JPH0880497A - Nitrator - Google Patents

Abstract

PURPOSE: To maintain the pH in a nitration tank with the range where the activity of nitrating bacteria is enhanced even when the pH, NH4 <+> concn. or alkalinity of the water to be treated are fluctuated at a low cost and with a simple operation at the time of biologically nitrating the water with the plug-flow nitration tank and consequently to stably conduct nitration at a high rate. CONSTITUTION: The water 11 to be treated is introduced into a pH regulating tank 1, and an alkaline agent is added from its storage tank 3. In this case, the pH is measured by a first pH measuring device 2, and the water is controlled to pH 6.0-9.7 where the activity of the nitrating bacteria is enhanced. The pH-regulated water is introduced into a plug-flow nitration tank 4 and biologically nitrated. The pH of the nitrated water (outlet water) is measured by a second pH measuring device 5, and carbon dioxide is injected into the alkaline agent in the tank 3 to keep the pH at 6.0-9.7, and a buffer capacity is imparted to the water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrification apparatus for biologically nitrifying nitrogen compounds in water to be treated by using a plug flow type nitrification tank. The present invention relates to usable nitrification equipment.

[0002]

2. Description of the Related Art As a method for treating an effluent containing an ammoniacal or organic nitrogen compound, there is a biological nitrification denitrification treatment method. This method decomposes COD and BOD components in the effluent by aerobic treatment in the presence of activated sludge, converts organic nitrogen compounds into ammonia nitrogen, and then aerates in the presence of activated sludge in which nitrifying bacteria have proliferated. After nitrifying (oxidizing) ammoniacal nitrogen (NH ₄ —N) into nitrite or nitrate nitrogen (hereinafter collectively referred to as NOx-N) by nitrifying bacteria, denitrifying bacteria grow. This is a method of denitrifying by reducing nitrite or nitrate nitrogen to nitrogen gas by maintaining it in an anaerobic state in the presence of the activated sludge.

Both nitrification and denitrification reactions are reactions involving pH changes. Particularly, in the nitrification reaction, 2 mol of H ⁺ is generated when 1 mol of NH ₄ ⁺ is nitrified, so that nitrification-treated water is treated. The pH of is drastically reduced. However, the nitrifying activity of nitrifying bacteria is greatly affected by pH as shown in FIG. 3, so it is necessary to control the pH in the nitrifying tank within a range where the activity of nitrifying bacteria is high by some means.

The pH change in nitrification is determined by the NH ₄ ⁺ concentration and alkalinity of the water to be treated.
That is, when the alkalinity of the water to be treated is sufficiently higher than the NH ₄ ⁺ concentration, the pH drop due to nitrification is small, and conversely, when the alkalinity is small compared to the NH ₄ ⁺ concentration, the pH drop is low. Grows.

Conventionally, in order to deal with the decrease in pH due to nitrification, an alkali such as sodium hydroxide is added as a pH adjusting agent to maintain the pH at a predetermined value. It is also possible to use an alkali (for example, JP-A-56-111097 and JP-A-55-11550).
-102498, 59-139987). However, the nitrification shown in these conventional examples is of a completely mixed type, and no application to a plug flow type nitrification tank is suggested.

When nitrification is carried out by a complete mixing type floating method such as the activated sludge method, the water to be treated is in a nearly completely mixed state. Therefore, a pH sensor is put in the nitrification tank liquid to control the pH. It can be easily controlled by adding an alkali such as NaOH so as to fall within the range.

On the other hand, when nitrification is carried out using a nitrification tank having a biological filtration layer in which nitrifying bacteria have proliferated, the pH of the whole nitrification tank falls within a predetermined range because the water to be treated flows in a plug flow. It is difficult to adjust and p
H decreases. Even in this case, it is possible to install a pH adjustment tank at the front stage of the nitrification tank and adjust the pH at the entrance of the nitrification tank, but if the alkalinity of the water to be treated is lower than the NH ₄ ⁺ concentration, In this case, it is difficult to maintain the activity of nitrifying bacteria at a high level due to a large decrease in pH, and therefore nitrification cannot be stably performed at a high nitrification rate (NH ₄ -N removal rate). Also, if the pH at the entrance of the nitrification tank is set to a high value in anticipation of a decrease in pH in the nitrification tank, the pH at the entrance of the nitrification tank becomes too high, and the reaction of nitrifying bacteria may be hindered.

To prevent the pH from decreasing in the nitrification tank,
For example, it is possible to circulate the nitrification-treated water flowing out from the nitrification tank again to the inlet, and to adjust the pH in a state where the water to be treated and the circulating water are mixed. In this case, since the NH ₄ ⁺ concentration at the entrance of the nitrification tank becomes smaller than the alkalinity, the pH drop in the nitrification tank becomes small. Theoretically, as the circulation ratio (ratio of the circulating water amount to the treated water flow rate) is increased, the flow of the treated water approaches a completely mixed state, and the conditions similar to those of the floating method are approached. However, in practice, there is a limit in the above method due to an increase in power cost of the circulation pump and an increase in pressure loss due to an increase in liquid flow rate in the nitrification tank. Therefore, when nitrification is performed by a plug flow type nitrification tank, there is a demand for a nitrification method capable of easily adjusting the pH at low cost and thereby stably nitrifying at a high nitrification rate.

[0009]

An object of the present invention is to provide a, upon biologically nitrifying using nitrification tank plug flow of nitrogen compounds in the water to be treated, in the for-treatment water pH, NH ₄ ⁺
Even when the concentration, organic nitrogen compound content or alkalinity changes, the pH in the nitrification tank can be easily maintained at a low cost so that the nitrifying activity of nitrifying bacteria becomes high, and thereby stable An object of the present invention is to provide a nitrification apparatus capable of nitrifying at a high nitrification rate.

[0010]

SUMMARY OF THE INVENTION The present invention is based on p
A pH adjusting tank for adjusting H, a plug flow type nitrification tank for biologically nitrifying the pH-adjusted water to be treated, and a first pH measurement for measuring the pH of the water to be introduced to the nitrification tank The measurement value of the device and the first pH measuring device is pH 6.
A chemical injection device for adding an alkaline agent to the pH adjusting tank so as to be 0 to 9.7, a second pH measuring device for measuring the pH of the nitrification-treated water, and a measurement value of the second pH measuring device. Is p
A nitrification device comprising: a carbon dioxide injection device for injecting carbon dioxide into the alkali agent so as to maintain H 6.0 to 9.7.

The water to be treated in the nitrification apparatus of the present invention is a liquid containing ammoniacal nitrogen or an organic nitrogen compound and may contain other impurities. Especially the alkalinity (M-alkalinity, the same applies below) is N
An effluent which is lower than the H ₄ ⁺ concentration and whose pH is greatly lowered by nitrification, or an effluent whose pH, NH ₄ ⁺ concentration, organic nitrogen compound content or alkalinity varies is suitable for the treatment. Such water to be treated may be subjected to a treatment such as decomposing organic matter by aerobic treatment using activated sludge or performing a denitrification process by circulating nitrification treated water before introducing it into the nitrification tank.

In the plug flow type nitrification tank used in the present invention, a biological sludge layer in which nitrifying bacteria have grown is filled in the tank, and the water to be treated is passed through this packed layer by plug flow (one-way flow). Then, it is a device for nitrifying by contacting under aerobic conditions. As a method for forming a biological sludge layer, a method of filling the granulated sludge, or a method of attaching the biological sludge to the packed layer,
Any type such as a fixed bed type and a fluidized bed type can be adopted.

The pH adjusting tank constituting the nitrification apparatus of the present invention is constructed so that the water to be treated is introduced, an alkaline agent is added and the mixture is uniformly mixed to adjust the pH. Any stirring means can be used for uniform mixing. The pH adjusting tank is preferably configured to circulate and mix the nitrification-treated water from the nitrification tank.
When the value is too high, it is preferable to add an acid such as hydrochloric acid or sulfuric acid to the pH adjusting tank.

The first pH measuring device measures the pH of the water to be treated which is introduced into the nitrification tank, and based on the measured value, an alkaline agent or an acid is added to the water to be treated as a pH adjuster to obtain the water to be treated. Is controlled to the above pH. Even when the raw water falls within the above pH range, the pH is lowered by circulating the nitrification-treated water, so that the alkaline agent is injected to control the pH in an average state.

The second pH measuring device measures the pH of the nitrification-treated water nitrified in the nitrification tank, and controls the amount of carbon dioxide injected into the alkaline agent so that the measured value maintains the pH value. To configure. Carbon dioxide can be injected by a method of directly injecting from a gas cylinder or a method of diffusing air containing carbon dioxide. The above control is feedback control, and when the pH of the nitrification-treated water falls below the lower limit value or approaches the lower limit value, the amount of carbon dioxide added is increased and exceeds the upper limit value or approaches the upper limit value. At times, control is performed so as to reduce the amount of carbon dioxide added.

[0016]

In the present invention, the pH is adjusted in the pH adjusting tank as described above.
The water to be treated adjusted to H 6.0 to 9.7, preferably 6.5 to 9.5, and more preferably 7.5 to 9.5 was introduced into a plug flow type nitrification tank, and aerobically operated. Water is passed through the plug flow and nitrification is performed by nitrifying bacteria. Nitrification in the nitrification tank oxidizes ammoniacal nitrogen to nitrous acid or nitrate nitrogen.Therefore, if organic matter is present in the water to be treated, it should be removed by activated sludge treatment beforehand. Bacteria can be predominant and nitrification can be performed efficiently.

In the present invention, the pH of the water to be treated is within the above range, and the pH of the nitrification treated water is 6.0 to 9.7, preferably 6.5 to 9.5, more preferably 6.5 to 7. .5
By adding carbon dioxide to the alkaline agent so as to maintain the above range, nitrification is performed in a pH range where the nitrifying activity of nitrifying bacteria is high, and moreover, the water to be treated is buffered, so that the nitrification reaction Even if nitrous acid or nitric acid is produced, the pH is prevented from lowering due to the buffer action, and nitrification is efficiently performed even in the case of plug flow. As the alkaline agent, alkali hydroxides such as sodium hydroxide and potassium hydroxide are preferable. The concentration of these is preferably such that the precipitation of alkali carbonate does not occur by blowing carbon dioxide, for example, 5 to 15% by weight in the case of sodium hydroxide.

The nitrification apparatus of the present invention is used as a nitrification apparatus in a biological nitrification denitrification method of an ammonia-containing liquid or an organic waste liquid, but it can also be used when only nitrification is intended.

When used as a biological nitrification / denitrification method, it is preferable to previously decompose an organic matter by an aerobic treatment such as an activated sludge method and simultaneously convert an organic nitrogen compound into ammoniacal nitrogen. In addition, a denitrification tank was installed in the preceding stage of the nitrification tank to circulate the nitrification-treated water, and the water to be treated was introduced into this denitrification tank, and denitrification was performed by maintaining the anaerobic state in the presence of denitrification bacteria , Can be introduced into a nitrification tank to perform nitrification. In this case, a denitrification tank and a nitrification tank can be provided in one tank. For example, an air diffuser is provided in the middle of the biological filtration device to keep the upper part in an aerobic state and the treated water is treated in an upward flow. When water is passed, the upper part can be integrated with the nitrification tank and the lower part with the denitrification tank. Even in such a case, nitrification can be efficiently performed by controlling as described above.

[0020]

Embodiments of the present invention will now be described with reference to the drawings.
FIG. 1 is a system diagram showing the nitrification apparatus of the embodiment. In FIG. 1, 1 is a pH adjusting tank, 2 is a first pH measuring device, 3 is an alkaline agent storage tank, 4 is a plug flow type nitrification tank, 5 is a second pH measuring device, 6 is a pressure adjusting tank, 7 Is a control device.

The pH adjusting tank 1 is connected to a water passage 11 to be treated, an alkali agent injecting passage 12 and a circulation passage 13, and a first pH measuring device 2 for measuring the pH of the liquid in the tank, a stirrer 14 and a liquid supply pump. 15 is provided, and the communication passage 16 communicates with the pressure adjusting tank 6 from the liquid supply pump 15. The treated water passage 11 is provided with a treated water pump 17, the alkaline agent injection passage 12 is provided with a chemical injection pump 18, and the circulation passage 13 is provided with a circulation pump 19.

A biological filtration layer 21 containing nitrifying bacteria is formed inside the nitrification tank 4. An air diffuser 22 is provided below the biological filtration layer 21 and connected to the air supply passage 23, and a second pH measuring device 5 for measuring the pH of the nitrification-treated water is provided above the nitrification tank 4. There is. Further, the lower part of the nitrification tank 4 is a communication path 24 from the pressure adjusting tank 6, the upper part of the biological filtration layer 21 is a treated water path 25, and a circulation path 1 to the pH adjusting tank 1.
An exhaust gas passage 26 is connected to the upper portion of the nitrification tank 3 and the nitrification tank 4.

An air diffuser 31 is provided below the alkaline agent storage tank 3.
Is provided and connected to the carbon dioxide supply path 32. The carbon dioxide supply path 32 communicates with the blower 33, and a flow rate control valve 34 is provided on the way. Reference numeral 35 is a gas cylinder used selectively. In addition, a water level gauge 36 is provided in the alkaline agent storage tank 3, and the alkaline agent is replenished from a separately provided alkaline agent supply source according to the detection signal so that the alkaline agent in a predetermined range can be constantly stored. It is configured. The size of the alkaline agent storage tank 3 is preferably small so that the pH can be easily adjusted by blowing carbon dioxide.

The control device 7 inputs the measured pH signal of the first pH measuring device 2, and when the measured value is lower than pH 6.0, preferably 6.5, more preferably 7.5, the dosing pump 18 Output a drive signal to the measured value of pH 9.7,
It is preferably configured to output a stop signal when it is higher than 9.5. In addition, the control device 7 controls the second pH.
When the measured pH signal of the measuring device 5 is input and the measured value is feedback-controlled, the required carbon dioxide injection amount is calculated when the measured value is lower than 6.0, preferably 6.5, and a drive signal is supplied to the blower 33 and the flow rate control valve 34. It is configured to output.

Alkaline agent storage tank 3, alkaline agent injection passage 1
2 and the chemical injection pump 18 constitute a chemical injection device, and the alkaline agent is injected into the pH adjusting tank 1 by a control signal of the control device 7 according to the measured pH value of the first pH measuring device 2. Has been done. Further, the air diffuser 31, the carbon dioxide supply path 32, the blower 33, the flow rate control valve 34, and the gas cylinder 35 constitute a carbon dioxide injecting device, and a control signal of the control device 7 according to the measured pH of the second pH measuring device 5. Is configured to inject carbon dioxide.

In FIG. 1, reference numerals 22a and 23a show the positions of the air diffuser 22 and the air supply passage 23 in the nitrification tank 4 when performing denitrification in addition to nitrification, and the air diffuser 22 and the air supply are provided at these positions. By arranging the passage 23, the nitrification part 21a is formed above the air diffuser 22a in the biological filtration layer 21, and the denitrification part 21b is formed below the air diffuser 22a.

In order to carry out nitrification by the apparatus of FIG. 1, first, the treated water pump 17 is driven to introduce the treated water from the treated water passage 11 into the pH adjusting tank 1, and the circulation pump 19 is driven to drive the circulation passage. Nitrification-treated water is introduced from 13 and stirred by a stirrer 14. The pH of the liquid in the pH adjusting tank 1 is set to the first pH.
It is measured by the measuring device 2 and the measured pH value is input to the control device 7. A control signal is output from the control device 7 in accordance with the measured pH value to drive the chemical injection pump 18 so that the liquid in the tank has the above-mentioned pH value.
In this way, the alkaline agent in the alkaline agent storage tank 3 is injected through the alkaline agent injection passage 12.

The pH-adjusted water to be treated (solution in the tank) is
The liquid supply pump 15 sends it to the pressure adjusting tank 6 through the communication path 16.
From here, it is introduced into the nitrification tank 4 at a constant pressure. here
Uses the air diffuser 22 to supply the air supplied from the air supply path 23.
The water to be treated flows upward in the biological filtration layer 21 in an aerated state.
NH3 in the water to be treated due to the action of nitrifying bacteria._Four
Biologically nitrify -N to NOx-N. In the water to be treated
If organic nitrogen compounds are contained, this organic substance
Nitrogen compounds are converted into NH by the action of BOD-degrading bacteria. _Four-N
Is decomposed into NOx-N by the action of nitrifying bacteria.
Nitrified.

A part of the nitrification-treated water is circulated from the circulation path 13 to the pH adjusting tank 1 by the circulation pump 19. The rest is taken out from the treated water channel 25 as treated water. By circulating a part of the nitrification-treated water and mixing it with the water to be treated, the NH ₄ ⁺ concentration at the inlet of the nitrification tank 4 becomes smaller than the alkalinity, so that the decrease in pH can be reduced. The circulation of the nitrification-treated water is not always necessary and may be omitted in some cases.

In the above treatment, the pH of the nitrification-treated water is measured by the second pH measuring device 5, and the measured pH value is input to the control device 7. The controller 7 calculates the required amount of alkali carbonate based on the measured pH value and outputs a control signal,
The blower 33 is driven and the flow rate control valve 34 is opened and closed to regulate the flow rate. As a result, air is supplied from the carbon dioxide supply path 32 and diffused from the air diffuser 31, carbon dioxide in the air is dissolved in the alkaline agent, and alkali carbonate is generated.
At this time, the flow rate of the flow rate control valve 34 is adjusted so that the pH of the nitrification-treated water falls within the above range. Instead of the blower 33, carbon dioxide may be directly supplied from the gas cylinder 35. Since the carbon dioxide addition position and the pH measurement position are distant from each other, it is preferable to calculate and control the required addition amount by feedback control. By adding carbon dioxide and circulating the nitrifying water, the pH of the tank liquid in the pH adjusting tank 1
When is out of the predetermined pH range, the pH is adjusted by adding an alkali or an acid according to the judgment of the controller 7.

When the above-described operation is repeated, the buffering effect of the alkali carbonate produced will cause the p in the nitrification tank 4 to rise.
It is possible to prevent reduction of H and stably perform nitrification at a high nitrification rate. At this time, pH adjustment is performed in the pH adjustment tank 1 by using the P alkalinity of the alkali carbonate, pH adjustment is performed in the nitrification tank 4 by using the M alkalinity, and the nitrification tank 4 may generate nitric acid. Instead, it is maintained at a pH throughout which the activity of nitrifying bacteria becomes high. In this case, even if the pH of the water to be treated, the NH ₄ ⁺ concentration, the organic nitrogen compound content or the alkalinity changes, the pH is adjusted accordingly, so that a high nitrification rate can be maintained, and a chemical to be injected The amount of can be minimized.

When the air diffuser 22 and the air supply passage 23 are arranged at the positions 22a, 23a in FIG. 1, the same operation as described above can be performed. At this time, the inside of the nitrification tank 4 becomes anaerobic below the air diffuser 22a.
The biological filtration layer 21 has a denitrification section 21b containing denitrification bacteria at the bottom,
And a nitrification part 21a containing nitrifying bacteria is formed in the upper part,
Denitrification and nitrification are performed in one tank.

Example 1, Comparative Example 1 NH ₄ ⁺ = 50 mg-N / l, BOD = 2-5 mg / l,
M- alkalinity = 70~160mg-CaCO ₃ / l,
pH = 6.6 to 7.3 (NH ₄ ⁺ concentration is 50 mg-
It was artificially controlled to be N / l, but other values varied within the range of the above values).
(However, the air diffuser 22 was placed in the position indicated by the solid line) to perform nitrification. Inside the nitrification tank 4, the diameter is 3.5 mm.
The biological filtration layer 21 was formed by adhering microbial sludge containing nitrifying bacteria to the polystyrene floatable filter medium of No. 1. Sodium hydroxide was used as the alkaline agent, and carbon dioxide was injected from the gas cylinder 35. The amount of circulation from the circulation passage 13 was the same as the amount of treated water from the treated water passage 11.

The operation of nitrification was performed as follows. That is, after the biological filtration layer 21 became steady, carbon dioxide was not added for the first month, and 25 wt% sodium hydroxide was added to control the pH in the pH adjusting tank 1 to 8.5. Nitrification was performed (Comparative Example 1). For the next month, control is performed by adding 10 wt% sodium hydroxide so that the pH inside the pH adjusting tank 1 becomes 8.5, and further injecting carbon dioxide so that the nitrification-treated water becomes pH 6.5. It did (Example 1). The other conditions were exactly the same during the test period, and the system was operated at a nitrification load of 1.5 kg-N / m ³ · day. The pH of the nitrification-treated water at the outlet of the nitrification tank 4 and the NH ₄ ⁺ removal rate during the test period are shown in FIG.

As can be seen from FIG. 2, the pH of the nitrification-treated water fluctuates during the first month (test period as a comparative example) due to the fluctuation of the alkalinity of the water to be treated, and accordingly NH ₄ ^+.
The removal rate of is also fluctuating. On the other hand, the following 1 in which carbon dioxide was injected so that the pH of the nitrification-treated water was 6.5:
The removal rate of NH ₄ ⁺ showed a stable value during the month (the test period of the example), and the removal rate increased by 18% on average.

[0036]

The nitrification apparatus of the present invention has a pH of nitrification-treated water.
A carbon dioxide for injecting carbon dioxide into an alkaline agent that adjusts the pH of the water to be treated so that the pH of the nitrification-treated water falls within a specific range according to the pH measuring device for measuring Since it is equipped with an injection device, the nitrification tank can be operated with a simple structure and by simple operation even when the pH, NH ₄ ⁺ concentration, organic nitrogen compound content or alkalinity of the water to be treated fluctuates. It is possible to maintain the internal pH within the range where the nitrifying activity of nitrifying bacteria is high,
This enables stable nitrification at a high nitrification rate.

[Brief description of drawings]

FIG. 1 is a system diagram showing a nitrification apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing test results of Example 1 and Comparative Example 1.

FIG. 3 is a graph showing the relationship between nitrifying activity of nitrifying bacteria and pH.

[Explanation of symbols]

 1 pH adjusting tank 2 First pH measuring device 3 Alkaline agent storage tank 4 Nitrification tank 5 Second pH measuring device 6 Pressure adjusting tank 7 Control device 11 Treated water channel 12 Alkaline agent injecting channel 13 Circulating channel 14 Stirrer 15 Liquid feeding pump 16, 24 Communication path 17 Treated water pump 18 Chemical injection pump 19 Circulation pump 21 Biological filtration layer 22, 31 Air diffuser 23 Air supply channel 25 Treatment water channel 26 Exhaust gas channel 32 Carbon dioxide supply channel 33 Blower 34 Flow control valve 35 Gas cylinder 36 Water gauge

Claims (1)

[Claims] 1. A pH adjusting tank for adjusting the pH of the water to be treated, a plug flow type nitrification tank for biologically nitrifying the pH-adjusted water, and the water to be introduced into the nitrification tank. A first pH measuring device for measuring pH, and a measurement value of the first pH measuring device is pH 6.0 to 9.7.
So that the pH adjustment tank contains an alkaline agent, a second pH measuring device for measuring the pH of the nitrification-treated water, and a measurement value of the second pH measuring device is pH 6.0 to 6.0. 9.7
And a carbon dioxide injection device for injecting carbon dioxide into the alkali agent so as to maintain the above.