JPH08117789A - Operation control of two-stage activated sludge circulation variation - Google Patents

Abstract

PURPOSE: To provide an operation control method which can maintain denitrification reaction and nitration reaction satisfactorily in a two-stage active sludge circulation variation method. CONSTITUTION: A first aerobic tank 2a, anaerobic/aerobic doubling tanks 13a, 13b and a second aerobic tank 2b are connected in series to an anaerobic tank 1a, and nitration liquid circulation pumps 6a, 6b for feeding a nitration liquid to the anaerobic tank 1a are arranged from each aerobic tank 2a, 2b to the anaerobic tank 1a. Under this constitution, an ATU-rr meter is installed in the rear stage part of the first aerobic tank 2a. A progress status of nitration reaction in the first aerobic tank 2a is judged based on the readings obtained using the ATU-rr meter. In addition, the anaerobic/aerobic doubling tank 13a, 13b are caused to operate as the anaerobic tank or the aerobic tank, depending upon the completion or non-completion of the nitration reaction. At the same time, the nitration liquid is returned to the anaerobic tank 1a through the first and the second nitration liquid circullation pump 6a, 6b to enhance the denitrification effect. Thus operation of the two-stage active sludge circulation variation method is controlled as described above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operating method with a high nitrogen removal rate in a system for highly efficiently removing organic matter and nitrogen in wastewater by using a modified two-stage activated sludge circulation 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. . This eutrophication refers to an increase in the concentration of nutrient salts such as N, P in the water area, which activates biological activities using these nutrients as nutrients and changes the ecosystem. In particular, it is known that the above-mentioned eutrophication rapidly progresses when a large amount of domestic wastewater or industrial wastewater flows into lakes and the like.

Recently, it has been required to increase the removal rate of nitrogen, and it is expected that the regulations on nitrogen will be stricter. Therefore, the number of facilities adopting an advanced treatment process capable of removing this will increase. it is conceivable that.

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.

On the other hand, as a biological biological method for simultaneously removing nitrogen and phosphorus, an anaerobic method is a modification of the conventional activated sludge method.
The aerobic activated sludge method is drawing attention. The anaerobic-aerobic activated sludge method is, for example, as shown in FIG. 2, a biological reaction tank is an anaerobic tank 1a in which dissolved oxygen (hereinafter abbreviated as DO) does not exist,
Denitrification tank 1b and multi-stage aerobic tanks 2a, 2 with DO
b, 2c, and the anaerobic tank 1a and the denitrification tank 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 sent to the anaerobic tank 1a by using the nitrification solution circulation pump 6, whereby the denitrification effect in the anaerobic tank 1a and the denitrification tank 1b is promoted.

Since the activity of the above nitrifying bacteria decreases as the DO concentration decreases, the DO of the last aerobic tank 2c is measured and D
It is customary that the O controller 12 controls the drive of the blower 5.

Reference numeral 7 is a final sedimentation pond. This final sedimentation pond 7
The supernatant liquid is discharged as treated water 11 after passing through a disinfecting tank or the like (not shown), and a part of the sludge settled in the final settling tank 7 is returned to the anaerobic tank 1a by the sludge returning pump 8. Other sludge is sent from the excess sludge drawing pump 9 to an excess sludge treatment device (not shown) for treatment.

FIG. 3 is a "two-stage activated sludge circulation modified method" in which an anaerobic tank (denitrification tank) 1a and an aerobic tank 2a and an anaerobic tank 1b and an aerobic tank 2b are connected in series for the purpose of improving the nitrogen removal rate. The example of composition of is shown. The other components are basically the same as the example shown in FIG.

In the case of this two-stage activated sludge circulation modification method, the circulation mechanism of the nitrification liquid from each aerobic tank 2a, 2b to the anaerobic tank 1a, 1b is also the two of the first circulation path 15 and the second circulation path 16. It is a system.

The denitrifying bacterium is a bacterium which reduces N0 ₂ -N and N0 ₃ -N to N ₂ and NO ₂ by respiration of nitric acid under anaerobic conditions. Further, phosphorus in the raw water is released in the anaerobic tank 1a, and is taken in and removed by the activated sludge in the aerobic tanks 2a, 2b, 2c.

By using the anaerobic-aerobic activated sludge treatment method and the modified two-stage activated sludge circulation method, an effect similar to the organic matter removal effect achieved by the ordinary standard activated sludge method can be obtained, and nitrogen can be obtained. For phosphorus and phosphorus, a higher removal rate than the activated sludge method is achieved.

[0012]

However, in the case of such a conventional activated sludge circulation modification method, it is difficult to establish an efficient operation control method. Particularly, in the aerobic tank, the nitrification efficiency and the anaerobic tank associated therewith are difficult to establish. There is a problem that it is difficult to increase the denitrification efficiency sufficiently.

That is, the operation modes in the anaerobic-aerobic activated sludge method shown in FIG. 2 are roughly divided into a denitrification reaction in the anaerobic tanks 1a and 1b and a nitrification reaction in the aerobic tanks 2a, 2b and 2c. However, 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 affected by the nitrification process, so that the nitrification process must be performed well in order to perform good nitrogen removal.

Especially, since the denitrification reaction is nitrate respiration under the condition that dissolved oxygen does not exist, it is desirable that DO does not exist. However, actually, a backflow phenomenon of the mixed liquid from the aerobic tanks 2a, 2b, and 2c can be mentioned as a factor for bringing the DO into the anaerobic tanks 1a and 1b. In particular, in the example of the "two-stage activated sludge circulation modified method" described above, since the anaerobic tank at the rear stage has aerobic tanks at the front and rear, the effect of bringing in DO is large and the anaerobic state can be maintained in a good state. There is a problem that it is difficult. The latter anaerobic tank has the implication that the nitrogen removal rate is increased by denitrifying the nitrification liquid flowing out from the aerobic tank of the previous stage without going through the denitrification process, and therefore the anaerobic state of the latter anaerobic tank is good. Keeping on is becoming important.

The above nitrification reaction is caused by nitrifying bacteria, and it is known that the activity of the nitrifying bacteria is easily affected by subtle changes in pH, water temperature and the like. In addition, in order to obtain sufficient aeration time, it is necessary to increase the volume of the biological reaction tank by a factor of 2 to 3 compared with the standard activated sludge method, and under conditions where it is difficult to secure land for urban areas. There is a problem that it is difficult to adopt.

When the nitrification progresses satisfactorily, the quality of the denitrification reaction influences the nitrogen removal rate. Therefore, in order to maintain a high nitrogen removal rate, a good balance between the nitrification reaction and the denitrification reaction is maintained. Required to do so.

Therefore, the present invention solves the problems of the modified activated sludge circulation method, in particular, the modified two-stage activated sludge circulation method, and eliminates the denitrification reaction in this modified two-stage activated sludge circulation method. It is an object of the present invention to provide an operation control method capable of promoting the operation and increasing the nitrogen removal rate.

[0018]

In order to achieve the above object, the present invention provides an anaerobic tank for denitrification and a first aerobic tank for nitrification, and an anaerobic-aerobic tank. A second niobium tank is connected in series, and a first nitrification solution circulation pump for sending the nitrification solution from the first aerobic tank to the anaerobic tank is provided.
A second nitrification solution circulation pump for sending the nitrification solution from the second aerobic tank to the anaerobic tank is provided, and a sludge return pump for returning a part of the sludge discharged from the final settling tank to the anaerobic tank is provided. In the modified two-stage activated sludge circulation method, an ATU-rr meter is installed at the rear stage of the first aerobic tank.
The progress of the nitrification reaction in the first aerobic tank is judged based on the value measured by the rr meter, and when the nitrification reaction is completed, the nitrification solution circulation pump is used to feed the nitrification solution. The anaerobic-aerobic tank while acting as an anaerobic tank to enhance the denitrification effect, and when the nitrification reaction is not completed, the anaerobic-aerobic tank serves as an aerobic tank. Of the two-stage activated sludge circulation modified method, in which the volume ratio of the second aerobic tank is increased to promote nitrification and the nitrification solution is returned to the anaerobic tank via the second nitrification solution circulation pump. An operation control method is provided.

[0019]

By adopting the operation control method of the modified two-stage activated sludge circulation method, the oxygen consumption rate [Nit] for the nitrification reaction in the first aerobic tank by the ATU-rr meter [Nit
-Rr] is measured, the progress of the nitrification reaction in the first aerobic tank is judged by this, and when it is judged from the measurement result that the nitrification reaction in the aerobic tank is completed, By activating the first nitrification solution circulation pump, the nitrification solution in the first aerobic tank is sent to the anaerobic tank, and the denitrification effect is promoted. At the same time, by driving the stirring mechanism of the anaerobic-aerobic tank and stopping the aeration, the anaerobic-aerobic tank substantially functions as an anaerobic tank.
In the aerobic tank, the nitrate nitrogen that has flown out without being denitrified is denitrified by the internal denitrification phenomenon.

When it is judged that the nitrification reaction in the first aerobic tank is not completed based on the oxygen consumption rate [Nit-rr] value concerning the nitrification reaction measured by the ATU-rr meter 14. Of the second aerobic tank, the anaerobic-aerobic tank acts as an aerobic tank by stopping the driving of the stirring mechanism of the anaerobic-aerobic tank and starting aeration from the air diffuser. The volume ratio is expanded and the nitrification reaction is promoted. Then, by activating the second nitrification solution circulation pump, the nitrification solution in the second aerobic tank is sent to the anaerobic tank, and the denitrification effect in the anaerobic tank is promoted.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an operation control method of a two-stage activated sludge circulation modification according to the present invention will be described below with reference to the drawings, in which the same reference numerals are given to the same components as the conventional components. Detailed description. In FIG. 1, 1a is an anaerobic tank, and 2a is a first aerobic tank for nitrification. Further, 13a is a first anaerobic-aerobic tank, 13b is a second anaerobic-aerobic tank, and 2b is a second tank.
Aerobic tanks, each of which is configured by dividing the same biological reaction tank by partition plates 14 and 14 and connected in series.

The anaerobic tank 1a is provided with a stirring mechanism 10 such as a submersible stirrer, and the first aerobic tank 2a and the second aerobic tank 2a.
In the aerobic tank 2b of the air diffuser 4, 4 as an air blowing mechanism
Is arranged. Outside the reaction tank, each of the air diffusers 4,
The blower 5 for supplying air to 4 is provided.

The first and second anaerobic-aerobic tanks 13
A diffuser pipes 4 and 4 are provided in a and 13b together with the stirring mechanisms 10 and 10, and the diffuser pipes 4 and 4 and the blower 5 are provided.
Air flow rate adjusting valves 17 and 17 are provided between and.

Reference numeral 6a denotes a first nitrification solution circulation pump for feeding the nitrification solution from the first aerobic tank 2a to the anaerobic tank 1a, and 6b.
Is a second nitrification solution circulation pump for feeding the nitrification solution from the second aerobic tank 2b to the anaerobic tank 1a.

Reference numeral 7 is a final sedimentation pond, and this final sedimentation pond 7
A part of the sludge discharged from the sludge is returned to the anaerobic tank 1a by the sludge return pump 8. Reference numeral 9 denotes a surplus sludge drawing pump for feeding surplus sludge to a 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, an ATU-rr meter 14 is installed near the rear stage of the first aerobic tank 2a.
The [Nit-rr] value 18 calculated based on the value measured by the TU-Rr meter 14 is input to the controller 19. The output signal of the controller 19 controls the drive states of the blower 5, the air flow rate adjusting valves 17, 17 and the nitrification solution circulation pumps 6a, 6b.

The basic operation of such a device is as follows. As shown in FIG. 1, first, raw water 3 as waste flows into the anaerobic tank 1a, based on the stirring action and the action of denitrifying bacteria stirring mechanism 10 in the water, NO ₃ -N, NO ₂ - N
Reduction of ions to N ₂ , that is, denitrification is performed. Next, raw water 3 flows into the first aerobic tank 2a, and aeration by aeration from the diffuser pipe 4 is performed as the blower 5 is driven. Based on the action of nitrifying bacteria, ammoniacal nitrogen N
Oxidation of H ₄ -N to NO ₂ -N or NO ₃ -N, that is, nitrification is performed. The nitrification speed of the time, can be expressed as a rate of increase in the rate of decrease in ammonia nitrogen, or _{NO X -N (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. Subsequently, the raw water 3 sequentially flows into the second aerobic tank 2b from the first and second anaerobic-aerobic tanks 13a and 13b, and the same denitrification and nitrification as described above are repeated.

During the above operation, the sample sampled from the first aerobic tank 2a is guided to the ATU-rr meter 14,
The ATU-rr meter 14 measures the oxygen consumption rate [Nit-rr] value 18 involved in the nitrification reaction.
It-rr] value 18 is used to determine whether the nitrification reaction has ended. That is, when the nitrification reaction proceeds smoothly and the concentration of ammoniacal nitrogen decreases, the above [Nit
Since the −rr] value 18 also rapidly decreases, it can be seen that this completes the nitrification reaction in the first aerobic tank 2a.

Then, the nitrification solution in the first aerobic tank 2a is sent to the anaerobic tank 1a by activating the first nitrifying solution circulation pump 6a based on the output signal of the controller 19, and the anaerobic tank 1a is operated. The denitrification effect is promoted. At the same time, the nitrification liquid sequentially flows from the first anaerobic-aerobic tank 13a into the second anaerobic-aerobic tank 13b, and at this time, the stirring mechanism 10 of the anaerobic-aerobic tanks 13a and 13b is driven. The air flow rate adjusting valves 17 and 17 are closed to stop aeration from the air diffusers 4 and 4. As a result, the anaerobic-aerobic tanks 13a and 13b substantially function as an anaerobic tank, so that the nitrate nitrogen that has flowed out without being denitrified in the first aerobic tank 2a is stored in the anaerobic-aerobic tanks 13a and 13b. It is denitrified by the internal denitrification phenomenon.

On the other hand, the oxygen consumption rate [Nit-r] related to the nitrification reaction measured by the ATU-rr meter 14 is measured.
If the r] value 18 is large, it is determined that the nitrification reaction in the first aerobic tank 2a has not ended. At this time, the driving of the stirring mechanism 10 of the anaerobic-aerobic tanks 13a and 13b is stopped and the air flow rate adjusting valves 17 and 17 are appropriately opened to control the amount of air blown from the blower 5 so that the ideal nitrification speed is reached. Then, start aeration from the air diffusers 4 and 4. As a result, the anaerobic / aerobic tank 13a,
Since 13b substantially functions as an aerobic tank, the volume ratio of the second aerobic tank 2b is expanded and the nitrification reaction is promoted. Therefore, the second nitrification solution circulation pump 6b is started based on the output signal of the controller 19 to cause the second aerobic tank 2 to operate.
The nitrification liquid in b is sent to the anaerobic tank 1a, and the denitrification effect in the anaerobic tank 1a is promoted.

When the nitrification reaction must be specially enhanced, the driving force of the blower 5 is increased to accelerate the nitrification, while the blower 5 is adjusted to adjust the excessively accelerated nitrification rate when the water temperature is high. The nitrification liquid circulation pumps 6a and 6b for adjusting the nitrification rate to an ideal nitrification rate by appropriately controlling the air flow rate of
Based on the above action, it is possible to increase the removal rate of nitrogen by increasing the returning amount of the nitrification liquid from the aerobic tanks 2a and 2b to the anaerobic tank 1a.

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. It The supernatant of the final settling tank 7 is discharged as treated water 11 after passing through a disinfection tank (not shown).

As described above, the ATU-Rr meter 14 is used to monitor the progress of the nitrification reaction in the first aerobic tank 2a. That is, the oxygen utilization rate (oxygen u
tilization rate respiration, hereafter 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.

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 determined from 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 above difference is [Nit-rr], [Nit-rr] = [rr]-[ATU-rr] (1) That is, the [Nit-rr] value 18 is the oxygen consumption rate associated with nitrification, and if this value is small, it can be determined that the nitrification reaction has ended, and if it is large, the nitrification reaction has not ended.

Since the above [Nit-Rr] represents the oxygen consumption amount based on the nitrification reaction, it is possible to estimate the nitrification rate in the first aerobic tank 2a from this value. From this measurement result, the controller 19 controls the first and second aerobic tanks 2
The ideal nitrification rate and the actual nitrification rate are calculated from the volumes of a and 2b, the hydraulic retention time, etc., and [N
[it-rr] is large and it is necessary to enhance the nitrification reaction, the driving force of the blower 5 is increased to promote nitrification, while at the time of high water temperature or the like, in order to adjust the excessively accelerated nitrification rate. The amount of air blown by the blower 5 is appropriately controlled to adjust to an ideal nitrification rate. Also, the nitrification solution circulation pumps 6a, 6b
The nitrogen removal rate can be increased by increasing the amount of the nitrification solution returned from the aerobic tanks 2a and 2b to the denitrification tank 1a based on the above action to increase the circulation ratio of the solution.

Particularly in this embodiment, the [Nit-rr] value is 1
The progress status of the nitrification reaction in the first aerobic tank 2a is judged based on 8, and when the nitrification reaction is completed, the first and second anaerobic-aerobic tanks 13a and 13b are anaerobic. When the nitrification reaction is not completed, the first and second anaerobic-aerobic tanks 13a and 13b are used as aerobic tanks to increase the denitrification effect. Two
An operational feature is that the volume ratio of b is increased and the nitrification reaction is promoted and then the driving states of the nitrification liquid circulation pumps 6a and 6b are controlled to enhance the denitrification effect of the anaerobic tank 1a. There is.

[0039]

As described in detail above, according to the operating method of the two-stage activated sludge circulation method according to the present invention, raw water is denitrified in the anaerobic tank, aeration in the aerobic tank and nitrifying bacteria are performed. While the nitrification is carried out based on the action of, the progress of the nitrification reaction in the first aerobic tank is judged by the ATU-rr meter from the oxygen consumption rate involved in the nitrification reaction in the first aerobic tank. When the nitrification reaction of the aerobic tank is completed, the denitrifying effect of the anaerobic tank is promoted by starting the first nitrification solution circulation pump, and at the same time, the anaerobic-aerobic tank is substantially used as the anaerobic tank. As a result, the nitrate nitrogen flowing out without being denitrified in the first aerobic tank can be denitrified by the internal denitrification phenomenon.

When it is judged by the ATU-rr meter that the nitrification reaction in the first aerobic tank has not ended, the anaerobic-aerobic tank is made to substantially function as an aerobic tank. As a result, the volume ratio of the second aerobic tank is expanded, and the nitrification reaction can be promoted. At the same time, by activating the first and second nitrification solution circulation pumps, the nitrification solution in the aerobic tank is sent to the anaerobic tank to enhance the denitrification reaction in the anaerobic tank.
The nitrogen removal rate can be increased.

When the nitrification reaction has to be enhanced, the driving force of the blower or the like is increased to accelerate the nitrification, while at the time of high water temperature or the like, the blower air flow rate is adjusted to adjust the nitrification rate that has been excessively promoted. The nitrogen removal rate is increased by increasing the amount of nitrification solution returned from the aerobic tank to the anaerobic tank based on the action of the nitrification solution circulation pump. can do.

Since the nitrification and denitrification reactions are stabilized as described above, it is not necessary to increase the volume of the biological reaction tank as compared with the standard activated sludge method, and it is difficult to secure a site in urban areas. There is an effect that it can be adopted under the conditions. In particular, the amount of electric power and the amount of chemicals used for nitrification can be reduced, which is advantageous in terms of cost.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a specific example of an operation control method of a modified two-stage activated sludge circulation method according to this embodiment.

FIG. 2 is a schematic diagram showing an example of conventional anaerobic-aerobic activated sludge treatment.

FIG. 3 is a schematic view showing an example of a conventional two-stage activated sludge circulation modification method.

[Explanation of symbols]

 1a ... Anaerobic tank 2a ... 1st aerobic tank 2b ... 2nd aerobic tank 4 ... Diffuser pipe 5 ... Blower 6a ... 1st nitrification liquid circulation pump 6b ... 2nd nitrification liquid circulation pump 7 ... Final sedimentation tank 8 ... Sludge return pump 9 ... Excess sludge extraction pump 10 ... Stirring mechanism 13a ... First anaerobic-aerobic tank 13b ... Second anaerobic-aerobic tank 14 ... ATU-Rr meter 17 ... Air flow control valve 19 …controller

Claims (2)

[Claims] 1. An anaerobic-aerobic both-use tank and a second aerobic tank are connected in series to an anaerobic tank for denitrification and a first aerobic tank for nitrification, and a first aerobic tank is connected. In addition to deploying the first nitrification solution circulation pump that sends nitrification solution from the aerobic tank to the anaerobic tank,
A second nitrification solution circulation pump for sending the nitrification solution from the second aerobic tank to the anaerobic tank is provided, and a sludge return pump for returning a part of the sludge discharged from the final settling tank to the anaerobic tank is provided. In the two-stage activated sludge circulation modified method consisting of, an ATU-rr meter is installed at the rear stage of the first aerobic tank,
The progress of the nitrification reaction in the first aerobic tank is judged based on the value measured by the ATU-rr meter, and when the nitrification reaction is completed, the first nitrification solution circulation pump is used. The nitrification solution is returned to the anaerobic tank while the anaerobic-aerobic tank works as an anaerobic tank to enhance the denitrification effect, and when the nitrification reaction is not completed, the anaerobic-aerobic tank is aerobic. A two-stage activity characterized by acting as a tank to increase the volume ratio of the second aerobic tank to promote nitrification and returning the nitrification solution to the anaerobic tank via the second nitrification solution circulation pump. Sludge circulation modified operation control method. 2. The operation control method according to claim 1, wherein the ATU-rr meter is a value obtained by subtracting the oxygen consumption rate associated with the nitrification reaction from the total oxygen consumption rate. .