JP7251526B2 - Method for treating coke oven wastewater - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for treating coke oven wastewater generated during carbonization of coal in a coke oven, and more particularly to biological denitrification treatment of ammoniacal nitrogen contained in coke oven wastewater.

Coke oven wastewater (ammonia water) generated during coal carbonization in coke ovens contains a large amount of chemical oxygen demand (COD) components, which are mainly composed of phenol, and ammonia. Appropriate treatment is required before release.

In Japan, ammonia stripping treatment is mainly performed to reduce the concentration of ammonia in ammonia water, and then biological treatment is performed to decompose COD components. In this biological treatment, aeration or the like is generally performed to dissolve oxygen in the wastewater, and the COD components are removed using biological respiration. Therefore, nitrification from ammonia to nitrite and nitric acid by living organisms, and denitrification by providing an oxygen-free tank, ie, removal of nitrogen components, are expected together with removal of COD components.

For example, Patent Document 1 describes a treatment in which ammonia stripping treatment is followed by a combination of denitrification (oxygen-free)-nitrification (aerobic) nitrifying solution circulating biological denitrification treatment. In addition, in Patent Document 2, in ammonia stripping treatment, denitrification (anoxic) treatment, and nitrification (aerobic) treatment, the ammonia concentration after stripping treatment and the pH of the reaction tank are specified, and high-concentration ammonia A method for the efficient and stable removal of nitrogen from effluents containing toxic nitrogen is described.

In addition, Patent Document 3 describes a method for efficiently and stably removing nitrogen from wastewater containing COD and ammonia nitrogen by specifying the COD/N ratio after stripping in a similar treatment method. there is Further, Patent Document 4 describes that diluting raw water with seawater improves the sedimentation properties of sludge after nitrogen treatment.

Originally, biological nitrogen treatment is a common method in sewage treatment and the like, and many actual facilities are being constructed and operated. However, the treatment of ammonia water has not been widely used because of its strong toxicity and persistent COD components.

For example, Non-Patent Document 1 describes the relationship between the nitrification rate of ammonia-oxidizing bacteria Nitrosomonas and nitrite-oxidizing bacteria Nitrobacter and the pH of the treatment tank. When the ammonia concentration in the tank is high and the pH increases (from 8.3), the amount of free ammonia increases and the nitrifying bacteria are significantly inhibited. In addition, Non-Patent Document 2 summarizes the relationship between the cyanide concentration and the nitrification rate in the raw water, and reports that the nitrification rate decreases as the cyanide concentration increases.

In addition, Patent Document 5 defines the concentration of cyanide and the total nitrogen load to the nitrification tank as well as ammonia nitrogen as conditions for good treatment. Non-Patent Document 3 describes that while phenol and thiosulfate decompose quickly, thiocyanate decomposes slowly and is sensitive to fluctuations in load and treatment conditions, which is a major control item.

Sulfur compounds such as thiosulfuric acid and thiocyanate can be used as hydrogen donors during denitrification. Since the addition of an external hydrogen donor such as methanol can be reduced at the same time as the treatment of sulfur compounds, research is also being conducted on the use of sulfur compounds as hydrogen donors. For example, Patent Documents 6 and 7 describe methods of using thiocyanate as a hydrogen donor during denitrification. Further, Patent Documents 8 and 9 describe that sulfur-oxidizing bacteria are attached to a fixed-bed bioreactor, and sulfur oxides are used as hydrogen donors in denitrification of nitrous acid and nitric acid.

The biggest problem with biological nitrogen treatment of ammonia is that nitrification stops at nitrite. It is widely known that nitrous acid is highly toxic to heterotrophic bacteria and acts as an inhibitor to treatment (see, for example, Patent Document 7). In actual treatment, when oxygen supply becomes excessive, nitrification occurs and ammonia is oxidized to nitrite, but nitric acid is not oxidized due to the toxicity of ammonia water, so nitrite accumulates and the treatment of thiocyanate deteriorates. has been empirically reported. For this reason, as described in Patent Document 10, water quality is improved by adjusting the aeration (oxygen supply) in the aeration tank and controlling the oxidation-reduction potential so that COD decomposition occurs but ammonia oxidation does not occur. Much of the status quo remains.

In addition, since nitrous acid is also detected as COD, it directly causes deterioration of water quality. Non-Patent Document 4 reports that the theoretical COD of nitrous acid is 1.14 g/g, and that 96.5% of the actual COD is detected as COD. On the other hand, since ammonia is hardly oxidized, it is not detected as COD. Nitric acid, which is in a stable form, is naturally not detected as COD.

There are several reasons why the oxidation of ammonia is stopped by nitrous acid in the nitrification reaction of ammonia, one of which is inhibition by thiosulfuric acid. Non-Patent Document 5 confirms that 300 mg/L of thiosulfuric acid acts as an inhibitor in an experiment using artificial ammonia, and that nitrous acid accumulates when thiosulfuric acid is added.

In Patent Document 11, nitrous acid is actively used to stop nitrification by adding a sulfur compound. The ammonia-oxidizing bacterium Nitrosomonas is more resistant than the nitrite-oxidizing bacterium Nitrobacter, it consumes less oxygen when stopped by nitrous acid, which is advantageous in terms of energy, and the number of hydrogen donors required for denitrification is small. advantages are stated. However, since nitrous acid itself is highly toxic, there are many restrictions on the properties of raw water and operating conditions, and it has not been put to practical use.

Non-Patent Documents 7 and 8 also propose a process in which COD components including toxic substances are roughly removed in the former stage, and nitrification and denitrification are carried out in the latter stage. However, in this method, multistage tanks cannot be avoided, and application is limited in terms of construction cost and installation area. Moreover, since most of the COD components are removed in the former stage, almost all of the hydrogen donor for denitrification in the latter stage must be added from the outside, which increases the operating cost. In addition, if the latter stage is performed in the order of nitrification and denitrification aiming at a high nitrogen removal rate, the COD component of the hydrogen donor remaining in the final denitrification process is removed, so further COD removal as described in Patent Document 12 An additional process is required, which also puts pressure on the cost.

JP-A-8-141552 Japanese Patent Application Laid-Open No. 2001-212592 JP-A-2003-53383 JP-A-9-290292 JP-A-9-290296 JP-A-9-290290 JP-A-2001-79593 JP-A-11-299481 JP 2015-136677 A JP-A-54-152351 JP 2005-211832 A

Historical Consideration of Biological Denitrification Method Yasunori Toya, Water and Wastewater Vol.13 No.11 10-22 1971. Application of biological nitrification and denitrification to coke oven effluent Togame et al. Tetsu to Hagane Vol.82 No.5 103-108 1996. Gas-Liquid Treatment Activated Sludge Process Sato et al. Water Treatment Technology Vol.19 No.7 65-71 1978. Effect of Inorganic Nitrogen on CODMn Value in Treated Human Waste Water, etc. Nobuyuki Hayashi Journal of Waste Management Society Vol.4 No.1 84-89 1993. Behavior of nitrite oxidizers in the nitrification/denitrification process for the treatment of simulated coke-oven wastewater Takasaki, Y., et.al. J. Water Environ. Technol. Vol.5 No.1 29-36 2007. Study on Nitrogen Removal from Gas Liquid Sato et al. Water Treatment Technology Vol.21 No.3 41-50 1980. Biological nitrogen removal from coke plant wastewater with external carbon addition. Lee, M. W. et.al. Water Environ. Res. Vol.70 No.5 1090-1095 1998. Control of External Carbon Addition in Biological Nitrogen Removal Process for the Treatment of Coke-Plant Wastewater. Lee, M. W. et.al. Water Environ. Res. Vol.73 No.4 415-425 2001.

As mentioned above, the biological denitrification of ammonia water has not become widespread. The main reason is that ammonia nitrification stops with nitrous acid due to the toxicity of ammonia water, which directly or indirectly deteriorates the quality of treated water.

The present invention has been developed in view of the above circumstances, and an object of the present invention is to provide a method for biologically denitrifying coke oven wastewater with a simple equipment configuration.

The inventors have made various studies to search for a novel technique that can effectively perform biological nitrogen treatment using the ammonia water actually discharged from the factory. Specifically, we constructed a bench plant adjacent to the ammonia water treatment facility, continuously treated the ammonia water over a long period of time, and investigated the treatment behavior of the ammonia water, especially nitrogen behavior, under various conditions. did As a result, by nitrifying the ammonia in the ammonia to nitric acid, the inventors came up with a biological nitrogen treatment method that can stably obtain water quality.

The present invention has been completed based on the above findings, and the gist thereof is as follows.
[1] Coke oven effluent containing ammonia nitrogen is introduced into a denitrification tank having an oxygen-free atmosphere, and the treatment liquid that has passed through the denitrification tank is introduced into a nitrification tank having an aerobic atmosphere to remove ammonia contained in the treatment liquid. After the nitrogen is oxidized to nitrate nitrogen, part of the resulting nitrified liquid is extracted and solid-liquid separated to obtain treated water while the precipitated sludge is returned to the denitrification tank, while the remainder of the nitrified liquid is removed. It is returned to the denitrification tank to denitrify the nitrate nitrogen contained in the nitrification liquid, circulate the coke oven effluent between the denitrification tank and the nitrification tank, and remove ammonia contained in the coke oven effluent. In a method of treating coke oven effluent treated with nitrogen,
The coke oven waste water to be introduced into the denitrification tank is adjusted in advance to have a predetermined water quality, and a sufficient acclimation period is taken in the nitrification tank to cause a nitric acid generation type nitrification reaction to occur in the nitrification tank. A method for treating coke oven wastewater.

[2] The coke oven waste water according to [1] above, wherein the predetermined water quality is 1000 mg/L or less of ammonia nitrogen, a ratio of COD to the amount of COD/removed nitrogen is 2 or more, and 100 mg/L or less of thiosulfate ions. How to handle.

[3] The method for treating coke oven wastewater according to [1] or [2], wherein the acclimatization period is one month or longer.

[4] The method for treating coke oven wastewater according to any one of [1] to [3], wherein the pH of the treatment liquid in the nitrification tank is 7 or more and 8 or less.

According to the present invention, coke oven waste water can be biologically denitrified with a simple equipment configuration.

1 is a flow diagram of a method for treating coke oven wastewater according to the present invention; FIG. FIG. 4 is a transition diagram of the concentration of nitrogen in the nitrification tank in the example of the present invention. FIG. 4 is a transition diagram of nitrogen concentration in a denitrification tank in an example of the present invention. FIG. 4 is a plot of total nitrogen concentrations before and after biological treatment in Examples of the present invention. FIG. 2 is a diagram showing analysis results of phenolic raw water (immediately before biological treatment), denitrification tank, nitrification tank, and treated water in a period when nitric acid generation is dominant in the example of the present invention. FIG. 4 is a diagram showing analysis results of raw water (immediately before biological treatment), denitrification tank, nitrification tank, and treated water of thiocyanate ions in a period when nitric acid generation is dominant in the example of the present invention. FIG. 3 is a diagram showing analysis results of raw water (immediately before biological treatment), a denitrification tank, a nitrification tank, and treated water for thiosulfate ions when nitric acid generation is predominant, in an example of the present invention.

The present invention will be specifically described below. A specific procedure of the present invention is shown in FIG. The following description is based on this procedure. First, ammonia is primarily removed from ammonia water 1, which is coke oven waste water, in an ammonia stripping step 2. Ammonia is removed as exhaust gas 3 . The conditions for the stripping treatment at this time are appropriately determined in consideration of the water quality after the treatment.

The ammonia water 1 after the stripping treatment can be diluted by mixing with seawater or industrial water 4 depending on the water quality, and the subsequent treatment can be performed without dilution. The concentration of ammonia nitrogen in the diluted ammonia water is preferably 1000 mg/L or less. If the ammoniacal nitrogen concentration is 1000 mg/L or less, it is possible to prevent the treated water from becoming toxic due to an increase in free ammonia in the subsequent biological treatment. However, excessive removal of ammonia nitrogen results in an increase in stripping cost, so the operating conditions should be determined by balancing removal performance and cost.

The ammonia water 1 thus prepared is introduced into the subsequent biological treatment process. The subsequent biological treatment process can be a conventional standard nitrifying liquid circulation type biological treatment process. A conventional biological treatment process will be briefly described below.

First, the ammonia-stripped ammonia water 1 is sent to the denitrification tank 5 and added to the nitrification liquid circulated from the nitrification tank 6 in the subsequent stage to the denitrification tank 5 . In the denitrification tank 5, COD components in the added ammonia water 1, mainly organic substances such as phenol, are used to convert nitric acid and nitrous acid contained in the nitrifying liquid into nitrogen gas for denitrification.

At this time, the ratio of COD contained in the ammonia water 1 in the denitrification tank 5 to the amount of nitrogen removed, that is, COD/removed N, is preferably 2 or more, more preferably 3 or more. By setting the value of COD/removed N to 2 or more, it is possible to prevent the shortage of COD with respect to the removed N, and to perform the treatment without adding an organic substance such as methanol from the outside. On the other hand, the value of COD/removed N is preferably 4 or less, more preferably 3.5 or less. As a result, it is possible to prevent the nitric acid and nitrous acid from being completely treated due to an excessive amount of COD. The value of COD/removed N is a value related to COD contained in the ammonia water 1 at the stage of introduction into the denitrification tank 5 .

The denitrification tank 5 is operated under anoxic conditions to allow nitric acid respiration. Therefore, the ammoniacal nitrogen contained in the ammonia water 1 does not react in the denitrification tank 5 and is sent to the nitrification tank 6 in the latter stage by the overflow. In the nitrification tank 6, ammonia nitrogen is oxidized to nitrous acid and nitric acid under aerobic conditions. Nitrogen is removed from the ammonia water by circulating the nitrifying liquid containing nitrate nitrogen after completion of the nitrification reaction through the circulation line 7 to the denitrification tank 5 to denitrify the nitrifying liquid. At the same time, remaining COD components are also aerobically decomposed in the nitrification tank 6 and reduced.

Along with the above circulation, a portion of the nitrifying liquid is introduced from the nitrifying tank 6 into the sedimentation tank 8 and solid-liquid separated to obtain treated water 9 . The sludge precipitated at that time is returned to the denitrification tank 5 as the return sludge 10, and a part of it is withdrawn as excess sludge 11 from the system, thereby increasing the concentration of activated sludge (Mixed Liquor Suspended Solids, MLSS) in the nitrification tank 6. is kept constant.

However, in the conventional treatment of ammonia, various toxic substances are mixed in as described above, so in the treatment in the nitrification tank 6, nitrification is stopped up to toxic nitrous acid. As a result, the nitrification solution containing nitrous acid circulates between the denitrification tank 5 and the nitrification tank 6, causing damage to the microorganisms and deteriorating the quality of the treated water. In particular, the treatment of thiocyanate is likely to be deteriorated by nitrous acid, which poses a problem in terms of operation management. Thiosulfuric acid is known as a major toxic substance that stops nitrification with nitrous acid.

If the nitrifying solution circulation treatment is started with the sludge that is aerated and aerobically treated as the seed sludge, as in the main ammonia water treatment in Japan, nitrous acid is generated and the quality of the treated water deteriorates. However, the inventors have found that if acclimatization is continued while treating Ammonia Water 1 of appropriate water quality for a long period of time, an oxidation reaction from nitrous acid to nitric acid is induced, and the treated water quality is improved.

That is, in conventional aerobic treatment, thiosulfuric acid, which is a nitrification inhibitor, is considered to be aerobically decomposed (oxidized) according to the following formula (1) (for example, patent Reference 11).
_S2O32- ⁺ _2O2 + _H2O → _{2SO42- +} ^{2H +} (1)

Therefore, thiosulfuric acid cannot be decomposed in the denitrification tank 5 under oxygen-free conditions and flows into the nitrification tank 6, inhibiting nitrification and stopping it with nitrous acid, and the accumulated nitrous acid adversely affects COD treatment.

However, when sulfur-oxidizing bacteria capable of using nitric acid are induced by acclimation, thiosulfuric acid can be treated even in the denitrification tank 5 under anoxic conditions according to the following formulas (2) and (3) (for example, , see Patent Document 9).
_{5S2O32- + 8NO3-} + _H2O → _10SO42- ^{+ 4N2} ↑ ₊ ^{2H +} (2)
3S ₂ O ₃ ^2- + 8NO ₂ ^- + 2H ⁺ → 6SO ₄ ^2- + 4N ₂ ↑ + H ₂ O (3)

Since thiosulfuric acid is treated by such sulfur oxidation, the inflow of thiosulfuric acid into the nitrification tank 6 in the latter stage can be significantly reduced, and the nitrification reaction in the nitrification tank 6 can be The reaction can proceed up to However, there is a limit to the processing speed, and sulfur oxidation in the denitrification tank 5 takes a long time in the presence of a large amount of thiosulfuric acid.

According to the study of the inventors, when the retention time in the general denitrification tank 5 is 1 to 2 days, the nitric acid generation type Nitrification reaction is more likely to be induced. The concentration of thiosulfate ions is determined by the sulfur content of coal, stripping conditions, and the like.

When acclimatization is continued, not only thiosulfate but also thiocyanate are processed under anoxic conditions by sulfur-oxidizing bacteria that can utilize nitric acid (see, for example, Patent Documents 9 and 11).

Conventional aerobic sulfur oxidation is as shown in Equation (4) below.
^SCN- _{+ 2O2} + _2H2O → _SO42- + ^CO2 + _NH4 ⁺ (4)

In contrast, the anoxic sulfur oxidation reaction is as shown in Equations (5) and (6) below.
5SCN ^- +8NO ₃ ^- +H ₂ O→5SO ₄ ^2- +5CNO ^- +4N ₂ ↑ +2H ⁺ (5)
3SCN ^- +8NO ₂ ^- +2H ⁺ →3SO ₄ ^2- +3CNO ^- +4N ₂ ↑ +H ₂ O (6)

Furthermore, anoxic sulfur-oxidizing bacteria that cause these reactions are known to have significantly higher resistance to toxic substances such as nitrous acid than bacteria that perform aerobic sulfur oxidation (see, for example, Patent Document 7). ). Therefore, even if the nitrous acid from the nitrification tank 6 is circulated to the denitrification tank 5, it is possible to prevent the treatment of thiocyanate from rapidly deteriorating as in the prior art (see Non-Patent Document 3).

In this way, when coke oven wastewater is treated, nitric acid-producing nitrification can be developed, and denitrification of ammonia nitrogen and treatment of COD can be achieved at a high level.

When acclimatization is performed from conventional aerobic ammoniated water-treated sludge, it is necessary to provide a sufficient acclimatization period. The acclimation period is preferably 1 month or longer, more preferably 3 months or longer.

The pH of the treated liquid in the nitrification tank 6 is an important adjustment parameter. Even if the pH is within the range where biological activity can be maintained, if the pH is too high, depending on the ammonia concentration, free ammonia may increase and toxicity may increase. In addition, the optimum pH of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria is slightly different, and the optimum pH of nitrite-oxidizing bacteria may be slightly lower than that of ammonia bacteria. Therefore, it is necessary to carefully set the pH of the nitrification tank 6, but it is preferable to set the pH to 7 or more and 8 or less, and it is preferable to determine the optimum treatment conditions by making fine adjustments within that range. The pH of the treated liquid in the denitrification tank 5 becomes somewhat higher than that in the nitrification tank 6 due to the increase in alkalinity due to denitrification, but there is no particular need for adjustment and the denitrification reaction is not hindered. . The above pH adjustment can be performed by adding an alkali such as sodium hydroxide.

According to the present invention, in the biological denitrification treatment of ammonia in ammonia water, a simple equipment configuration is used to nitrify to nitric acid that is neither toxic nor has an effect on COD, thereby obtaining treated water quality that is stable for a long period of time. becomes possible. INDUSTRIAL APPLICABILITY The present invention realizes the removal of ammoniacal nitrogen from ammonia water by a practical method, and therefore has great industrial significance.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these.

Coke oven wastewater was treated according to the flow diagram shown in FIG. First, the ammonia water 1 discharged from the coke oven (not shown) is sent to the ammonia stripping process 2, the ammonia contained in the ammonia water 1 is removed as the exhaust gas 3, and the ammonia concentration in the ammonia water 1 is reduced. . Subsequently, without diluting with industrial water or seawater 4, ammonia concentration-reduced ammonia water 1 was subjected to subsequent biological treatment. Prior to this, various operating conditions including the mixing ratio of the coal species to be treated in the coke oven were adjusted, and the water quality of the ammonia water 1 immediately before the biological treatment was adjusted as shown in Table 1.

Ammonia water 1 whose water quality is adjusted as shown in Table 1 is introduced into the denitrification tank 5 as it is, and the nitrate nitrogen contained in the nitrified liquid circulated from the nitrification tank 6 is converted into nitrogen gas using the COD component of the ammonia water 1. Transformed and denitrified. At that time, no external COD source such as methanol was added, but a small amount of rice bran was periodically added as a micronutrient element.

Ammonia water 1 was allowed to overflow from the denitrification tank 5 to the nitrification tank 6, and in the nitrification tank 6, oxygen supplied by aeration was used to carry out a nitrification reaction in which ammonia was converted to nitrate nitrogen. A part of the sludge in the nitrification tank 6 was circulated to the denitrification tank 5 through a circulation line 7, while the rest was introduced to the sedimentation tank 8, where solid-liquid separation was performed. Thereafter, part of the sludge portion was returned to the denitrification tank 5 as returned sludge 10, and the rest was withdrawn as surplus sludge 11. Clear supernatant water in the sedimentation tank 8 was removed out of the system as treated water 9 . Table 2 shows the treatment conditions.

The pH of the treated water in the nitrification tank 6 was controlled to 7.8±0.2 with sodium hydroxide. On the other hand, the pH of the denitrification tank 5 was not controlled. In both the nitrification tank 6 and the denitrification tank 5, the temperature of the treated water was controlled at 30° C. by heating with a heater.

At the start of the treatment, sludge was introduced into the denitrification tank 5 and the nitrification tank 6 from an apparatus in which only COD treatment was performed without nitrification or denitrification. Therefore, for a while after introduction, the ammonia water 1 was not treated, and was circulated between the denitrification tank 5 and the nitrification tank 6 . After about two weeks, a nitrification reaction was observed, so the addition of ammonia water 1 was started, and the amount added was increased to 0.5 and 1 times the set amount, and the treatment was continued.

FIG. 2 shows the transition of the in-tank nitrogen concentration in the nitrification tank 6 when the input amount is 1, that is, when the operation is performed at the set value. As is clear from FIG. 2, almost no nitric acid (NO ₃ —N) is produced in the initial stage of treatment, nitrous acid (NO ₂ —N) is predominant, and most of the nitrogen concentration (TN) in the tank is was accounted for by nitrous acid (NO ₂ -N). However, if acclimatization was continued, nitric acid (NO ₃ --N) began to form after about 2.5 months, and finally a treatment in which nitric acid was dominant was established.

FIG. 3 shows changes in the concentration of nitrogen in the denitrification tank 5 . From FIG. 3, it can be seen that all of the circulated nitrate nitrogen was denitrified, no nitrate nitrogen remained in the tank, and a good nitrogen treatment was carried out.

FIG. 4 shows the nitrogen concentration before biological treatment and the nitrogen concentration after treatment. From FIG. 4, it can be seen that the nitrogen removal rate was around 60-70%, which is the upper limit of the nitrifying liquid circulation system, and good treatment was maintained.

Fig. 5-7 shows phenols (Fig. 5), thiocyanate ions (Fig. 6), and thiosulfate ions (Fig. 7) in the period when nitric acid generation is dominant, raw water (immediately before biological treatment), denitrification tank 5, nitrification tank 6, shows the analysis results of the treated water (4 times in total).

From FIG. 5, it was confirmed that the phenols were used as a COD source for denitrification and were almost completely consumed in the denitrification tank 5 . Further, from FIG. 6, it was confirmed that most of the thiocyanate ions were also consumed for denitrification in the denitrification tank 5, and that thiocyanate ions were oxidized by sulfur-oxidizing bacteria. Similarly, as for thiosulfuric acid, as shown in FIG.

Thus, by appropriately adjusting the water quality of the ammonia water 1 before biological treatment, a nitric acid-producing nitrification reaction could be carried out in the biological nitrogen treatment of the ammonia water. As a result, deterioration of the treatment due to accumulation of nitrous acid can be prevented, and stable treatment of ammonia water can be realized.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to biologically denitrify coke oven waste water with a simple equipment configuration, which is useful in the steel industry.

1 Coke oven wastewater (ammonia water)
2 Ammonia stripping process 3 Exhaust gas 4 Industrial water or seawater 5 Denitrification tank 6 Nitrification tank 7 Circulation line 8 Sedimentation tank 9 Treated water 10 Returned sludge 11 Excess sludge

Claims (3)

Coke oven effluent containing ammonia nitrogen is introduced into a denitrification tank having an oxygen-free atmosphere, and the treated liquid that has passed through the denitrification tank is introduced into a nitrification tank having an aerobic atmosphere to convert the ammonia nitrogen contained in the treatment liquid into nitric acid. After oxidizing to form nitrogen, part of the obtained nitrified liquid is extracted and solid-liquid separated to obtain treated water, and the precipitated sludge is returned to the denitrification tank, while the rest of the nitrified liquid is returned to the denitrification tank. to denitrify the nitrate nitrogen contained in the nitrifying liquid, circulate the coke oven effluent between the denitrification tank and the nitrification tank, and treat the ammonia nitrogen contained in the coke oven effluent. In the method of treating coke oven wastewater,
The coke oven wastewater to be introduced into the denitrification tank is adjusted in advance to have a predetermined water quality, and a sufficient acclimation period is taken in the nitrification tank to cause a nitric acid generation type nitrification reaction in the nitrification tank ,
A method for treating coke oven wastewater, wherein the predetermined water quality is 1000 mg/L or less of ammonia nitrogen, a ratio of COD to the amount of COD/removed nitrogen is 2 or more and 4 or less, and thiosulfate ion is 80 mg/L or less. . The method for treating coke oven wastewater according to claim 1 , wherein the acclimatization period is one month or more. The method for treating coke oven wastewater according to claim 1 or 2 , wherein the treated water in the nitrification tank has a pH of 7 or more and 8 or less.

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