JPH10249393A - Method for simultaneously removing phenol, ammoniacal nitrogen and nitrate nitrogen in waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique by which the phenol, ammoniacal nitrogen and nitrate nitrogen contained in the waste water discharged from the petroleum refining, heavy oil reforming, thermal cracking, etc. SOLUTION: The raw water contg. phenol, ammoniacal nitrogen and nitrate nitrogen is treated by a biological circulation-type nitrating and denitrifying method. In this case, the water to be treated is passed successively through a denitrification tank 1 packed with a suspended filter medium 3 on which phenol-resistant bacteria are immobilized and acclimatized and the nitration tank 2 packed with the suspended filter medium 4 on which nitrating bacteria are immobilized and acclimatized and treated, a part of of the water at the outlet of the nitration tank 2 is obtained as the treated water, a part of the treated water at the outlet of the tank 2 is circulated to a treated water tank 6 through a water dividing tank 5, the raw water and the circulating water are mixed and treated in the denitrification tank 1, and the water is controlled to pH6.5 to 9.0 and the weight ratio of the chemical oxygen demand to nitrate nitrogen to 2 to 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simultaneously removing phenol, ammonia nitrogen and nitrate nitrogen contained in wastewater from an oil refinery or the like.

[0002]

2. Description of the Related Art At a petroleum refinery, wastewater discharged from equipment such as a petroleum refinery, heavy oil reforming / pyrolysis equipment contains phenol, ammonia nitrogen and nitrate nitrogen which are hardly decomposable substances. Etc. are included. Nitrogen is required to be eliminated below the regulation level as a measure of eutrophication in closed water bodies, and phenol is a substance that is regulated for release into water bodies and has an inhibitory effect on biological treatment Therefore, proper treatment of the above-mentioned hardly decomposable substances is one of the important issues in a petroleum refinery.

Conventionally, there has been an activated sludge method using suspended microorganisms as one of the methods for treating wastewater containing phenol having a low concentration of about several tens of mg / l. Biological nitrification and denitrification by suspended microorganisms is applied to the field of human waste treatment and sewage, but it requires a large tank capacity and a large installation area, and there is a problem that nitrifying bacteria with a slow growth rate run off and sludge management is required. It needed to be done carefully.

By the way, phenol has a concentration of 1 to 1.
It is widely known that 3% is a medical drug used as a disinfecting sterilant, and nitrifying bacteria and denitrifying bacteria almost die at the phenol concentration. in this way,
Because phenol has a bactericidal effect on microorganisms, it is considered difficult to treat phenol, ammonia nitrogen and nitrate nitrogen in wastewater containing these at the same time, and phenol is first treated by the activated sludge method. And
Next, the treatment was performed by arranging the nitrification tank and the denitrification tank in this order.
That is, the method does not perform circulation.

In this method, organic substances must be removed for complete nitrification in the first nitrification tank. When organic matter is present, aerobic decomposing bacteria predominate at the entrance of the nitrification tank, and the activity of nitrifying bacteria, which is an autotrophic bacterium, is extremely inhibited.
Must be less than or equal to the degree. However, since there is no organic substance that is a hydrogen donor necessary for the reduction of nitrate nitrogen in the denitrification tank,
For example, it was necessary to inject a whole amount of an organic substance such as methanol in an amount corresponding to the removal of nitrate nitrogen. That is, in this method, the organic matter in the wastewater cannot be used. This method is suitable when the amount of organic matter in the raw water is small, but is difficult to apply when the amount of organic matter is considerable, such as wastewater from an oil refinery.

Further, in this method, in order to completely perform nitrification in the first nitrification tank, the chemical oxygen demand (hereinafter referred to as COD) and the biological oxygen demand (hereinafter referred to as BOD) contained in the raw water. ) Must be removed. COD 20mg / at the entrance of the nitrification tank
At about 1 or more, aerobic BOD-degrading bacteria predominate and the activity of nitrifying bacteria is extremely inhibited. For this reason, wastewater containing a small amount of organic substances having a COD / ammonia nitrogen weight ratio of about 2 or less is targeted. As described above, COD is removed by aerobic treatment, and COD at the entrance of the nitrification tank becomes 2%.
If the amount is set to about 0 mg / l or less, ammonia is oxidized to nitric acid. In addition, in order to promote nitrification at this time, it is necessary that the amount of inorganic carbon used for oxidation is included in an amount corresponding to the amount of ammonia nitrogen. When nitrification is progressing, the weight ratio of the reduction of inorganic carbon / ammonia nitrogen becomes about 1.5 to 2.0. At this time, countermeasures such as injecting an alkali so that the COD decomposed by the aerobic treatment is dissolved in the wastewater as inorganic carbon are taken. Further, in the subsequent denitrification tank, it is necessary to inject an organic substance such as methanol several times the stoichiometric amount as a hydrogen donor for reducing nitric acid to nitrogen gas. For example, in the case of methanol, 3 g-methanol / g-nitrogen nitrate is injected.
This method can be said to be a method that can be effectively applied when the amount of organic matter in the raw water is small. This method is suitable when the weight ratio of COD / nitrate nitrogen is less than about 2 in the composition of raw water, but it is difficult to apply to a petroleum refinery where the weight ratio is 2 or more and 10 or less.

Under these circumstances, the biological nitrification and denitrification method using suspended microorganisms is carried out at 50 to 500 mg / phenol as phenol.
Even if it is directly applied to wastewater treatment of a petroleum refining plant containing 30 to 50 mg / l as nitrogen and ammonia nitrogen, there is a problem that the treatment of water becomes unstable due to severe fluctuations in the water quality of the wastewater and sludge management is difficult. It was expected and had not yet been put to practical use.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a petroleum refinery,
It is an object of the present invention to provide a rational technique capable of simultaneously processing phenol, ammonia nitrogen, and nitrate nitrogen contained in wastewater discharged from equipment such as a heavy oil reforming / pyrolysis apparatus.

[0009]

The present invention has been made in view of the above circumstances, and the object of the present invention is achieved by the following means. That is, the present invention provides (1) a method for treating raw water containing phenol, ammonia nitrogen and nitrate nitrogen by a biological circulation type nitrification denitrification method, wherein the treated water is adhered to phenol-resistant denitrifying bacteria. And treated through a denitrification tank filled with the floating filter medium filled therein and a nitrification tank filled with the floating filter medium adhering to the nitrifying bacteria to obtain treated water from the outlet of the nitrification tank and treatment at the outlet of the nitrification tank. A method of circulating a part of the used water to a denitrification tank, mixing the raw water and the circulating water and treating the mixed water as water to be treated, wherein the pH of the mixed water to be treated is 6.5 or more and 9.0 or less. Adjust, and
A method for simultaneously removing phenol, ammonia nitrogen and nitrate nitrogen in wastewater, wherein the weight ratio of chemical oxygen demand / nitrate nitrogen in the water to be treated is adjusted to 2 to 10,
(2) The concentration of nitric acid in the treated water at the outlet of the denitrification tank is 3 mg /
Including the method for simultaneously removing phenol, ammonia nitrogen and nitrate nitrogen in wastewater as described in (1) above, wherein an organic substance is injected into the water to be treated so as to be 1 or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have determined that a phenol concentration of 500
The present inventors have found that if the amount is not more than about mg / l, it is possible to biologically perform the denitrification treatment, and have reached the present invention.

According to the present invention, as shown in FIG. 1, the water to be treated is treated in the order of a denitrification tank and a nitrification tank, a part of the treated water in the nitrification tank is extracted as treated water, and the remaining treated water is mixed with raw water. Water to be treated.

The symbols and units representing the water quality used in the following description are as follows. Regarding the unit of the concentration of water quality, biological oxygen demand (hereinafter, referred to as BOD), chemical oxygen demand (hereinafter, referred to as COD), total nitrogen (hereinafter, referred to as COD)
TN), ammonia nitrogen (hereinafter referred to as NH ₄ ⁺ -N), nitrate nitrogen (hereinafter referred to as NO ₃ ^-- N), nitrite nitrogen (hereinafter referred to as NO ₂ ^-- N) And the unit of inorganic carbon (hereinafter referred to as IC) is mg / l, and their weight ratios, for example, COD / NO ₃ ⁻ −N, IC / NH ₄ ⁺
-N is dimensionless. TN is NH ₄ ⁺ -N, NO
It is the sum of ₃ ^-- N and NO ₂ ^-- N. Further, the phenol of the present invention is meant to include a phenol derivative.

In the present invention, the floating filter medium to be filled in the denitrification tank and the nitrification tank is of a high molecular weight that is lighter than water, is a known material such as polypropylene, polyethylene, etc., and is not particularly limited as to whether or not it is foamed. . Although the shape is not particularly limited, the particle size distribution is 5 mm to 15 mm.
Are usually selected.

Activated sludge is attached to the floating filter medium, and the denitrification tank is operated independently in a one-pass system to gradually increase the phenol concentration of the raw water from a low concentration so as to have phenol-resistant assimilation characteristics. Can be acclimated. Nitrifying bacteria can be phenol-resistant if the nitrification tank is operated alone in a one-pass system and acclimated. Even if it is not a one-pass system but a recirculation system, recuperation is possible. Incidentally, the denitrifying bacteria and the nitrifying bacteria are bacteria present in so-called activated sludge, and can be collected from a usual activated sludge treatment device.

[0015] When a biofilm is formed on the surface of the filter medium as in the method of the present invention, the microorganisms tend to have resistance to phenol. Since the bacterium has a certain thickness and adheres to the floating filter medium, the whole bacterium does not die. This is because some of the bacteria on the surface that directly comes into contact with phenol in the wastewater are killed, but bacteria existing in the thickness formed from the surface to the floating filter medium are alive. Furthermore, the bacteria on the surface may be almost completely killed due to the phenol concentration in the initial stage, but the bacteria on the dead surface will peel off and new bacteria will appear on the surface. Phenol resistance develops. In the circulating nitrification denitrification method according to the present invention, denitrification bacteria can almost completely decompose phenol in the denitrification tank, and therefore, in the next nitrification tank, phenol inhibition on nitrification bacteria is reduced.

In the present invention, the denitrification tank and the nitrification tank are connected in the order of the denitrification tank and the nitrification tank, and a part of the treated water treated in the nitrification tank is circulated to the denitrification tank so that phenol and ammonia nitrogen and nitrogen are removed. The nitrate nitrogen is removed at the same time.

In the denitrification tank, phenol is used as a hydrogen donor for reducing nitrate nitrogen under anaerobic conditions, and phenol is removed and nitrate nitrogen is converted to ammonia nitrogen. In the above-described method of processing in the usual order of aerobic treatment, nitrification, and denitrification, phenol, which is an organic substance, is removed at the stage of aerobic treatment, and it is necessary to newly add an organic substance such as methanol in denitrification. However, in the present invention, phenol can be used as a hydrogen donor required for denitrification, so that it is not necessary. Total amount of phenol in raw water and COD other than phenol
In addition, it is used in a denitrification tank for the reduction of NO ₃ ⁻ -N. In a denitrification tank, phenol works effectively as a hydrogen donor at 500 mg / l or less, and does not differ from other organic substances. Organic matter may be insufficient in the treatment of the water to be treated having a high content of nitrate nitrogen, and methanol or the like is added.
The biochemical reaction equation in the denitrification tank is represented by the following equation.

[0018] The formula _{5C 6 H 5 OH + 28NO 3} - → 14N 2 + 30CO 2 + H 2 O + 28OH - (1)

This biological reaction does not depend much on the pH, and if the pH in the denitrification tank is in the range of 6.0 to 9.0, it is almost the same. However, in order to absorb carbon dioxide gas generated by the decomposition of COD as bicarbonate ions, it is necessary to maintain the pH at 6.5 or higher by injecting an alkali agent such as sodium hydroxide, sodium bicarbonate, or calcium hydroxide. is necessary. However, even if the pH is too high, there is a limit to the amount of dissolved carbonic acid.
It is not effective because H becomes high. When the pH at the entrance of the denitrification tank is adjusted to 6.5 to 9.0, carbonic acid when COD is decomposed effectively dissolves and the amount of IC increases.

The concentration of phenol in the water to be treated is 500 m
The treatment can be performed up to about g / l, and at the outlet of the denitrification tank, the treatment is performed at 1 mg / l or less as shown in Example 1 described later. This makes it possible to eliminate the biological inhibition of phenol from nitrifying bacteria in the nitrification tank oxidizing ammonia.

In the present invention, the composition and concentration of the circulating water returning from the nitrification tank to the denitrification tank have the same composition and concentration as the treated water. When high-concentration raw water flows in, it is diluted and then treated with circulating water, so that fluctuations in the raw water concentration are alleviated and the denitrification and nitrification treatment is stabilized. In the nitrification tank, the ammonia nitrogen is oxidized to nitrate nitrogen by the action of nitrifying bacteria according to the following equation (2). The nitrate nitrogen is contained in the circulating water and sent to the denitrification tank, where it is used for the treatment of phenol and organic substances in the wastewater.

[0022] Formula ^{_{NH 4 + + 2O 2 → NO}} 3 - + 2H + + H 2 O (2)

In the ordinary nitrification and denitrification method using suspended microorganisms,
In the denitrification tank, the nitrogen load per volume is 0.3
kg-N / m ³ · d, 0.15 kg in a nitrification tank
-N / m ³ · d, the nitrogen load per filter medium volume in the present invention is 1.0 kg-N /
m ³ · d or less, and 0.3 kg-N
/ M ³ · d or less. Although it is possible to further reduce the size of the equipment by applying a load more than that, it is not preferable to apply an excessive load in order to perform stable processing with little load fluctuation. The nitrogen load per filter medium volume is the amount of nitrogen to be processed per unit time per unit filter medium volume.

The ratio of circulating water to raw water is referred to as a circulating ratio r. Nitrogen nitrogen is supplied to the denitrification tank by circulating a part of the outlet effluent of the nitrification tank at a circulation ratio r. In the recirculating denitrification nitrification method of the present invention, if the respective treatments in the denitrification tank and the nitrification tank are completely performed, the total nitrogen concentration which is the total of ammonia nitrogen and nitrate nitrogen, the removal rate of TN, η is It is given by the following equation.

Equation η = r / (r + 1) (3)

From this equation, for example, when the removal rate is 80%, r = 4. Total nitrogen concentration of raw water, TN 40mg / l
Then, when the treatment is performed at a removal rate of 80%, the total nitrogen concentration and TN of the treated water are reduced to 8 mg / l. Thus, the circulation ratio r
Is determined by the total nitrogen concentration of the raw water, TN and the total nitrogen concentration at the outlet of the nitrification tank, TN. Although r can be determined at the time of design, 2 to 6 are usually selected. When r is less than 2, the nitrogen removal rate drops to about 66% or less by 2/3 from the equation (3) and is not so effective. When it exceeds 6, the pressure loss in the fixed bed tends to increase, and in the nitrification tank, Of nitrifying bacteria is undesirably increased.

When the nitrogen concentration of the raw water fluctuates greatly, there is also an operation method in which the circulation ratio is adjusted by equipment. That is, when the nitrogen concentration of the raw water is low, the flow rate of the circulation pump is reduced to prevent an unnecessary circulation amount from flowing, and when the nitrogen concentration is high, the circulation amount is increased.

In order for nitric acid to be sufficiently reduced to nitrogen gas in the denitrification tank and COD to be removed satisfactorily, COD / NO ₃ ⁻ −N
Must be adjusted to 2.0 or more and 10.0 or less. If it is less than 2.0, it is necessary to inject an organic substance such as methanol. If it exceeds 10.0, undecomposed COD may flow into the nitrification tank and inhibit nitrification. Note that 10.0
Pre-aeration to reduce COD
D / NO ₃ ^- the weight ratio of -N to be processed by the circulating nitrification denitrification to 10 below. When it becomes 10.0 or more and about 20.0, nitrogen removal is desirably performed by a usual aerobic treatment method.

At the entrance of the denitrification tank, the pH was
Decomposed by adjusting the pH to 6.5 to 9.0
D is efficiently converted to an IC. When the nitrification in the nitrification tank is good, the weight ratio of the decrease of IC and the decrease of ammonia nitrogen is taken, that is, IC / NH ₄ ⁺ −N becomes 1.5 or more and 2.0 or less. In the method of the present invention, COD in wastewater in a denitrification tank can be used for reduction of nitrate nitrogen,
Since the IC produced by the decomposition of COD is used for oxidizing ammonia nitrogen in the nitrification tank, it is resource saving.

A change in pH occurs as the biochemical reaction proceeds. In the reaction in the nitrification tank, as shown by the equation (2), hydrogen ions are generated, and the pH decreases from the lower part to the upper part of the floating filter medium tank. The optimum pH of nitrifying bacteria is said to be optimal around 8, so it is desirable to make the pH optimal from the lower part to the upper part of the filter medium tank. The reaction in the denitrification tank generally includes a plurality of types of substances in the wastewater, and in such a case, the reaction cannot be expressed by the reaction formula such as the formula (1). However, since the organic substance serves as a hydrogen donor to reduce nitric acid, it can be expressed by the following formula.

Formula 2NO ₃ ⁻ +10 [H] → N ₂ + 4H ₂ O + 2OH ⁻ (4) where [H] is hydrogen supplied from a hydrogen donor.

Since hydroxyl ions are generated from this formula,
Should actually rise, but in practice the pH does not change much. This is probably because organic substances are decomposed to generate bicarbonate ions instead of eliminating nitrate ions. When an alkaline agent is injected at the entrance of the denitrification tank to make the pH 6.5 to 9.0 in order to dissolve the bicarbonate ions, the pH at the exit of the denitrification tank becomes about 8 to 9. This means that the optimal p
It is effective in maintaining H.

If the water quality fluctuates or the COD in the water to be treated is small and insufficient compared to the amount of nitrate nitrogen contained, nitric acid remains at the outlet of the denitrification tank. And if the nitric acid concentration is too high,
It is necessary to inject an organic substance such as methanol as a carbon source. COD / N for Reaction Scheme (4) to Properly Proceed
The weight ratio of O ₃ ⁻ —N is 2.0 to 10.0. 2.0
When the amount is less than the above, the amount of the organic matter is small, so that the nitric acid is not completely reduced and remains. When the amount exceeds 10.0, the organic matter flows into the nitrification tank and inhibits the activity of the nitrifying bacteria.

In the present invention, it is determined whether or not COD is insufficient by measuring the nitrate nitrogen concentration at the outlet of the denitrification tank. If COD is insufficient, a method of injecting an organic substance such as methanol is used. 10mg of total nitrogen in treated water
/ L or less, it is desirable that the nitrate nitrogen concentration at the outlet of the denitrification tank be 2 mg / l or less. 2mg / l
When the temperature exceeds, nitric acid gradually accumulates in the circulating water, and the nitric acid concentration tends to increase. Note that a method of calculating and injecting an amount of methanol or the like by continuously measuring COD in raw water is also possible, but it is not always an effective method because it is complicated.

FIG. 1 is a conceptual diagram showing an embodiment of the present invention. Needless to say, the present invention is not limited to this.

The preparation of denitrifying bacteria and nitrifying bacteria, which is a preparation for starting up, was performed by one of the above-described procedures. The denitrifying bacteria were attached to the floating filter medium 3 and the floating filter medium 4 filled in the nitrification tank 2, respectively.

Hereinafter, description will be made with reference to FIG. Phenol 50-500 mg / l and ammonia nitrogen as 3
0-50mg / l and 30-50m as nitrate nitrogen
Raw water containing g / l is supplied to a raw water tank 8 through a line 9, and fluctuations in the flow rate and concentration of the above components are mitigated in the raw water tank 8. After the circulating water circulated in the line 10 from the raw water tank 8 and in the line 16 from the water separation tank 5 merges in the water tank 6 to be treated,
Through the line 11, the air is supplied to the denitrification tank 1 filled with the floating filter medium 3 in an upward flow at a superficial velocity of 0.5 to 5 m / s. The same applies to the nitrification tank 2 filled with a floating filter medium 4 described later. In the denitrification tank 1 and the nitrification tank 2, the floating filter medium 3 and the floating filter medium 4 form a so-called extrusion flow. Therefore,
Unlike the complete mixing tank having no floating filter medium, the reactions of the above-described formulas (1) and (2) are easy to proceed, and thus are preferable. In addition, in this invention, although it can implement also with an upward flow and a downward flow, the upward flow is especially preferable. The filter media layers in the denitrification tank 1 and the nitrification tank 2 are closed by the denitrifying bacteria and nitrifying bacteria grown in the floating filter medium 3 and the floating filter medium 4, and the pressure difference in the tanks increases. In order to operate while detecting the differential pressure for moving to the backwashing step, an upward flow is preferable. Although a downward flow can be caused by gravity flow, the water level rises due to the pressure loss of the filter medium layer, which is not preferable. The backwashing operation is performed by a known method.

The raw water contains phenol, ammonia nitrogen and nitrate nitrogen, and contains the above-mentioned line 16
The circulating water from contains mainly nitrate nitrogen. These are mixed in the treated water tank 6 and denitrification tank 1
Sent to The nitrate nitrogen is converted from the nitrate nitrogen to nitrogen in the denitrification tank 1. At this time, the phenol is eaten by the denitrifying bacteria as a COD source as shown in the above formula (1), and becomes approximately 1 mg / l or less at the outlet of the denitrification tank 1. On the other hand, the ammonia nitrogen passes through the denitrification tank 1 at almost the same concentration, and the water to be treated passes through the line 13 and is guided to the nitrification tank 2 by a pump (not shown in this figure). In the nitrification tank 2, ammonia nitrogen is converted into nitrate nitrogen by nitrifying bacteria as shown in equation (2).
The superficial velocity in the nitrification tank varies depending on the nitrogen concentration and the circulation ratio, but is about 1 to 5 m / h. In addition, the water supply from the denitrification tank 1 to the nitrification tank 2 is set such that the water surface of the denitrification tank 1 is two times larger than that of the nitrification tank 2.
By increasing the height by 0 to 30 cm, the pump can be omitted due to gravity flow due to the difference in water level, and power can be saved.
In the drawing, reference numeral 20 denotes a chemical injection facility for adding methanol to the line 11, reference numeral 21 denotes a chemical injection facility for adding an alkali to the line 11, reference numeral 22 denotes a nitrate ion detector, and reference numeral 23 denotes a pH meter.

The outlet waste water of the nitrification tank 2 is sent to a water separation tank 5 by a line 14 and separated into circulating water and treated water in the water separation tank 5. The circulating water passes through the line 16 to the denitrification tank 1 in a circulation ratio r.
Sent by When the COD in the circulating water is insufficient, for example, methanol is supplied to the water tank 6 to be treated, and the concentration of nitrate nitrogen at the outlet of the denitrification tank 1 is 3 mg / l or less, preferably 2 m / l.
g / l or less. The supply method may be manual or automatic, but automatic injection is preferred. Sodium hydroxide is supplied as an alkaline agent to the water tank 6 to be treated, and the pH at the inlet of the denitrification tank 1 is adjusted to 6.5 to 9.0. By adjusting this pH, the denitrification tank 1
In the above, carbon dioxide generated when the COD component used in the formula (3) is decomposed dissolves in the liquid as bicarbonate ions. Although not shown in this figure, as in the treatment of the wastewater from a petroleum refinery, an injection facility for potassium phosphate as a nutrient and an iron salt for preventing hydrogen sulfide can be further provided. In this case, phosphorus is not contained in the raw water, and therefore depends on the chemical injection. However, the amount thereof is required to be a minimum and phosphorus of 1 to 2 mg / l or less per raw water may be given as a nutrient salt.

The drainage water from the outlet of the nitrification tank 2 is separated into circulating water and treated water in a water separation tank 5. The circulating water has been described above. On the other hand, the treated water is discharged out of the system through the line 15. If necessary, the treated water is sent to a sedimentation tank (not shown), and solid-liquid separation of the treated water is performed, so that clearer treated water is obtained. The settled sludge containing nitrifying bacteria from the settling tank can be returned to the nitrification tank 2. Since nitrifying bacteria are slow-growing bacteria, returning the nitrifying bacteria to the nitrification tank 2 is an effective method. Ammonia, which is a nutrient of nitrifying bacteria, can be injected until the amount of cells becomes sufficient and the treatment becomes stable.

The clearer treated water from the settling tank is discharged as effluent, which is not shown in this figure,
The discharged water can also be used as backwash water for the denitrification tank 1 and the nitrification tank 2.

[0042]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1 An experiment was conducted using the apparatus shown in FIG. The denitrification tank 1 and the nitrification tank 2 have an inner diameter of 100 mm and a height of 3.7 m, respectively.
A polypropylene filter material having a particle size distribution of 5 mm to 15 mm and a height of 3 m was filled therein.
Raw water uses wastewater containing only phenol and ammonia,
Nitrifying bacteria and denitrifying bacteria were obtained by adding activated sludge obtained from an ordinary treatment plant as a seed sludge to a nitrification tank and a denitrification tank, and adhered to a floating filter medium for acclimation. In the acclimatization operation, the treatment is started with a mixture of glucose and ammonia as raw water, and the phenol concentration of the raw water is gradually increased to make it phenol-resistant. In the denitrification tank, the denitrifying bacteria and in the nitrification tank, the nitrifying bacteria, respectively. Nourished. Finally, the mixed waste water which became 100% using only ammonia and phenol as hydrogen donors was treated.
Table 1 shows the conditions and results.

[0044]

[Table 1]

In this example, since sodium bicarbonate is injected as an alkaline agent, the pH and IC are high. Some of the phenol is removed by sludge when the reduced and circulating water mix at the entrance of the denitrification tank.

Example 2 An experiment was conducted using the same apparatus as in Example 1. The denitrification tank 1 and the nitrification tank 2 have an inner diameter of 350 mm and a height of 4.2, respectively.
m, a floating filter medium made of polypropylene having a particle size distribution of 5 to 15 mm was filled therein to a height of 2.4 m. In the acclimatization operation, seed sludge containing denitrifying bacteria was first injected into the denitrification tank 1. Raw water containing phenol, ammonia and nitric acid shown in Table 2 was directly added to a relatively low superficial velocity of 0.2 m /
In h, water was passed in a one-pass system. CO at denitrification tank 1 outlet
The treatment was carried out at a D concentration of about 20 mg / l, a decrease in nitric acid concentration was observed, and denitrifying bacteria which had phenol resistance and were compatible with actual wastewater were acclimated. In addition, the superficial superficial velocity at the time of recuperation during circulation operation was also set to 0.2 m / h. Also in the nitrification tank 2, seed sludge containing nitrifying bacteria was injected, and the effluent from the denitrification tank was introduced to start the treatment. The superficial tower speed was 0.2 m / h, and it was confirmed that the nitrification bacteria had acclimated due to the decrease in the outlet ammonia concentration in the nitrification tank 2. He was acclimated at the same time. P at the entrance of the denitrification tank
H is 6.8, COD / NO ₃ ^- -N was 5.3. Table 2 shows the operating conditions and results. Although the treatment of wastewater having a constant water quality is shown in the first embodiment, factory wastewater is accompanied by fluctuations in water quality. In this example, the chemical solution was manually injected to cope with this variation.

[0047]

[Table 2]

[0048] In the denitrification tank COD / NO ₃ ^- -N nitrate body nitrogen for higher and 5.3 is equal to or less than sufficiently removed 2 mg / l. At the outlet of the denitrification tank, the concentration of phenol is zero and there is no effect on the nitrification tank, and the ammonia at the inlet of the nitrification tank is almost changed to nitric acid.

Comparative Example 1 This comparative example is an example in which raw water having a low COD is continuously treated in the continuation of Example 2. Table 3 shows the operating conditions and results. In this example, the COD of raw water is 11 mg / l, COD / T
N is 0.25, COD / NO ₃ denitrification tank inlet ^- -N is less there in the water to be treated organic matter 0.8. For this reason, nitric acid in the denitrification tank is not so much removed from 12.1 to 9.9 mg / l. Although the pH was not necessarily high, sufficient IC for oxidizing ammonia was secured. The nitric acid tank had an IC / NH ₄ ⁺ -N of 1.5, and ammonia was sufficiently removed to form nitric acid. However, the nitric acid accumulated during the circulation treatment and the concentration increased. It is necessary to add methanol and the like as organic matter to the denitrification tank.

[0050]

[Table 3]

[0051]

The present invention removes phenol and nitrate nitrogen by using phenol in wastewater as a hydrogen donor for nitrate nitrogen in a denitrification tank, and converts ammonia nitrogen not treated in the denitrification tank to nitrate nitrogen in a nitrification tank. In order to return a part of the treatment liquid to the denitrification tank again, the following effects can be obtained. (1) Phenol, ammonia nitrogen and nitrate nitrogen contained in wastewater from an oil refinery can be simultaneously treated. The phenol in the wastewater acts as a hydrogen donor, which is a resource-saving process. (2) Even if there is a fluctuation in the above components in the waste water, the raw water is diluted to circulate the treated water. (3) By changing the circulation ratio, the quality of the discharged water can be arbitrarily changed. Although the circulation ratio changes depending on the nitrogen removal rate, the minimum circulation ratio required can be selected. (4) It is a space-saving process. Since the nitrogen load can be larger than that of the conventional suspended microorganisms, space can be saved. (5) An energy-saving process. Although circulating fluid pump power is required, denitrification tanks do not require aeration and power is saved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Denitrification tank 2 Nitrification tank 3, 4 Floating filter medium 5 Separation tank 6 Water tank to be treated 8 Raw water tank 9-16 lines 20 Chemical injection equipment (methanol) 21 Chemical injection equipment (alkali) 22 Nitrate detector 23 pH meter

Claims (2)

[Claims] 1. A method for treating raw water containing phenol, ammonia nitrogen and nitrate nitrogen by a biological circulation type nitrification and denitrification method, wherein the treated water is provided with a phenol-resistant denitrifying bacterium attached to the floating filter medium. The treatment is carried out by passing through a filled denitrification tank and a nitrification tank filled with a floating filter medium to which nitrifying bacteria have been adhered and acclimated, to obtain treated water from the nitrification tank outlet, and one of the treated water at the nitrification tank outlet. The raw water and the circulating water are mixed and treated as water to be treated, wherein the pH of the water to be treated is adjusted to 6.5 or more and 9.0 or less, and A method for simultaneously removing phenol, ammonia nitrogen and nitrate nitrogen in wastewater, wherein the weight ratio of chemical oxygen demand / nitrate nitrogen in the water to be treated is adjusted to 2 to 10. 2. The phenol and ammonia nitrogen in the wastewater according to claim 1, wherein an organic substance is injected into the water to be treated so that the concentration of nitric acid in the treated water at the outlet of the denitrification tank becomes 3 mg / l or less. And a method for simultaneously removing nitrate nitrogen.