JP2000061493A - Denitrification equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent reduction in denitrification performance due to the contamination of a denitrification vessel by oxygen and also any risk of explosion from being caused in the equipment. SOLUTION: In this equipment, oxygen that is originally dissolved in wastewater itself to be treated and carried into a denitrification vessel 12, or oxygen that is dissolved into the wastewater through air entrainment in wastewater due to cavitation or the like, in a raw water pump 18 and carried into a denitrification vessel 12, is purged from the wastewater to be treated, with gaseous hydrogen supplied to the denitrification vessel 12 and then, together with the gaseous hydrogen supplied to the vessel 12 and gaseous nitrogen generated by denitrification reaction, is recycled through a recycle gas line 22. When the oxygen concn. in the recycle gas reaches >1%, the recycle gas is allowed to flow through a bypass line 44 to absorb oxygen with an oxygen absorber.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a denitrification device,
In particular, the present invention relates to a denitrification device for denitrifying water to be treated having a low organic matter concentration and containing nitrate nitrogen or nitrite nitrogen using hydrogen gas.

[0002]

2. Description of the Related Art A conventional denitrification apparatus for circulating hydrogen gas in a denitrification tank to perform biological or chemical denitrification has a structure in which the denitrification tank itself has a hermeticity such as a hermetic type or a gas holder type. The denitrification tank is filled with a contact material holding denitrifying bacteria or a hydrogenation catalyst. Then, hydrogen gas is blown from the lower part of the denitrification tank, and the gas above the tank is circulated to the lower part of the tank. The following formula is a reaction formula of denitrification reaction using hydrogen gas.

2NO ₃ ⁻ + 5H ₂ → N ₂ + 4H ₂ O + 2OH ⁻ As can be seen from the above formula, this reaction is carried out with nitrate nitrogen 2mo
Since 5 mol of hydrogen gas is consumed for 1 l, the pressure inside the tank is reduced in the case of the closed type denitrification tank, and the holder portion is lowered in the case of the gas holder type denitrification tank. And
In the case of a closed type denitrification tank, when the pressure drops to the specified lower limit value, in the case of a gas holder type denitrification tank, when the holder part has dropped to the specified lower limit value, or when the hydrogen concentration in the denitrification tank drops. When it is detected, supply of hydrogen gas to the denitrification tank is started. Similarly, the supply of hydrogen gas is stopped when the pressure rises to a predetermined upper limit value, when the holder portion rises to a predetermined upper limit value, or when an increase in the hydrogen concentration in the denitrification tank is detected.

A denitrification apparatus using hydrogen gas decomposes nitrate nitrogen or nitrite nitrogen in the water to be treated into nitrogen gas by repeating such an intermittent or continuous supply step of hydrogen gas. As described above, in the denitrification device using hydrogen gas, since the denitrification tank is a closed type or a gas holder type and has a hermeticity as described above, conventionally, it is considered that air is hardly mixed into the denitrification tank. Came.

[0005]

However, when the water to be treated is supplied to the denitrification tank, fine bubbles are generated in the water to be treated due to sudden cavitation of the raw water pump, etc.
Oxygen is mixed in the denitrification tank due to the bubbles. Mixing oxygen into the denitrification tank has a drawback that the denitrification performance is lowered when biologically performing denitrification treatment. In addition, since flammable hydrogen gas supplied to the denitrification tank is often used at a concentration within the range of explosion, there is a problem that the mixture of the combustion-supporting oxygen gas causes a risk of explosion.

In addition to a sudden factor such as cavitation of a raw water pump, in the case of a wastewater treatment device such as a modified activated sludge circulation method in which a denitrification device is combined with a nitrification device, nitrification of a nitrification tank for aeration is performed. Since the liquid is circulated in the denitrification tank, oxygen derived from aeration is continuously mixed in the water to be treated in the denitrification tank. Against this background,
The conventional denitrification device does not have effective measures for removing dissolved oxygen in the water to be treated.

The present invention has been made in view of the above circumstances. Since the dissolved oxygen mixed in the water to be treated can be reduced quickly and efficiently, the denitrification performance is lowered and the risk of explosion is increased. An object of the present invention is to provide a denitrification method and device capable of surely preventing the above.

[0008]

In order to achieve the above-mentioned object, the present invention supplies hydrogen gas into the water to be treated in a denitrifying tank having a hermeticity so that the nitrogen or nitrite property in the water to be treated is In a denitrification device equipped with a gas circulation line for biologically or chemically denitrifying nitrogen, connecting the tank upper part and the tank lower part of the denitrification tank and circulating the gas accumulated in the tank upper part to the tank lower part An oxygen absorption device is provided in the gas circulation line.

According to the present invention, oxygen dissolved in the water to be treated and brought into the denitrification tank and oxygen dissolved in the water to be treated and brought into the denitrification tank due to cavitation of the raw water pump are desorbed. The hydrogen gas supplied into the nitrification tank is expelled from the water to be treated and circulates in the circulation line together with the hydrogen gas supplied into the denitrification tank and the nitrogen gas generated by the denitrification reaction. Oxygen of the gas circulating in the circulation line is quickly and efficiently absorbed by the oxygen absorber. As a result, the oxygen concentration in the water to be treated can be reduced, so that the denitrification performance will not be reduced in the biological denitrification reaction, and in the biological and chemical denitrification reactions, oxygen and hydrogen It can also prevent an explosion accident.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the denitrification apparatus of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a configuration diagram of a denitrification device 10 according to the present invention, which is a denitrification system for biologically denitrifying nitrate nitrogen and nitrite nitrogen in raw water, which is water to be treated, using hydrogen gas. It is an example of an apparatus.

As shown in FIG. 1, the denitrifying tank 12 is filled with a contact material 14 while holding denitrifying bacteria, and the water to be treated is supplied to a lower portion of the denitrifying tank 12 by a raw water pump 18 through a raw water pipe 16. Flows into the denitrification tank 12. Further, a diffusing member 20 for diffusing hydrogen gas is arranged at a lower portion in the denitrification tank 12, and the diffusing member 20 is provided with a denitrification tank 1 via a gas circulation pipe 22.
2 is connected to the head space portion 24 in the upper part of the inside. The gas circulation pipe 22 is provided with a blower device 26 for circulating gas, and a hydrogen gas supply pipe 28 is connected to the gas circulation pipe 22 on the suction side of the blower device 26. As a result, the hydrogen gas is supplied from the hydrogen gas supply pipe 28 to the gas circulation pipe 22 and mixed with the flow of the circulation gas (gas such as hydrogen gas, nitrogen gas, oxygen gas accumulated in the head space portion) flowing through the gas circulation pipe 22. Is sent to the air diffuser 20 and is diffused from the air diffuser 20 toward the contact member 14.

Further, the head space portion 24 of the denitrification tank 12
A pressure detector 30 for communicating with the head space portion 24 for detecting a pressure change in the head space portion 24 is provided, and the gas circulation pipe 2
2 is provided with a hydrogen gas detector 32 for detecting the concentration of hydrogen gas in the circulating gas. These detectors 30 and 32 are connected to a controller 34 via a signal cable, and the controller 34 is connected to a hydrogen gas automatic supply valve 36 provided in the hydrogen gas supply pipe 28 via a signal cable. The controller 34 uses the hydrogen gas automatic supply valve 36 based on the detection results of the pressure detector 30 and the hydrogen gas detector 32.
Open or close, or adjust the opening and closing amount. Further, a gas discharge pipe 38 is provided in communication with the head space portion 24 of the denitrification tank 12, and the gas discharge pipe 38 is provided with a gas discharge automatic valve 40. The automatic gas discharge valve 40 is connected to the controller 34 via a signal cable. The controller 34 opens and closes the automatic gas discharge valve based on the detection results of the pressure detector 30 and the hydrogen gas detector 32. Incidentally, only one of the pressure detector 30 and the hydrogen gas detector 32 may be used.

Then, in the denitrification tank 12, the denitrifying bacteria retained on the contact material 14 perform a denitrification reaction by using hydrogen gas as a hydrogen donor to convert nitrate nitrogen or nitrite nitrogen in the water to be treated into nitrogen gas. Disassemble. The denitrified treated water is the denitrification tank 1
It is discharged to the outside of the denitrification tank 12 from the treated water pipe 42 connected to the upper part of 2. As the denitrification reaction proceeds, nitrogen gas is generated and hydrogen gas is consumed, and the headspace 2
The pressure of 4 and the hydrogen gas concentration decrease. The change in the pressure and the hydrogen gas is detected by the pressure detector 30 and the hydrogen gas detector 32, and the detected values are sequentially transmitted to the controller 34. At the controller 34, when the detected value reaches a predetermined lower limit value,
The hydrogen gas automatic supply valve 36 is opened, and hydrogen gas is supplied from the hydrogen gas supply pipe 28 to the gas circulation pipe 22. As a result, the circulating gas having an increased hydrogen gas concentration is diffused from the diffuser member 20 into the denitrification tank 12. On the other hand, when the detection values of the pressure detector 30 and the hydrogen gas detector 32 reach a predetermined upper limit value, the controller 34 closes the hydrogen gas automatic supply valve 36 and connects the hydrogen gas supply pipe 28 to the gas circulation pipe 22. Stop the supply of hydrogen gas. As described above, the supply / stop of the hydrogen gas into the denitrification tank 12 is automatically performed between the pressure in the head space portion 24 or the upper limit value and the lower limit value of the hydrogen concentration in the circulating gas circulating in the gas circulation pipe 22. Controlled by.

The automatic gas discharge valve 40 prevents the pressure in the denitrification tank 12 from becoming too high by circulating the gas having a high nitrogen gas concentration generated by the denitrification reaction from the head space portion 24, and circulates the gas. It serves to keep the hydrogen gas concentration in the gas above a certain level. That is, when the detected value of the pressure detector 30 exceeds the upper limit required for gas discharge due to an increase in nitrogen gas generated by the denitrification reaction, or the detected value of the hydrogen gas detector 32 is lower limit required for gas discharge. When the temperature falls below the range, the controller 34 opens the automatic gas exhaust valve 40 to release the gas in the head space portion 24 for a certain period of time.
Then, the controller 34 closes the automatic gas exhaust valve 40 after releasing the gas for a certain period of time, or controls the pressure detector 30.
The automatic gas discharge valve 40 is closed when the detected value of is about atmospheric pressure. After the gas is released, the controller 34 opens the hydrogen gas automatic supply valve 36 to supply the hydrogen gas, thereby rapidly increasing the hydrogen gas concentration in the circulating gas flowing through the gas circulating pipe 22.

Further, the gas circulation pipe 22 is formed with a bypass pipe 44 which branches from the gas circulation pipe 22 and joins again, and an oxygen absorber 46 is arranged in the bypass pipe 44. An oxygen detector 47 that detects the concentration of oxygen gas in the circulating gas is provided in the gas circulation pipe 22 before the branch, and the oxygen concentration detected by the oxygen detector 47 is sequentially transmitted to the controller 34. Further, the bypass pipe 44 is provided with a first automatic opening / closing valve 48 and a second automatic opening / closing valve 50 in front of and behind the oxygen absorber 46, respectively, and the gas circulation pipe 22 between the branch position and the merging position.
Also provided with a third automatic opening / closing valve 52. Then, the controller 34 opens / closes these three automatic opening / closing valves 48, 50, 52 based on the oxygen concentration from the oxygen detector 47, thereby causing the flow of the circulating gas to the gas circulation pipe 22 and the bypass pipe 44. Switch.

Next, the operation of the denitrification device 10 of the present invention configured as described above will be described. The water to be treated supplied into the denitrification tank 12 by the raw water pump 18 and the denitrifying bacteria held in the contact material 14 come into contact with each other, so that the aeration member 2
A denitrification reaction is performed using hydrogen gas from 0 as a hydrogen donor, and nitrate nitrogen and nitrite nitrogen in the water to be treated are decomposed into nitrogen gas. The decomposed nitrogen gas rises to the headspace 24 together with the hydrogen gas that has been diffused into the water to be treated and not consumed in the denitrification reaction, and is circulated again to the diffuser member 20 through the gas circulation pipe 22.

In this denitrification process, oxygen derived from air dissolved in the water to be treated and brought into the denitrification tank 12 or oxygen derived from air dissolved in the water to be treated by cavitation of the raw water pump 18 or the like. Etc. are brought into the denitrification tank 12, and increase with the progress of the denitrification treatment and accumulated in the denitrification tank 12. The accumulation of oxygen brought into the denitrification tank 12 reduces the denitrification performance of denitrifying bacteria and causes an explosion accident due to contact with hydrogen gas. That is, in the case of a biological denitrification reaction in which nitrate nitrogen etc. is decomposed by denitrifying bacteria,
This is done by nitric acid respiration of the denitrifying bacteria, but if oxygen is present in the water to be treated, the denitrifying bacteria prioritize oxygen respiration. For this reason, nitric acid respiration decreases, so the denitrification performance decreases. Further, since hydrogen gas is used within the range of explosion, mixing of oxygen gas into the denitrification tank 12 leads to danger of explosion.

Incidentally, FIG. 2 shows the effect of the oxygen concentration in the headspace portion 24 on the biological denitrification reaction, in which all the nitrate nitrogen of 15 mg / L concentration contained in the water to be treated is converted into nitrogen. The denitrification reaction time until decomposition into gas is compared between the case where the oxygen concentration in the head space portion 24 is 1% and the case where the oxygen concentration is 10%. The water to be supplied to the denitrification tank 12 has a KNO ₃ concentration of 15 mg-N
/ L and KH ₂ PO ₄ concentration of 1 mg-P / L simulated waste water was used. Further, in the gas composition of the head space portion 24, all gases other than oxygen were hydrogen gas. Further, the gas superficial velocity was set to 20 m / hour.

As can be seen from FIG. 2, when the oxygen concentration in the headspace 24 is 1%, the denitrification reaction time is about 0.8 hours, whereas when it is 10%, the denitrification reaction time is about 1. 8
It's time. This means that the denitrification performance when the oxygen concentration in the head space portion 24 is 10% is less than half of the denitrification performance when the oxygen concentration is 1%, and the oxygen concentration has a great influence on the denitrification reaction time. To do. In addition, the head space portion 24
The denitrification reaction rate remained almost unchanged even when the oxygen concentration of 1 was less than 1%.

On the other hand, although not shown, regarding the danger of explosion due to the presence of oxygen, even if the hydrogen gas concentration is within the explosion range, if the oxygen concentration in the circulating gas does not reach 5% or more, the Explosion can be prevented even if there is a fire source. Therefore, in the denitrification device 10 of the present invention, the oxygen absorption device 4 is provided in the bypass pipe 44 branched to the gas circulation pipe 22.
6 is provided, an oxygen detector 47 is provided in the gas circulation pipe 22 before branching, and the flow of the circulating gas is switched between the gas circulation pipe 22 and the bypass pipe 44 based on the oxygen gas concentration detected by the oxygen detector 47. I did it. For example,
The oxygen concentration in the circulating gas detected by the oxygen detector 47 is 1%
When it exceeds the above, the first and second automatic opening / closing valves 48 and 50 are opened, the third automatic opening / closing valve 52 is closed, and the circulating gas is flown to the bypass pipe 44. As a result, the circulating gas passes through the oxygen absorbing device 46, so that the oxygen gas in the circulating gas is absorbed by the oxygen absorbing device 46. Therefore, since the circulating gas having a concentration of oxygen concentration of 1% or less and hardly affecting the denitrification reaction time is supplied into the denitrification tank 12, a high denitrification performance can be maintained. When the oxygen concentration in the circulating gas detected by the oxygen detector 47 becomes 1% or less, the first and second automatic opening / closing valves 48 and 50 are closed and the third automatic opening / closing valve 52 is opened to circulate the circulating gas. To the gas circulation pipe 22. in this way,
At the oxygen concentration where the denitrification performance is not deteriorated and there is no danger of explosion, the circulating gas is prevented from flowing into the bypass pipe 44, so that the life of the oxygen absorbing material filled in the oxygen absorbing device 46 is extended. be able to.

Even if these oxygen absorption operations are performed, the oxygen concentration does not decrease, and when the oxygen concentration in the circulating gas reaches 5%, the automatic gas exhaust valve 40 is opened to open the head space portion 24.
After exhausting the gas having a high oxygen concentration therein, the hydrogen gas automatic supply valve 36 is opened to supply the hydrogen gas to the gas circulation pipe 22. Thereby, the oxygen gas concentration in the circulation gas flowing through the gas circulation pipe 22 can be rapidly reduced, and the hydrogen gas concentration can be rapidly increased. Therefore, the danger of explosion can be prevented.

Generally, as a method for absorbing oxygen in a gas, there are an oxygen absorption method using a reducing chemical, a catalytic resin reduction method, a catalytic combustion method, and the like. FIG. 3 shows an example of an oxygen absorption device 46 by the catalytic resin reduction method. Is shown. As the oxygen absorbent, SO ₃ type anion exchange resin was used, and the space velocity (or superficial velocity) [SV] was 40 (gas flow rate m ³ / packed bed m ³ · hour), and oxygen concentration in the circulating gas Was set to 10%. Here, the SO ₃ type anion exchange resin is an ion exchange resin to which a reducing group is attached, and in the case of the SO ₃ type, SO ₃ is attached. The space velocity is the gas flow rate per hour passing through the packed bed of the oxygen absorbent filled in the oxygen absorber divided by the capacity of the packed bed.

Curve A in FIG. 3 shows the oxygen absorption amount with respect to the absorption time. As can be seen from the curve A of FIG. 3, the oxygen gas of 10% concentration in the circulating gas is instantaneously reduced to 0.5% or less by passing through the oxygen absorbent.
Therefore, by disposing the oxygen absorbing device 46 in the bypass pipe 44, the oxygen concentration in the circulating gas can be reliably and promptly reduced, and the denitrification performance can be reduced and the risk of explosion can be prevented. .

In the above embodiment, the bypass pipe 4 is used.
4 is provided with an oxygen absorber 46 and the flow of the circulating gas is switched between the bypass pipe 22 and the gas circulating pipe 22 in accordance with the oxygen concentration in the circulating gas, but the bypass pipe 44 is not provided and the gas circulating pipe 22 is not provided. It is also possible to provide an oxygen absorber 46 and to pass the circulating gas through the oxygen absorber 46 regardless of the oxygen concentration. However, as can be seen from the oxygen absorption amount with respect to the absorption time shown by the curve B in FIG. 3, in the case of oxygen gas with a concentration of 10%, the absorption of the oxygen absorbent reaches saturation within about 20 minutes from the start of absorption, and the curve A The oxygen concentration in the gas increases rapidly.
This means that regardless of the oxygen concentration in the circulating gas, if the circulating gas is constantly passed through the oxygen absorbing device, the frequency of replacement of the oxygen absorbent becomes frequent. Therefore, from the economical aspect such as the life of the oxygen absorber, the flow of the circulating gas is changed according to the oxygen concentration.
4 and the gas circulation pipe 22 are more preferable, and it is preferable to control the switching based on, for example, an oxygen concentration of 1%.

Further, the gas circulation pipe 22 and the bypass pipe 4
4 is not completely switched, but first, second, third
It is also possible to adjust the valve opening degree of the automatic open / close valves 48, 50, 52 so that some percentage of the circulating gas always flows to the bypass pipe 44. Further, in the present embodiment, the description has been made on the biological denitrification device using hydrogen gas, but in the case of a chemical denitrification device using a hydrogenation catalyst, when the oxygen concentration becomes high, the nitrate nitrogen The present invention can be similarly applied since there is a risk of degrading the decomposition performance and explosion.

[0026]

As described above, according to the denitrification apparatus of the present invention, the dissolved oxygen mixed in the water to be treated can be reduced quickly and efficiently, so that the denitrification performance is lowered and the explosion is prevented. The danger can be surely prevented.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing the configuration of a denitrification device of the present invention.

FIG. 2 is an explanatory diagram illustrating the relationship between denitrification reaction time and oxygen concentration.

FIG. 3 is an explanatory diagram illustrating an effect of the present invention.

[Explanation of symbols]

10 ... Denitrification device 12 ... Denitrification tank 14 ... Contact material 16 ... Raw water piping 20 ... Hydrogen gas diffuser 22 ... Gas circulation piping 24 ... Headspace section 26. Blower device 28 ... Hydrogen gas supply pipe 30 ... Pressure detector 32 ... Hydrogen gas detector 34 ... Controller 36 ... Hydrogen gas automatic supply valve 38 ... Gas discharge pipe 40 ... Automatic gas discharge valve 42 ... Treated water piping 44 ... Bypass piping 46 ... Oxygen absorber 47 ... Oxygen detector 48, 50, 52 ... Automatic open / close valve

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4D020 AA02 BA18 BA19 BA21 BB01                       DA01 DA02                 4D040 BB52 BB82 BB91                 4D050 AB37 BA14 BD08 CA17

Claims (3)

[Claims] 1. A hydrogen gas is supplied into the water to be treated in a denitrifying tank having a hermeticity to biologically or chemically denitrify nitrate nitrogen and nitrite nitrogen in the water to be treated, and In a denitrification device provided with a gas circulation line that connects a tank upper part and a tank lower part of a denitrification tank and circulates a gas accumulated in the tank upper part to the tank lower part, an oxygen absorption device is provided in the gas circulation line. And denitrification equipment. 2. The gas circulation line is formed by a gas circulation pipe and a bypass pipe branched from the gas circulation pipe and joined again, and the oxygen absorption means is provided in the bypass pipe,
Oxygen concentration measuring means for detecting the oxygen concentration in the circulating gas is provided in the gas circulation pipe before the branch position, and the flow of the circulating gas is changed by the switching means on the basis of the oxygen concentration in the oxygen concentration measuring means. The denitrification device according to claim 1, wherein the denitrification device is switched to a bypass line. 3. When the measured value of the oxygen concentration measuring means exceeds 1%, the flow of the circulating gas is switched to the bypass piping side,
3. The denitrification device according to claim 2, further comprising control means for controlling the switching means so as to switch to the gas circulation pipe when the gas concentration becomes 1% or less.