JP2003300073A - Method for treating waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating waste water capable of decomposing the waste water containing at least either of a DMI (1,3-dimethyl-2- imidazolidinone) and DMSO (dimethylsulfoxide) to inorganic compounds, such as gaseous nitrogen, gaseous carbon dioxide, water and sulfuric acid, and of reducing a COD as well without generating by-products which are harmful and emit malodors. <P>SOLUTION: The waste water containing at least either of the DMI and the DMSO is electrolytically decomposed by using a conductive diamond electrode. The current density of the conductive diamond electrode surface is regulated to 10 to 100,000 A/m<SP>2</SP>and the linear velocity of passing liquid of the waste water to 10 to 1,000 m/hr. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to 1,3-dimethyl-2-imidazolidinone (DM) as an organic nitrogen compound.
I), dimethyl sulfoxide (D) as an organic sulfur compound
MSO), at least one of these compounds can be decomposed into inorganic compounds such as nitrogen gas, carbon dioxide gas, water, sulfuric acid, etc. without generating harmful and malodorous by-products. Moreover, the present invention relates to a wastewater treatment method capable of reducing chemical oxygen consumption (COD).

[0002]

[Technical background] Organic nitrogen compounds cause eutrophication when released into water, and when released into the atmosphere, they are not only harmful per se, but also participate in photochemical reactions and cause secondary complex pollution phenomenon. Contribute to. Emission sources of organic nitrogen compounds include
For example, there are those derived from proteins and the like used as raw materials in the feed manufacturing industry for livestock, poultry, fish and the like, or in the human food manufacturing industry. In particular, the organic nitrogen compound is
COD is often large. Therefore, when treating the organic nitrogen compound-containing wastewater, it is necessary to reduce the COD as well as the decomposition of the organic nitrogen compound.

As a typical treatment method of organic nitrogen compounds, a biological treatment method, an activated carbon treatment method and the like are known. However, the biological treatment method has a problem that since the reaction time is slow, the time required for decomposition is long, a large-capacity biological reaction tank is required, and a large amount of excess sludge is generated. On the other hand, the activated carbon treatment method requires regeneration of the activated carbon when the adsorption equilibrium is reached. At the time of this regeneration, there is a problem that a high-concentration regenerated drainage liquid is generated, and therefore the treatment is further required. To eliminate these problems,
The applicant of the present application has already proposed a method of electrolyzing an organic nitrogen compound (Japanese Patent Laid-Open No. 10-174976). According to this method, nitrogen compounds can be decomposed to remove all nitrogen (TN) and COD at the same time.

DMSO among organic sulfur compounds
Is frequently used in semiconductor manufacturing plants and liquid crystal panel manufacturing plants, and efficient removal of DMSO contained in wastewater is an important issue. Moreover, these manufacturing plants use organic cleaning agents containing coexisting organic compounds such as isopropyl alcohol and surfactants, and it is also necessary to treat cleaning waste water using these cleaning agents.

As a method for treating DMSO-containing wastewater, in addition to the biological treatment method, ozone oxidation method, hydrogen peroxide oxidation method, U
A physicochemical decomposition treatment method using the V oxidation method or the like alone or in an appropriate combination is known. But,
In the biological treatment method, it is difficult to maintain the inside of the reaction vessel under aerobic conditions, and when DMSO is decomposed under anaerobic conditions, toxic substances such as methyl mercaptan and hydrogen sulfide, which emit a foul odor, are generated from the wastewater. However, there is a problem that it diffuses into the atmosphere and deteriorates the environment. In the decomposition treatment method of No. 3, the hardly-decomposable DMSO is not completely decomposed into carbon dioxide, water, and inorganic substances such as sulfuric acid, but only converted into dimethyl sulfone (DMSO ₂ ) or methane sulfone (MSA). The oxidative decomposition reaction of does not proceed.

Therefore, a method for treating DMSO ₂ by combining the decomposition treatment method and the biological treatment method has been developed (Japanese Patent Laid-Open Nos. 12-263069 and 13-212597). Further, even in this combination method, the oxidizing agent is consumed only for the oxidation of the coexisting organic compound, and the decomposition efficiency of DMSO to DMSO ₂ is remarkably lowered, so that the pretreatment for removing the coexisting organic compound is performed. Ingenuity is needed. Under these circumstances, DMS is usually used.
Most of the O-containing wastewater is treated as industrial waste.

[0007]

It is an object of the present invention to remove wastewater containing at least one of DMI of the above organic nitrogen compounds and DMSO of the above organic sulfur compounds with higher efficiency than that obtained by the conventional electrolysis treatment method. Provided is a wastewater treatment method which eliminates the use of an oxidizing agent in a conventional electrolysis treatment method and eliminates a pretreatment for removing the organic compound even when a coexisting organic compound is contained. The purpose is to

[0008]

SUMMARY OF THE INVENTION The inventors of the present invention have conducted extensive studies to achieve the above object. As a result, when a conductive diamond electrode is used, hydrogen generation and oxygen generation due to electrolysis of water are suppressed, while DMI and DMSO are suppressed. It was found that only oxidative decomposition can be carried out efficiently.

The wastewater treatment method of the present invention is based on the above findings and is characterized in that wastewater containing at least one of DMI and DMSO is electrolyzed using a conductive diamond electrode. At this time, the current density on the surface of the conductive diamond electrode is 10 to 100,000 A / m ²
It is preferable that the liquid passing linear velocity of the drainage is 10 to 1,000 m / hr.

Objects to be processed in the present invention are DMI and DM.
Wastewater containing at least one of SO, and as described above, various wastewater from a feed manufacturing factory for livestock, poultry, fish and the like, a human food manufacturing factory, or a semiconductor manufacturing factory or a liquid crystal panel manufacturing factory. In addition to various kinds of wastewater such as general industrial wastewater, domestic wastewater, and miscellaneous wastewater, DMI and DM containing the coexisting organic compounds, ammonia, hydrazine, various metal ions, etc.
It is suitable for SO-containing wastewater and can obtain a remarkable effect.

The conductive diamond electrode used in the present invention uses a conductive metal material such as Ni, Ta, Ti, Mo, W or Zr as a substrate, and a conductive diamond thin film is deposited on the surface of these substrates. Examples thereof include a semiconductor material such as a silicon wafer used as a substrate, and a conductive diamond thin film synthesized on the surface of the wafer, or a conductive polycrystalline diamond material deposited and synthesized in a plate-like condition without using the substrate. Incidentally, the conductive (polycrystalline) diamond thin film is one in which conductivity is imparted by doping a predetermined amount of boron or nitrogen when the diamond thin film is prepared,
It is generally doped with boron. If the doping amount is too small, the technical significance of doping will not be expressed, and if the doping amount is too large, the doping effect will be saturated. Therefore, it is suitable that the doping amount is within the range of 50 to 10,000 ppm with respect to the carbon amount of the diamond thin film material. ing.

In the present invention, the conductive diamond electrode is generally a plate-shaped one, but a plate-shaped mesh structure or the like can also be used.

The conductive diamond electrode used in the present invention has an extremely wide potential window as compared with a conventional metal electrode such as platinum, and suppresses hydrogen generation and oxygen generation due to electrolysis of water, while performing electrolysis in the present invention. Target DMI and DM
Only SO can be efficiently oxidatively decomposed.

The treatment method of the present invention generally uses an electrolytic reaction tank in which a plurality of the above-mentioned conductive diamond electrodes are arranged at intervals of several mm to several cm (specifically about 2 mm to 2 cm). The above waste water is passed between the electrodes of the reaction tank, and DMI or DMS is applied on the surface of the conductive diamond electrode.
O is electrolyzed into harmless inorganic compounds such as nitrogen gas, carbon dioxide gas, water and sulfuric acid. At this time, the current density on the surface of the conductive diamond electrode is 10 to 100,0.
It is important that the flow rate of the drainage to the electrolytic reaction tank is 10 A / m ² and the linear flow velocity of the drainage is 10 to 1,000 m / hr.

If the current density is less than the above value, the current efficiency of the conductive diamond electrode is good, but in order to perform sufficient electrolysis treatment of DMI and DMSO in wastewater, a certain large electrode area is required. It is necessary, and the electrolytic reaction tank applied to the treatment method of the present invention must have a large capacity, resulting in enormous equipment cost and running cost. On the other hand, if the above value is exceeded, the inter-electrode resistance increases and the heat energy is consumed, which is uneconomical.

Further, if the drainage passage speed is set to be 10 to 1,000 m / hr in terms of linear velocity (LV), if it is too fast, the contact time between the drainage and the electrode surface will be sufficient. As a result, the electrolysis of DMI and DMSO cannot be progressed sufficiently, and if it is too slow, the sufficient effect cannot be exhibited and the treatment efficiency of waste water is extremely reduced.

The liquid temperature in the electrolytic reaction tank is not particularly limited, but if the temperature is too low, the electrolysis of DMI and DMSO does not proceed well, and if the temperature is too high, the drainage and the electrode surface may come into contact with each other. In the present invention, it is desirable to set the temperature to about 10 to 95 ° C., because the generation of the gas component that inhibits increases.

In the processing method of the present invention, DMI and DMSO are used.
The wastewater containing is to be electrolyzed by passing through an electrolytic reaction tank using a conductive diamond electrode as described above, for example, at this time, simply by applying a predetermined current to the conductive diamond electrode. Often, it is not necessary to add an oxidizing agent such as hydrogen peroxide or sodium hypochlorite which is required for the conventional electrolysis treatment of organic nitrogen compounds and organic sulfur compounds. Therefore, not only the control of the addition amount of the oxidizing agent required in the conventional electrolysis treatment, but also the addition of a reducing agent for treating the excess oxidizing agent, the complicated control such as the control of the addition amount of the reducing agent is not performed at all. It becomes unnecessary.

In the treatment method of the present invention, it is not particularly necessary to add an electrolyte substance, and an electrolyte substance contained in wastewater containing DMI or DMSO, such as KCl or KCl.
O, NaCl, NaClO, H ₂ SO ₄ , Na ₂ SO ₄
Etc. directly act as an electrolyte substance. The concentration of these electrolyte substances in the waste water is not particularly limited, and is 50 to 50,000 mg / liter (hereinafter, liter is “L”, milliliter is “mL”) required for conventional electrolytic treatment.
However, even if it is less than 6,000 mg / L, the efficiency of conventional electrolytic treatment is extremely poor, the conductive diamond electrode having high current efficiency is used, so that the treatment should be performed efficiently. You can

Since the crystal of the conductive diamond electrode used in the present invention is extremely dense and stable, there is no fear of deterioration or wear even if it is energized at a high current density. . Therefore, it can be used at a high current density, and in the treatment method of the present invention, the wetted area of the conductive diamond electrode is smaller than the wetted area of the platinum-based electrode or the like used in conventional electrolysis. can do.
As a result, the electrolytic reaction tank for carrying out the treatment method of the present invention can be made compact.

Further, the conductive diamond electrode is excellent in chemical stability in addition to suppressing the phenomenon that other crystal grains such as calcium carbonate are deposited due to the uniform crystal structure of diamond. No erosion by normal acid or alkali. Therefore, the conductive diamond electrode can maintain stable treatment performance for a long period of time without corrosion or adhesion of scale to the cathode surface, and replacement of the electrode or cleaning of the electrode surface becomes unnecessary. .

According to the treatment method of the present invention using such a conductive diamond electrode, DMI and DMSO are
It is possible not only to satisfactorily electrolyze inorganic compounds such as nitrogen gas, carbon dioxide gas, water and sulfuric acid, but also to reduce COD, without generating harmful and foul-smelling by-products. In the present invention, DMI and D
It is also possible to subject water containing MSO to adsorption treatment with activated carbon or biological treatment in advance to reduce DMI and DMSO, and then subject it to electrolysis treatment using a conductive diamond electrode.

[0023]

EXAMPLES Example 1 A laminated polycrystalline conductive diamond electrode plate (5 × 5 × 0.05 cm) 2 vapor-deposited and synthesized using a boron doping method 2
Using one plate as an electrode, the distance between the electrodes was set to 1 cm to form an electrolytic reaction tank. Waste water containing 1,000 mg / L of DMI (total nitrogen << TN >>: 246 mg / L, total organic carbon compound << TOC >>: 526 mg / L, oxygen consumption due to potassium permanganate peroxide at 100 [deg.] COD: 9
50 mg / L, sodium chloride: 10,000 mg /
L, pH: 9.7) Put 1,000 mL in the electrolytic storage tank,
While stirring with a stirrer, the solution was pumped into the electrolytic reaction tank at a flow rate of 110 mL / min, and the overflow solution in the electrolytic reaction tank was returned to the electrolytic storage tank again for circulation treatment. The amount of electricity input to the electrolytic reaction tank was 0.
It was set to be 1 A / cm ² (1000 A / m ² ).

Water was collected from the outlet of the electrolytic reaction tank at a time point 2 or 4 or 6 hours after the start of the electrolytic treatment, and the water quality was analyzed. The results are shown in Table 1. As is clear from Table 1,
It was confirmed that any of TN, TOC, and COD can be efficiently removed.

[0025]

[Table 1]

Comparative Example 1 In the same manner as in Example 1 except that the conductive diamond electrode plate used in Example 1 was replaced with two platinum-plated titanium plates (5 × 5 × 0.3 cm). Electrolysis treatment by circulation treatment was performed. The electrolysis treatment was performed for up to 10 hours. The results are shown in Table 2. As is clear from the comparison between Table 2 and Table 1, it was confirmed that the reaction rate was slower than that of Example 1 and that the water quality after 10 hours was inferior to that after Example 6 after 6 hours. Was done.

[0027]

[Table 2]

Example 2 The same conductive diamond as in Example 1 except for the size.
Two electrode plates (2 x 2 x 0.05 cm) are used as electrodes
And set the distance between the electrodes to 0.5 cm to configure the electrolytic reaction tank.
It was The amount of electricity input to the electrolytic reaction tank is a current density of 0.625A.
/ Cm^Two(6250A / m ^Two).
Except for these, the electric power generated by the circulation treatment was the same as in Example 1.
A gasolysis treatment was performed. The results are shown in Table 3. Table 3 and table
As is clear from comparison of Example 1, as compared with Example 1,
6.25 times the current density on the pole surface, the linear velocity of liquid passing through the electrolytic reaction tank
5 times higher than the result of Example 1 with much higher efficiency
It was confirmed that electrolysis proceeded.

[0029]

[Table 3]

Comparative Example 2 Instead of the conductive diamond electrode plate used in Example 2, two platinum-based electrode plates used in Comparative Example 1 were used as electrodes, and the distance between the electrodes was set to 0.5 cm to form an electrolytic reaction tank. An electrolysis treatment by a circulation treatment was performed in the same manner as in Example 2 except that the constitution was adopted. The results are shown in Table 4. As is clear from the comparison between Table 3 and Table 4, it was confirmed that the reaction rate was slower than in Example 2 and the water quality was poor. This means that the platinum-based electrode is not suitable for the electrolysis treatment under the condition of high current density.

[0031]

[Table 4]

Example 3 The same electrolytic reaction vessel as in Example 1 was constructed, and DMSO was added to 250
Wastewater containing mg / L (TOC: 75 mg / L) 1,000
Electrolysis treatment by circulation treatment was carried out in the same manner as in Example 1 except that mL was placed in an electrolytic storage tank and stirred with a stirrer, and liquid was sent to the above electrolytic reaction tank with a liquid feed pump at a flow rate of 150 mL / min. It was

Water at the outlet of the electrolytic reaction tank was sampled 3 and 6 hours after the start of electrolytic treatment, and the water quality was analyzed.
The results are shown in Table 5. As is clear from Table 5, TO
It was confirmed that C can be efficiently removed.

[0034]

[Table 5]

Comparative Example 3 The conductive diamond electrode plate used in Example 3 was replaced with two platinum-based electrode plates used in Comparative Example 1 as electrodes.
Electrolysis treatment by circulation treatment was performed in the same manner as in Example 3. The results are shown in Table 6. As is clear from Table 6, it is understood that there is no TOC reducing effect. From the analysis result of the treated water, it was confirmed that this was because DMSO was only oxidized to DMSO ₂ and the further oxidative decomposition reaction did not proceed.

[0036]

[Table 6]

Comparative Example 4 Except that two platinum-based electrode plates used in Comparative Example 3 were used as electrodes and sodium hypochlorite was added as an oxidant so as to be 1.2 times (300 mg / L) DMSO concentration. In the same manner as in Example 3, electrolysis treatment by circulation treatment was performed. The results are shown in Table 7. As is clear from Tables 7 and 6, although the TOC reduction effect is higher than that of Comparative Example 3,
It turns out that it is extremely low. It was also confirmed that, despite the addition of the oxidizing agent, most of DMSO was oxidized only to DMSO ₂ and MSA, and further oxidative decomposition reaction did not proceed.

[0038]

[Table 7]

Example 4 An electrolysis treatment by circulation treatment was carried out in the same manner as in Example 3 except that the same electrolytic reaction tank as in Example 2 was constructed and the same amount of electricity as in Example 2 was used. The results are shown in Table 8.
As is clear from comparison between Table 8 and Table 5, compared with Example 3, the current density on the electrode surface was 6.25 times and the liquid passing linear velocity of the electrolytic reaction tank was 5 times that of Example 3. It was confirmed that the electrolysis proceeded with much higher efficiency than the results.

[0040]

[Table 8]

Example 5 The same as Example 3 except that DMSO of 250 mg / L, isopropyl alcohol of 25 mg / L, and a surfactant of 2 mg / L of waste water (TOC: 90 mg / L) of 1,000 mL were used. Then, electrolysis treatment by circulation treatment was performed. The results are shown in Table 9. As is clear from Table 9, it was confirmed that TOC could be efficiently removed as in the case of Example 3 even when the organic compound such as isopropyl alcohol and surfactant was contained.

[0042]

[Table 9]

Example 7 Electricity by circulating treatment was carried out in the same manner as in Example 1 except that the mixed wastewater of 500 mL of Example 1 and the mixed wastewater of 500 mL of Example 6 were mixed wastewater of 1,000 mL. A decomposition process was performed. The results are shown in Table 10.
As is clear from Table 10, even if both DMI and DMSO are contained and the coexisting organic compound is also contained, T-N, T
It was confirmed that both OC and COD could be efficiently removed, and coexisting organic compounds could also be efficiently removed.

[0044]

[Table 10]

[0045]

As described above, according to the treatment method of the present invention, wastewater containing DMI as an organic nitrogen compound and DMSO as an organic sulfur compound can be treated with nitrogen without generating harmful and foul-smelling by-products. Not only can it be decomposed into inorganic compounds such as gas, carbon dioxide, water and sulfuric acid, but also COD can be greatly reduced.

According to the processing method of the present invention, the following effects can be obtained. (1) As in the case of treating wastewater containing DMI or wastewater containing DMSO by a conventional biological treatment method, it takes a long time to decompose, aftertreatment of a large amount of excess sludge, and complicated. There are no problems such as maintaining stable operating conditions and the generation of offensive odor by-products. (2) As in the case of treating wastewater containing DMI or treating wastewater containing DMSO by the conventional activated carbon treatment method,
There are no problems such as limited treatment performance, regeneration or replacement of activated carbon whose performance has deteriorated, or treatment of highly concentrated regenerated effluent generated during activated carbon regeneration. (3) As in the case of electrolyzing wastewater containing persistent DMSO using a conventional platinum-based electrode, DMSO ₂ or M
There is no problem that not only SA is not generated, but also the oxidizing agent in the case where the coexisting organic compound is contained is consumed only for the oxidation of the coexisting organic compound and the decomposition efficiency of DMSO to DMSO ₂ is remarkably lowered.

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Claims (2)

[Claims] 1. A method for treating wastewater, which comprises subjecting wastewater containing at least one of 1,3-dimethyl-2-imidazolidinone and dimethyl sulfoxide to electrolysis treatment using a conductive diamond electrode. 2. A conductive diamond electrode surface having a current density of 10 to 100,000 A / m ² and a drainage liquid flow velocity of 10 to 1,000 m / hr. Wastewater treatment method.