JP2947684B2 - Nitrogen removal equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for removing nitrate nitrogen contained in, for example, raw drinking water and sewage.

[0002]

2. Description of the Related Art In recent years, the concentration of nitrogen oxides in drinking water, especially well water, has increased. For example, the concentration of nitrate nitrogen has often exceeded 10 mg N / liter, which is the standard for drinking. The main cause of such an increase in oxidized nitrogen is mainly that nitrification of a fertilizer applied to agricultural land is nitrified in a natural environment.

[0003] Nitric oxide is known as a methemoglobinemia-causing substance and is also a precursor of N-nitroso compounds, which are powerful mutagenic substances. As described above, nitric oxide is a substance that causes serious health problems in humans, and in particular, needs to be removed from drinking water.

[0004] As a conventional removal technique, an ion exchange method using an anion exchange resin can be mentioned as a typical method. This method is to concentrate and remove oxidized nitrogen in water. This requires a treatment and cannot be said to be a fundamental method for removing nitrogen oxides.

Another removal technique is biological treatment. Examples of the method include a method using heterotrophic bacteria using an organic substance such as ethanol and acetic acid as a hydrogen donor, and a method using autotrophic bacteria using hydrogen gas as a hydrogen donor. These methods convert oxidized nitrogen in water into harmless nitrogen gas by the following chemical reaction formula, and are a fundamental method for removing oxidized nitrogen.

Reaction by heterotrophic bacteria (hydrogen donor: ethanol) 6NO ₃ ⁻ + C ₂ H ₅ OH → 6NO ₂ ⁻ + 2CO ₂ + 3H ₂ O 6NO ₂ ⁻ + C ₂ H ₅ OH → 3N ₂ + 2CO ₂ + 3H ₂ O + 6OH ^- ...

[0007] - autotrophic bacteria by the reaction ^{_{2NO 3 - + 2H 2 → 2NO}} 2 - + 2H 2 O ... 2NO 2 - + 3H 2 → N 2 + 2H 2 O + 2OH - ...

[0008]

However, the biological treatment method also has the following problems. In other words, when trying to almost completely decompose nitrate nitrogen to nitrogen by a biological treatment method, the reaction rate is slower than usual chemical reaction as usual in biological treatment, so the volume load must be kept fairly low. On the other hand, in order to increase the capacity of the apparatus and to apply a high volume load, the amount of microorganisms must be increased, but it is not so easy in practice.

[0009] The reduction reaction (chemical reaction or) from nitrite nitrogen is not a problem if the condition of the microorganisms is good, but the reaction does not proceed when the acclimatization time is insufficient or the reaction conditions fluctuate. Unnecessary accumulation of nitrogen occurs in the treated water, which is not preferable.

The present invention solves the above-mentioned problems in the biological treatment method, and reduces the capacity of the apparatus and supplies safe water suitable for drinking or having no problem even if discharged to rivers. It is an object of the present invention to provide a nitrogen removing device that can always supply.

[0011]

Means for Solving the Problems The present invention has been made to achieve the above-mentioned object. The present invention provides a method for biologically decomposing nitrate nitrogen in water using a microorganism in the presence of a hydrogen donor. A biological means for producing nitrate nitrogen and a chemical means for reducing nitrite nitrogen in water to nitrogen gas using a hydrogenation catalyst in the presence of hydrogen gas, and downstream of the biological means A gist of the present invention is a nitrogen removing device in which the chemical means are arranged and connected.

In the present invention, "the biological decomposition of nitrate nitrogen in water using a microorganism in the presence of a hydrogen donor to actively produce nitrite nitrogen" means that the nitrate nitrogen is substantially converted into water. Instead of completely decomposing to nitrogen gas, the above reaction should be stopped as far as possible at the stage of nitrite nitrogen generation, that is, when using heterotrophic bacteria, the reaction of the above formula, using autotrophic bacteria In this case, it means that the reaction of the above formula is controlled so as to proceed exclusively.

[0013] If the decomposition reaction of nitrate nitrogen can be stopped at the stage of nitrite nitrogen generation, compared to the case where nitrate nitrogen is almost completely decomposed into nitrogen gas by biological means, the use of an apparatus can be improved. The volume loading can be significantly increased, and thus the volume of the biological reactor can be reduced.

If the nitrogen load in the biological means can be increased and the decomposition reaction of nitrate nitrogen can be stopped at the stage of nitrite nitrogen generation, the amount of the hydrogen donor to be supplied can also be represented by the above formula or The chemical equivalent calculated from the formula is sufficient.

On the other hand, nitrite nitrogen generated by the above biological means is rapidly decomposed into nitrogen gas by the catalytic action of the hydrogenation catalyst in the subsequent chemical means. Since this reaction is a chemical reaction using a catalyst and proceeds instantaneously, the apparatus can be made extremely small. Therefore, even if both biological means and chemical means are required, the entire apparatus is smaller than the case where nitrate nitrogen is almost completely decomposed into nitrogen gas by the biological means alone. It is possible to completely decompose and remove undesired nitrite nitrogen by a chemical means using an apparatus.

The biological means employed in the present invention may be any biological means having a structure that enables efficient contact between microorganisms and raw water containing nitrate nitrogen in the presence of a hydrogen donor. So-called fixed-bed reactors, activated carbon, ceramic balls, which are filled with granular materials such as activated carbon and ceramic balls, and carriers such as plastics of various shapes, and adhere microorganisms to the surface of the carriers for treatment. A so-called fluidized-bed type reaction apparatus or the like, in which microorganisms are adhered to the surface of a granular material and processed while being fluidized.

The chemical means employed in the present invention means that a raw water containing nitrite nitrogen and a hydrogenation catalyst are efficiently brought into contact with each other in the presence of hydrogen gas, and the nitrite nitrogen is obtained by the following chemical reaction formula. Is decomposed into nitrogen gas and water by adding hydrogen to the gas. 2NO ₂ ⁻ + 3H ₂ → N ₂ + 2H ₂ O + 2OH ⁻ .. As the catalyst used here, for example, palladium (Pd),
Metals such as rhodium (Rh) and platinum (Pt) can be mentioned, but palladium is preferable from the viewpoint of economical efficiency and reducing power. The contact system may be a batch system or a continuous system.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of a flow showing an embodiment of the present invention. A biological reaction tank (1) has a raw water supply line (2) at a lower part and a biological treatment water line (3) at an upper part. Is communicated. The reaction tank (1) is filled with an activated carbon carrier (5) to which microorganisms composed of heterotrophic denitrifying bacteria have been attached in advance. The reaction tower (7) is a chemical reaction tower arranged and connected downstream of the biological reaction tank (1) via the biological treatment water line (3), and the reaction tower (7) is provided at the bottom thereof with the biological treatment tank (7). The water line (3) communicates with the final treated water line (6) at the top. The reaction tower (7) is filled with a granular palladium catalyst (9).

The raw water containing nitrate nitrogen flows into the reaction tank (1) via the raw water supply line (2). In addition,
A nutrient addition line (4) is connected to the raw water supply line (2), and an organic substance (ethanol, acetic acid, etc.) serving as a hydrogen donor is added to the raw water through the nutrient addition line (4), and if necessary. Nutrient sources such as inorganic salts are added accordingly.

Microorganisms composed of heterotrophic denitrifying bacteria are actively propagated on the surface of the activated carbon carrier (5), and nitrate nitrogen in water is actively promoted by the above-mentioned chemical reaction formula by the action of the microorganisms. The treated water is introduced from the lower part of the reaction tower (7) filled with the subsequent palladium catalyst (9) through the biological treated water line (3). The introduced biologically treated water flows through the reaction tower (7) in an upward flow, and a hydrogen gas supply line communicated with a lower portion of the reaction tower (7) by the action of a palladium catalyst (9) filled in the tower. The hydrogen gas introduced via (8) and the nitrite nitrogen in the biological treatment water react, and are rapidly decomposed into nitrogen gas and water by the above-mentioned chemical reaction formula.

The final treated water from which nitrate nitrogen has been completely removed is taken out through the final treated water line (6). The nitrogen gas generated by the decomposition is discharged outside through a gas discharge line (10) provided at the upper part of the tower (7).

A turbidity separation means using a membrane such as a microfiltration membrane is installed in the middle of the biological treatment water line (3), and suspended substances contained in the biological treatment water in the biological reaction tank (1) are installed. May be removed. Further, an air aeration tank may be provided downstream of the chemical reaction tower (7) to remove hydrogen gas remaining in water or volatile organic substances.

FIG. 2 is an explanatory diagram of a flow showing another example of the embodiment of the present invention. The lower part of the biological reaction tank (1) communicates with a raw water supply line (2) and a hydrogen gas supply line (11), and the upper part communicates with a biological treatment water line (3). The inside of the reaction tank (1) is filled with a fibrous plastic carrier (12) to which microorganisms consisting of autotrophic denitrifying bacteria have been previously adhered. The reaction tank (15) is a chemical reaction tank arranged and connected downstream of the biological reaction tank (1) via a biological treatment water line (3), and the reaction tank (15) is provided at the top thereof with the biological treatment tank (15). The water line (3) and the final treated water line (6) are connected to each other, and a powdery palladium catalyst is suspended in the reaction tank (15).

Raw water containing nitrate nitrogen flows into the reaction tank (1) through a raw water supply line (2), and hydrogen gas serving as a hydrogen donor is supplied through a hydrogen gas supply line (11). You. Note that a nutrient source such as inorganic salts may be added to the raw water as needed.

Thus, the fibrous plastic carrier (12)
Microorganisms consisting of autotrophic denitrifying bacteria are actively breeding on the surface of the water, so the nitrate nitrogen in the water is actively reduced to nitrite nitrogen by the above chemical reaction formula by the action of the microorganisms. Then, the treated water is introduced from the upper part through a biological treated water line (3) into a reaction tank (15) in which a subsequent palladium catalyst (9) is floating.

The introduced biologically treated water is introduced through a hydrogen gas supply line (8) connected to the lower part of the reaction tank (15) by the action of the palladium catalyst (9) in the reaction tank (15). The hydrogen gas reacts with the nitrite nitrogen in the biological treatment water, and is rapidly decomposed into nitrogen gas and water by the above-mentioned chemical reaction formula. At this time, stirring is performed by the stirrer (13) so that the reactant and the catalyst come into efficient contact with each other.

The final treated water from which nitrate nitrogen has been completely removed is taken out through a final treated water line (6). Further, the nitrogen gas generated by the decomposition is discharged outside through a gas discharge line (10) provided at the upper part of the tank (15). In addition, (14) is a baffle plate for preventing palladium catalyst particles from flowing out into treated water.

Further, a membrane such as a microfiltration membrane is installed at the subsequent stage of the chemical reaction tank (15) so that a part of the catalyst flowing out together with the final treated water is captured and returned to the reaction tank (15). You may.

[0030]

According to the present invention, in biological means,
By increasing the volumetric load, or
The nitrate nitrogen contained in the raw water is actively reduced to nitrite nitrogen by biological means by limiting the supply amount, and nitrite nitrogen generated by chemical means installed at the subsequent stage Can be rapidly decomposed and removed, so that the device capacity can be reduced and the nitrate state can be reduced as compared with the case where nitrate nitrogen in water is almost completely decomposed into nitrogen gas by biological means alone. Water suitable for drinking, which has a low nitrogen concentration and does not detect oxidized nitrogen, can be obtained.

[0031]

Next, an embodiment of the present invention will be described below.

(Example 1): FIG. 1 A reaction tank (1) having a capacity of 1 liter was filled with an activated carbon carrier (5) on which microorganisms composed of heterotrophic denitrifying bacteria had previously grown. Reagent K in tap water as simulated raw water
The NO _3, so that the nitrate nitrogen concentration in the water becomes 20MgN / liter, also with KH ₂ PO ₄ concentration of phosphorus in water 0.2mg
What was added so that it might become P / liter was used. The amount of ethanol as a hydrogen donor was limited to 1.2 times the amount required to reduce the inflowing nitrate nitrogen to nitrite nitrogen, that is, 13 mg / liter.

A granular Pd—Al ₂ O ₃ catalyst (Pd content: 5 mm) having a diameter of about 1 mm was placed in a reaction column (7) having a capacity of 20 ml.
%) Was charged. The amount of hydrogen gas supplied to the reaction tower (7) is an amount necessary for reducing nitrate nitrogen to nitrogen gas with respect to the amount of nitrogen when nitrate nitrogen is completely reduced to nitrite nitrogen in the reaction tank (1). 3 times as large as Further, carbon dioxide gas was supplied to make the inside of the tank near neutral.

First, after the microorganisms were sufficiently acclimated, the operation was started at a nitrogen load (1 m ^{3 in} the reaction tank, the amount of nitrate nitrogen in terms of N per day) of 0.1 kgN / m ³ / day.

Thereafter, the load was gradually increased, and after 4 weeks, the nitrogen load was adjusted to 4.5 kgN / m ³ / day. The treatment performance at this time was as follows: the biologically treated water had an average nitrate nitrogen removal rate of 90%, the average nitrite nitrogen concentration was 18 mg / liter, and the removed nitrate nitrogen was decomposed to almost 100% nitrite nitrogen. I was However, nitrite nitrogen was not detected in the final treated water obtained by treating this treated biological water with the reaction tower (7).

(Example 2): FIG. 2 In a biological reaction tank (1) having a capacity of 1 liter, a fibrous plastic carrier (12) on which microorganisms composed of autotrophic denitrifying bacteria were preliminarily grown was placed. Filled. KNO ₃ 20mgN / liter, KH ₂ PO ₄ 0.2mg in tap water as simulated raw water
What was added so that it might become P / liter was used. The amount of hydrogen gas as the hydrogen donor was set to be three times the amount required to reduce the inflowing nitrate nitrogen to nitrogen gas.

A powdery Pd-Al ₂ O ₃ catalyst having a diameter of about 150 μm (P
(d content: 5%) was stirred uniformly with a magnetic stirrer. The amount of hydrogen gas supplied to the reaction tank (15) was sufficient if the amount of hydrogen gas dissolved in water in the reaction tank (1) was sufficient, but was supplied as needed.

First, after the microorganisms were sufficiently acclimated, the operation was started with a nitrogen load of 1 kgN / m ³ / day. One week after the start, the average nitrate nitrogen removal rate in biological treated water is 95% or more, and the amount of nitrite nitrogen is 1 mg / liter or less. The nitrate nitrogen in raw water is almost completely decomposed into nitrogen gas by biological treatment alone. It was done. At this time, nitrite nitrogen was not detected in the final treated water obtained from the final treated water line (6).

Thereafter, the load was increased and the processing performance was examined when the nitrogen load was set to 2, 3, 4, and 5 kgN / m ³ / day, respectively. The results are shown in Table 1 below. In any of the above treatments, nitrite nitrogen was not detected in the final treated water.

[0040]

[Table 1]

(Example 3): FIG. 2 In a biological reaction tank (1) having a capacity of 1 liter, a fibrous plastic carrier (12) on which microorganisms composed of autotrophic denitrifying bacteria were preliminarily grown was placed. Filled. As simulated raw water, tap water was used in which KNO ₃ was added to a concentration of 20 mgN / liter, and KH ₂ PO ₄ was further added to a concentration of 0.2 mgP / liter. The amount of hydrogen gas used as the hydrogen donor was limited to 1.2 times the amount required to reduce the inflowing nitrate nitrogen to nitrite nitrogen. Further, carbon dioxide gas was supplied to make the inside of the tank near neutral.

In the latter stage of the above-mentioned reaction tank, a powdery Pd-A having a diameter of about 150 μm was placed in a chemical reaction tank (15) having a capacity of 500 ml.
5 g of l ₂ O ₃ catalyst (Pd content: 5%) was charged, and the mixture was stirred with a magnetic stirrer so as to be uniform. The amount of hydrogen gas supplied to the reaction tank (15) is the amount required to reduce the amount of nitrogen gas to nitrogen gas with respect to the amount of nitrogen when nitrate nitrogen was completely reduced to nitrite nitrogen in the reaction tank (1). It was three times.

First, after the microorganisms were sufficiently acclimated, the operation was started with a nitrogen load of 0.1 kgN / m ³ / day. Thereafter, the load was gradually increased, and after 6 weeks, the nitrogen load was 4.5 kgN / m ³ / day. At this time, the treatment performance is
Nitrate nitrogen removal rate average 90%, nitrite nitrogen concentration average 1
Although it was 8 mg / liter, nitrite nitrogen was not detected in the final treated water.

Incidentally, hydrogen gas is supplied in an amount sufficient to reduce nitrate nitrogen in raw water to N ₂ gas, and nitrate nitrogen in raw water is almost completely converted into nitrogen gas by biological means alone. Then, as described in the second embodiment, the processing performance is:
Nitrogen load 2 kgN / m ³ / day or less 95% removal of nitrate nitrogen
As described above, the nitrite nitrogen production concentration is relatively low, average 3 mg / liter, but when the nitrogen load exceeds 2 kgN / m ³ / day, the amount of nitrite nitrogen production increases remarkably. Cannot be used for drinking.

As is clear from the above Examples 2 and 3, the nitrogen load was at most 2 k with the biological means alone.
The limit is about gN / m ³ / day, but by combining chemical means after biological means, there is no restriction on nitrogen load, which is advantageous for industrial implementation.

The upper limit of the nitrogen load when using an autotrophic bacterium is not particularly limited. However, from the viewpoint of the decomposition rate of nitrate nitrogen to nitrite nitrogen and the operation efficiency of the apparatus, the nitrogen load is 3%. It is preferably in the range of kgN / m ³ / day to 10 kgN / m ³ / day.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a denitrification apparatus used in an embodiment of the present invention.

FIG. 2 is a schematic explanatory view of a denitrification apparatus used in Examples 2 and 3 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Biological reaction tank 2 Raw water supply line 3 Biological treatment water line 4 Nutrient addition line 5 Activated carbon carrier 6 Final treatment water line 7 Chemical reaction tower 8 Hydrogen gas supply line 9 Palladium catalyst 10 Gas discharge line 11 Hydrogen gas supply line 12 fibrous plastic carrier 13 stirrer 14 baffle 15 chemical reactor

Continuation of the front page (56) References JP-A-5-317881 (JP, A) JP-A-1-2692992 (JP, A) JP-A-62-197196 (JP, A) JP-A-60-54792 (JP) JP-A-4-94799 (JP, A) JP-A-6-154786 (JP, A) JP-B 64-6840 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB Name) C02F 3/34 101 B01J 23/44 C02F 1/70 CDK

Claims (5)

(57) [Claims] 1. A biological means for biologically decomposing nitrate nitrogen in water using a microorganism in the presence of a hydrogen donor and actively producing nitrite nitrogen, and a nitrite form in water. A chemical means for reducing nitrogen to nitrogen gas using a hydrogenation catalyst in the presence of hydrogen gas, wherein the chemical means is arranged and connected downstream of the biological means. . 2. The biological means uses hydrogen gas as a hydrogen donor, and the volume load (the amount of nitrate nitrogen in terms of N per day in a reaction tank of 1 m ³ ) is set to 3 kgN / m ³ / day or more. The nitrogen removing device according to claim 1. 3. The method according to claim 1, wherein the biological means uses hydrogen gas as a hydrogen donor and sets the amount of the hydrogen gas to a chemical equivalent for reducing nitrate nitrogen to nitrite nitrogen. Nitrogen removal equipment. 4. The nitrogen removing apparatus according to claim 1, wherein the biological means uses an organic substance as a hydrogen donor, and the amount of the organic substance is set to a chemical equivalent for reducing nitrate nitrogen to nitrite nitrogen. 5. The nitrogen removing device according to claim 1, wherein the hydrogenation catalyst used for the chemical means is a palladium catalyst.