JP2011240303A - Treatment method of wastewater containing hydrazine and complex-forming organic compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently decompose hydrazine in a waste water containing hydrazine and a complex-forming organic compound, and to easily treat the remaining complex-forming organic compound by a biotreatment such as a usual activated sludge process.SOLUTION: A treatment method of waster water containing hydrazine and a complex-forming organic compound comprises an oxidation step of adding a metal powder to the waster water containing hydrazine and a complex-forming organic compound, and oxidizing and decomposing hydrazine by an oxygen-containing gas; a reduction step of reducing metal ions produced in the waste water and partially dissolved in the oxidation step, with a reducing agent; and a separation step of subjecting the treated waste water containing the metal powder produced in the reduction step to a solid-liquid separation to separate a concentrated water of the metal powder from a treated water as a separated water.

Description

  The present invention relates to a method for treating waste water containing hydrazine and a complex-forming organic compound.

  Hydrazine is used as a deoxidizer and cleaning agent for preventing corrosion of boiler feedwater, but its toxicity and high COD value indicate that it requires wastewater treatment, and there are various treatment methods for wastewater containing hydrazine than before. Proposed. For example, Patent Document 1 describes a method in which cobalt ions are added and air oxidation is performed at a pH of 8 or more. Patent Document 2 describes a method in which a copper compound such as copper sulfate, copper chloride or copper oxide is added, air-oxidized with neutrality or weak alkali, and then copper is collected by filtration and returned to the air oxidation tank. Has been. Furthermore, Patent Document 3 describes a method of oxidizing hydrazine in air by adding metallic copper or copper ions such as machined copper or powdered copper.

  On the other hand, for waste water containing hydrazine and a complex-forming organic compound, at least one metal element of iron, manganese, zinc, chromium, nickel, cobalt, copper (any of ions, simple metals, insoluble compounds is acceptable, simple metals) Patent Documents 4 and 5 describe a method of adding 0.1 to 100 mg / L) and oxidizing hydrazine with an oxygen-containing gas, followed by biological treatment. The BOD component containing the complex-forming organic compound is treated by biological treatment such as activated sludge method. However, when hydrazine is contained in the wastewater, the hydrazine content is high, so the content of hydrazine is reduced. It is necessary to make it 1 mg / L or less.

  From this point of view, Patent Document 6 discloses that wastewater containing hydrazine and a complex-forming organic compound is added with high-concentration metal ions (10 to 1000 mg / L) and oxidized with an oxygen-containing gas, and remains after oxidation. A method is described in which an oxidizing agent is reduced with a reducing agent, metal ions in the treated water after the reduction are removed using a chelate resin, and then the remaining organic compound is biologically treated.

JP 49-9859 A JP-A-56-136695 Japanese Unexamined Patent Publication No. 57-27193 JP 2002-79278 A JP 2002-79279 A JP 2003-39083 A

  As a treatment technique of hydrazine, a method of adding metal ions and easily decomposing with oxygen under alkaline conditions has been established. At this time, the added metal ions can be recovered to some extent by filtering in the form of hydroxide, and can be reused. However, in the presence of a complex-forming organic compound, metal ions form complex ions, making it impossible to recover them as hydroxides. In addition, as a result of the metal ions forming a complex, the concentration of metal ions that should function as an oxidation catalyst for hydrazine is reduced. Therefore, high concentrations of metal ions are added in anticipation of this. Is extremely inefficient. In addition, in order to treat complex-forming organic compounds, biological treatment (activated sludge method, etc.) is required after hydrazine decomposition, but many metal ions are harmful, and metal ions are completely removed before biological treatment. There is a need to.

  In Patent Document 6 described above, a large amount of metal ions is used to maintain the oxidation catalytic ability of hydrazine, and the metal ions used are removed with a chelate resin. The chelate resin that adsorbs the metal has a high cost because it needs to be replaced because the adsorption ability gradually decreases, or a treatment such as recovery of metal ions adsorbed to the chelate resin must be performed.

  The present invention has been made in view of the above circumstances, can efficiently decompose hydrazine, and the remaining organic matter such as a complex-forming organic compound can be easily treated by a biological treatment such as a normal activated sludge method. It aims at providing the processing method of the waste_water | drain containing possible hydrazine and a complex formation organic compound.

  The method for treating wastewater containing hydrazine and a complex-forming organic compound according to the present invention includes an oxidation step of adding metal powder to wastewater containing hydrazine and a complex-forming organic compound, and oxidatively decomposing hydrazine with an oxygen-containing gas. A reduction step of reducing metal ions partially dissolved from the metal powder produced in the wastewater into a metal powder with a reducing agent, and a treatment wastewater containing the metal powder produced in the reduction step are solid-liquid separated, and the metal powder It consists of a separation step of separating into concentrated water and treated water as separation water.

It is preferable that the method further includes a returning step of returning the concentrated water of the metal powder separated in the separating step to the oxidizing step.
The reducing agent is preferably at least one selected from the group consisting of lithium aluminum hydride, sodium borohydride, hypophosphorous acid, phosphinic acid, phosphonic acid, and hydrosulfite.

It is good also as an aspect which provides the 2nd oxidation process which further oxidatively decomposes the hydrazine which remains in the said oxidation process with an oxidizing agent between the said oxidation process and the said reduction process.
The separation step is preferably performed by a membrane separation apparatus.
It is preferable to biologically treat the treated water in the separation step.

  The method for treating wastewater containing hydrazine and a complex-forming organic compound according to the present invention includes an oxidation step of adding metal powder to wastewater containing hydrazine and a complex-forming organic compound, and oxidatively decomposing hydrazine with an oxygen-containing gas. The metal ion partially dissolved from the metal powder generated in the waste water is reduced to metal powder with a reducing agent, and the treated waste water containing the metal powder generated in this reduction process is separated into solid and liquid, and the metal powder concentrated water And a separation step of separating into treated water as separation water, and metal powder is used for oxidative decomposition of hydrazine, so that the reduction of hydrazine's oxidation catalytic ability is suppressed compared to the case of using metal ions. Therefore, it is not necessary to use an unnecessarily large amount of metal powder in anticipation of a decrease in oxidation catalyst ability, and metal ions partially dissolved from the metal powder can be reduced. In so reduced to metal powder, can be separated into treatment and water is separated water and concentrated water of the metal powder prior to biological treatment, it is easy to completely remove the metal ions.

  If the metal powder concentrated water separated in the separation process is further returned to the oxidation process, the metal powder concentrated water separated in the separation process should be reused as the metal powder in the oxidation process. This makes it possible to reduce the absolute amount of metal powder used for wastewater treatment, leading to a reduction in costs for wastewater treatment methods containing hydrazine and complex-forming organic compounds, and being reusable. In the case where the metal is not separated in the state, the industrial waste disposal cost of the metal is necessary. However, since such a cost does not occur in the present invention, the cost can be further reduced.

It is a flowchart which shows one embodiment of the processing method of the waste_water | drain containing the hydrazine and complex formation organic compound of this invention. It is a flowchart which shows another embodiment of the processing method of the waste_water | drain containing the hydrazine and complex forming organic compound of this invention. It is a flowchart which shows another one Embodiment of the processing method of the waste_water | drain containing the hydrazine and complex formation organic compound of this invention.

  Hereinafter, a method for treating waste water containing hydrazine and a complex-forming organic compound of the present invention will be described in detail with reference to the drawings. FIG. 1 is a flow chart showing an embodiment of a method for treating wastewater containing hydrazine and a complex-forming organic compound of the present invention (hereinafter also simply referred to as wastewater treatment method of the present invention). As shown in FIG. 1, the wastewater treatment method of the present invention includes an oxidation step of adding metal powder to wastewater containing hydrazine and a complex-forming organic compound, and oxidizing and decomposing hydrazine with an oxygen-containing gas. The metal ion partially dissolved from the metal powder produced in the process is reduced to a metal powder with a reducing agent, and the treatment wastewater containing the metal powder produced in this reduction process is solid-liquid separated in a precipitation tank to concentrate the metal powder. It consists of a separation step of separating into water and treated water which is separated water. In FIG. 1, M is a motor for driving the stirrer, B is a blower for sending an oxygen-containing gas, and P is a pump (the same applies to other drawings hereinafter).

  Since the wastewater generally contains suspended solids (SS), it is preferable that the wastewater supplied to the oxidation step is removed from the wastewater by a known means such as coagulation precipitation separation. In addition, when ammonium ions that react with metal ions to form a complex are contained in the wastewater, the ammonium ions in the wastewater can be removed by a known means such as ammonia stripping in the previous step of the oxidation step. preferable.

  As the metal powder added in the oxidation step, iron, manganese, nickel, cobalt and copper can be preferably used. In particular, copper can be used more preferably because hydrazine has a high decomposition rate and is effective. The amount of metal powder added depends on the amount of hydrazine contained in the wastewater, but is generally in the range of 10 to 500 mg / L, and more preferably in the range of 20 to 200 mg / L. Since part of the metal powder dissolves during the hydrazine oxidation process, an increase in the amount added is not preferable because the amount of reducing agent added to reduce the dissolved metal ions to the metal powder increases, resulting in increased costs. .

  The pH of the hydrazine oxidation step may be alkaline, preferably 9 to 13, and more preferably 11 to 12. For pH control, an alkaline substance such as sodium hydroxide or potassium hydroxide or an acidic substance such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid or carboxylic acid is added as it is or as an aqueous solution as necessary. Also good.

  In order to improve the oxidation rate of hydrazine, it is effective to raise the temperature of the waste water. The temperature of the waste water is preferably 30 ° C. or higher, and more preferably in the range of 40 to 50 ° C. Since biological treatment of complex-forming organic compounds is required after hydrazine decomposition, heating and cooling energies are required at water temperatures higher than 50 ° C, and there are restrictions on the materials used in the oxidation process. Because it comes, it is not preferable.

As the oxygen-containing gas, air, pure oxygen gas, or oxygen-enriched gas can be preferably used. The supply amount of the oxygen-containing gas is determined by the content of hydrazine contained in the waste water. Hydrazine in the waste water is decomposed by the supplied oxygen according to the following formula.
N ₂ H ₄ + O ₂ → N ₂ + 2H ₂ O

  For this reason, it is necessary to supply oxygen (molecular weight 32) equal to or more than the content of hydrazine (molecular weight 32). When the hydrazine concentration is high, a device having a high oxygen supply capability is required. However, when the hydrazine concentration is low, a device having a low oxygen supply capability may be used. However, it is preferable to install a separate stirring device when the stirring power sufficient to uniformly disperse the metal powder added in the oxidation tank for performing the oxidation step is insufficient (in FIG. 1, a separate stirring device is provided. Embodiment).

  There are no particular restrictions on the contact method between the waste water and the oxygen-containing gas, and various methods such as batch, continuous, and multi-stage continuous can be used, but operation is easy and two or more stages in series that can reduce the oxidation tank capacity. A multistage continuous type is preferable. As the reaction tank shape, an aeration tank, a packed tower, a wet wall tower, a bubble tower, a scrubber, and the like can be used. When a packed tower or a wet wall tower is used, it is preferable to devise such as stirring the lower receiving tank for circulating the reaction liquid so that the metal powder does not collect in one place.

  Although the mechanism of oxidative decomposition of hydrazine by metal powder is not clear, a phenomenon that the added metal powder partially dissolves as ions is observed with the decomposition of hydrazine, and the synergistic effect of the catalytic action of both metal powder and metal ion is observed. It is considered an effect. Usually, in the case of copper ions, a copper ion concentration of about 1 mg / L is sufficient for the hydrazine oxidation reaction. However, in the presence of a complex-forming organic compound, a complex with copper ions is formed and the hydrazine oxidation reaction is suppressed. . Therefore, by adding metal powder, both metal powder and metal ions are present in the oxidation step, and hydrazine can be more efficiently oxidatively decomposed than when added as metal ions.

  The metal ions dissolved in the oxidation step form a complex with the complex-forming organic compound in the waste water, and are stable as a soluble compound without becoming a precipitate even at high pH. As a method for removing metal ions that have become such a soluble compound, conventionally, the adsorption technique using a chelate resin or the like has been limited, but in the present invention, metal ions that have formed such a complex are converted into a metal powder using a reducing agent. It is possible to easily perform solid-liquid separation by reducing to a low level.

The reducing agent to be used is not particularly limited as long as it is a reducing agent capable of reducing metal ions to metal powder, but lithium aluminum hydride, sodium borohydride, hypophosphorous acid, phosphinic acid, phosphonic acid, It is preferably at least one selected from the group consisting of hydrosulfite (sodium dinitrite dihydrate: S ₂ O ₄ ²⁻ ), and these are used alone or in appropriate combination of two or more. May be. In view of price, toxicity, environmental load, etc., hydrosulfite can be used more preferably.

  The amount of reducing agent added can be quantitatively injected when the concentration of the metal ion to be produced is small, but if the concentration of the metal ion varies, the injection of the reducing agent should be controlled by an ORP meter. You can also. In this case, the control ORP is preferably −400 mv or less, more preferably −500 mv or less.

  After the reduction treatment, the treated wastewater containing the generated metal powder is subjected to solid-liquid separation, and separated into concentrated water of metal powder and treated water which is separated water. As a solid-liquid separation method, a membrane separation apparatus as shown in FIG. 2 can be used in addition to a precipitation tank as shown in FIG. In the case of the membrane separation apparatus, since the metal powder can be completely captured, the metal powder does not flow out into the treated water, and good treated water can be obtained.

  As the membrane of the membrane separator, a flat membrane, a hollow fiber membrane, a tubular membrane, or the like can be used. In addition, when the membrane of the membrane separator is a flat membrane or a hollow fiber membrane, aeration with a gas is necessary to prevent solid matter adhesion to the membrane surface, and normally air is used for this, When used in a reducing atmosphere as in the present invention, as a result of supplying oxygen, there is a fear of decomposition of the reducing agent and remelting of the metal powder. For this reason, it is preferable to use nitrogen and other inert gas which do not contain oxygen. In the case of a tubular membrane, since aeration is not required to prevent adhesion of solid matter to the membrane surface, oxygen is not dissolved, and metal powder is not redissolved, which is more preferable.

  When the membrane is a tubular membrane, a concentration tank is provided as shown in FIG. 2, and the treated wastewater containing the reduced metal powder is passed through the tubular membrane module by a pressure pump to obtain membrane filtrate and concentration. The liquid is returned to the concentration tank. On the other hand, when the membrane is a flat membrane or a hollow fiber membrane, the concentration tank can be built in the membrane separation device.

  The treated wastewater containing the metal powder produced in the reduction step is solid-liquid separated by a sedimentation tank or a membrane separator, and separated into concentrated water of the metal powder and treated water which is separated water. Since the hydrazine in the wastewater is removed by oxidative decomposition and the metal ions are removed as a metal powder by the above process, even if the treated water is subjected to biological treatment, the treatment of the complex-forming organic compound is inhibited by hydrazine or metal ions. Can be prevented. The biological treatment method used in the present invention is not particularly limited, and examples thereof include an aerobic biological treatment such as an activated sludge method and a biofilm method, and an anaerobic biological treatment. Among these, the activated sludge method can be suitably used.

  It is preferable that the concentrated water of the metal powder separated in the separation step is returned to the oxidation step (or together with waste water introduced into the oxidation step) by a pump or the like. By reusing the concentrated water of the metal powder as the metal powder in the oxidation process in this way, it becomes possible to reduce the absolute amount of the metal powder used in the wastewater treatment of the present invention, thereby reducing the cost of wastewater treatment. can do. Further, when the metal is not separated in a state where it can be reused, the cost of processing the industrial waste of the metal is necessary. However, in the present invention, such a cost does not occur, and therefore, further cost reduction can be achieved.

  When the oxidative decomposition of hydrazine by the above oxidation step is not sufficient, as shown in FIG. 3, a second oxidation step for further oxidative decomposition with an oxidizing agent may be provided between the oxidation step and the reduction step. Good. As the oxidizing agent, hydrogen peroxide, ozone, sodium hypochlorite, or the like can be used alone or in appropriate combination. The addition amount of the oxidizing agent is 1.1 to 10 times, preferably 2 to 6 times the stoichiometric amount necessary for the oxidation of hydrazine.

  There is no particular limitation on the contact method in the second oxidation step, and batch, continuous, and multi-stage continuous methods can be used. However, the operation is easy and the amount of oxidant added can be reduced, leading to cost reduction. It is preferable to use a series multi-stage continuous type with two or more stages. In the case of two or more series multi-stage continuous systems, the oxidant is preferably dispensed into each reaction tank, and the lower the hydrazine concentration, the lower the decomposition action. It is more preferable to increase the addition ratio of the oxidizing agent. In addition, the same thing may be used for the oxidizing agent of each reaction tank, and a different thing may be used. This second oxidation step performs mechanical stirring, but may be stirring by air supply. In this case, it is preferable to adjust to a sufficient stirring strength so that the metal powder does not precipitate.

Moreover, it is preferable that pH and water temperature in the second oxidation step are both equal to those in the oxidation step using the oxygen-containing gas. In order to maintain a stable decomposition treatment of hydrazine, the concentration of hydrazine in the final tank of the second oxidation step It is preferable to install a control system that measures the hydrazine meter and increases or decreases the amount of oxidant added in the previous stage according to the concentration difference from the target water quality.
Hereinafter, the waste water treatment method of the present invention will be described in more detail by way of examples.

Example 1
2 L reaction vessel installed in a thermostatic bath that can maintain a water temperature of approximately 30 ° C. by adding copper powder to 1 L of industrial wastewater of hydrazine 4000 mg / L, citric acid 3000 mg / L, pH 13.1. The air was introduced into the interior, and 3 L / min of air was supplied through an air diffuser while stirring with a stirrer. The hydrazine concentration in the waste water after 10 hours was 230 mg / L, pH 11.3, and copper ions 15 mg / L.

(Example 2)
In the same manner as in Example 1, air oxidation treatment was performed with the addition amount of copper powder being 2 mg / L, 200 mg / L, 500 mg / L, and 1000 mg / L. The hydrazine concentrations in the waste water after 10 hours were 3700 mg / L, 110 mg / L, 78 mg / L, and 70 mg / L, respectively.

(Example 3)
After stripping of Example 1, 550 mg / L of hydrogen peroxide was added, and the water temperature was maintained at approximately 30 ° C., followed by stirring with a stirrer for 1 hour. The hydrazine concentration in the waste water was 17.5 mg / L. When 150 mg / L of hydrogen peroxide was added again, the hydrazine concentration in the wastewater decreased to 3.5 mg / L and was pH 10.0.

Example 4
The treated water of Example 3 was transferred to a separate container, hydrosulfite 80 mg / L was added, and the mixture was stirred with a stirrer. The quality of the treated water after 1 hour was pH 9.5, ORP was -580 mV, and the filtrate was collected and analyzed with a 0.45 μm membrane filter. As a result, copper powder was not present and the copper ion was 0.1 mg / L or less.

  From the results of Examples 1 and 2 above, in the case of the hydrazine concentration of the wastewater in the examples, the copper powder concentration can be 200 to 500 mg / L, and the hydrazine concentration of the wastewater can be 110 mg / L or less. When the oxidation step was added (Example 3), even when the copper powder concentration was 20 mg / L, the hydrazine concentration was 17.5 mg / L, and the second oxidation step was further divided into two stages. The hydrazine concentration could be reduced to 3.5 mg / L. And what was reduce | restored with the reducing agent of the treated water of this Example 3 did not have copper powder as described in Example 4, and the copper ion was 0.1 mg / L or less.

  Since treated water treated with a reducing agent as described above does not contain copper ions or hydrazine at a concentration that inhibits biological treatment, organic substances such as complex-forming organic compounds remaining in the treated water are usually used in the activated sludge process, etc. Can be easily processed by biological treatment. Moreover, if the collected metal powder is returned to the wastewater oxidation process, the metal powder to be input to the oxidation process can be reused, leading to a reduction in the cost of wastewater treatment. In addition, if the metal is not separated in a state where it can be reused, metal industrial waste disposal costs are required. However, the present invention does not incur such costs, which can lead to further cost reduction.

Claims (6)

  Addition of metal powder to waste water containing hydrazine and a complex-forming organic compound, oxidation process for oxidative decomposition of hydrazine with oxygen-containing gas, and reduction of metal ions partially dissolved from the metal powder generated in the waste water in the oxidation process A reduction step of reducing to metal powder with an agent, and a separation step of solid-liquid separation of the treated wastewater containing the metal powder generated in the reduction step and separating it into concentrated water of the metal powder and treated water as separation water A method for treating wastewater containing hydrazine and a complex-forming organic compound.   The method for treating waste water containing hydrazine and a complex-forming organic compound according to claim 1, further comprising a returning step of returning the concentrated water of the metal powder separated in the separating step to the oxidizing step.   3. The reducing agent is at least one selected from the group consisting of lithium aluminum hydride, sodium borohydride, hypophosphorous acid, phosphinic acid, phosphonic acid, and hydrosulfite. Of waste water containing hydrazine and a complex-forming organic compound.   The hydrazine according to claim 1, 2 or 3, wherein a second oxidation step is further provided between the oxidation step and the reduction step to further oxidatively decompose hydrazine remaining in the oxidation step with an oxidizing agent. A method for treating wastewater containing a complex-forming organic compound.   The method for treating waste water containing hydrazine and a complex-forming organic compound according to any one of claims 1 to 4, wherein the separation step is performed by a membrane separation device.   The method for treating waste water containing hydrazine and a complex-forming organic compound according to any one of claims 1 to 5, wherein the treated water in the separation step is biologically treated.

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