JPH08267088A - Nitrator - Google Patents

Abstract

PURPOSE: To obtain a nitrator maintaining the pH in a nitration tank in the range where the activity of nitration bacteria is increased even in the case when the pH, NH<4> concn. or alkalinity of a liq. to be treated are fluctuated in the biological nitration using a plug-flow nitration tank. CONSTITUTION: A part of a liq. to be treated is introduced into the lower part of a nitration tank 1 from a first liq. feed line 2a. At this time, the pH of the liq. is measured by a first pH measuring device 8a, the amt. of alkali to be added to control the liq. to pH6 to 9.7 is calculated from the pH value in a controller 10, and the addition of alkali is adjusted by controlling a first chemical injection pump 6a. The liq. is passed upward through the nitration tank 1 and biologically nitrated. Menwhile, the remainder of the liq. is introduced into an intermediate part from a second liq. feed line 2b. At this time, the pH of the liq. is measured by a second pH measuring device 8b, the amt. of alkali to be added to control the liq. to pH6.5 to 11.5 is calculated from the pH value in the controller 10, and the addition of alkali is adjusted by controlling a second chemical injection pump 6b.

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 a liquid to be treated by using a plug flow type nitrification tank, and more particularly to biology of waste liquid containing nitrogen compounds. The present invention relates to a nitrification apparatus that can be used in a nitrification denitrification method.

[0002]

2. Description of the Related Art Ammoniacal or organic nitrogen compounds in sewage are said to be the cause of eutrophication in closed water areas such as lakes and bays. As a method of removing ammoniacal or organic nitrogen compounds from such waste liquid, there is a biological nitrification denitrification treatment method using microorganisms,
Most proven and highly reliable. In this method, aerobic treatment is performed in the presence of activated sludge to remove COD and BO in the effluent.
Along with decomposing the D component, the organic nitrogen compound is converted to ammonia nitrogen, and then aerated in the presence of activated sludge in which nitrifying bacteria have proliferated, and the ammonia nitrogen is nitrified by nitrifying bacteria to nitrite or nitrate nitrogen (oxidation). After that, the nitrite or nitrate nitrogen is reduced to nitrogen gas to denitrify it by maintaining it in an anaerobic state in the presence of activated sludge in which denitrifying bacteria have grown. As such a biological nitrification denitrification treatment method, a floating method using floating bacteria, or a fixed bed method in which bacterial cells adhere to and grow on the surface of a carrier or a method called a biological filtration method has been put into practical use. In particular, a method called a fixed bed method or a biofiltration method is superior to the floating method in the ability to retain nitrifying bacteria having a small growth rate in a reaction tank, and therefore, it is attracting attention as a highly efficient nitrification denitrification method.

Both nitrification and denitrification reactions are reactions involving pH changes.

Embedded image According to the reaction of NH ₄ ⁺ + 3 / 2O ₂ −> NO ₂ ⁻ + 2H ⁺ + H ₂ O (1), 2 mol of H ⁺ is converted when 1 mol of NH ₄ ⁺ is nitrified. As a result, the pH of the nitrification treatment liquid drops significantly. However, the nitrifying activity of nitrifying bacteria is greatly affected by pH as shown in FIG. 5, 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 liquid to be treated.
That is, when the alkalinity of the liquid to be treated is sufficiently large compared with the NH ₄ ⁺ concentration, the pH decrease due to nitrification is small, and conversely, when the alkalinity is small compared with the NH ₄ ⁺ concentration, the pH decrease is caused. Grows. Conventionally, in order to cope with a decrease in pH due to nitrification, an alkali such as sodium hydroxide is added as a pH adjuster to maintain the pH at a predetermined value.

When nitrification is carried out by a complete mixing type floating method such as the activated sludge method, the liquid to be treated is in a nearly completely mixed state. Therefore, pH control is carried out by putting a pH sensor in the nitrification tank liquid. It can be easily controlled by adding an alkali such as sodium hydroxide 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, such a plug flow occurs because the liquid to be treated flows in a plug flow (one-way flow). It is difficult to adjust the pH of the entire nitrification tank of the mold within a predetermined range, and the pH decreases in the downward direction. Even in the case of the plug flow type, it is possible to install a pH adjustment tank in front of the nitrification tank and add sodium hydroxide at the inlet of the nitrification tank to adjust the pH, but the alkalinity of the liquid to be treated is equal to the NH ₄ ⁺ concentration. If the pH is low, the pH drop in the nitrification tank becomes large, and it becomes difficult to maintain high activity of nitrifying bacteria. Therefore, stable nitrification cannot be performed at a high nitrification rate (ammonia nitrogen removal rate). .

The pH can be adjusted by adding an alkali having a buffering ability such as sodium hydrogen carbonate or sodium carbonate at the entrance of the nitrification tank. The method of adding such a carbonate can suppress the decrease in pH in the nitrification tank as compared with the method of adding sodium hydroxide,
There is a limit to the prevention of pH drop. On the other hand, the equipment costs such as silos for storing powders of sodium hydrogen carbonate, sodium carbonate and the like, and melting equipment are much higher than those for sodium hydroxide. In addition, p in the nitrification tank in advance
The pH at the entrance of the nitrification tank can be set high in anticipation of a decrease in H, but in this case, the pH of the entrance of the nitrification tank becomes too high, and the reaction of nitrifying bacteria may be inhibited.

To prevent the pH from decreasing in the nitrification tank,
For example, it is possible to circulate the nitrification treatment liquid flowing out of the nitrification tank again to the inlet, and adjust the pH in a state where the liquid to be treated and the circulation liquid 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, the larger the circulation ratio (the ratio of the amount of circulating liquid to the amount of liquid to be treated), the closer the flow of the liquid to be treated becomes to 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.

By the way, JP-A-53-76550 discloses that
It describes a method for treating wastewater in which a liquid to be treated, which has been flowed for two minutes into a tray type nitrification denitrification tower, is dispensed and biologically nitrification denitrification is performed. However, this conventional method is a method of supplying the BOD necessary for denitrification into a two-part flow of the liquid to be treated and supplying it to the top (nitrification section inlet) and intermediate section (denitrification section inlet) of the reaction tower. This method cannot prevent a decrease in pH in the nitrification part.

[0010]

Purpose, upon biologically nitrifying using nitrification tank plug flow of nitrogen compounds in the liquid to be treated, pH of the liquid to be treated, NH ₄ ⁺ concentration in the present invention is to solve] The pH in the nitrification tank can be easily maintained at low cost so that the nitrification activity of nitrifying bacteria becomes high, even when the alkalinity, the content of organic nitrogen compounds, etc. fluctuate. An object of the present invention is to provide a nitrification apparatus capable of nitrifying at a nitrification rate.

[0011]

According to the present invention, a plug flow type nitrification tank for receiving a liquid to be treated and nitrifying it biologically, and a part of the liquid to be treated are supplied from one end of the nitrification tank. A first liquid supply device, a first pH adjusting device for adjusting the pH of a liquid to be treated supplied from the first liquid supply device to 6 to 9.7, and an intermediate portion of the plug flow type nitrification tank. From the second liquid supply device that supplies the other part of the liquid to be processed from the second liquid supply device, and the pH of the liquid to be processed supplied from the second liquid supply device is 6.5 to 11.
And a second pH adjusting device for adjusting to pH 5.

The liquid 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. Before being supplied to the nitrification tank, such a liquid to be treated may be subjected to a treatment such as decomposing organic matter by aerobic treatment using activated sludge, or performing a denitrification step by circulating the nitrification treatment liquid.

The plug-flow type nitrification tank constituting the nitrification apparatus of the present invention is filled with a biological sludge layer in which nitrifying bacteria have proliferated, and the liquid to be treated is plug-flowed (one-way flow) into this packed layer. It is a device that passes liquid and contacts it under aerobic conditions to nitrify. The flow direction of the liquid to be treated may be an upward flow or a downward flow. The method for forming the biological sludge layer can be arbitrarily selected, such as a method of filling the granulated sludge or a method of attaching the biological sludge to the packed layer, and can be of any form such as a fixed bed type or a fluidized bed type. Things can be adopted.

In the nitrification apparatus of the present invention, the liquid to be treated is divided into a part and the other part is supplied from the first liquid supply device and the second liquid supply device to the plug flow type nitrification tank. . Further, the liquid may be supplied stepwise from the third, fourth, ... The first liquid supply device is a device that supplies the liquid to be treated from one end of the plug flow type nitrification tank to the nitrification tank.

The first pH adjusting device is a device for adjusting the pH of the liquid to be treated supplied from the first liquid supplying device.
Here, the first pH measuring device is provided, and the measured value is pH 6
It can be configured to control the amount of alkaline agent injected from the first dosing device so as to maintain ˜9.7, preferably 7-9.5. The pH is controlled by increasing the addition amount of the alkaline agent when the pH of the liquid to be treated is below the lower limit value or approaching the lower limit value, and exceeds the upper limit value or approaching the upper limit value. Control is performed so as to reduce the addition amount of. As an alkaline agent,
Sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, calcium hydroxide and the like can be used. Among these, sodium carbonate and sodium hydrogen carbonate are preferable from the viewpoint of pH adjustment and residual alkalinity, but sodium hydroxide is most preferable from the viewpoint of the cost of injection equipment.

The second liquid supply device is a device for supplying another part of the liquid to be treated to the nitrification tank from an intermediate portion of the plug flow type nitrification tank. The second pH adjusting device is a device that adjusts the pH of the liquid to be treated supplied from the second liquid supply device. A second pH measuring device is installed here, and the measured value is p
It can be configured to control the amount of alkaline agent injected from the second dosing device so as to maintain H6.5-11.5, preferably 7-11. The pH is controlled by increasing the addition amount of the alkaline agent when the pH of the liquid to be treated is below the lower limit value or approaching the lower limit value, and exceeds the upper limit value or approaching the upper limit value. Control is performed so as to reduce the addition amount of. As the alkaline agent, the same ones as described above can be used.

[0017]

In the nitrification apparatus of the present invention, a part of the liquid to be treated is treated by the first pH adjusting apparatus to have a pH of 6 to 9.7, preferably 7 to 9.
5 and supply it from one end of the plug flow type nitrification tank by the first liquid supply device, and supply another part of the liquid to be treated by the second pH adjusting device to pH 6.5 to 11.5. Preferably, it is adjusted to 7 to 11 and is supplied from the middle part of the plug flow type nitrification tank by the second liquid supply device, and is aerobically passed through the plug flow to carry out nitrification by nitrifying bacteria.
Nitrification in the nitrification tank oxidizes ammoniacal nitrogen to nitrite or nitrate nitrogen.Therefore, if organic matter is present in the liquid to be treated, remove it by activated sludge treatment beforehand. It is possible to dominate nitrifying bacteria and efficiently perform nitrification.

In the nitrification apparatus of the present invention, since the pH-adjusted liquid to be treated is supplied from the intermediate portion of the nitrification tank by the second liquid supply device, the liquid to be treated and the liquid in the tank (nitrification liquid). And are mixed in the middle part of the nitrification tank. As a result, the liquid in the tank (nitrification treatment liquid) whose pH has decreased due to the progress of the nitrification reaction,
It is mixed with the pH-adjusted liquid to be treated supplied from the intermediate portion and neutralized to prevent the pH from decreasing. Therefore, even in the case of the plug flow, the nitrifying activity of nitrifying bacteria can be maintained high and efficient nitrification can be performed.

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 at the same time convert an organic nitrogen compound into ammoniacal nitrogen. In addition, a denitrification tank is installed in the preceding stage of the nitrification tank to circulate the nitrification treatment liquid to the denitrification tank, and the liquid to be treated is supplied from the first liquid supply device to this denitrification tank to anaerobicize in the presence of denitrification bacteria It is also possible to carry out denitrification by maintaining the temperature at 1, and then to supply it to the nitrification tank for nitrification.
In this case, the denitrification tank and the 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 liquid to be treated is directed upward. When liquid is passed, the upper part can be integrated into a nitrification tank and the lower part can be integrated into a denitrification tank. Even in such a case, nitrification can be efficiently performed by supplying the liquid to be treated whose pH is adjusted from the intermediate portion of the nitrification tank by the second liquid supply device 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 a nitrification apparatus of the embodiment, and FIG. 2 is a system diagram showing a nitrification apparatus in which a nitrification tank and a denitrification tank are integrated.
In FIG. 1, 1 is a nitrification tank, 2 is a liquid passage to be treated, which branches into a first liquid supply passage 2a and a second liquid supply passage 2b, and first and second liquid supply pumps 3a, 3b, respectively. In addition, first and second pH adjusters 4a and 4b are provided. The pH adjusting devices 4a and 4b are first and second medicines having first and second mixers (line mixers) 5a and 5b, respectively, and first and second chemical injection pumps 6a and 6b connected in front of them. It is composed of injection channels 7a and 7b, and first and second pH measuring devices 8a and 8b to be connected later. The first and second chemical injection passages 7a and 7b merge to form one chemical injection passage 7, which is connected to the alkaline agent storage tank 9. Reference numeral 10 is a control device, and 11 is a third pH measuring device.

A first liquid supply path 2a is connected to the lower part of the nitrification tank 1. A second liquid supply path 2b is connected to an intermediate portion of the nitrification tank 1. The second liquid supply passage 2b is connected to a liquid extraction passage 13b to be treated having a valve 12. A treatment liquid passage 21 and an exhaust gas passage 22 are connected to the upper part of the nitrification tank 1. A circulation path 23 branches from the processing liquid path 21 and is connected to the first liquid supply path 2a. A circulation pump 24 is provided in the middle of the circulation path 23.

Inside the nitrification tank 1, a biological filtration layer 31 containing nitrifying bacteria is formed. An air diffuser 32 is provided below the biological filtration layer 31 and is connected to the air supply passage 33. Further, a sprinkler device 34 is provided at an intermediate portion of the biological filtration layer 31 and is connected to the second liquid supply passage 2b. An in-tank liquid withdrawing liquid passage 13 a having a valve 35 is connected to a lower portion of the liquid spraying device 34. The in-tank liquid drawing liquid path 13a and the liquid to be treated drawing liquid path 13b join to form one drawing liquid path 13, and the third pH measuring device 11 is provided in the drawing liquid path 13.

In FIG. 2, reference numeral 41 denotes a denitrification nitrification tank, which has a structure in which an upper nitrification tank and a lower denitrification tank are integrated. In the denitrification and nitrification tank 41, an air diffuser 32 is provided between the biological filtration layers 42 and 43 that are integrally filled in the tank.
Is provided, the biological filter layer 42 containing nitrifying bacteria is formed on the upper part of the air diffuser 32, and the biological filter layer 43 containing denitrifying bacteria is formed on the lower part, which constitute a nitrification section 44 and a denitrification section 45, respectively. The circulation passage 23 is connected to the first liquid supply passage 2a so that the nitrification treatment liquid circulates in the denitrification unit 45. Further, in the nitrification device of FIG. 2, the drawing liquid passage 13 is provided above the liquid dispersion device 34. Other configurations are the same as those in FIG.

In order to carry out nitrification by the nitrification apparatus of FIG. 1, first, the first feed liquid pump 3a is driven to drive a part of the liquid to be treated (hereinafter referred to as the first liquid to be treated) from the first liquid feed passage 2a. In some cases) to the lower part of the nitrification tank 1. At this time, the first p
The H measuring device 8a measures the pH of the first liquid to be treated and outputs the pH value to the control device 10. The controller 10 calculates the addition amount of the alkaline agent such that the pH of the first liquid to be treated becomes a predetermined value, outputs the signal to the first chemical injection pump 6a, and adjusts the addition amount of the alkaline agent. . The first liquid to be treated and the alkaline agent are mixed in the first mixer 5a.

The first liquid to be treated whose pH has been adjusted in this manner passes through the biological filtration layer 31 in an upward flow, and at the same time, the air supplied from the air supply passage 33 is diffused from the diffuser 32. Biological nitrification of ammoniacal nitrogen in the liquid to be treated into nitrite or nitrate nitrogen by the action of nitrifying bacteria.
When the liquid to be treated contains an organic nitrogen compound, this organic nitrogen compound is decomposed into ammonia nitrogen by the action of BOD-decomposing bacteria, and further converted into nitrite or nitrate nitrogen by the action of nitrifying bacteria. Nitrified. It should be noted that there is almost no case where the pH of the first liquid to be treated exceeds 9.7.
Is adjusted to 9.7 or less.

On the other hand, by driving the second liquid supply pump 3b,
The remaining part of the liquid to be treated (hereinafter, sometimes referred to as the second liquid to be treated) is supplied from the sprinkling device 34 to the middle part of the nitrification tank 1 through the second liquid supply passage 2b. At this time, the second pH measuring device 8b measures the pH of the second liquid to be treated and outputs the pH value to the control device 10. The controller 10 calculates the addition amount of the alkaline agent such that the pH of the second liquid to be treated becomes a predetermined value, outputs the signal to the second chemical injection pump 6b, and adjusts the addition amount of the alkaline agent. . The second liquid to be treated and the alkaline agent are mixed in the second mixer 5b.

The second liquid to be treated whose pH has been adjusted in this manner is mixed with the nitrifying liquid (in-tank liquid) rising in the nitrification tank 1 and nitrified. In this case, the split ratio of the first liquid to be treated and the second liquid to be treated is 1 to 5: 1, preferably 1 to 2 in terms of a volume ratio of the first liquid to be treated: the second liquid to be treated. It is desirable to set it to: 1. Here, since the nitrification treatment liquid (in-tank liquid) having a lowered pH is mixed with the second liquid to be treated whose pH has been adjusted, the nitrification treatment liquid (in-tank liquid) is neutralized to increase the pH. This enables efficient nitrification.

The nitrification treatment liquid (solution in the bath) and the second liquid to be treated are preferably mixed so that the nitrification activity of nitrifying bacteria becomes high at pH 8-9. To do so, adjust the split ratio of the first liquid to be treated and the second liquid to be treated,
Alternatively, it can be performed by a method such as adjusting the pH of the second liquid to be treated.

The pH of the mixed liquid in the tank after supplying the second liquid to be treated can be controlled to a predetermined value as follows. That is, the liquids are drawn from the in-tank liquid drawing liquid passage 13a and the liquid to be treated drawing liquid passage 13b and mixed, the pH of the drawn liquid mixture is measured by the third pH measuring device 11, and this pH value is controlled by the control device 10. Output to. In the control device 10, this p
From the H value, the first and / or second pH adjusting device 4a,
Set the target pH value of 4b. This adjusts the amount of the alkaline agent added to the first and / or second liquid to be treated in the first and / or second pH adjusters 4a and 4b. In this case, adjust valves 12 and 35,
The in-tank liquid and the second liquid to be treated are drawn out and mixed so that the split flow ratio between the first liquid to be treated and the second liquid to be treated becomes equal.

A part of the nitrification treatment liquid is circulated by the circulation pump 24 through the circulation passage 23 to the first liquid supply passage 2a. The rest is taken out from the processing liquid passage 21 as the processing liquid. The exhaust gas is discharged from the exhaust gas passage 22. By circulating a part of the nitrification treatment liquid and mixing it with the liquid to be treated, the NH ₄ ⁺ concentration at the inlet of the nitrification tank 1 becomes smaller than the alkalinity.
The decrease in H can be reduced. It should be noted that the circulation of the nitrification treatment liquid is not always necessary and may be omitted in some cases.

When nitrification is performed as described above, the nitrification tank 1
Since the liquid is mixed in the middle part of the, the pH in the nitrification tank 1 is prevented from lowering, the pH of the nitrification tank 1 is maintained at a level at which the activity of nitrifying bacteria becomes high, and nitrification is stably performed at a high nitrification rate. be able to. In this case, even if the pH, NH ₄ ⁺ concentration, alkalinity or organic nitrogen compound content of the liquid to be treated changes, the pH is adjusted accordingly, so that a high nitrification rate can be maintained and the alkali The amount of the agent can be suppressed to the necessary minimum. Moreover, since a part of the liquid to be treated is supplied from the intermediate portion of the nitrification tank 1, the pressure loss can be reduced.

The nitrification apparatus of FIG. 2 can be operated in the same manner as in the case of FIG. In the case of FIG. 2, the inside of the denitrification and nitrification tank 41 is in an anaerobic state below the aeration device 32. Therefore, the biological filtration layers 42 and 43 have a denitrification section 45 containing denitrification bacteria at the bottom and a nitrification bacterium at the top. Is formed, and denitrification and nitrification are performed in one tank. In FIG. 2, since the extraction liquid passage 13 is provided above the liquid dispersion device 34, the pH of the in-tank mixed liquid can be directly measured. In the case of FIG. 2, the pH of the denitrification treatment liquid becomes higher than the pH of the liquid to be treated supplied to the denitrification unit by performing the denitrification in the denitrification unit 45. It is preferable to adjust the pH to be lower by about 0 to 1 as compared with the case where the nitrification unit 45 is not provided.

Test Example 1 Factory wastewater of the following water quality: NH ₄ ⁺ concentration: 100 mg-N / l BOD: 2-5 mg / l M-alkalinity: 150 mg-CaCO ₃ / l pH: 6.8-7.1 Nitrification was performed by the nitrification apparatus shown in FIG. The nitrification tank is filled with 3.5 mm diameter polystyrene floatable filter media,
A 300 cm high biofiltration layer was formed. The second liquid to be treated was configured so as to be supplied from just in the center of the biological filtration layer (position 150 cm from the bottom).

Nitrification was performed as follows. First, after the nitrification tank becomes steady, all the liquid to be treated is supplied to the nitrification tank from the first supply line for the first month, and the nitrification load is 1.5 kg-
It was operated at N / m ³ · day (comparative example). The pH of the liquid to be treated at this time was adjusted to 8.5 by adding sodium hydroxide. After that, an equal amount was supplied to the nitrification tank from the first liquid supply passage and the second liquid supply passage to operate (Example). The pH of the first liquid to be treated at this time is 8.5, and the pH of the second liquid to be treated is
Was adjusted to 9.5 with sodium hydroxide. The NH ₄ ⁺ removal rate during the test period is shown in FIG. 3, and the pH of the solution in the nitrification tank is shown in FIG.

As can be seen from FIG. 3, the removal rate of NH ₄ ⁺ is greatly increased by supplying the second liquid to be treated adjusted to pH 9.5 from the middle part of the nitrification tank, and the removal rate is 22 on average.
% High removal rate was obtained. Also, as can be seen from FIG.
Regarding the pH of the in-tank liquid, the range of pH decrease was reduced by supplying the second liquid to be treated, which was adjusted to pH 9.5 from the middle part of the nitrification tank.

[0036]

According to the nitrification apparatus of the present invention, the second liquid supply device for supplying the liquid to be treated from the intermediate portion of the nitrification tank and the pH of the liquid to be treated supplied from the second liquid supply device are set to 6. 5-11.5
Since it has a second pH adjusting device for adjusting the pH of the liquid to be treated, even if the pH, NH ₄ ⁺ concentration, alkalinity or organic nitrogen compound content of the liquid to be treated changes, a device with a simple structure is used. Moreover, the pH in the nitrification tank can be maintained within a range where the nitrifying activity of the nitrifying bacteria is high by a simple operation, whereby stable nitrification can be performed 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 system diagram showing a nitrification apparatus according to another embodiment of the present invention.

FIG. 3 is a graph showing the results of Test Example 1.

FIG. 4 is a graph showing the results of Test Example 1.

FIG. 5 is a graph showing the relationship between nitrifying activity of nitrifying bacteria and pH.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nitrification tank 2 Liquid to be processed 2a 1st liquid supply path 2b 2nd liquid supply path 3a 1st liquid supply pump 3b 2nd liquid supply pump 4a 1st pH adjusting device 4b 2nd pH adjusting device 5a 1st mixer 5b 2nd mixer 6a 1st chemical injection pump 6b 2nd chemical injection pump 7 chemical injection path 7a 1st chemical injection path 7b 2nd chemical injection path 8a 1st pH measurement Device 8b Second pH measuring device 9 Alkaline agent storage tank 10 Control device 11 Third pH measuring device 12, 35 Valve 13 Extraction liquid passage 13a In-tank liquid extraction liquid passage 13b Treatment liquid extraction liquid passage 21 Treatment liquid passage 22 Exhaust gas Channel 23 Circulation channel 24 Circulation pump 31, 42, 43 Biological filtration layer 32 Air diffuser 33 Air supply channel 34 Fluidizer 41 Denitrification nitrification tank 44 Nitrification section 45 Denitrification section

Claims (1)

[Claims] 1. A plug flow type nitrification tank for receiving a liquid to be treated and nitrifying it biologically, and a first liquid supply device for supplying a part of the liquid to be treated from one end of the nitrification tank. The pH of the liquid to be treated supplied from the first liquid supply device is 6 to
A first pH adjusting device for adjusting to 9.7; a second liquid supplying device for supplying another part of the liquid to be treated from an intermediate portion of the plug flow type nitrification tank; The pH of the liquid to be treated supplied from the apparatus is 6.
A nitrification device comprising a second pH adjusting device for adjusting the pH to 5 to 11.5.