JP2000051892A - Method and apparatus for nitrating waste water and activity detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the subject method and apparatus capable of obtaining proper nitration capacity in nitration treatment in a nitration tank and capable of ensuring proper aeration quantity and achieving the conservation of energy and an activity detector capable of reducing the damage of a carrier to the most. SOLUTION: The NH4-N concn. in a nitration tank 16 and the nitration speed of a carrier 11 are measured and, when the measured NH4-N concn. is 0.3 mg/l or more, the aeration quantity from a blower 18 is increased to adjust the concn. of dissolved oxygen in the nitration tank 16 to maximize a nitration speed. When the NH4-N concn. is less than 0.3 mg/l, the aeration quantity is reduced so as to return the NH4-N concn. in the nitration tank to 0.3 mg/l and the nitration speed is again controlled based on DO concn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for nitrifying wastewater and an activity detector, and more particularly to an improvement in nitrification treatment for removing ammonia nitrogen in wastewater such as sewage.

[0002]

2. Description of the Related Art In a nitrogen removal apparatus for wastewater provided with a denitrification tank and a nitrification tank, nitrifying bacteria oxidize ammonia nitrogen (NH ₄ -N) to nitrite nitrogen or nitrate nitrogen in the nitrification tank. Is performed. Then, in actual wastewater treatment such as sewage, in order to maintain a stable high nitrogen removal rate against fluctuations in the ammonia nitrogen load of the wastewater raw water and annual fluctuations or daily fluctuations in the water temperature, it is necessary to use a nitrification tank. It is necessary to complete the nitrification treatment almost completely.

[0003] However, nitrifying bacteria are autotrophic bacteria,
The growth reaction is extremely slow compared to general heterotrophic bacteria such as denitrifying bacteria. Therefore, in the nitrification reaction using suspended sludge, it is important to strictly control the residence time (hereinafter referred to as “SRT”) of the suspended sludge in order to retain nitrifying bacteria in the suspended sludge and obtain high nitrification performance. . The nitrification performance is
It is relatively susceptible to the concentration of dissolved oxygen (hereinafter referred to as "DO concentration") dissolved in the wastewater in the nitrification tank, and appropriate management of the DO concentration is required.

For this reason, in the case of a wastewater nitrogen removal apparatus in which only suspended sludge is floated in a nitrification tank for nitrification treatment as in the activated sludge circulation modified method, the residence time of wastewater raw water in the nitrification tank is 7 to 9 times. It is necessary to control the two factors of SRT and DO concentration after preparing conditions for ensuring a long SRT for keeping nitrifying bacteria in suspended sludge even in the winter period. In addition, many items such as the amount of raw wastewater and the sludge concentration (MLSS) are measured, and the sludge which is a direct factor in controlling the DO concentration of the SRT by making full use of the kinetic equation and the like on the measured data. It was necessary to calculate the target values of the amount of extraction and the amount of aeration of the aerator of the nitrification tank. As described above, in the case of the suspended sludge type nitrogen removing apparatus, since the two factors of SRT and DO concentration are simultaneously controlled, the control system becomes complicated and it is difficult to perform high-precision control.

[0005] From such a background, a nitrifying bacterium which can stably retain a high concentration of nitrifying bacteria in the system of the apparatus, which is the biggest problem of the suspended sludge type nitrogen removing apparatus, has been proposed. A microorganism-immobilized carrier having immobilized
A nitrification-promoting type nitrogen removal device (commonly referred to as a nitrification-promoting modified circulation method) in which a "carrier" is added into a nitrification tank has been developed. In this nitrification-promoting type nitrogen removal device, the nitrification reaction is promoted even at a low water temperature in winter, so that the residence time of the raw wastewater in the nitrification tank can be reduced to about 3 hours. In addition, among the carrier and suspended sludge coexisting in the nitrification tank, most of the nitrification reaction is borne by the carrier, and there is no outflow of the carrier from the nitrification tank. Need not be strictly managed. Thus, there is a great merit that only the DO concentration of the SRT and the DO concentration needs to be managed. For this reason, in the nitrification-promoting type wastewater nitrogen removing apparatus, a nitrification method of performing nitrification while maintaining a constant amount of aeration in the nitrification tank has been performed.

[0006]

However, according to the conventional nitrification method for performing nitrification with a constant aeration amount, it is difficult to control the ammonia nitrogen concentration which fluctuates daily with an appropriate aeration amount. It is easy for excess or deficiency to occur. As a result, if the aeration is insufficient, the quality of the treated water is deteriorated, and if the aeration is excessive, there is a disadvantage that the blower power cost for the aeration is wasted.

FIG. 10 shows an example in which sewage is actually treated while the aeration amount of the nitrification tank is kept constant throughout the year. As can be seen from this result, when the ammonia nitrogen concentration in the wastewater raw water decreases at a high water temperature, the ammonia nitrogen concentration in the nitrification tank falls to, for example, about 0.1 mg / L, but the DO concentration in the nitrification tank at this time becomes lower. 6 mg / L was exceeded. This clearly indicates that the aeration amount tends to be excessive.

As a countermeasure, a nitrification method for nitrifying while maintaining a constant DO concentration in a nitrification tank has been attempted. However, in this nitrification method, it is necessary to increase the nitrification rate when the ammonia nitrogen concentration rises extremely or when the temperature of the wastewater decreases, but when the DO concentration is kept constant, a sufficient nitrification rate is obtained. It becomes difficult to obtain. As a result, the ammonia nitrogen concentration of the treated water increases. Conversely, if the ammonia nitrogen concentration is extremely low or the temperature of the wastewater is high, the nitrification performance can have a margin, so that the DO concentration becomes too high with respect to the ammonia nitrogen concentration, resulting in excessive aeration. You are doing. As a result, not only will the blower power cost be wasted, but also the sludge sedimentation in the final sedimentation tank due to the disintegration of the floc from the suspended sludge will lower the quality of the treated water, and the dissolved water will be introduced into the denitrification tank due to the circulation of nitrification liquid. Increased oxygen content inhibits denitrification reactions that require anaerobic conditions. In particular, blower power costs account for a significant proportion of the total power cost of nitrogen removal equipment,
It is not preferable from the viewpoint of energy saving.

Incidentally, in the case of a nitrification-promoting type nitrogen removing apparatus in which a carrier is added to a nitrification tank, the nitrification rate of the carrier is measured by an activity detector to accurately grasp the operation, and operation is performed so as to exhibit the maximum nitrification rate. It is necessary. However, the conventional activity detection device has a drawback that the carrier is damaged by abrasion or the like when a part of the nitrification solution (measurement liquid) in the nitrification tank and a part of the carrier are supplied to the activity detection device. is there. The reason why the carrier is worn is that the carrier is damaged when the carrier passes through a pump for sending the carrier from the nitrification tank to the measurement tank of the activity detecting device. In addition, the damage rate of the carrier that causes this damage increases as the time for replacing the liquid to be measured containing the carrier in the measurement tank increases. If the carrier is damaged, the nitrification tank must be replenished with the carrier every time measurement is performed, which is not economical, and returning a damaged carrier to the nitrification tank is a factor that deteriorates the nitrification performance.

[0010] Conventionally, there has been no activity detection for detecting an accurate nitrification rate with respect to the ammonia nitrogen concentration, which is one of the causes of the excess or deficiency of the aeration amount. For this reason, there has been a demand for an activity detection device capable of accurately detecting the nitrification rate without damaging the carrier. The present invention has been made in view of such circumstances, and it is possible to obtain appropriate nitrification performance in nitrification treatment in a nitrification tank, and to eliminate waste of excess or insufficient aeration and save energy. It is an object to provide a nitrification method and apparatus.

It is another object of the present invention to provide an activity detecting device capable of minimizing damage to a carrier.

[0012]

According to the present invention, in order to achieve the above object, the microorganism immobilizing carrier and waste water added to the nitrification tank by aerating air from aeration means to the waste water in the nitrification tank. In the wastewater nitrification method of nitrifying ammonia nitrogen in the wastewater by contacting under aerobic conditions, the nitrification rate of the ammonia nitrogen concentration in the nitrification tank and the microorganism immobilization carrier was measured, If the measured ammonia nitrogen concentration is equal to or higher than a predetermined value, the dissolved oxygen concentration in the nitrification tank is adjusted so that the nitrification rate becomes the maximum nitrification rate by controlling the amount of aeration from the aeration means, When the ammonia nitrogen concentration falls below the predetermined value, the ammonia nitrogen concentration is adjusted to the predetermined value by controlling the amount of aeration from the aeration means and adjusting the dissolved oxygen concentration in the nitrification tank. And returning at least the value.

[0013] Further, in order to achieve the above object, the present invention provides a method for aerating a wastewater in a nitrification tank by aerating air from an aeration means to form the microorganism-immobilized carrier and the wastewater added in the nitrification tank under aerobic conditions. In a waste water nitrification device for nitrifying ammonia nitrogen in the waste water by contacting under, an activity detection device for measuring the nitrification rate of the ammonia nitrogen concentration in the nitrification tank and the microorganism immobilizing carrier, The amount of aeration of the aeration means based on the ammonia nitrogen concentration measured by an activity detector and the nitrification rate of the microorganism-immobilized carrier,
When the ammonia nitrogen concentration is equal to or higher than a predetermined value, the nitrification rate is increased by increasing and adjusting the dissolved oxygen concentration in the nitrification tank, and when the ammonia nitrogen concentration falls below the predetermined value. And control means for controlling the concentration of dissolved oxygen in the nitrification tank so as to reduce the concentration of ammonia nitrogen to a value equal to or higher than the predetermined value.

According to the present invention, the ammonia nitrogen concentration in the nitrification tank and the nitrification rate of the microorganism-immobilized carrier are measured, and when the measured ammonia nitrogen concentration is a predetermined value or more, the amount of aeration from the aeration means is measured. Is controlled to adjust the dissolved oxygen concentration in the nitrification tank so that the nitrification rate is maximized. That is, if the ammonia nitrogen concentration in the nitrification tank is equal to or higher than a predetermined value, the nitrification speed is controlled by the DO concentration without being affected by the ammonia nitrogen concentration. Can be. Therefore, by controlling the amount of aeration so that the DO concentration attains the maximum nitrification rate, appropriate nitrification performance in the nitrification treatment can be obtained, and the amount of aeration does not become excessive or insufficient. Further, when the ammonia nitrogen concentration falls below a predetermined value, the nitrification speed is affected by the ammonia nitrogen concentration in addition to the DO concentration, so that the nitrification speed cannot be accurately controlled by the DO concentration. For this reason, even if the amount of aeration is controlled so that the DO concentration attains the maximum nitrification rate, the amount of aeration is too large and adversely affects the denitrification tank. Therefore, in this case, after reducing the amount of aeration so that the ammonia nitrogen concentration in the nitrification tank returns to the predetermined value, the nitrification rate is controlled again with the DO concentration.

In order to achieve the above object, a measuring tank to which a liquid to be measured and a microorganism-immobilized carrier in a nitrification tank are supplied, an aeration means for measurement for aerating air into the measuring tank, A DO measuring means for measuring the concentration of dissolved oxygen in the measuring tank; and an activity detecting device for measuring the concentration of ammoniacal nitrogen in the nitrifying tank and the nitrification rate of the microorganism-immobilized carrier added to the nitrifying tank. The inside of the nitrification tank, a reaction unit containing the microorganism-immobilized carrier, a separation unit that divides the liquid to be measured into and out of a separation unit that does not contain the microorganism-immobilized carrier, A first feeding means for feeding the liquid to be measured containing the microorganism-immobilized carrier to the measuring tank, and a second feeding means for feeding only the liquid to be measured from the separating section to the measuring tank, Switching between the first feeding means and the second feeding means And switching means that, characterized by comprising a.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method and apparatus for nitrifying waste water and the activity detecting apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. First, the theoretical basis in the nitrification method of the present invention will be described. The inventors investigated the influence of various factors affecting the nitrification rate in order to find a control index when a carrier having microorganisms immobilized thereon was added to a nitrification tank. First, the ammonia nitrogen concentration (hereinafter referred to as “NH ₄ -N concentration”)
) Will be described.

The effect of NH ₄ —N concentration on the nitrification rate was investigated when a carrier was added to the nitrification tank and the actual sewage was continuously treated as wastewater. As a nitrogen removing apparatus for the test, the reaction tank was composed of a denitrification tank and a nitrification tank, and the nitrification tank ratio (the ratio of the nitrification tank volume to the entire reaction tank) was 0.4. The carrier addition amount (volume ratio of carrier per nitrification tank volume) was 7.5% by volume. The residence time of the raw wastewater in the reaction tank was set to be about 6 to 8 hours. The carrier and suspended sludge were collected from the nitrification tank, and the respective nitrification rates were measured.

FIG. 1 shows the relationship between the NH ₄ —N concentration in the nitrification tank and the nitrification rate of the carrier in the continuous treatment, and FIG. 2 shows the relationship between the NH ₄ —N concentration and the nitrification rate of the suspended sludge. In each case, the nitrification rate was converted into a value at a water temperature of 20 ° C. using a temperature coefficient obtained empirically. As is clear from FIGS. 1 and 2, the nitrification rate was greatly affected by the NH ₄ —N concentration in both the carrier and the suspended sludge. That is, in the case of a carrier, the NH ₄ —N concentration is 0.3 mg /
If L or more, the nitrification rate becomes constant at the maximum value. When the NH ₄ —N concentration falls below 0.3 mg / L, the nitrification rate sharply decreases. Depending on the total nitrogen (TN) load of the nitrification tank, the nitrification rate is approximately 100 to 550 mg-O ₂ / L. L
-It changed greatly in the range of the carrier.h.

On the other hand, in the case of suspended sludge, the nitrification rate became constant at the maximum value when the NH ₄ -N concentration was 0.2 mg / L or more, which was slightly lower than that in the case of the carrier. In addition, when the amount was less than 0.2 mg / L, the amount rapidly decreased. However, the total nitrogen in the nitrification tank (T-
N) The change in the nitrification rate depending on the load amount is approximately 2 to 5.5 m.
The range was g-O ₂ / g · SS · h, which was considerably smaller than that of the carrier.

[0020] From the above results, the carrier and the floating sludge, unlike the effect of NH ₄ -N concentration on the nitrification rate, NH ₄ -N
When the concentration is lower than 0.3 mg / L, the nitrification rate of the carrier is remarkably reduced as compared with the suspended sludge. This is considered to be because the nitrifying bacteria are fixed on the surface or inside of the carrier in the case of the carrier, and therefore have lower affinity for ammonia nitrogen than the suspended sludge. In addition, the suspended sludge circulates between the denitrification tank, the nitrification tank, and the final sedimentation tank, while the carrier is held in the nitrification tank and is always under aerobic conditions, so the low NH ₄ -N concentration is low. Below, it is considered that the autolysis of nitrifying bacteria is likely to proceed.

From these results, the inventors have found that the nitrification rate is not affected by the NH ₄ —N concentration unless the NH ₄ —N concentration in the nitrification tank is lower than 0.3 mg / L. I got Next, the nitrification sharing ratio of the carrier in the nitrification rate of the entire nitrification tank will be described. From the nitrification rates of the carrier and suspended sludge, the ratio of the carrier to the nitrification rate of the entire nitrification tank in the continuous treatment was determined. The nitrification rate in the entire nitrification tank was calculated from the following equation (1).

[0022]

[N−Kr] _T = [N−Kr] _P · η + [N−Kr] _S · X · (1−η) (1) where [N−Kr] _{T is the} nitrification tank Nitrification rate related to nitrification (mg-O ₂ / L · tank / h) [N-Kr] _P : nitrification rate of carrier [N-Kr] _S : nitrification speed of suspended sludge η: amount of carrier added (per nitrification tank volume) X: Suspended sludge concentration (g-SS / L) Further, the nitrification sharing ratio [P _N ] of the carrier in the entire nitrification tank was defined by the following equation (2) based on the nitrification rate. .

[0023]

(Equation 2) FIG. 3 shows the relationship between the nitrification sharing ratio [P _N ] of the carrier and the NH ₄ —N concentration in the nitrification tank in the case of actual sewage treatment (η = 0.075).

As can be seen from FIG._Four-N concentration
In the vicinity of 0.2 mg / L, the nitrification sharing ratio of the carrier [P_N〕But
About 0.5, but NH_Four-N concentration 0.3mg / L or less
On the top, the nitrification sharing ratio of the carrier [P_NIs stable.
Maintain a high value of about 9. This is NH_Four-N concentration
If it is less than 0.3 mg / L, the carrier will float as described above.
Less affinity for ammonia nitrogen than sludge
The nitrification sharing ratio of the carrier [P _N] Is relatively small
It is considered that the share ratio of suspended sludge increases. one
One, NH_FourWhen the -N concentration is 0.3 mg / L or more,
The nitrification share ratio is significantly higher than that of suspended sludge,
It governs about 90% of the body's nitrification rate.

From these results, the inventors have found that if the NH ₄ —N concentration in the nitrification tank does not fall below 0.3 mg / L,
It has been found that the carrier substantially controls the nitrification rate of the entire nitrification tank. Next, the effect of the DO concentration on the nitrification rate will be described. As the nitrogen removal apparatus used for the test, a reaction tank composed of a denitrification tank and a nitrification tank was used in the same manner as described above, and synthetic sewage was used as the wastewater used for the test.

The nitrification tank ratio in the whole reaction tank is 0.2,
The carrier addition amount was 20% by volume, and the DO concentration in the nitrification tank was 5 to 5.
The concentration was changed to three stages of 1.5, 3.0, and 5.0 mg / L every 10 days, and the effect of the DO concentration on the nitrification rate was examined. The nitrification tank ratio was set to 0.4, the carrier addition amount was set to 10% by volume, and the DO concentration in the nitrification tank was changed in units of time, and the effect of the DO concentration on the nitrification rate was examined. The residence time of the wastewater in the reaction tank was fixed at 8.5 hours, and the nitrification liquid circulation ratio (the ratio of the nitrification liquid circulation amount to the raw water amount, including the returned sludge ratio) was 3.5.

[0027] Then, in the NH ₄ -N concentration 0.3 mg / L satisfies more 1.5 mg / L or more NH ₄ -N concentration conditions that can be regarded as nitrification speed is not affected by the NH ₄ -N concentration, nitrification The relationship between speed and DO concentration was investigated. FIG.
FIG. 6 shows the case where the O concentration was changed every 5 to 10 days.
Is a case where the DO concentration is changed in units of time.

As can be seen from FIGS. 5 and 6, in each case, the nitrification rate is greatly affected by the DO concentration in the nitrification tank, and the half-saturation constant [K _S ] for the DO concentration is 9.1.
The following formula (3) of a Monod type of ９9.2 mg / L was obtained.

[0029]

(Equation 3) Here, K _N max: the maximum nitrification rate under conditions where the nitrification rate is not affected by the ammonia concentration DO: the DO concentration in the nitrification tank k: the constant K _S : the half-saturation constant relating to the DO concentration (mg / L) This half-saturation constant [K _S ] is reported to be as low as about 0.4 to 2 mg / L in nitrification by suspended sludge, whereas in the case of a nitrification tank using a carrier, as can be seen from the above results, A high value of 9 mg / L or more was obtained.
This means that the nitrification rate by the carrier is greatly affected by the DO concentration as compared with the suspended sludge.

From these results, the inventors have found that when a nitrification reaction is carried out by adding a carrier to a nitrification tank, in order to obtain a maximum nitrification rate [K _N max] commensurate with the NH ₄ —N concentration of the wastewater,
It has been found that accurate control can be achieved by controlling the DO concentration in the nitrification tank, that is, the amount of aeration. In other words, when the carrier is added to the nitrification tank to perform the nitrification reaction,
It means that the maximum nitrification performance can be obtained by properly controlling the aeration amount 1 factor.

From the results described above and above, the following findings could be obtained as a control index when a carrier in which microorganisms were immobilized was added to the nitrification tank. (1) If the NH ₄ —N concentration in the nitrification tank does not fall below 0.3 mg / L, the ammonia nitrogen concentration does not affect the nitrification rate of the carrier.

(2) The NH ₄ —N concentration in the nitrification tank is 0.3 mg
If it is not less than / L, the nitrification rate of the entire nitrification tank (total nitrification rate of the carrier and suspended sludge) is governed by the nitrification rate of the carrier. (3) The nitrification rate of the carrier is greatly affected by the DO concentration in the nitrification tank, and in order to obtain a maximum nitrification rate [K _N max] corresponding to the NH ₄ -N concentration of the wastewater, the DO concentration in the nitrification tank is That is, it can be performed accurately by controlling the amount of aeration.

The present invention is based on the findings of the above (1) to (3), and based on the findings of the above (1) to (3), air is aerated from the aeration means to the wastewater in the nitrification tank, and the microorganism-immobilized carrier and wastewater added to the nitrification tank are combined with the wastewater. In the wastewater nitrification method of nitrifying the ammonia nitrogen in the waste water by contacting it under aerobic conditions, the ammonia nitrogen concentration in the nitrification tank and the nitrification rate of the microorganism-immobilized carrier are measured, and the measurement is performed. When the ammonia nitrogen concentration obtained is equal to or higher than a predetermined value, the dissolved oxygen concentration in the nitrification tank is adjusted so that the nitrification rate becomes the maximum nitrification rate by controlling the amount of aeration from the aeration means, and the ammonia When the nitrogen concentration falls below the predetermined value, the ammonia nitrogen concentration is returned to the predetermined value or more by controlling the amount of aeration from the aeration unit and adjusting the dissolved oxygen concentration in the nitrification tank. Yo It is those that you have configured.

FIG. 6 shows a nitrogen removal apparatus 40 incorporating the nitrification apparatus 10 of the present invention.
4 and one nitrification tank 16. The wastewater supplied from the raw water supply pipe 12 to the denitrification tank 14 is
After being mixed with the suspended sludge, the mixture flows into the nitrification tank 16 to which the carrier has been added. The ammonia nitrogen in the wastewater flowing into the nitrification tank 16 is nitrified by the carrier and suspended sludge under aerobic conditions by aeration from the blower device 18 to become a nitrification liquid. Then, a part of the nitrification liquid including the suspended sludge is circulated to the denitrification tank 14 through the nitrification liquid circulation path 20, is subjected to the denitrification treatment, and is released as nitrogen gas. The remaining nitrification liquid is sent to the final sedimentation tank 22, where the sludge is settled and separated to become treated water. A part of the settled sludge settled in the final settling tank 22 is returned to the denitrification tank 14 through a sludge return path 24, and the rest is drawn out of the system as a surplus sludge from a drawing pipe 25.

The nitrification apparatus 10 has an activity detector 26 for detecting the concentration of NH ₄ —N in the nitrification tank 16 and the nitrification rate.
A DO detector 28 for detecting a DO concentration in the nitrification tank;
A control system including a controller 30 for controlling the amount of aeration for aerating the nitrification tank 16 from the blower device 18 based on the detection results of the activity detection device 26 and the DO detector 28 is provided. A raw water amount detector 32 is provided in the raw water supply pipe 12, and data on the amount of raw waste water flowing into the denitrification tank 14 is sent to the controller 30.

Next, the nitrification apparatus 10 constructed as described above
A method for controlling the amount of aeration of the nitrification tank 16 will be described. The nitrification solution containing the carrier in the nitrification tank 16 is periodically supplied to the activity detection device 26, and the NH ₄ —N in the nitrification tank 16 is
The concentration [ _Nemea ] and the nitrification rate of the carrier [ _KNmea ] are detected. Further, the DO detector 28 detects the DO in the nitrification tank 16.
The concentration [DO _mea ] is detected, and the raw water amount detector 32 detects the raw waste water amount [Q]. Then, these detection data are sent to the controller 30. Controller 30
The lower limit of the NH ₄ —N concentration in the nitrification tank 16 is 0.3 mg
/ L and a setting range [Ne _SET ] in which the upper limit is, for example, 1.5 mg / L. Setting range [N
_It is preferable that the upper limit of [e _SET ] is not less than 0.3 mg / L, but the lower the better, the more difficult it is to control the NH ₄ -N concentration if the setting range [Ne _SET ] is too narrow.
Since the frequency below g / L increases, there is a problem on the contrary. In the controller 30, if the NH ₄ -N concentration detected by the activity detecting device 26 is within the set range [Ne _SET ], the DO concentration set value at which the nitrification tank initially set reaches the maximum nitrification rate is set. To maintain. The maximum nitrification rate of the nitrification tank 16, which is governed by the nitrification rate of the carrier 11, is obtained by the above equation (3).

If the NH ₄ -N concentration is outside the lower or upper limit of the set range, a new target DO concentration set value [DO _SET ] is calculated by the following calculation. That is,
The NH ₄ —N concentration detected by the activity detector 26 [Ne
_The target nitrification rate [KN _SET ] is calculated from the following equation (4) based on the difference between the _mea ] and the set NH ₄ -N concentration [Ne _SET ].

[0038]

(Equation 4) Here, Vn is the nitrification tank volume, and Q is the amount of raw wastewater. As the value of Ne _SET , for example, 1 mg / L, which is a substantially middle value of 0.3 to 1.5 mg / L, which is the set value of the NH ₄ -N concentration, is used. Then, the DO concentration [DO _mea ] and the target DO concentration set value [DO _SET ] of the nitrification tank 16 are calculated based on the following equations (5) and (6) in which the measured value and the target value are substituted into the nitrification rate equation. I do.

[0039]

(Equation 5)

[0040]

(Equation 6) k 'is a constant.

Then, from the above equations (5) and (6),
DO_meaIs DO_SETAs shown in FIG.
The aeration amount for aerating the inside of the gasification tank 16 is controlled. That is, activity detection
NH detected by the discharge device 26_Four-N concentration [Ne_meaIs set
Constant NH_Four-N concentration [Ne_SET0.3 mg /
L, the nitrification rate of the carrier 11 becomes NH_Four-N
Due to the influence of the concentration, the DO concentration cannot be controlled accurately.
You. Therefore, the measured NH_Four-N concentration [Ne_mea]
Constant NH_Four-N concentration [Ne_SETTarget DO concentration for returning to
Set value [DO_SET] And calculate DO_meaIs DO_SETBecome
As described above, the aeration from the blower device 18 into the nitrification tank 16
The nitrification rate is intentionally reduced by reducing the air volume. Also,
NH detected by the activity detector 26_Four-N concentration [Ne
 _mea] Is the setting NH_Four-N concentration [Ne_SETIs the upper limit of
If it exceeds 1.5 mg / L, the nitrification speed in the nitrification tank
The degree may not be at the maximum. Therefore, measured
NH _Four-N concentration [Ne_mea] Set NH_Four-N concentration [N
e_SET], The target DO concentration set value for returning to
[DO for obtaining nitrification rate]_SET] And calculate DO
_{me a}Is DO_SETSo that the nitrification tank
The amount of aeration to be aerated in the inside 16 is increased.

Here, DO _mea calculated from equation (5)
Instead of using the value detected by the DO detector 28, the value of the DO concentration detected by the DO detector 28 may be used.
00% does not contribute to the nitrification rate. Therefore, it is better to use the DO concentration [DO _mea ] calculated from the nitrification rate [KN _mea ] measured by the activity detector 26, that is, the DO concentration substantially contributing to the nitrification rate. DO detector 28
The DO concentration detected in is used as an index for controlling the nitrification rate.

Incidentally, as DO _mea becomes DO _SET, as a method for controlling the aeration amount of aeration to the nitrification tank 16 from the blower unit 18, for example, DO _mea performs proportional control based on the deviation of the DO _SET The aeration amount of the blower device 18 can be changed by, for example, an inverter. Next, the effect of the nitrification treatment according to the nitrification method of the present invention will be described in comparison with a conventional nitrification method. [1] Conditions [Configuration of nitrogen removal equipment] (1) Reaction tank: 1 tank each of denitrification tank (push flow) and nitrification tank (complete mixing tank) (2) Nitrification liquid circulation ratio: 3 (including returned sludge amount) (3) Carrier addition amount: 10% [wastewater raw water] (1) Residence time: denitrification tank 4.8 hours (h), nitrification tank 3.2
The time (h) was 8 hours (h) in total, and the amount of raw water was constant.

(2) NH_Four-N concentration: 20 to 40 mg / L
Fluctuates and the concentration peaks twice a day.
NH_Four-N synthetic wastewater was used). (3) BOD / N ratio: 3 [Supply and consumption of oxygen] (1) Oxygen utilization efficiency of aeration: 23.5% (2) NH_FourDO consumption with respect to nitrification amount of -N: 4.57 m
g-O^Two/ Mg-NH _Four-N) (3) DO consumption to BOD oxygen: 1 mg-O^Two
/ Mg-BOD (However, 50% of the BOD is oxidized and the rest consumes oxygen.
(It is consumed by denitrification and sludge extraction)
Equation (constant k '= 35, water temperature of wastewater was 15 ° C)
Calculated based on However, NH_Four-N by nitrification reaction
Only removed. [2] Under the above conditions, the following three nitrification methods
The nitrification method of the chemical tank was performed.

The amount of aeration into the nitrification tank was 1.5 m ³ / m ³
-Conventional nitrification method to keep constant in nitrification tank-h Conventional nitrification method in which the aeration amount is controlled so that the DO concentration in the nitrification tank becomes constant at 4.2 mg / L Nitrification method of the present invention (3) Results FIG. 7 shows the results of daily variations in the aeration amount (Gs), the nitrification tank DO concentration (DO), and the nitrification tank NH ₄ —N (Ne) in each of the nitrification methods.

As a result, in the nitrification method, since the aeration amount was kept constant, the concentration of DO in the nitrification tank decreased when the concentration of NH ₄ —N in the wastewater was peaked. Thereby, the NH of the nitrification tank
_4- N increased to about 3 mg / L, and the quality of treated water deteriorated. In the nitrification method, the NH ₄ -N concentration peak in the nitrification tank was slightly lowered in order to keep the DO concentration constant, but still showed a value exceeding 2 mg / L.

On the other hand, in the nitrification method of the present invention, the aeration amount is increased so that the maximum nitrification rate is obtained so that the DO concentration becomes high at the time of the NH ₄ -N concentration peak of the raw wastewater. Thereby, the nitrification treatment can be effectively performed,
The NH ₄ —N concentration in the nitrification tank can be stabilized.
When the NH ₄ —N concentration of the raw wastewater is low, the DO concentration and the aeration amount are reduced, and the NH ₄ —N concentration in the nitrification tank is reduced to 0.3.
mg / L, 0.3-1.5 mg / L
After being in the range of L, the nitrification rate is controlled by the DO concentration. As a result, the nitrification rate is accurately controlled by the DO concentration, so that the amount of aeration does not become excessive or insufficient.

As shown in FIG. 7, when the required amount of aeration per day was measured based on the daily variation of the aeration amount, and the nitrification method was set to 100%, the nitrification method was 84%.
%, The nitrification method of the present invention reduced to 77.3%. From the above results, the nitrification method of the present invention is different from the conventional nitrification method in that the NH ₄ —N
Since the concentration can be stabilized and the nitrification rate can be accurately controlled by the DO concentration, there is no excess or deficiency of the aeration amount. Therefore, the amount of aeration can be reduced by 20% or more compared to the nitrification method, and about 7% can be reduced compared to the nitrification method, so that the power cost of the blower device is reduced.

FIG. 8 is a block diagram of another nitrogen removing device 41 incorporating the nitrification device 10 of the present invention. The same members and devices as those of the nitrogen removing device 40 of FIG. . This nitrogen removal device 41 is a further improvement of the nitrogen removal device 40 described with reference to FIG. 6, and a single aerobic tank 34 is provided downstream of the nitrification tank 16. Then, a part of the suspended sludge mixed liquid in the aerobic tank 34 is circulated to the denitrification tank 14, and the remaining liquid is sent to the final settling tank 22. The nitrification tank 16 shown in FIG. 8 is equipped with the same control system as that shown in FIG. 6, but is partially shown in the figure. In the nitrification tank 16, a separation screen 42 is provided so that the carrier 11 does not flow out to the aerobic tank 34.

In the nitrification tank 16, an activity detector 26, DO
A control system such as the detector 28 and the controller 30 is set, and the aeration amount of the blower device 18 is adjusted by the same control as described with reference to FIG. Apart from the control system of the nitrification tank 16, the aerobic tank 34 uses another DO detector 36 so that the DO concentration in the aerobic tank 34 becomes 2 mg / L or less. The aeration amount is adjusted.

Next, the operation of the nitrogen removing devices 40 and 41 configured as described above will be described. In the case of the nitrogen removing device 40 of FIG. 6, NH ₄ —N of wastewater supplied to the nitrification tank 16 is used.
The DO concentration is set to obtain the maximum nitrification rate commensurate with the concentration. Therefore, when the concentration of NH ₄ —N in the wastewater raw water is at its peak, the amount of aeration increases significantly. There is a risk.

Therefore, in the nitrogen removing apparatus 41 shown in FIG. 8, the aerobic tank 3 having a low DO concentration of 2 mg / L is provided downstream of the nitrification tank 16.
4 is provided, and a part of the nitrification liquid is supplied from the aerobic tank 34 to the denitrification tank 1.
4 or the remaining nitrification liquid was sent to the final sedimentation tank 22. This makes it possible to prevent the suspended sludge from being disintegrated by flocking to prevent sedimentation in the final sedimentation tank 22 and to reliably prevent the risk of remaining air being brought into the denitrification tank 14.

Further, the aerobic tank 34 in which the suspended sludge floats,
Compared with the nitrification tank 16 to which the carrier 11 is added, the aerobic tank 34
Even if the NH ₄ -N concentration in the inside is less than 0.3 mg / L, the nitrification performance does not extremely decrease. Therefore, the remaining NH ₄ -N remaining in the nitrification tank 16 is further nitrified in the aerobic tank 34. be able to. Thereby, the quality of the treated water can be further improved. The half-saturation constant of the nitrification rate of the suspended sludge with respect to the DO concentration is 0.4 to 2 m as described above.
g / L, and the DO concentration of the aerobic tank 34 is 2 mg / L.
It is enough.

By the way, in the case of a nitrification-promoting type nitrogen removing apparatus in which the carrier 11 is added to the nitrification tank 16, the nitrification rate of the carrier 11 is measured by the activity detector 26 to accurately grasp the nitrification rate, and the maximum nitrification rate is exhibited. It is necessary to drive like that.
FIG. 9 shows the N in the nitrification tank 16 without damaging the carrier 11.
FIG. 2 is a configuration diagram illustrating a configuration of an activity detection device 26 of the present invention that can detect the H ₄ —N concentration and the nitrification rate of a carrier 11. The same members and devices as those in FIG. 6 are described with the same reference numerals.

As shown in FIG. 9, the nitrification tank 16 has a screen 42 provided therein, and a reaction section 16A, which is a region of the nitrification liquid containing the carrier 11, and a region of only the nitrification liquid not containing the carrier 11. And a separation unit 16B. And the first having the intake port 44A in the reaction section 16A
Of the three-way switching valve 46 and the one-axis eccentric pump 4
8 is connected to the measuring tank 50. On the other hand, the separation unit 16
A second supply pipe 52 having an inlet 52A at B is connected to the three-way switching valve 46. Thereby, when the three-way switching valve 46 is switched by operating the one-axis eccentric pump 48, it is possible to switch between supply from the separation unit 16B to the measurement tank 50 and supply from the reaction unit 16A to the measurement tank 50. Therefore, only the liquid to be measured that is a part of the nitrification liquid in the nitrification tank 16 is supplied from the separation unit 16B to the measurement tank 50, and the reaction unit 1
From 6A, the liquid to be measured including the carrier 11 is supplied to the measuring tank 50. The three-way switching valve 46 is connected to a timer mechanism 56 via a signal cable 54, and time control of the switching timing of the three-way switching valve 46 is performed.

A return pipe 58 is provided from the upper part of the measurement tank 50 to the reaction section 16A of the nitrification tank 16, and an overflow of the liquid to be measured in the measurement tank 50 is returned from the return pipe 58 to the nitrification tank. The measuring tank 50 is provided with an air pump 60 for aerating air into the measuring tank 50 and a DO concentration meter 62 for measuring the DO concentration in the measuring tank 50. Then, a certain amount of the liquid to be measured in the nitrification tank 16 and a certain amount of the carrier 11 are sampled in the measurement tank 50 via the first supply pipe 44 and the second supply pipe 52, and the DO concentration value of the liquid to be measured is measured. The air is pumped from the air pump 60 until the value no longer changes, and the NH ₄ —N concentration and the nitrification rate are determined from the amount of change in the liquid to be measured during that time. By performing this measurement operation periodically, the nitrification performance of the nitrification tank 16 is grasped. Generally, D in the measuring tank 50 after the measurement is completed.
Although the O concentration value is 7 to 8 mg / L, the DO concentration value in the measurement tank 50 is reduced to the DO concentration value (normally, 2 to 3 mg / L) in the nitrification tank 16 before the next measurement is started. I need to lower it. The carrier and the liquid to be measured in the nitrification tank 16 are transferred to the measurement tank 50.
Sampling time is usually about 30 seconds until the liquid to be measured in the measuring tank 50 is replaced with the liquid to be measured next, but the DO concentration meter 62 determines the DO concentration value after the measurement. The response time until the DO concentration in the nitrification tank 16 drops to a DO concentration value is usually as long as 3 minutes. Therefore, the liquid to be measured including the carrier 11 is continuously supplied from the nitrification tank 16 to the measurement tank 50 for 3 minutes, and the liquid to be measured that has overflowed in the measurement tank 50 is returned to the nitrification tank 16 via the return pipe 58. The long response time of the DO densitometer 62 increases the damage rate of the carrier 11.

The operation of the activity detecting device constructed as described above will be described with reference to a case where after the first measurement is completed in the measuring tank 50, the liquid to be measured in the measuring tank 50 is replaced for the next measurement. When the first measurement in the measuring tank 50 is completed, the DO concentration in the measuring tank 50 is reduced from 7 to 8 mg / L to the DO concentration in the nitrifying tank 16 by about 2 to 3 mg / L.
For 30 minutes, the three-way switching valve 46 is switched to the second supply pipe 52, and only the liquid to be measured is supplied to the measurement tank 50 from the separation unit 16B. Next, the three-way switching valve 46 is switched from the second feed pipe 52 to the first feed pipe 44, and the carrier containing the carrier 11 is left in the remaining 30 seconds of 3 minutes which is the response time of the DO concentration meter 62. The measurement liquid is sent to the measurement tank 50.

Thus, the liquid to be measured containing the carrier 11 is 1
The time to pass through the shaft eccentric pump 48 is only 30 seconds.
Therefore, the activity detecting device of the present invention can greatly reduce the damage rate of the carrier 11 as compared with the conventional activity detecting device in which the liquid to be measured including the carrier 11 is passed through the uniaxial eccentric pump 48 for 3 minutes. it can. Thereby, the nitrification rate of the carrier 11 can be accurately measured, and even if the carrier 11 used for the measurement is returned to the nitrification tank 16, the nitrification tank 1 is measured by the measurement.
The nitrification rate of No. 6 hardly decreases. Furthermore, since the carrier 11 is hardly damaged, the life of the carrier can be extended.

When the damage rate of the activity detecting device of the present invention was compared with that of the conventional activity detecting device, it was found that the time required for passing through the single-axis eccentric pump 48 was 1/5 that of the conventional one. The damage rate was also reduced to 1/5.

[0060]

As described above, according to the method and apparatus for nitrifying wastewater of the present invention, the concentration of ammonia nitrogen in a nitrification tank can be stabilized at a low value, and the nitrification rate can be reduced by the concentration of dissolved oxygen. The aeration amount can be controlled accurately, so that the amount of aeration does not become excessive or insufficient. Therefore, the amount of aeration can be significantly reduced as compared with the conventional nitrification method, and the power cost of the blower device is reduced.

Further, according to the activity detecting device of the present invention, the rate of damage to the carrier can be greatly reduced, and the nitrification rate can be accurately measured, so that the nitrification rate of the nitrification tank can be accurately grasped. . In addition, since the carrier is not easily damaged, the life of the carrier can be extended.

[Brief description of the drawings]

FIG. 1 is a graph illustrating the effect of ammonia nitrogen concentration on the nitrification rate of a carrier.

FIG. 2 is a graph for explaining the effect of ammonia nitrogen concentration on the nitrification rate of suspended sludge.

FIG. 3 is a graph illustrating the nitrification sharing ratio of a carrier in nitrification in which a carrier and suspended sludge coexist.

FIG. 4 is a graph illustrating the effect of DO concentration on the nitrification rate of a carrier.

FIG. 5 is a graph illustrating the effect of DO concentration on the nitrification rate of suspended sludge.

FIG. 6 is a configuration diagram of a nitrogen removal device incorporating the nitrification device of the present invention.

FIG. 7 is a graph comparing the effects of a nitrogen removal device incorporating a nitrification device of the present invention and a conventional nitrogen removal device.

FIG. 8 is a configuration diagram showing another embodiment of the nitrogen removal device incorporating the nitrification device of the present invention.

FIG. 9 is a configuration diagram illustrating a configuration of an activity detection device of the present invention.

FIG. 10 is an explanatory diagram showing a change in the concentration of ammonia nitrogen in a nitrification tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Nitrification apparatus 11 ... Carrier 12 ... Raw water supply pipe 14 ... Denitrification tank 16 ... Nitrification tank 16A ... Reaction part 16B ... Separation part 18 ... Blower apparatus 20 ... Nitrification liquid circulation path 22 ... Final sedimentation tank 24 ... Sludge return path 26 ... Activity detectors 28, 36 DO detector 30 Controller 32 Raw water detector 34 Aerobic tank 38 Blower device for aerobic tank 40, 41 Nitrogen remover 42 Screen 44 First feed pipe 46 ... three-way switching valve 48 ... one-axis eccentric pump 50 ... measuring tank 52 ... second feed pipe 56 ... timer mechanism 58 ... return pipe 60 ... air pump 62 ... DO concentration meter

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Yoshikawa 1-1-14 Uchikanda, Chiyoda-ku, Tokyo Inside Hitachi Plant Construction Co., Ltd. (72) Keisuke Nakamura 1-1-1, Uchikanda, Chiyoda-ku, Tokyo No. 14 F-term in Hitachi Plant Construction Co., Ltd. (reference) 4D028 AA08 BB02 CA07 CA09 CC07 4D040 BB02 BB42 BB52 BB82 BB91

Claims (6)

[Claims] An aerating means for aerating air from waste water in a nitrification tank and contacting the microorganism-immobilized carrier added into the nitrification tank with the waste water under aerobic conditions to thereby reduce the ammonia content in the waste water. In the nitrification method of wastewater for nitrifying nitrogen, the ammonia nitrogen concentration in the nitrification tank and the nitrification rate of the microorganism-immobilized carrier are measured.If the measured ammonia nitrogen concentration is equal to or higher than a predetermined value, By controlling the amount of aeration from the aeration means and adjusting the dissolved oxygen concentration in the nitrification tank so that the nitrification rate becomes the maximum nitrification rate, when the ammonia nitrogen concentration falls below the predetermined value, A nitrification method for wastewater, wherein the concentration of dissolved oxygen in the nitrification tank is adjusted by controlling the amount of aeration from an aeration unit to return the ammonia nitrogen concentration to or above the predetermined value. 2. The method according to claim 1, wherein the predetermined value is 0.3 mg / L. 3. The wastewater in the nitrification tank is aerated with air from aeration means, and the microorganism-immobilized carrier added to the nitrification tank is brought into contact with the wastewater under aerobic conditions, whereby the ammonia in the wastewater is reduced. In a nitrification apparatus for wastewater for nitrifying nitrogen, an activity detector for measuring the ammonia nitrogen concentration in the nitrification tank and the nitrification rate of the microorganism-immobilized carrier, and the ammonia nitrogen concentration measured by the activity detector, The aeration amount of the aeration means based on the nitrification rate of the microorganism-immobilized carrier, if the ammonia nitrogen concentration is equal to or higher than a predetermined value, the nitrification rate is increased by adjusting the dissolved oxygen concentration in the nitrification tank. When the ammonia nitrogen concentration is less than the predetermined value, the concentration is decreased to adjust the dissolved oxygen concentration in the nitrification tank so that the ammonia nitrogen concentration is reduced. Serial nitrification device wastewater characterized by comprising a controller that controls back to the predetermined value or more. 4. The waste water nitrification apparatus according to claim 3, wherein said predetermined value is 0.3 mg / L. 5. A denitrification tank is provided in the preceding stage of the nitrification apparatus according to claim 3, and a suspended sludge type aerobic tank in which the dissolved oxygen concentration is maintained at 2 mg / L or less is provided in a subsequent stage. A nitrogen removal apparatus for removing nitrogen in wastewater by subjecting the wastewater to a denitrification treatment in the denitrification tank. 6. A measuring tank in which a liquid to be measured and a microorganism-immobilized carrier in a nitrification tank are supplied, an aeration unit for measuring air in the measuring tank, and a concentration of dissolved oxygen in the measuring tank. A DO measuring means for measuring, the activity detection device for measuring the nitric acid concentration of the ammonia-immobilized nitrogen concentration in the nitrification tank and the microorganism-immobilized carrier added in the nitrification tank, the inside of the nitrification tank, A reaction unit including the microorganism-immobilized carrier, a separation unit that allows the liquid to be measured to flow to and from a separation unit that does not include the microorganism-immobilized carrier, and the microorganism-immobilized carrier from the reaction unit to the measurement tank. A first feeding means for feeding a liquid to be measured containing: a second feeding means for feeding a liquid to be measured not containing the microorganism-immobilized carrier from the separation section to the measuring tank; Switching for switching between the first feeding means and the second feeding means Means for detecting activity.