Activated sludge-based decomposition treatment method, wastewater treatment device, and activated sludge

Abstract

[Problem] To provide: an activated sludge-based decomposition treatment method for a substance to be treated that contains at least one from among phthalic acids and esters thereof and oligomers of the preceding; a wastewater treatment device; and an activated sludge. [Solution] An activated sludge-based decomposition treatment method is provided according to one embodiment of the present invention. This decomposition treatment method comprises: a first step for preparing an activated sludge in a wastewater treatment device that treats wastewater generated in a process of lowering the molecular weight of an aromatic polyester; and a second step for decomposing the substance to be treated in a mixed liquid obtained by mixing the activated sludge and a liquid to be treated containing a substance to be treated that contains at least one from among phthalic acids and esters thereof and oligomers of the preceding. Potassium ion is added to the activated sludge in the second step.

Description

Decomposition treatment method using activated sludge, wastewater treatment device, and activated sludge

[0001] The present invention relates to a decomposition treatment method using activated sludge, and more particularly to a decomposition treatment method using activated sludge for a substance to be treated that contains at least one of phthalic acid, a phthalate ester, and an oligomer thereof, a wastewater treatment device, and activated sludge.

[0002] With growing awareness of environmental issues, standards for industrial wastewater are becoming stricter around the world. When building a new factory, evidence must be presented that the wastewater treatment can meet the standards. Thus, wastewater treatment is now positioned as an important technology as part of the manufacturing process. Polyethylene terephthalate (hereinafter also referred to as "PET"), which is used in beverage bottles and polyester fibers, often generates wastewater during its manufacturing and recycling processes. This wastewater can contain high concentrations of PET decomposition products, which are difficult to adequately decompose using existing activated sludge.

[0003] For example, wastewater discharged in the chemical recycling process of PET contains bis(2-hydroxyethyl terephthalate) (hereinafter also referred to as "BHET"), which is difficult to decompose using existing activated sludge. In such cases, it is necessary to pay for external wastewater treatment or adjust operations, which has a significant impact on the operating costs of the plant. It has been reported that Enterobacter sp. has been isolated as a microorganism capable of decomposing BHET, but it was only able to decompose about 30% of 2000 mg / L (approximately 8 mM) of BHET even after 120 hours (see Non-Patent Document 1). Furthermore, when isolated microorganisms are used to treat wastewater, they are preyed upon by the contaminating activated sludge, which results in the problem of the activity of the isolated microorganisms not being maintained.

[0004] Lequan Qiu et al. , J Basic Microbiol. 2020;60:699-711

[0005] In view of the above circumstances, the present invention provides a method for decomposing a substance to be treated, which contains at least one of phthalic acids, esters thereof, and oligomers thereof, using activated sludge, a wastewater treatment device, and activated sludge.

[0006] According to one aspect of the present invention, there is provided a decomposition treatment method using activated sludge. The decomposition treatment method includes a first step of preparing activated sludge in a wastewater treatment device for treating wastewater generated in the process of decomposing aromatic polyesters into lower molecular weight compounds, and a second step of decomposing the target substance in a mixed solution obtained by mixing the activated sludge with a target substance containing at least one of phthalic acids, their esters, and their oligomers. In the second step, potassium ions are added to the activated sludge.

[0007] According to this embodiment, it becomes possible to rapidly treat a substance to be treated that contains at least one of phthalic acids, esters thereof, and oligomers thereof, which have been difficult to decompose in the past.

[0008] Preferred embodiments of the activated sludge decomposition treatment method, wastewater treatment device, and activated sludge of the present invention are described in detail below. In this specification, "polyester" refers to a polymer compound having an ester bond in the main chain. Also, in this specification, "aromatic polyester" refers to a polyester containing an aromatic component as a repeating unit. The content of such a repeating unit is approximately 50% by mass to 100% by mass (preferably approximately 70% by mass to 100% by mass, more preferably approximately 90% by mass to 100% by mass, and even more preferably approximately 95% by mass to 100% by mass) relative to the entire compound. Examples of aromatic polyesters include PET, and PET containing 95% by mass or more of ethylene terephthalate repeating units is preferred.

[0009] Aromatic polyesters can be produced by polycondensation of a dicarboxylic acid component and a diol component. For example, PET can be produced by using terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component. Examples of dicarboxylic acid components other than terephthalic acid include aromatic dicarboxylic acids or derivatives thereof, such as phthalic acid, isophthalic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, and 2,5-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids or derivatives thereof, such as succinic acid, adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid. Examples of diol components other than ethylene glycol include diethylene glycol, trimethylene glycol, tetramethylene glycol, propylene glycol, pentamethylene glycol, hexamethylene glycol, and decamethylene glycol.

[0010] The activated sludge decomposition treatment method of the present invention comprises a first step of preparing activated sludge for a wastewater treatment device that treats wastewater generated during the process of decomposing aromatic polyesters into lower molecular weight compounds, and a second step of decomposing the treated substance in a mixed liquid obtained by mixing the activated sludge with a liquid to be treated that contains the treated substance, the liquid including at least one of phthalic acids, their esters, and their oligomers. Each step will be described in order below. [1] First Step: First, in the first step, activated sludge for a wastewater treatment device that treats wastewater generated during the process of decomposing aromatic polyesters into lower molecular weight compounds is prepared. This activated sludge may be used directly in the activated sludge tank of the wastewater treatment device, or it may be recovered and stored in a separate storage tank (storage section) for further use.

[0011] The form of the aromatic polyester to be depolymerized is not particularly limited, but may be, for example, fibers, granules, flakes, pellets, films, blocks, bottles, or a mixture thereof. Examples of processes for depolymerizing aromatic polyesters include chemical recycling processes that chemically decompose PET, such as methanolysis, glycolysis, and hydrolysis. In the chemical recycling process of PET, PET is depolymerized using ethylene glycol to produce the intermediate BHET. Next, to increase its purity, BHET is purified (distilled and recrystallized). The wastewater discharged during recrystallization contains primarily BHET, along with high concentrations of related substances such as monohydroxyethyl terephthalate (hereinafter also referred to as "MHET") and terephthalic acid (hereinafter also referred to as "TPA"). The wastewater treatment device treats the wastewater generated during this chemical recycling process, i.e., wastewater containing primarily BHET.

[0012] In the present invention, activated sludge is used in a wastewater treatment device to treat such wastewater. Therefore, such activated sludge can decompose PET degradation products, mainly containing BHET. In other words, the liquid to be treated, which is the target of the decomposition treatment using activated sludge in the present invention, mainly contains BHET as the substance to be treated. Here, activated sludge is a general term for "living" floating organic sludge containing aerobic microorganisms cultivated artificially or technologically. Activated sludge is widely used as a means of purifying wastewater or polluted water in sewage treatment plants, sewage treatment plants, septic tanks, and the like. However, even with such activated sludge, degradation products of aromatic polyesters such as BHET cannot be sufficiently decomposed. Therefore, degradation products of aromatic polyesters such as BHET usually remain in wastewater (waste) treated with activated sludge generated in the chemical recycling process of PET.

[0013] [2] Second Step Next, in the second step, activated sludge is mixed with a liquid to be treated containing a substance to be treated, including at least one of phthalic acids, their esters, and their oligomers, and the substance to be treated is decomposed in the mixed liquid. Examples of the substance to be treated include BHET, as well as TPA, MHET, dimethyl terephthalate (DMT), isophthalic acid (IPA), and phthalic acid. Examples of oligomers include polymers containing 2 to 10 phthalic acids or esters of phthalic acids as structural units. These substances are produced in high proportions during the process of decomposing the aromatic polyester into smaller molecules, and are easily decomposed by the activated sludge prepared in the first step.

[0014] In the present invention, potassium ions are added to the activated sludge in this second step. The inventors have conducted extensive research into methods for treating wastewater containing decomposition products of aromatic polyesters such as PET, for example, wastewater (liquid to be treated) generated during the chemical recycling of aromatic polyesters. As a result, they have discovered that adding an appropriate amount of potassium ions to activated sludge enables rapid treatment of wastewater (liquid to be treated) containing BHET (chemical substance to be treated), which has traditionally been difficult to decompose, and have thus completed the present invention. The potassium-containing substance used when adding potassium ions is not particularly limited, but examples include potassium chloride, potassium bromide, and potassium hydroxide. It is also effective to use seawater, artificial seawater, or industrial water to add potassium ions.

[0015] In the second step, the potassium ion concentration in the activated sludge is preferably about 1 ppm to 200 ppm, more preferably about 5 ppm to 100 ppm, and even more preferably about 10 ppm to 50 ppm. This allows for further improvement in the treatment efficiency of the liquid to be treated containing the target substance. In the second step, the suspended solids concentration (MLSS) in the activated sludge is preferably about 2000 mg / L to 7000 mg / L, more preferably about 3000 mg / L to 6500 mg / L, and even more preferably about 4000 mg / L to 6000 mg / L. This allows for good decomposition of the target substance while maintaining the sedimentation properties of the sludge, allowing for smooth separation of the treated water and the sludge.

[0016] In the second step, the temperature of the activated sludge is preferably about 10°C or higher and 40°C or lower, more preferably about 15°C or higher and 35°C or lower, and even more preferably about 20°C or higher and 30°C or lower. This allows the decomposition of the target substance by the activated sludge to be maintained at a high level. In the second step, the dissolved oxygen concentration (DO) in the activated sludge is preferably about 0.5 mg / L or higher, more preferably about 0.5 mg / L or higher and 4 mg / L or lower, and even more preferably about 1 mg / L or higher and 3 mg / L or lower. This allows the activity of microorganisms that contribute to the decomposition of the target substance to be maintained at a high level. In the second step, the pH of the activated sludge is preferably about 5.5 or higher and 8.5 or lower, more preferably about 6 or higher and 8 or lower, and even more preferably about 6.5 or higher and 7.5 or lower. This allows the activity of microorganisms that contribute to the decomposition of the target substance to be maintained at a high level. The pH of the activated sludge can be controlled by adjusting the amount of oxygen supplied to the mixed liquor (aeration rate).

[0017] In the second step, the total nitrogen concentration in the activated sludge is preferably about 1 ppm to 50 ppm, more preferably about 3 ppm to 20 ppm, and even more preferably about 5 ppm to 15 ppm per 100 ppm of chemical oxygen demand (COD). The total nitrogen concentration in the activated sludge can be adjusted, for example, by adding nitrate, urea, or the like to the activated sludge. In the second step, the total phosphorus concentration in the activated sludge is preferably about 0.1 ppm to 5 ppm, more preferably about 0.2 ppm to 3 ppm, and even more preferably about 0.4 ppm to 1.5 ppm per 100 ppm of chemical oxygen demand (COD). The total phosphorus concentration in the activated sludge can be adjusted, for example, by adding phosphate, or the like to the activated sludge. By adjusting the total nitrogen concentration and / or total phosphorus concentration in activated sludge to fall within the above range, the activity of microorganisms that contribute to the decomposition of the substances to be treated can be maintained at a high level.

[0018] In the second step, the time for storing the liquid to be treated in the storage section (activated sludge tank) storing activated sludge is preferably about 10 to 100 hours, more preferably about 15 to 75 hours, and even more preferably about 20 to 50 hours. This ensures sufficient contact time between the substance to be treated and the activated sludge (microorganisms that contribute to the decomposition of the substance to be treated), thereby further increasing the decomposition efficiency of the substance to be treated. Furthermore, in the second step, the concentration of the substance to be treated in the liquid to be treated is preferably about 0.01 to 10% by mass, more preferably about 0.05 to 5% by mass, and even more preferably about 0.1 to 1% by mass. This ensures an appropriate amount of the substance to be treated exposed to the activated sludge, thereby maintaining a high decomposition efficiency of the substance to be treated.

[0019] The decomposition efficiency (decomposition ability) of the target substance by activated sludge can be determined by measuring the amount of the target substance remaining in the target liquid after the decomposition treatment, for example, by thin layer chromatography (TLC), high performance liquid chromatography (HPLC), etc. The wastewater treatment device of the present invention includes an activated sludge tank for storing activated sludge and is configured to perform the above-mentioned decomposition treatment method using activated sludge. With this wastewater treatment device, even wastewater containing high concentrations of PET decomposition products can be effectively decomposed.

[0020] The activated sludge of the present invention is used to decompose a substance to be treated, in a mixed solution containing the substance to be treated, which contains at least one of phthalic acids, their esters, and their oligomers. This activated sludge is obtained from a wastewater treatment device that treats wastewater generated in the process of decomposing aromatic polyesters into lower molecular weight compounds, and potassium ions have been added to the activated sludge. As described above, by adding an appropriate amount of potassium ions to the activated sludge, it is possible to rapidly treat wastewater (a liquid to be treated) containing BHET (a substance to be treated), which has previously been difficult to decompose.

[0021] The potassium ion concentration in the activated sludge is preferably about 1 ppm to 200 ppm, more preferably about 5 ppm to 100 ppm, and even more preferably about 10 ppm to 50 ppm. This can further improve the treatment efficiency of the liquid to be treated containing the substance to be treated. Note that other details of the activated sludge and the substance to be treated can be the same as those described in the above-mentioned decomposition treatment method using activated sludge. Furthermore, the activated sludge may be provided in each of the following forms.

[0022] (1) A decomposition treatment method using activated sludge, comprising: a first step of preparing activated sludge in a wastewater treatment device for treating wastewater generated in the process of decomposing aromatic polyesters into lower molecular weight substances; and a second step of decomposing the substance to be treated in a mixed liquid obtained by mixing the activated sludge with a liquid to be treated containing the substance to be treated, the liquid containing the substance to be treated including at least one of phthalic acids, esters thereof, and oligomers thereof, wherein potassium ions are added to the activated sludge in the second step.

[0023] (2) The decomposition treatment method using activated sludge according to (1) above, wherein in the second step, the concentration of the potassium ions in the activated sludge is 1 ppm or more and 200 ppm or less.

[0024] (3) The decomposition treatment method using activated sludge according to (1) or (2) above, wherein in the second step, the concentration of suspended solids (MLSS) in the activated sludge is 2000 mg / L or more and 7000 mg / L or less.

[0025] (4) The decomposition treatment method using activated sludge according to any one of (1) to (3) above, wherein in the second step, the temperature of the activated sludge is 10°C or higher and 40°C or lower.

[0026] (5) The decomposition treatment method using activated sludge according to any one of (1) to (4) above, wherein in the second step, the dissolved oxygen concentration in the activated sludge is 0.5 mg / L or more.

[0027] (6) The decomposition treatment method using activated sludge according to any one of (1) to (5) above, wherein in the second step, the pH of the activated sludge is 5.5 or more and 8.5 or less.

[0028] (7) The decomposition treatment method using activated sludge according to any one of (1) to (6) above, wherein in the second step, the total nitrogen concentration in the activated sludge is 1 ppm or more and 50 ppm or less per 100 ppm of chemical oxygen demand (COD).

[0029] (8) The decomposition treatment method using activated sludge according to any one of (1) to (7) above, wherein in the second step, the total phosphorus concentration in the activated sludge is 0.1 ppm or more and 5 ppm or less per 100 ppm of chemical oxygen demand (COD).

[0030] (9) In the activated sludge decomposition treatment method according to any one of (1) to (8) above, in the second step, the time for storing the liquid to be treated in the storage section storing the activated sludge is 10 hours or more and 100 hours or less.

[0031] (10) In the activated sludge decomposition treatment method according to any one of (1) to (9) above, in the second step, the concentration of the substance to be treated in the liquid to be treated is 0.01% by mass or more and 10% by mass or less.

[0032] (11) The decomposition treatment method using activated sludge according to any one of (1) to (10) above, wherein the liquid to be treated is generated in the process of chemically recycling aromatic polyester.

[0033] (12) The activated sludge decomposition treatment method according to any one of (1) to (11) above, wherein the liquid to be treated contains mainly bis(2-hydroxyethyl) terephthalate (BHET) as the substance to be treated.

[0034] (13) A wastewater treatment device comprising an activated sludge tank for storing activated sludge, and configured to perform the activated sludge decomposition treatment method described in any one of (1) to (12) above.

[0035] (14) Activated sludge used to decompose a substance to be treated in a mixed liquid containing the substance to be treated, the substance including at least one of phthalic acids, esters thereof, and oligomers thereof, the activated sludge being obtained from a wastewater treatment device that treats wastewater generated in the process of depolymerizing aromatic polyesters, and having potassium ions added thereto.

[0036] (15) The activated sludge according to (14) above, wherein the concentration of the potassium ions in the activated sludge is 1 ppm or more and 200 ppm or less. Of course, this is not a limitation.

[0037] As described above, various embodiments of the present invention have been described, but these are presented as examples and do not limit the scope of the invention in any way. The novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Such embodiments and their modifications are intended to be included within the scope and spirit of the invention, as well as within the scope of the inventions and their equivalents as set forth in the claims.

[0038] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. 1. Advance Preparation 1-1. Preparation of BHET, activated sludge, seawater, and artificial seawater BHET: BHET manufactured by Pet Refine Technology Co., Ltd. Activated sludge: Activated sludge collected from the activated sludge tank of a wastewater treatment device (a wastewater treatment device that treats wastewater discharged in the chemical recycling process of PET) at the Kitakyushu Hibikinada Plant of JEPLAN Co., Ltd. Seawater: Seawater collected in Shimoda City, Shizuoka Prefecture Artificial seawater: "Marine Art SF-1" manufactured by Osaka Yaken Co., Ltd.

[0039] The artificial seawater was prepared by adding distilled water to a composition containing each component in the amounts shown in Table 1 below so that the total volume was 1000 mL.

[0040] 1-2. Demineralization of activated sludge The activated sludge was subjected to a demineralization treatment. Specifically, 50 mL of activated sludge was first weighed into a centrifuge tube and centrifuged at room temperature at 700 G for 1 minute to separate the activated sludge layer from the supernatant. Next, 40 mL of the supernatant was removed, and 40 mL of ion-exchanged water was added to the centrifuge tube and mixed to uniformly disperse the sludge. This series of operations was repeated three times.

[0041] 1-3. Preparation of Activation Solution and Treatment Solution The activation solution was prepared by adding 1.2 g of BHET (the substance to be treated) to 270 mL of ion-exchanged water, dissolving the solution by heating, and then adding 30 mL of 1 M phosphate buffer solution containing 1.2 g of ammonium sulfate. The concentration of BHET in the activation solution was approximately 0.4 mass%. The treatment solution was prepared by adding 0.6 g of BHET (the substance to be treated) to 150 mL of ion-exchanged water, dissolving the solution by heating, and then adding 150 mL of 1 M phosphate buffer solution containing 0.6 g of ammonium sulfate. The concentration of BHET in the treatment solution was approximately 0.2 mass%.

[0042] 2. Decomposition Treatment Experiment (Example 1) First, 15 mL of demineralized activated sludge, 30 μL of a 1% by mass potassium chloride aqueous solution, 270 μL of ion-exchanged water, and 15 mL of an activation solution were added to a Sakaguchi flask, and the mixture was treated at 30° C. for 2 days while stirring with a magnetic stirrer at a rotation speed of 135 rpm. Next, 15 mL was removed from the treated solution, and then 15 mL of the activation solution, 30 μL of a 1% by mass potassium chloride aqueous solution, and 270 μL of ion-exchanged water were added, and the mixture was treated at 30° C. for another 2 days while stirring with a magnetic stirrer at a rotation speed of 135 rpm.

[0043] Next, 15 mL of the treated liquid was added to 15 mL of the treated liquid after 4 days of treatment, and the resulting mixture was treated at 30°C for 3 hours while stirring with a magnetic stirrer at a rotation speed of 160 rpm. The potassium ion concentration in the treated liquid after 4 days of treatment was approximately 8 ppm, and the pH was approximately 7. After 3 hours, 0.5 mL was taken from the treated liquid, and 0.5 mL of HPLC-grade acetonitrile was added to prepare a sample for HPLC measurement. The above treatment was performed twice to prepare two samples for HPLC measurement.

[0044] Example 2 A decomposition treatment was carried out in the same manner as in Example 1, except that 150 μL of a 1 mass % potassium chloride aqueous solution and 150 μL of ion-exchanged water were used instead of 30 μL of a 1 mass % potassium chloride aqueous solution and 270 μL of ion-exchanged water. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 40 ppm, and the pH was approximately 7. Example 3 A decomposition treatment was carried out in the same manner as in Example 1, except that 300 μL of a 1 mass % potassium chloride aqueous solution was used instead of 30 μL of a 1 mass % potassium chloride aqueous solution and 270 μL of ion-exchanged water. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 80 ppm, and the pH was approximately 7.

[0045] Example 4 A decomposition treatment was carried out in the same manner as in Example 1, except that 500 μL of seawater (potassium ion concentration: approximately 400 ppm) was used instead of 30 μL of a 1% by mass potassium chloride aqueous solution and 270 μL of ion-exchanged water. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 10 ppm, and the pH was approximately 7. Example 5 A decomposition treatment was carried out in the same manner as in Example 1, except that 500 μL of artificial seawater (potassium ion concentration: approximately 300 ppm) was used instead of 30 μL of a 1% by mass potassium chloride aqueous solution and 270 μL of ion-exchanged water. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 8 ppm, and the pH was approximately 7.

[0046] Example 6: A decomposition treatment was carried out in the same manner as in Example 1, except that 75 μL of a 10% by mass sodium chloride aqueous solution, 60 μL of a 5% by mass magnesium sulfate aqueous solution, and 30 μL of a 5% by mass calcium chloride aqueous solution were used instead of 270 μL of ion-exchanged water. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 8 ppm, and the pH was approximately 7. Comparative Example 1: A decomposition treatment was carried out in the same manner as in Example 1, except that 75 μL of a 10% by mass sodium chloride aqueous solution and 225 μL of ion-exchanged water were used instead of 30 μL of a 1% by mass potassium chloride aqueous solution and 270 μL of ion-exchanged water. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 0 ppm, and the pH was approximately 7.

[0047] (Comparative Example 2) A decomposition treatment was carried out in the same manner as in Example 1, except that 60 μL of a 5% by mass magnesium sulfate aqueous solution and 240 μL of ion-exchanged water were used instead of 30 μL of a 1% by mass potassium chloride aqueous solution and 270 μL of ion-exchanged water. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 0 ppm, and the pH was approximately 7. (Comparative Example 3) A decomposition treatment was carried out in the same manner as in Example 1, except that 30 μL of a 5% by mass calcium chloride aqueous solution and 270 μL of ion-exchanged water were used instead of 30 μL of a 1% by mass potassium chloride aqueous solution and 270 μL of ion-exchanged water. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 0 ppm, and the pH was approximately 7.

[0048] (Comparative Example 4) Decomposition treatment was performed in the same manner as in Example 1, except that the addition of 30 μL of 1% by mass potassium chloride aqueous solution and 270 μL of ion-exchanged water was omitted. The potassium ion concentration in the treated solution after 4 days of treatment was approximately 0 ppm, and the pH was approximately 7. (Reference Sample) First, 15 mL of activation solution was added to 15 mL of ion-exchanged water and thoroughly mixed. 15 mL was then removed, and another 15 mL of activation solution was added and thoroughly mixed. Next, 15 mL was removed from this mixture, and 15 mL of the liquid to be treated was added and thoroughly mixed. Finally, 0.5 mL was removed from this mixture, and 0.5 mL of HPLC-grade acetonitrile was added to prepare a reference sample for HPLC measurement.

[0049] 2. Measurement 2-1. Measurement of Decomposition Rates of BHET, MHET, and TPA 0.1 mL of the HPLC measurement sample obtained in each Example and Comparative Example or 0.1 mL of the standard HPLC measurement sample was diluted 10-fold with mobile phase (formic acid / acetonitrile / water = 1 / 2 / 7 by volume), stirred, filtered through a 0.2 μm filter, and then analyzed by HPLC. For HPLC analysis, an "LC-2010A HT" manufactured by Shimadzu Corporation was used as the apparatus, and a "COSMOCIL 5C18-AR-II (4.6 ID x 250 mm)" and "5C18-AR-II guard column" manufactured by Nacalai Tesque were used as the column.

[0050] The analysis was performed using isocratic elution with a mobile phase at a flow rate of 1 mL / min and a column temperature of 40°C, as described above, and detection was performed at a wavelength of 254 nm. The peaks of BHET, MHET, and TPA contained in the HPLC measurement sample were identified from the elution time, and the peak areas of each were calculated. Regarding BHET, a calibration curve of BHET concentration versus peak area was prepared using an aqueous BHET solution dissolved at 70°C, and quantitative analysis was also performed.

[0051] The above results are summarized in Table 2. BHET residual rate 1 [%]: BHET peak area in sample / BHET peak area in reference sample × 100 BHET residual rate 2 [%]: BHET peak area in sample / BHET peak area in treated liquid × 100 The values ​​in Table 2 are the average values ​​of two samples.

[0052]

[0053] Furthermore, the residual rates of MHET and TPA in the samples obtained in each Example were 70% or less relative to the MHET and TPA in the reference sample.

[0054] In each of Examples 1 to 6, the suspended solids concentration (MLSS) in the treated liquid after 4 days of treatment is preferably 2000 mg / L or more and 7000 mg / L or less, the dissolved oxygen concentration is 0.5 mg / L or more, the total nitrogen concentration is 1 ppm or more and 50 ppm or less per 100 ppm of chemical oxygen demand (COD), and the total phosphorus concentration is 0.1 ppm or more and 5 ppm or less per 100 ppm of chemical oxygen demand (COD).

[0055] Furthermore, when the activated sludge stored in the storage section of the wastewater treatment device is pre-treated in the same manner as in Examples 1 to 6, and then the liquid to be treated is supplied to the storage section to perform the BHET decomposition treatment, the time for which the liquid to be treated is stored in the storage section is preferably 10 hours or more and 100 hours or less.

Claims

1. A decomposition treatment method using activated sludge, comprising: a first step of preparing the activated sludge in a wastewater treatment apparatus for treating wastewater generated in the process of reducing the molecular weight of an aromatic polyester; and a second step of decomposing a substance to be treated, which contains the activated sludge and a liquid to be treated containing at least one of phthalic acids and their esters and their oligomers, in a mixed liquid obtained by mixing them, wherein in the second step, potassium ions are added to the activated sludge.

2. The decomposition treatment method using activated sludge according to claim 1, wherein in the second step, the concentration of the potassium ions in the activated sludge is 1 ppm or more and 200 ppm or less.

3. The decomposition treatment method using activated sludge according to claim 1 or 2, wherein in the second step, the suspended solid concentration (MLSS) in the activated sludge is 2000 mg / L or more and 7000 mg / L or less.

4. The decomposition treatment method using activated sludge according to any one of claims 1 to 3, wherein in the second step, the temperature of the activated sludge is 10°C or more and 40°C or less.

5. The decomposition treatment method using activated sludge according to any one of claims 1 to 4, wherein in the second step, the dissolved oxygen concentration in the activated sludge is 0.5 mg / L or more.

6. The decomposition treatment method using activated sludge according to any one of claims 1 to 5, wherein in the second step, the pH of the activated sludge is 5.5 or more and 8.5 or less.

7. The decomposition treatment method using activated sludge according to any one of claims 1 to 6, wherein in the second step, the total nitrogen concentration in the activated sludge is 1 ppm or more and 50 ppm or less per 100 ppm of the chemical oxygen demand (COD).

8. The decomposition treatment method using activated sludge according to any one of claims 1 to 7, wherein in the second step, the total phosphorus concentration in the activated sludge is 0.1 ppm or more and 5 ppm or less per 100 ppm of the chemical oxygen demand (COD).

9. In the decomposition treatment method using activated sludge according to any one of claims 1 to 8, in the second step, the time for storing the liquid to be treated in the storage section storing the activated sludge is 10 hours or more and 100 hours or less. A decomposition treatment method using activated sludge.

10. In the decomposition treatment method using activated sludge according to any one of claims 1 to 9, in the second step, the concentration of the substance to be treated in the liquid to be treated is 0.01% by mass or more and 10% by mass or less. A decomposition treatment method using activated sludge.

11. In the decomposition treatment method using activated sludge according to any one of claims 1 to 10, the liquid to be treated is generated in the process of chemical recycling of aromatic polyester. A decomposition treatment method using activated sludge.

12. In the decomposition treatment method using activated sludge according to any one of claims 1 to 11, the liquid to be treated mainly contains bis(2-hydroxyethyl) terephthalate (BHET) as the substance to be treated. A decomposition treatment method using activated sludge.

13. A wastewater treatment device comprising an activated sludge tank for storing activated sludge, and configured to perform the decomposition treatment method using activated sludge according to any one of claims 1 to 12.

14. Activated sludge used for decomposing a substance to be treated in a mixed liquid mixed with a liquid to be treated containing at least one of phthalic acids and their esters, and their oligomers, which is obtained from a wastewater treatment device for treating wastewater generated in the process of reducing the molecular weight of aromatic polyester, and potassium ions are added.

15. The activated sludge according to claim 14, wherein the concentration of potassium ions in the activated sludge is 1 ppm or more and 200 ppm or less.

Images