JP4106203B2 - How to remove nitrogen from water - Google Patents

Description

【００５７】
【発明の効果】
本発明により、ＣＯＤ成分とアンモニア性窒素を高濃度に含有する廃水から、廃水中のＣＯＤ成分を用いて安価に安定した窒素除去が可能となる。
【図面の簡単な説明】
【図１】アンモニアストリッピング装置と硝化細菌および脱窒細菌（従属栄養細菌および硫黄酸化細菌）を用いる脱窒素処理プロセスである。
【符号の説明】
（1）安水
（2）アルカリ剤（ＮａＯＨ）
（3）アンモニアストリッピング塔
（4）蓄熱式アンモニアガス分解炉
（5）循環ブロワー
（6）ボイラー給水
（7）ボイラー
（8）希釈水（海水または淡水）
（9）リン酸
（10）調整槽
（11）給水ポンプ
（12）ｐＨ計
（13）脱窒槽
（14）好気槽
（15）沈殿池
（16）硝化液
（17）返送汚泥
（18）処理水
（19）ブロワー
（20）ＯＲＰ計
（21）汚泥返送ポンプ#
（22）循環ポンプ
（23）窒素測定装置
（24）ＣＯＤ測定装置[0001]
BACKGROUND OF THE INVENTION
An object of the present invention is to stably and efficiently remove high-concentration ammoniacal nitrogen compounds contained in wastewater.
[0002]
[Prior art]
Wastewater containing high concentrations of ammonia nitrogen is generated from steelworks coke plants, manure, fertilizer plants, semiconductor factories, leather factories, and sewage treatment plant sludge treatment processes.
[0003]
Such ammonia in wastewater is classified and called as follows depending on whether it can be easily released as ammonia gas in the air by heating operation (using heated air or steam).
(1) Free ammonia: NH_Three
(2) Fixed ammonia: NH_FourCl, (NH _Four )₂SO_FourSuch
This expression of immobilization means that ammonia is ammonium ion (NH_Four ⁺) Because it cannot be easily dissipated as ammonia gas. In order to convert the fixed ammonia into free ammonia, the pH and the water temperature may be increased.
[0004]
NH_Four ⁺  + OH^-→ NH_Three+ H₂O (1)
The reaction of formula (1) proceeds to the right side due to the increase in water pH and temperature, and free ammonia (NH_Three) Is increased. For example, in wastewater having a water temperature of 20 ° C. and pH = 8, free ammonia (NH_Three) Is only about 5%. If this pH is increased to 9, about 30% will be present in the water as free ammonia, and if the pH is increased to 10, about 80% will be present in the water as free ammonia. Further, when the water temperature reaches 80 ° C., if the pH is increased to 9, about 90% becomes free ammonia. Therefore, the ratio of free ammonia varies greatly depending on the pH and temperature of the wastewater.
[0005]
The following methods are widely known as methods for removing ammonia in such waste water.
[0006]
First, there is an ammonia stripping method. The ammonia stripping method basically uses the reaction of the formula (1) and is widely put into practical use mainly in ironworks coke factories. The method is as follows. First, the pH of wastewater is raised using slaked lime or sodium hydroxide, and the water temperature is adjusted as necessary. If the factory has a heating source and the pH is high to some extent, the pH may not be adjusted and only the water temperature may be raised. In any case, the proportion of free ammonia in the wastewater is increased. Thereafter, the wastewater is sprayed from the upper part of the stripping tower filled with various fillers, and a large amount of air is blown from the lower part, whereby free ammonia in the wastewater is diffused into the air. In this case, the ratio of the waste water to be treated and the amount of air blown (hereinafter referred to as the gas-liquid ratio) is also an important factor that affects the ammonia removal rate. Usually, the gas-liquid ratio is several thousand times.
[0007]
In addition, a biological nitrification-denitrogenation method is widely used as a biological removal method of ammonia nitrogen from wastewater. This principle is as follows. That is, it consists of a combination of biological oxidation by aerobic autotrophic bacteria (nitrifying bacteria such as nitrozomonas and nitrobacter) and biological reduction by facultative anaerobic heterotrophic bacteria (such as Pseudomonas).
[0008]
First, the nitrification process consists of the following two-stage reaction, and the types of nitrifying bacteria involved are different.
[0009]
2NH_Four ⁺+ 3O₂→ 2NO₂ ^-+ 2H₂O + 4H⁺(2)
2NO₂ ^-+ O₂→ 2NO_Three ^-(3)
The reaction shown in the formula (2) is brought about by nitrite bacteria having nitrozomonas as a representative species, and the reaction shown in the formula (3) is brought about by nitrate bacteria having a nitrobacter as a representative species.
[0010]
The nitrite nitrogen and nitrate nitrogen produced by the above reaction are generally reduced by the following method using a facultative anaerobic heterotrophic bacterium, under the condition of anoxic conditions, and nitrogen oxide gas (N₂O) or nitrogen gas (N₂) And released into the atmosphere.
[0011]
2NO₂ ^-+ 6H₂→ N₂ + 2H₂O + 2OH^-  (4)
2NO_Three ^-+ 10H₂→ N₂+ 4H₂O + 2OH^-  (5)
The denitrification reaction requires a hydrogen donor, and organic substances are usually used. In municipal sewage and the like, organic matter in sewage is used as it is, and in wastewater not containing organic matter, methanol or the like is often added. This biological nitrification-denitrogenation method is the cheapest and most stable treatment method for wastewater with an ammoniacal nitrogen concentration of 100 mg / l or less, and is widely used in municipal wastewater treatment and the like.
[0012]
In addition, a method of oxidizing and decomposing ammonia in water with chlorine gas has been reported, but practical examples of practical use are hardly seen from the viewpoint of running cost and the like in the case of wastewater containing ammonia at a high concentration.
[0013]
[Problems to be solved by the invention]
First, the problem of the ammonia stripping method will be described.
[0014]
One is the high running cost. As described above, in order to increase the ammonia removal rate, it is necessary to considerably increase the water temperature and pH. Otherwise, only a portion of the free ammonia can be removed.
[0015]
For example, according to an experiment report for municipal sewage treated water (Yokosuka City Sewerage Department: Report on tertiary treatment experiment of sewage in Yokosuka City, Showa 49, 1950), pH = 10, gas-liquid ratio 1000-1100, water temperature 14 The removal rate of ammonia nitrogen under the condition of ° C. is only about 33%. In addition, according to a report (desalting technology, desalination promotion center, p313-320) targeting steel industry coke oven factory gas wastewater (hereinafter referred to as “ansan”), the ammonia concentration in the sanitary water is 3000 to 3000. There is also 5000 mg / l, of which the proportion of free ammonia is 65-80%. When ammonia stripping was performed on this water with pH = 10, gas-liquid ratio of 3000, and water temperature of 80 ° C., 5000 mg / l of ammonia in the water could be reduced to 100 mg / l (removal rate: 98%). It is stated that.
[0016]
From these results, it is easily estimated that enormous running costs are required to reduce nitrogen in wastewater by the ammonia stripping method alone. For example, according to a report on the safety treatment, in order to increase the pH from 8.5 to 10 at 80 ° C,^ThreeIt is stated that about 6.4 L of sodium hydroxide solution (50%) was required. Temporarily, the amount of generated water will be 1400m^Three/ Day, the amount of sodium hydroxide solution required for pH adjustment is about 9 t / day, that is, about 3300 t per year, which is a running cost on the order of several hundred million yen per year. Furthermore, since the cost for raising the water temperature and the power cost for the blower and the like are added, the running cost becomes enormous. Therefore, it is not a good idea to remove nitrogen from wastewater containing high concentrations of ammonia by ammonia stripping alone. Another problem is that it is necessary to treat the ammonia gas that is emitted. There are four treatment methods: recovery as ammonia water, recovery as ammonium sulfate, combustion, and catalytic combustion (for example, fixation from wastewater and removal of free ammonia, water and wastewater, 37, 9, p56-60, 1995) . In both cases, the equipment cost and running cost are further increased.
[0017]
Next, the subject of biological nitrification-denitrification method is described.
[0018]
The biggest problem of the wastewater treatment method using microorganisms is the inhibition of organic matter and free ammonia in the wastewater to microorganisms.
[0019]
First, there is an inhibition of various organic substances contained in wastewater to nitrifying bacteria. Since nitrifying bacteria are autotrophic bacteria and are extremely susceptible to inhibition, substances that suppress the nitrifying reaction have been investigated relatively widely (eg, historical considerations of biological denitrification, water and wastewater, 13 11, p. 1362-1374, 1974). According to this, for example, the amount of phenol contained in a large amount in the water produced from a coke plant is only 5.6 mg / l, and nitrification per unit microorganism compared to the case of containing ammonia nitrogen alone. It has been reported that the rate is reduced by 75%. Therefore, in order to promote the nitrification of wastewater containing such organic matter, it is necessary to remove the organic matter as much as possible.
[0020]
However, in order to promote denitrification in the denitrification tank, conversely, a hydrogen donor such as an organic substance is required. In addition to organic substances, there are also sulfur compounds as hydrogen donors. Such organic substances and sulfur compounds are measured as COD, but have a small effect on denitrifying bacteria. Rather, if the COD in such wastewater is insufficient, the denitrification removal performance tends to decrease.
[0021]
As described above, when the waste water contains a COD component that affects nitrifying bacteria, the biological denitrification method is examined from both aspects of prevention of inhibition of the nitrification reaction by the COD component and effective use in the denitrification reaction of the COD component. It is necessary and the reaction control is quite difficult.
[0022]
Moreover, although it is free ammonia contained in wastewater, it is said that normally, when the concentration of free ammoniacal nitrogen exceeds 100 mg / l, various problems occur and stable treatment becomes difficult. That is, when the concentration of free ammoniacal nitrogen exceeds 100 mg / l, nitrobacter, which is a nitrite oxidizing bacterium, is inhibited in the nitrification process of the aerobic tank, and as a result, nitrite nitrogen in the treated water accumulates. Cheap. In particular, if the pH of the wastewater becomes too high, the proportion of free ammonia increases, and it is said that nitrification inhibition tends to occur.
[0023]
For these reasons, the application of the biological nitrification-denitrogenation method is quite difficult in the case of wastewater having a high COD concentration and a free ammoniacal nitrogen concentration exceeding 100 mg / l.
[0024]
[Means for Solving the Problems]
As a result of repeated studies to solve the above-mentioned problems, the present inventors have succeeded in stably and efficiently treating wastewater containing high-concentration COD components and ammonia nitrogen by the following method. . The gist of the present invention is the following (1) to (8).
(1) Contains COD component and ammoniacal nitrogenCheapThe water,CheapThe ratio of COD concentration to nitrogen concentration (COD / N ratio) in water is 22.9After removing ammonia with an ammonia stripping device,One stepDenitrification tankImmediately afterAerobic tankHaveThrough the biological denitrification process and in the aerobic tankAdjust the pH to be maintained from 6.0 to 7.5,Oxidizing ammonia in water using nitrifying bacteria to nitrite nitrogen andGlassAcid nitrogen is produced and this water is circulated to the denitrification tank.Adjust the pH to be maintained from 6.0 to 7.5,By denitrifying bacteriaCheapUsing COD components in water, nitrite nitrogen andGlassRemove acidic nitrogen as nitrogen gasAt the same time, aeration and / or stirring is performed to promote the removal of COD components in the denitrification tank and to promote the growth of nitrifying bacteria in the aerobic tankIt is characterized byCheapHow to remove nitrogen from water.
(2)Aeration and / or agitation in the denitrification tank is performed at the start of operation, and organic compounds and sulfur compounds are decomposed using oxygen.As described in (1),CheapHow to remove nitrogen from water.
(3)Cheap(1) or (2) characterized in that the main component of the COD component in water is phenol and the denitrification tank is aerated and / or stirred to remove phenol at the denitrification tank outlet to 30 mg / l or less. DescribedCheapHow to remove nitrogen from water.
(4) The aeration amount of the denitrification tank and / or the rotation speed of the stirrer are adjusted so that the oxidation-reduction potential of the denitrification tank in the biological denitrification process is -100 mV to -300 mV (1) ~ (3) any one ofCheapHow to remove nitrogen from waterLaw.
(5)CheapThe COD component in water is an organic substance and / or a sulfur compound, and the denitrifying bacteria in the denitrifying tank are heterotrophic bacteria and / or sulfur oxidizing bacteria (1) to (4)CheapHow to remove nitrogen from waterLaw.
(6) The microorganism-immobilized carrier is introduced (installed) into the denitrification tank and / or the aerobic tank (1) to (5)ZAs describedCheapHow to remove nitrogen from water.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The inventors have devised the following method in order to remove nitrogen stably and efficiently from wastewater containing a COD component and ammonia. An example of the processing flow is shown in FIG. This is an example of application to wastewater generated from a coke factory (hereinafter referred to as “anshin”) as wastewater containing a COD component and ammonia.
[0026]
First, ammonia concentration is reduced by using an ammonia stripping method for the aqueous water (1), and the COD / N ratio (mass of COD per unit volume / mass of nitrogen per unit volume) is 2 to 3 Adjust to .5. By the ammonia stripping method, there is no need to unnecessarily completely reduce the ammonia in the wastewater, and the COD / N ratio may be reduced to about 2-3.5. Specifically, when the COD concentration is 2000 mg / l, ammonia may be removed so that the ammoniacal nitrogen concentration is 700 mg / l to 1000 mg / l. Steam may be generated in the boiler (7), and ammonia stripping by increasing the water temperature may be applied. When ammonia is present in a large amount and most of it is present as fixed ammonia, the water temperature is raised and an alkaline agent (2) such as sodium hydroxide is added to raise the pH to about 10-11. Also good. The water treated by ammonia stripping in this way often has a considerably high water temperature, so it is cooled with a cooler after heat exchange with the original waste water, or diluted with seawater or industrial water, and 30- It is desirable to set the temperature at 38 ° C. for biological treatment.
[0027]
Next, an operation method of biological treatment will be described.
[0028]
In the aerobic tank (14), nitrate nitrogen and nitrite nitrogen are produced from ammonia by nitrite bacteria represented by nitrozomonas and nitrate bacteria represented by nitrobacter.
[0029]
2NH_Four ⁺+ 3O₂→ 2NO₂ ^-+ 2H₂O + 4H⁺(2)
2NO₂ ^-+ O₂→ 2NO_Three ^-(3)
In the denitrification tank (13), nitrate nitrogen and nitrite nitrogen generated in the aerobic tank (14) are reduced to nitrogen gas using denitrification bacteria (heterotrophic bacteria and / or sulfur-oxidizing bacteria). In order to proceed with the denitrification reaction, organic substances and sulfur compounds are required. Usually, organic compounds and sulfur compounds such as thiosulfuric acid are measured as COD. In practice, since it is difficult to specify all the components in the wastewater, it is realistic to estimate the total amount of organic substances and sulfur compounds using COD.
[0030]
For example, when the organic substance is phenol, the denitrification reaction by heterotrophic bacteria is expressed by the following formula.
[0031]
5C₆H_FiveOH + 28NO_Three ^-            14N₂  + 30CO₂+ H₂O + 28OH^-(6)
In this case, the phenol required for 1 g of nitrogen is 1.2 g. Furthermore, 1 g of phenol is measured as 1.8 to 2.4 g-COD as COD. Therefore, the required COD / N ratio is about 2.2-2.9.
[0032]
Moreover, when performing denitrification using sulfur oxidation bacteria, a sulfur source is required. As a sulfur source, thiosulfuric acid, sulfur granules, sodium sulfite, and the like are used. For example, when the sulfur source is thiosulfuric acid, the denitrification reaction by sulfur-oxidizing bacteria is expressed by the following formula.
[0033]
5S₂O_Three ^2-+ 8NO_Three ^-  + H₂O 4N₂  + 10SO_Four ²+ 2H⁺  (7)
In this case, thiosulfuric acid required for 1 g of nitrogen is 5.0 g. Furthermore, 1 g of thiosulfuric acid is measured as 0.4 to 0.5 g-COD as COD. Therefore, the required COD / N ratio is about 2.0-2.5.
[0034]
From these results, the COD / N ratio is desirably about 2 to 3.5. When the COD / N ratio is higher than 3.5, COD tends to remain and adversely affects the subsequent nitrification reaction. On the other hand, when the COD / N ratio is lower than 2, COD shortage tends to adversely affect the denitrification reaction.
[0035]
More specifically, the COD / N ratio is about 2 to 3 when the COD source is mainly a sulfur compound, and the COD / N ratio is 2.5 to 3 when the COD source is an organic compound such as phenol. It is desirable to set to about .5. Detailed figures will vary slightly depending on the wastewater content.
[0036]
If there are sufficient denitrifying bacteria, the COD component of the wastewater is removed by the denitrification reaction.
However, in the initial stage of startup, the concentration of nitrate nitrogen and nitrite nitrogen generated in the aerobic tank (14) is not sufficient, so the denitrification reaction in the denitrification tank (13) does not proceed, and the COD component A certain phenol or sulfur compound flows directly into the aerobic tank (14). For this reason, acclimatization of nitrifying bacteria in the aerobic tank (14) may not progress at all. In such a case, air is sent to the denitrification tank (13) with a blower, or the rotation speed of the stirrer is adjusted, and in the denitrification tank (13), organic compounds and sulfur compounds are decomposed using oxygen. It is desirable to do. Promoting the growth of nitrifying bacteria in the aerobic tank (14) by aeration and / or agitation of the denitrifying tank (13) to remove COD components having an inhibitory function against nitrifying bacteria in the denitrification tank (13) be able to.
[0037]
When the main component (30% or more) of the COD component in the wastewater is phenol, inhibition of phenol to nitrifying bacteria can be considered. As described above, the inhibitory concentration has been reported to be 5.6 mg / l. However, in the research conducted by the inventors, practically no inhibition of nitrification was observed until the phenol concentration at the denitrification tank outlet was about 30 mg / l. . Therefore, it is desirable to aerate and / or agitate the denitrification tank (13) to remove the phenol concentration at the outlet of the denitrification tank (13) to 30 mg / l or less where inhibition of nitrifying bacteria can be almost ignored.
[0038]
There are the following methods for blowing air in the denitrification tank (12) and / or adjusting the rotation speed of the stirrer. First, the amount of aeration in the denitrification tank (13) and / or the rotational speed of the stirrer so that the redox potential of the denitrification tank in the biological denitrification process is -100 mV to -300 mV (silver / silver chloride composite electrode standard). It is desirable to adjust. If it is less than −300 mV, it is expected that a large amount of COD components are present, which adversely affects the aerobic tank (14). Conversely, if it exceeds -100 mV, residual dissolved oxygen, NO_Three-N accumulation is expected, and there is no adverse effect on the aerobic tank (14), but denitrification reaction will not proceed.
[0039]
More precisely, the COD concentration at the outlet of the denitrification tank in the biological denitrification process is continuously measured, and the denitrification tank is set such that the measured value is a COD concentration that does not inhibit inhibition of nitrifying bacteria. What is necessary is just to adjust the aeration quantity of (13) and / or the rotation speed of a stirrer. However, the COD concentration at the outlet of the denitrification tank (13) must be determined by individual basic experiments because the concentration at which nitrifying bacteria are inhibited varies depending on the type of wastewater.
[0040]
When the COD component in the wastewater is an organic substance, the denitrifying bacteria in the denitrification tank (13) are mainly heterotrophic bacteria, and when the COD component in the wastewater is a sulfur compound, sulfur oxidizing bacteria are the main components. When the main components of the COD component in the wastewater are phenol and sulfur compounds (containing 30% or more respectively), the denitrifying bacteria in the denitrification tank (13) are a mixture of heterotrophic bacteria and sulfur oxidizing bacteria.
[0041]
When the waste water is an aqueous water generated from a coke plant, the main component of the COD component is phenol, and the COD attributed to phenol accounts for 30% or more of the total COD. It is highly desirable to apply the method of the present invention to the low water generated from a coke plant.
[0042]
Further, since nitrifying bacteria are also vulnerable to free ammonia as described above, it is desirable that the concentration of free ammonia in the aerobic tank (14) be 100 mg / l or less. Ammonium ion (NH_Four ⁺) To increase the ratio, it is better that the pH of the aerobic tank (14) is lower. However, if the pH is lowered too much, the nitrifying bacteria are inhibited by the pH, and the oxidation rate of ammonia is lowered. Therefore, it is desirable to maintain the pH of the aerobic tank (14) at 6 to 7.5. If the pH is less than 6, inhibition of nitrifying bacteria due to pH is prominent, and if the pH exceeds 7.5, inhibition of nitrifying bacteria due to free ammonia tends to occur.
[0043]
In addition, although denitrifying bacteria are more resistant than nitrifying bacteria, it is also desirable to control the pH of the denitrifying tank (13) to 6 to 7.5. The pH of normal biological treatment is about 6 to 8.5, and the optimum pH of nitrifying bacteria is about 8. However, this finding cannot be applied to wastewater having an ammoniacal nitrogen concentration exceeding 100 mg / l. The pH control of the reaction tank is much more important than the normal biological treatment method. However, conversely, if pH control is accurately performed, it is possible to stably treat even wastewater with a high ammoniacal nitrogen concentration, which has conventionally been difficult.
[0044]
Although these pH control methods are used, when the apparatus is enlarged and uniform pH adjustment in a denitrification tank or aerobic tank is difficult, the pH of ammonia stripping water (biological treatment inflow water) is adjusted to a denitrification tank ( It is desirable to adjust the pH of the influent wastewater with acid and / or alkali so that the pH of 13) and the aerobic tank (14) is maintained at 6.0 to 7.5.
[0045]
More efficient treatment can be achieved by introducing microorganism immobilization carriers (plastics, ceramics, slag, gel, etc.) into the denitrification tank (13) and / or aerobic tank (14) and increasing the concentration of microorganisms in each tank. Is possible. A sulfur-oxidizing bacterium having a self-granulating action or a sulfur-oxidizing bacterium granulated with a coagulant may be used in the denitrification tank.
[0046]
【Example】
Examples of the present invention will be described below.
(Example) Application to steelworks coke factory water treatment
The method of the present invention was applied to the removal of nitrogen from the safety water generated from the A steelworks coke plant. As shown in Table 1, the water is phenol-based waste water (48% of the total COD is phenol-derived COD), but also contains sulfur compounds. Here, 1 g of phenol was assumed to be 2.4 g-COD. The COD is 6200 mg / l. It also contains 8000 mg / l of ammoniacal nitrogen. The pH is quite high at 9.2.
[0047]
Therefore, first, NaOH (2) as an alkaline agent is added to the water (1), the pH is adjusted to 9.4 to 10.5, the gas-liquid ratio is 3000, and the water temperature is 40 ° C. The ammonia stripping tower (3) Drove. As a result of the ammonia stripping, about 90% of ammonia nitrogen in the water was removed as ammonia gas, and the concentration of ammonia nitrogen in the water became 800 mg / l. As a result, the COD / N ratio was 2.1. The ammonia gas generated by the ammonia stripping was incinerated at 1000 ° C. using a heat storage type decomposition furnace (4) filled with magnetic ceramics.
[0048]
After ammonia stripping, the mixture was diluted about 2.5 times with seawater and / or fresh water (8) in the adjustment tank (10), and phosphoric acid (9) was added. Further, the pH (12) of the denitrification tank (13) and the aerobic tank (14) was measured, and NaOH (2) was added so as to be 6-7.5.
[0049]
Next, the operation method of the biological nitrification-denitrification method is described below.
[0050]
First, the operation method of an aerobic tank (14) is demonstrated.
[0051]
Ammonia nitrogen is oxidized to nitrite nitrogen and nitrate nitrogen by nitrifying bacteria in the aerobic tank (14). In the aerobic tank (14), 15% of the floating cylindrical plastic carrier (inner diameter: 3 mm; length: 4 mm) is introduced (installed or present) per tank volume to attach nitrite and nitrate bacteria. It was. The pH (12) of the aerobic tank (14) was controlled to 6 to 7.5 by adjusting the pH of the inflow raw water as described above. Moreover, it operated so that DO might be maintained at 2 mg / l or more, ORP (20) +150 mV (silver / silver chloride standard) or more, and water temperature at 30 to 38 ° C. by air. As a result, under the condition that the aerobic tank (14) has an HRT (hydraulic residence time) of 24 hours, ammonia nitrogen (800 mg / l) is 80% nitrate nitrogen and 10% nitrite nitrogen. I was able to oxidize. About 10% of ammoniacal nitrogen remained. This nitrification solution was returned to the denitrification tank (12) using a circulation pump (22) twice the amount of raw water.
[0052]
Next, the operation method of the denitrification tank (13) will be described.
[0053]
Heterotrophic bacteria such as activated sludge from sewage were introduced into the denitrification tank (13). The pH (12) of the denitrification tank (13) was controlled to 6 to 7.5 by adjusting the pH of the inflow raw water as described above. Further, the ORP (20) of the denitrification tank (13) was supplied with air by changing the rotational speed of the blower (19) so as to be maintained at -150 to -200 mV (silver / silver chloride standard). The HRT of the denitrification tank (13) was operated under conditions of 12 hours. The phenol at the exit of the denitrification tank (13) was 1 mg / l.
[0054]
A sedimentation basin (15) was installed after the aerobic tank (14) to separate microorganisms and treated water (18). Microorganisms concentrated in the sedimentation basin (15) were returned to the denitrification tank (13) in an amount equal to the amount of raw water by the sludge return pump (15) as return sludge (17). Part of it was scraped off as excess sludge.
[0055]
By the above method, COD of treated water (18) became 120 mg / l and nitrogen became 100 mg / l or less. These results are shown in Table 1.
[0056]
[Table 1]

[0057]
【The invention's effect】
According to the present invention, it is possible to stably remove nitrogen at low cost from a wastewater containing a COD component and ammonia nitrogen in a high concentration by using the COD component in the wastewater.
[Brief description of the drawings]
FIG. 1 is a denitrification process using an ammonia stripping apparatus and nitrifying bacteria and denitrifying bacteria (heterotrophic bacteria and sulfur-oxidizing bacteria).
[Explanation of symbols]
(1) Ansui
(2) Alkaline agent (NaOH)
(3) Ammonia stripping tower
(4) Regenerative ammonia gas decomposition furnace
(5) Circulation blower
(6) Boiler water supply
(7) Boiler
(8) Diluted water (sea water or fresh water)
(9) Phosphoric acid
(10) Adjustment tank
(11) Water supply pump
(12) pH meter
(13) Denitrification tank
(14) Aerobic tank
(15) Sedimentation pond
(16) Nitrification solution
(17) Return sludge
(18) Treated water
(19) Blower
(20) ORP meter
(21) Sludge return pump #
(22) Circulation pump
(23) Nitrogen measuring device
(24) COD measuring device

Claims (6)

After the ammonia liquor containing COD components and ammonia nitrogen to remove ammonia ammonia stripping device so that the ratio of the COD concentration and the nitrogen concentration of Ahn water (COD / N ratio) of 2 to 2.9, Rohm & biological denitrification process with aerobic tank of one stage immediately after the first stage of the denitrification tank, the aerobic tank, and adjusted to pH is maintained from 6.0 to 7.5 , the oxidation of ammonia in water with nitrifying bacteria generate nitrite nitrogen and nitrate acidic nitrogen circulates the water in the denitrification tank, the denitrification tank, pH from 6.0 7.5 adjust so is maintained, by utilizing a cheap water COD components by denitrifying bacteria and nitrite nitrogen and nitrate acidic nitrogen with removed as nitrogen gas, aeration and / or stirring, de Promotes the removal of COD components in the nitrogen tank, and in the aerobic tank Nitrogen method of removing from the safe water, characterized in that to promote the development of nitrifying bacteria Te. Aeration and / or stirring in the denitrification tank, made at the start-up operation, the method for removing nitrogen from ammonia liquor according to claim 1, wherein the decomposing the organic compound or a sulfur compound with oxygen. From principal water COD components is phenol, a denitrification tank and aeration and / or stirring, cheap according to claim 1 or 2, characterized in that the removal of phenol denitrification tank outlet to below 30 mg / l How to remove nitrogen from water. The aeration amount in the denitrification tank and / or the rotational speed of the stirrer are adjusted so that the redox potential of the denitrification tank in the biological denitrification process is -100 mV to -300 mV. A method for removing nitrogen from the cold water. COD components Ahn water is organic matter and / or sulfur compounds, ammonia liquor as claimed in claim 1-4 or, wherein the denitrifying bacteria denitrification tank are heterotrophic bacteria and / or sulfur-oxidizing bacteria To remove nitrogen from water. Method for removing nitrogen from aqueous ammonia according to claim 1-5 Izu Re or characterized by introducing microorganism-immobilized carrier denitrification tank and / or aerobic tank.

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