JP2003154394A - Biological denitrification method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biological denitrification method and apparatus for organic sewage, capable of easily obtaining high treated water quality at a low cost. SOLUTION: The biological denitrification method comprises a denitrification process, wherein organic sewage containing ammoniacal nitrogen and characterized in that C-BOD is 1/2 or less ammoniacal nitrogen is denitrified under a microaerobic condition and/or an intermittent aeration condition and a propagation condition of an ammonia oxidizing bacteria group and an autotrophic denitrification bacteria group in the presence of free ammonia, and a solid-liquid separation process in the rear stage of the denitrification process and the pH of the circulating sludge from the solid-liquid separation process is controlled to 7.5-10.5. The biological denitrification apparatus is also disclosed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a biological nitrogen removing method and apparatus for biologically purifying organic wastewater containing ammoniacal nitrogen.

[0002]

2. Description of the Related Art Ammoniacal nitrogen contained in organic sewage (also referred to simply as "sewage") is one of the causative substances of eutrophication in rivers, lakes and oceans, and is effectively used in the sewage treatment process. It is desired to be removed. Generally, ammoniacal nitrogen in wastewater is decomposed into nitrogen gas by a nitrification process and a denitrification process. Specifically, in the nitrification step, ammoniacal nitrogen is oxidized to nitrite nitrogen by an autotrophic bacterium, an ammonia-oxidizing bacterium under aerobic conditions, and the nitrite nitrogen is an autotrophic bacterium, a nitrite-oxidizing bacterium. Is oxidized to nitrate nitrogen. Next, in the denitrification step, these nitrite nitrogen and nitrate nitrogen are decomposed into nitrogen gas under anaerobic conditions by a denitrifying bacterium, which is a heterotrophic bacterium, while utilizing organic substances as electron donors.

In such a conventional biological nitrogen removal method, a large amount of oxygen is required in the nitrification process for oxidizing ammoniacal nitrogen to nitrite nitrogen and nitrate nitrogen, and denitrification which is a heterotrophic bacterium is required. In the denitrification process using nitrogen bacteria,
Since it is necessary to add a large amount of an organic substance such as methanol as an electron donor, the running cost is increased.

By the way, recently, under anaerobic conditions, ammonia nitrogen is used as an electron donor and nitrate nitrogen is used as an electron acceptor to react with each other to produce nitrogen gas. Nitrogen treatment technology is being developed. For example, in one proposed nitrogen treatment method, the wastewater containing ammoniacal nitrogen is partially nitrified in a nitrification tank, and after the partial nitrification step in which a part of the ammoniacal nitrogen remains, the ammonia in the effluent of the partial nitrification step is Nitrogen,
Nitrite nitrogen and nitrate nitrogen are removed by reacting with autotrophic microorganisms in the combined oxygen denitrification process. However, in such a method, there is a problem that the treatment is extremely unstable due to the following phenomenon, nitrogen removal is insufficient, and practicability is poor. That is, in general, the nitrification reaction is set to a state where almost no ammoniacal nitrogen remains, and in order to leave ammoniacal nitrogen in the partial nitrification process to nitrite nitrogen or nitrate nitrogen, DO or M
It is necessary to adjust LSS (sludge concentration) with extremely high accuracy according to raw water conditions. In the combined oxygen denitrification process,
If the ammoniacal nitrogen remains excessively, the nitrite nitrogen and the nitrate nitrogen become equal to or more than the equivalence ratio, and as a result, the ammoniacal nitrogen remains. Conversely, when the amount of ammonia nitrogen is small and the amounts of nitrite nitrogen and nitrate nitrogen are equal to or more than the equivalence ratio, nitrite nitrogen and nitrate nitrogen remain.

Further, in another proposed nitrogen treatment method,
Part of the wastewater is introduced into the nitrite tank, mixed with the biological sludge containing ammonia-oxidizing bacteria in the tank, and aerated from the air diffuser, and the ammonia-oxidizing bacteria oxidize the ammoniacal nitrogen to nitrite nitrogen. . The nitrite solution in the nitrite tank is introduced into the autotrophic denitrification tank and at the same time, another part of the wastewater is introduced from the bypass wastewater channel and mixed with the biological sludge containing the autotrophic denitrifying bacteria in the tank. However, a method for denitrifying under anaerobic conditions is disclosed. However, even with this method,
Even in the nitrite tank, depending on the aeration time and pH conditions, the reaction of ammonia nitrogen in sewage proceeds to nitrification, resulting in insufficient denitrification by autotrophic denitrifying bacteria under anaerobic conditions. In many cases, the treatment was not stable and there was a problem in practicality.

Furthermore, the recently proposed method introduces raw water containing ammoniacal nitrogen into a nitrite / denitrification tank and inhibits the growth of autotrophic denitrifying bacteria from an air diffuser provided at the bottom of the tank. While aerating a certain amount of air, by mixing with ammonia-oxidizing bacteria and autotrophic denitrifying bacteria, nitrite and denitrification are simultaneously performed in parallel, ammonia nitrogen is completely removed, and the tank liquid is pumped. There is disclosed a technique in which the separation membrane is permeated to be moved to the permeate chamber side by suction by and the permeate is discharged as treated water from the treated water channel. However, when this method was tested, it was found that when ammonia nitrogen was completely removed, nitrite nitrogen was oxidized to nitrate nitrogen by the nitrite bacteria in the nitrite / denitrification tank. . Furthermore, when the separation membrane is put into a nitrite and denitrification tank, aeration with a large amount of air is necessary to bring out the performance of the separation membrane, and the inside of the tank is an air that does not inhibit the growth of autotrophic denitrifying bacteria. It became impossible to control the quantity.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for removing biological nitrogen which is low in cost and can easily obtain high treated water quality. Another object of the present invention is to provide a biological nitrogen removing apparatus that can easily obtain high quality of treated water at low cost.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above problems by a method and apparatus for removing biological nitrogen having the following constitution. (1) Organic wastewater containing ammonia nitrogen and having C-BOD of 1/2 or less of that of ammonia nitrogen is treated under microaerobic conditions and / or intermittent aeration conditions, and free ammonia is present. Further, under the growth conditions of the ammonia-oxidizing bacteria and the autotrophic denitrifying bacteria group, it comprises a nitrogen removal step and a solid-liquid separation step subsequent to the nitrogen removal step, and the pH of the circulating sludge from the solid-liquid separation step is adjusted to 7 A method for biological nitrogen removal of organic wastewater controlled to 0.5 to 10.5. (2) The method for removing biological nitrogen according to (1), wherein the filter in the solid-liquid separation step is a dynamic filtration membrane and / or a polymer membrane that blocks activated sludge. (3) The method for removing biological nitrogen according to (1) or (2) above, wherein a microorganism carrier and / or a zeolite molded product and activated sludge are present in the nitrogen removal step. (4) Any one of the above (1) to (3), wherein the air supply under the slightly aerobic condition and / or the intermittent aeration condition in the nitrogen removal step is controlled by ORP. Biological nitrogen removal method.

(5) C-B containing ammoniacal nitrogen
The organic sewage having an OD of 1/2 or less of that of ammonia nitrogen is set under microaerobic conditions and / or intermittent aeration conditions and in the presence of free ammonia, and further, ammonia-oxidizing bacteria and autotrophic denitrification. It is composed of a nitrogen removing device that is treated under the growth conditions of bacterial groups, and a solid-liquid separator that is a latter stage of the nitrogen removing device, and controls the pH of the circulating sludge from the solid-liquid separator to 7.5 to 10.5. Biological nitrogen removal equipment for organic wastewater.

In the present invention, "denitrification" means denitrification by autotrophic denitrifying bacteria unless otherwise specified. Also,
BOD is a BOD derived from a carbon-based organic substance, and is disclosed in P.I. It means the biochemical oxygen demand (C-BOD) with inhibition of nitrification as defined in 144. The organic wastewater to be treated in the present invention contains ammonia nitrogen and has a BOD of 1/2 that of ammonia nitrogen.
The target is the following organic sewage, and may contain nitrite nitrogen, other impurities, and the like. The sewage containing the organic nitrogen compound may be directly used in the present invention, or may be used in the present invention after converting the organic nitrogen compound into ammonia nitrogen by anaerobic treatment or aerobic treatment. Examples of wastewater to be treated in the present invention include anaerobic nitrification tank desorbed liquid, waste leachate, fertilizer factory wastewater, and the like.

The biological nitrogen removal method of the present invention comprises treating wastewater containing ammoniacal nitrogen under microaerobic conditions and / or intermittent aeration conditions in the presence of ammonia-oxidizing bacteria and autotrophic nitrogenous bacteria. It is a biological treatment method characterized in that the treatment is carried out in a nitrogen removing step of denitrifying ammonia nitrogen and nitrite nitrogen and / or nitrate nitrogen as nitrogen gas while leaving ammonia nitrogen remaining.

In the step of removing nitrogen, about 1/3 to 1/2 of the amount of ammonia nitrogen in wastewater is oxidized to nitrite nitrogen or nitrate nitrogen, and at the same time, nitrite nitrogen produced by residual ammonia nitrogen is produced. Alternatively, denitrifying nitrate nitrogen.

The reaction equations are as shown in equations (1) to (4). 1) Generation of nitrite nitrogen ^{_{NH 4 + + 3 / 2O 2}} → NO 2 - + 2H + + H 2 O ····· (1) 2) generation of nitrate nitrogen ^{_{NO 2 - + 1 / 2O 2}} → NO 3 - · ........... (2) 3) denitrification with ammonia nitrogen and autotrophic denitrification bacteria group using nitrous acid bound oxygen ^{_{NH 4 + + NO 2 - →}} N 2 + 2H 2 O .......... (3) 4) denitrified by ammonia nitrogen and nitrate-bonded oxygen autotrophic denitrifying bacteria group using the reaction ^{_{NH 4 + + 2 / 3NO 3}} - → 5 / 6N 2 + 2H ₂ O ... ・ (4)

In the nitrogen removing step of the present invention, the reactions of formulas (1) and (3) are predominantly predominant, and the reactions of formulas (2) and (4) are extremely unlikely to occur. Furthermore, equation (1)
And the trigger of the reaction of the formula (3) is about 1 mg / liter or more, preferably 3 mg / liter in the liquid of the nitrogen removing step.
Liters of free ammonia is present. The amount of free ammonia present is preferably 50 mg / liter or less at the outlet of the nitrogen removal step. When the amount of free ammonia increases, water quality deteriorates,
Ammonia gas is released and the environment is deteriorated. In order to allow free ammonia to exist, it is preferable to control the water temperature and / or pH depending on the inflowing ammoniacal nitrogen. Equations (5) and (6) that are used as a guide
Shown in.

[NH ₃ -N] = {[NH ₄ ⁺ -N] [10 ^pH ]} / {(Kb / Kw) +10 ^pH } ... (5) (Kb / Kw) = exp (6334 ^{/ (273 + T)) ......} (6) where [NH ₃ -N] the free ammonia concentration (mg-
N / liter), [NH ₄ ⁺ -N] is the concentration of ammonia nitrogen (mg-N / liter), and T is the temperature (° C.).

In the biological treatment, it is general to stabilize the treatment by dilution. Even when a few thousand mg / liter of ammoniacal nitrogen is introduced, the reaction tank contains at most several hundred mg / liter of ammoniacal nitrogen. It is a concentration.
Therefore, it is preferable to set the water temperature and / or the pH to be slightly higher than the value obtained by the formula (5). Furthermore, the reaction of the nitrogen removal step is also promoted by adding the above-mentioned autotrophic denitrifying bacteria group, which has been subjected to increasing culture under conditions of pH 7.5 or higher.

According to the results of long-term experiments conducted by the present inventors, the water temperature is 10 ° C. to 80 ° C., preferably 20 ° C. to 60 ° C., and the pH is 7.5 or more, so that the amount of free ammonia is about 1 mg / min. The reaction amount of liters or more was overwhelmingly reached, and the reactions of the formulas (1) and (3) proceeded predominantly in the nitrogen removal step. At pH 7 or less, free (gaseous) ammonia is 1.0 mg / liter or less, but at 7.5 or more, it is 3 mg / liter or more, and the growth of nitrite-oxidizing bacteria that convert nitrite to nitric acid is significantly suppressed. Most of the ammoniacal nitrogen is nitrous acid and the reaction is stopped. The method of controlling the pH in the nitrogen removal step is performed by directly adding the pH adjuster to the nitrogen removal step, or by adjusting the pH of the circulating sludge or the returning sludge to 7.5 to 10.
In some cases, the nitrogen removal step is performed after controlling to 5. When the pH adjustor is directly added to the nitrogen removal step, if the pH locally rises to 10 or higher, ammoniacal nitrogen derived from sewage is gasified by stripping. By controlling the pH of the circulating sludge having a low ammonia nitrogen concentration or the returning sludge to 7.5 to 10.5, it was found that the stripping of ammonia nitrogen was eliminated and the biological reaction was promoted. In addition, the effect of suppressing the increase in excess sludge by advancing the liquefaction of sludge by increasing the pH of the circulating sludge or the returning sludge was also recognized.

Further, it has been clarified in a long-term experiment that the DO (dissolved oxygen) concentration in the process is an important operating condition for removing nitrogen. That is, as shown in the formulas (1) and (2), all the ammoniacal nitrogen is not converted into nitrate nitrogen as well as nitrite nitrogen, and DO is supplied for denitrification of the converted nitrite nitrogen. Limitation has been found to be an important factor in stabilizing the process. Therefore, in this nitrogen removing step, the oxygen-containing gas is aerated so that the dissolved oxygen concentration is constantly less than 1 mg / liter and the conditions are set to aerobic conditions, or when the dissolved oxygen concentration is 1 mg / liter or more, the dissolved oxygen concentration is 0. 0.2 mg / liter or less, preferably 0 mg
It is important to perform intermittent aeration so that there is a time zone of 1 / liter. In the case of intermittent aeration, it is preferable to take the time when the DO concentration is 0.2 mg / liter or less longer than the time when the DO concentration is 0.2 mg / liter or more. The DO supply method may be a combination of slightly aerobic and intermittent. Also, DO control is O
It is also possible to carry out using the measured value of RP, and this nitrogen removal step aerates the oxygen-containing gas so that the ORP is always less than 50 mV, or when it is 50 mV or more, the ORP is 20 mV or less. It is important to perform intermittent aeration so that there is a time zone of preferably less than 0 mV.
In the case of intermittent aeration, the time when ORP is 20 mV or less is 20 m
It is preferable to take longer than V or more.

Further, in the present invention, the autotrophic denitrifying bacteria group and the ammonia-oxidizing bacteria can be grown only by the activated sludge (suspended microorganisms), and the reaction in the nitrogen removing step is possible, but the microbial carrier is used in the nitrogen removing step. When added, biofilms of autotrophic denitrifying bacteria and ammonia-oxidizing bacteria are formed on this surface to accelerate the reaction. The number of bacteria on the surface of the activated sludge and that on the surface of the microbial carrier are slightly different, so the mutual effects exert each other, so not only the reaction time for nitrogen removal is shortened, but also a treatment that can cope with fluctuations in ammonia nitrogen in the wastewater. Is extremely stable. Further, in the present invention, when a zeolite molded body is added as a microbial carrier in the nitrogen removal step, a biofilm of autotrophic denitrifying bacteria and ammonia-oxidizing bacteria is formed on this surface, and ammonia nitrogen in wastewater is The reaction is promoted by being adsorbed on the zeolite compact and being concentrated. Since the number of bacteria and the concentration of ammonia nitrogen on the surface of the activated sludge and the zeolite molded body are slightly different from each other, the effects are mutually exerted, and there is a greater effect than in the case of using a general microbial carrier.

Further, in the present invention, solid-liquid separation by a sedimentation basin is also possible as a solid-liquid separation means for activated sludge and microbial carrier. This embodiment is shown in FIG. However, when the sludge floats up due to a part of the residual nitrate nitrogen, it is extremely effective to apply the solid-liquid separation step in which the filter body is installed by immersion.
Since it is possible to reliably prevent the outflow of the activated sludge and the microbial carrier, it becomes possible to maintain the denitrifying bacteria and the nitrifying bacteria in the biological denitrification reaction tank at a high concentration. In addition, by making the inside of the nitrogen removal step multistage, it is possible to select an appropriate pH and sludge concentration according to the ammonia nitrogen concentration in the wastewater, and more stable nitrogen removal processing becomes possible. Specifically, it is possible to set a lower pH on the inflow end side of sewage, lower the MLSS to increase the nitrogen load, and set a higher pH on the outflow side of the process to raise the MLSS. .

For the nitrogen removing device constituting the biological nitrogen removing device of the present invention, not only the above-mentioned activated sludge type and activated sludge + microbial carrier addition method but also a treatment method in which an activated sludge is immersed in a filter medium is used. it can. Further, by making the inside of the nitrogen removal device multi-stage, it is possible to select appropriate pH and sludge concentration according to the ammonia concentration in the wastewater, and more stable denitrification treatment becomes possible.

The nitrogen removing device is controlled so that the activity of the ammonia-oxidizing bacteria is high and the activity of the nitrite-oxidizing bacteria is low, and is denitrified by ammonia by the autotrophic denitrifying bacteria group. In addition, it is a device that does not convert all ammoniacal nitrogen into nitrite nitrogen as well as nitrate nitrogen. That is, the water temperature is 10 ° C to 80 ° C, preferably 20 ° C to 60 ° C, and the pH is 7.5 to 10.5.
It is preferably set to 7.5 to 9.5. Furthermore, the oxygen-containing gas is aerated so that the dissolved oxygen concentration is constantly less than 1 mg / liter, and the condition is set to a microaerobic condition, or 1 mg / liter.
Dissolved oxygen concentration is 0.2 mg in case of liter or more
It is important to perform intermittent aeration so that there is a time zone of 1 / liter or less, preferably 0 mg / liter. In the case of intermittent aeration, it is preferable to take the time when the DO concentration is 0.2 mg / liter or less longer than the time when the DO concentration is 0.2 mg / liter or more. The nitrogen load is controlled so as to be ³ kg-N / m ³ · day or less.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these drawings. In all the drawings for explaining the embodiments and examples, constituent elements having the same functions are designated by the same reference numerals. FIG. 2 shows an example of a flow sheet in which the dynamic filter is used in the solid-liquid separation step in the treatment method of the present invention.

FIG. 2 shows an example of a flow sheet according to the method of the present invention, which uses a dynamic filter in the solid-liquid separation step. As for the constitution of the treatment device of FIG. 2, a nitrogen removal device 1 and a solid-liquid separation device 3 in which a dynamic filter body is installed by immersion.
Consists of. Hereinafter, wastewater containing ammoniacal nitrogen will be referred to as raw water. The entire amount of raw water 4 is supplied to the nitrogen removing device 1. At that time, the circulating sludge 30 from the solid-liquid separator 3 is also supplied to the nitrogen removing device 1. Raw water input is nitrogen load 3
The control is carried out so that it is not more than kg-N / m ³ · d. The nitrogen removing device 1 uses the air diffuser 10, and the air 9 is intermittently supplied. The supply timing of the air 9 is DO of 0.2 m.
The time period of g / liter or less is longer than the time period of 0.2 mg / liter or more, and further, the time period of 0 mg / liter is controlled. In addition, the pH is 7.5
By returning the circulating sludge of 10.5, p
H is controlled within the range of 7.5 to 10.5, preferably 7.5 to 9.5. In the nitrogen removal device 1, raw water 4
1/3 to 1/2 of the ammoniacal nitrogen is oxidized to nitrite nitrogen and some is oxidized to nitrate nitrogen. In parallel with this reaction, the ammonia nitrogen in the raw water 4 is nitrite nitrogen and nitrate nitrogen. Nitrogen reacts to denitrify as nitrogen gas.

As shown in FIG. 2, the treated mixed liquid from the nitrogen removing device 1 is supplied to the solid-liquid separation device 3 from the sludge supply pump 16. The treated mixed liquid that has flowed into the solid-liquid separation device 3 is filtered by the filter module 18 at a water head pressure H, filtered water is obtained from the filtered water line 27, and flows into the treated water tank 25 through the filtered water valve 19. The treated water 5 is obtained from the treated water tank 25. In addition, the sludge mixture after filtration is treated as the circulating sludge 30.
After the pH is controlled to 7.5 to 10.5 by the H control device 11, it is returned to the nitrogen removing device 1.

As a method of cleaning the filtration module 18, the surface of the module is washed by air, backwashed with water and air, and the sludge is discharged. As a method of air-washing the surface of the module, the air-washing blower 24 is activated at regular intervals, and air is supplied to the air-washing diffuser pipe 17 below the filter through the air-washing valve 21. In the water backwashing, the filtered water in the treated water tank 25 is supplied from the water backwashing pump 26 and introduced into the inside of the filter through the water backwashing line 28. The backwashing with water is performed immediately after empty washing or after 0.5 to 5 minutes. The sludge discharge line 23 is used to discharge the invading sludge through the sludge discharge valve 23.
More discharged to the nitrogen removing device 1. When sludge is discharged at the same time as backwashing with water, the invading sludge can be discharged together with the backwashing water, so that the accumulation of invading sludge is reduced. The internal air washing is performed by activating the air washing blower 24 and aerating the inside of the module 18 through the internal air washing valve 22. The air supplied to the lower part of the module 18 passes through the inside of the module 18 and is released to the atmosphere from the air bleeding valve 20.

The same effect can be obtained by using any of a non-woven fabric, a woven fabric, a metal net or the like as the filter. The shape of the filter body is mainly a plane type, but it is also possible to use a cylindrical type or a hollow type, and it is possible to bundle a plurality of them and use them as a module filter body. 1 and 2, the nitrogen removing device 1 shows an addition method of activated sludge + microbial carrier to which the carrier 15 is added, but the above-mentioned activated sludge method of only activated sludge can be used. Further, by making the inside of the nitrogen removing device 1 multi-staged, it is possible to select appropriate pH and sludge concentration according to the ammonia concentration in the wastewater, and more stable denitrification treatment becomes possible.

FIG. 3 shows another processing flow according to the present invention. The structure of the processing apparatus of FIG. 3 comprises a nitrogen removing apparatus 1 and a solid-liquid separating apparatus 3. As shown in FIG. 3, the raw water 4 flows into the nitrogen removing device 1, and the treatment mixture liquid from which nitrogen has been removed by the biological nitrogen removing reaction is sent to the lower part of the solid-liquid separation device 3 by the sludge supply pump 16. The filtration module 18 is immersed and installed in the membrane filtration tank. Membrane filtration is module 1
The treated water 5 is obtained by filtering with a suction pump 31 while supplying air from the air-washing blower 24 to the air-washing diffuser 17 at the lower part of 8.
The sludge mixed liquid and the microbial carrier separated and concentrated by the filtration membrane are treated as the circulating sludge 30 by the pH controller 11 to adjust the pH to 7.5
After controlling to 10.5, it is returned to the nitrogen removing apparatus 1.
As the shape of the filtration membrane, flat membrane, MF membrane such as hollow fiber membrane, UF
The same effect can be obtained by using any of the films. Further, the same effect can be obtained by using any of polymer, metal, ceramics, etc. as the film material. It is desirable that the pore size of the membrane is not more than μm, which can sufficiently block the activated sludge particles.

[0029]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 In this example, waste leachate was treated by the flow shown in FIG. Nitrogen remover 1; 10m ³
Consists of. First, the quality of the waste leachate, which is raw water 4, is first
Shown in the table. In this case, BOD is 20 mg / liter and ammoniacal nitrogen is 390 mg / liter, and BOD is 1/2 or less with respect to ammoniacal nitrogen.

[0031]

[Table 1]

The raw water 4 was supplied to the nitrogen removing device 1 to remove nitrogen. Table 2 shows the operating conditions of the nitrogen removing apparatus 1. The nitrogen removing device 1 was charged with a sponge carrier of 5 mm × 5 mm × 5 mm at 10 v / v% of the device volume, and the agitator 14
Was used for continuous stirring. DO control is aeration for 3 minutes, 9
It was performed by intermittent aeration with a stop of 1 minute. For the pH control, a pH controller is used, and when it becomes higher than 8.7 in the circulation sludge path, H ₂ SO ₄ is added, and the pH is adjusted to 8.5.
If it was lower, it was done by adding NaOH. The consumption amount of NaOH is 1.6 to 2.2 g / d, H
₂ SO ₄ was hardly consumed. Table 2 shows the operating conditions of the nitrogen removal device.

[0033]

[Table 2]

Table 3 shows the water quality of the raw water 4 and the treated water 5. In the nitrogen removing apparatus 1, the pH was 8.5, the water temperature was 30 ° C., the ammoniacal nitrogen was 17.8 mg / liter, and the amount of free ammonia was 8.6 mg / liter. In the nitrogen removing apparatus 1, the amount of ammonia nitrogen was reduced by about 95%, nitrite nitrogen and nitrate nitrogen were hardly generated at 5 mg / liter or less, and nitrogen was almost removed.

[0035]

[Table 3]

Opening 150 mesh, hole diameter 114 μm,
In the dynamic filtration by the filtration module 18 using a 0.1 mm-thick polyester woven fabric as the filter body, 6 m ³ / d of treated water was stably obtained. Further, the treated water SS was always about 5 mg / liter, and high filtration performance was obtained.

Example 2 In the flow of FIG. 3, the same raw water 4 as in Example 1 was treated with the nitrogen removing apparatus 1. The operating conditions of the nitrogen removing device 1 were the same as in Example 1, but DO was controlled by the amount of circulating sludge from the solid-liquid separation device 3 without aeration in the nitrogen removing device 1. In the membrane filtration tank, a flat precision M with a pore size of 0.4 μm
Using an F membrane, suction filtration was performed so that the filtration flux was always 0.3 m / d. The suction filtration was intermittent operation for 13 minutes ON and 2 minutes OFF. Aeration was always performed, and the amount of aeration air was set to be 2.5 m ³ / m ² / min per sludge channel area. Table 4 shows the water quality of raw water 4 and treated water 5 of each device. In the nitrogen removing device 1, the pH is 8.
5, water temperature was 30 ° C., ammoniacal nitrogen was 18.2 mg / liter, and free ammonia amounted to 9.3 mg / liter. In the nitrogen removing device 1, the amount of ammonia nitrogen was reduced by about 95%, and the amount of nitrite nitrogen and nitrate nitrogen was 5 mg /
Almost no nitrogen was removed even when the amount was less than 1 liter. The treated water SS was 1 mg / liter or less, and clear treated water having no SS was obtained by membrane filtration. Furthermore, during the continuous experiment period of about 3 months, the filtration flux is 0.3 m / d, and the suction pressure is about 0.1 to 0.15 kg /
With cm ² , the treatment was stable.

[0038]

[Table 4]

Example 3 In the flow of FIG. 2, the same raw water 4 as in Example 1 was treated with the nitrogen removing apparatus 1. The operating conditions of the nitrogen removing device 1 were the same as in Example 1, but a zeolite compact having a particle diameter of 2 mm was used as the carrier charged into the nitrogen removing device 1. Table 5 shows the water quality of raw water 4 and treated water 5 of each device. In the nitrogen removing device 1, the amount of ammonia nitrogen is 12.8 mg / liter, which is reduced by about 97%, and the amount of nitrite nitrogen and nitrate nitrogen is 5 mg / liter.
Almost no liters were produced, and the result was that nitrogen was removed more than in Examples 1 and 2. In addition, in the dynamic filtration, 6 m ³ / d of treated water was stably obtained. Further, the treated water SS was always about 5 mg / liter, and high filtration performance was obtained.

[0040]

[Table 5]

Comparative Example 1 Biological nitrogen removal was performed by injecting methanol, which is a conventional nitrification denitrification method. The nitrification apparatus 1A has a capacity of 10 m ³ , and the denitrification apparatus 2 has a capacity of 10 m ³ . The flow is shown in FIG. The nitrogen removing device 1 was continuously aerated, and the denitrifying device was installed in the subsequent stage of the normal nitrification tank without controlling the pH, and the device was operated. Table 6 shows the operating conditions of the nitrogen removing device. A sponge carrier of 5 mm × 5 mm × 5 mm was put into the nitrification apparatus 1A at 10 v / v% of the apparatus volume, and continuous stirring was performed using a stirrer. The denitrification apparatus was continuously stirred and the injection amount of methanol was 0 g / d.

[0042]

[Table 6]

Table 7 shows the water quality at the inlet and outlet of each device. In the nitrification apparatus 1A, 100% of the nitric acid nitrogen was nitrified, and most of it was changed to nitric acid nitrogen. In addition, the pH was lowered to 6.5 because the pH was not controlled. Denitrification device 2
Nitrate nitrogen was hardly removed in. In addition, when solid-liquid separation was performed in a sedimentation tank, sludge floated due to denitrification in the sedimentation tank and the sludge management was difficult. Nitrification device 1A
The nitrogen removal rate of the denitrification apparatus 2 was 21%, and the removal rate was very small as compared with Examples 1 and 2.

[0044]

[Table 7]

Comparative Example 2 As in Comparative Example 1, biological nitrogen removal by methanol injection, which is a conventional nitrification denitrification method, was performed. The flow is shown in FIG. The nitrification apparatus 1A was continuously aerated and operated as a normal nitrification tank without controlling the pH, and 8.0 g / d of methanol was added to the denitrification apparatus 2 for continuous stirring to form a denitrification tank. Since there was residue, a 3 liter re-aeration tank (not shown) was installed in front of the solid-liquid separation device 3 to operate. Table 8 shows the water quality at the inlet and outlet of each device. In the nitrification apparatus 1A, 100% of the nitric acid nitrogen was nitrified, and most of it was changed to nitric acid nitrogen. In addition, the pH was lowered to 6.5 because the pH was not controlled. In the denitrification device 2, denitrification proceeded by adding methanol, and 90% of nitrate nitrogen was removed. The nitrogen removal rate of both the nitrification apparatus 1A and the denitrification apparatus 2 was about 90%, and in the case of the conventional nitrification and denitrification method, methanol was added 3.4 times as much as the amount of nitrogen, 8.0 g /
Despite the addition of d, the quality of the treated water was worse than that of Example 1.

[0046]

[Table 8]

[0047]

EFFECTS OF THE INVENTION According to the present invention, in the treatment of wastewater containing ammoniacal nitrogen, organic wastewater is removed by a biological nitrogen removal method by a nitrogen removal device with DO and pH control. The required oxygen amount can be reduced as compared with the conventional method, and nitrogen can be denitrified up to nitrogen gas without using an electron donor such as methanol, so that the cost can be reduced. Furthermore, the effect of accelerating the reaction between nitrite nitrogen and ammonia nitrogen while at the same time preferentially generating nitrite nitrogen is recognized, and nitrogen can be reliably removed by easy control. In order to perform solid-liquid separation of the sludge mixture after the biological denitrification treatment and the microbial carrier,
If filtration is performed using the solid-liquid separation tank in which the filter body is immersed, good water quality can be obtained, and outflow of denitrifying bacteria and nitrifying bacteria can be prevented. Can be maintained and stable processing can be obtained.

[Brief description of drawings]

FIG. 1 is a flow chart showing a biological nitrogen removing apparatus of the present invention using a sedimentation tank as a solid-liquid separation apparatus.

FIG. 2 is a flow chart showing the biological nitrogen removing apparatus of the present invention using dynamic filtration in the solid-liquid separation apparatus.

FIG. 3 is a flow chart showing a biological nitrogen removing apparatus of the present invention using a membrane separation for a solid-liquid separation apparatus.

FIG. 4 is a flow chart of a biological nitrogen removing apparatus by adding methanol, which is a conventional nitrification denitrification method.

[Explanation of symbols]

1 Nitrogen removal device 1A Nitrification device 2 Denitrification equipment 3 Solid-liquid separator 4 Raw water 5 treated water 6 Return sludge 7 Nitrogen removal device effluent 9 air 10 Air diffuser 11 pH controller 12 Surplus sludge 13 Gas exhaust pipe 14 Stirrer 15 Carrier 16 Sludge supply pump 17 Air diffuser for air washing 18 Filtration module 19 Filtration water valve 20 Air bleeding valve 21 Flush valve 22 Internal flush valve 23 Sludge discharge valve 24 Air-washing blower 25 treated water tank 26 Water backwash pump 27 Filtered water line 28 Water backwash line 29 Sludge discharge line 30 circulating sludge 31 Suction pump 32 Methanol addition device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C02F 1/28 C02F 1/28 M 1/44 1/44 F 3/10 3/10 Z (72) Invention Toshihiro Tanaka 11-1 Haneda Asahi-cho, Ota-ku, Tokyo (72) Inventor Akira Yamaguchi Akira Yamaguchi 11-1 Haneda-Asahi-cho, Ota-ku, Tokyo (72) Inventor, Katsuyuki Kataoka Tokyo 11-1 Haneda Asahi-cho, Ota-ku, Tokyo F-term in EBARA CORPORATION (reference) 4D003 AA01 AA12 AB01 BA02 BA03 CA02 CA10 EA22 FA05 FA06 4D006 GA06 GA07 HA01 HA41 HA93 KA01 KA31 KA43 KB12 KB23 KC03 KC14 MA16 MC02 MC62 MC09 PB20 4D024 AA04 AB13 BA07 BB01 BC04 DB16 4D040 BB02 BB42 BB52 BB82 BB91 BB92 4D066 BA01 BB02 BB12 DA03

Claims (5)

[Claims] 1. C-BOD containing ammoniacal nitrogen
The organic sewage containing less than 1/2 of ammonia nitrogen under microaerobic conditions and / or intermittent aeration conditions and in the presence of free ammonia, and further, ammonia oxidizing bacteria and autotrophic denitrifying bacteria Under the growth conditions of the group, consisting of a nitrogen removal step and a solid-liquid separation step after the nitrogen removal step,
The pH of the circulating sludge from the solid-liquid separation step is 7.5 to 10.
A method for removing biological nitrogen from organic wastewater controlled to 5. 2. The method for removing biological nitrogen according to claim 1, wherein the filter in the solid-liquid separation step is a dynamic filtration membrane and / or a polymer membrane that blocks activated sludge. 3. The method for removing biological nitrogen according to claim 1 or 2, wherein a microbial carrier and / or a zeolite molded product and activated sludge are present in the nitrogen removing step. 4. The air supply is controlled by OR when the microaerobic condition and / or the intermittent aeration condition are set in the nitrogen removing step.
The biological nitrogen removal method according to any one of claims 1 to 3, which is controlled by P. 5. C-BOD containing ammoniacal nitrogen
The organic sewage containing less than 1/2 of ammonia nitrogen under microaerobic conditions and / or intermittent aeration conditions and in the presence of free ammonia, and further, ammonia oxidizing bacteria and autotrophic denitrifying bacteria It consists of a nitrogen removal device for treating under group growth conditions, and a solid-liquid separation device after the nitrogen removal device, and the pH of the circulating sludge from the solid-liquid separation device is 7.5.
Biological nitrogen removal device for organic sewage controlled to ~ 10.5.