l) Also, per MLSS The nitrification rate R is given by the following equation.

R = (μ _N · X / Y / Vt) / MLSS / 24 (4) where R: nitrification rate (mg− N / g-ss · h), X: Amount of nitrifying bacteria (mg) Y = Nitrifying bacteria yield (-), MLSS: Activated sludge concentration, Vt: Reaction tank volume (l) Growth of nitrifying bacteria by nitrification for 1 day The amount DX (mg) is expressed by the following equations (5) and (6), with the maximum when 60% of the inflowing nitrogen is nitrified.

DX = μ ・ X ・ (V _O / Vt) TN ・ Q ・ 0.6 ・ Y ＞ μ ・ X ・ (V _O / Vt) ・ ・ ・ ・ ・ (5) ＝ TN ・ Q ・ 0.6 ・ Y TN・ Q ・ 0.6 ・ Y <μ ・ X ・ (V _O / Vt) (6) where V _O : nitrification tank volume (l), TN: inflow nitrogen concentration (mg / l),
Q: Raw water inflow (l / d) Further, the amount of nitrifying bacteria in the system X _NEW (mg) is expressed by equation (7).

X _NEW = X + DX-X / SRT-X ··· (7) where SRT: sludge retention time (d), b = self-decomposition coefficient (l /
day) Using the nonlinear simplex method to determine the dynamic constants of μ _max , θ, Kdo, and b in the above equation and the amount of initial nitrifying bacteria, the difference between the measured nitrification rate and the above equation (4) is minimized. When the calculation is performed by optimizing as follows, μ _max = 0.514, θ
= 0.01, Kdo = 2.01, b = 0.1, amount of nitrifying bacteria =
It became 123 mg. The value of the amount of nitrifying bacteria of 123 mg is the initial value of the amount of nitrifying bacteria X in the formula (4), and the amount of nitrifying bacteria from the second time is X _NEW of the formula (7).

The actual nitrification rate prediction method using the above nitrification reaction model will be described with reference to FIG. First, in step 200, the control starts, and in step 201, the analytical value and the measured value regarding nitrogen are input. Analytical values for nitrogen are total nitrogen and nitrate nitrogen in the inflow water, and measured values for nitrogen are respiratory rate, DO, MLSS, pH and water temperature.

Next, in step 202, model model optimization processing, which will be described in detail later, is performed, and in step 203, prediction conditions based on past data are input. These prediction conditions are prediction of water temperature change and load fluctuation prediction.

At step 204, a prediction is calculated based on the model formula, and at step 205, the calculated predicted value and the target value are compared. Here, if YES, that is, if there is an abnormality, the procedure returns to step 201, and if NO, that is, if there is no abnormality, the coping method is set to step 206. This coping method includes DO, SRT, p
Means for changing part or all of each of H, circulation ratio, and anaerobic / aerobic volume ratio are included, and from this result, prediction calculation is performed again based on the model formula in step 207, and calculation is performed in step 208. Is determined to be valid or not. If NO, that is, if it is invalid, the procedure returns to step 206 and the next coping method is set. If YES, that is, if it is valid, the predetermined operation is performed in step 209. This operation is the operation amount of the blower, the sludge withdrawal amount by the excess sludge pump, or the circulation amount of the nitrification liquid to the anaerobic tank.

The model formula optimizing process in step 202 is the DO in step 301 as shown in FIG.
The pH and water temperature are read to calculate μ (specific growth rate), and R is calculated in step 302 based on the obtained μ value and MLSS value.
Calculate (nitrification rate). Next, in step 303, X _NEW (amount of nitrifying bacteria) is obtained by calculation. After such an optimization process, in step 304, the predicted value is calculated by simulation based on the model formula based on the prediction of the water temperature or the load fluctuation, and in step 305, the calculated predicted value and the target value are compared. Then, the process returns to the flow after step 205 in FIG.

The optimization treatment of this model formula does not require data in a steady state, and moreover, the nitrification reaction changes momentarily in the treatment process in which the nitrogen component in the raw water is oxidized to nitrate nitrogen and is released. The situation can be easily estimated.

FIG. 6 shows the result of time-based comparison between the measured value of the nitrification rate and the calculated value of this example. The nitrification rate was determined once every one or two weeks from the results of water quality analysis taken from the activated sludge experimental plant. Other data such as water temperature, DO, pH and MLSS were measured daily.

According to FIG. 6, it can be seen that the actually measured value of the nitrification rate and the calculated value according to the present embodiment agree very well. Therefore, it is possible to improve the accuracy of the nitrification reaction model by using the time-series water quality analysis value and the measurement value. Among the water quality analysis values, the nitrification rate may be an estimated value obtained from a value obtained by subtracting the oxygen consumption rate associated with the nitrification reaction from the total oxygen consumption rate measured by the ATU-Rr meter.

Another feature of this embodiment is that the change in the water temperature at the treatment plant is predicted, and the SRT control is performed in accordance with the change in the water temperature and in response to the sudden change in the water temperature. ing. An actual example of SRT control corresponding to such a rapid change in water temperature will be described. This SR
As described above, T is given as the reciprocal of the specific growth rate μ (l / day) of sludge. That is, SRT = 1 / μ (8) As shown in the equation (3), the specific growth rate μ is the water temperature. , It is a function of pH and DO, and therefore it is necessary to change the SRT setting when the temperature changes. However, when this setting is changed, it takes 2-3 times longer to stabilize. Is believed to be. Therefore, even if the SRT setting is changed after a drastic change in water temperature, a large effect cannot be expected. However, if it is known in advance how the water temperature will change after this point in time, an SRT suitable for this water temperature change can be set.

FIG. 7 shows the result of checking the water temperature change in a typical sewage treatment plant every two months for two years. According to the figure, for example, from late November to 12
The water temperature has dropped by 2.3 ° C in the first two months of the month, but if this temperature change is predictable, control the SRT to raise the set value in advance to suit that time. Good. Furthermore, in April, the water temperature is 2.1 in one week.
Although the temperature rises by 0 ° C., in this case as well, control may be performed in advance so as to lower the set value of the SRT so as to suit the time.

A specific control example of the SRT based on the water temperature will be described with reference to FIG. First, in step 400, the control starts, and in step 401, the analysis value and the measurement value regarding nitrogen are input. Next, in step 402, a model formula optimization process is performed in the same manner as in the above example, in step 403 the water temperature in the treatment plant is measured, and the transition of the water temperature is predicted based on the data measured in step 404. .

Next, it is judged from the transition of the water temperature predicted in step 405 whether or not the SRT needs to be changed. If YES, that is, if it is judged that the SRT needs to be changed, step 406 is executed. After the optimum SRT is estimated in step S407, the set value of SRT is output in step 407. Step 4
When the result of 05 is NO, that is, when it is determined that the change is unnecessary, the process returns to step 401 and the same control is repeated. S
The setting of RT is, specifically, an operation of adjusting the driving state of the excess sludge extraction pump 9 in FIG. 1 to increase the concentration of activated sludge and reducing the amount of excess sludge drawn out so that nitrifying bacteria are not discharged to the outside of the system, Or, it means the opposite operation.

The model formula optimization processing in step 402 is the calculation of μ (specific growth rate) from DO or pH as in the above description, and R (nitrification rate) is calculated based on the obtained μ value and MLSS value. ) Is calculated and then X _NEW (amount of nitrifying bacteria) is calculated.

As described above, according to the present embodiment, the progress of the nitrification reaction can be estimated by using the nitrification reaction model with respect to the predicted water temperature, the inflow water quality and the change in the water amount. If it is determined that the nitrification rate is low and sufficient nitrification cannot be maintained, it is important to take prompt measures, and whether the measures are effective or not can be determined using the above model. it can.

As a method of predicting the water temperature, a method of averaging past data or a method of using a moving average can be considered. Particularly, according to FIG. 7, since the change of the water temperature is relatively small compared to the change of the air temperature, it can be calculated every year. It is understood that there is no big difference in the change situation of water temperature in. Therefore, the method of averaging the data of the past few years is a powerful method for predicting water temperature.

[0074]

As described in detail above, according to the method for promoting nitrification in the modified activated sludge circulation method according to the present invention,
Raw water is denitrified in the anaerobic tank, and aeration in the aerobic tank and nitrification based on the action of nitrifying bacteria are performed. On the other hand, the oxygen consumption rate and DO measurement results in the aerobic tank indicate the aerobic tank The actual nitrification rate of activated sludge is estimated, and the SRT control to secure the target nitrification rate is made possible.
O control is carried out to prevent a decrease in nitrification efficiency due to fluctuations in inflow load or the amount of water, to promote the nitrification reaction in the aerobic tank as a whole based on the activity of nitrifying bacteria, and eventually to remove nitrogen in the anaerobic tank. The effect that the rate is improved is obtained.

In particular, since the nitrification efficiency in the nitrification tank is increased, it is not necessary to increase the volume of the bioreaction tank as compared with the standard activated sludge method, and it is difficult to secure a site in an urban area. There is an advantage that it can be adopted.

Further, according to the above nitrification rate prediction method, D
Specific growth rate is calculated based on O, pH, and water temperature, and nitrification rate and nitrifying bacterium amount are calculated based on MLSS value. Based on model conditions together with prediction conditions such as water temperature change prediction and load change prediction. Calculations of nitrification rate predictions can be made.

Further, it is possible to maintain the activity of nitrifying bacteria at a high level by predicting a change in the water temperature in a sewage treatment plant or the like and performing an appropriate SRT control corresponding to the sudden change in the water temperature. it can.

The predicted value calculated as described above is compared with the target value to set a countermeasure for DO or SRT, and an appropriate countermeasure for preventing nitrification failure due to a decrease in water temperature or load fluctuation. Even if it is desired to suppress the nitrification reaction by carrying out, the operating conditions can be quickly obtained.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram showing a configuration example of a modified activated sludge circulation method according to the present embodiment.

2 is a flowchart showing an actual example of control in the control system of FIG.

FIG. 3 is a schematic diagram showing an example of a reaction device equipped with a DO control device used as a preliminary experiment of the present embodiment.

FIG. 4 is a flow chart showing an actual example of a nitrification rate prediction method using a nitrification reaction model.

5 is a flowchart showing an example of optimization processing in FIG.

FIG. 6 is a graph showing the results of comparison between the actual measurement value of the nitrification rate and the calculated value according to the present embodiment over time.

FIG. 7 is a graph showing the results of checking changes in water temperature at a sewage treatment plant.

FIG. 8 is a flowchart showing a specific control example of SRT based on water temperature.

FIG. 9 is a schematic diagram showing an example of conventional anaerobic-aerobic activated sludge treatment.

[Explanation of symbols]

 1a, 1b ... Anaerobic tank 2a, 2b, 2c ... Aerobic tank 3 ... Raw water 4 ... Diffuser pipe 5 ... Blower 6 ... Nitrification solution circulation pump 7 ... Final sedimentation tank 8 ... Sludge return pump 9 ... Excess sludge extraction pump 11 ... Treatment Water 15 ... Flowmeter 16 ... ATU-Rr meter 19 ... Control system 20 ... DO control 21 ... SRT control

Claims (7)

[Claims] 1. A step of denitrifying raw water with denitrifying bacteria in an anaerobic tank, a step of nitrifying with nitrifying bacteria in a plurality of aerobic tanks, and solid-liquid separation in a precipitation tank to treat a supernatant. In the activated sludge circulation modification method including the step of discharging as water, a flow meter of raw water flowing into the anaerobic tank is provided, and the total oxygen consumption rate is accompanied by the nitrification reaction in the upstream part of the multi-stage aerobic tank. A measuring instrument for the value minus the oxygen consumption rate is attached, and the nitrification rate in the aerobic tank is estimated from the oxygen consumption based on the nitrification reaction and the amount of dissolved oxygen, and the target is set according to that value and the inflow of raw water. A method for promoting nitrification in a modified activated sludge circulation method, which comprises performing DO control for controlling an air flow rate of a blower to an aerobic tank so as to enable SRT control for securing a nitrification rate. 2. A change in water temperature at a treatment plant is predicted from past data, and when a decrease in water temperature is predicted, an SRT set value is increased to suit the time while a rise in water temperature is predicted. If so, by controlling to lower the SRT set value to suit that time,
A method for promoting nitrification in a modified activated sludge circulation method, which is adapted to a change in water temperature and to perform an appropriate SRT control in response to a sudden change in water temperature. 3. The setting of the SRT is an operation of adjusting the excess sludge withdrawal amount to increase the concentration of activated sludge and reducing the excess sludge withdrawal amount so that nitrifying bacteria are not discharged to the outside of the system, or vice versa. The nitrification promoting method in the modified activated sludge circulation method according to claim 2, which is an operation. 4. A specific growth rate is calculated based on an analysis value and a measured value of nitrogen, and an optimization process is performed to calculate the nitrification rate and the amount of nitrifying bacteria from the obtained specific growth rate and the activated sludge concentration value. After the optimization process, the prediction conditions such as water temperature change prediction and load change prediction based on the past data are input, and the calculation of predicting the nitrification rate based on the nitrification reaction model formula is performed. Method for predicting nitrification rate in the method. 5. The nitrification rate R (mg-N / g-ss · h) for completing the nitrification reaction at the end of the nitrification tank against the inflow load is R = (TN × Q) / (MLSS × V) TN: total inflow nitrogen concentration (mg / l), Q = inflow water amount (l
/ H) MLSS: concentration of suspended matter in activated sludge, V: volume of nitrification tank (l) The method for predicting nitrification rate in the modified activated sludge circulation method according to claim 2, characterized in that it is obtained. 6. The specific growth rate μ of nitrifying bacteria is expressed by μ = μ _max · [exp (θ (t−15))] · [1−0.833 (7.2−pH)] · [DO
/ (DO + Kdo)] μ _max = maximum specific velocity (1 / d), θ: temperature coefficient (-), Kd
o: Saturation constant (mg / l), DO: Dissolved oxygen (mg / l) Determined based on the formula, and the nitrification rate R per MLSS (mg-
The N / g-ss · h) , R = (μ N · X / Y / Vt) / MLSS / 24 X: amount nitrifying bacteria (mg), Y = nitrification KinOsamuritsu (-), MLSS: activated sludge concentration , Vt: volume of the reaction tank (l) is calculated based on the equation, the method for predicting nitrification rate in the modified activated sludge circulation method according to claim 2 or 3. 7. The analytical values for nitrogen are total nitrogen and nitrate nitrogen in the inflow water, and the measured values for nitrogen are respiratory rate, DO, MLSS, pH and water temperature.
3. A method for predicting nitrification rate in the modified activated sludge circulation method according to 3, 4.