JP5027000B2 - Nitrification processing method and nitrification processing apparatus - Google Patents

Description

  The present invention relates to a nitrification treatment method and a nitrification treatment apparatus for nitrifying raw water containing ammonia nitrogen by biological treatment.

  Conventionally, hydrofluoric acid, ammonia, nitric acid, and the like are used in the manufacturing process of a semiconductor such as an IC (integrated circuit). For this reason, waste water containing fluorine (hydrofluoric acid) and nitrogen (ammonia, nitric acid) is discharged as the waste liquid. For example, chemicals containing these chemical substances are used in processes such as etching, and waste water containing these chemical substances is discharged as a cleaning waste liquid when the semiconductor substrate is cleaned with ultrapure water or the like. The LCD (liquid crystal display) manufacturing process basically has the same process as the semiconductor manufacturing process, and the same waste water is discharged. Furthermore, wastewater containing nitrogen is also discharged at coal-fired power plants, glass surface processing plants, and the like. Furthermore, general domestic wastewater may also contain nitrogen (ammonia, nitric acid).

  As a method for removing nitrogen from waste water, a biological nitrification denitrification method is generally employed. In this biological nitrification / denitrification treatment method, the wastewater is first nitrified, and ammonia nitrogen in the wastewater is changed to nitrite nitrogen or nitrate nitrogen, and then a hydrogen donor such as methanol is added to make it oxygen-free. It removes nitrogen by using nitrate respiration in the anoxic state of denitrifying bacteria which are facultative anaerobic bacteria. Here, in the biological treatment method in which ammonia nitrogen in the wastewater is converted into nitrite nitrogen or nitrate nitrogen by the action of aerobic autotrophic bacteria, the carbon necessary for the growth of nitrifying bacteria along with the conversion Consume dissolved inorganic carbon in water as a source. At this time, the weight ratio of necessary inorganic carbon to ammonia nitrogen to be treated is 0.081 g-C / g-N in the oxidation from ammonia nitrogen to nitrite nitrogen by ammonia oxidizing bacteria, When oxidizing from ammonia nitrogen to nitrite nitrogen to nitrate nitrogen by nitrifying bacteria, an inorganic carbon source corresponding to 0.088 g-C / g-N is required.

In general, in the case of a low-load nitrification treatment (for example, 0.1 to 0.5 kg-N / m ³ / day) such as the activated sludge method, the carbon dioxide in the air is accompanied by aeration for supplying oxygen from the air. It is possible to ensure the above-mentioned amount of inorganic carbon by dissolving carbon into the waste water. However, a biofilm method (for example, a fixed bed method or a fluidized bed method) in which a biofixation carrier is introduced into the treatment system and the bacteria are retained in the treatment system, or microorganisms are self-granulated in the biotreatment tank. In the granule method for maintaining a high concentration, nitrification treatment with a high load (for example, 0.5 to 4.0 kg-N / m ³ / day) is performed, so that inorganic carbon necessary for the growth of nitrifying bacteria is insufficient. Tend to. Therefore, it is necessary to replenish inorganic carbon.

  To replenish inorganic carbon, carbonates such as sodium carbonate and bicarbonates such as sodium bicarbonate are added, and alkali agents such as sodium hydroxide added to the nitrification tank to maintain pH are removed. There is a method of adding a large amount of inorganic carbon in an alkaline agent by adding a gas containing a lot of carbon dioxide generated when nitrogen or organic substances are biologically removed, or air or carbon dioxide gas itself. It has been proposed (for example, Patent Documents 1 to 4).

JP 2006-320844 A Japanese Patent Laid-Open No. 5-138193 Japanese Patent Laid-Open No. 8-80497 JP-A-55-102498

  When inorganic carbon is to be supplied to the nitrification tank using carbonates such as sodium carbonate or bicarbonates such as sodium hydrogen carbonate, they are relatively insoluble in water. It was necessary to adjust to a dilute liquid with a weight percent or less. In addition, carbonates such as sodium carbonate and bicarbonates such as sodium bicarbonate are hygroscopic, and in order to store these in solid form, you must fully consider the moisture resistance after installing the equipment indoors. As a result, there is a problem that the addition equipment is expensive and complicated.

  On the other hand, as in Patent Documents 1 to 4, when a gas containing a large amount of carbon dioxide generated when denitrification or organic matter is biologically removed is passed through an alkali agent such as sodium hydroxide, the gas is recovered and re-generated. The gas recovery method is complicated to use. In addition, when such gas, air, or carbon dioxide gas is passed through the alkaline agent, it is necessary to consider the prevention of scattering of the alkaline agent after installing a blower. Furthermore, when the amount of the alkaline agent added to adjust the pH to the nitrification tank changes for some reason, the amount of inorganic carbon to be supplied also changes, so it is difficult to stably supply inorganic carbon quantitatively. There is a problem that.

  The present invention is a nitrification treatment method and a nitrification treatment apparatus that can easily and inexpensively supply inorganic carbon necessary for nitrification treatment of ammonia nitrogen in raw water.

The present invention, ammonium nitrogen in the raw water, a nitrification treatment process for nitrifying the biologically nitrite nitrogen or nitrate nitrogen by nitrifying bacteria in the granules method using nitrification tank, to the nitrification tank Carbon dioxide gas is supplied in the gaseous state as inorganic carbon, and the conversion load of the ammonia nitrogen per unit tank volume per day flowing into the nitrification tank into the nitrite nitrogen or the nitrate nitrogen is 0. a 5kg-N / m ³ / day or more der Ru nitrification treatment method.

  In the nitrification method, it is preferable to supply the carbon dioxide gas to an air supply line to the nitrification tank.

The present invention also provides a nitrification tank for biologically nitrifying ammonia nitrogen in raw water to nitrite nitrogen or nitrate nitrogen by nitrifying bacteria using the granule method, and carbon dioxide gas to the nitrification tank. Carbon dioxide supply means for supplying in a gaseous state, and the conversion load of the ammonia nitrogen per unit tank volume per day flowing into the nitrification tank into the nitrite nitrogen or the nitrate nitrogen is 0 a nitrification treatment apparatus shall be the .5kg-N / m ³ / day or more.

  In the nitrification apparatus, the carbon dioxide supply means preferably supplies the carbon dioxide gas to an air supply line to the nitrification tank.

  In the present invention, by supplying carbon dioxide gas in a gaseous state to the nitrification tank, inorganic carbon necessary for nitrification of ammonia nitrogen in the raw water can be supplied inexpensively and easily.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  An outline of an example of a nitrification apparatus according to an embodiment of the present invention is shown in FIG. The nitrification apparatus 1 includes a nitrification tank 10, a precipitation tank 12 that is a solid-liquid separation means, a blower 14 that is an air supply means, and a carbon dioxide supply device 16 that is a carbon dioxide supply means.

  1, the raw water supply pipe 18 is connected to the inlet of the nitrification tank 10, and the nitrification liquid discharge pipe 24 is connected to the outlet. A nitrification treatment liquid discharge pipe 24 is connected to the inlet of the sedimentation tank 12, and a treated water discharge pipe 26 is connected to the outlet. An air supply pipe 20 from the blower 14 is connected to the lower part of the nitrification tank 10, and a carbon dioxide supply pipe 22 from the carbon dioxide supply device 16 is connected to the middle of the air supply pipe 20. The lower part of the sedimentation tank 12 and the middle of the raw water supply pipe 18 are connected by a return sludge pipe 28.

  The operation of the nitrification method and the nitrification apparatus 1 according to this embodiment will be described.

  First, raw water (treated water) containing ammonia nitrogen is fed to the nitrification tank 10 through the raw water supply pipe 18. On the other hand, in the air supply pipe 20, the carbon dioxide gas from the carbon dioxide supply device 16 is mixed with the air from the blower 14 through the carbon dioxide supply pipe 22. The carbon dioxide-containing air is supplied to the nitrification tank 10 from below through the air supply pipe 20. In the nitrification tank 10, there are ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, which are autotrophic bacteria. In the nitrification tank 10, ammonia nitrogen contained in the raw water is oxidized to nitrite nitrogen by ammonia oxidizing bacteria, and this nitrite nitrogen is further oxidized to nitrate nitrogen by nitrite oxidizing bacteria (nitrification step). . The nitrification liquid subjected to nitrification is sent to the precipitation tank 12 through the nitrification liquid discharge pipe 24, where solid-liquid separation is performed. The treated water subjected to the solid-liquid separation is discharged from the sedimentation tank 12 through the treated water discharge pipe 26. The sludge separated into solid and liquid is discharged from the settling tank 12. Further, at least a part of the solid-liquid separated sludge may be returned to the raw water supply pipe 18 through the return sludge pipe 28 as a return sludge (return process).

  Thereafter, in a denitrification apparatus (not shown), nitrite nitrogen and nitrate nitrogen remaining in the treated water are reduced to nitrogen gas by using organic matter such as methanol as an electron donor by denitrification bacteria, which are heterotrophic bacteria. Decomposed (denitrification process).

  When the raw water contains fluorine, the treated water may be obtained by adding a calcium compound or the like to the denitrified water in the fluorine treatment apparatus after the denitrification reaction to treat the fluorine (fluorine treatment step).

  The nitrification method according to the present embodiment is a method of supplying inorganic carbon necessary for nitrification at low cost and easily by supplying carbon dioxide gas in a gaseous state to the nitrification tank 10. Generally, carbon dioxide gas is liquid and filled in a container, so it has high pressure when stored and can be easily supplied by installing a supply line without using a blower. It is. The supply equipment is simple and can be installed outdoors, and is relatively inexpensive. Furthermore, by installing a flow meter, a flow controller, etc., inorganic carbon can be supplied stably while maintaining quantitativeness.

In the present embodiment, the target nitrification treatment is a conversion load of ammonia nitrogen to nitrite nitrogen or nitrate nitrogen per unit tank volume per day flowing into the nitrification tank 10 is 0.5 kg-N / m. ³ / day or more is preferable. When this conversion load is less than 0.5 kg-N / m ³ / day, the supply of carbon dioxide contained in the air from the blower 14 is often sufficient to supply inorganic carbon. Moreover, the conversion rate of nitrate nitrogen to nitrite nitrogen or nitrate nitrogen per unit tank volume per day flowing into the nitrification tank 10 is 0.5 kg-N / m ³ / day or more. It is preferable.

In the present embodiment, as a nitrification treatment method for treatment with a high conversion load of 0.5 kg-N / m ³ / day or more, for example, a sponge-like biofixation carrier is introduced into the nitrification tank 10 and the bacteria are introduced. A biofilm method (for example, a fixed bed method or a fluidized bed method) that is retained in the treatment system, a granule method in which microorganisms are self-granulated and maintained at a high concentration in the nitrification tank 10 are suitably applied. Therefore, when these methods are used, if carbon dioxide gas is supplied in a gaseous state to the nitrification tank, the effect is more exhibited.

  Moreover, it is preferable that the pH of the liquid of the nitrification tank 10 is the range of 7.0-8.5. Since the method according to the present embodiment is more effective when carbon dioxide gas is dissolved in raw water in the nitrification tank 10, the theoretical solubility of carbon dioxide gas in water is less than pH 7.0. It may be significantly reduced, and the dissolution efficiency may be reduced. On the other hand, when the pH rises, the solubility of carbon dioxide gas in water increases. However, if the pH exceeds 8.5, the proportion of free ammonia in the dissolved ammoniacal nitrogen that flows in increases, which adversely affects the nitrification treatment. There is a case.

  The pH of the liquid in the nitrification tank 10 can be adjusted by adding a pH adjusting agent such as alkali by a pH adjusting means. Examples of the alkali include sodium hydroxide (NaOH).

  The required amount of carbon dioxide gas supplied by a method other than that derived from aeration air by the blower 14 or the like differs depending on factors such as the carbon dioxide gas supply method and factors such as the pH in the nitrification tank 10, but the factors such as pH. In terms of carbon in carbon, the required amount of inorganic carbon is preferably in the range of 1.1 times to 4.0 times, more preferably in the range of 1.6 times to 4.0 times. . If the required amount of carbon dioxide gas is less than 1.1 times, the amount of inorganic carbon may be insufficient, and if it exceeds 4.0 times, the cost may increase. Moreover, when this required amount of carbon dioxide gas is 1.1 times to less than 1.6 times, a sufficient effect may not be obtained from the viewpoint of the dissolution efficiency of carbon dioxide gas and the utilization efficiency of microorganisms.

As the concentration of carbon dioxide in the aerated air, the higher the concentration, the better the solubility in water, but 2000 ppmV to 8000 ppmV (integral integral ratio of millions of carbon dioxide per 1 Nm ^{3 of} air). A range is more preferred. When the carbon dioxide concentration in the aerated air exceeds 20000 ppmV, safety precautions may be required.

  Control of the supply amount and concentration of carbon dioxide gas to the aerated air or the nitrification tank 10 can be easily set by a commercially available flow meter, flow controller or the like. Further, the use of a diffuser that can generate fine bubbles during aeration also improves the efficiency of dissolving carbon dioxide gas in water. When such improvements are made, a sufficient effect can be obtained even when the necessary amount of carbon dioxide gas supplied by a method other than that derived from aerated air is in the range of 1.1 to 1.6 times.

  The supply method for supplying carbon dioxide gas to the nitrification tank 10 in a gaseous state is not particularly limited, but as shown in FIG. 1, a method for supplying carbon dioxide gas to the nitrification tank 10 by mixing it with air, for example, using a blower 14 There is a method of directly injecting a line from an aeration air suction port to an arbitrary place in an air supply line including an air supply pipe 20 to the nitrification tank 10. Further, an air suction line may be provided in the blower 14, and the line may be directly injected into an arbitrary place in the air suction line. Further, carbon dioxide gas may be mixed with oxygen gas and nitrogen gas and supplied to the nitrification tank 10. In addition to this, as shown in FIG. 2, a method of directly supplying from the carbon dioxide supply device 16 to the nitrification tank 10 can be mentioned. In FIG. 2, a carbon dioxide supply pipe 22 from the carbon dioxide supply device 16 is connected to the lower part of the nitrification tank 10. Any of these methods may be used, but line injection into the air supply line of the blower 14 is preferable in consideration of the simplicity of the apparatus and stirring in the nitrification tank 10.

  As the carbon dioxide supply means, in addition to the carbon dioxide supply device 16, a liquefied carbon dioxide supply line or the like may be used.

  As described above, by supplying carbon dioxide gas to the nitrification tank 10 in a gaseous state, inorganic carbon necessary for nitrification can be supplied inexpensively and easily.

  In the denitrification step, treatment may be performed using autotrophic denitrification microorganisms (ANAMMOX microorganisms) instead of the aforementioned method.

  In this case, in FIG. 1, raw water (treated water) containing ammoniacal nitrogen is sent to the nitrification tank 10 through the raw water supply pipe 18. On the other hand, carbon dioxide-containing air is supplied to the nitrification tank 10 from below through the air supply pipe 20. In addition, ammonia oxidizing bacteria which are autotrophic bacteria exist in the nitrification tank 10, and in the nitrification tank 10, a part of the ammonia nitrogen contained in the raw water is oxidized to nitrite nitrogen by the ammonia oxidizing bacteria. (Nitrite process). The nitrification liquid subjected to the nitrification treatment is sent to the precipitation tank 12 through the nitrification liquid discharge pipe 24, and solid-liquid separation is performed. The treated water subjected to the solid-liquid separation is discharged from the sedimentation tank 12 through the treated water discharge pipe 26. Next, in a denitrification apparatus (not shown), ammonia nitrogen remaining in the nitrification solution is used as an electron donor, nitrite nitrogen nitritized in the nitritation step is used as an electron acceptor, and inorganic carbon is used as a carbon source. The denitrification reaction is carried out by the ANAMMOX microorganisms while consuming (denitrification step).

Since the method of denitrifying with the ANAMOX microorganism does not require the addition of organic matter, the cost can be reduced as compared with a method using heterotrophic denitrifying bacteria. Moreover, since the yield of autotrophic microorganisms is low and the amount of sludge generated is significantly less than that of heterotrophic microorganisms, the amount of surplus sludge generated can be suppressed. Further, there is a feature that N ₂ O is hardly generated as observed by the conventional nitrification denitrification method, and the burden on the environment can be reduced.

In the treatment using the ANAMMOX microorganism, for example, a biofixation carrier such as a sponge is introduced into the nitrification tank 10 as a biofixation carrier, and the raw water is nitrified with a conversion load of ^{3 to 5} kg-N / m ³ / day Thus, it is possible to perform partial nitrite nitrification in which about 60% of ammonia nitrogen in raw water is oxidized to nitrite nitrogen.

  As the nitrification treatment conditions in this case, for example, the pH of the nitrification tank 10 is preferably in the range of 5 to 9 so that the activity of ammonia-oxidizing bacteria is maintained high and the activity of nitrite-oxidizing bacteria is low. More preferably in the range of 7-8, DO concentration is preferably in the range of 0-6 mg-N / L, temperature is preferably in the range of 10-40 ° C, more preferably in the range of 20-35 ° C. do it. At this time, when the nitrification treatment apparatus and the nitrification treatment method according to the present embodiment are applied, not only can the inorganic carbon source be easily supplied, but also the inorganic carbon concentration in the treated water after nitrification increases, A large amount of inorganic carbon can be supplied to the denitrification step, which brings about a favorable effect on the entire treatment step.

  The nitrification apparatus and the nitrification method according to the present embodiment are waste water discharged from a semiconductor manufacturing process such as an IC, for example, a cleaning waste liquid when a semiconductor substrate is cleaned with ultrapure water or the like in a process such as an etching process. Wastewater discharged as an electronic industry wastewater discharged from the LCD (liquid crystal display) manufacturing process, wastewater discharged from coal-fired power plants, glass surface processing plants, and general domestic wastewater, It can be applied to wastewater containing nitrogen (ammonia, nitric acid) and wastewater containing fluorine (hydrofluoric acid) and nitrogen (ammonia, nitric acid).

  The ammoniacal nitrogen contained in the raw water to be treated in the present embodiment is, for example, ammonia, ammonium compounds, amine compounds such as TMAH (tetramethylammonium hydroxide), MEA (monoethanolamine), and other amino acids. This is due to organic nitrogen compounds such as

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

(Examples 1-3)
The nitrification apparatus shown in FIG. 1 was used. Filling 500 L nitrification tank 10 with nitrification granules 5000 mg / L and aeration with air at 0.108 Nm ³ / min, keeping DO (dissolved oxygen) in nitrification tank 10 at 2.0 mg / L or more In addition, simulated waste water adjusted to 5 mg-P / L of phosphorus and 500 mg-N / L of ammonia nitrogen is used as raw water for industrial water, and continuous flow is performed so that the inflow nitrogen conversion load is 1.6 kg / m ³ / day. Watered. At this time, carbon dioxide gas was injected as an inorganic carbon supply into the air line of the blower 14 (the concentration of carbon dioxide in the aerated air was 1900 ppmV in Example 1, 3800 ppmV in Example 2, and 5500 ppmV in Example 3). went. The pH of the liquid in the nitrification tank 10 was adjusted to 7.2 ± 0.2 with an aqueous sodium hydroxide solution. The water temperature was controlled with a heater so as to be constant at 20 ° C.

Table 1 shows the inorganic carbon supply conditions and nitrate nitrogen conversion rate in each experimental system. The “supply amount by addition to the required amount” in Table 1 is the ratio of the inorganic carbon supply amount from carbon dioxide or sodium carbonate to the theoretically required inorganic carbon supply amount. The “total supply amount relative to the required amount” is a ratio when the inorganic carbon amount derived from aeration air is added to the supply amount. “Nitrate nitrogen conversion rate” was calculated as the amount of nitrate nitrogen converted from ammonia nitrogen per m ³ per day. The “ammonia nitrogen concentration in treated water” was measured by a method according to JIS K0101 (1998) 36.2.

(Comparative Example 1)
Using the nitrification apparatus shown in FIG. 3, the test was performed in the same manner as in Examples 1 to 3 in the case where a 2.5% sodium carbonate solution was supplied as inorganic carbon. In the nitrification apparatus shown in FIG. 3, a sodium carbonate supply pipe 32 from the sodium carbonate supply apparatus 30 is connected to the raw water supply pipe 18. The results are shown in Table 1.

(Comparative Example 2)
About the case where inorganic carbon is not added, it tested similarly to Examples 1-3. The results are shown in Table 1.

From Example 3 and Comparative Example 1, it can be seen that sodium carbonate can be substituted by supplying carbon dioxide gas in the gaseous state as an inorganic carbon source. Although effective in the range where the supply amount of carbon dioxide gas supplied by a method other than that derived from aeration air is about 1.1 times to less than 1.6 times the required amount from Example 2, carbon dioxide gas is effective. From the viewpoint of the dissolution efficiency, the amount of inorganic carbon required cannot be supplied to the nitrifying bacteria, so the conversion rate of nitrate nitrogen is lower than 1.6 kg-N / m ³ / day, and ammonia nitrogen remains. I understand that. Further, from Example 1, when the supply amount of carbon dioxide gas supplied by a method other than aeration air is less than 1.1 times the required amount, there is an effect, but ammonia nitrogen still remains. I understand that.
On the other hand, in Comparative Example 1, although the treatment effect of ammonia nitrogen is seen, the cost for the supply equipment is significantly increased. In Comparative Example 2, it can be seen that ammonia nitrogen remains because inorganic carbon is not supplied. Moreover, in the comparative example 2, when processing time became long, the tendency for ammonia nitrogen to remain further was seen.

It is a schematic structure figure showing an example of the nitrification processing device concerning the embodiment of the present invention. It is a schematic block diagram which shows the other example of the nitrification processing apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows the nitrification processing apparatus used in the comparative example 1 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,3 Nitrification processing apparatus, 10 Nitrification tank, 12 Precipitation tank, 14 Blower, 16 Carbon dioxide supply apparatus, 18 Raw water supply piping, 20 Air supply piping, 22 Carbon dioxide supply piping, 24 Nitrification liquid discharge piping, 26 Treated water Discharge piping, 28 return sludge piping, 30 sodium carbonate supply device, 32 sodium carbonate supply piping.

Claims (4)

A nitrification treatment method in which ammoniacal nitrogen in raw water is biologically nitrified to nitrite nitrogen or nitrate nitrogen by nitrifying bacteria using a granulation method using a nitrification tank,
Supply carbon dioxide gas in the gaseous state as inorganic carbon to the nitrification tank ,
The conversion load on the nitrite nitrogen or a nitrate nitrogen of the ammonium nitrogen per unit cell volume per day flowing into the nitrification tank, der Rukoto 0.5kg-N / m ³ / day or more A nitrification method characterized by the above. The nitrification method according to claim 1,
A nitrification method comprising supplying the carbon dioxide gas to an air supply line to the nitrification tank. A nitrification tank for nitrifying ammonia nitrogen in raw water to nitrite nitrogen or nitrate nitrogen biologically by nitrifying bacteria using the granule method ,
Carbon dioxide supply means for supplying carbon dioxide gas in a gaseous state to the nitrification tank;
Equipped with a,
The conversion load on the nitrite nitrogen or a nitrate nitrogen of the ammonium nitrogen per unit cell volume per day flowing into the nitrification ^{tank, 0.5kg-N / m 3 /} day or more and be Rukoto A nitrification apparatus characterized by The nitrification apparatus according to claim 3 , wherein
The nitrification apparatus according to claim 1, wherein the carbon dioxide supply means supplies the carbon dioxide gas to an air supply line to the nitrification tank.

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