JP4750873B2 - Method for treating waste liquid containing phenols - Google Patents

Description

  The present invention relates to a method for decomposing phenols in waste liquid containing phenols to render them harmless to living organisms and making them suitable for activated sludge treatment to be performed later.

  Waste liquids containing phenols may be generated in various industries such as the semiconductor industry. However, since they are highly toxic to living organisms, if they flow into a wastewater treatment facility using the activated sludge method, they kill bacteria and become an obstacle to treatment. Therefore, it is required that the waste liquid containing phenols be removed before being sent to a normal wastewater treatment process.

  As a means for decomposing and removing harmful chemical substances such as phenols in the waste liquid, an electrochemical oxidation method is known. For example, Japanese Patent Application Laid-Open No. 7-299467 (Patent Document 1) describes a method of decomposing toxic substances by electrolysis using an anode containing diamond made conductive by doping. It is described that an anode using diamond has better current efficiency than an anode such as platinum which has been generally used in the past, and enables electrolysis even for a material which is not effective in the conventional electrode.

As electrolysis conditions described in the above-mentioned JP-A-7-299467, for example, the voltage between the electrodes is 4 to 7 V, and the current density is 50 to 100 mA / cm ^{2 with} respect to the electrode area, such as phenol or aminocarboxylic acid chelate. Can be broken down.

Japanese Patent Laid-Open No. 7-299467

  In the waste liquid treatment method described in JP-A-7-299467, a large amount of oxygen or hydrogen is generated by the electrolytic reaction, and these gas components cover the electrode surface and prevent contact between the electrode and the waste liquid. Efficiency will be reduced. In some cases, the current density of the electrode becomes extremely large locally and affects the life of the electrode. However, on the other hand, the electrolysis of water is necessary for the decomposition of the organic matter in the waste liquid, and the oxidation of the organic matter proceeds by the active oxygen generated by the electrolysis.

  Therefore, in the apparatus used for electrolysis in Japanese Patent Application Laid-Open No. 7-299467, when a voltage that does not cause water electrolysis and a diamond electrode as an anode is applied, for example, 2 V is applied, Since it is not supplied, the decomposition of organic matter itself stops, and the purpose of waste liquid treatment cannot be achieved. Therefore, an object of the present invention is to decompose phenols in waste liquid by electrolysis without depending on oxygen generated by electrolysis of water.

This invention solves the said subject, Comprising: In the processing method of the waste liquid containing phenols, the working electrode by which the electroconductive diamond film was formed in at least one surface of the electrode plate of a conductor, and thickness is 0 .05 to 1.0 mm, an electrically insulating spacer having a hole in the surface, and a counter electrode made of a conductor having a surface opposite to the surface on which the diamond film of the working electrode is formed across the spacer. And an electrolytic device in which a liquid introduction port and a discharge port are respectively formed in one space formed by the hole of the spacer, and 1.5 to 2.5 V between the working electrode and the counter electrode. The waste liquid containing phenols is characterized by cleaving and decomposing the cyclic bonds of phenols by circulating the waste liquid while applying a voltage of. Further, the electrolysis apparatus is also characterized in that a reference electrode is provided so as to face the counter electrode side surface of the working electrode.

  According to the present invention, phenols in waste liquid can be decomposed with high efficiency without consuming energy for electrolysis of water. As a result, the toxicity of the waste liquid to bacteria can be eliminated, so that if the treatment according to the present invention is preceded, there will be no obstacle to the wastewater treatment by the activated sludge.

It is sectional drawing parallel to an axial direction which shows the electrolysis apparatus used for this invention. It is AA 'arrow sectional drawing in FIG.

  The method of the present invention decomposes the phenols contained by passing waste liquid through an electrolyzer unique to the present invention, and breaks the cyclic bonds of the phenolic molecules at a voltage within a range where water electrolysis does not occur. be able to. That is, the electrolysis apparatus used in the method of the present invention comprises a working electrode having a conductive diamond film formed on at least one surface of an electrode plate of a conductor, a surface having a diamond film of the working electrode, and 0.05 to 1.0 mm. And a counter electrode made of a conductor opposed to each other.

  1 and 2 are views showing an electrolysis apparatus used in the present invention. FIG. 1 is a cross-sectional view parallel to the axial direction, and FIG. 2 is a cross-sectional view taken along line AA ′ in FIG. In these figures, reference numeral 11 denotes a working electrode (in FIG. 2, the positional relationship is indicated by a two-dot chain line), which is on at least the front surface of the thin plate-like conductive substrate, ie, at least the left surface in FIG. A conductive diamond film is formed. Reference numeral 12 denotes a spacer made of a chemical-resistant electrical insulator such as fluorine resin, and has one elongated hole 121 as shown in FIG. Reference numeral 13 denotes a counter electrode made of a corrosion-resistant conductor block such as titanium, which faces the surface of the working electrode 11 on which the diamond is formed with the spacer 12 interposed therebetween. Therefore, the distance between the working electrode and the counter electrode is determined by the thickness of the spacer.

  The working electrode 11 is a conductive thin plate, for example, a conductive silicon single crystal plate having a thickness of about 0.7 mm, and has a thickness of about 30 μm made of fine diamond crystals of several μm in size. Created by forming a coating. The diamond film can be formed by plasma CVD in hydrogen gas containing a carbon source such as acetone. In order to impart conductivity to diamond, boron oxide or the like is doped in boron by dissolving it in the carbon source.

  Each of the spaces 14 formed by the holes 121 of the spacer 12 is opened to have an inlet 15 and an outlet 16 for the liquid to be processed, both of which are provided in the block of the counter electrode 13. That is, the inlet 15 and the outlet 16 of the liquid to be processed are formed by making holes in the block of the counter electrode 13, and fluid couplings 17 and 18 for introducing and discharging the liquid to be processed are screwed into the block of the counter electrode. . Reference numeral 19 denotes an energization terminal for the counter electrode 13.

  Reference numeral 30 denotes a reference electrode, which is screwed into a counter electrode block so that its tip is flush with the counter electrode. Here, an example of an Ag-AgCl system is shown, but a chemical resistant container 301 such as a fluororesin in which a saturated KCl solution is gelatinized with gelatin is filled as an electrolytic solution 302. Further, an Ag wire having a surface made of AgCl is inserted as an electrode material 303 therein. Reference numeral 304 denotes a filter made of porous ceramic or the like that separates the electrolyte solution 302 of the reference electrode from the liquid to be treated. Although the reference electrode is not essential for the electrolytic treatment apparatus of the present invention, it is preferable to provide the reference electrode in order to measure an accurate voltage between the working electrode and the counter electrode.

  Further, on the back surface of the electrode plate of the working electrode 11, that is, on the opposite side of the surface facing the counter electrode 13, an energizing plate 20 for the working electrode is provided and is in contact with the working electrode 11. Reference numeral 21 denotes an energization terminal for the working electrode 11. Reference numeral 22 denotes a seal cover made of a chemical-resistant electrical insulator, which is connected to the block of the counter electrode 13 by a plurality of set screws (not shown). Seal the inside. In addition, an O-ring 26 is provided in a part of the energizing plate 20 so that the liquid to be treated does not enter inside thereof, and the energizing plate is directly brought into electrical contact with the back surface of the electrode plate without passing through the liquid. A plastic insulating cover 27 covers the entire metal block of the counter electrode 13.

  As will be described later, in the present invention, by utilizing the fact that the diamond electrode does not cause water electrolysis even in a relatively high voltage range, phenols are decomposed without causing water electrolysis. However, the back surface and the end surface of the working electrode 11 are not necessarily formed with a diamond coating, and the current-carrying plate 20 naturally has no diamond coating. Accordingly, when the liquid to be treated wraps around a portion of the electrode plate or the like where there is no diamond coating, water electrolysis may occur. However, the end surface of the electrode plate of the working electrode 11 and the back surface other than the contact portion with the energizing plate are also treated. The structure allows contact with liquid. Even in this way, even if bubbles are generated in a place where there is no flow of the liquid, it stops at that portion, and since the metal surface is covered with bubbles and is not energized, electrolysis of water does not proceed any further. If the liquid to be treated is to be sealed so as to remain within the range facing the spacer hole 121 of the working electrode, it is difficult to press the gap between the working electrode and the counter electrode with a large force, which is difficult due to the problem of damage to the electrode plate. It is. Therefore, as described above, it is practically important to have a structure that allows contact with the liquid to be treated except for a portion of the surface of the working electrode opposite to the surface facing the counter electrode, that is, the energized portion.

  In the method of the present invention, electrolysis is performed by applying a voltage of 1.5 to 2.5 V between the working electrode and the counter electrode using the above-described electrolysis apparatus. The electrolytic treatment in the present invention is carried out at a voltage that does not cause electrolysis of water, but as described above, by using a diamond electrode as the working electrode of the electrolysis apparatus, electrolysis is performed by applying a higher voltage than before. Is possible. That is, the electrolysis of water occurs when the working electrode in the conventional electrolysis apparatus such as a platinum electrode exceeds 1.2 V, but the electrolysis apparatus used in the present invention is about 2.5 V (relative to the Ag / AgCl reference electrode). ) Water electrolysis does not occur. Therefore, in an electrolysis apparatus using a diamond electrode as a working electrode, it is possible to break bonds between atoms of molecules that cannot be decomposed unless the voltage is high, and the phenols targeted by the present invention can be decomposed.

  In the present invention, in order to break bonds between molecular atoms in a voltage range in which water is not electrolyzed, the gap between the surface of the working electrode 11 having the diamond coating and the counter electrode 13 is as narrow as 1.0 mm or less as described above. It is necessary to. In addition, since there exists a possibility that a working electrode and a counter electrode may contact if the space | interval of a working electrode and a counter electrode is smaller than 0.05 mm, 0.05 mm or more is suitable. It is unclear why the bond breakage between molecular atoms due to electrolysis occurs only when the working electrode and the counter electrode face each other with a narrow gap of 0.05 to 1.0 mm.

As described in Japanese Patent Laid-Open No. 7-299467 described above, if electrolysis is performed at a high voltage at which water electrolysis occurs, for example, 5 V, the electrolysis apparatus is conventional or unique to the present invention. It is possible to decompose phenols in the solution in parallel with the electrolysis of water, regardless of whether they are of the same type. Such decomposition is not performed directly by electrolysis, but it is considered that oxidation proceeds rapidly due to active oxygen generated by electrolysis of water, that is, highly reactive OH radicals. Such decomposition accompanying water electrolysis is performed at a high current density of 50 to 100 mA / cm ^{2 with} respect to the electrode area as described in JP-A-7-299467. For example, water and carbon dioxide can be seen, and the degree of decomposition is very advanced.

On the other hand, in the electrolysis method of the present invention, the cyclic bond of phenols is cleaved to change to a substance that is not toxic to living organisms, and is converted to a waste liquid suitable for the activated sludge treatment to be performed later. is there. For this reason, electrolysis in a solution containing KH ₂ PO ₄ is preferable because it is a substance that promotes activated sludge treatment. Phenols include drugs such as p-nonylphenol, bisphenol A, BHT (dibutylhydroxytoluene), and phenylphenol. Note that, when the liquid to be treated is passed through the electrolysis apparatus, for example, when the component concentration is 100 mM, it is about 3 to 5% of the original component amount. Therefore, for the treatment of the waste liquid, the solution may be circulated through the electrolyzer and repeatedly electrolyzed.

The electrolysis current when phenols are decomposed by the electrolyzer according to the present invention depends on the component concentration, unlike the case of electrolyzing water, but is, for example, 1 μA to 10 μA per component concentration of 10 μM (10 pmol / μl) in the solution. The current density with respect to the effective area of the working electrode, that is, the area of the portion facing the spacer hole 121 is about 5 mA / cm ² even when the component concentration is 100 mM, and the component concentration decreases accordingly. Lower. The current density in the case of electrolysis of water as described in JP-A-7-299467 is 50 to 100 mA / cm ² regardless of the component concentration, but in the electrolytic treatment of the present invention, the current efficiency is much smaller than this and the current efficiency is very low. Good for.

  Even when the distance between the working electrode and the counter electrode is larger than 1.0 mm, an electrolysis current is observed in a voltage range in which electrolysis of water does not occur, but this is not due to decomposition of components but due to detachment of electrons from molecules. Is. In this case, the current detected by the sample having a concentration of 100 μM is about 0.4 μA, which is much smaller than that in the case of the present invention.

Example 1
Electrolysis was performed with the electrolysis apparatus shown in FIGS. 1 and 2 to decompose phenol in the sample solution. The distance between the working electrode 11 and the counter electrode 13 was changed to 0.2 mm, 0.5 mm, 1.0 mm, and 2.0 mm by using an electrolysis apparatus having spacers 11 having different thicknesses. In addition, since the tip position of the reference electrode 30 is the same as the electrode surface of the counter electrode in any case, the distance between the reference electrode and the counter electrode is also the same as the distance between the working electrode and the counter electrode. The applied voltage of the working electrode of the electrolyzer was set to 2.1 V with respect to the Ag / AgCl reference electrode (about 2.4 V with respect to the counter electrode). Did not occur.

With the 100 mM-KH ₂ PO ₄ solution supplied to the electrolyzer at a rate of 0.5 ml / min, a sample solution having a concentration of phenol of 0.5 μg / μl (about 5 mM) was placed in front of the 20 μl electrolyzer. When injected into the flow path, electrolytic current peaks of 380 μA, 350 μA, and 270 μA were detected when the distance between the working electrode and the counter electrode was 0.2 mm, 0.5 mm, and 1.0 mm, respectively, but 2.0 mm In the case of, only a small amount of electrolysis current was detected with the same measurement sensitivity. Analysis of the solution after passing through the electrolytic apparatus by NMR and LC-MS confirmed that phenol was decomposed.

(Example 2)
In the electrolysis apparatus used in Example 1, the interval between the working electrode and the counter electrode was 0.5 mm, and the working electrode applied voltage of the electrolysis apparatus was the same as that in Example 1. Here, in a state where the 100 mM-KH ₂ PO ₄ solution is supplied at a rate of 0.5 ml / min, phenol is 0.2 μg / μl (about 2 mM), 0.5 μg / μl (about 5 mM), 1.0 μg. / Μl (about 11 mM) and 2.0 μg / μl (about 21 mM) of the sample solution were injected into the flow path in front of the 20 μl electrolysis device, and peaks of electrolytic currents of 140 μA, 350 μA, 690 μA, and 1330 μA were detected, respectively. It was done. As the concentration increases, the electrolysis current increases proportionally, but there is a tendency to peak in the range where the concentration is large.

(Example 3)
In the electrolysis apparatus used in Example 1, electrolysis was performed with the distance between the working electrode and the counter electrode set to 0.5 mm. The sample was 30 ml of an aqueous solution containing 1500 ppm (about 16 mM) of phenol in a 100 mM KH ₂ PO ₄ solution, and the electrolyzer was circulated at a rate of 2 ml for 1 minute. The working electrode applied voltage of the electrolyzer was set to 1.9 V (about 2.1 V for the counter electrode) with respect to the Ag / AgCl reference electrode, but the electrolysis current was 1.2 mA at maximum and decreased with time. did. The effective area of the working electrode, that is, the area of the part facing the hole 121 of the spacer is about 2.8 cm ² . When the concentration of phenol in the solution was analyzed after 1 hour, phenol was reduced by 94%.

DESCRIPTION OF SYMBOLS 11 Working electrode 12 Spacer 121 Hole 13 Counter electrode 14 Space 15, 16 Eluate inlet and outlet 17, 18 Fluid coupling 19 Current terminal 20 Current plate 21 Current terminal 22 Seal cover 23, 24, 26 O-ring 27 Insulating cover 30 Reference electrode 301 Container 302 Electrolyte 303 Electrode material 304 Filter

Claims (2)

In a method for treating a waste liquid containing phenols, a working electrode having a conductive diamond film formed on at least one surface of an electrode plate of a conductor, and a thickness of 0.05 to 1.0 mm and a hole in the surface And a counter electrode made of a conductor having a surface opposite to the surface on which the diamond film of the working electrode is formed across the spacer, and further formed by a hole in the spacer. By using an electrolytic device in which a liquid inlet and outlet are formed in the space, respectively, the waste liquid is circulated while applying a voltage of 1.5 to 2.5 V between the working electrode and the counter electrode. A method for treating a waste liquid containing phenols, wherein the cyclic bonds of phenols are cleaved and decomposed. 2. The method for treating a waste liquid containing phenols according to claim 1, wherein the electrolysis apparatus is provided with a reference electrode so as to face a surface on the counter electrode side of the working electrode.

Images