JP4037491B2 - Nitrogen removal method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to nitrogen that can remove nitrogen from wastewater containing nitrate nitrogen or nitrite nitrogen, such as waste liquid and domestic wastewater after being used for metal surface treatment discharged from a metal material factory. The present invention relates to a removal method and apparatus.
[0002]
[Prior art]
For example, since nitrate nitrogen is an oxidizing substance, the oxidation-reduction potential value (hereinafter referred to as ORP value) increases as the concentration of nitrate nitrogen in the drainage increases.
[0003]
Further, when nitrate nitrogen is reduced and removed as nitrogen gas by the denitrification reaction, the nitrate nitrogen concentration decreases, and when the nitrate nitrogen concentration decreases, the ORP value decreases. In other words, the wastewater containing nitrate nitrogen changes its ORP value according to the concentration of nitrate nitrogen.
[0004]
Therefore, using this principle, the nitrate nitrogen concentration in the wastewater is detected as an ORP value, and the detected ORP value is used to control the amount of organic matter sources such as methanol required for denitrification. Various chemical denitrification methods have been proposed.
[0005]
Thus, as such a biological denitrification treatment method, for example, (1) the amount of methanol supplied to the wastewater is set so that the ORP value that allows good denitrification is set and the ORP value of the wastewater becomes the set value. One-value control method to control (2) Binary value to control the amount of methanol supplied to the waste water so that the ORP value that allows good denitrification is wide and the ORP value of the waste water is between the upper and lower limits There are control methods.
[0006]
In the above-mentioned conventional method, in any one of (1) and (2), the temperature, pH, type and amount of contained substances, the amount of dissolved oxygen, etc. do not change, and in the system where the properties are substantially constant, ORP The relationship between the value and the nitrate nitrogen concentration is reproducible. For this reason, the ORP value when denitrification is performed well and the ORP value when denitrification ends (end point of denitrification) are substantially constant, and ORP One-value control and binary control by value can be performed satisfactorily.
[0007]
[Problems to be solved by the invention]
However, even if the concentration of nitrate nitrogen in the wastewater does not change, if the wastewater temperature, pH, type and amount of contained substances, dissolved oxygen amount, etc. change and the properties of the wastewater change, denitrification is good. Since the ORP value at the time of execution and the ORP value at the end point of denitrification fluctuate from the original value (base fluctuation), good one-value control is necessary unless the set value of the ORP value is changed in accordance with the change in drainage properties Binary control cannot be performed.
[0008]
However, in the case of binary control, since the set value of the ORP value has a range, it is possible to cope with fluctuations in the ORP value due to the change in the property of drainage to some extent as compared with the single value control. If the change is large, we can't cope with it.
[0009]
In general, when the nitrate nitrogen concentration changes, a time delay of several tens of minutes occurs until the ORP value becomes a stable value corresponding to the nitrate nitrogen concentration. Although the nitrate nitrogen concentration is lower than the reference value, and in the case of binary control, methanol is supplied into the waste water even though the nitrate nitrogen concentration is lower than the lower limit value. There is a possibility that a good denitrification treatment cannot be performed due to an excessive supply.
[0010]
By the way, the relationship between time and ORP value in the case of performing conventional binary control is shown in the graphs of FIGS.
[0011]
FIG. 4 is a graph showing the relationship between the time and the ORP value when the conventional binary control is satisfactorily performed. In line (i), the supply of methanol is started at the ORP value of −190 mV, and methanol at −210 mV. The case where the supply of is stopped is shown.
[0012]
FIG. 5 is a graph showing an enlarged part of the curve of FIG. 4 and also showing the relationship between time and nitrate nitrogen concentration. During time T, although nitrate nitrogen is not detected, This shows that methanol is being supplied, and that methanol is excessively supplied.
[0013]
Further, FIG. 6 is a graph showing the relationship between the time and the ORP value when an abnormality occurs in the conventional binary control. The supply of methanol is started when the ORP value is −160 mV, and the supply of methanol is stopped when the ORP value is −180 mV. Shows when to do. However, the ORP value at the start of the supply of methanol causes base fluctuations as indicated by the straight line B rising to the right in FIG. 6, indicating that normal control is not performed.
[0014]
In view of the above situation, the present invention detects the nitrogen nitrate concentration in the waste water and the nitrogen nitrogen is no longer present. It was made for the purpose of making it possible to perform removal.
[0015]
[Principle of the present invention]
When shifting from a state in which nitrate nitrogen is present in the waste water to a state in which nitrate nitrogen is not present, the change in the ORP value indicated to the ORP detector is slow, and therefore the ORP value indicated to the ORP detector is determined to be nitrate. It takes several tens of minutes (refer to the portion of time T in FIG. 5) to reach the original ORP value in which no nitrogen exists.
[0016]
However, the rate of change of the ORP value per unit time (hereinafter referred to as the time rate of change of the ORP value) changes immediately when the nitrate nitrogen concentration changes.
[0017]
Therefore, in the present invention, not the ORP value itself, but the time change rate of the ORP value is obtained, and when the time change rate of the ORP value becomes a certain value or more, it is determined that nitrate nitrogen exists. When the time change rate of the ORP value became a certain value or less, it was determined that nitrate nitrogen was not present, and the supply of methanol was stopped.
[0018]
Thus, by performing such control, it is possible to quickly detect a state in which nitrate nitrogen does not exist, and it is possible to prevent wasteful supply of methanol and perform nitrogen removal satisfactorily.
[0019]
[Means for Solving the Problems]
In the present invention, when wastewater containing at least one of nitrate nitrogen and nitrite nitrogen is biologically reduced and denitrified, the concentration of nitrate nitrogen or nitrite nitrogen concentration in the wastewater is reduced. A nitrogen removal method for controlling the amount of organic matter added according to fluctuations,
Regardless of the oxidation-reduction potential value in the wastewater,
When the time change rate of the oxidation-reduction potential value in the wastewater is equal to or higher than a predetermined upper limit value, supply organic matter into the wastewater,
The supply of the organic matter to the waste water is stopped when the value becomes equal to or lower than a predetermined lower limit value smaller than a predetermined zero.
[0020]
Further, the present invention provides a concentration of nitrate nitrogen or nitrite nitrogen in wastewater when biologically reducing and denitrifying wastewater containing at least one of nitrate nitrogen and nitrite nitrogen. A nitrogen removal device that controls the amount of organic matter added according to concentration fluctuations,
An oxidation-reduction potential detector for detecting the oxidation-reduction potential value of the wastewater in the flow denitrification tank that reduces nitrate nitrogen or nitrite nitrogen to nitrogen gas by the action of denitrifying bacteria, and this time detected by the oxidation-reduction potential detector From the oxidation-reduction potential value of and the oxidation-reduction potential value detected a predetermined time ago, the time change rate of the oxidation-reduction potential value is obtained,
When the obtained time change rate is equal to or higher than a predetermined upper limit value of the time change rate, a command signal for driving a pump for supplying organic matter to the fluid denitrification tank is output regardless of the oxidation-reduction potential value in the waste water ,
An arithmetic control device is provided that outputs a command signal for stopping the pump regardless of the oxidation-reduction potential value in the waste water when the obtained time change rate is equal to or less than a lower limit value smaller than zero of the predetermined time change rate. Is.
[0021]
Therefore, in the present invention, the base fluctuation is also affected when the ORP value at the time of denitrification being favorably performed due to the change in the properties of the waste water or the ORP value at the end point of the denitrification changes. Therefore, it is possible to detect the nitrate nitrogen concentration or the nitrite nitrogen concentration instantly and accurately.
[0022]
For this reason, it is possible to supply an appropriate amount of organic matter to the fluidized denitrification tank, eliminating denitrification failure due to lack of organic matter, eliminating excessive organic matter supply, and saving the cost of organic matter. it can.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0024]
FIG. 1 shows an example of an embodiment of the present invention.
[0025]
In the figure, 1 is a fluid denitrification tank. Thus, the fluid denitrification tank 1 keeps the waste water mixed with the raw water W1, the treated water W2, and the methanol M in the tank 1 in an anaerobic state without dissolved oxygen, and attaches denitrifying bacteria as a biofilm to the surface. The solid particulate carrier is fluidized in the tank 1, and nitrate nitrogen NO ₃ ⁻ in the waste water is reduced to nitrogen gas N ₂ and removed by the action of denitrifying bacteria.
[0026]
Reference numeral 2 denotes an aerobic filter bed installed downstream of the fluid denitrification tank 1. Thus, the aerobic filter bed 2 holds a solid particulate carrier in which the wastewater from the fluid denitrification tank 1 is dissolved and in which oxygen is dissolved and a BOD-degrading bacterium and nitrifying bacteria are attached to the surface as a biofilm. 2 slowly move upward from below, decompose and remove organic matter and BOD in the wastewater by BOD-degrading bacteria, nitrify ammonia nitrogen to convert ammonia into nitric acid by nitrifying bacteria, and treat treated water W2 To obtain (nitrification step).
[0027]
3 is a control tank for storing process waste water and domestic waste water containing nitrate nitrogen, and 4 is a pump for feeding waste water in the control tank 3 as raw water W1 to the fluid denitrification tank 1 via the pipeline 5.
[0028]
A methanol storage tank 6 stores methanol as an organic substance, and a pump 7 supplies the methanol M in the methanol storage tank 6 into the pipe line 5 through the pipe line 8.
[0029]
9 is a pump for circulating a part of the treated water W2 that has been treated and flowed out in the aerobic filter bed 2 downstream of the pipe 8 connection portion of the pipe 5 through the pipe 10, and the remaining treatment. The water W2 passes through a pipe line 10a branched from the pipe line 10 on the upstream side of the pump 9, and can be supplied to a disinfection tank (not shown).
[0030]
11 is an ORP detector for continuously detecting the ORP value (oxidation-reduction potential value ORP) of the waste water in the flow denitrification tank 1, and 12 is the ORP value from the ORP value detected by the ORP detector 11. The time change rate ΔORP is obtained, and when the time change rate ΔORP reaches a predetermined upper limit value ΔORPMAX, a start command is given to the pump 7, and when the time change rate ΔORP reaches a predetermined lower limit value ΔORPMIN, a stop command is given to the pump 7. This is an arithmetic control device. As an electrode of the ORP detector 11, a saturated KCl silver chloride electrode, a saturated KCl sugar cane electrode, a 3.3MKCl chloride electrode, a 3MKCl electrode, etc. are used. In the case of a saturated KCl silver chloride electrode, a reference hydrogen electrode is used. The potential value is about 200 mV lower than that when it was present. Hereinafter, the ORP value described in the present specification is a value based on a saturated KCl silver chloride electrode as an electrode of the ORP detector.
[0031]
Next, the operation of the embodiment of the present invention will be described.
[0032]
The waste water in the adjustment tank 3 is supplied from the pipe 5 to the fluid denitrification tank 1 by the pump 4 as raw water W1.
[0033]
At the same time, a part of the treated water W2 from the aerobic filter bed 2 is supplied to the fluid denitrification tank 1 through the pipes 10 and 5 by the pump 9.
[0034]
Further, when the time change rate ΔORP of the ORP value obtained by the arithmetic control device 12 based on the ORP value detected by the ORP detector 11 is equal to or higher than a predetermined upper limit value ΔORPMAX, a command given from the arithmetic control device 12 is used. Since the pump 7 is driven, the methanol M from the methanol storage tank 6 is supplied into the fluid denitrification tank 1 via the pipe lines 8 and 5 by the pump 7.
[0035]
In the fluid denitrification tank 1, the carrier to which the denitrifying bacteria are attached is fluidized, and the denitrifying bacteria are converted into BOD or methanol M in the raw water W1 and the treated water W2 from the aerobic filter bed 2 in an oxygen-free state. including nitrate nitrogen (NO ₃ ^-) and performs nitrate respiration by.
[0036]
As a result, in the fluid denitrification tank 1, nitrate nitrogen is reduced to generate nitrogen gas (N ₂ gas), and the generated nitrogen gas is released into the atmosphere and removed from the waste water, completing the denitrification.
[0037]
The reason why methanol M is added in the above operation is as follows. That is, denitrification requires 2 to 6 times the BOD (organic matter) of nitrate nitrogen or nitrite nitrogen, and if the organic matter is insufficient, it is necessary to add the organic matter. Is used.
[0038]
The reaction at the time of denitrification is as shown in [Chemical Formula 1] in the case of nitrate nitrogen and as shown in [Chemical Formula 2] in the case of nitrite nitrogen.
[0039]
[Chemical 1]
CH ₃ OH + H ₂ O → CO ₂ +3 (H ₂ )
2NO ₃ ⁻ +5 (H ₂ ) → N ₂ + 2OH ⁻ + 4H ₂ O
[0040]
[Chemical 2]
2NO ₂ ⁻ +3 (H ₂ ) → N ₂ + 2OH ⁻ + 2H ₂ O
[0041]
Wastewater denitrified in the fluid denitrification tank 1 overflows and is supplied to the aerobic filter bed 2, and BOD in wastewater and organic substances other than BOD are decomposed by BOD-degrading bacteria to become ammoniacal nitrogen, and ammonia nitrogen Is nitrated by nitrifying bacteria to become nitrate nitrogen (nitrification process).
[0042]
Thus, the treated water W2 generated by treating the waste water in the aerobic filter bed 2 in this way is pumped by the pump 9, and a part of the fluid denitrification tank 1 from the pipe line 10 through the pipe line 5 is fed. circulated to, nitrate nitrogen NO ₃ contained in the treated water W2 as described above ^- by the denitrifying bacteria performs nitrate respiration, are reduced nitrogen gas is generated, the nitrogen gas generated is discharged into the atmosphere Is removed from the wastewater, and denitrification is completed.
[0043]
On the other hand, the ORP value of the waste water in the flow denitrification tank 1 is detected by the ORP detector 11 at a constant time interval (for example, every 6 seconds) and given to the arithmetic control device 12, and the arithmetic control device 12 gives the ORP given this time. From the value ORP1 and the ORP value ORP2 given before the predetermined time TX (for example, 10 minutes before), the time change rate ΔORP of the ORP value is calculated at a constant time interval (for example, every 6 seconds) by [Equation 1].
[0044]
[Expression 1]
ΔORP = (ORP1-ORP2) / TX
[0045]
The ORP value temporal change rate ΔORP obtained by the arithmetic and control unit 12 is compared with a preset upper limit value ΔORPMAX and lower limit value ΔORPMIN of the ORP value.
[0046]
Thus, when the time rate of change ΔORP of the ORP value is equal to or greater than the upper limit value ΔORPMAX (ΔORP ≧ ΔORPMAX), a start command is given from the arithmetic control unit 12 to the pump 7, and methanol 7 is supplied to the pipes 8 and 5 by the pump 7. To the fluid denitrification tank 1 and added to the waste water in the fluid denitrification tank 1. The upper limit value ΔORPMAX is, for example, 10 mV / 10 minutes.
[0047]
When denitrification progresses and nitrate nitrogen in the flow denitrification tank 1 decreases, the ORP value detected by the ORP detector 11 decreases, and when nitrate nitrogen is reduced to a certain state, the decrease rate of nitrate nitrogen. Decreases, the ORP value temporal change rate ΔORP also decreases.
[0048]
Thus, when the time change rate ΔORP of the ORP value falls below the lower limit value ΔORPMIN (ΔORP ≦ ΔORPMIN), a stop command is given from the arithmetic and control unit 12 to the pump 7, and the pump 7 is stopped and the supply of methanol M is stopped. . The lower limit value ΔORPMIN is, for example, −10 mV / 10 minutes.
[0049]
When the pump 7 is stopped and the supply of methanol M to the fluid denitrification tank 1 is stopped, and as a result, the nitrate nitrogen in the fluid denitrification tank 1 starts to increase again, the ORP value detected by the ORP detector 11 increases. In addition, since the increase rate of nitrate nitrogen increases, the time change rate ΔORP of the ORP value also increases.
[0050]
Thus, when the time change rate ΔORP of the ORP value rises to the upper limit value ΔORPMAX, the operation control device 12 gives a start command to the pump 7 again to start the pump 7, and the supply of the methanol M to the fluid denitrification tank 1 is started. Resumed.
[0051]
The upper limit value ΔORPMAX and the lower limit value ΔORPMIN of the time change rate ΔORP of the ORP value are determined as follows. That is, the ORP value temporal change rate ΔORP that changes rapidly depending on the denitrification situation is associated with changes in the temperature, pH, type and amount of contained substances, the amount of dissolved oxygen, in other words, changes in the properties of the drainage. Since it is sufficiently larger than the time change rate ΔORP of the ORP value, nitrate nitrogen can be reliably detected by setting the set value between X and Y. Therefore, the upper limit value and the lower limit value of the time change rate ΔORP of the ORP value are between X and Y.
[0052]
At the start of operation of the device (at the start), there is no ORP value data from the start of the operation until a predetermined time (for example, 10 minutes before). Since this is not possible, the ORP value is initially set based on experience and the like.
[0053]
As described above, the relationship between the time and the ORP value when the ORP value is controlled based on the time change rate ΔORP is shown in the graph of FIG. 2, and a part of the graph of FIG. The relationship is shown in the graph of FIG. In the graphs of FIGS. 2 and 3, the supply of methanol is started at an ORP value of about −390 mV, and the supply of methanol is stopped at an ORP value of about −180 mV.
[0054]
Thus, in the graph of FIG. 2, when the supply amount of methanol is controlled by the time rate of change of the ORP value, the ORP is more effective than when the supply amount of methanol is controlled by the ORP value itself (see FIG. 4). It can be seen that the absolute value of the time change rate of the value is large (the peak is sharp).
[0055]
This is because when the amount of methanol supplied is controlled by the rate of change of the ORP value over time, the presence or absence of nitrate nitrogen (about 0.1 mg / L) is shorter than when the amount of methanol supplied is controlled by the ORP value. This means that the methanol can be reliably detected and the methanol is being supplied efficiently.
[0056]
Also, the graph of FIG. 3 shows that in the embodiment of the present invention, when nitrate nitrogen is reduced, the pump 7 is stopped without causing a time delay, and therefore methanol M is excessively supplied. It shows that there is no.
[0057]
In the embodiment of the present invention, since the time change rate ΔORP of the ORP value is detected to supply and stop the methanol M, the denitrification is favorably performed due to the change in the properties of the waste water. Even if the ORP value at the time or the ORP value at the end point of denitrification changes and the base fluctuates, a minute amount of nitrate nitrogen in the fluid denitrification tank 1 is instantly and accurately not affected by the base fluctuation. It becomes possible to detect.
[0058]
For this reason, an appropriate amount of methanol can be supplied to the fluid denitrification tank 1, denitrification failure due to methanol shortage can be eliminated, and excessive methanol supply can be eliminated, thereby saving the cost of methanol. Can do.
[0059]
In the embodiment of the present invention, the case where methanol is used as the organic substance has been described. However, the organic carbon source is not limited to methanol, and various organic substances (for example, ethanol, acetic acid, etc.) can be used, ORP detection. It is possible to use a so-called microbial sensor in which microorganisms such as sulfate-reducing bacteria are attached to the electrode of the detector, and can be applied not only to nitrate nitrogen but also to nitrite nitrogen Of course, various modifications can be made without departing from the scope of the present invention.
[0060]
【The invention's effect】
According to the nitrogen removing method and apparatus of the present invention, since it is possible to supply an appropriate organic matter, it is possible to eliminate the denitrification failure due to the shortage of the organic matter and eliminate the supply of the excessive organic matter, thereby saving the cost of the organic matter. It is possible to achieve an excellent effect of being able to.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of an embodiment of a nitrogen removal method and apparatus according to the present invention.
FIG. 2 is a graph showing the relationship between time and ORP value in the embodiment of the present invention.
FIG. 3 is a graph showing a relationship between time and nitrate nitrogen concentration while enlarging a part of the graph of FIG. 2;
FIG. 4 is a graph showing the relationship between time and ORP value when control is performed well in a conventional nitrogen removal method.
FIG. 5 is a graph showing a relationship between time and nitrate nitrogen concentration while enlarging a part of the graph of FIG. 4;
FIG. 6 is a graph showing a relationship between time and ORP value when abnormality occurs in control in a conventional nitrogen removal method.
[Explanation of symbols]
1 Flow denitrification tank 7 Pump 11 ORP detector (redox potential detector)
12 Arithmetic control device M Methanol (organic)
ORP Redox potential value ΔORP Time change rate ΔORPMAX Upper limit ΔORPMIN Lower limit

Claims (2)

When wastewater containing at least one of nitrate nitrogen or nitrite nitrogen is biologically reduced and denitrified, depending on the fluctuation of nitrate nitrogen concentration or nitrite nitrogen concentration in the wastewater A nitrogen removal method for controlling the amount of organic matter added,
Regardless of the oxidation-reduction potential value in the wastewater,
When the rate of time change of the oxidation-reduction potential value in the wastewater is equal to or higher than a predetermined upper limit value, supply organic matter into the wastewater,
A method for removing nitrogen, comprising: stopping supply of organic matter to the waste water when a predetermined lower limit value smaller than a predetermined zero is reached. When wastewater containing at least one of nitrate nitrogen or nitrite nitrogen is biologically reduced and denitrified, depending on the fluctuation of nitrate nitrogen concentration or nitrite nitrogen concentration in the wastewater A nitrogen removal device for controlling the amount of organic matter added,
An oxidation-reduction potential detector that detects the oxidation-reduction potential value of the waste water in the flow denitrification tank that reduces nitrate nitrogen or nitrite nitrogen to nitrogen gas by the action of denitrifying bacteria, and this time detected by the oxidation-reduction potential detector From the oxidation-reduction potential value of and the oxidation-reduction potential value detected a predetermined time ago, the time change rate of the oxidation-reduction potential value is obtained,
When the obtained time change rate is equal to or higher than a predetermined upper limit value of the time change rate, a command signal for driving a pump for supplying organic matter to the fluid denitrification tank is output regardless of the oxidation-reduction potential value in the waste water ,
An arithmetic control device is provided for outputting a command signal for stopping the pump regardless of the oxidation-reduction potential value in the waste water when the obtained time change rate is equal to or less than a lower limit value smaller than zero of the predetermined time change rate. A nitrogen removing apparatus characterized by that.

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