JP2000325985A - Method and apparatus for biological treatment of nitrate nitrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a proper amt. of nitrogen corresponding to fluctuations in the generation amt. of nitrate nitrogen by calculating the reduction amt. from the generation amt. of nitrate nitrogen necessary for setting nitrate nitrogen contained in waste water to a predetermined target concn. or less and applying a nutrient source soln. to microorganisms in the amt. corresponding to this reduction amt. SOLUTION: A processing circuit 71 predetermines target concn. to obtain respective values at first from the input of respective signals to calculate the generation amt. of waste water and that of nitrate nitrogen contained in waste water and calculates the reduction amt. from the generation amt. of nitrate nitrogen necessary for setting nitrate nitrogen to the amt. corresponding to a predetermined target concn. Further, the processing circuit 71 calculates the amt. of a BOD source (nitrient source) soln. to be applied to denitrifying bacteria contained in sludge in a denitrification tank 27. The calculated amt. of the BOD source soln. is pumped up by a BOD source soln. supply pump 52 to be applied to the denitrification tank 27. By this constitution, the concn. of nitrate nitrogen in waste water can be reduced to a predetermined target concn. or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for treating nitrogen contained in wastewater, and more particularly, to a method and an apparatus for treating nitrate nitrogen contained in wastewater using microorganisms.

[0002]

2. Description of the Related Art In recent years, eutrophication problems have frequently occurred, such as red tide caused by plankton breeding in the ocean and water bloom caused by algae breeding in lakes and marshes. The cause is
The accumulation of nutrients such as nitrogen.

[0003] The Water Pollution Prevention Law is one of the laws and regulations for controlling drainage to public water bodies such as rivers, lakes, and coastal sea areas to prevent pollution of public water. In this Water Pollution Control Law, the daily average value of nitrogen contained in wastewater per liter is 60 mg / l or less, and the daily maximum value is 12 mg / l.
It is regulated to have a concentration of 0 mg / l or less. For this reason, in the wastewater treatment equipment for treating the wastewater to the public water area, nitrogen is removed from the wastewater so that the daily average value and the daily maximum value of the nitrogen contained in the wastewater are equal to or less than the above-described concentration. ing.

[0004]

SUMMARY OF THE INVENTION A wastewater treatment facility as described above has a wastewater treatment tank into which wastewater from a plurality of systems flows, and the wastewater flowing into the wastewater treatment tank does not contain nitrogen. In the case where wastewater is also included, the flow rate of the entire wastewater flowing into the wastewater treatment tank varies every moment. If the flow rate of the entire wastewater flowing into the wastewater treatment tank fluctuates in this manner, the degree of mixing of the wastewater in the wastewater treatment tank fluctuates, and the nitrogen concentration in the wastewater treatment tank fluctuates. The amount of nitrogen to be removed from the inside varies from moment to moment.

[0005] In such a wastewater treatment facility, the amount of nitrogen to be removed from the wastewater is not fixed, so that there is a tendency that excessive nitrogen is removed from the wastewater in order to always achieve legal regulations. Such excessive removal of nitrogen in wastewater leads to an increase in running costs. In addition, the nitrogen concentration according to the above-mentioned laws and regulations may be achieved as a daily average unless the nitrogen concentration exceeds the daily maximum.

An object of the present invention is to provide a method and an apparatus capable of removing an appropriate amount of nitrogen from wastewater in accordance with fluctuations in the amount of nitrate nitrogen contained in the wastewater.

[0007]

Means for Solving the Problems The present invention according to claim 1 utilizes a microorganism which breathes nitrate nitrogen contained in wastewater in an anaerobic state by using a nutrient solution as a feed and using oxygen in nitric acid. A method for reducing and removing nitrogen gas to reduce the concentration to below a predetermined target concentration, wherein the amounts of generated wastewater and nitrate nitrogen are determined, and the nitrate nitrogen contained in the wastewater is removed. A nitrate state characterized in that a reduction amount from the generation amount required to obtain an amount corresponding to the target concentration is calculated, and a nutrient source solution in an amount corresponding to the calculated reduction amount is fed to the microorganism as a feed. This is a nitrogen biological treatment method.

According to the present invention, the amount of reduction in the amount of nitrate nitrogen required to reduce the amount of nitrate nitrogen contained in the wastewater to a predetermined target concentration or less is determined, and the amount of reduction is determined. An amount of nutrient solution is provided to the microorganism. The microorganisms breathe in an anaerobic condition using the nutrient source solution as a feed using oxygen in nitric acid, and reduce and remove an amount of nitrate nitrogen corresponding to the reduced amount. Thereby, the concentration of nitrate nitrogen in the wastewater can be reduced to a predetermined target concentration or less. Therefore, compared to a conventional treatment method in which a nutrient source solution is given to microorganisms such that the nitrate nitrogen in the wastewater is always equal to or lower than the target concentration regardless of the amount of nitrate nitrogen contained in the wastewater, The amount of the nutrient source solution given to the microorganism can be reduced, and the running cost can be reduced.

The present invention according to claim 2 divides the wastewater containing nitrate nitrogen into a system for discharging the wastewater as it is, and a system for discharging the nitrate nitrogen after reducing the amount of nitrate nitrogen using the microorganism. The amount of reduction is determined so that the amount of nitrate nitrogen in the entire wastewater can be reduced to the target concentration or less.

According to the present invention, the wastewater containing nitrate nitrogen is divided into a system for discharging the wastewater as it is and a system for discharging the nitrate nitrogen after reducing the amount of the nitrate nitrogen by utilizing the microorganisms. The amount of reduction is determined so that the amount of nitrogen can be reduced below the target concentration. This makes it possible to reduce the size of the treatment apparatus as compared with a case where the amount of nitrate nitrogen is reduced by using one of the microorganisms without dividing into two lines. Also, a treatment method for reducing the amount of nitrate nitrogen in the wastewater divided into a plurality of systems and reducing the amount of nitrate nitrogen by utilizing microorganisms for each system and reducing the amount of nitrate nitrogen in the entire wastewater to the target concentration or less. In comparison, there is no need to provide a plurality of apparatuses for performing the nitrate-nitrogen biological treatment method, so that the treatment method can be realized more easily and the cost can be reduced.

According to a third aspect of the present invention, the nitric acid state in the wastewater actually discharged during the predetermined period is set so as to satisfy the condition that the target concentration is maintained at or below the reference concentration every predetermined period. It is characterized in that it is changed according to the amount of nitrogen.

According to the present invention, the target concentration is changed according to the amount of nitrate nitrogen in the wastewater actually discharged during the preset period so that the target concentration becomes equal to or lower than the reference concentration at each preset period. Thus, for example, the nitrate nitrogen concentration in the wastewater can be determined every hour, and the target concentration can be changed according to the determined nitrate nitrogen concentration. And the daily average concentration can be controlled to be equal to or lower than the reference concentration. Therefore, compared to a processing method in which the target concentration is not changed at all, the amount of the nutrient source solution given to the microorganism within the preset period can be reduced, and the running cost can be further reduced.

According to a fourth aspect of the present invention, nitrate nitrogen contained in wastewater is reduced to nitrogen gas by utilizing microorganisms that breathe in a anaerobic condition using a nutrient solution as a feed and using oxygen in nitric acid. A treatment device for removing and reducing the concentration to a predetermined target concentration or less, and a raw water tank for receiving wastewater containing nitrate nitrogen generated as raw water, raw water is supplied from the raw water tank, and A denitrification tank in which nitrogen reduction treatment is performed, raw water reduced in the denitrification tank is supplied, and an aeration tank into which air is blown, and raw water treated in the aeration tank is supplied, and the supernatant from which sludge is precipitated is supplied. A sedimentation tank that is discharged as treated water, and a nutrient source solution necessary for reduction treatment that reduces the concentration of nitrate nitrogen contained in raw water to a target concentration in the discharged wastewater is controlled to be supplied to the denitrification tank. Including control unit A nitrate nitrogen biological treatment device according to symptoms.

According to the present invention, the apparatus for treating nitrate nitrogen is provided with a raw water tank for receiving wastewater containing nitrate nitrogen as raw water, a raw water tank supplied with raw water, and a nutrient source solution fed to the nitrate in an anaerobic state. A denitrification tank in which nitrate nitrogen contained in the wastewater is subjected to a reduction treatment by utilizing microorganisms that breathe using oxygen, an aeration tank in which raw water reduced in the denitrification tank is supplied and air is blown, A sedimentation tank for supplying the raw water treated in the tank and discharging the supernatant obtained by sedimenting the sludge as treated water. As a result, it is possible to perform a process of reducing and removing nitrate nitrogen contained in the wastewater to nitrogen gas using the microorganism so that the concentration of nitrate nitrogen is equal to or lower than a predetermined target concentration.

Further, the above-mentioned nitrate nitrogen biological treatment apparatus controls the denitrification tank to supply an amount of a nutrient source solution necessary for the reduction treatment for reducing the concentration of nitrate nitrogen contained in the raw water to the target concentration. In order to reduce the concentration of nitrate nitrogen contained in the raw water to the target concentration, an appropriate amount of a nutrient source solution can be provided to the microorganisms in the denitrification tank. Thereby, compared to a configuration in which the nitrate nitrogen biological treatment device does not include the control device,
Irrespective of the amount of wastewater containing nitrate nitrogen, the amount of nutrient solution given to constantly reduce the concentration of nitrate nitrogen in the wastewater to the target concentration can be reduced. Therefore, running costs can be reduced.

Further, the controller can automatically supply the nutrient source solution in an amount necessary for the reduction treatment for reducing the concentration of nitrate nitrogen contained in the raw water to the target concentration, so that unmanned Nitrate nitrogen biological treatment can be realized.

According to a fifth aspect of the present invention, there is further provided a sludge return device for decomposing sludge settled in the settling tank with ozone and supplying the sludge as a part of a nutrient source solution to the denitrification tank. .

According to the present invention, the nitrate nitrogen biological treatment apparatus decomposes sludge settling in a settling tank with ozone,
Since the apparatus further includes a sludge return device for supplying the decomposed sludge to the microorganisms in the denitrification tank as a part of the nutrient source solution, the sludge settled in the settling tank can be reused without being discarded. Therefore, the generation of industrial waste can be prevented as compared with a configuration in which the nitrate nitrogen biological treatment device does not include the sludge return device.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram showing a schematic configuration of a nitrate nitrogen biological treatment apparatus 1 for carrying out a nitrate nitrogen biological treatment method according to an embodiment of the present invention, and FIG. 1 is a block diagram showing an electrical configuration of a nitrate-nitrogen biological treatment device 1 of FIG. The nitrate nitrogen biological treatment device 1 is a device for reducing and removing nitrate nitrogen in wastewater by microorganisms, and is a wastewater for treating wastewater discharged to public water bodies including rivers, lakes, marshes, and coastal seas. It is suitably used in processing equipment and the like. Such a nitrate nitrogen biological treatment apparatus 1
Is basically a first to third drainage supply sources 2 to 4,
A denitrification device 5, a wastewater treatment tank 6, and a control device 7 are provided.

The wastewater that is divided and discharged into a plurality of systems flows into the nitrate nitrogen biological treatment apparatus 1. The wastewater is divided into, for example, first to third system wastewater, and flows into first to third system wastewater supply sources 2 to 4, respectively.

[0021] The first and second lines wastewater flows into the first and second lines wastewater sources 2 and 3, for example, a spent acid from the annealing Pickling, nitrate nitrogen ^- mainly containing (NO ₃₎ . Among such wastewater containing mainly nitrate nitrogen, the first system wastewater is discharged to the wastewater treatment tank 6 after passing through the denitrification device 5, and the second system wastewater is directly passed without passing through the denitrification device 5. It is discharged to the wastewater treatment tank 6.

The first system wastewater supply source 2 includes first and second wastewater supply devices 11 and 12 in this embodiment.
The first and second drainage supply devices 11 and 12 have first and second drainage supply tanks 13 and 14, respectively, and first and second pumps 15 and 16, respectively. The first system wastewater flowing into the nitrate nitrogen biological treatment apparatus 1 is first collected in the first and second wastewater supply tanks 13 and 14. The first and second drainage supply tanks 13 and 14 are provided with first and second pH meters 93 and 94, respectively. By the first and second pH meters 93 and 94, the first and second pH meters are provided.
P of each first system wastewater in the wastewater supply tanks 13 and 14
H is measured. The first and second pumps 15, 16
Are respectively the first and second drainage supply tanks 13 and 14,
It is interposed in the first and second drainage supply passages 17 and 18 connecting the below-described raw water tank 26 of the denitrification device 5. The first system wastewater in the first and second wastewater supply tanks 13 and 14 is pumped from the first and second wastewater supply tanks 13 and 14 by first and second pumps 15 and 16, respectively. The raw water is supplied to the raw water tank 26 through the second drain supply passages 17 and 18. The first system wastewater after passing through the denitrification device 5 is discharged to the wastewater treatment tank 6 via the first discharge passage 21.

The denitrification device 5 through which the first system wastewater passes
Basically has a raw water tank 26, a denitrification tank 27, an aeration tank 28, a settling tank 29, and a BOD source solution supply device 31. The raw water tank 26 includes the first and second drainage supply passages 1.
The first system wastewater supplied through 7, 18 is received as raw water. The raw water is a raw water tank 26 of the first system wastewater that passes through the denitrification device 5 and is discharged to the wastewater treatment tank 6.
Is supplied to the sedimentation tank 29 as treated water described later.
Means wastewater in the stage before it is discharged from Such a raw water tank 26 is provided with a first nitrogen concentration meter 37 for measuring the nitrogen concentration of the raw water in the raw water tank 26. The first
The nitrogen concentration meter 37 measures the nitrogen concentration n1 (mg / l) of nitrate nitrogen contained in raw water in the raw water tank 26 per liter.
And a signal output representing the measured nitrogen concentration n1 is given to the processing circuit 71 of the control device 7. The above-mentioned nitrogen concentration is measured, for example, once every 16 minutes according to JIS K010.
It is measured by automatically performing the pyrolysis method specified in 2.

Between the raw water tank 26 and the denitrification tank 27, a first
A raw water supply passage 38 is interposed. First raw water supply passage 38
The raw water is pumped from the raw water tank 26 by the third pump 39 and supplied to the denitrification tank 27. The third pump 39 in the first raw water supply passage 38
The first flow meter 4 mounted on the panel is closer to the denitrification tank 27 side.
0 is interposed. The first flow meter 40 measures the volume flow rate Q1 (m ^{3) of} raw water passing through the first raw water supply passage 38 per hour.
/ H) to indicate the flow rate and to provide a signal output representing the measured flow rate Q1 to the processing circuit 71 of the control device 7.

The first raw water supply passage 38 branches off to a bypass passage 41 on the denitrification tank 27 side of the first flow meter 40. The bypass passage 41 communicates with the first discharge passage 21 described above. A first valve 43 is provided on the denitrification tank 27 side of the first raw water supply passage 38 with respect to a branch point 42 between the first raw water supply passage 38 and the bypass passage 41.
Is interposed. Similarly, a second valve 44 is provided in the bypass passage 41.
Is interposed. The first valve 43 and the second valve 44 change the degree of opening and closing according to control commands 69 and 70 given from the control device 7, respectively. As a result, the raw water having a flow rate corresponding to the degree of opening and closing of the first valve 43 is supplied to the denitrification tank 27, and the raw water having a flow rate corresponding to the degree of opening and closing of the second valve 44 is passed through the bypass passage 41. Discharge path 2
The wastewater is discharged to the wastewater treatment tank 6 through the first tank 1.

As described above, the inside of the denitrification tank 27 to which the raw water from the raw water tank 26 is supplied is generally in an anaerobic state. Such a denitrification tank 27 uses a sludge containing a denitrifying bacterium, which is a microorganism having a property of reducing nitrate nitrogen to nitrogen gas in an anaerobic state, to perform a reduction treatment of nitrate nitrogen contained in the raw water. Do. The above-mentioned generally anaerobic state refers to an anaerobic state in which denitrifying bacteria can reduce nitrate nitrogen and aerobic bacteria described below stop their activities.

Denitrifying bacteria include, for example, Bacillus SP (Baci
llus SP.), Hyphomicrobium SP
SP.), Pseudomonas SP., Etc., and BOD (Bi
Ochemical Oxygen Demand) When a source solution is given as food, it has a property of performing so-called nitrate respiration using nitric acid instead of oxygen. In the denitrification pathway, nitrate nitrogen (NO ₃ ⁻ ) is reduced to nitrite nitrogen (NO ₂ ⁻ ) by nitrate reductase, and then nitrite nitrogen is reduced to nitric oxide (NO) by nitrite reductase in order. Then, nitric oxide is reduced to nitrous oxide (N ₂ O) by nitric oxide reductase, and nitrous oxide is reduced to nitrogen gas (N ₂ ) by nitrous oxide reductase.
Such nitrate respiration is, in other words, catabolic nitrification reduction, and the BOD source solution provided as food serves strictly as a hydrogen donor. In the present embodiment, the reaction rate of the reduction reaction from nitrate nitrogen to nitrogen gas by nitrate respiration is controlled by the administration of the BOD source solution from the BOD source solution supply device 31. That is, sludge containing the microorganisms is always supplied in the denitrification tank 27 in a sufficient amount for the reduction reaction.
The nitrate nitrogen contained in the raw water is supplied to the BOD
It is reduced to nitrogen gas according to the amount of the source solution.

As described above, in the present embodiment, B
Methanol is used as the OD source solution. At this time, the denitrification reaction chemical formula performed in the body of the denitrifying bacterium is considered as follows. ^{_{5CH 3 OH + 6NO 3 - →}} 5HCO 3 - + OH - + 7H 2
O + 3N ₂ ↑

The sludge contains aerobic bacteria that use oxygen in the BOD source solution for respiration in an aerobic state. However, as described above, the sludge is kept in an anaerobic state in the denitrification tank 27, and Only active, aerobic bacteria are quiescent.

As shown in FIG. 1, the denitrification tank 27 includes a temperature controller 71 and an oxidation-reduction potentiometer 72. The temperature controller 71 adjusts the temperature so that the temperature of the raw water in the denitrification tank 27 is kept in a temperature range of 20 to 38 ° C. suitable for the denitrification reaction by the denitrifying bacteria. Also, an oxidation-reduction potentiometer 72
Is the oxidation-reduction potential (ORP) caused by the denitrification reaction of the denitrifying bacteria in the denitrification tank 27.
ial) (-mA) is measured.

The raw water in the denitrification tank 27 is preferably agitated by a machine, and in this embodiment, is aerated to such an extent that the inside of the denitrification tank 27 is kept slightly anaerobic compared to the aeration of the aeration tank 28. Thereby, the reactivity of the denitrification reaction by the denitrifying bacteria is improved.

The raw water in the denitrification tank 27 is always filled to the full capacity of the denitrification tank 27. The raw water reduced in the denitrification tank 27 overflows in accordance with the flow rate of the raw water newly flowing into the denitrification tank 27 from the raw water tank 26 and flows into the second raw water supply passage 4.
6 and flow into the aeration tank 28. Air is blown into the aeration tank 28 by a blower (not shown) driven by a motor, and the aeration tank 28 is brought into an aerobic state. Thereby, the aeration tank 28
In the raw water after the reduction treatment including the sludge supplied into the denitrification tank 27, the aerobic bacteria that had been inactive in the denitrification tank 27 started to operate, and the denitrification bacteria that had been active in the denitrification tank 27 were inactive. Become. The aerobic bacteria active in the aerobic state oxidize and consume the excess BOD source solution contained in the raw water after the reduction treatment in the aeration tank 28, and decompose into carbon dioxide gas and water.

The air is blown into the aeration tank 28 as described above, so that the nitrogen gas (N ₂ ) attached to the sludge supplied together with the raw water from the denitrification tank 27 is also removed. That is, at the time when the nitric nitrogen contained in the raw water is reduced in the denitrification tank 27 by the denitrifying bacteria, the nitrogen gas generated by the reduction of the nitrate nitrogen adheres to the sludge. If the sludge to which nitrogen gas is attached is supplied directly from the denitrification tank 27 to the sedimentation tank 29 without passing through the aeration tank 28, there is a problem that the sludge does not settle in the sedimentation tank 29. In order to eliminate such a problem, nitrogen gas is removed from the sludge by blowing air into the sludge to which the nitrogen gas is attached in the aeration tank 28.

The raw water treated in the aeration tank 28 is supplied to the aeration tank 2
The raw water 8 overflows in accordance with the amount of raw water newly flowing into it, and is supplied to the settling tank 29 via the third raw water supply passage 47. In the sedimentation tank 29, sludge contained in the raw water after the treatment in the aeration tank 28 is settled, and the supernatant excluding the sludge similarly overflows and is discharged according to the amount of the raw water newly flowing into the sedimentation tank 29. . That is, when the second valve 44 is completely closed, the flow rate of the supernatant treated water discharged from the sedimentation tank 29 is equal to the amount of raw water newly flowing from the raw water tank 26 into the denitrification tank 27. The treated water is discharged to the wastewater treatment tank 6 via the treated water discharge passage 48 and the first discharge passage 21. The sludge settled in the settling tank 29 is
Discarded regularly.

The sedimentation tank 29 is provided with a second nitrogen concentration meter 49 for measuring the nitrogen concentration of the raw water in the sedimentation tank 29. The second nitrogen concentration meter 49 measures the nitrogen concentration n2 (mg / l) per liter of nitrate nitrogen contained in the raw water in the settling tank 29 in the same manner as the first nitrogen concentration meter 37 described above, A signal output indicating the measured nitrogen concentration n2 is given to the processing circuit 71 of the control device 7. Further, a second flowmeter 50 mounted on a panel is interposed in the treated water discharge passage 48. Second
The flow meter 50 controls the flow rate of the treated water passing through the treated water discharge passage 48.
The volume flow rate per hour Q2 (m ³ / H) is measured, the flow rate is indicated, and a signal output indicating the measured flow rate Q2 is given to the processing circuit 71 of the control device 7.

The BOD source solution supply device 31 has a BOD source solution tank 51 and a BOD source solution supply pump 52. The BOD source solution in the BOD source solution tank 51 is BO
B source solution tank 5 by D source solution supply pump 52
1 and is supplied to the denitrification tank 27 via a BOD source solution supply passage 53. In the present embodiment, B
For example, 50% methanol is used as the OD source solution. A panel-mounted fifth flowmeter 54 is interposed in the BOD source solution supply passage 53. The fifth flow meter 54
The volume flow rate (m ³ / H) per hour of the BOD source solution passing through the OD source solution supply passage 53 is measured, and the flow rate is indicated.

The BOD source solution supply pump 52 is a pump driven by an induction motor 55 controlled by a primary frequency (inverter control).
5, the flow rate of the BOD source solution supplied to the denitrification tank 27 is adjusted. The primary frequency control refers to a control method in which the voltage and frequency of the primary input are changed by a variable voltage and variable frequency power supply.

The denitrification apparatus 5 includes a raw water tank 26 and a denitrification tank 2.
7. The pH of the raw water at each stage is measured by the third to fifth pH meters 95 to 97 provided in the aeration tank 28, respectively.
Is measured. In the denitrification tank 27, the pH of the raw water in the denitrification tank 27 tends to increase due to the above-described reduction treatment.

In order to prevent this, the denitrification device 5 has a pH adjusting device 101. The pH adjusting device 101 includes a tank 102 and a pump 103. The tank 102 stores an acid such as hydrochloric acid (HCl). Tank 10
According to the rise of the pH of the raw water in the denitrification tank 27 measured by the fourth pH meter 96, the acid in the second 2 becomes pH = 6 suitable for reduction treatment by microorganisms in the raw water in the denitrification tank 27.
To 9 if necessary.
3 is automatically controlled by the control device 7 and a corresponding amount of acid is pumped into the tank 1 by the pump 103.
02 and supplied to the raw water in the denitrification tank 27.

Of the wastewater containing mainly nitrate nitrogen, the second system wastewater does not pass through the denitrification device 5. The second drainage supply source 3 includes a third drainage supply device 56. The third
The drainage supply device 56 has a third drainage supply tank 57. The second system wastewater flowing into the nitrate nitrogen biological treatment apparatus 1 is first collected in the third wastewater supply tank 57, and then collected in the second wastewater supply tank 57.
It is discharged to the wastewater treatment tank 6 via the discharge path 58.

The third drain supply tank 57 described above is provided with a third nitrogen concentration meter 59 for measuring the nitrogen concentration of the second system waste water in the third drain supply tank 57. The third nitrogen concentration meter 59 is provided with the first and second nitrogen concentration meters 3 described above.
7 and 49, the nitrogen concentration n3 (mg / l) per liter of nitrate nitrogen contained in the second system wastewater in the third wastewater supply tank 57 is measured.
To give a signal output representing the measured nitrogen concentration n3. A panel mounted third flow meter 60 is interposed in the second discharge path 58. The third flow meter 60 is connected to the second discharge path 58.
Hourly volumetric flow rate Q3 of the second system wastewater passing through
(M ³ / H), indicating the flow rate,
A signal output indicating the measured flow rate Q3 is given to the processing circuit 71 of the control device 7. The third drainage supply tank 57 has a 6p
An H meter 98 is provided, and the pH of the second system wastewater in the third wastewater supply tank 57 is measured by the sixth pH meter 98.

The third system wastewater flowing into the third system wastewater supply source 4 is, for example, industrial water and rainwater containing no waste acid. Such third system wastewater does not mainly contain nitrate nitrogen. The third drainage supply source 4 includes a fourth drainage supply tank 6.
One. Third flow into nitrate nitrogen biological treatment device 1
The system wastewater is first collected in the fourth wastewater supply tank 61, and then discharged to the wastewater treatment tank 6 via the third discharge path 62.

As described above, the first to third wastewater treatment tanks 6
The first system wastewater and the second and third system wastewater that have been denitrified flow through the discharge passages 21, 58, and 62. The wastewater in the wastewater treatment tank 6 is discharged to the public water area as discharge wastewater through the discharge passage 66 according to the amount of wastewater newly flowing into the wastewater treatment tank 6. The public water area refers to rivers, lakes and marshes, coastal waters, and public sewers without a terminal treatment plant.

The drainage to such public water bodies is regulated by the Water Pollution Control Law (enacted from October 1, 1998), which is a law for preventing pollution of public water. According to the Water Pollution Control Law, the daily average value of nitrogen contained in drainage water to public water bodies is controlled to a concentration of 60 mg / l or less, and the daily maximum value is controlled to a concentration of 120 mg / l or less. Is done. Therefore, in the nitrate-nitrogen biological treatment device 1 of the present embodiment, the daily average nitrogen concentration and the daily maximum nitrogen concentration of the nitrate nitrogen contained in the wastewater in the wastewater treatment tank 6 are not more than the concentrations determined by the above-mentioned laws and regulations. As a result, the nitrate nitrogen contained in the first system wastewater is removed by the denitrification device 5.

The wastewater treatment tank 6 is provided with a nitrogen concentration measuring device 67. The nitrogen concentration measuring device 67 is different from the first to third nitrogen concentration meters 37, 49, and 59 described above, and in the present embodiment, the nitrogen concentration measuring device 67 complies with the wastewater standard determined by the Commissioner of the Environment Agency based on the regulations of the Prime Minister's Ordinance that sets the wastewater standard. One such test method is
The nitrogen concentration n4 (mg / l) of nitrate nitrogen contained in the wastewater in the wastewater treatment tank 6 per liter is measured by the ultraviolet absorption spectrophotometry specified in JIS KO102. The nitrogen concentration measuring device 67 is realized by, for example, a measuring device having an analysis performance close to that of a manual analysis, performs measurement once a hour, and indicates the nitrogen concentration n4 measured by the processing circuit 71 of the control device 7. Give signal output. The discharge channel 66
, A panel-mounted fourth flow meter 68 is interposed. The fourth flow meter 68 measures an hourly volume flow rate Q4 (m ³ / H) of the discharged effluent passing through the discharge flow path 66, indicates the flow rate, and is measured by the processing circuit 71 of the control device 7. A signal output indicating the flow rate Q4 is given. The wastewater treatment tank 6 is provided with a seventh pH meter 99.
The pH of the wastewater in the wastewater treatment tank 6 is measured by the meter 99.

Control device 7 includes, for example, a CPU (Central
(Processing Unit). As shown in FIG. 2, the processing circuit 71 includes, as described above, signal outputs indicating the nitrogen concentrations n1 to n3 from the first to third nitrogen concentration meters 37, 49, and 59, respectively, and a nitrogen concentration measuring device 67. A signal output representing the nitrogen concentration n4 from
Also, signal outputs representing the flow rates Q1 to Q4 from the first to fourth flow meters 40, 50, 60, 68 are input, respectively.

The processing circuit 71 determines the target concentration n6 in advance, obtains each value from each of the above-mentioned signal inputs, obtains the wastewater and the amount of nitrate nitrogen contained in the wastewater, and calculates the nitrate nitrogen. The amount of reduction from the amount of nitrate nitrogen required to make the amount correspond to the above-described predetermined target concentration is calculated. Further, the processing circuit 71 calculates the amount of the BOD source solution to be given to the denitrifying bacteria contained in the sludge in the denitrification tank 27 in accordance with the calculated decrease amount, and pumps up this amount of the BOD source solution. The frequency of the induction motor 55 when the BOD source solution supply pump 52 is driven is calculated. The frequency calculated in this way is given to the induction motor 55 as a control command 65. As a result, the amount of the BOD source solution calculated as described above becomes B
It is pumped up by the OD source solution supply pump 52 and provided to the denitrification tank 27.

Further, the processing circuit 71 calculates the amount of raw water that is to be newly introduced from the raw water tank 26 into the denitrification tank 27 to be denitrified in accordance with the above-mentioned amount of decrease. The control commands 69 and 70 respectively correspond to the first valve 4 according to the calculated flow rate of the raw water.
3 and the second valve 44. The degree of opening and closing of the first valve 43 and the second valve 44 varies depending on the control commands 69 and 70, and the amount of raw water passing through the first raw water supply passage 38 is stored in the denitrification tank 27. The amount of the flowing water is controlled in the bypass passage 41. The calculation and control operations by the processing circuit 71 are performed continuously, and are repeated in accordance with updating of the value of the nitrogen concentration n4 of the wastewater in the wastewater treatment tank 6 measured by the nitrogen concentration measuring device 67 every hour. It is.

FIG. 3 is a flowchart for explaining the operation and control operation of the processing circuit 71. Here, it is assumed that the processing circuit 71 performs the i-th calculation (i is a natural number) and the control operation. The processing circuit 71 updates the (i−1) th nitrogen concentration n4 value n4 (i−1) by the i-th measurement of the nitrogen concentration measuring device 67.
When the value n4i of the nitrogen concentration n4 for the second time is obtained, the i-th calculation and control operation is started.

The process proceeds from step s0 to step s1, and the processing circuit 71 acquires the i-th nitrogen concentration values n1i to n3i and the flow rate values Q1i to Q4i from the input signal described above. More specifically, the first nitrogen concentration meter 37
Of the raw water in the raw water tank 26, i.e., the nitrogen concentration of the nitrate nitrogen contained in the first system wastewater before the nitrogen is removed, in the sedimentation tank 29 measured by the second nitrogen concentration meter 49. Value of the nitrogen concentration of nitrate nitrogen contained in the first system wastewater after removing the raw water, that is, nitrogen
2i, the value n3i of the nitrogen concentration of nitrate nitrogen contained in the second system wastewater in the third wastewater supply tank 57 measured by the third nitrogen concentration meter 59, and the wastewater treatment measured by the nitrogen concentration measuring device 67 The value n4i of the nitrogen concentration of the nitrate nitrogen contained in the wastewater in the tank 6 is obtained. At the same time, the raw water passing through the first raw water supply passage 38 measured by the first flow meter 40, that is, the first raw water before the nitrogen is removed is removed.
The value Q1i of the flow rate of the system wastewater, the value Q2i of the flow rate of the first system wastewater after removal of the treated water passing through the treated water discharge passage 48, that is, nitrogen, measured by the second flowmeter 50, the third flowmeter 60 The value Q3i of the flow rate of the second system wastewater passing through the second discharge path 58 measured by the second flow path 58, and the discharge water discharged through the discharge path 66 detected by the fourth flow meter 68, that is, the wastewater treatment that is the generated amount of the entire wastewater The value Q4i of the total flow rate of the first to third drainage flowing into the tank 6 is obtained.

The values n1i to n3i of the nitrogen concentration and the values Q1i to Q3i of the flow rate are obtained so as not to cause a time lag. That is, depending on the location where the respective nitrogen concentration meters and flow meters are installed, obtaining the respective values at the time when the i-th nitrogen concentration value n4i is updated may cause a time lag. For example, assuming that it takes 30 minutes from the time when the second system wastewater is discharged from the third wastewater supply tank 57 to the time when the second system wastewater flows into the wastewater treatment tank 6, the nitrogen concentration to be obtained corresponding to the time when the value n4i is updated Value n3i is 3
It is the nitrogen concentration n3 measured at the closest point in time 0 minutes ago. As described above, the above-described values are obtained in consideration of the time lag caused by the location where the respective nitrogen concentration meters and flow meters are installed.

In the following step s2, each value n1
Based on i to n4i and Q1i to Q4i, a value N4i of the nitrogen load of the wastewater in the wastewater treatment tank 6, which is the amount of nitrate nitrogen contained in the wastewater, is calculated.

FIG. 4 is a flowchart for explaining the specific operation of step s2 in FIG. Steps
In 2a1, a value Q5i of the i-th flow rate of the flow rate Q5 of the third system drainage passing through the third discharge path 62 is calculated. As described above, in the present embodiment, since the flow meter is not interposed in the third discharge path 62 through which the third system drainage passes, the flow rate Q5i is obtained by calculation. The flow rate Q5 of the third system wastewater flowing into the wastewater treatment tank 6 is a factor that changes the nitrogen concentration n4 of the wastewater in the wastewater treatment tank 6. That is, when the flow rates Q2 and Q3 of the first and second system wastewater flowing into the wastewater treatment tank 6 are constant, the flow rate Q5 of the third system wastewater is
Becomes large, the nitrogen concentration n4 of the wastewater in the wastewater treatment tank 6 is increased.
Decreases, and conversely, as the flow rate Q5 decreases, the nitrogen concentration n4 increases. The value Q5i of the i-th flow of the flow Q5 of the third drainage is calculated by the following equation. Q5i = Q4i-Q1i-Q3i

That is, from the flow rate value Q4i of the discharged wastewater passing through the discharge flow path 66 measured by the fourth flow meter 68, each value Q1i of the flow rate of the first and second system wastewater flowing into the wastewater treatment tank 6 is calculated. It is calculated by subtracting Q3i.

In step s2a2, the nitrogen load values N1i, N1 before and after the nitrogen removal of the first system wastewater are performed.
2i and the values N3i and N5i of the nitrogen load of the second and third drainage are calculated. The value of the nitrogen load is calculated by integrating the value of the nitrogen concentration in the wastewater and the value of the flow rate of the wastewater. That is, each value N1 of the nitrogen load
i to N3i and N5i are obtained by the following equations, respectively. N1i = n1i * Q1i N2i = n2i * Q2i N3i = n3i * Q3i N5i = n5i * Q5i

In the following step s2a3, the wastewater treatment tank 6
The value N4i of the nitrogen load of the wastewater in the inside is obtained. The nitrogen load value N4i is obtained as the sum of the nitrogen load value N2i of the first system wastewater after nitrogen removal and the nitrogen load values N3i and N5i of the second and third system wastewater. That is, it is calculated by the following equation. N4i = N2i + N3i + N5i

Returning to FIG. 3, in step s3, the value of the nitrogen concentration of the wastewater in the wastewater treatment tank 6 is determined by the predetermined i.
Assuming that the value is equal to the value n6i of the target concentration n6 for the second time, the nitrogen load value N6i of the wastewater in the wastewater treatment tank 6 in this case is calculated. The value N6i of the nitrogen load is obtained by the following equation. N6i = n6i × Q4i

In the following step s4, the nitrogen load value N4i, which is the amount of nitrate nitrogen contained in the wastewater in the wastewater treatment tank 6, is changed to the predetermined target concentration n6 value n6i.
Is calculated, the nitrogen load value N7i to be removed by the denitrification device 5 is calculated, which is the amount of decrease required to make the nitrogen load value N6i the amount corresponding to. The nitrogen load value N7i to be removed is represented by the following equation. N7i = N4i-N6i = n4i.times.Q4i-n6i.times.Q4i = (n4i-n6i) .times.Q4i

In the following step s5, the above-mentioned step s
From the nitrogen load value N7i to be removed obtained in step 4 and the nitrogen concentration value n1i of nitrate nitrogen contained in the raw water in the raw water tank 26 measured by the first nitrogen concentration meter 37, the raw water tank 26
Q8 of the flow rate of raw water to be newly supplied to the denitrification tank 27
Calculate i. The value Q8i of the flow rate is obtained by the following equation. Q8i = (N7i / n1i) + Q9i

The flow rate value Q9i is a flow rate value added extra for feedback correction. The correction value Q9i is increased by the flow rate Q9 corresponding to the value Q9i, and the raw water is newly supplied from the raw water tank 26 to the denitrification tank 27, so that the processing circuit 71 obtains the (i + 1) -th time in the wastewater processing tank 6. Value of the nitrogen concentration n4 of the wastewater n4 (i +
1) is added so as to be smaller than the predetermined target density value n6i as described above. The value Q of this flow rate
9i is represented by the following equation. Q9i = {(n4i-n6i) × Q4i × 1.2} /n1i=N7i×1.2/n1i

That is, the flow rate Q8i of the raw water to be newly supplied to the denitrification tank 27 can be rewritten as follows. Q8i = (N7i / n1i) + Q9i = (N7i / n1i) + (1.2N7i / n1i) = 2.2N7i / n1i

That is, as described above, the flow rate Q8i of the raw water to be newly supplied to the denitrification tank 27 according to the nitrogen load value N7i to be removed is determined by changing the nitrogen load value N4i to the nitrogen load value N6i. It is calculated as 2.2 times the supply amount of raw water necessary for

In the following step s6, the flow rate value Q10i of the BOD source solution to be supplied to the denitrification tank 27 is calculated from the flow rate value Q8i obtained as described above. As described above, in this embodiment, 50% of the BOD source solution is used.
Since% methanol is used, the value Q10i of the dose of the BOD source solution is obtained by the following equation.

[0064]

(Equation 1)

The value Q10i of the dose of methanol is determined so that its unit is 1 / H. The value M in the equation is
The coefficient of methanol, a numerical value representing the ratio between the amount of methanol consumed by the denitrifying bacteria and the amount of methanol administered to the denitrifying bacteria, which is necessary for the denitrifying bacteria to breathe using the oxygen in the nitrate with methanol as a feed is there. This methanol coefficient varies depending on the nitrogen load of the raw water in the denitrification tank 27,
It is given as a numerical value in the range of 3.0. In addition, the numerical value 0.92
Is the density of 50% methanol at 20 ° C. (g / cm
³ ).

FIG. 5 shows a frequency fi given as a control command 65 to the induction motor 55 of FIG.
5 is a graph showing the relationship with the flow rate of the BOD source solution pumped through the BOD source solution supply pump 52 by the reference numeral 5. The vertical axis of the graph indicates the frequency value fi, and the horizontal axis indicates the BO pumped by the BOD source solution supply pump 52.
The flow rate (l / H) of the D source solution is shown. Referring also to FIG.
In step s7, when the BOD source solution supply pump 52 is driven to flow the BOD source solution at a flow rate corresponding to the value Q10i of the amount of the BOD source solution to be administered to the denitrification tank 27 calculated in step s6 described above. , The value fi of the frequency of the induction motor 55 is calculated. The value fi of the frequency is obtained from the relationship shown in the graph of FIG. Such a frequency value fi has, for example, a lower limit value of 6 and an upper limit value of 60. In the present embodiment, as shown in FIG. 5, when the frequency given to the induction motor 55 is 60 Hz, the discharge amount of the BOD source solution supply pump 52 is 72
0 l / H.

In the following step s8, the frequency value fi obtained in step s7 is given to the induction motor 55 as a control command 65. Thereby, the induction motor 55
Is B at the rotation speed corresponding to the given frequency value fi.
The OD source solution supply pump 52 is driven. In this way, a denitrifying bacterium is provided with an amount of the BOD source solution corresponding to the amount of reduction of the nitrate nitrogen for reducing the nitrogen concentration of the wastewater in the wastewater treatment tank 6 to the predetermined target concentration or less.

At the same time, in step s8, as described above, the flow rate Q8 of the raw water to be newly supplied to the denitrification tank 27 is set.
A control command 69 corresponding to i is given to the first valve 43.
When the i-th target concentration value n6i is sufficiently low and it is not necessary to perform the denitrification processing on all the raw water pumped from the raw water tank 26 by the third pump 39, the raw water that does not need to be subjected to the denitrification processing is used. Is given to the second valve 44 to set the valve opening of the second valve 44. Thereby, the raw water tank 2 is moved by the third pump 39.
A part of the raw water pumped from 6 flows directly into the wastewater treatment tank 6 without being subjected to the denitrification treatment through the bypass passage 41.

The process proceeds from step s8 to step s9, and the i-th calculation and control operation by the processing circuit 71 ends. As described above, a series of calculation and control operations by the processing circuit 71 are started and repeated every time the value of the nitrogen concentration n4 of the wastewater in the wastewater treatment tank 6 measured by the nitrogen concentration measuring device 67 is updated. That is, a series of calculation and control operations by the processing circuit 71 shown in the flowchart of FIG. 3 are repeated every hour in this embodiment in accordance with the measurement cycle of the nitrogen concentration measuring device 67.

As described above, in step s4 of the flowchart of FIG. 3, the nitrogen load N7i to be removed from the wastewater in the wastewater treatment tank 6 is determined by the amount of nitrate nitrogen contained in the wastewater in the wastewater treatment tank 6. Is calculated as a decrease amount for setting the nitrogen load value N4i as a nitrogen load value N6i, which is an amount corresponding to a predetermined target concentration n6i. The target concentration is a daily average value of 60 mg / l according to laws and regulations.
Is assumed. However, if the daily average value according to this regulation is not greater than 120 mg / l, the daily average value of the wastewater in the wastewater treatment tank 6 measured at each measurement cycle of the nitrogen concentration measuring device 67 provided in the wastewater treatment tank 6 will be described. This is achieved when the average daily nitrogen concentration is below 60 mg / l.

In the present embodiment, the nitrogen concentration measuring device 67 measures the nitrogen concentration n4 of the wastewater in the wastewater treatment tank 6 every hour as described above. The value of the nitrogen concentration n4 of the wastewater in the wastewater treatment tank 6 per 24 hours per day is measured, and the correction is performed so that the average value of these 24 values is equal to or less than the daily average value according to the above-mentioned laws and regulations. A daily average correction is made. In other words, the target concentration is adjusted according to the amount of nitrate nitrogen in the wastewater actually discharged during the preset period so that the condition for keeping the target concentration at or below the reference concentration for each preset period is satisfied by the daily average correction. It changes every hour. In the present embodiment, the preset period is 24 hours, and the reference concentration is 60 mg / l.

FIG. 6 shows the target density n of the processing circuit 71 of FIG.
6 is a flowchart for explaining an operation of a 6-day average correction. The processing circuit 71 corrects the value of the target density n6 in accordance with the above-described calculation and control operations, and
Update the value of 6. The value of the target density n6 updated by the daily average correction is input as the value of the target density n6 in the next repeated calculation and control operation. That is, it is used in step s3 in the (j + 1) -th (j is any natural number from 1 to 23) calculation and control operation of the processing circuit 71, which is repeated 24 times every hour within 24 hours. The (j + 1) -th target density value n6 (j + 1) is calculated by the daily average correction operation shown in the flowchart of FIG. 6 in accordance with the j-th calculation and control operation of the processing circuit 71, and is determined in advance.

With the start of the first calculation and control operation of the processing circuit 71 shown in the flowchart of FIG. 3, which is repeated every hour, 24 times a day, the correction operation of the processing circuit 71 shown in FIG. 6 is started. Moves from step r0 to step r1. At this time, a value j (j is any natural number from 1 to 23) indicating the number of times the above-described operation and control operation of the processing circuit 71 repeated 24 hours a day and every hour. Is given an initial value of j = 1.

At Step r2, the nitrogen concentration n4 of the wastewater in the wastewater treatment tank 6 measured by the nitrogen concentration measuring device 67
To obtain the j-th value n4j. Here, since the initial value of j = 1 is given in step r1 as described above, in step r2, the processing circuit 71 performs the wastewater treatment by the first measurement of the nitrogen concentration measuring device 67 in one day. The value n41 of the nitrogen concentration of the wastewater in the tank 6 is obtained.

At step r3, based on the detected nitrogen concentration values n41 to n4j up to the j-th time, (j + 1)
(J) used for the arithmetic and control operations of the processing circuit
A value n6 (j + 1) of the (+1) th target density is calculated. This (j + 1) th target density value n6 (j + 1)
Is calculated by the following equation.

[0076]

(Equation 2)

Here, assuming that the nitrogen concentration n41 of the wastewater in the jth or first wastewater treatment tank 6 is 40 mg / l, the (j + 1) th or second time treatment circuit 7
1 target density n62 used in the calculation and control operation
Is calculated as follows.

[0078]

(Equation 3)

The value calculated in this way becomes the next target density n62. That is, the second target density is 60.8
7 mg / l.

The process proceeds to step r4, where it is determined whether or not the value j is 23. Since j = 1 here, j = 23
Is not determined, and the routine goes to Step r5.

At step r5, the value j is updated to the value (j + 1), and the process returns to step r2. Here, j = 1, j
= 2 is updated. Thus, steps r2 to r5 are:
The value j is updated in step r5 and repeated until it is determined in step r4 that j = 23.

For example, when j = 5, step r2
The nitrogen concentration values n41 to n45 of the wastewater in the wastewater treatment tanks 6 for j = 1 to 5 repeatedly obtained in the above are respectively n41 = 40, n42 = 45, n43 = 50, and n44 =
Assuming that 55 and n45 = 55, the target density n66 used for the (j + 1) th, that is, the sixth calculation and control operation of the processing circuit 71 is calculated by the following equation.

[0083]

(Equation 4)

The value calculated in this way becomes the next target density. That is, the sixth target density is 62.89 m
g / l.

If it is determined in step r4 that j = 23, the process proceeds to step r6, where the daily average correction operation of the processing circuit 71 is terminated. The operation of the daily average correction is similarly repeated on the next day.

As described above, the (j + 1) th target concentration value n6 (j + 1) is determined according to the sum of the actual nitrogen concentration values n41 to n4j of the wastewater in the wastewater treatment tank 6 up to the jth time.
The reference concentration is 60 within 24 hours, which is a predetermined period.
Correction is made so as to satisfy the condition to be kept at or below mg / l. However, the target density value n6 (j
+1) has an upper limit. In the present embodiment, for example, the upper limit is 100.

FIG. 7 is a graph showing an example of a temporal change of the nitrogen concentration in the wastewater in the wastewater treatment tank 6 of FIG. The vertical axis of FIG. 7 shows the nitrogen concentration (mg / l) of nitrate nitrogen contained in the wastewater in the wastewater treatment tank 6, and the horizontal axis shows the time from 1:00 to 0:00 of the day. . Nitrogen concentration measuring instrument 6
Since the measurement of the nitrogen concentration of the wastewater in the wastewater treatment tank 6 is performed every hour, the nitrogen concentration shows a stepwise change over time as shown by a solid line 73 in FIG.
Further, the actual nitrogen concentration of the wastewater in the wastewater treatment tank 6 predicted from the solid line 73 is indicated by a curve 74 that smoothly follows the stepwise change of the nitrogen concentration with time. A two-dot chain line 75 in FIG. 7 indicates a reference density, and in the present embodiment,
60 mg / l. The nitrogen concentration shown by the solid line 73 is
For example, the density exceeds the reference density at the measurement at 2:00. However, since a series of calculation and control operations by the processing circuit 71 described above are performed, the denitrification tank 2
7, the flow rate of the first system wastewater and the supply amount of the BOD source solution are increased, so that the measured value at the time 3:00 is smaller than that at the time 2:00, and further reduced at the time 4:00. Thereafter, the daily average correction is performed so that the average of the measured values of the respective nitrogen concentrations in one day is maintained at or below the reference concentration. For example, a part of the raw water pumped by the third pump 39 passes through the bypass passage 41. For example, in the measurement after 5:00, the control is performed so that the nitrogen concentration of the wastewater in the wastewater treatment tank 6 gradually increases.

The nitrate nitrogen biological treatment apparatus 1 for carrying out the nitrate nitrogen biological treatment method of the present embodiment comprises a nitrate nitrogen necessary for reducing the concentration of nitrate nitrogen contained in wastewater to a predetermined concentration or less. The amount of the BOD source solution corresponding to the reduced amount is given to the denitrifying bacteria. Thereby, the concentration of nitrate nitrogen in the wastewater can be reduced to a predetermined target concentration or less. Therefore, a conventional processing apparatus which performs a processing method of giving a BOD source solution to a denitrifying bacterium such that the nitrate nitrogen in the wastewater is always equal to or lower than the target concentration regardless of the amount of nitrate nitrogen contained in the wastewater. The amount of the BOD source solution given to the denitrifying bacteria can be reduced, and the running cost can be reduced. Although excessive administration of the BOD source solution leads to an increase in the amount of suspended solids (SS) in the wastewater, the nitrate-nitrogen biological treatment device 1 uses an appropriate amount of BO.
Since the D source solution can be given to the denitrifying bacteria, an increase in the amount of suspended solids in the wastewater can be suppressed.

Further, the nitrate nitrogen biological treatment apparatus 1 includes a first system wastewater of a system for discharging the wastewater containing the nitrate nitrogen after reducing the nitrogen load which is the amount of the nitrate nitrogen using a denitrifying bacterium. The system is divided into a second system wastewater that is discharged as it is, and the amount of reduction is determined so that the nitrogen load in the entire wastewater can be reduced to the target concentration or less. This gives 2
The amount of nitrate nitrogen in the entire wastewater can be reduced to the target concentration or less by reducing the nitrate nitrogen contained in the wastewater of the first system in one system without being divided into systems. Therefore, the size of the processing apparatus is reduced compared to a processing apparatus that uses a denitrifying bacterium in the entire wastewater containing nitrate nitrogen to reduce the amount of nitrate nitrogen in the entire wastewater to a target concentration or less. can do. Further, a treatment method for reducing the amount of nitrate nitrogen in the wastewater divided into a plurality of systems by using a denitrifying bacterium for each system and then discharging the wastewater to reduce the amount of nitrate nitrogen in the entire wastewater to the target concentration or less. It is not necessary to provide a plurality of denitrification apparatuses 5 as compared with a processing apparatus that performs the above-described processing, and the above-described processing method can be realized more easily, and costs can be reduced.

Further, in the nitrate nitrogen biological treatment apparatus 1, the target concentration is controlled according to the amount of nitrate nitrogen in the wastewater actually discharged during the predetermined period so that the target concentration becomes equal to or lower than the reference concentration every predetermined period. Be changed. Thus, as in the present embodiment, the nitrate nitrogen concentration in the wastewater in the wastewater treatment tank 6 can be determined every hour, and the target concentration can be changed according to the determined nitrate nitrogen concentration. The right amount of BOD
The source solution can be provided to the denitrifying bacteria and the average daily concentration can be controlled to be below the reference concentration. Therefore, as compared with a processing method in which the target concentration is not changed at all, the amount of the BOD source solution given to the denitrifying bacteria within the preset period can be reduced, and the running cost can be further reduced. .

Further, the nitrate nitrogen biological treatment apparatus 1 is
Since the control device 7 for controlling the supply of the BOD source solution in an amount necessary for the reduction treatment for reducing the concentration of nitrate nitrogen contained in the raw water to the target concentration to the denitrification tank 27 is included, the raw water contains An appropriate amount of a BOD source solution can be provided to the denitrifying bacteria in the denitrification tank 27 to reduce the concentration of the contained nitrate nitrogen to the target concentration. As a result, the concentration of nitrate nitrogen in the wastewater is constantly reduced to the target concentration regardless of the amount of wastewater containing nitrate nitrogen, as compared with a configuration in which the nitrate nitrogen biological treatment apparatus does not include the control device. The amount of the BOD source solution to be supplied can be reduced. Therefore, running costs can be reduced.

Further, the control device 7 can automatically supply the amount of the BOD source solution necessary for the reduction treatment for reducing the concentration of nitrate nitrogen contained in the raw water to the target concentration or less. It is possible to realize an unmanned nitrate nitrogen biological treatment.

In the above-mentioned method for treating nitrate-nitrogen biological treatment, the wastewater containing nitrate-nitrogen is divided into a system for discharging the wastewater as it is and a system for passing the same through the denitrification device 5. Achieve the reduction of nitrate nitrogen in the entire wastewater, but do not divide the wastewater containing nitrate nitrogen into separate systems, and use one system to reduce the concentration of nitrate nitrogen contained in the wastewater to a target concentration below a predetermined target concentration. In addition, the amount of reduction from the amount of generated nitrate nitrogen is determined, and the amount of BO corresponding to the amount of reduction is determined.
It may be realized to provide the D source solution to the denitrifying bacteria.

In the above-mentioned method for treating nitrate nitrogen, the target concentration is changed according to the actual amount of nitrate nitrogen in the wastewater while maintaining the target concentration at or below the reference concentration every predetermined period. The following fixed concentration is set, the amount of reduction required to make the amount of nitrate nitrogen contained in the wastewater correspond to the target concentration is determined, and the amount of the BOD source solution corresponding to the reduced amount is removed. It may be realized to feed on nitrifying bacteria.

FIG. 8 shows a nitrate nitrogen biological treatment apparatus 11 for carrying out a nitrate nitrogen biological treatment method according to another embodiment of the present invention.
FIG. 9 is a system diagram showing a schematic configuration of the denitrification apparatus 112 of FIG. 1. FIG. 9 shows the decomposition of microorganisms contained in sludge by ozone (O ₃ ) performed in the sludge return device 13 of the denitrification apparatus 112 of FIG. It is a figure which shows a mechanism typically. This embodiment is similar to the nitrate nitrogen biological treatment apparatus 1 that performs the nitrate nitrogen biological treatment method of the above-described embodiment, and the corresponding parts are denoted by the same reference numerals and description thereof is omitted. .

Nitrate-nitrogen biological treatment apparatus 1 of the present embodiment
11 is different from the above-mentioned nitrate nitrogen biological treatment apparatus 1 in a denitrification apparatus 112. Denitrification apparatus 1 of the present embodiment
12 further has a sludge return device 113. The microorganisms 122 such as denitrifying bacteria and aerobic bacteria contained in the sludge propagate while passing from the denitrifying tank 27 to the sedimentation tank 29 through the aeration tank 28. The sludge at the time of being supplied to the sedimentation tank 29 contains the above-mentioned microorganisms 122 in excess, and cannot be reused again in the denitrification tank 27 as it is.

As described above, in the sedimentation tank 29, the aeration tank 2
The raw water treated in step 8 is supplied, and the supernatant from which the sludge has settled is discharged as treated water. At this time, the sludge settled in the settling tank 29 is supplied to the sludge return device 113. The sludge returning device 113 basically includes a sludge reducing device 114,
An ozone generator 115 and an ozone monitor 116 are provided.

The sludge settled in the settling tank 29 passes through a first sludge return passage 117 interposed between the settling tank 29 and the sludge reducing device 114 and is supplied to the sludge reducing device 114. The first sludge return passage 117 branches between the sedimentation tank 29 and the sludge return device 113, and a second sludge return passage 118 branched from the first sludge return passage 117 leads to the denitrification tank 27. That is, a part of the sludge settling in the sedimentation tank 29 does not pass through the sludge return device 113 but passes through the second sludge return passage 118 and is directly supplied to the denitrification tank so that the amount becomes sufficient for the reduction reaction in the denitrification tank 27. Returned to 27.

The sludge return device 113 decomposes microorganisms 122 such as denitrifying bacteria and aerobic bacteria contained in the sludge precipitated in the sedimentation tank 29 with ozone, and transfers the decomposed sludge to the denitrification tank 27 as part of the BOD source solution. It is a device for supplying as. That is, by applying ozone to the sludge transferred from the denitrification tank 27 to the settling tank 29 via the aeration tank 28, the excessively propagated microorganisms 122 contained in the sludge are decomposed. Feed as feed to denitrifying bacteria contained in sludge.

In the sludge volume reducing device 114, hydrochloric acid (HCl) is first added to the settled sludge supplied through the first sludge return passage 117 so as to adjust the pH to 3. After the above pH adjustment, ozone supplied from the ozone generator 115 is applied to the sludge. When ozone acts on the sludge, as shown in FIG. 9, the cell wall 123 of the microorganism 122 contained in the sludge is destroyed by the oxidizing power of the ozone. As a result, the microorganisms 122 die and fly out of the cell wall 123 where the cytoplasm 124 has been destroyed. The sludge containing the microorganisms 122 thus sterilized is
Biodegradability is improved.

The sludge after sterilization by such ozone is as follows:
The sludge is supplied to the denitrification tank 27 through a third sludge return passage 119 interposed between the sludge reduction device 114 and the denitrification tank 27. The sludge thus supplied to the denitrification tank 27 is reused as a BOD source, eaten by denitrifying bacteria contained in the sludge in the denitrification tank 27, and decomposed into carbon dioxide gas and the like. As a result, it is possible to reuse the sludge containing the microorganisms that have surplusly propagated without discarding the sludge.

The above-described ozone treatment of microorganisms does not need to be performed on all the settled sludge supplied from the settling tank 29 to the sludge return device 113. That is, if ozone acts on a part of the entire sludge, the sludge reduction device 1
Since ozone oxidation can be caused in a chain of sludge in the entirety of the sludge 14, microorganisms contained in the whole sludge can be killed. In the present embodiment, as described above, the ozone treatment is performed for about 1. 1 of the entire sludge supplied to the sludge return device 113.
Performed for 1%. That is, for example, the sludge volume reducing device 114 from the settling tank 29 through the first sludge return passage 117
Is about 390 m ³ / H, the ozone treatment is performed on the sludge of about 4.5 m ³ / H.

A sixth flow meter 120 is interposed between the branch point of the second sludge return passage 118 of the first sludge return passage 117 and the sludge reduction device 114. A seventh flowmeter 121 is interposed in the second sludge return passage 118.
These sixth and seventh flow meters 120 and 121 are settled in the settling tank 29 passing through the sludge volume reduction device 114 from the branch point of the first sludge return passage 117 and the second sludge return passage 118, respectively. The flow rate of the sludge is measured, the flow rate is indicated, and an output signal indicating the flow rate is given to the control device 7.

The ozone supplied to the sludge volume reducing device 114 is generated by the ozone generator 115 in accordance with the amount of sludge flowing into the sludge returning device 113. That is, the amount of ozone generated by the ozone generator 115 is automatically controlled by the control device 7 based on the output from the sixth flow meter 120 described above. Note that the amount of ozone generated by the ozone generator 115 can be monitored by the ozone monitor 116 when there is a monitor. In this case, the monitor monitors the ozone monitor 116 while the ozone generator 11
It is also possible to adjust the amount of ozone generated by 5.

The microorganisms contained in the sludge settled in the sedimentation tank 29 are treated with ozone and returned to the denitrification tank 27 for use as bait, whereby the sludge settled in the sedimentation tank 29 is reused without being discarded. can do. Therefore, compared to a configuration in which the nitrate nitrogen biological treatment apparatus does not include the sludge return device, the sludge settled in the settling tank 29 can be used without wasting, and the generation of industrial waste is prevented. be able to. For example, when the BOD source solution is methanol, the supply of the BOD source solution from the BOD source solution supply device 31 to the denitrification tank 27 can be reduced by about 10%.

[0106]

EXAMPLE Using the nitrate nitrogen biological treatment apparatus 1 shown in FIG. 1, waste water treatment was carried out by the nitrate nitrogen biological treatment method shown in FIGS. 3, 4 and 6. Table 1 shows the results.

[0107]

[Table 1]

Table 1 shows that the first system drainage before passing through the first raw water supply passage 38 and the denitrification after passing through the treated water discharge passage 48 at the time of normal drainage and at the time of drought, respectively. 1st system drainage, 2nd and 3rd discharge way 5
8 and 62, and the respective flow rates (m ³ / H) and nitrogen concentration (mg / mg) of the discharge wastewater that is the wastewater that passes through the discharge passage 66.
1), and nitrogen load (kg / H). The normal drainage refers to when the flow rate of rainwater or the like contained in the third system drainage is an average amount. And when drought,
It indicates when the flow rate of rainwater or the like contained in the third system drainage is significantly lower than the average flow rate.

As shown in Table 1, during normal drainage, the flow rate of the first system drainage is 320 m ³ / H, and the total flow rate of the second and third system drainage is 858 m ³ / H. The nitrogen concentration of the nitrate nitrogen contained in the wastewater of the first system is reduced by passing through the denitrification tank 27 and subjected to a reduction treatment.
It is reduced from 6 mg / l to 162.2 mg / l. That is, the nitrogen load representing the amount of nitrate nitrogen contained in the first system wastewater was 69.0 kg by the reduction treatment in the denitrification tank 27.
/ H to 51.9 kg / H. As a result, the nitrogen concentration of nitrate nitrogen contained in the discharged wastewater discharged from the wastewater treatment tank 6 into which the first to third system wastewaters flow is 60%.
mg / l to achieve the reference concentration.

The nitrogen concentration of the nitrate nitrogen contained in the discharged effluent assuming that the first system effluent was not subjected to the reduction treatment by the denitrification tank 27 was calculated to be 74.5 mg /
l. Similarly, when the nitrogen load of the discharged effluent in this case is calculated to be 87.8 kg / H, the nitrogen reduction amount representing the treatment capacity of the denitrification tank 27 during normal drainage is calculated as follows. (87.8-70.7) × 24 ≒ 400 (kg / da
y)

That is, the denitrification tank 27 is normally set at 1 during drainage.
It has the ability to remove about 400 kg of nitrogen per day.

At the time of drought, the flow rate of the third system wastewater is reduced. Thereby, the total flow rate of the second and third system drainage is 858 m ³ / H at the time of normal drainage, but is reduced to 160 m ³ / H at the time of drought. Conversely, since the flow rate of the third system wastewater, which is wastewater containing no nitrate nitrogen, is reduced, the nitrogen concentration of the nitrate nitrogen in the combined wastewater of the second and third system wastewaters increases. In other words, it was 21.9 mg / l during normal drainage, but 118 mg / l during drought. Second and third during drought
The nitrogen load of the wastewater combined with the system wastewater was 18.8 kg / H, which was the same as during normal drainage. At this time, the flow rate of the entire wastewater flowing into the wastewater treatment tank 6 is 117 times larger than that during normal drainage.
It has been reduced from 8 m ³ / H to 480 m ³ / H.

As in the case of normal drainage, the nitrogen concentration of nitrate nitrogen contained in the discharged wastewater when the first system wastewater is assumed to flow into the wastewater treatment tank 6 without being reduced by the denitrification tank 27 is calculated. Then, it becomes 182.9 mg / l. In this case, the nitrogen load of the discharged effluent is 87.8 kg / H as in the case of normal drainage. In order to reduce the calculated nitrogen concentration of the discharged effluent to 60 mg / l as in the case of normal drainage, a larger amount of nitrate nitrogen must be removed as compared with the case of normal drainage. . Table 1
In the denitrification tank at the time of drought, the BOD source solution is supplied in a larger amount than at the time of normal drainage, and the capacity for reduction treatment by denitrifying bacteria is further increased. That is, in the case of drought, the denitrification tank 2
7 reduces the nitrogen concentration of nitrate nitrogen contained in the first system wastewater from 215.6 mg / l to 31.
Reduced to 3 mg / l. As a result, the reference concentration can be achieved even during drought.

The nitrogen reduction amount representing the processing capacity of the denitrification tank 27 at the time of this water shortage is obtained as follows. (87.8-28.8) × 24 ≒ 1416 (kg / da
y)

That is, the denitrification tank 27 has the ability to remove about 1416 kg of nitrogen per day when water is short.

The processing capacity of the denitrification tank 27 at the time of drought shown in Table 1 is the maximum processing capacity of the denitrification tank 27. At this time, how much of the nitrate nitrogen contained in the first system wastewater should be removed. Is calculated by the following equation. (215.6-31.3) /21.5×100≒85
(%)

That is, the denitrification tank 27 can remove about 85% of the nitrate nitrogen contained in the wastewater of the first system at the time of drought that exhibits the maximum treatment capacity.

The present invention is not limited to the above-described embodiments, and modifications can be made without departing from the scope of the claims. The nitrate nitrogen biological treatment method and apparatus of the present invention can be realized in combination with an apparatus that previously converts nitrogen contained in wastewater flowing into a nitrate nitrogen biological treatment apparatus into nitrate nitrogen. As a result, the method and apparatus for treating biologically treated nitrate nitrogen of the present invention are suitable for wastewater having a form other than nitrate nitrogen, such as when the nitrogen contained in the wastewater is ammonium ion (NH ₄ ⁺ ). Can be implemented.

When the raw water tank 26 needs to be emptied once, the first valve 43 is completely closed and the second valve 44 is opened using the bypass passage 41, so that all the water in the raw water tank 26 is Can be pumped by the third pump 39 and passed through the bypass passage 41 and the first discharge passage 21 to be discharged to the wastewater treatment tank 6.

[0120]

According to the first aspect of the present invention, an appropriate amount of nitrogen is removed from the wastewater in accordance with the amount of nitrate nitrogen contained in the wastewater, and the nitrogen concentration of the wastewater is determined in advance. It can be reduced below the target concentration. Therefore, compared to a conventional treatment method in which a nutrient source solution is given to microorganisms such that the nitrate nitrogen in the wastewater is always equal to or lower than the target concentration regardless of the amount of nitrate nitrogen contained in the wastewater, The amount of the nutrient source solution given to the microorganism can be reduced, and the running cost can be reduced.

According to the second aspect of the present invention, the wastewater containing nitrate nitrogen is not divided into two systems, and the amount of nitrate nitrogen is reduced by using one of the microorganisms in one system instead of the two systems. Can be reduced in size. Also, a treatment method for reducing the amount of nitrate nitrogen in the wastewater divided into a plurality of systems and reducing the amount of nitrate nitrogen by utilizing microorganisms for each system and reducing the amount of nitrate nitrogen in the entire wastewater to the target concentration or less. In comparison, there is no need to provide a plurality of apparatuses for performing the nitrate-nitrogen biological treatment method, so that the treatment method can be realized more easily and the cost can be reduced.

According to the third aspect of the present invention, an appropriate amount of a nutrient solution can be given to a microorganism, and the average daily concentration can be controlled to be equal to or lower than a reference concentration. Therefore, compared to a processing method in which the target concentration is not changed at all, the amount of the nutrient source solution given to the microorganism within the preset period can be reduced, and the running cost can be further reduced.

According to the fourth aspect of the present invention, there is provided a treatment for reducing and removing nitrate nitrogen contained in wastewater to nitrogen gas by using the microorganism so that the concentration becomes lower than a predetermined target concentration. It is possible to provide the microorganisms in the denitrification tank with an appropriate amount of a nutrient source solution for reducing the concentration of nitrate nitrogen contained in the wastewater to the target concentration. This makes it possible to reduce the amount of the nutrient source solution given to constantly reduce the concentration of nitrate nitrogen in the wastewater to the target concentration regardless of the amount of the wastewater containing nitrate nitrogen. Therefore, running costs can be reduced. Further, it is possible to realize an unmanned nitrate nitrogen biological treatment.

According to the present invention, the sludge settled in the settling tank can be reused without being discarded. Therefore, the generation of industrial waste can be prevented as compared with a configuration in which the nitrate nitrogen biological treatment device does not include the sludge return device.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a schematic configuration of a nitrate nitrogen biological treatment apparatus 1 that performs a nitrate nitrogen biological treatment method according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the nitrate-nitrogen biological treatment device 1 of FIG.

FIG. 3 is a flowchart showing a calculation and control operation of a processing circuit 71 of FIG. 1;

FIG. 4 is a flowchart showing a specific operation of step s2 in FIG. 3;

5 is a diagram illustrating a frequency value fi given as a control command 65 to the induction motor 55 in FIG.
BOD pumped through OD source solution supply pump 52
It is a graph which shows the relationship with the flow rate of a source solution.

FIG. 6 is a flowchart showing an operation of a daily average correction of the processing circuit 71 of FIG. 1;

FIG. 7 is a graph showing an example of a temporal change of a nitrogen concentration in wastewater in the wastewater treatment tank 6 of FIG.

FIG. 8 is a system diagram showing a schematic configuration of a denitrification device 112 of a nitrate nitrogen biological treatment apparatus 111 for performing a nitrate nitrogen biological treatment method according to another embodiment of the present invention.

9 shows microorganisms 12 in sludge return device 113 in FIG.
FIG. 4 is a diagram schematically showing a decomposition mechanism of No. 2.

[Explanation of symbols]

 Reference Signs List 1,111 nitrate nitrogen biological treatment apparatus 5,112 denitrification apparatus 6 wastewater treatment tank 7 control device 21 first discharge path 26 raw water tank 27 denitrification tank 28 aeration tank 29 sedimentation tank 31 BOD source solution supply device 67 nitrogen concentration measuring instrument 113 Sludge return device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Minoru Tokuhara 4976 Nomura Minami-cho, Shinnanyo-shi, Yamaguchi Prefecture Nisshin Steel Co., Ltd. Shunan Steel Works (72) Inventor Mikio Kitagawa 3-4-2 Nishishinjuku, Shinjuku-ku, Tokyo No. Kurita Kogyo Co., Ltd. (72) Inventor Hitoshi Okano 3-4-7 Nishi Shinjuku, Shinjuku-ku, Tokyo F-term in Kurita Kogyo Co., Ltd. 4D040 AA01 AA31 4D059 AA03 BC02 BF12 CA28 DA32 DA43 EB11

Claims (5)

[Claims] 1. Nitrate nitrogen contained in waste water is reduced to nitrogen gas by using a microorganism that breathes in a anaerobic condition using a nutrient source solution as a feed and using oxygen in nitric acid, and is then removed. A treatment method for reducing the concentration to below the target concentration, wherein the amounts of generated wastewater and nitrate nitrogen are determined, and the amount of nitrate nitrogen contained in the wastewater is required to be an amount corresponding to the target concentration. A method for treating a nitrate-nitrogen organism, comprising: calculating a reduced amount from the generated amount; and feeding a nutrient source solution in an amount corresponding to the calculated reduced amount to the microorganism as food. 2. A system for discharging the wastewater containing nitrate nitrogen as it is, and a system for discharging the wastewater after reducing the amount of nitrate nitrogen by utilizing the microorganism, wherein the decrease amount is:
The nitrate nitrogen biological treatment method according to claim 1, wherein the amount of nitrate nitrogen in the entire wastewater is determined so as to be reduced to the target concentration or less. 3. The target concentration is changed according to the amount of nitrate nitrogen in wastewater actually discharged within the period so as to satisfy a condition for keeping the target concentration at or below the reference concentration for each preset period. 3. The method for treating a nitrate-nitrogen organism according to claim 1, wherein: 4. Nitrogen-containing nitrogen contained in waste water is reduced to nitrogen gas by using a microorganism that breathes in an anaerobic condition using a nutrient source solution as a feed and using oxygen in nitric acid to remove the nitrate-nitrogen, and the nitrate nitrogen is determined in advance. It is a treatment device for reducing the concentration to below the target concentration, and a raw water tank for receiving waste water containing nitrate nitrogen generated as raw water, and raw water is supplied from the raw water tank, and the microorganisms are subjected to nitrogen reduction treatment. Denitrification tank, Raw water reduced in the denitrification tank is supplied, aeration tank into which air is blown, raw water treated in the aeration tank is supplied, and sedimentation tank that discharges supernatant from sludge sedimentation as treated water And a control device for controlling the concentration of nitrate nitrogen contained in the raw water to a target concentration in the discharged wastewater to supply a nutrient source solution necessary for the reduction treatment to the denitrification tank. Characteristic nitrate nitrogen Thing processing equipment. 5. The nitrate state according to claim 4, further comprising a sludge return device that decomposes the sludge settled in the settling tank by ozone and supplies the sludge to the denitrification tank as a part of a nutrient source solution. Nitrogen biological treatment equipment.