JP4859863B2 - Water treatment method and water treatment apparatus - Google Patents

Description

  The present invention relates to a water treatment method and a water treatment apparatus for efficiently treating both raw water containing tetraalkylammonium hydroxide and a fluorinated organic compound.

  Fluorine organic compounds have a very chemically stable nature and have been widely used in various applications such as water repellents, surface treatment agents, and coating agents.

  A typical use example of the fluorine-based organic compound is use in a semiconductor etching process or the like. In this process, with development of the semiconductor substrate, a resist and tetraalkylammonium hydroxide such as about 0.002 to 2% by weight of tetramethylammonium hydroxide (hereinafter sometimes referred to as TMAH as a hydroxide). And perfluorooctanoic acid (hereinafter sometimes referred to as PFOA), perfluorooctanesulfonic acid (hereinafter sometimes referred to as PFOS), and the like, to alkyl groups in which all hydrogen atoms are substituted with fluorine atoms Then, washing water containing a fluorine-based organic compound to which a sulfo group, a carboxyl group or the like is bonded is drained. Therefore, treatment of fluorine-based organic compounds such as PFOS coexisting with TMAH and the like is urgently required.

  Examples of the treatment of fluorine-based organic compounds that coexist with TMAH in wastewater include an ultraviolet irradiation method as shown in Patent Document 1, a subcritical water oxidation method in which iron powder as shown in Non-Patent Document 1 coexists, and the like. A decomposition process has been proposed.

  On the other hand, focusing on only the treatment of a fluorine-based organic compound as a treatment by adsorption, a method using an ion exchange resin as in Patent Document 2 and a method of removing adsorption by activated carbon have been proposed.

JP 2003-040805 A JP 2002-059160 A Environmental Science & Technology, Vol. 40, no. 3,2006, p1049-1054

  However, with regard to the decomposition treatments such as Patent Document 1 and Non-Patent Document 1, originally, the fluorine-based organic compound is a very stable substance, so it is difficult to decompose, and when TMAH or the like coexists, the decomposition treatment is applied. However, there was a drawback that a lot of energy was required.

  In addition, in the treatment method using an ion exchange resin as in Patent Document 2, a fluorine-based organic compound can be efficiently removed. However, when about 0.002 to 2 wt% of TMAH coexists, a large amount of coexisting salt is present. Therefore, there is a problem that the performance of removing the ion exchange resin is greatly lowered. As for the activated carbon adsorption treatment, conventionally, activated carbon treatment biologically treats TMAH and the like, and then performs activated carbon treatment as a finishing treatment. Therefore, in the wastewater to be treated, SS components generated by biological treatment, TMAH, etc. Components that inhibit the adsorption of decomposition byproducts and the like are present at a relatively high concentration. In addition, since the activated carbon treatment is the final treatment step, it is diluted with other wastewater and diluted, resulting in a decrease in the concentration of the fluorinated organic compound, which significantly reduces the adsorption efficiency of the fluorinated organic compound on the activated carbon. There was a problem.

  As described above, various techniques have been proposed for the sole treatment of a fluorine-based organic compound. However, when a tetraalkylammonium hydroxide and a fluorine-based organic compound coexist in raw water, the present invention relates to a technique that can efficiently treat both. There is little knowledge.

  The present invention is a water treatment method and a water treatment apparatus capable of efficiently treating both raw water containing tetraalkylammonium hydroxide and a fluorinated organic compound.

The present invention is seen containing activated carbon treatment step of activated carbon treatment raw water containing the tetraalkylammonium hydroxide and the fluorine-based organic compound, a biological treatment process of biological treatment with activated carbon treatment solution described above activated carbon treatment, wherein the fluorine-based In the water treatment method, the organic compound is a fluorine-based organic compound in which at least one group selected from a sulfo group, a carboxyl group, and an amino group is bonded to an alkyl group in which all hydrogen atoms are substituted with fluorine atoms .

The present invention also includes a pH adjustment step for adjusting the pH of raw water containing tetraalkylammonium hydroxide and a fluorine-based organic compound to 7.5 or less, an activated carbon treatment step for treating the pH-adjusted pH-adjusted solution with activated carbon, the activated carbon treatment and the biological treatment step for biological treatment of activated carbon treatment liquid within the pH5.5~7.5 was, only containing the fluorine-based organic compound, the hydrogen atoms are replaced in all fluorine atom alkyl The water treatment method is a fluorine-based organic compound in which at least one group selected from a sulfo group, a carboxyl group, and an amino group is bonded to the group .

Further, the present invention is that the raw water containing the tetraalkylammonium hydroxide and fluorine-based organic compound possess and activated carbon treatment means for the activated carbon treatment, a biological treatment means for biological treatment of activated carbon treatment solution described above activated carbon treatment, the said fluorine-based organic compound, the alkyl group in which a hydrogen atom has been substituted in all fluorine atom, a sulfo group, a carboxyl group, at least one of the groups bonded to are fluorine organic compounds der Ru water treatment device selected from amino group It is.

The present invention also includes a pH adjusting means for adjusting the pH of raw water containing tetraalkylammonium hydroxide and a fluorine-based organic compound to 7.5 or less, and an activated carbon treatment means for treating the pH-adjusted pH-adjusted solution with activated carbon. the activated carbon-treated activated carbon treatment solution have a, a biological treatment means for biological treatment in the range of PH5.5～7.5, the fluorine-based organic compound, the hydrogen atoms are replaced in all fluorine atom alkyl a group, a sulfo group, a carboxyl group, at least one fluorinated organic compound der groups bound of Ru water treatment device selected from the amino group.

  In this invention, in the process of raw | natural water containing a tetraalkyl ammonium hydroxide and a fluorine-type organic compound, both can be processed efficiently by performing a biological treatment after performing an activated carbon treatment.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  As a result of intensive studies, the present inventors have found that the fluorine-based organic compound is efficiently adsorbed by adjusting the pH to, for example, 7.5 or lower even in the presence of tetraalkylammonium hydroxide in the activated carbon treatment. Moreover, in the process of tetraalkylammonium hydroxide, it discovered that tetraalkylammonium hydroxide could be decomposed | disassembled most efficiently by adjusting to pH 5.5-7.5, for example, and performing a biological process. As a result, in the treatment of raw water containing tetraalkylammonium hydroxide and a fluorinated organic compound, the activated carbon treatment, which has been the final treatment step in the past, is carried out before the biological treatment, preferably under the appropriate pH conditions in each. Thus, it was found that the fluorine-based organic compound can be efficiently removed by the activated carbon treatment in the former stage, and the tetraalkylammonium hydroxide can be efficiently removed by the biological treatment in the latter stage.

  An example of a water treatment apparatus according to an embodiment of the present invention is schematically shown in FIG. The water treatment apparatus 1 includes a pH adjustment tank 10 that is a pH adjustment means, an activated carbon treatment apparatus 12 that is an activated carbon treatment means, and a biological treatment tank 14 that is a biological treatment means.

  In the water treatment apparatus 1 of FIG. 1, the outlet of the pH adjustment tank 10 and the inlet of the activated carbon treatment apparatus 12, and the outlet of the activated carbon treatment apparatus 12 and the inlet of the biological treatment tank 14 are connected by piping or the like.

  A water treatment method using the water treatment apparatus according to the embodiment of the present invention will be described.

  Raw water containing tetraalkylammonium hydroxide and a fluorine-based organic compound is sent from the raw water tank or the like to the pH adjustment tank 10 through a raw water supply pipe or the like. Here, a pH adjusting agent such as an acid or alkali is added from a pH adjusting agent storage tank or the like by a pH adjusting agent adding means such as a pump, and the pH of the raw water is adjusted to, for example, 7.5 or less (pH adjusting step). . Depending on the characteristics of the raw water, this pH adjustment step is not always necessary.

  Next, the pH adjustment solution adjusted in pH in the pH adjustment tank 10 is sent to the activated carbon treatment apparatus 12 through a pH adjustment solution pipe or the like. Here, activated carbon treatment is performed, and mainly the fluorinated organic compound is adsorbed on the activated carbon (activated carbon treatment step). Depending on the characteristics of the raw water, the raw water may be subjected to activated carbon treatment.

  Next, the activated carbon treatment liquid treated with the activated carbon in the activated carbon treatment apparatus 12 is sent to the biological treatment tank 14 through an activated carbon treatment liquid pipe or the like. Here, the biological treatment is performed within the range of pH of the activated carbon treatment liquid, for example, in the range of 5.5 to 7.5, and mainly the tetraalkylammonium hydroxide is decomposed to obtain the treatment liquid (biological treatment step). The processing liquid is discharged out of the system.

  Even if the activated carbon treatment process and the biological treatment process are mixed, the purpose cannot be achieved. When the activated carbon treatment is performed after the biological treatment, as described above, the biologically treated water has a relatively high concentration of components that inhibit the adsorption of SS components generated by the biological treatment and decomposition byproducts such as TMAH. This is because the adsorption efficiency of the fluorinated organic compound on the activated carbon is significantly reduced. Instead of providing the activated carbon treatment device 12, in the pH adjustment step, activated carbon such as pulverized coal may be added to the pH adjustment tank 10 to perform the adsorption treatment together with pH adjustment.

  The raw water to be treated in this embodiment is not particularly limited as long as it is a raw water containing a tetraalkylammonium hydroxide and a fluorine-based organic compound, but further, a resist such as a resist resin used for a resist such as a photoresist. May contain ingredients. The resist resin is not particularly limited as long as it is a resin used for a resist such as a photoresist. As a kind of the photoresist, there are a positive type photoresist in which the exposed portion is soluble (etched) in the developer and a negative photoresist in which the exposed portion is insoluble in the developer. Such raw water includes, for example, development waste liquid discharged from a semiconductor etching process or the like.

  Examples of the tetraalkylammonium hydroxide contained in the raw water include tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltriethylammonium hydroxide, and trimethylethylammonium hydroxide. Dimethyldiethylammonium hydroxide, trimethyl (2-hydroxyethyl) ammonium hydroxide (ie choline), triethyl (2-hydroxyethyl) ammonium hydroxide, dimethyldi (2-hydroxyethyl) ammonium hydroxide, diethyldi (2- Hydroxyethyl) ammonium hydroxide, methyltri (2-hydroxyethyl) ammonium Examples thereof include hydroxide, ethyltri (2-hydroxyethyl) ammonium hydroxide, tetra (2-hydroxyethyl) ammonium hydroxide and the like, and TMAH, tetraethylammonium hydroxide and choline which are usually used in a developing solution are preferable, and TMAH is particularly preferable. Is preferred. In this specification, tetraalkylammonium hydroxide includes salts thereof.

The fluorine-based organic compound contained in the raw water is not particularly limited as long as it is an organic compound containing a fluorine atom in the molecule, but perfluorooctanoic acid (PFOA), perfluorodecanoic acid (PFDA), perfluorooctanesulfone. An alkyl group in which all hydrogen atoms are substituted with fluorine atoms, such as acid (PFOS) and perfluorobutane sulfonic acid (PFBS), sulfo group (—SO ₃ H group), carboxyl group (—COOH group), amino group It is preferably a fluorine-based organic compound such as perfluoroalkyl sulfonic acids, perfluoroalkyl carboxylic acids, perfluoroalkyl amines and the like to which at least one group selected from (—NH ₂ group) is bonded, an alkyl group all straight chain substituted by a fluorine atom, a sulfo group (-SO 3 _H group , A carboxyl group (-COOH group), more preferably at least one group selected from amino group (-NH ₂ group) is a fluorine-based organic compound bound. In this specification, a fluorine-based organic compound to which at least one group selected from a sulfo group (—SO ₃ H group), a carboxyl group (—COOH group), and an amino group (—NH ₂ group) is bonded is used. Also include their salts.

  In this embodiment, it is preferable to adjust the pH of raw water to 7.5 or less in the pH adjustment step. When the pH exceeds 7.5, when the resist component is included, it cannot be removed by precipitating the resist component. Further, TMAH existing under alkalinity in the subsequent activated carbon treatment process deteriorates the activated carbon, and fluorine In some cases, the adsorption ability of organic organic compounds may be impaired.

  In the pH adjusting step, it is more preferable to adjust the pH of the raw water to a range of 5.5 to 7.5. When the pH is lower than 5.5, activated carbon treatment is possible, but there may be a case where it becomes necessary to adjust the pH again in the previous stage of the biological treatment process of the latter stage.

  Examples of the pH adjuster include acids such as sulfuric acid and hydrochloric acid, and alkalis such as sodium hydroxide.

  In general, the raw water to be treated in this embodiment is often an alkali having a pH of 12 or more. Therefore, in the pH adjustment step, it is preferable to adjust the pH of the raw water to 7.5 or less with an acid such as sulfuric acid or hydrochloric acid.

  In the pH adjustment step, when the raw water contains a resist component, the resist component can be coagulated and precipitated by adjusting the pH, for example, in the range of pH 4-7. At this time, in order to reduce the influence in the activated carbon treatment of the next step, as shown in FIG. May be installed to remove SS (solid-liquid separation step).

  Adsorption treatment in the adsorption treatment process should be any of treatment using a complete mixing tank using pulverized coal, water treatment using a fixed bed using granular activated carbon using an activated carbon tower, and water treatment using a fluidized bed using granular activated carbon. However, in consideration of convenience in solid-liquid separation, treatment with a fixed bed or a fluidized bed is preferable.

  As described above, the pH when water is passed through the activated carbon treatment device 12 is preferably in the range of pH 5.5 to 7.5. At this time, since TMAH is in a state of high polarity, it hardly adsorbs on the activated carbon and flows out to the subsequent stage. The superficial velocity during water flow to the activated carbon treatment device 12 is preferably in the range of 1 to 20 [1 / hr].

  In the biological treatment process, the pH during the treatment is preferably controlled so as to be 5.5 to 7.5, but more preferably in the range of pH 6 to 7. If the pH during the treatment is out of the range of 5.5 to 7.5, the decomposition performance of TMAH may be deteriorated. As described above, if the pH of the raw water is adjusted to the range of 5.5 to 7.5 in the pH adjustment step, it is not necessary to adjust the pH again in the biological treatment step.

  In addition to adding phosphorus in the biological treatment process, it is preferable to add elements required for trace amounts such as sodium, potassium, magnesium, calcium, iron, manganese, and copper.

  Any type of biological treatment may be used, such as a floating type, a fixed bed, a fluidized bed by adding a carrier, or an immersion membrane activated sludge method.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

(Examples 1-4)
For simulated wastewater in which TMAH and a fluorine-based organic compound coexist, adsorption treatment with activated carbon was performed for each pH shown in Table 1.

  TMAH was added to pure water at 0.18 wt% and PFOS at 100 ppb to obtain simulated waste water. After 300 mL of this wastewater was collected in an Erlenmeyer flask, it was adjusted with hydrochloric acid or sodium hydroxide so as to have a predetermined pH, 1000 mg / L of coal-based powdered activated carbon was added, and 20 hours at 20 ° C., 120 rpm, The concentration of TMAH in the treated water was measured by shaking. The results are shown in Table 1. The concentration of TMAH in the treated water was measured by capillary electrophoresis (manufactured by Otsuka Electronics Co., Ltd., CAPI-3300 type).

  Table 1 shows that TMAH hardly adsorbs on activated carbon.

  Next, the simulated waste water in which TMAH and the fluorine-based organic compound coexist was subjected to adsorption treatment with activated carbon for each pH shown in Table 2.

TMAH was added to pure water at 0.18 wt% and PFOS at 100 ppb to obtain simulated waste water. After 300 mL of this wastewater was collected in an Erlenmeyer flask, it was adjusted with hydrochloric acid or sodium hydroxide so as to have a predetermined pH, and was dropped into a column packed with 120 cm ³ of coal-based granular activated carbon in a downward flow. Water was passed at a speed of 5 [1 / hr]. The results are shown in Table 2. The concentration of PFOS in the treated water was measured by LC-MS / MS (HPLC: Agilent 1100, mass spectrometer: 3200QTRAP).

  From Table 2, it can be seen that PFOS is adsorbed on activated carbon even in the presence of TMAH.

Next, biological treatment was performed on the waste water in which TMAH remained in order to treat TMAH. At this time, water was continuously passed through a carrier-added fluidized bed acclimatized with TMAH-degrading bacteria so that the TMAH load was 1.0 kg TMAH / m ³ / day. The pH during the treatment is adjusted with hydrochloric acid or sodium hydroxide so as to be a predetermined value, and phosphorus is 5 mg / L as nutrient salt and Organamine 10 (manufactured by Organo Corporation) is 0.1 mL / L. Was added as follows. The results are shown in Table 3.

  From Table 3, it can be seen that TMAH can be satisfactorily decomposed. In particular, it can be seen that TMAH can be satisfactorily decomposed in the range of pH 7.5 or less, and further in the range of pH 5.5 to 7.5.

  From the above results, it can be seen that TMAH and PFOS can be efficiently removed by activated carbon treatment → biological treatment.

(Comparative Example 1)
As Comparative Example 1, using waste water containing 0.2 wt% of TMAH and an average of 100 ppb of PFOS, as shown in FIG. 2, pH adjustment in the pH adjustment tank 50 → biological treatment in the biological treatment tank 54 → in the activated carbon treatment apparatus 52 Activated carbon treatment was performed. The pH of each step was adjusted to be constant at 7.5. First, the wastewater was set to pH 7.5 in the pH adjusting tank 50, and SS generated at that time was removed by the subsequent pressurized flotation. Thereafter, biological treatment was performed. The TMAH load at that time was 1.0 kg TMAH / m ³ / day. In the latter-stage activated carbon treatment, water was passed through an activated carbon tower packed with coal-based granular activated carbon at a superficial velocity of 5 [1 / hr]. As a result, in the final treated water, TMAH was 1 mg / L or less, but PFOS remained 2.6 μL / L.

  From the above, it can be seen that TMAH and PFOS can be efficiently removed by changing the process to activated carbon treatment → biological treatment, in particular, pH adjustment → activated carbon treatment → biological treatment.

It is a schematic structure figure showing an example of the water treatment equipment concerning the embodiment of the present invention. It is a schematic block diagram which shows the other example of the water treatment apparatus which concerns on embodiment of this invention. It is a schematic block diagram which shows the water treatment apparatus used in the comparative example 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,3 Water treatment apparatus, 10,50 pH adjustment tank, 12,52 Activated carbon treatment apparatus, 14,54 Biological treatment tank, 16 Solid-liquid separation apparatus.

Claims (4)

An activated carbon treatment step in which raw water containing tetraalkylammonium hydroxide and a fluorinated organic compound is treated with activated carbon;
A biological treatment step for biologically treating the activated carbon treatment liquid treated with the activated carbon;
Only including,
The fluorine-based organic compound is a fluorine-based organic compound in which at least one group selected from a sulfo group, a carboxyl group, and an amino group is bonded to an alkyl group in which all hydrogen atoms are substituted with fluorine atoms. Water treatment method. A pH adjusting step for adjusting the pH of raw water containing tetraalkylammonium hydroxide and a fluorine-based organic compound to 7.5 or less;
An activated carbon treatment step of treating the pH-adjusted liquid adjusted with activated carbon,
A biological treatment step of biologically treating the activated carbon treatment liquid treated with activated carbon within a range of pH 5.5 to 7.5;
Only including,
The fluorine-based organic compound is a fluorine-based organic compound in which at least one group selected from a sulfo group, a carboxyl group, and an amino group is bonded to an alkyl group in which all hydrogen atoms are substituted with fluorine atoms. Water treatment method. Activated carbon treatment means for subjecting raw water containing tetraalkylammonium hydroxide and a fluorine-based organic compound to activated carbon;
A biological treatment means for biologically treating the activated carbon treatment liquid treated with the activated carbon;
I have a,
The fluorine-based organic compound, the alkyl group in which a hydrogen atom has been substituted in all fluorine atom, a sulfo group, a carboxyl group, at least fluorine-based organic compound der Rukoto which one group is attached is selected from amino group A water treatment device characterized. PH adjusting means for adjusting the pH of raw water containing tetraalkylammonium hydroxide and a fluorine-based organic compound to 7.5 or less;
Activated carbon treatment means for treating the pH-adjusted liquid adjusted with activated carbon;
A biological treatment means for biologically treating the activated carbon treatment liquid treated with the activated carbon within a range of pH 5.5 to 7.5;
I have a,
The fluorine-based organic compound, the alkyl group in which a hydrogen atom has been substituted in all fluorine atom, a sulfo group, a carboxyl group, at least fluorine-based organic compound der Rukoto which one group is attached is selected from amino group A water treatment device characterized.

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