JP4031597B2 - How to remove nitrogen from wastewater - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for efficiently removing nitrogen compounds contained in sewage / drainage using autotrophic bacteria.
[0002]
[Prior art]
Biological denitrification methods are widely known as methods for removing nitrogen from sewage and wastewater. The nitrogen is often contained in the form of ammoniacal nitrogen. For example, wastewater containing high concentrations of ammonia nitrogen is generated from steelworks coke factories, manure, fertilizer factories, semiconductor factories, leather factories, and the like. Ammonia nitrogen-containing wastewater generated from a steelworks coke factory is also referred to as an aqueous water, and contains several hundred to several thousand mg / l of ammoniacal nitrogen. On the other hand, municipal sewage contains about several tens mg / l of ammonia nitrogen and about several mg / l of farm effluent.
[0003]
Biological removal of ammoniacal nitrogen from sewage and wastewater includes biological oxidation by aerobic autotrophic bacteria (nitrifying bacteria such as nitrozomonas and nitrobacter) and facultative anaerobic heterotrophic bacteria (pseudomonas, etc.) A biological nitrification-denitrogenation method comprising a combination of biological reductions by
[0004]
First, the nitrification process consists of the following two-stage reaction, and the types of nitrifying bacteria involved are different.
[0005]
2NH ₄ ⁺ + 3O ₂ → 2NO ₂ ⁻ + 2H ₂ O + 4H ⁺ (1)
[0006]
^{_{2NO 2 - + O 2 → 2NO}} 3 - (2)
[0007]
The reaction shown in the formula (1) is brought about by nitrite bacteria having nitrozomonas as a representative species, and the reaction shown in the formula (2) is brought about by nitrate bacteria having a nitrobacter as a representative species.
[0008]
Nitrite nitrogen and nitrate nitrogen generated by the above reaction are generally reduced using facultative anaerobic heterotrophic bacteria to form nitric oxide gas (N ₂ O) or nitrogen gas (N ₂ ), which is To be dissipated.
[0009]
2NO ₂ ⁻ + 6H ₂ → N ₂ + 2H ₂ O + 2OH ⁻ (3)
[0010]
2NO ₃ ⁻ + 10H ₂ → N ₂ + 4H ₂ O + 2OH ⁻ (4)
[0011]
Facultative anaerobic heterotrophic bacteria require hydrogen donors and organic substances are usually used. In urban sewage, organic matter in sewage is used as it is, and in wastewater that does not contain organic matter, methanol is added.
[0012]
This biological nitrification-denitrification method has few problems when the ammoniacal nitrogen concentration is 100 mg / l or less, and is the most inexpensive and stable treatment method.
[0013]
[Problems to be solved by the invention]
However, in the biological nitrification-denitrogenation method, various problems occur when the ammoniacal nitrogen concentration exceeds 100 mg / l, and stable treatment becomes difficult. That is, when the ammonia nitrogen concentration exceeds 100 mg / l, the oxidation of ammonia nitrogen does not proceed to nitrate nitrogen in the nitrification process, that is, nitrobacter is inhibited and nitrite nitrogen in the treated water accumulates. It has been found that it is easy to do. As the cause of this, inhibition of free ammonium ions to nitrobacter is known. In particular, when the pH is high, free ammonium ions are generated.
[0014]
It is widely known that nitrite nitrogen is highly toxic to heterotrophic bacteria and the quality of treated water is likely to deteriorate (for example, Yasunori Toya, “Sewerage Association Journal”, VOL7, NO74, 1970). Since bacteria used for denitrification are usually heterotrophic bacteria, accumulation of nitrite nitrogen inhibits the progress of the denitrification reaction. When the progress of the denitrification reaction stops, nitrite nitrogen flows out into the treated water, and not only the nitrogen regulation cannot be cleared, but also the COD (chemical oxygen demand) due to nitrite nitrogen increases.
[0015]
For this reason, it is quite difficult to apply the conventional biological nitrification-denitrogenation method in the case of wastewater whose ammonia nitrogen concentration exceeds 100 mg / l.
[0016]
On the other hand, bacteria having denitrification performance are not limited to heterotrophic bacteria. It is well known that autotrophic bacteria such as hydrogen bacteria and sulfur-oxidizing bacteria also have a denitrification function in the absence of oxygen. Each of these autotrophic bacteria synthesizes and proliferates from the energy generated when hydrogen or reducing sulfur compounds are oxidized and carbon dioxide in the air. Although these bacteria are known for denitrification due to their low growth rate and weak floc-forming ability, there have been few examples of their use for denitrification.
[0017]
However, the inventors have found that these autotrophic bacteria have a very strong resistance to nitrite nitrogen compared to heterotrophic bacteria. That is, even when the nitrite nitrogen concentration was increased to 2000 mg / l, no decrease in the denitrification rate was observed. Therefore, in the case of wastewater treatment containing ammonia nitrogen at a high concentration, the use of autotrophic bacteria as the bacteria for denitrification brings about stabilization of the treatment (Japanese Patent Application No. 11-117410). In addition, among the autotrophic bacteria, the inventors of the present invention can easily increase the concentration in the denitrification tank because the sulfur-oxidizing bacteria may have a self-granulating action, and the processing efficiency can be improved. It is known that this is possible (Japanese Patent Application No. 10-122719).
[0018]
Thus, by using autotrophic bacteria resistant to nitrite nitrogen instead of heterotrophic bacteria, stable treatment of wastewater containing high concentration ammoniacal nitrogen, which has been difficult in the past, becomes possible.
[0019]
However, when the nitrogen concentration in the wastewater is high, the amount of nitrogen gas generated in the denitrification process increases. This nitrogen gas tends to adhere to autotrophic bacteria and float on the denitrification tank, and tends to flow out of the denitrification tank. Therefore, in order to obtain more stable processing performance, it is necessary to take measures to prevent the outflow of autotrophic bacteria. The present invention solves the above problems.
[0020]
[Means for Solving the Problems]
The gist of the present invention is the following (1) to (6).
[0021]
(1) In the denitrification method of reducing nitrite nitrogen and nitrate nitrogen in wastewater to nitrogen gas using autotrophic bacteria and removing them from wastewater, self-granulated sulfur-oxidizing bacteria are used as autotrophic bacteria The treated water in the denitrification tank is filtered through a filtration device filled with a subsequent filter medium, and the precipitate in the filtration device is returned to the denitrification tank to prevent the outflow of the autotrophic bacteria from the denitrification tank. A method for removing nitrogen from wastewater, wherein the concentration of autotrophic bacteria is increased in the denitrification tank.
[0022]
(2) In the denitrification method of reducing nitrite nitrogen and nitrate nitrogen in wastewater to nitrogen gas using autotrophic bacteria and removing them from wastewater, self-granulated sulfur-oxidizing bacteria are used as autotrophic bacteria In addition, the concentration of autotrophic bacteria in the denitrification tank is increased by preventing the floating outflow of the autotrophic bacteria from the denitrification tank using a filtration unit filled with a filter medium provided in the upper part of the denitrification tank. A method for removing nitrogen from wastewater.
[0024]
(3) The method for removing nitrogen from waste water according to (1) or (2), wherein the filter medium is sand, gravel, ceramics, anthracite, or a floating filter medium.
[0025]
(4) The method for removing nitrogen from the waste water of (1), (2) or (3) above, wherein a filtration device or a filtration part filled with a filter medium having a diameter of 3 mm or less is used.
[0026]
(5) The method for removing nitrogen from waste water according to (2) to (4) above, wherein an underwater stirrer is provided at the lower part of the denitrification tank and / or the lower part of the filtration part.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
In the denitrification process, using a method that reduces nitrite nitrogen to nitrogen gas using autotrophic bacteria resistant to nitrite nitrogen, the nitrite nitrogen is completely converted to nitrate nitrogen in the nitrification process. It is no longer necessary to oxidize, and the processing time of the denitrification tank is shortened and maintenance is facilitated. However, if the nitrogen concentration in the wastewater exceeds 100 mg / l, the autotrophic bacteria may float due to the nitrogen gas generated by the denitrification reaction. Among the autotrophic bacteria, when self-granulated sulfur-oxidizing bacteria are used, the flying height is considerably suppressed because the particle diameter is 1 to 3 mm. However, complete control is difficult.
[0028]
By the way, many application examples of the membrane separation apparatus have been reported in the activated sludge treatment of sewage and manure. In this method, the activated sludge is maintained at a high concentration inside the reaction tank using a membrane separation device, and a high-efficiency treatment is performed. As the membrane, an ultrafiltration membrane (UF) or a microfiltration membrane (MF) is used. By using the membrane, the activated sludge concentration (MLSS) inside the reaction vessel can be maintained at 6000 to 10,000 mg / l. And since it is intended for activated sludge (floc of about several tens of microns) with a small floating particle size, a membrane with a small pore diameter is often used. For this reason, the amount of permeated water is small and the required pressure is excessive (for example, Yoroku Wada, “Water Recycling”, Jinshokan, pages 179-180).
[0029]
In the reference embodiment of the present invention, as shown in FIG. 1, the outflow of autotrophic bacteria from the denitrification tank 2 is prevented by a membrane separation device 4 using an MF membrane (pore diameter: 0.1 to 1 micron) or the like. . In particular, when a self-granulated sulfur-oxidizing bacterium having a particle size of about 1 to 3 mm is used, it is not necessary to use a membrane with a small pore size as used in activated sludge treatment, and the pore size is from 10 microns. Even filtration membranes that are extremely large compared to conventional membranes of 500 microns can be adequately accommodated. For this reason, the amount of permeated water can be as large as 20 to 50 m ³ / m ² . When the pore diameter is 500 microns or more, the self-granulated sulfur-oxidizing bacteria are soft, so that they easily enter the pore diameter. Further, not only sulfur-oxidizing bacteria that are self-granulated but also sulfur-oxidizing bacteria that are forcibly granulated by adding a flocculant or the like can be used.
[0030]
Further, in the embodiment of the present invention, as shown in FIG. 2, even if the filtration device 8 filled with sand, gravel, ceramics or floating filter medium is used as a filter medium, the denitrification tank 2 for the autotrophic bacteria is used. Can be prevented from flowing out. As in the case of the membrane separator, when a self-granulated sulfur-oxidizing bacterium having a particle size of about 1 to 3 mm is used, the filter medium diameter used in the conventional sand filter: 0.45 There is no need to use sand having a small particle diameter of ˜0.7 mm, and gravel of 1 to 3 mm can be used. The filtration rate was also possible up to about 200 to 500 m / day. In general, filtration is completely different in membrane separation and removal mechanism, and transport of the substance to be removed to the filter medium surface (blocking action and gravity sedimentation action) and adhesion of the substance to be removed on the filter medium are important factors. . Therefore, the optimum filter medium diameter and filtration rate must be obtained experimentally. In addition, in the experiment using 1 to 3 mm gravel as a filter medium, when the filtration rate was increased to 500 m / day or more, outflow of sulfur-oxidizing bacteria was observed in the treated water.
[0031]
As a kind of the filter medium, not only sand and gravel but also formed ceramics, anthracite, or floating filter medium can be used. Furthermore, as shown in FIG. 3, the filtration unit 9 can be integrated with the denitrification tank 2 by being installed in the upper part of the denitrification tank 2. In this case, it is desirable to provide a gas vent pipe 12 for promoting the diffusion of nitrogen gas. Furthermore, when combined with a filtration unit, it is desirable to provide an underwater agitator 10 at the lower part of the denitrification tank and / or the lower part of the filtration unit in order to prevent the sulfur-oxidizing bacteria that have floated from adhering to the filter medium.
[0032]
【Example】
Examples of the present invention will be described below.
[0033]
(Example 1) Application to steelworks coke factory water treatment [0034]
The method of the present invention was applied to denitrification of activated water sludge treated water generated from a steelworks coke plant. Awamizu is a wastewater mainly composed of phenol, but contains about 1000 to 5000 mg / l of ammoniacal nitrogen. Conventionally, it has been diluted 3 to 5 times with seawater and decomposed and removed mainly with phenol by activated sludge. Such a water-activated activated sludge treated water often contains 300 to 1000 mg / l of ammoniacal nitrogen, although organic substances such as phenol are removed by the activated sludge.
[0035]
The processing flow is shown in FIG.
[0036]
In order to oxidize ammonia nitrogen to nitrite nitrogen in the nitrification tank 14, the nitrification tank 14 was operated under the following operating conditions. First, 70% of the ceramic carrier was introduced into the nitrification tank 14 per reactor volume to allow nitrifying bacteria to adhere (fixed bed type bioreactor). Next, the pH is controlled to 7-8 with sulfuric acid and sodium hydroxide, and DO and air are maintained at 2 mg / l or more and ORP at +150 mV (silver / silver chloride standard) or more by air and / or oxygen. Drove. Ammonia nitrogen (850 mg / l) became 80% nitrite nitrogen and 20% nitrate nitrogen when the ammonia nitrogen volume load was in the range of 5 kg-N / m ³ · day.
[0037]
The sulfur-oxidizing bacteria self-granulated were put into the denitrification tank 2, and thiosulfuric acid was used as sulfur as a sulfur source, and 3 times the amount of nitrogen was added. When the pH was controlled to 7-8 with sulfuric acid and sodium hydroxide, and the volumetric load of nitrate nitrogen and nitrite nitrogen was operated at 10 kg-N / m ³ · day, the nitrogen concentration in the treated water was 10 mg. / L or less. A filtration device 8 filled with saddle type ceramics (size: 1 inch) was installed in the rear stage. Although the filtration rate was operated at 200 m / day, the outflow of sulfur-oxidizing bacteria self-granulated in the treated water 5 was not observed.
[0038]
The thiosulfuric acid remaining in the treated water was oxidized to sulfate ions in the biological oxidation tank 16 using aerobic sulfur-oxidizing bacteria. In the biological oxidation tank 16, the dissolved oxygen was maintained at 2 mg / l or more by aeration. The residence time in the biological oxidation tank 16 was 1 hour, and thiosulfuric acid was oxidized to sulfate ions, and the COD was 20 mg / l or less.
[0039]
(Example 2) Application to treated sewage sludge treated water [0040]
In the conventional standard denitrification method, collected manure was diluted about 10 to 20 times, and then treated with activated sludge to remove organic matter (BOD). When nitrogen removal is also performed, the nitrification solution is circulated to the denitrification tank, denitrification is performed with organic matter in the waste water, and a circulation type nitrification-denitrification method is adopted that results in a denitrification-nitrification flow. There are many cases. However, when nitrogen removal is performed, nitrite nitrogen accumulation tends to occur, and the nitrogen removal efficiency tends to decrease. For this reason, a dilution rate becomes large and the facility will be enlarged. The water quality of the collected manure is about BOD of 10,000 to 20000 mg / l, COD of 5000 to 10,000 mg / l, and TN of 5000 to 10,000 mg / l (mostly organic nitrogen and ammoniacal nitrogen).
[0041]
In the processing flow shown in FIG. 5, the present invention is applied to the manure treatment. After diluting manure three times with fresh water, organic substances were first removed with activated sludge.
[0042]
Thereafter, in order to oxidize ammonia nitrogen to nitrite nitrogen in the nitrification tank 14, the nitrification tank 14 was operated under the following operating conditions. First, a floating cylindrical plastic carrier (inner diameter: 3 mm, length: 4 mm) was introduced into the nitrification tank 14 by 25% per nitrification tank volume to allow nitrification bacteria to adhere (fluidized bed bioreactor). Next, the pH is controlled to 7-8 with sulfuric acid and sodium hydroxide, and the air and / or oxygen is operated so as to maintain DO at 2 mg / l or more and ORP at +150 mV (silver / silver chloride standard) or more. did. Under the condition that the ammonia nitrogen volume load of the nitrification tank 14 is 5 kg-N / m ³ · day, 90% of the total of organic nitrogen and ammonia nitrogen (2500 mg / l) is nitrite nitrogen and 10% is nitric acid. Became nitrogen.
[0043]
Further, sulfur-oxidizing bacteria self-granulated were put into the denitrification tank 2, and thiosulfuric acid was used as sulfur as a sulfur source, and 3 times the amount of nitrogen was added. A floating cylindrical plastic carrier (inner diameter: 3 mm; length: 4 mm) was introduced into the upper part of the denitrification tank 2 by 25% per volume of the denitrification tank 2. In addition, an underwater stirrer was installed in the center of the lower part of the denitrification tank 2 and was constantly stirred to prevent the sulfur-oxidizing bacteria floating on the plastics carrier from sticking. The pH was controlled to 7-8 with sulfuric acid and sodium hydroxide, and the operation was performed under the condition that the volume load of nitrate nitrogen and nitrite nitrogen was 15 kg-N / m ³ · day, but the nitrogen concentration in the treated water was 5 mg. / L or less. Furthermore, the thiosulfuric acid remaining in the treated water was oxidized to sulfate ions by the biological oxidation tank 16. In the biological oxidation tank 16, the dissolved oxygen was maintained at 2 mg / l or more by aeration. With a residence time of 1 hour, thiosulfuric acid was oxidized to sulfate ions, and COD was 20 mg / l or less.
[0044]
【The invention's effect】
According to the present invention, it is possible to prevent a reduction in processing efficiency due to the floating outflow of bacteria, which occurs when processing wastewater containing ammonia nitrogen at a high concentration using autotrophic bacteria, and stable nitrogen removal becomes possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing an apparatus for carrying out a method according to a reference embodiment of the present invention using a membrane separation apparatus.
FIG. 2 is a diagram showing an apparatus for carrying out the method of the present invention using a filtration apparatus.
FIG. 3 is a view showing an apparatus for carrying out the method of the present invention using a filtration part in a denitrification tank.
FIG. 4 is a diagram showing a processing flow using a filtration device in the method of the present invention.
FIG. 5 is a diagram showing a processing flow using a denitrification tank having a filtration part in the method of the present invention.

Claims (5)

In the denitrification method, which uses autotrophic bacteria to reduce nitrite nitrogen and nitrate nitrogen in wastewater to nitrogen gas and remove them from wastewater, denitrification using self-granulated sulfur-oxidizing bacteria as autotrophic bacteria By filtering the treated water in the tank with a filtration device filled with a subsequent filter medium, returning the precipitate of the filtration device to the denitrification tank, and preventing the outflow of the autotrophic bacteria from the denitrification tank A method for removing nitrogen from wastewater, characterized by increasing the concentration of autotrophic bacteria inside a denitrification tank. In the denitrification method of reducing nitrite nitrogen and nitrate nitrogen in wastewater to nitrogen gas using autotrophic bacteria and removing them from wastewater, self-granulated sulfur-oxidizing bacteria are used as the autotrophic bacteria. It is characterized by increasing the concentration of autotrophic bacteria inside the denitrification tank by preventing the floating outflow of vegetative bacteria from the denitrification tank using a filtration unit filled with a filter medium provided in the upper part of the denitrification tank. To remove nitrogen from wastewater.   The method for removing nitrogen from wastewater according to claim 1 or 2, wherein the filter medium is sand, gravel, ceramics, anthracite, or a floating filter medium.   The method for removing nitrogen from wastewater according to claim 1, 2 or 3, wherein a filtration device or a filtration part filled with a filter medium having a diameter of 3 mm or less is used.   The method for removing nitrogen from waste water according to any one of claims 2 to 4, further comprising an underwater stirrer at a lower part of the denitrification tank and / or a lower part of the filtration part.

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