JP2003285092A - Treatment method for anaerobic/aerobic activated sludge and apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anaerobic/aerobic activated sludge treatment method capable of removing nitrogen and phosphorus in water to be treated stably. <P>SOLUTION: In the anaerobic/aerobic activated sludge treatment method for performing the treatment of organic wastewater in an intermittent aeration tank 4 by biological treatment repeating a cycle comprising an aeration process and a non-aeration process, a predetermined ratio of an aerobic time and an oxygen-free time in the intermittent aeration tank 4 is set to a target ratio α<SB>0</SB>and the time Kx required until the concentration of dissolved oxygen DO becomes a predetermined value or less after the completion of the aeration process is calculated by measuring the DO in the intermittent aeration tank 4 before the front cycle. On the basis of this time Kx, the time of the aeration process and the time of the non-aeration process are controlled so that the ratio of the aerobic time and the oxygen-free time of the cycle of this time becomes the target ratio α<SB>0</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anaerobic / aerobic activated sludge treatment method and apparatus for treating organic wastewater by biological treatment by repeating a cycle consisting of an aeration step and a non-aeration step in an intermittent aeration tank. Is.

[0002]

2. Description of the Related Art Conventionally, an organic substrate in water to be treated such as sewage is biologically treated mainly by activated sludge which is a group of microorganisms in an aeration tank. However, recently, in order to prevent eutrophication in closed water areas, it has been required to remove nutrients such as nitrogen and phosphorus in the water to be treated at the same time as the conventional purpose of removing organic substances. A cost-effective biological treatment method has been introduced for the purpose of removal.

One of biological treatment methods for removing nutrients
As an example, the intermittent aeration type activated sludge method, which is an application of the conventional standard activated sludge method, is often adopted. In this treatment method, the water to be treated is continuously flowed into the activated sludge treatment tank, and the aeration process for performing aeration and the non-aeration process for stopping aeration are alternately repeated to cause biological nitrification / denitrification and release / excess of phosphorus. Treatment by ingestion, nitrogen as nitrogen gas into the atmosphere, phosphorus as accumulated in activated sludge and removed as surplus sludge outside the water treatment system, respectively, and the mixed liquid of biological treatment liquid is solid-liquid in the subsequent settling tank etc. It is a method of separating and discharging supernatant water as treated water.

[0004]

In the intermittent aeration type activated sludge method, facility managers often operate timers for the aeration / non-aeration process, but the aeration / non-aeration process time is set to nitrogen / phosphorus. In many cases, the ratio of aerobic time to anaerobic time for efficient and stable removal was not set, and the original processing capacity of the processing facility was often not exhibited.

In the method of controlling only the aeration step time as disclosed in Japanese Patent Laid-Open No. 5-264426 proposed as a control method for the intermittent aeration type activated sludge method, the non-aeration step time is longer than the aeration step time. There is a problem that it may become too long, and the phosphorus ingested in the sludge is released, and the phosphorus removal performance deteriorates.

Further, as shown in FIG. 2, the actual aerobic time To (DO is a predetermined value or more) and anaerobic time Ta (DO is a predetermined value or less) in the intermittent aeration tank after the aeration process is stopped. Since it changes depending on the time Kx until the value becomes equal to or less than a predetermined value, even if the aeration process time TA and the non-aeration process time TN are controlled, the aerobic time To and the anoxic time Ta are the optimum ratios for removing nitrogen and phosphorus. It was often not.

Various control methods by simulation of the activated sludge treatment method have already been proposed, but when it is applied to an actual facility where various kinds of microorganisms exist and the amount of influent water, components, and other conditions constantly change, many control methods are used. , Which was not practical in terms of cost and management.

An object of the present invention is to solve the above-mentioned problems of the conventional example.

[0009]

The present invention provides a method for treating anaerobic / aerobic activated sludge in which treatment of organic wastewater is carried out by biological treatment by repeating a cycle consisting of an aeration step and a non-aeration step in an intermittent aeration tank, A predetermined ratio of aerobic time and anoxic time in the intermittent aeration tank is set as a target ratio α ₀ , and the DO is determined to be a predetermined value after completion of the aeration step by measuring the dissolved oxygen concentration DO in the intermittent aeration tank before the previous cycle. The time Kx until it becomes below is obtained, and based on this time Kx, the aeration process time and the non-aeration process time are controlled so that the aerobic time and the anoxic time of this cycle become the target ratio α _0. To do.

The operation of the present invention is as follows. That is, nitrogen or phosphorus can be stably removed by the intermittent aeration type activated sludge method by the ratio α of the aerobic time To and the anoxic time Ta.
Is within the optimum range for the processing purpose. If α is not within the optimum range, the nitrogen / phosphorus removal performance deteriorates significantly. For example, when α is out of the optimum range, the required aerobic time cannot be secured, the nitrification / phosphorus absorption reaction does not proceed sufficiently, and the anoxic time becomes too long for the aerobic time. The inside becomes anaerobic, and the phosphorus accumulated in the sludge is released. On the other hand, when α is out of the optimum range and is large, the required anoxic time cannot be secured and the denitrification reaction does not proceed sufficiently. The present invention pays attention to this point, and the optimum α obtained by the experience of experts and the simulation method described later.
Is set as the target ratio α _0, and the aeration process time and non-aeration process time are controlled so that this is always α ₀ , the intermittent aeration tank is operated, and nitrogen and phosphorus in the water to be treated are stably removed. It was made possible. Then, the DO change in the intermittent aeration tank before the previous cycle is measured to obtain the Kx, and based on this Kx, the aeration process time and the non-aeration process time at which the target ratio α ₀ is maintained can be calculated. I did.

For example, when the intermittent aeration tank is operated with the non-aeration process time being constant, the aeration process time is obtained by calculation when α ₀ and Kx are given.

In the above structure, the removal rate of either nitrogen or phosphorus is calculated by an arithmetic unit using a water quality simulation model such as ASM2d based on input values indicating inflow load, activated sludge concentration and other various conditions in the intermittent aeration tank. Or the ratio of aerobic time and anaerobic time at which the total of the removal rates of both is highest, aeration process time, non-aeration process time,
If one of the one cycle time, the aerobic time, and the anoxic time is calculated and the ratio is set to the target ratio α ₀ , the α ₀ can be calculated more accurately and automatically. The optimum aeration process time and the like can be automatically obtained.

Further, in the above structure, the pH of the treatment liquid discharged in or from the intermittent aeration tank and the nitrogen concentration and phosphorus concentration of the treatment liquid discharged from the intermittent aeration tank are measured, and based on these measured values When it is configured to correct the target ratio α ₀ , α obtained by simulation or the like
_It is possible to make ₀ as close as possible to the value suitable for the actual installation, and even if for some reason the initially set α ₀ is not suitable for the actual installation, it becomes possible to automatically correct it.
Nitrogen / phosphorus removal performance can be improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

FIG. 1 is a block diagram showing an anaerobic / aerobic sludge treatment device according to an embodiment of the present invention.

The water to be treated 1 is sent from the intermittent aeration tank or anaerobic tank 2 in the previous stage to the intermittent aeration tank 4 and mixed with the sludge 3, and the aeration device 5 performs biological treatment by repeating a cycle including an aeration step and a non-aeration step. Done. By operating the aeration device 5, the inside of the intermittent aeration tank 4 becomes an aerobic state (the state in which dissolved oxygen exists), the organic substrate contained in the water to be treated is treated, and the nitrogen component reacts with the nitrification reaction (NH ₄ −
The reaction in which N is oxidized to NOx-N) progresses, and the phosphorus component is further taken into the sludge 3. After that, when the aeration device 5 is stopped, the DO in the intermittent aeration tank 4 begins to decrease, and eventually becomes anoxic (a state in which dissolved oxygen does not exist, but NOx-N exists), and a denitrification reaction progresses to nitrify. The nitrogen component is released into the atmosphere as nitrogen gas. Further, when the anoxic state continues and the denitrification reaction is completed, the state becomes anaerobic (a state in which neither dissolved oxygen nor NOx-N exists), and the phosphorus component is released from the sludge 3.

A control device (control means) 8 for controlling the operation of the aeration device 5 has a target ratio considered to be optimum as a ratio α (= T ₀ / Ta) of the aerobic time T ₀ and the anoxic time Ta. α ₀ and the optimum non-aeration process time TN are
It is set.

A DO meter 6 is installed in the intermittent aeration tank 4, and the measured DO is sent to the controller 8. After the aeration process is completed, the control device 8 has a predetermined value of DO (0 to 0.5 mg).
The time Kx until it becomes less than or equal to (about L) is memorized. From the time Kx thus obtained, the target ratio α ₀ , and the non-aeration process time TN, the control device 8 calculates the aeration process time TA by the following equation (1).

TA = α ₀ (TN−Kx) + Kx (1) The controller 8 controls the DO before the previous cycle as described above.
By the measurement, the time Kx is obtained, and the aeration process time TA of the current cycle is obtained based on the time Kx.
Control the operation of.

The Kx before the previous cycle means the Kx of the immediately preceding cycle or the Kx selected based on the past history such as the daily fluctuation or the weekly fluctuation pattern.

The target ratio α ₀ may be determined according to the processing purpose. That is, nitrogen removal, particularly in general as long as emphasis on nitrification may be greater than 1 to alpha _0, the alpha ₀ if the emphasis on phosphorus release in front of the tank in the multistage intermittent aeration It should be as small as possible. Further, α ₀ may be determined based on experience by a skilled manager and manually input to the control device 8, or may be determined by a simulation method described later and automatically input to the control device 8. Good.

Further, the input value of the initial aeration process time TN can be determined from the operation manual or past cases. Although it depends on the purpose of treatment, TN = 30 to 150 minutes is generally common. For example, TN = 60 minutes may be set. The control device 8
The input method may be determined based on the experience of a skilled manager and may be manually input, or the result determined by the simulation method described below may be automatically input.

An example of control of the aeration device 5 by the control device 8 is shown in FIG. In FIG. 2, the vertical axis represents DO in the intermittent aeration tank, and the horizontal axis represents time, showing changes in DO. The length of Kx varies depending on the DO and inflow load conditions at the end of the aeration process. For example, if the DO at the end of the aeration process is high, K
x becomes longer, and conversely, when DO is low, Kx becomes short.
Further, when the inflow load is low, Kx becomes long, and conversely, when the inflow load is high, Kx becomes short. In the present embodiment, the aeration step time TA is calculated by calculation (the non-aeration step time TN is constant) so as to adapt to the length of Kx, and the above α is always the target ratio α ₀ .

The processing liquid 7 processed in the intermittent aeration tank 4 is sent to the solid-liquid separation tank 17 in the subsequent stage. In the solid-liquid separation tank 17, sludge in the liquid settles to the bottom of the tank due to gravity settling, and the supernatant liquid is discharged outside the system as treated water 18. The sludge settling at the bottom of the tank is in a state of ingesting a phosphorus component, part of which is sent to the anaerobic tank 2 as return sludge 19, and part of it is discharged to the outside of the system as excess sludge 20. When the anaerobic tank 2 is not set, the returned sludge 19 is returned to the intermittent aeration tank. Further, in FIG. 1, the solid-liquid separation tank 17
Is shown by gravity settling (generally called a settling tank), but other solid-liquid separation means such as membrane separation or pressure floating separation may be used.

The target ratio α ₀ and the non-aeration process time T
There is a method of using simulation as a method of calculating N. Specifically, the items shown in Table 1 are input to the arithmetic unit 9 in which the reactions shown in Table 2 are programmed, and a simulation is performed by combining several hundred to several thousand patterns of the aeration process time TA and the non-aeration process time TN. , The removal rate of either phosphorus, or the range of α ₀ and the aeration step time TA or the non-aeration step time TN in which the removal rate of both is the highest.

The simulation here means
IAWQ (International Association on Water Quali
ty; ASM2d (IA
WQ Activated Sludge Model No.2d)
This is done using a water quality simulation model created using commonly used computer languages such as isual Basic, FORTRAN, and C language.

[0027]

[Table 1]

[0028]

[Table 2] An example of how to obtain the target ratio α ₀ and the non-aeration process time TN by simulation is shown below.

Input to the arithmetic unit Table 1 is shown in the arithmetic unit 9 in which the reactions shown in Table 2 are programmed.
Enter the inflow load, activated sludge concentration, and other conditions shown in. The input to the arithmetic unit 9 may be an automatic input by an automatic measuring device, or if the value does not change frequently, the value collected and analyzed at a certain point in time, and there is not much difference in the value between treatment facilities. For items that are not, you may manually enter the values quoted from documents etc. as representative values. When inputting automatically, as shown in FIG. 1, a component analyzer 13 (for example, a BOD meter, a nitrogen concentration meter, a phosphorus concentration meter, etc.) of the organic wastewater 12, an inflow flow meter 14 and an MLSS meter 15 in the intermittent aeration tank 4. May be installed, and the inflow load and the activated sludge concentration may be input to the arithmetic unit 9. Moreover, it is also effective to judge the state of the inflow load from the DO reduction rate of the intermittent aeration tank 4 when the aeration process is changed to the non-aeration process. Although a measuring device not shown in the present embodiment may be used for input to the arithmetic unit 9, it is advantageous from the viewpoint of cost and management to limit the measuring device to the minimum required device. Creation of Optimal Operating Range Graph Next, a simulation is performed by the arithmetic unit 9 by a combination of several hundred to several thousand patterns of aeration process time TA and non-aeration process time TN, and the result is α on one axis and non-aeration on the other axis. When the aeration step time TN is represented and the removal rates of nitrogen and phosphorus are represented by contour lines, a graph as shown in FIG. 3 can be created. Although FIG. 3 shows the total removal rate of nitrogen and phosphorus by contour lines, the contour line of the removal rate may be selected according to the target processing purpose.
That is, if nitrogen removal is emphasized, only the nitrogen removal rate may be represented by contour lines as shown in FIG. 4, and if phosphorus removal is emphasized, only phosphorus removal rate may be represented by contour lines as shown in FIG. . Although the frequency of performing the simulation is not particularly limited, it is preferable to increase the frequency when the input value changes frequently such as when the inflow load is largely changed.

From this graph, a region (the range of 1.55 in FIG. 3) where the removal rate of nitrogen or phosphorus or the sum of the removal rates of both is highest is determined, and the coordinates near the center of the region are determined to be the highest. The target ratio α ₀ and the non-aeration process time TN (α ₀ = 1.20, TN = 30 minutes in the case of FIG. 3) can be determined by determining that the removal rate is high and stable.

These values α ₀ and TN are automatically input from the arithmetic unit 9 to the control unit 8 and stored in the control unit 8.

Although the control device 8 and the arithmetic device 9 are separate devices in the present embodiment, it is also possible to use a device in which the control device 8 and the arithmetic device 9 are integrated.

Further, in the present embodiment, the target ratio α ₀ and the non-aeration process time TN are obtained by simulation, but the non-aeration process time TN is defined as the aeration process time TA, the cycle time Tc, and the aerobic time To. , And the anoxic time Ta may be replaced.

In the apparatus shown in FIG. 1, the target ratio α
₀ and the non-aeration process time TN are given to the controller 8 in advance, and Kx
Although the aeration process time TA is calculated based on the change in the treatment, the treatment is performed, but when the target treated water quality cannot be achieved by such treatment, the nitrogen / phosphorus automatic analyzer (nitrogen / phosphorus concentration shown in Fig. 1 Nitrogen concentration, phosphorus concentration and p of the treatment liquid discharged from the intermittent aeration tank 4 measured by the measuring instrument 22
Based on the pH of the treatment liquid discharged in or from the intermittent aeration tank 4 measured by the H meter 11, as shown in Table 3, by gradually increasing or decreasing the target ratio α ₀ , a more actual result can be obtained. It will be possible to perform operation suitable for the facility.

[0035]

[Table 3] With reference to Table 3 above, a method of correcting the α ₀ by the control device 8 will be specifically described.

When the target value of the treated water nitrogen (TN) concentration is 10 mg / L and the target value of the treated water phosphorus (TP) concentration is 1.0 mg / L in the general composition sewage treatment,
There are the following three main reasons why the target value cannot be achieved, and the control device 8 corrects α ₀ so as to cope with the following three reasons. The nitrogen component detected as the NH ₄ —N residual treated water (TN) concentration in the treated water is usually almost NO ₃ —N. However, if the alpha ₀ is too small, for example when the alpha ₀ in an intermittent aeration tank which is intended to nitrification and denitrification set to 0.5 because the nitrification does not proceed sufficiently, NО ₃ -N in the treated water Less, NH ₄
-N may remain. At this time, the pH in the intermittent aeration tank 4 is higher than usual (generally, about 6.7 to 7.0 or higher). Therefore, when the treated water (TN) concentration is equal to or higher than the target value, it is determined that α ₀ is smaller than the pH of the intermittent aeration tank 4, and the α ₀ is gradually increased. Residual NO ₃ -N in treated water As described above, the nitrogen component detected as the concentration of treated water (TN) is usually almost NO ₃ -N. However, since the case alpha ₀ is too large, for example when the alpha ₀ in the intermittent aeration tank 4 that the nitrification and denitrification purposes set 2.5, nitrification can proceed sufficiently denitrification does not proceed, sometimes in the treated water NО ₃ -N remains at a high concentration. At this time, in the intermittent aeration tank 4, only nitrification proceeds and denitrification does not proceed (normally denitrification raises the pH), so p
H decreases (generally, 6.0 to 6.3 or less).
Therefore, when the treated water (TN) concentration is equal to or higher than the target value, it is determined that the α ₀ is higher than the pH of the intermittent aeration tank 4, and the α ₀ is gradually reduced. The phosphorus component detected as the concentration of PO ₄ -P residual treated water (TP) in the treated water is usually almost PO ₄ -P. However, if the alpha ₀ is too small, for example when the alpha ₀ in an intermittent aeration tank which is intended to phosphorus absorption is set to 0.5, the result of anoxia time phosphorus absorption does not proceed sufficiently is too long An anaerobic condition occurs, and phosphorus absorbed by the activated sludge is released to the outside of the cell, so that PO ₄ -P may remain at a high concentration in the treated water. At this time, the pH in the intermittent aeration tank 4 is higher than usual (generally, about 6.7 to 7.0 or higher). Therefore, when the treated water (TP) concentration is equal to or higher than the target value, p of the intermittent aeration tank 4 is increased.
It is determined that α ₀ is smaller than H, and α ₀ is gradually increased.

It is desirable that the gradual increase and the gradual decrease of α ₀ be performed within the range where the removal rate is the highest obtained by the above simulation. That is, in the case of FIG. 3, the non-aeration process time TN may be fixed (30 minutes), and the α ₀ may be gradually increased or decreased in the range of 0.9 to 1.4. In addition, continuous measurement with an automatic analyzer is preferable for measuring nitrogen and phosphorus concentrations, but if the measured values do not fluctuate with time or day, the control device uses the result of actual water sampling at a certain point as a representative value. You may manually enter 8.

[0038]

As described in detail above, according to the present invention, nitrogen and phosphorus in the water to be treated can be stably removed.

Further, according to the present invention, it is possible to obtain the optimum range of the target ratio α ₀ and the time such as the non-aeration process time by simulation, and it is possible to remove nitrogen and phosphorus in the water to be treated with higher accuracy. It can be performed.

Further, according to the present invention, the target ratio α
By correcting ₀ , it is possible to perform processing more suitable for the implementation.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of an aeration / non-aeration process.

FIG. 3 is a diagram showing an example of a nitrogen / phosphorus removal simulation.

FIG. 4 is a diagram showing an example of a nitrogen removal simulation.

FIG. 5 is a diagram showing an example of a phosphorus removal simulation.

[Explanation of symbols]

2 Anaerobic tank 4 Intermittent aeration tank 5 Aeration device 6 DO meter 8 control device 9 arithmetic unit 17 Solid-liquid separation tank 22 Nitrogen and phosphorus automatic analyzer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Ohara             Matsushita 3-28-33, Tarumi-cho, Suita City, Osaka Prefecture             Environmental Air Conditioning Engineering Co., Ltd. Osaka             Within the branch F term (reference) 4D040 BB22 BB32 BB72 BB91

Claims (6)

[Claims] 1. Treatment of organic wastewater in an intermittent aeration tank
For repeating cycle consisting of aeration process and non-aeration process
Odor of anaerobic and aerobic activated sludge treated by biological treatment
The aerobic time and anoxic time in the intermittent aeration tank.
The constant ratio is the target ratio α₀Set as before the previous cycle
Aeration process by measuring the dissolved oxygen concentration DO in the intermittent aeration tank
Time Kx from the end to the time when the DO becomes below a predetermined value
And based on this time Kx, the aerobic time of this cycle
And the anoxic time is the target ratio α ₀Aeration process so that
Anaerobic characterized by controlling the time and non-aeration process time
-Aerobic activated sludge treatment method. 2. The ASM2 based on input values indicating inflow load, activated sludge concentration, and other various conditions in the intermittent aeration tank.
By using an arithmetic unit using a water quality simulation model such as d, the removal rate of either nitrogen or phosphorus or the sum of the removal rates of both is highest, the ratio of aerobic time and anoxic time, aeration process time, non-aeration Process time, 1 cycle time,
2. One of aerobic time and anaerobic time is obtained, and the ratio is set to the target ratio α _0.
Anaerobic / aerobic activated sludge treatment method described. 3. The pH of the treatment liquid discharged in or from the intermittent aeration tank and the nitrogen concentration and phosphorus concentration of the treatment liquid discharged from the intermittent aeration tank are measured, and the target ratio is determined based on these measured values. The anaerobic / aerobic activated sludge treatment method according to claim 1 or 2, wherein α ₀ is corrected. 4. An anaerobic / aerobic activated sludge treatment device for treating organic wastewater by biological treatment by repeating a cycle of an aeration process and a non-aeration process in an intermittent aeration tank, wherein the intermittent aeration tank for performing the biological treatment. And a DO meter for measuring the dissolved oxygen concentration DO in the intermittent aeration tank, a predetermined ratio of aerobic time and anoxic time in the intermittent aeration tank is set as a target ratio α ₀ , and the aeration process time, Non-aeration process time, 1 cycle time, aerobic time,
Any one of the anaerobic time is set, and the time Kx from the end of the aeration step until the DO becomes below a predetermined value is obtained based on the measurement result before the previous cycle of the DO meter, and the time Kx of this time is calculated based on this time Kx. An anaerobic / aerobic activated sludge treatment device, comprising: control means for controlling the aeration process time and the non-aeration process time so that the aerobic time and the anoxic time of the cycle become the target ratio α _0. . 5. The ASM2 based on input values indicating inflow load, activated sludge concentration, and other various conditions in the intermittent aeration tank.
An arithmetic unit using a water quality simulation model such as d, wherein the removal rate of either nitrogen or phosphorus or the sum of the removal rates of both is highest, the ratio of aerobic time and anoxic time, and the aeration process time, Aeration process time, 1 cycle time,
An arithmetic unit for determining any one of the aerobic time and the anaerobic period is provided, and the ratio obtained by this arithmetic unit is input to the control means together with any one of the times as the target ratio α _0. The anaerobic / aerobic activated sludge treatment device according to claim 4, which is configured as follows. 6. A pH meter for measuring the pH of a treatment liquid discharged in or from the intermittent aeration tank, and a nitrogen / phosphorus concentration for measuring the nitrogen concentration and the phosphorus concentration of the treatment liquid discharged from the intermittent aeration tank. And a control unit for controlling the target ratio α based on the measured pH, nitrogen concentration, and phosphorus concentration.
The anaerobic / aerobic activated sludge treatment device according to claim 4 or 5, which has a function of correcting ₀ .