JPH11128958A - Water denitrification treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus which can carry out denitrification at high efficiency while heightening the utilization ratio of supplied hydrogen gas at the time when water containing nitric acid nitrogen is treated by a biological denitrification method or a chemical denitrification method by supplying hydrogen gas as hydrogen donor. SOLUTION: An electrolytic tank 3 to continuously supply hydrogen gas in the equivalent amount necessary to decompose nitric acid and/or nitrous acid-nitrogen in water into nitrogen gas is installed in a denitrification tank 1, a gas discharge pipe 7 to discharge nitrogen-containing gas generated in the tank 1 to the outside and a gas circulation pipe to circulate a mixed gas of an upper part of the denitrification tank 1 to the bottom part are also installed in the denitrification tank 1 and, while the hydrogen gas concentration in the mixed gas being measured by a hydrogen monitor 14, the supply amount of hydrogen gas is increased or decreased by a hydrogen gas supply control system 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
Alternatively, the present invention relates to a denitrification treatment apparatus for biologically and / or chemically treating water containing nitrite nitrogen using hydrogen gas.

[0002]

2. Description of the Related Art Wastewater containing nitrate nitrogen includes nitrate washing wastewater discharged from metal surface treatment and high-concentration ammonia wastewater from a power plant. Also, nitrate contamination of groundwater has been a problem for several years, and removal of nitrate nitrogen or nitrite nitrogen has become a serious problem at water treatment plants that take in contaminated well water. Nitrate nitrogen or nitrite nitrogen in tap water is both a causative agent of methemoglobinemia and a precursor of carcinogenic nitrosamines. Nearly, raw water with nitrate nitrogen of 5ppm or more is taken.

[0003] As a method of denitrifying water containing nitrate nitrogen and / or nitrite nitrogen, a biological denitrification method, an ion exchange method, a reverse osmosis membrane method and the like are conventionally known. However, in the conventional biological denitrification method, generation of sludge, difficulty in controlling the quality of treated water becomes a problem, and when the concentration of organic matter in wastewater is low, acetic acid or methanol such as hydrogen donor is used as a hydrogen donor. Organic matter is added to raw water for treatment. To completely remove nitrate and nitrite nitrogen, it is necessary to supply an excess of organic matter two to three times the reaction equivalent required for nitrogen removal. Organic matter remains in the effluent from the denitrification tank. Therefore, a method is employed in which a re-aeration tank is provided after the denitrification tank to treat residual organic matter.

In addition, the ion exchange method has a limitation in the exchange capacity of a resin used, and it is necessary to regenerate the resin at regular time intervals, and simultaneously remove ions other than nitrate nitrogen contained in water. It is not always suitable for producing tap water. On the other hand, in the reverse osmosis membrane method, since there is no regeneration operation, there is no problem in treating the regenerated medicine, but the treatment of the concentrated liquid concentrated in the reverse osmosis membrane becomes a new problem. Since the concentrated liquid contains a high concentration of nitrate nitrogen and the like, it is necessary to separately treat the concentrated liquid, and the concentrated liquid having a water amount close to 20 to 30% of the raw water applied to the reverse osmosis device is discharged. As described above, although a number of nitrate nitrogen removal methods for drinking water have been studied, there are still many problems to be solved and a large increase in treatment cost.

[0005] Further, in order to remove nitrate nitrogen and / or nitrite nitrogen, there is a method other than the above-mentioned method, in which reduction is performed using hydrogen gas. This method is represented by the following equation (1) or (2). ^{_{2NO 3 - + 5H 2 → N}} 2 + 4H 2 O + 2OH - ··· (1) 2NO 2 - + 3H 2 → N 2 + 2H 2 O + 2OH - ··· (2)

As a method for reducing nitrate and / or nitrite nitrogen to nitrogen gas with hydrogen gas, a method utilizing the denitrification ability of a hydrogen oxidizing bacterium using hydrogen gas as a hydrogen donor,
There is a method using a hydrogenation catalyst such as t or Pd alloy.
The former is a biological treatment method utilizing the nitrate respiration ability of autotrophic bacteria, and is proposed in Japanese Patent Application Laid-Open No. 8-39095. The latter is a physicochemical catalytic reduction method, which is disclosed in JP-A-6-154786 and JP-A-7-3.
No. 28651 discloses this. However, such a reactor using hydrogen gas supplies pure hydrogen gas, and the unused hydrogen gas is diluted and evacuated as it is.
It was only 0%. Hydrogen gas is a flammable gas, and there is a high risk of explosion at a concentration of tens of percent. Therefore, exhausting a large amount of high-concentration hydrogen gas from the reactor is not preferable in terms of safety.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and provides a biological denitrification method in which hydrogen gas is supplied as a hydrogen donor, or reduction by hydrogen gas in the presence of a hydrogenation catalyst. It is an object of the present invention to provide a device capable of efficiently denitrifying by increasing the utilization rate of a supplied hydrogen gas when treating nitrate- and / or nitrite-containing water by a chemical denitrification method.

[0008]

According to the present invention, hydrogen gas required for denitrification is continuously supplied into a denitrification tank, and a hydrogen mixed gas in the denitrification tank is circulated to the bottom of the denitrification tank. It has been completed based on the knowledge that the problem can be solved.

That is, the water denitrification treatment apparatus of the present invention comprises:
In a denitrification treatment apparatus for water containing nitrate nitrogen and / or nitrite nitrogen, a denitrification tank continuously feeds hydrogen gas necessary for decomposing nitrate and / or nitrite nitrogen in water into nitrogen gas. A hydrogen gas supply means for supplying, a gas exhaust pipe for exhausting a nitrogen-containing gas generated in the tank to the outside, and a gas circulation pipe for circulating a mixed gas at the top of the denitrification tank to the bottom are provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The denitrification treatment apparatus of the present invention performs nitric acid treatment by continuously supplying hydrogen gas containing nitrate nitrogen and / or nitrite nitrogen to a denitrification tank with hydrogen gas. Nitrogen and / or nitrite nitrogen are decomposed into nitrogen gas and removed. Hereinafter, for the sake of simplicity, the description will be made simply as water containing nitrate nitrogen.

In the denitrification treatment apparatus of the present invention, the denitrification tank is a biological denitrification tank filled with a contact material to which denitrifying bacteria are attached, or a hydrogenation catalyst such as a Cu / Pd catalyst or a Cu / Pd catalyst.
It may be a chemical denitrification tank filled with a Pt catalyst, a Cu / Rh catalyst, or the like. When the concentration of nitrate nitrogen in the target water to be treated is high (50 mg / L or more), the treatment may end in an insufficient state due to a rise in pH in the biological denitrification tank alone. In this case, it is preferable to connect a chemical denitrification tank after the biological denitrification tank.

The hydrogen gas supply means connected to the bottom of the denitrification tank is not particularly limited as long as it can continuously supply hydrogen gas, and may be a hydrogen gas cylinder or a water electrolysis apparatus. The hydrogen gas generated from the decomposition device may be temporarily stored in a pressure-resistant container, and supplied from the pressure-resistant container according to the required amount of the hydrogen gas. The electrolyzer is preferably a diaphragm electrolyzer. The hydrogen gas supplied by the denitrification reaction is consumed, and 1/5 the amount of nitrogen gas is generated. The gas phase above the denitrification tank is a hydrogen-containing mixed gas. In the present invention, in order to improve the utilization efficiency of the continuously supplied hydrogen gas, a configuration in which the mixed gas in the upper part of the denitrification tank is supplied to the lower part of the tank via a gas circulation pipe (using a gas blower or an ejector) to circulate the gas. And

Further, in the present invention, although the hydrogen gas is supplied continuously, it is preferable to automatically increase or decrease the supply amount according to the hydrogen gas concentration in the mixed gas in the upper part of the denitrification tank. Therefore, a hydrogen monitor is installed to monitor the concentration of hydrogen gas in the gas mixture above the denitrification tank (gas phase). If the hydrogen gas concentration exceeds the set value, the supply amount of hydrogen gas is reduced, and the hydrogen gas concentration is set It is preferable to provide a hydrogen gas supply control system that increases the hydrogen gas supply amount when the value becomes lower than the value. As the installation location of the hydrogen monitor, for example,
The upper part of the denitrification tank (gas phase part), near the inlet of the gas discharge pipe, near the inlet of the gas circulation pipe, and the like. According to the present invention, the gas mixture in the gas phase is circulated, and the supply rate of the hydrogen gas is automatically increased or decreased in accordance with the hydrogen gas concentration in the gas mixture in the gas phase. The denitrification can be performed efficiently.

Further, the mixed gas in the upper part (gas phase part) of the denitrification tank is continuously exhausted. Hydrogen gas is a flammable gas,
Since there is a danger of explosion, to prevent the outside air from entering the denitrification tank and contacting the hydrogen gas and the oxygen of the oxidizing gas in the denitrification tank, use a gas discharge pipe, such as a check valve or water. It is preferable to provide an outside air blocking device such as a sealed tank. It is preferable from the viewpoint of safety that the mixed gas discharged through the outside air cutoff device is burned by the hydrogen gas combustion means and then released to the outside air. The combustion of the hydrogen gas is preferably performed at a temperature of 100 ° C. or lower using an alumina carrier containing 0.1 to 0.5% by volume of platinum or palladium as a catalyst. At that time, if the concentration of hydrogen gas is high, there is a danger of explosion,
Since the temperature rises to about 100 ° C. at a hydrogen gas concentration of 1% due to reaction heat, the hydrogen gas concentration is reduced to 1% by a diluting means.
It is preferable to burn after diluting to the following. Further, oxygen gas generated at the anode of the electrolytic cell may be supplied as a combustion assisting gas for hydrogen gas combustion.

The effluent from the denitrification tank is allowed to flow into an aeration tank to recover from an anaerobic atmosphere to an aerobic atmosphere, and to decompose and remove organic substances that may be present in some cases, making it suitable for drinking water. Blow air into the aeration tank,
Alternatively, oxygen generated from a diaphragm electrolytic cell as hydrogen gas supply means can be blown alone or together with air.

[0016]

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a system diagram of a denitrification treatment apparatus showing a first embodiment of the present invention. The denitrification treatment apparatus shown in FIG. 1 mainly includes a denitrification tank 1, an aeration tank 2, and a water electrolysis tank 3. The denitrification tank 1 is filled with a filler to which denitrifying bacteria have adhered or a filler made of a hydrogenation catalyst, and the liquid to be treated containing nitrate nitrogen flows into the denitrification tank 1 by the raw water supply pump 4. Hydrogen gas generated by electrolysis of water in the electrolytic cell 3 is introduced from the bottom of the denitrification tank 1 through a hydrogen gas supply pipe 8. When a diaphragm electrolytic cell is used as the hydrogen gas supply means, oxygen gas is generated from the anode at the same time as hydrogen gas is generated from the cathode. This oxygen gas can be supplied from the oxygen gas supply pipe 9 to the hydrogen gas combustion means 13 as an auxiliary combustion gas.

Further, a hydrogen mixed gas is sent to the bottom of the denitrification tank 1 from a gas circulation pipe 6 connected to a gas phase portion of the denitrification tank 1 by a gas circulation device 5 such as a gas blower or an ejector. Gas is provided for utilization. In the denitrification tank 1, the above formula (1) using hydrogen gas as a hydrogen donor
The denitrification reaction shown in (2) proceeds, the nitrate nitrogen is decomposed into nitrogen gas, and the effluent from the denitrification tank is introduced into the aeration tank 2, where the anaerobic atmosphere is restored to the aerobic atmosphere, and the beverage is recovered. It is suitable for water and can decompose and remove organic substances contained in the effluent of the denitrification tank.

In the denitrification tank 1, nitrogen gas is generated and hydrogen gas is consumed as the nitrate nitrogen is decomposed. An amount of hydrogen gas consumed relative to the planned nitrogen removal amount is supplied from the electrolytic cell 3 as the hydrogen gas supply means via the hydrogen gas supply pipe 8,
A mixed gas of nitrogen and unreacted hydrogen, which is one fifth of the consumed hydrogen gas, is continuously exhausted from the gas discharge pipe 7. A hydrogen monitor 14 for monitoring the concentration of hydrogen gas in the mixed gas in the upper part (gas phase) of the denitrification tank 1 is provided near the inlet of the gas discharge pipe 7. A hydrogen gas supply control system 15 for reducing the supply amount and conversely increasing the hydrogen gas supply amount when the hydrogen gas concentration becomes lower than the set value is connected. As a result, unnecessary supply and exhaust of hydrogen gas can be prevented, and conversely, a decrease in denitrification performance due to insufficient hydrogen can be prevented.

Since hydrogen gas is a flammable gas and has a risk of explosion, the gas exhaust pipe 7 is provided with an outside air shutoff device 12 to prevent air from entering the denitrification tank 1. When the outside air shutoff device 12 is a water sealing tank, there is an advantage that the pressure in the denitrification tank can be easily maintained at a constant value. The mixed gas discharged from the outside air shut-off device 12 is released into the atmosphere after being burned by the hydrogen gas combustion means 13. At this time, since the combustion of the hydrogen gas is performed at a low temperature of 100 ° C. or less, the dilution means 16 Reduce the hydrogen gas concentration in the mixed gas to 1
% And then sent to the hydrogen gas combustion means 13.
The oxygen gas generated from the anode section of the electrolytic cell 3 is sent to the hydrogen gas combustion means 13 through the oxygen gas supply pipe 9 to burn the hydrogen gas, thereby directly discharging the combustible gas to the atmosphere. Can be prevented.

FIG. 2 is a system diagram of a denitrification treatment apparatus showing a second embodiment of the present invention. The denitrification treatment apparatus shown in FIG. 2 stores hydrogen gas generated in the electrolytic cell 3 in a hydrogen gas storage tank 17, and connects an adjusting valve and a hydrogen monitor 14 added to this tank to the hydrogen gas supply control system 15. The first embodiment differs from the first embodiment in that a connection is made and the supply amount of hydrogen gas is controlled.

Next, the influence of the hydrogen concentration on the denitrification rate when the denitrification treatment is performed using the apparatus of the present invention in the biological denitrification method will be described. FIG. 3 shows nitrate nitrogen 10
3000 mg of hydrogen oxidizing bacteria as SS concentration at 0 mg / L
It is a hydrogen concentration-denitrification rate relationship diagram showing the result of a batch test in which g / L was inoculated and the denitrification rate was measured by changing the hydrogen gas concentration. As can be seen from FIG. 3, when the gas circulation rate was set to 60 m / h as the superficial velocity, the denitrification rate was 20 mg / h.
The hydrogen concentration for obtaining L · h was about 10%. When the gas circulation rate is changed, the hydrogen concentration required to obtain the same denitrification rate is about 30 at a gas superficial velocity of 10 m / h.
%, About 5% at 170 m / h, different results were obtained. As described above, the rate of dissolution of hydrogen that is rate-limiting for the denitrification reaction depends on the hydrogen concentration and the gas circulation amount. Therefore, it is preferable that the optimum hydrogen concentration and gas circulation amount for the given nitrate nitrogen load be obtained in advance together with the device characteristics.

In the denitrification treatment apparatus shown in FIG. 1, a denitrification tank was filled with 6 liters of a contact material to which hydrogen oxidizing bacteria had adhered, and an effective liquid volume of 12 mg / L for nitrate nitrogen was used as ground water. Liter, nitrate nitrogen load 20 mg / Lh per packed bed volume, liquid flow rate 0.13 L / min,
Recirculating gas superficial velocity 60m / h, exhaust concentration of hydrogen gas 10
FIG. 4 shows the results of measuring the nitrate nitrogen in the raw water and the treated water by continuously passing water as the% setting condition. As can be seen from FIG. 4, the nitrate nitrogen contained in the groundwater could be removed to 1 mg / L or less (removal rate 95% or more) by this continuous treatment. With this denitrification treatment apparatus, the hydrogen gas concentration in the gas mixture in the gas phase is stabilized at 10 to 12%, and the amount of gas discharged to the gas discharge pipe is also small. there were.

Further, after the elapse of 30 days, nitrate nitrogen 5
mg / L groundwater, and after setting the hydrogen gas concentration in the mixed gas of the gas phase to 3%, the same treatment was performed.
The good removal performance shown in FIG. 4 was obtained. Therefore, by setting the concentration of hydrogen gas in the mixed gas in the gas phase to a constant value according to the amount of nitrate nitrogen in the water to be treated flowing into the biological denitrification tank, optimization of the hydrogen utilization rate and treatment performance Was possible. In addition, in the same denitrification tank configuration as above, instead of the contact material to which the denitrifying bacteria adhered, a hydrogenation catalyst such as Pt or Pd was filled, and the same test was performed.
A removal rate of nitrate nitrogen of 80% or more was obtained.

[0024]

By using the denitrification treatment apparatus of the present invention, hydrogen gas is continuously supplied as a hydrogen donor necessary for the denitrification reaction, and the nitrate nitrogen in the wastewater can be removed with high hydrogen gas utilization efficiency. It can be removed efficiently. Further, the hydrogen gas in the discharged mixed gas can be burned and released into the atmosphere as a safe gas free from explosion. Furthermore, by automatically controlling the concentration of hydrogen gas in the gas mixture in the gas phase of the denitrification tank to a constant value in accordance with the concentration of nitrate nitrogen in the water to be treated, the hydrogen usage efficiency and the processing performance are automatically optimized. Can be achieved. When the concentration of nitrate nitrogen in the target water to be treated is high (50 mg / L or more),
Since the pH of the biological denitrification tank alone increases greatly and the treatment may end in an insufficient state, by connecting the chemical denitrification tank to the latter stage of the biological denitrification tank, sufficient nitrogen Elimination can be achieved.

[Brief description of the drawings]

FIG. 1 is a system diagram of a denitrification treatment apparatus showing one embodiment of the present invention.

FIG. 2 is a system diagram of a denitrification apparatus showing another embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a hydrogen concentration and a denitrification rate, showing a result of a batch test in which a denitrification treatment is performed at a constant gas circulation amount.

FIG. 4 is a graph showing the daily change of the nitrate nitrogen concentration of raw water and treated water showing the results of a continuous test in the biological denitrification apparatus of the present invention.

[Description of Signs] 1 Denitrification tank 2 Aeration tank 3 Electrolysis tank 4 Raw water supply pump 5 Gas circulation device 6 Gas circulation pipe 7 Gas discharge pipe 8 Hydrogen gas supply pipe 9 Oxygen gas supply pipe 10 Filling material 11 Filling material 12 Outside air cutoff device 13 Hydrogen gas combustion means 14 Hydrogen monitor 15 Hydrogen gas supply control system 16 Dilution means 17 Hydrogen gas storage tank

Claims (6)

[Claims] In a denitrification treatment apparatus for water containing nitrate nitrogen and / or nitrite nitrogen, a denitrification tank is required to decompose nitrate and / or nitrite nitrogen in water into nitrogen gas. Hydrogen gas supply means for continuously supplying a hydrogen gas having a high reaction equivalent, a gas discharge pipe for exhausting nitrogen-containing gas generated in the tank to the outside, and a gas circulation pipe for circulating the mixed gas at the top of the denitrification tank to the bottom. A denitrification treatment device for water, which is provided. 2. A hydrogen monitor for monitoring the concentration of hydrogen gas in the mixed gas in the upper part of the denitrification tank is provided. When the concentration of hydrogen gas exceeds a set value, the supply amount of hydrogen gas is reduced. 2. The water denitrification treatment apparatus according to claim 1, further comprising a hydrogen gas supply control system for increasing the supply amount of hydrogen gas when the hydrogen gas becomes low. 3. The water denitrification treatment device according to claim 1, wherein an outside air shutoff device for preventing air from entering the denitrification tank is provided in the gas discharge pipe. 4. The denitrification tank is a biological denitrification tank using a denitrification bacterium or a chemical denitrification tank using a hydrogenation catalyst.
The water denitrification treatment apparatus according to claim 1, wherein the biological denitrification tank and the chemical denitrification tank are connected. 5. The water denitrification treatment apparatus according to claim 3, wherein a dilution means and a hydrogen gas combustion means are provided after the outside air cutoff apparatus provided in the gas discharge pipe. 6. A diaphragm electrolytic cell is used as hydrogen gas supply means, and oxygen gas generated at the anode of the electrolytic cell is supplied as auxiliary gas for hydrogen gas combustion means, or connected to the latter stage of the denitrification tank. The water denitrification treatment device according to claim 1, which is supplied to an aeration tank.