JP2003039092A - Biological denitrification treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To denitrify ammonia nitrogen in raw water with a batch treatment tank to thereby make a denitrification treatment apparatus at the later step unnecessary. SOLUTION: A raw water supply step for supplying raw water containing ammonia nitrogen to a batch treatment tank 1, the first denitrification step for removing ammonia nitrogen in the presence of nitrite nitrogen by the action of denitrification microorganisms using ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor, the second denitrification step for further denitrifying by adding an electron donor to the denitrified water resulting from the first denitrification step, a separation step for separating the denitrified water resulting from the second denitrification step into a supernatant and precipitated sludge, and a discharge step for discharging the supernatant are repeated in the biological denitrification treatment method.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the action of a denitrifying microorganism that uses ammoniacal nitrogen in raw water containing ammoniacal nitrogen as an electron donor for ammoniacal nitrogen and nitrite nitrogen as an electron acceptor. The present invention relates to a biological denitrification treatment method in which biological denitrification is performed in the presence of nitrate nitrogen.

[0002]

2. Description of the Related Art Ammoniacal nitrogen contained in drainage is one of the causative substances of eutrophication in rivers, lakes and oceans, and it is necessary to remove it efficiently in the drainage treatment process. Generally, ammoniacal nitrogen in wastewater is a nitrification process in which ammoniacal nitrogen is oxidized to nitrite nitrogen by ammonia-oxidizing bacteria, and this nitrite nitrogen is further oxidized to nitrate nitrogen by nitrite-oxidizing bacteria. Nitrogen gas and nitrogen gas are transformed into nitrogen gas by a denitrification process in which organic substances are used as electron donors to decompose them into nitrogen gas by denitrifying bacteria, which are heterotrophic bacteria. Be disassembled.

However, in such a conventional nitrification denitrification method, a large amount of an organic substance such as methanol is required as an electron donor in the denitrification step, and a large amount of oxygen is required in the nitrification step, so that the running cost is high. There is a drawback that.

On the other hand, in recent years, an autotrophic microorganism having ammonia nitrogen as an electron donor and nitrite nitrogen as an electron acceptor has been used to react ammonia nitrogen with nitrite nitrogen. A method of denitrification was proposed. This method does not require addition of organic matter, and thus can reduce the cost as compared with the method using heterotrophic denitrifying bacteria. Also, the yield of autotrophic microorganisms is low,
Since the amount of sludge generated is significantly smaller than that of the heterotrophic microorganisms, the amount of excess sludge generated can be suppressed. Furthermore, there is a feature that N ₂ O generated by the conventional nitrification denitrification method is not generated and the load on the environment can be reduced.

This autotrophic denitrifying microorganism (hereinafter referred to as "ANA
MMOX microorganism ". ) Is used in Strous, M. et. A.
l., Appl. Microbiol. Biotechnol. Vol.50, p.589-596
(1998), it is considered that ammoniacal nitrogen and nitrite nitrogen react with each other in the following reaction to decompose into nitrogen gas.

[0006]

[Chemical 1]

[0007] That is, when denitrification treatment is carried out using the ANAMMOX microorganism, the A that holds the ANAMMOX microorganism is used.
The water to be treated (raw water) flowing into the NAMMOX reaction tank is 0.5 to 2 times, particularly 1 to 1.5 times, nitrite nitrogen (NO ₂ -N) with respect to ammonia nitrogen (NH ₄ -N). It is preferable to include it in a double ratio.

The use of the above-mentioned ANAMMOX microorganism makes it possible to reduce the amount of aeration, the amount of organic substances such as methanol added, and the amount of excess sludge as compared with the conventional nitrification denitrification.

In addition to nitrogen, nitric acid is produced as a reaction product. For this reason, a denitrification process for reducing the nitric acid produced after the ANAMMOX reaction and converting it to nitrogen gas is required.

By the way, the ANAMMOX microorganism is an autotrophic microorganism and has a low yield and a slow growth rate. The specific growth rate is 0.065 day ^{-1 at} maximum (1.
It grows 065 times). In actual culture, the substrate concentration in the treated water is low and the substrate does not sufficiently penetrate into the flocs of the organism, so the specific growth rate is 0.02.
The value is about 0.05 day ⁻¹ .

Factors that impede the activity of the ANAMMOX microorganism are oxygen contamination and exposure to high concentrations of nitrite. That is, the ANAMMOX microorganism has low resistance to oxygen and is irreversibly inhibited even at an oxygen partial pressure of 1%. Inhibition by nitrite is based on nitrite nitrogen concentration of 50 to 2
It occurs from about 00 mg / L, and it is said that the higher the concentration, the greater the inhibitory effect (Strous, M. et. Al., Appl. En.
viron. Microbiol. Vol.65 (7), p.3248-3250 (199
9)).

As a reaction tank system using ANAMMOX microorganisms, for example, a column packed with a carrier to which microorganisms are adhered, such as sand, plastic, sponge or gel, is used.
A method of passing drainage in an upflow or a downflow is used.
The load of the reaction tank is determined by the amount of microorganisms adhering to the surface of the carrier. The larger the specific surface area of the carrier, the larger the amount of microorganisms that can be retained, and the higher the load can be.

Further, a method of utilizing microorganisms held in a floating state in the tank is also used. In the case of this method, there is a method in which a solid-liquid separation device is provided in the subsequent stage, the concentrated microorganisms are returned to the reaction tank, and the concentration of the microorganisms in the reaction tank is increased to obtain a high load.

Further, a USB (Upflow Sludge) which is filled with granulated sludge in a reaction tank and flows in an upward flow.
Bed: Upflow sludge bed) system is also available. In this case, the concentration of microorganisms that can be retained in the tank can be made higher than that in the above-mentioned carrier addition or floating type, and therefore a high volume load can be obtained. In terms of processing efficiency, it is preferable to maintain the diameter of the granule at 0.25 to 2.5 mm. The diameter of the granule is affected by the shearing force generated by stirring the liquid in the tank by the gas generated by the reaction and the flow velocity of the upward flow in the tank. In order to effectively contact the water to be treated and obtain high treatment efficiency,
It is important to control the upward flow velocity during operation. For this reason, the generated gas is used to stir the liquid in the tank and to circulate a part of the treated water to ensure an appropriate upward flow velocity. Further, the amount of granules that can be held in the tank is also affected by the performance of the GSS (solid-liquid separation device) installed in the upper part of the device, so this shape is also important.

As the reaction system, the SBR system (batch reaction system) has also been reported (Strous, M. et. Al., Ap.
Pl. Microbiol. Biotechnol. Vol.50, p.589-596 (199
8). In this method, sludge in the floating state or pellet state is held in the reaction tank, the water to be treated is added and stirred to bring the water to be treated into contact with the microorganisms, and after the treatment is completed, the stirring is stopped and the reaction tank is At this point, microorganisms are precipitated and the supernatant water is discharged as treated water. The advantages of this reaction tank are that it does not require a separate solid-liquid separation device, the installation area of the reaction tank can be reduced, the reaction tank is a single tank, and it is easy to manage. It can be used and does not require rigorous control of stirring strength as in the case of the USB method and USB method. Since the inside of the tank is completely mixed, it is immediately diluted even if high-concentration raw water flows in, depending on the high-concentration substrate. It is difficult to cause inhibition.

[0016]

However, in the prior art, SB has been used for denitrification treatment by ANAMMOX microorganisms.
The technology that uses the R method is not well established.

Conventionally, ANAMMO using the SBR system
As the X reaction, it has been reported that synthetic wastewater containing ammoniacal nitrogen and nitrite nitrogen at the same concentration is treated.
In this case, nitrite nitrogen is not detected in the reaction tank after completion of the reaction, and ammonia nitrogen and nitrate nitrogen are always present. That is, as is clear from the above-described reaction formula of the ANAMMOX reaction, the reaction requires a large amount of nitrite nitrogen with respect to ammonia nitrogen, and nitrate nitrogen is produced as a reaction product. Therefore, when the wastewater containing the same concentration of ammonia nitrogen and nitrite nitrogen is treated, the nitrite nitrogen is consumed, the ammonia nitrogen remains, and nitrate nitrogen is produced.

It is known that nitrate nitrogen is produced as a reaction product in the ANAMMOX reaction. Therefore, a denitrification treatment for reducing the nitrate nitrogen and converting it into nitrogen gas is required in the latter stage. Nitrogen treatment cannot treat residual ammoniacal nitrogen. Therefore, in order to treat the ammoniacal nitrogen and the nitrate nitrogen that remain in the SBR reaction tank, it is necessary to perform a two-stage treatment of oxidizing the ammoniacal nitrogen and denitrifying the oxidized nitrogen in the latter stage.
Not practical.

On the other hand, when the ammonia nitrogen is insufficient in the ANAMMOX reaction, the nitrite nitrogen remains after the reaction, and the high concentration of the remaining nitrite nitrogen causes the ANAMM.
OX microbes may be inhibited.

Therefore, the SBR carrying out the ANAMMOX reaction
In order to prevent both ammoniacal nitrogen and nitrite nitrogen from remaining in a high concentration in the reaction tank, the ratio of the ammoniacal nitrogen and the nitrite nitrogen of the water to be treated introduced into the SBR reaction tank is set to the SBR. It is necessary to adjust the value to an appropriate value depending on the processing conditions of the reaction tank. For this purpose, it is important to manage the operation in the preceding ammonia oxidation step in which the wastewater containing ammoniacal nitrogen is nitrified and a part of the ammoniacal nitrogen in the wastewater is converted to nitrite nitrogen. At present, there is no established operation management method capable of adjusting the ratio of nitrogen dioxide to nitrite nitrogen to an appropriate value.

In the course of the research leading to the present invention, the inventors of the present invention conducted an ammonia nitrogen concentration of 300 mg-N / L, 800
Each of the mg-N / L and 1500 mg-N / L wastewater was introduced into a nitrification tank having a volume of 10 L to oxidize a part of ammoniacal nitrogen into nitrite nitrogen, and the nitrification solution was used as a cylindrical SBR having a volume of 10 L. The denitrification process was performed by the ANAMMOX reaction in the reaction tank. If the amount of aeration is increased in the ammonia oxidation step and the nitrite nitrogen is operated to be 1.5 times or more of the ammonia nitrogen in order to prevent the ammonia nitrogen from remaining after the ANAMMOX reaction, the nitrogen content in the actual nitrification solution is increased. The ratio of nitrate nitrogen is 1.8 to 2.0 times that of ammonia nitrogen, and nitrite nitrogen remains unprocessed in the ANAMMOX reaction tank, especially in the case of waste water containing a high concentration of ammonia nitrogen. Contains 350 mg of residual nitrite nitrogen
-N / L was also reached, which caused the problem that the ANAMMOX microorganism was inhibited and lost the denitrification ability. Therefore, in order to prevent the inhibition by nitrite nitrogen, nitrite nitrogen should be 1.3% of that of ammonia nitrogen in the ammonia oxidation step.
When operating as a guide, the actual ratio of nitrite nitrogen in the treated water is 1.0 to 10% of that of ammonia nitrogen.
It becomes 1.3 times, and ammoniacal nitrogen remains in the ANAMMOX reaction tank, and when treating wastewater containing particularly high concentration of ammoniacal nitrogen, the residual ammoniacal nitrogen concentration is as high as 175 mg-N / L. However, there was a problem that the load of the subsequent nitrification denitrification treatment was high.

As described above, it is very difficult to set the nitrite conversion rate in the ammonia oxidation step according to the denitrification situation in the latter stage.

The present invention has been made in view of the above conventional circumstances, and as described above, it is possible to reduce the installation area of the reaction tank without separately providing a solid-liquid separation device; because the reaction tank is one tank. Easy management; mechanical stirring or gas stirring can be used for stirring, and strict control of stirring speed is not required as in the case of adding a carrier or USB method; high concentration for complete mixing in the tank Using the SBR system (batch system) reaction tank, which has the excellent advantages of being diluted immediately after the inflow of raw water of (1) and being less likely to be inhibited by high-concentration substrates, ammonia nitrogen is removed by the ANAMMOX reaction. After that, by denitrifying the remaining nitrite nitrogen and the generated nitrate nitrogen in the same reaction tank, it is an object to provide a biological denitrification treatment method that does not require a denitrification treatment device in the subsequent stage. .

[0024] Another object of the present invention is to provide a biological denitrification treatment method which can prevent ammonia nitrogen from remaining in the ANAMMOX reaction treated water and stably obtain treated water containing almost no nitrogen component. To do.

[0025]

The method for biological denitrification of the present invention is a method for biological denitrification in which raw water containing ammoniacal nitrogen is supplied to a batch treatment tank and denitrified by the action of microorganisms in the tank. That is, a raw water supply step of supplying raw water containing ammoniacal nitrogen to a batch treatment tank, and ammoniacal nitrogen in the presence of nitrite nitrogen, using ammoniacal nitrogen as an electron donor, and nitrite nitrogen A first denitrification step of denitrifying by the action of a denitrifying microorganism serving as an electron acceptor, and a second denitrification step of adding an electron donor to the denitrification treatment liquid of the first denitrification step and further denitrifying, The method is characterized in that the separation step of separating the denitrification treatment liquid of the second denitrification step from the supernatant liquid and the sedimentation sludge by sedimentation and the discharging step of discharging the supernatant liquid are repeated.

In the present invention, raw water containing ammoniacal nitrogen is supplied to the batch treatment tank, and the ammoniacal nitrogen is removed by the ANAMMOX microorganism in the first denitrification step. Then, in the second denitrification step, the nitrite nitrogen remaining in the first denitrification step and the generated nitric nitrogen are subjected to a denitrification treatment to remove ammoniacal nitrogen, nitrite nitrogen and nitrate nitrogen. It is possible to obtain treated water of good water quality and to eliminate the need for a denitrification treatment device in the latter stage.

In particular, according to the method of claim 2, particularly the methods of claims 3 and 4 or claims 5 and 6, it is possible to prevent the ammonia nitrogen from remaining by the ANAMMOX reaction, and to leave the nitrite nitrogen remaining after the reaction and the generated nitric acid. By performing denitrification treatment of neutral nitrogen in the second denitrification step, it is possible to obtain treated water of high water quality containing almost no nitrogen component.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the biological denitrification treatment method of the present invention will be described in detail below with reference to the drawings.

1 to 3 are system diagrams showing a batch treatment tank (SBR denitrification tank) suitable for carrying out the biological denitrification processing method of the present invention. In FIGS. 1 to 3, members having the same functions are designated by the same reference numerals.

The batch treatment tank 1 in FIG. 1 is equipped with an agitator 2, a raw water supply pipe 3 for supplying raw water, a treated water discharge pipe 4 for discharging treated water, and nitrous acid as an electron acceptor in the first denitrification step. A nitrous acid addition pipe 5 for adding a nitrogen-containing liquid and a methanol addition pipe 6 for adding methanol as an electron donor in the second denitrification step are provided. Each pipe 3, 4, 5,
Pumps P ₁ , P ₂ , P ₃ , and P ₄ are provided at 6, respectively. The batch treatment tank 1 holds sludge containing ANAMMOX microorganisms.

In the batch treatment tank 1 of FIG. 1, the biological denitrification process is performed in a batch manner as follows.

Raw Water Supply Step In the raw water supply step, the pump P ₁ is operated to supply a predetermined amount of raw water containing ammoniacal nitrogen to the batch treatment tank 1.

First denitrification step The ammoniacal nitrogen in the raw water supplied to the batch treatment tank 1 is denitrified under stirring in the presence of nitrite nitrogen by the action of the ANAMMOX microorganism in the tank. Therefore, when the raw water does not contain nitrite nitrogen, or
When the nitrite nitrogen necessary for the X reaction is insufficient, the pump P ₃ is operated to add the liquid containing the nitrite nitrogen to the batch treatment tank 1.

The nitrite nitrogen-containing liquid may be an aqueous solution of a chemical such as nitrous acid or sodium nitrite.
A part of the raw water may be nitrification-treated with ammonia-oxidizing bacteria to convert ammoniacal nitrogen into nitrite nitrogen, or wastewater containing nitrite nitrogen of another system may be used.

If the raw water containing ammoniacal nitrogen is nitrified in advance and a part of the ammoniacal nitrogen in the raw water is converted to nitrite nitrogen by an ammonia-oxidizing bacterium, such a nitrite The addition of the nitrogen-containing liquid can be eliminated.

In this case, the ratio of the concentration of ammonia nitrogen to the concentration of nitrite nitrogen in the treatment liquid obtained by nitrifying raw water is NH ₄ —N: NO ₂ —N = 1: 1 to 2, especially NH. _Four
-N: NO 2 -N = _1: is preferably in the range of 1 to 1.3. If there is more ammonia nitrogen than this range,
As is clear from the results of Example 4 described later, ANAM
Ammoniacal nitrogen remains in the denitrification treatment in the first denitrification step by the MOX microorganism, and this ammoniacible nitrogen is not treated in the second denitrification step as well, so ammoniacal nitrogen remains in the treated water. Further, when the amount of nitrite nitrogen is higher than this range, as is clear from the results of Example 4 described below, the high concentration of nitrite nitrogen in the batch treatment tank reduces the activity of the ANAMMOX microorganism, In the denitrification step, ammoniacal nitrogen and nitrite nitrogen remain. The nitrite nitrogen remaining in the first denitrification step is treated in the second denitrification step, but the ammoniacal nitrogen is not treated, so that the ammoniacal nitrogen remains in the treated water.

Similarly, when the nitrite nitrogen-containing liquid is added to the batch treatment tank 1 in the first denitrification step, the ammonia nitrogen introduced into the batch treatment tank 1 and the nitrite in the batch treatment tank 1 are also added. It is preferable to control the addition amount of the nitrite nitrogen-containing liquid so that the neutral nitrogen falls within the above range.

Second denitrification step After the first denitrification step is completed, the pump P ₄ is operated to add methanol to the batch treatment tank 1, and the mixture is stirred under stirring with ANAMMO.
The nitric acid nitrogen generated by the X reaction and the residual nitrite nitrogen are denitrified. Although an organic substance (BOD) such as methanol is used as the electron donor added in the second denitrification step, the yield to microorganisms is low and the growth of heterotrophic microorganisms in the batch treatment tank 1 is minimized. It is preferable to use methanol because it can be suppressed.

The amount of methanol added is preferably 0.4 to 0.6 mol per 1 mol of the residual nitrite nitrogen, and 0.8 to 1 mol per 1 mol of the nitrate nitrogen. .

Separation Step After completion of the second denitrification step, the agitation in the batch treatment tank 1 is stopped and the liquid in the tank is allowed to stand, whereby the sludge is settled and separated.

After the liquid in the discharge step tank is separated into solid and liquid, the pump P ₂ is operated to discharge the supernatant in the batch processing tank 1 as treated water.

After discharging the supernatant, the above steps 1 to 3 are repeated.

The supply step and the first denitrification step may be performed at the same time. In this case, for example, the first denitrification step is started by starting the supply of the raw water, or after the start of the supply of the raw water and before the end of the supply of the raw water, the addition of the nitrite nitrogen-containing liquid is started.

By the way, in the first denitrification step, if the amount of nitrite nitrogen coexisting with the amount of ammonia nitrogen in the raw water is excessive or insufficient, as described above, ammonia nitrogen or nitrite nitrogen is present. It becomes impossible to obtain treated water having good water quality due to the residual amount. Therefore, in the first denitrification step, when the nitrite nitrogen-containing liquid is added to the batch treatment tank 1, the nitrite nitrogen-containing liquid is continuously or stepwise added to It is preferable to finish the addition of the nitrite nitrogen-containing liquid based on the nitrogen concentration or the ammonia nitrogen concentration.

The nitrite nitrogen concentration or the ammonia nitrogen concentration in the batch treatment tank 1 is detected by automatically or manually sampling the liquid in the batch treatment tank 1 to determine the nitrite nitrogen concentration or the ammonia nitrogen concentration. Can be measured. For the measurement, there are a colorimetric quantification method using a reagent, an ion chromatograph method for measuring conductivity, an ion electrode method, etc., but an ion electrode method is preferable from the viewpoints of equipment cost, promptness, and reliability. . The principle of the ion electrode method is basically similar to that of the pH electrode, and the concentration of the target component in the liquid is detected from the ion concentration in the electrode by using the diaphragm that selectively passes the target component. In either method, the concentration is calculated using a device, so the detected concentration can be electrically output. Then, based on this signal, the operation of the addition pump of the nitrite nitrogen-containing liquid can be controlled.

Specifically, the addition control of the liquid containing nitrite nitrogen can be controlled as follows.

(1) Addition Control Based on Nitrite Nitrogen Concentration As shown in FIG. 2, a nitrite concentration detecting device 8 for detecting the nitrite nitrogen concentration in the batch treatment tank 1 is provided, and The addition of the nitrite nitrogen-containing liquid is controlled based on the nitrogen concentration.

The nitrite concentration detector 8 detects the nitrite nitrogen concentration by the nitrite electrode 8A. Since pH adjustment is necessary to detect the nitrite nitrogen concentration, in FIG. 2, the liquid in the batch treatment tank 1 is taken out to the container 7, the pH adjusting liquid is added, and the nitrite electrode 8A is used to add nitrite. Measure the nitrogen concentration. The nitrite concentration detection device 8 is configured to be able to control the operation of the addition pump P _{3 for} the nitrite nitrogen-containing liquid based on this measured value.

To perform control based on the nitrite nitrogen concentration in the batch treatment tank 1, a nitrite nitrogen-containing liquid is added continuously or stepwise. The addition rate is preferably determined according to the activity of the sludge retained in the tank. For example, sludge in a tank is sampled in advance, ammoniacal nitrogen and nitrite nitrogen are added in an amount of 10 to 100 mg-N / L, and the nitrite nitrogen removal rate per sludge is measured. The removal rate of nitrite nitrogen in the whole tank is calculated from the total amount of sludge retained in the tank (for example, a · gNO ₂ —N / hr). In the case of continuous addition, the addition rate should be equal to or less than the removal rate of nitrite nitrogen (for example, 0.1 to 0.9 × a · g).
NO ₂ -N / hr), and when the nitrite nitrogen in the tank liquid reaches or exceeds a predetermined value, the addition of the nitrite nitrogen-containing liquid is stopped. When adding stepwise, for example, once every 5 to 60 minutes, about 5 to 50 mg-N / L of nitrite nitrogen is added to the in-tank solution, and the nitrous acid of the in-tank solution immediately before the next addition is added. The addition of the nitrite nitrogen-containing liquid is stopped when the nitrate nitrogen concentration exceeds a predetermined value.

If this predetermined value is too low, nitrite nitrogen may be insufficient and ammoniacal nitrogen may remain, and if it is too high, ANAMMOX microorganisms may be inhibited due to high concentration of nitrite nitrogen. From 1 to 50 mg-N /
L, particularly 2 to 20 mg-N / L is preferable. Further, it is preferable to end the first denitrification step when the concentration of nitrite nitrogen in the liquid in the tank becomes equal to or higher than such a predetermined value.

Therefore, the nitrite concentration detection device 8 outputs a signal for stopping the operation of the addition pump P _{3 for} the nitrite nitrogen-containing liquid based on the detection result of the nitrite concentration in the tank, and thereafter methanol. The operation signal of the addition pump P ₄ may be output.

(2) Addition Control Based on Ammonia Nitrogen Concentration As shown in FIG. 3, an ammonia concentration detecting device 9 for detecting the ammonia nitrogen concentration in the batch treatment tank 1 is provided, and the addition is based on the ammonia nitrogen concentration in the tank. Control the addition of the nitrite nitrogen-containing liquid.

The ammonia concentration detecting device 9 detects the concentration of ammonia nitrogen by the ammonia electrode 9A. The ammonia concentration detection device 9 is configured to be able to control the operation of the addition pump P _{3 for} the nitrite nitrogen-containing liquid based on this measured value.

In order to perform control based on the concentration of ammonia nitrogen in the batch treatment tank 1, a nitrite nitrogen-containing liquid is added continuously or stepwise. The addition rate is preferably determined according to the activity of the sludge retained in the tank. For example,
The sludge in the tank is sampled in advance, ammoniacal nitrogen and nitrite nitrogen are added in an amount of 10 to 100 mg-N / L, and the nitrite nitrogen removal rate per sludge is measured. The removal rate of nitrite nitrogen in the whole tank is calculated from the total amount of sludge retained in the tank (for example, a · gNO ₂ —N / hr). In the case of continuous addition, it is added at a rate equal to or less than the removal rate of nitrite nitrogen (for example, 0.1 to 0.9 × a).
· GNO 2 -N _/ hr), ammonium nitrogen intracisternal liquid stops addition of nitrite nitrogen-containing liquid when it becomes less than a predetermined value. When added in stages, for example, 5 to 60 m
5 to 50 mg-N / N in the tank liquid once per in
About N L of nitrite nitrogen is added, and the addition of the nitrite nitrogen-containing liquid is stopped when the concentration of ammonia nitrogen in the tank liquid immediately before the next addition becomes equal to or lower than a predetermined value.

If this predetermined value is too high, nitrite nitrogen may be insufficient and ammoniacal nitrogen may remain, and if it is too low, the high concentration of nitrite nitrogen may hinder ANAMMOX microorganisms. From 1 to 30 mg-N /
L, particularly 1 to 10 mg-N / L is preferable. Further, it is preferable to end the first denitrification step when the concentration of ammonia nitrogen in the liquid in the tank becomes equal to or less than such a predetermined value.

Therefore, the ammonia concentration detection device 9 outputs a signal for stopping the operation of the addition pump P _{3 for} the nitrite nitrogen-containing liquid based on the detection result of the ammonia concentration in the tank, and thereafter, the addition of methanol. It may be configured to output the operation signal of the pump P ₄ .

In this way, based on the concentration of nitrite nitrogen or ammonia nitrogen in the liquid in the batch treatment tank 1,
By controlling the addition of the nitrite nitrogen-containing liquid, detecting the end point of the first denitrification process, and shifting to the second denitrification process,
Prevents excess and deficiency of nitrite nitrogen in the denitrification process, suppresses residual nitrite nitrogen, and sufficiently removes ammonia nitrogen that cannot be removed in the second denitrification process, resulting in high water quality. Treated water can be obtained.

The end of the second denitrification step can be known by detecting that the concentration of nitrate nitrogen in the batch treatment tank 1 has become equal to or lower than the set concentration. Also, it can be known from the change of ORP as in the conventional denitrification reaction by heterotrophic microorganisms.

In the present invention, the raw water to be treated is
Water containing ammonia nitrogen, which may contain organic substances and organic nitrogen, is preferably decomposed in advance to ammonia nitrogen before denitrification. Generally, sewage, human waste, sludge digestion and desorption liquid, other factory wastewater, landfill leachate, and other wastewater containing ammonia nitrogen, organic nitrogen, and organic matter are often treated. It is preferable to treat the above with aerobic or anaerobic treatment to decompose organic matter to obtain raw water.

[0060]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 Raw water containing 400 mg-N / L of ammonia was treated in a batch treatment tank (volume: 10 L) shown in FIG. AN in the tank
Sludge containing AMMOX microorganisms at MLVSS concentration of 500
It was maintained at 0 mg / L, and the temperature was controlled at 30 ° C. and pH 7.5. It should be noted that nitrogen gas was ventilated in the upper gas phase part of the batch processing tank to prevent oxygen from being mixed.

The operation and required time in the batch treatment tank were as follows, and one cycle was operated for 6 hours. Raw water supply process: 1.5 hr 4 L of raw water is supplied to the batch treatment tank. First denitrification step: 2.5 hr During the first denitrification step, 1 mL of 10000 mg / L nitrous acid aqueous solution was added to the batch treatment tank once every 4 minutes and stirred. Second denitrification step: 1.0 hr After the addition of the nitrous acid aqueous solution was stopped and the first denitrification step was completed, 2.2 g of methanol was added and stirred to perform the second denitrification step. Separation step: 0.5 hr The stirring was stopped, and the liquid in the tank was allowed to stand and separated for precipitation. Discharge step: 0.5 hr, the supernatant was discharged out of the batch processing tank.

At this time, the liquid amount in the batch processing tank, NH ₄ −
The changes with time of the N concentration, NO ₂ —N concentration and NO ₃ —N concentration are as shown in FIG. 4, and it was possible to obtain the treated water containing almost no nitrogen component.

However, in this method, since the nitrous acid aqueous solution was added even after the ammonia in the tank was exhausted,
There was a problem that 100 mg-N / L of nitrous acid remained after completion of the denitrification process.

Example 2 In Example 1, the batch treatment tank shown in FIG. 2 was used as the batch treatment tank, and the nitrite concentration in the tank was 10 m in the first denitrification step.
The treatment was carried out in the same manner except that the addition of the nitrous acid aqueous solution was stopped when the g-N / L or more was reached.

A diaphragm type nitrite electrode was used for the measurement of the nitrite concentration, and a pH adjusting liquid (anhydrous sodium sulfate 190 g / L, sulfuric acid 53 ml / L) was added to adjust the pH to 1 to adjust the nitrite concentration. The nitrite concentration is 10 mg-N
When / L or more, an electric signal was output and the operation of stopping the nitrite addition pump was performed.

At this time, the amount of liquid in the batch processing tank, NH ₄ −
The changes with time of the N concentration, the NO ₂ —N concentration, and the NO ₃ —N concentration are as shown in FIG. 5, and it was possible to suppress the increase in the nitrite concentration and perform the efficient treatment. The amount of methanol added in the second denitrification step was 1.05 g.

Example 3 In Example 1, the batch treatment tank shown in FIG. 3 was used as the batch treatment tank, and when the ammonia concentration in the tank became 10 mg-N / L or less in the first denitrification process, the The same process was performed except that a signal was output, the nitrite addition pump was stopped, and the addition of the nitrite aqueous solution was terminated.

At this time, the amount of liquid in the batch processing tank, NH ₄ −
The changes with time of the N concentration, the NO ₂ —N concentration, and the NO ₃ —N concentration are as shown in FIG. 6, and it was possible to suppress the increase in the nitrite concentration and perform the efficient treatment. The amount of methanol added in the second denitrification step was 0.98 g.

[0070]

As described in detail above, according to the biological denitrification treatment method of the present invention, the same batch treatment tank can be used for ANAMMOX.
After removing ammoniacal nitrogen by the reaction, ANAMM
The nitrite nitrogen remaining in the OX reaction and the generated nitrate nitrogen can be subjected to denitrification treatment, whereby the denitrification treatment device in the subsequent stage can be eliminated.

In particular, according to the method of claim 2, in particular, the method of claims 3 and 4 or 5 and 6, the ammonia nitrogen is prevented from remaining by the ANAMMOX reaction, and the nitrite nitrogen remaining after the reaction and the generated nitric acid. By performing denitrification treatment of neutral nitrogen in the second denitrification step, it is possible to obtain treated water of high water quality containing almost no nitrogen component.

[Brief description of drawings]

FIG. 1 is a system diagram showing a batch treatment tank suitable for carrying out the biological denitrification treatment method of the present invention.

FIG. 2 is a system diagram showing a batch treatment tank particularly suitable for carrying out the biological denitrification treatment method of the present invention.

FIG. 3 is a system diagram showing a batch treatment tank particularly suitable for carrying out the biological denitrification treatment method of the present invention.

FIG. 4 shows the amount of liquid in the batch processing tank and NH ₄ in Example 1.
-N concentration is a graph showing the time course of _NO 2 -N concentration and _NO 3 -N concentration.

FIG. 5 shows the amount of liquid in the batch processing tank and NH ₄ in Example 2.
-N concentration is a graph showing the time course of _NO 2 -N concentration and _NO 3 -N concentration.

FIG. 6 shows the amount of liquid in the batch processing tank and NH ₄ in Example 3.
-N concentration is a graph showing the time course of _NO 2 -N concentration and _NO 3 -N concentration.

[Explanation of symbols]

One-time processing tank 2 stirrer 8 Nitrite concentration detector 8A Nitrite electrode 9 Ammonia concentration detector 9A ammonia electrode

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Claims (6)

[Claims] 1. A method for biological denitrification in which raw water containing ammoniacal nitrogen is supplied to a batch treatment tank and is denitrified by the action of microorganisms in the tank, wherein raw water containing ammoniacal nitrogen is batch treated. Raw water supply process to supply to the tank, and denitrification by the action of denitrifying microorganisms in which ammoniacal nitrogen is used as an electron donor and nitrite nitrogen is used as an electron acceptor in the presence of nitrite nitrogen. A first denitrification step, a second denitrification step of adding an electron donor to the denitrification treatment solution of the first denitrification step to further denitrify it, and a denitrification treatment solution of the second denitrification step as a supernatant liquid. A method for biological denitrification, which comprises repeatedly performing a separation step of separating the sludge from the settling sludge and a discharging step of discharging the supernatant. 2. The biological denitrification treatment method according to claim 1, wherein in the first denitrification step, nitrite nitrogen is added to the batch treatment tank. 3. In the first denitrification step, until the concentration of nitrite nitrogen in the batch treatment tank reaches a predetermined value or more,
The biological denitrification treatment method according to claim 2, wherein nitrite nitrogen is added stepwise. 4. The second denitrification step is performed when the concentration of nitrite nitrogen in the batch treatment tank reaches a predetermined value in the first denitrification step. 3. The biological denitrification treatment method according to item 3. 5. The nitrite nitrogen is added stepwise in the first denitrification step until the concentration of ammoniacal nitrogen in the batch treatment tank becomes a predetermined value or less. 2. The biological denitrification treatment method described in 2. 6. The method according to claim 5, wherein in the first denitrification step, the second denitrification step is started when the concentration of ammonia nitrogen in the batch treatment tank reaches a predetermined value.
The biological denitrification treatment method described in.