JP2001058197A - Treatment of wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently treat ethanolamine without forming a hardly biologically decomposable substance and to reduce the total nitrogen amt. of wastewater by preliminarily decomposing ethanolamine under an anaerobic condition by microorganisms before decomposing hydrazine. SOLUTION: Wastewater discharged from the secondary system of a PWM atomic power plant is treated by the process shown by a drawing. In the drawing, activated sludge is charged in a first anaerobic decomposition tank 1, a first aerobic decomposition tank 2, a second anaerobic decomposition tank 3 and a second aerobic decomposition tank 4. A separation membrane S5 for solid-liquid separation is connected to the second aerobic decomposition tank 4 to subject a treated liquid mixed with activated sludge to membrane separation. As the separation membrane S5, an immersion type membrane separator is used and continuous operation is performed at a filtering speed of 500 l/ m2.day. As a result, microorganisms in the respective tanks can be stably kept high in concn. and wastewater can be treated even if ethanolamine and hydrazine are contained in high concn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating ethanolamine-containing wastewater discharged from a heat exchanger or the like in a nuclear power plant or a thermal power plant.

[0002]

2. Description of the Related Art Conventionally, hydrazine (N ₂ ) is used as a rust inhibitor in a heat exchanger coolant used in a nuclear power plant or the like.
H ₄ ) and ammonium ion (NH ₄ ⁺ ) were added together. However, for this application, ethanolamine having a greater rust-preventing effect has begun to attract attention, and it is expected that a combination of hydrazine and ethanolamine will be used instead in the future. When a rust inhibitor containing ethanolamine is added to the coolant passing through the heat exchanger, ethanolamine is naturally contained in blow water discharged from the heat exchanger constantly or irregularly. come. However, ethanolamine increases the concentration of COD (Chemical Oxygen Demand), an environmentally regulated substance, and must be treated in some way before being discharged.

As a method for treating ethanolamine, a wet catalytic oxidation method, a submerged combustion method, and the like have already been proposed, but have not yet reached practical use at present. In addition, there is no report on the treatment method using microorganisms without any success.
Therefore, in order to overcome these unresolved problems, the present applicant (Mitsubishi Heavy Industries, Ltd.) has previously reported Pseudomonas sp. As a microorganism that decomposes ethanolamine in wastewater. Found that it has the ability, and it was found that Pseudomonas sp. Aerobically acting to decompose and remove ethanolamine was proposed (Japanese Patent Application No. Hei 8-214445).
No. FIG. 3). Further, when hydrazine coexists in the ethanolamine-containing wastewater, hydrazine is a reducing agent, so that when its concentration is increased, the activity of microorganisms, particularly aerobic microorganisms, may be greatly inhibited. Therefore, when ethanolamine in wastewater is decomposed by microorganisms, it is necessary to lower the hydrazine concentration to a predetermined value or less in advance. For that reason, a treatment method for decomposing and removing hydrazine by pretreatment has also been proposed. Together).

Hereinafter, the processing method proposed by the present applicant will be described with reference to FIG. FIG. 3 schematically shows what is described in the application specification.
Each code and name is not identical to that described therein. That is, the ethanolamine-containing wastewater a in which hydrazine coexists is introduced into the neutralization tank 11, and a copper compound k, for example, copper sulfate, is added so that the concentration thereof becomes about 0.1 mg / l. PH 8 ~
After the adjustment, the hydrazine in the wastewater is converted into nitrogen gas (N) by adding an oxidizing agent j, for example, hydrogen peroxide so that hydrogen peroxide / hydrazine (molar ratio) = 2.4. ₂ ) and water (H ₂ O). The treatment liquid after the hydrazine is decomposed and removed is led to the mixing tank 12, and a nutrient c, for example, phosphoric acid is added so that BOD: phosphoric acid (weight ratio) in the wastewater becomes 100: 2, and sodium hydroxide is added. After adjusting the pH to about 7 with a neutralizing agent b ′ such as Pseudomonas sp. Is guided to the aeration tank 13 where the inhabitants live. The neutralizing agent b ′ and the nutrient c may be added to the wastewater in the pipe on the way from the mixing tank 12 to the next aeration tank 13. The mixture 1 flowing into the aeration tank 13 is appropriately diluted with water and aerated with air f, whereby ethanolamine in the mixture 1 is converted into carbon dioxide (C
O ₂ ), water (H ₂ O), and ammonia (NH ₃ ), and this ammonia is finally converted to nitrate ions (NO ₃ ⁻ ) by nitrifying bacteria. The biologically treated water after the aeration treatment as described above is guided to the sedimentation tank 14 to settle and separate, thereby draining the treated water m, and a part of the generated sludge as returned sludge n '. 13 and the remainder is discharged out of the system as excess sludge n.

[0005] Table 1 shows that Pseudomonas sp. Is the experimental result obtained when ethanolamine was decomposed by using the test no. Experiment No. 1 was conducted when hydrazine was present in the wastewater. 2 shows the case where hydrazine does not exist in the waste water.

[0006]

[Table 1]

However, according to this treatment method, most of the hydrazine can be removed in the pretreatment step. Here, ethanolamine and a part of the hydrazine react under aerobic conditions, and biodegradation occurs. Can not do,
Biorefractory substances, including 1H-imidazole, piperazine, dimethylpiperazine, nitro-1H pyrazole and other unidentified substances, are by-produced, all of which appear as COD. As a result, as shown in Table 1, it was found that despite the fact that most of the ethanolamine was decomposed in the subsequent biological treatment step, COD remained as apparently untreated in the biologically treated water as if it had not been treated. It was also found that ammonium ions generated by the decomposition of ethanolamine were oxidized to nitrate ions, but the total nitrogen (TN) was hardly reduced. Here, total nitrogen and ammonium nitrogen (NH ₄ -N), nitrite nitrogen (NO ₂ -N), the total amount of nitrate nitrogen (NO ₃ -N). That is, only the conversion into nitrate ions by the decomposition of ethanolamine in the wastewater does not reduce the total nitrogen. And the higher the concentration of ethanolamine in the wastewater, the more this nitrate ion will remain as total nitrogen,
It is difficult to conform to the value specified in the nitrogen (N) regulation of the effluent, and in this case, it is necessary to separately remove all nitrogen.

[0008]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a method for treating wastewater containing ethanolamine and hydrazine, wherein ethanolamine can be efficiently treated without producing a biodegradable substance, Another object of the present invention is to provide a wastewater treatment method capable of reducing the total amount of nitrogen in the wastewater.

[0009]

As described above, when a wastewater in which ethanolamine and hydrazine coexist is treated under aerobic conditions, a biodegradable substance serving as a COD source is generated. The chemicals are mixed without contact with a gas containing, and before the mixture is treated under aerobic conditions, the anaerobic By previously decomposing ethanolamine by a microorganism under conditions and then decomposing hydrazine, the above-mentioned conventional problems could be solved.

That is, the present invention relates to a method for treating wastewater containing ethanolamine and hydrazine, wherein the wastewater is brought into contact with an anaerobic microorganism to decompose ethanolamine in an anaerobic manner; Contacting the treatment liquid produced in the aerobic decomposition step with an aerobic microorganism, aerobically decomposing the remaining ethanolamine and hydrazine, and treating the treatment liquid produced in the first aerobic decomposition step again. Provided is a method for treating wastewater, comprising: a second anaerobic decomposition step of bringing into contact with anaerobic microorganisms; and a second aerobic decomposition step of bringing the treatment liquid generated in the second anaerobic decomposition step back into contact with aerobic microorganisms. Is what you do. The present invention also provides a method for treating the wastewater, wherein methanol is added as an energy source for metabolizing anaerobic microorganisms used in the second anaerobic decomposition step. Further, the present invention provides the above-mentioned wastewater treatment method, wherein an organic substance having 2 or more carbon atoms is added as an energy source for metabolizing anaerobic microorganisms used in the second anaerobic decomposition step. Furthermore, the present invention provides a method wherein the microorganisms of the first anaerobic decomposition step, the first aerobic decomposition step, the second anaerobic decomposition step and the second aerobic decomposition step are supplied by activated sludge, and the second aerobic decomposition step is performed. An object of the present invention is to provide a method for treating the wastewater in which a part of the sludge after the step is returned to the first anaerobic decomposition step and / or the second anaerobic decomposition step.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, first, most of ethanolamine is decomposed in a first anaerobic treatment using a microorganism, and most of hydrazine is decomposed in a second aerobic treatment. Treating these residual components is most effective in reducing COD in the treated water, and in this case, a treatment solution that generates nitrite ions and nitrate ions necessary for the first-stage anaerobic treatment in the second-stage aerobic treatment. Is returned, so that it is not necessary to add a new chemical, and as a result, the nitrogen load of the wastewater can be reduced.

[0012] Microorganisms used for nitrification and denitrification of organic matter containing nitrogen bonded thereto include denitrifying bacteria (denitrifying bacteria) belonging to facultative anaerobic bacteria group, nitrite bacteria and nitric acid belonging to aerobic bacteria group. There are fungi. These microorganisms tend to acquire resistance and increase resistance levels to substances that inhibit their activity, generally by means of habituation. Among these microorganisms, aerobic microorganisms are considered to be less resistant to hydrazine, which has the effect of depriving oxygen as a reducing agent, than anaerobic microorganisms from the original habitat. Aerobic microorganisms are trained in the same manner as anaerobic microorganisms, or they gradually acquire resistance and increase their resistance concentration during long-term treatment with wastewater in which these hydrazines coexist, and degrade ethanolamine without practical problems. It has been found.

Embodiment 1 Next, the present invention will be described more specifically with reference to FIG. FIG. 1 shows an example of a treatment process for secondary blow water of a PWR type nuclear power plant. In order to prevent impurities from flowing in and accumulating in the secondary cooling water of the heat exchanger while being circulated, the cooling water is periodically purified by an ion exchange resin in order to prevent a decrease in heat exchange performance. Then, wastewater containing NaOH-based and HCl-based hydrazine and ethanolamine is discharged as a regeneration waste liquid when regenerating the ion-exchange resin having deteriorated performance.

(1) First Anaerobic Decomposition Step The ethanolamine-containing wastewater a is introduced into the first anaerobic decomposition tank 1 in which facultative anaerobic microorganisms inhabit as the dominant species while keeping the wastewater a containing ethanol from coming into contact with air as much as possible. Here, a nutrient c such as phosphoric acid or phosphate is added and mixed, and the pH is adjusted to 8.0 to 9.5 with a neutralizing agent b1 such as sodium hydroxide in the presence of sulfite ions and nitrate ions. Preferably, it is adjusted to 8.5 to 9.0 and held. The amount of nutrient c added is 2 per 100 parts by weight of BOD in the wastewater as phosphorus.
A suitable amount is about parts by weight. As the nitrite ion and nitrate ion required for this step, those contained in the circulating liquid d returned from the first aerobic decomposition step 2 described below can be used, in which case there is no need to add a chemical again. Very economical. The circulating liquid d is a part of the processing liquid in the first aerobic decomposition tank 2 and also includes some undecomposed organic substances such as ethanolamine. Thus, in the first anaerobic decomposition tank 1, most of the organic substances such as ethanolamine contained in the wastewater a are biochemically decomposed under the anaerobic conditions by the action of the denitrifying bacterium, which is a facultative anaerobic microorganism. Nitrite ions and nitrate ions are biochemically reduced to be decomposed into nitrogen gas, carbon dioxide gas, etc., and released as decomposed gas g. The reaction is shown below as chemical reaction formulas (1) and (2).

[0015]

Embedded image

At the beginning of this reaction, the presence of about 80 mg / l of hydrazine inhibited the activity of the microorganism, and the decomposition of ethanolamine was not sufficient, so that the microorganism could not be put to practical use. About 1 below
As a result of training for months, it was confirmed that the microorganisms acquired and improved resistance to hydrazine, and promoted the decomposition of ethanolamine even when hydrazine was present at about 200 mg / l.

(2) First Aerobic Decomposition Step Next, the treatment liquid from the first anaerobic decomposition tank 1 contains nitrite,
The aerobic microorganisms such as nitric acid bacteria and BOD oxidizing bacteria are led to the first aerobic decomposition tank 2 which lives as a dominant species. Here, the pH is adjusted to 7.0 to 8.0 with a neutralizing agent b2 such as sodium hydroxide.
5, preferably while adjusting and holding at 7.5 to 8.0,
By aerating with air f, organic substances such as ethanolamine which partially remain in the liquid are decomposed by the action of sulfite bacteria and nitrate bacteria under aerobic conditions, and furthermore, the generated ammonium ions are partially assimilated. Most of them are oxidized to nitrite ions and nitrate ions. Most of the hydrazine contained in the liquid is biodegraded by microorganisms to become nitrogen gas or the like. The reaction is represented by chemical reaction formulas (3) to (7).
As shown below.

[0018]

Embedded image

In this reaction, an aerobic microorganism consisting of nitrite and nitrate was trained for about one month. As a result, it was confirmed that these microorganisms were successfully treated without being inhibited by hydrazine, and had acquired hydrazine resistance. A part after the treatment is returned to the first anaerobic decomposition tank 1 described above, and the remaining part is supplied to the next step.

(3) Second Anaerobic Decomposition Step The remainder of the processing liquid in the first aerobic decomposition tank 2 is led to the second anaerobic decomposition tank 3. Here, a neutralizing agent b such as sodium hydroxide
At pH 8.0 to 9.5, preferably 8.5 to 9.0.
By adding and mixing an organic substance such as methanol e as an energy source for the metabolism of microorganisms while maintaining the pH, the action of denitrifying bacteria under anaerobic conditions is the same as in the case of the first anaerobic decomposition tank 1. This decomposes organic substances such as ethanolamine remaining in a part of the liquid, and reduces nitrite ions and nitrate ions to decompose them into nitrogen gas, carbon dioxide gas and the like, which are released as decomposed gas g ′.

(4) Second Aerobic Decomposition Step The processing liquid in the second anaerobic decomposition tank 3 is led to the second anaerobic decomposition tank 3. Here, p with neutralizing agent b4 such as sodium hydroxide
H is adjusted to 6.5 to 8.0, preferably 7.0 to 7.5, and is maintained in the solution by aeration with air f by aeration of BOD oxidizing bacteria under aerobic conditions. In the second anaerobic decomposition tank 3, the methanol and the organic substances such as ethanolamine remaining in a part of the liquid and hydrazine are decomposed. In the mixed liquid in the second aerobic decomposition tank 4, a separation membrane S5, that is, a submerged precision membrane filtration device is immersed. After the completion of the reaction, the treatment liquid is suctioned or depressurized through the separation membrane S5, that is, the microfiltration membrane, to separate a solid substance, and is discharged or reused as treated water h after passing through the membrane. In addition, part of the separated sludge is returned as sludge n '
And n ″ are returned to the first anaerobic decomposition tank 1 and the second anaerobic decomposition tank 3, respectively, to keep the microorganism concentration in the tank almost constant, and the remaining part is discharged out of the system as surplus sludge n. Here, the concentration of the denitrifying bacteria in the second anaerobic decomposition tank can be increased by introducing the returned sludge not only into the first anaerobic decomposition tank but also into the second anaerobic decomposition tank. The processing performance of the decomposition tank is improved. Since the reaction in the second anaerobic decomposition tank is the final step of removing nitrogen from water,
The denitrification rate here has to be kept at almost 100%. However, when methanol is added, it is less likely to be decomposed than ethanolamine, and the growth of methanol-using denitrifying bacteria tends to decrease. Therefore, when the sludge is returned only to the first anaerobic decomposition tank, the denitrifying bacteria utilizing ethanolamine grown in the first anaerobic decomposition tank become the priority species, and as a result, the ratio of methanol-using denitrifying bacteria decreases. The performance of the second anaerobic decomposition tank may be reduced. This tendency is particularly noticeable at a high load of 0.8 kg / d or more in the anaerobic decomposition tank. By returning the sludge to the second anaerobic decomposition tank, the methanol-utilizing denitrifying bacteria that have exited the second anaerobic decomposition tank are allowed to grow in the second aerobic decomposition tank (here, bacteria that aerobically decompose methanol grow). ), And returns to the second anaerobic decomposition tank again, so that the sludge concentration can be maintained without reducing the ratio of methanol-using denitrifying bacteria. Methanol-degrading bacteria that grow in the second aerobic digestion tank are basically methanol-utilizing denitrifying bacteria that act in the second anaerobic digestion tank (a facultative anaerobic bacterium that can live in both aerobic and anaerobic environments). Fungus),
Here too, it can be expected that denitrifying bacteria utilizing methanol will proliferate. In addition, by increasing the amount of methanol charged into the second anaerobic decomposition tank, excess methanol can be decomposed in the second aerobic decomposition tank to further increase the ratio of methanol-using denitrifying bacteria. (2) The processing efficiency in the anaerobic decomposition tank increases.

Here, as the operating conditions for the membrane separation by the separation membrane S5, the filtration speed is set to 250 to 700 l / m ² · day, and the suction of the microfiltration membrane is performed continuously, or
An intermittent operation is performed in which the interval of the pause is set to 5 minutes / 5 minutes to 25 minutes / 5 minutes. In the present embodiment, an example in which the submerged precision membrane filtration device is installed in the second aerobic decomposition tank 4 is exemplified. However, it may be installed outside the tank as long as the filtration conditions can be satisfied. It is not limited to.
Through the above steps, almost all of the ethanolamine and hydrazine in the wastewater are decomposed and removed as shown in the experimental results described below, and the COD and total nitrogen (TN) in the treated water become equal to or lower than the discharge reference value. However, when the growth conditions of the microorganisms are not sufficiently adjusted, hydrazine may rarely remain slightly in the treated water. Normally, a treatment for this purpose is not necessary, but in order to ensure completeness, a copper compound k, for example, copper sulfate is added to the treated water h so as to have a concentration of about 0.1 mg / l, and sodium hydroxide or the like is added. After adjusting the pH to 8 to 9 with a neutralizing agent, hydrogen peroxide / hydrazine (molar ratio) = 2.
The reaction may be carried out by adding the hydrazine to 4 to decompose hydrazine in the waste water into nitrogen gas and water (not shown).
(Same as the treatment in the neutralization tank 11 in FIG. 3).

(Specific Example) Wastewater discharged from the secondary system of the PWR nuclear power plant was treated in the step shown in FIG. In the figure,
Activated sludge was put into the first anaerobic decomposition tank 1, the first aerobic decomposition tank 2, the second anaerobic decomposition tank 3, and the second aerobic decomposition tank 4. In the second aerobic decomposition tank 4, a separation membrane S5 for solid-liquid separation was connected, and the treatment liquid mixed with activated sludge was subjected to membrane separation treatment. 0.4 μm pore membrane as separation membrane S5,
Submerged membrane separator in the filtration area 4m ² (manufactured by Kubota Co., Ltd.) was used, it was continuously operated at a filtration rate 500l / m ² · day. As a result, it was found that the concentration of microorganisms in each tank could be maintained stably and at a high concentration, and the treatment was performed without any problem even when ethanolamine and hydrazine were contained at a considerably high concentration. In addition, it was confirmed that components such as TN, TOC, CODMn and the like, which are causes of apparent deterioration of the processability, were lower than the effluent water standard value. The results are shown in Table 2 together with the results of the conventional method.

[0024]

[Table 2]

As described above, the present embodiment has been found to provide the following effects. (1) Ethanolamine contained in wastewater can be largely decomposed by denitrifying bacteria under anaerobic conditions,
The processing efficiency is extremely high as compared with the case where processing is performed only under aerobic conditions as in the conventional method. (2) In addition, ammonium ions generated by the decomposition of ethanolamine in the wastewater become nitrate ions under the action of nitrite or nitrate under aerobic conditions, and the treated solution containing these ions is converted under anaerobic conditions. By treating with denitrifying bacteria, almost all of nitrite and nitrate ions can be decomposed into nitrogen gas. Therefore,
Even when ethanolamine is contained in the wastewater at a high concentration, the value set in the nitrogen (N) regulation of the discharge water can be satisfied without remaining as total nitrogen in the treated water,
Thereby you do not need excessive facilities. (3) Ethanolamine and hydrazine are used in order to decompose most of the ethanolamine under anaerobic conditions without intervening oxygen-containing liquid such as air in the wastewater before the wastewater treatment. It is extremely effective in reducing COD in treated water without producing biodegradable substances despite coexistence. (4) By treating with a hydrazine-resistant microorganism having an ethanolamine decomposing function, ethanolamine remaining in the solution without being inhibited by hydrazine can be efficiently decomposed and removed. In particular, in the first anaerobic decomposition treatment, the presence of hydrazine acting as a reducing agent in the wastewater results in the deprivation of oxygen dissolved in the liquid to enhance anaerobic conditions, and rather activates anaerobic microorganisms. There is a preferred advantage of improving the processing efficiency. (5) Subsequent to the anaerobic treatment in the first stage, the remaining aerobic treatment in the latter stage decomposes only the remaining ethanolamine, thereby reducing the load on the BOD oxidizing bacteria and greatly reducing the amount of supply air for BOD oxidation. Can be. In addition, the nitrification reaction proceeds much more easily than when the treatment is performed only under aerobic conditions. For this reason, the peripheral devices such as the blower can be reduced in size, and the power cost and the like required for them can be reduced, which is extremely economical. (6) A part of the processing liquid generated in the aerobic processing is returned to the above-described anaerobic processing step, and the nitrite ions and nitrate ions contained in the processing liquid are used for the anaerobic decomposition processing of ethanolamine. Therefore, the cost of chemicals can be reduced without the necessity of adding a new nitrogen compound from the outside, and the nitrogen load in wastewater treatment is reduced. Can be. (7) By providing double return sludge in the first anaerobic digestion tank and the second anaerobic digestion tank, microorganisms suitable for the action in each anaerobic digestion tank can be maintained at a high concentration. Thus, even when ethanolamine is contained in a high concentration, the decomposition treatment can be performed extremely stably. (8) Since the sedimentation tank required in the conventional treatment can be omitted, it is possible to reduce the size and the installation area of the entire wastewater treatment facility. (9) As described above, the multi-stage treatment combining the anaerobic treatment and the aerobic treatment as in the present invention activates the microorganisms while maintaining and optimally inhabiting the microbial habitat, and reduces the components contained in the waste water such as ethanolamine and hydrazine. A suitable reliable and economical treatment process can be established.

Embodiment 2 Next, another embodiment of the present invention will be described with reference to FIG. The present embodiment shows an example of a treatment process for secondary blow water of a PWR type nuclear power plant, and includes (1) a first anaerobic decomposition process and (2) a first aerobic process. The decomposition step is the same as in the first embodiment. (3) Second Anaerobic Decomposition Step The remainder of the processing liquid in the first aerobic decomposition tank 2 is led to the second anaerobic decomposition tank 3. Here, a neutralizing agent b such as sodium hydroxide
Acetic acid, ethanol, lactic acid, butyric acid instead of methanol, which is commonly used as an energy source for microbial metabolism, while adjusting and maintaining the pH at 8.0 to 9.5, preferably 8.5 to 9.2 at 3 By adding and mixing an organic substance p having 2 or more carbon atoms, such as ethyl, the ethanol remaining only partially in the liquid by the action of denitrifying bacteria under anaerobic conditions as in the case of the first anaerobic decomposition tank. Organic substances such as amines are decomposed, and at the same time, nitrite ions and nitrate ions are reduced and decomposed into nitrogen gas, carbon dioxide gas, etc., and released as decomposed gas g ′. Since the reaction in the second anaerobic decomposition tank is the final step of removing nitrogen from water, the denitrification rate here is almost 10%.
0% must be maintained. In the first embodiment, a denitrifying bacterium utilizing methanol is used. However, in the present embodiment, an organic substance having a high growth rate is added to the second anaerobic decomposition tank 3 in place of methanol. By adding organic acids such as acetic acid, lactic acid, butyric acid, and propionic acid, and alcohols such as ethanol and propanol, the growth rate of the denitrifying bacteria is increased, and the denitrifying bacteria utilizing organic acids in the entire system are added. And the processing capacity of the second anaerobic decomposition tank 3 is stabilized. (4) Second aerobic decomposition step The treatment liquid in the second anaerobic decomposition tank 3 is led to the second anaerobic decomposition tank 3. Here, p with neutralizing agent b4 such as sodium hydroxide
H is adjusted to 6.5 to 8.0, preferably 7.0 to 7.5, and is maintained in the solution by aeration with air f by aeration of BOD oxidizing bacteria under aerobic conditions. In the second anaerobic decomposition tank 3 to be added, for example, acetic acid and organic substances such as ethanolamine, which remain only partially in the liquid, and hydrazine are decomposed. In the mixed liquid in the second aerobic decomposition tank 4, a separation membrane S5, that is, a submerged precision membrane filtration device is immersed. After the completion of the reaction, the treatment liquid is suctioned or depressurized through the separation membrane S5, that is, the microfiltration membrane, to separate a solid substance, and is discharged or reused as treated water h after passing through the membrane. In addition, part of the separated sludge is returned as sludge n '
To return to the first anaerobic decomposition tank 1 to keep the concentration of microorganisms in the tank almost constant, and to discharge the remainder as excess sludge n outside the system. In this embodiment, since an organic substance having a high growth rate is used instead of methanol,
Unlike Embodiment 1, it is not necessary to circulate sludge in the second anaerobic decomposition tank 3. Here, as the operating conditions of the membrane separation by the separation membrane S5, the filtration speed is set to 250 to 700 l / m ^2.
• Set the day and continuously perform suction of the microfiltration membrane, or perform an intermittent operation in which the interval between decompression and pause is set to 5 minutes / 5 minutes to 25 minutes / 5 minutes. In the present embodiment, an example in which the submerged precision membrane filtration device is installed in the second aerobic decomposition tank 4 is exemplified. However, it may be installed outside the tank as long as the filtration conditions can be satisfied. It is not limited to. Through the above steps, almost all of the ethanolamine and hydrazine in the wastewater are decomposed and removed as shown in the experimental results described below, and COD and total nitrogen (T-
N) is equal to or less than the discharge reference value. However, when the growth conditions of the microorganisms are not sufficiently adjusted, hydrazine may rarely remain slightly in the treated water. Usually, a treatment for this purpose is not necessary, but in order to ensure completeness, a copper compound k, for example, copper sulfate having a concentration of 0.1 m is added to the treated water h.
g / l, and the pH is adjusted to 8 to 9 with a neutralizing agent such as sodium hydroxide. Then, an oxidizing agent, for example, hydrogen peroxide is added to hydrogen peroxide / hydrazine (molar ratio) = 2. The hydrazine in the waste water may be decomposed into nitrogen gas and water (not shown; the same as the treatment in the neutralization tank 11 in FIG. 3).

(Specific Example) Wastewater discharged from the secondary system of the PWR nuclear power plant was treated in the process shown in FIG. In the figure,
Activated sludge was put into the first anaerobic decomposition tank 1, the first aerobic decomposition tank 2, the second anaerobic decomposition tank 3, and the second aerobic decomposition tank 4. In the second aerobic decomposition tank 4, a separation membrane S5 for solid-liquid separation was connected, and the treatment liquid mixed with activated sludge was subjected to membrane separation treatment. 0.4 μm pore membrane as separation membrane S5,
Submerged membrane separator in the filtration area 4m ² (manufactured by Kubota Co., Ltd.) was used, it was continuously operated at a filtration rate 500l / m ² · day. As a result, it was found that the concentration of microorganisms in each tank could be maintained stably and at a high concentration, and the treatment was performed without any problem even when ethanolamine and hydrazine were contained at a considerably high concentration. In addition, it was confirmed that components such as TN, TOC, CODMn and the like, which are causes of apparent deterioration of the processability, were lower than the effluent water standard value. The results are shown in Table 3 together with the results of the conventional method.

[0028]

[Table 3]

As described above, the present embodiment has been found to provide the following effects. (1) Ethanolamine contained in wastewater can be largely decomposed by denitrifying bacteria under anaerobic conditions,
The processing efficiency is extremely high as compared with the case where processing is performed only under aerobic conditions as in the conventional method. (2) In addition, ammonium ions generated by the decomposition of ethanolamine in the wastewater become nitrate ions under the action of nitrite or nitrate under aerobic conditions, and the treated solution containing these ions is converted under anaerobic conditions. By treating with denitrifying bacteria, almost all of nitrite and nitrate ions can be decomposed into nitrogen gas. Therefore,
Even when ethanolamine is contained in the wastewater at a high concentration, the value set in the nitrogen (N) regulation of the discharge water can be satisfied without remaining as total nitrogen in the treated water,
Thereby you do not need excessive facilities. (3) Ethanolamine and hydrazine are used in order to decompose most of the ethanolamine under anaerobic conditions without first interposing any liquid containing oxygen such as air in the wastewater before the wastewater treatment. Despite the coexistence, no biodegradable substance is generated, which is extremely effective in reducing COD in treated water. (4) By treating with a hydrazine-resistant microorganism having an ethanolamine decomposing function, ethanolamine remaining in the solution without being inhibited by hydrazine can be efficiently decomposed and removed. In particular, in the first anaerobic decomposition treatment, the presence of hydrazine acting as a reducing agent in the wastewater results in the deprivation of oxygen dissolved in the liquid to enhance anaerobic conditions, and rather activates anaerobic microorganisms. There is a preferred advantage of improving the processing efficiency. (5) Subsequent to the anaerobic treatment in the first stage, the remaining aerobic treatment in the latter stage decomposes only the remaining ethanolamine, thereby reducing the load on the BOD oxidizing bacteria and greatly reducing the amount of supply air for BOD oxidation. Can be. In addition, the nitrification reaction proceeds much more easily than when the treatment is performed only under aerobic conditions. For this reason, the peripheral devices such as the blower can be reduced in size, and the power cost and the like required for them can be reduced, which is extremely economical. (6) A part of the processing liquid generated in the aerobic processing is returned to the above-described anaerobic processing step, and the nitrite ions and nitrate ions contained in the processing liquid are used for the anaerobic decomposition processing of ethanolamine. Therefore, the cost of chemicals can be reduced without the necessity of adding a new nitrogen compound from the outside, and the nitrogen load in wastewater treatment is reduced. Can be. (7) The ratio of denitrifying bacteria in the second anaerobic decomposition tank can be maintained high by replacing the organic matter added to the second anaerobic decomposition tank with acetic acid or the like having a high growth rate, and stable processing performance And the quality of treated water can be obtained. (8) Since the sedimentation tank required in the conventional treatment can be omitted, it is possible to reduce the size and the installation area of the entire wastewater treatment facility. (9) As described above, the multi-stage treatment combining the anaerobic treatment and the aerobic treatment as in the present invention activates the microorganisms while maintaining and optimally inhabiting the microbial habitat, and reduces the components contained in the waste water such as ethanolamine and hydrazine. A suitable reliable and economical treatment process can be established.

[0030]

According to the present invention, in a method for treating wastewater containing ethanolamine and hydrazine, ethanolamine can be efficiently treated without producing a biodegradable substance, and the total amount of wastewater can be reduced. A method for treating wastewater capable of reducing the amount of nitrogen is provided.

[Brief description of the drawings]

FIG. 1 is a view for explaining one embodiment of a wastewater treatment method of the present invention.

FIG. 2 is a view for explaining another embodiment of the wastewater treatment method of the present invention.

FIG. 3 is a diagram for explaining an aspect of a conventional wastewater treatment method.

[Explanation of symbols]

 Reference Signs List 1 First anaerobic decomposition tank 2 First aerobic decomposition tank 3 Second anaerobic decomposition tank 4 Second aerobic decomposition tank a Ethanolamine-containing wastewater b Neutralizer e Methanol p Acetic acid

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kuniharu Wakuda, 1-1-1 Wadazakicho, Hyogo-ku, Kobe, Hyogo Prefecture Inside the Kobe Shipyard, Mitsubishi Heavy Industries, Ltd. (72) Inventor Toshio Hirata 2, Araimachi Shinama, Takasago-shi, Hyogo Prefecture No.8-25 Takahashi Engineering Co., Ltd. (72) Inventor Hiromi Harada 2-8-25 Niihama, Araimachi, Takasago City, Hyogo Prefecture F Term (Takahishi Engineering Co., Ltd.) 4D040 BB01 BB05 BB93 DD01 DD14

Claims (5)

[Claims] 1. A method for treating wastewater containing ethanolamine and hydrazine, comprising: a first anaerobic decomposition step of contacting the wastewater with an anaerobic microorganism to anaerobically decompose ethanolamine; and the first anaerobic decomposition step. Contacting the treatment liquid generated in step 1 with an aerobic microorganism to aerobicly decompose remaining ethanolamine and hydrazine; and treating the treatment liquid generated in the first aerobic decomposition step again with anaerobic microorganisms. A wastewater treatment method comprising: a second anaerobic decomposition step of bringing into contact with water; and a second aerobic decomposition step of bringing the treatment liquid generated in the second anaerobic decomposition step into contact with aerobic microorganisms again. 2. The method for treating wastewater according to claim 1, wherein in the second anaerobic decomposition step, methanol is added as an energy source for metabolizing anaerobic microorganisms to be used. 3. The method according to claim 2, wherein the anaerobic microorganism used in the second anaerobic decomposition step has 2 carbon atoms as an energy source for metabolism.
The method for treating wastewater according to claim 1, wherein the organic matter is added. 4. The microorganisms of each of the first anaerobic decomposition step, the first aerobic decomposition step, the second anaerobic decomposition step and the second aerobic decomposition step are supplied by activated sludge, and the second aerobic decomposition step The method for treating wastewater according to claim 1 or 2, wherein a part of the sludge after that is returned to the first anaerobic decomposition step and the second anaerobic decomposition step. 5. Each of the microorganisms in the first anaerobic decomposition step, the first aerobic decomposition step, the second anaerobic decomposition step and the second aerobic decomposition step is supplied by activated sludge, and the second aerobic decomposition step 4. The method for treating wastewater according to claim 3, wherein a part of the sludge after that is returned to the first anaerobic decomposition step.