Method for treating terephthalic acid production wastewater

Abstract

Provided is a method for treating high-concentration organic wastewater discharged in the process of producing terephthalic acid (TA) that serves as a raw material for polyethylene terephthalate (PET).　The inventors have found that TA production wastewater can be treated with higher efficiency than those in the existing treatment methods, by combining a bioreactor with a biostimulation strategy in an appropriate single column. Based on this finding, the present invention has been accomplished.

Description

Treatment method for wastewater from terephthalic acid production

[0001] The present invention relates to a method for treating high-concentration organic wastewater discharged in the process of producing terephthalic acid (TA), a raw material for polyethylene terephthalate (PET).

[0002] Polyethylene terephthalate (PET) is a plastic raw material widely used in the production of synthetic fibers, containers, and PET bottles. The PET market is extremely large, with approximately 33 Mtons of PET produced in 2015, accounting for 10% of total plastic production, and the average annual growth rate in recent years has reached 11% (Non-Patent Documents 1-3). PET is primarily used as a material for bottled beverage containers, with 488 billion PET bottles produced worldwide in 2016 (Non-Patent Document 4).

[0003] PET is synthesized by polymerizing petroleum-derived terephthalic acid (TA) or dimethyl terephthalate (DMT) with ethylene glycol (Non-Patent Document 4). PET production using TA has higher purity and yield than that using DMT, and solvent loss is reduced, so in recent years TA has been mainly used as the raw material for PET production (Non-Patent Document 5). TA and DMT are produced from petroleum-derived p-xylene, and large amounts of wastewater with high organic loads are discharged during the production process (3-10 tons per ton of TA / DMT produced) (Non-Patent Documents 6-8). Typical wastewater from TA production (5-20 g COD·L) －１ ) contains high concentrations (0.6-6 mM) of aromatic compounds (terephthalic acid (TA), benzoic acid (BZ), isophthalic acid (IA), orthophthalic acid (OA), and p-toluic acid (PT)) and more than 20 mM of methanol (MT) and acetic acid (AC) (Non-Patent Documents 6 and 9). －１ Regarding COD, the main components are AC and MT (accounting for more than 60% of COD), and it also contains other components such as formic acid (FM) and formaldehyde (Non-Patent Documents 8 and 10).

[0004] Since PET is a highly demanded material, its market size is expanding worldwide, and as a result, the amount of TA production wastewater requiring treatment is expected to increase further. Considering the expansion of the global PET market, a high-speed and stable TA production wastewater treatment technology is required to protect the environment from the high demand of PET production.

[0005] Although TA production wastewater is primarily treated using anaerobic biological wastewater treatment methods (Non-Patent Document 11), the aromatic compounds contained in TA production wastewater are not easily decomposed by microorganisms. Therefore, in order to meet the discharge standards for treated wastewater, measures such as extending the wastewater treatment time or providing ample space for the wastewater treatment system are required, which increases the costs of installation and operation. Therefore, technological development aimed at improving the efficiency of TA production wastewater treatment is expected to be in high demand, as it would significantly meet the needs of society as PET consumption continues to increase.

[0006] In anaerobic biological wastewater treatment processes for TA production wastewater, terephthalic acid and p-toluic acid are known to be rate-limiting substrates (Non-Patent Documents 12-14). Previous studies have reported that acetic acid and benzoic acid inhibit the decomposition of terephthalic acid and p-toluic acid, respectively, due to the accumulation of terephthalic acid decomposition by-products (causing thermodynamically unfavorable conditions) and the presence of competing substrates that are more easily decomposed than terephthalic acid (Non-Patent Document 12). TA production wastewater contains high concentrations of acetic acid and benzoic acid, and it is anticipated that a stage for decomposing these acids will be included to achieve stable treatment of TA production wastewater. In fact, a two-stage reactor system equipped with a process for decomposing acetic acid and benzoic acid has been developed, which achieved a COD of 5.8 to 22.5 kg COD / m. ３ / d has been achieved (Non-Patent Documents 6, 15 and 16).

[0007] On the other hand, biostimulation has also been attempted to promote the biological degradation of aromatic compounds by adding nutrients / co-substrates or inoculating activators such as inorganic nanoparticles. ３ O ４ / TiO ２It has been reported that nanoparticles have a positive effect on the degradation of terephthalic acid / isophthalic acid (Non-Patent Documents 17 and 18). On the other hand, simple carbohydrates such as glucose and sucrose are widely accepted as co-substrates for promoting the degradation of phenol and benzoic acid (Non-Patent Documents 19-21), but they have been reported to have a negative effect on the degradation of terephthalic acid in anaerobic bioreactors (Non-Patent Documents 13 and 18). Therefore, the selection of appropriate biostimulation is necessary to promote the degradation of aromatic compounds in TA production wastewater.

[0008] The present inventors have discovered a new biostimulation method using the addition of methanol / formic acid (Non-Patent Documents 8 and 10). When methanol / formic acid was added to TA production wastewater, the organic matter removal rate in a single anaerobic reactor was higher than that of previous studies (1.5 to 5.5 kg COD / m ３ / d) is higher than that of ３ / d) was achieved (Non-Patent Document 22). These results revealed that the activation of anaerobic syntrophic bacteria (syntrophs) by adding methanol / formic acid is important for improving TA production wastewater treatment. In this regard, it has been demonstrated that, since DMT production wastewater contains a large amount of methanol and formic acid, TA production wastewater can be treated more efficiently by mixing it with DMT production wastewater and treating them together.

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[0010] An object of the present invention is to provide a highly efficient method for treating high-concentration organic wastewater discharged in the process of producing terephthalic acid (TA), a raw material for polyethylene terephthalate (PET).

[0011] From the viewpoint of efficient wastewater treatment, reducing the number of steps in a TA production wastewater treatment system has great practical advantages, such as reducing design costs due to a simpler reactor structure, making the facility area more compact, and reducing the energy required for operation. The present invention is based on the new finding that simply adding a step of adding alkylene glycol as biostimulation can significantly improve the treatment efficiency of TA production wastewater without excessively increasing the number of treatment steps.

[0012] Alkylene glycols act as biostimulants to activate anaerobic symbiotic bacteria and their methanogenic archaeal partners used in anaerobic wastewater treatment. Ethylene glycol is known to be a substrate for several fatty acid-degrading oligotrophic bacteria, such as Pelotomaculum (23) and Clostridium (24). In an example of the present invention, ethylene glycol was introduced as such a biostimulation into an internal two-stage upflow anaerobic (ITUA) reactor, which had a first stage packed at the bottom with green tuff granules with a diameter of 1 to 5 mm that had the activity of decomposing fatty acids and benzoic acid, and a second stage packed with granular sludge on which methanogenic archaea and anaerobic symbiotic bacteria had been engrafted to treat the remaining aromatic compounds in TA production wastewater. By introducing ethylene glycol as such a biostimulation, we achieved a treatment efficiency comparable to that of two-stage treatment systems such as the UASB-UASB system, which had been required for conventional high-speed wastewater treatment.

[0013] Therefore, the present application provides the following inventions.

[0014] A schematic diagram of the internal two-stage upflow anaerobic (ITUA) reactor used in this study is shown. The first stage was packed with green tuff rocks 1 to 5 mm in diameter. The second stage was packed with granular anaerobic wastewater treatment sludge containing aggregates of methanogenic archaea and anaerobic symbiotic bacteria. The first and second stages of the ITUA reactor were separated by a separator plate that was permeable to wastewater but impermeable to the green tuff rocks and granular sludge.

[0015] The organic removal rates for phases 1 to 27 of the ITUA reactor are shown. "EG" indicates ethylene glycol addition, and "ITUA reactor" indicates the operation period of the ITUA reactor of the present invention.

[0016] The COD mass balance in the ITUA reactor is shown. The COD concentration was calculated as the average value for the most recent three operating days in each phase. "EG" indicates ethylene glycol addition, "ITUA reactor" indicates the operating period of the ITUA reactor system of the present invention, "I" indicates influent wastewater, "E" indicates effluent wastewater, "P1-27" indicates phases 1-27, and "unknown" indicates the value obtained by subtracting the sum of the COD concentrations of each detected substance from the total COD concentration. Methane gas production and volatile fatty acid (VFA) / aromatic compound concentrations were not measured in phases 1-3 and 1-5, respectively.

[0017] 1 shows methane conversion based on the relationship between methane production rate and organic removal rate in the ITUA reactor of the present invention.

[0018] The removal rates of orthophthalic acid, terephthalic acid, isophthalic acid, and p-toluic acid, as well as the removal efficiencies of COD, benzoic acid, and acetic acid, for phases 6-27 are shown graphically in FIG.

[0019] The present invention will be described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments and can be embodied in any form without departing from the spirit of the present invention.

[0020] The present invention relates to a method for treating wastewater from the production of terephthalic acid (TA). TA is a major raw material for the synthesis of polyethylene terephthalate (PET). PET is produced in large quantities, primarily as a material for plastic beverage bottles. As a result, TA, a raw material for PET, is also produced in large quantities, resulting in the discharge of large amounts of wastewater from TA production. The TA production process includes a step of wet-oxidizing the starting material p-xylene to obtain crude terephthalic acid, and a step of purifying the obtained crude terephthalic acid to obtain high-purity terephthalic acid (typically 99% by mass or higher) usable for PET production. The wastewater generated in either of these steps is treated as the TA production wastewater of the present invention and is subjected to the TA production wastewater treatment method of the present invention.

[0021] Although not limited thereto, TA production wastewater typically contains aromatic compounds with a total COD concentration of preferably 30,000 mg / L or less, more preferably 14,000 mg / L or less, and even more preferably 10,000 mg / L or less, as well as methanol (MT) and acetic acid (AC). Examples of aromatic compounds include aromatic carboxylic acids such as terephthalic acid (TA), benzoic acid (BZ), isophthalic acid (IA), orthophthalic acid (OA), and p-toluic acid (PT), as well as salts or esters thereof. Examples of aromatic compound salts include alkali metal salts such as sodium and potassium, and alkaline earth metal salts such as calcium and magnesium. Examples of aromatic compound esters include alkyl esters such as methyl esters and ethyl esters.

[0022] The aromatic compounds contained in TA production wastewater are not easily decomposed by anaerobic biological wastewater treatment, which is usually used to treat such wastewater, and it takes time and money to achieve the desired decomposition. In the present invention, biostimulation with alkylene glycol is carried out to more efficiently treat organic wastewater containing such aromatic compounds.

[0023] Anaerobic biological wastewater treatment is a common technique for treating organic wastewater, including wastewater from TA production. The organic wastewater and anaerobic microorganisms to be treated are maintained under anaerobic conditions in a reactor, and the anaerobic microorganisms decompose the organic matter in the wastewater into harmless or useful substances such as methane and carbon dioxide. However, microbial decomposition of aromatic compounds is not always easy. While the conditions for anaerobic biological wastewater treatment can be appropriately determined by those skilled in the art depending on the type and content of organic compounds to be decomposed, such as aromatic compounds, contained in the organic wastewater to be treated, and the desired treatment efficiency, it is common to extend the wastewater treatment time or design the wastewater treatment system to have a sufficient installation area.

[0024] Anaerobic biological wastewater treatment may include, but is not limited to, a reactor packed with granular sludge containing aggregates of methanogenic archaea and anaerobic symbiotic bacteria. In particular, it is preferable to treat wastewater in an upflow manner using a reactor packed with granular sludge containing aggregates of methanogenic archaea and anaerobic symbiotic bacteria. The type of reactor is not limited, but in one embodiment, an upflow anaerobic sludge blanket (UASB) reactor may be used. A high concentration of microbial aggregates is retained in the UASB reactor, and wastewater is treated in an upflow manner from the bottom, thereby decomposing organic matter into methane and carbon dioxide and recovering methane gas as energy. In other embodiments, the anaerobic biological wastewater treatment method of the present invention may include a UASB reactor connected to an upflow anaerobic fluidized bed (UAFB) reactor, an expanded granular sludge bed (EGSB) reactor, an internal circulation (IC) reactor, or the like.

[0025] In a preferred embodiment of the present invention, an internal two-stage upflow anaerobic (ITUA) reactor is used, which includes a lower tank (first stage) packed with inorganic carriers capable of improving the removal activity of fatty acids and benzoic acid by microbial communities, and an upper layer (second stage) packed with granular sludge in which methanogenic archaea and anaerobic symbiotic bacteria are aggregated. A wastewater inlet is located at the bottom of the first stage of the reactor, and a wastewater outlet is located above the second stage. Wastewater (influent wastewater) injected through the inlet first comes into contact with the microbial communities living on the inorganic carriers in the first stage, and then with the granular sludge in the second stage, during which organic matter in the wastewater is decomposed by anaerobic biological wastewater treatment.

[0026] The inorganic carrier packed in the first stage of the reactor is a natural rock containing various conductive and inorganic materials, preferably green tuff. The inventors have found that adding green tuff to an anaerobic biological wastewater treatment system promotes the degradation of fatty acids and benzoic acid by a specific bacterial flora that grows on the green tuff and decomposes organic acids (Non-Patent Document 25). As mentioned above, acetic acid and benzoic acid in TA production wastewater inhibit the degradation of aromatic compounds. Therefore, contact with the microbial community growing on the inorganic carrier in the first stage of the reactor is intended to remove these inhibitors, thereby promoting the degradation of aromatic compounds by the granular sludge in the subsequent second stage.

[0027] The second stage of the reactor is filled with granular sludge, which is a flocculation of anaerobic symbiotic bacteria and methanogenic archaea, and is brought into contact with the TA production wastewater to carry out anaerobic biological wastewater treatment.

[0028] In the present invention, granular sludge refers to a granular solid that aggregates microorganisms that decompose organic compounds and generate methane. In the anaerobic biological wastewater treatment of the present invention, the microorganisms present in the granular sludge packed into the reactor decompose organic compounds to be treated, such as aromatic compounds, in the TA production wastewater to generate methane. The microorganisms that aggregate in the granular sludge are not limited, but preferably include mainly anaerobic symbiotic bacteria and methanogenic archaea.

[0029] Anaerobic symbiotic bacteria are microorganisms that form a microbial symbiotic system with methanogenic archaea and decompose aromatic compounds such as terephthalic acid and benzoic acid, and volatile organic acids such as propionic acid and butyric acid, in an anoxic environment. In the present invention, anaerobic symbiotic bacteria that contribute to the decomposition of aromatic compounds include, but are not limited to, bacteria of the genera Syntrophus, Syntrophorhabdus, and Pelotomaculum.

[0030] Methanogenic archaea refers to archaea that produce methane gas from hydrogen, carbon dioxide, methanol, formic acid, acetic acid, etc. in an oxygen-free environment. In the present invention, methanogenic archaea that have a symbiotic relationship with anaerobic symbiotic bacteria include, but are not limited to, archaea of ​​the genera Methanobacterium, Methanolinea, Methanolegula, Methanothrix, Methanomethylovorans, and Methanomassiliococcus.

[0031] The decomposition of aromatic compounds by anaerobic symbiotic bacteria does not proceed in an environment with a high hydrogen concentration, but the coexistence of hydrogen-utilizing microorganisms such as methanogenic archaea rapidly removes hydrogen, maintaining a low hydrogen concentration environment, allowing the decomposition of aromatic compounds to proceed. Therefore, in the anaerobic biological wastewater treatment of the present invention, the symbiotic relationship between anaerobic symbiotic bacteria and methanogenic archaea is important for the decomposition of aromatic compounds and methane gas production.

[0032] In the TA production wastewater treatment method of the present invention, alkylene glycol is added as a biostimulation to activate the anaerobic symbiotic bacteria and methanogenic archaea introduced into the reactor. The following examples demonstrate that the addition of ethylene glycol significantly improves the efficiency of aromatic compound decomposition by anaerobic biological wastewater treatment. Preferably, the alkylene glycol is ethylene glycol.

[0033] The appropriate method, amount, and timing of addition of alkylene glycol to TA production wastewater may vary depending on the conditions of the anaerobic biological wastewater treatment for decomposing the mixed wastewater, such as the configuration and operating conditions of the reactor, the microbial activity profile in the reactor, the wastewater treatment efficiency, etc. However, a person skilled in the art can determine the appropriate method, amount, and timing of addition of alkylene glycol using appropriate preliminary tests without the need for excessive trial and error.

[0034] The present inventors have discovered a new biostimulation method using the addition of methanol / formic acid (Non-Patent Documents 8 and 10), and have demonstrated that mixing DMT production wastewater containing large amounts of methanol and formic acid with TA production wastewater and treating them together can result in more efficient treatment of TA production wastewater (Non-Patent Document 22). Based on this, in a preferred embodiment of the TA production wastewater treatment method of the present invention, DMT production wastewater may be added as an additional biostimulation. Here, the conditions for adding DMT production wastewater, like ethylene glycol, can be determined by those skilled in the art without undue trial and error, depending on the specific operating conditions of the TA production wastewater treatment method of the present invention.

[0035] In a preferred embodiment of the TA production wastewater treatment method of the present invention, the organic matter composition of the TA production wastewater (influent wastewater) injected into the reactor and the residual organic matter composition of the effluent wastewater discharged after passing through the reactor can be measured, and the efficiency of the wastewater treatment in the treatment method of the present invention can be monitored by comparing the results. This monitoring means can be designed appropriately by those skilled in the art depending on the embodiment of the treatment method of the present invention. Although not limited thereto, the "Analysis Method" section of the Examples below provides examples of the measurement means used in the tests in this Example.

[0036] In a preferred embodiment of the present invention, the operating conditions of the wastewater treatment method are adjusted according to the results of the monitoring. For example, the adjustment of the operating conditions is adjustment of the composition of the wastewater, adjustment of the reactor, or adjustment of the flow rate of the wastewater through the reactor. For example, the adjustment of the composition of the wastewater is adjustment of the amount of DMT production wastewater or ethylene glycol added to the wastewater. As an example of the adjustment of the operating conditions, but not limited to, in the following examples, the wastewater treatment process is divided into appropriate phases, and various conditions of the treatment method are adjusted while monitoring the wastewater treatment status in each phase, and the effects of the adjusted conditions are confirmed by monitoring.

[0037] In the wastewater treatment method for TA production of the present invention, aromatic compounds in the wastewater from TA production are decomposed by methanogenic archaea in the reactor, producing methane as a decomposition product. Therefore, in a preferred embodiment, the wastewater treatment method for TA production of the present invention may further include a step of recovering the produced methane from the reactor. The means for recovering methane from the reactor is not particularly limited, and any means known to those skilled in the art may be used. The recovered methane can be used as biomass energy, such as a heat source, power source, or power generation.

[0038] The present invention will be described in more detail below with reference to examples. However, these examples are merely examples shown for the convenience of explaining the present invention, and the present invention is not limited to these examples in any sense.

[0039] Internal Two-Stage Upflow Anaerobic (ITUA) Reactor: To test the TA production wastewater treatment method of the present invention, a laboratory-scale internal two-stage upflow anaerobic (ITUA) reactor of the present invention was designed. A schematic diagram of the ITUA reactor is shown in Figure 1. The ITUA reactor was installed in an incubator (MIR-554-PJ, PHC Corporation) maintained at 37°C. The width and depth of the ITUA reactor were 0.1 m and 0.05 m, respectively. The heights of the first and second stages of the ITUA reactor were 0.2 m (effective volume: 1 L) and 0.4 m (2 L), respectively. A gas-solid-liquid separator (GSS) was installed above the second stage. The ITUA reactor was made of transparent polyvinyl chloride, and the first and second stages were molded as a single unit. In the first stage, green tuff granules (1-5 mm in diameter, surface area approximately 4 m²) were used as a natural inorganic carrier capable of promoting methane production. ２ 1 / g (dry), Hinai Green (registered trademark, Towada Green Tuff Agroscience Co., Ltd.) was added on the 164th day of operation, and mesophilic granular sludge recovered from the UASB reactor used in the TA / DMT wastewater treatment test in our non-patent document 22 was loaded into the second stage on the 1st day of operation. To load the green tuff granules, the mesophilic granular sludge was discharged into the ITUA reactor on the 164th day of operation, and then the green tuff granules were loaded into the first stage, and the granular sludge originally added to the ITUA reactor was loaded into the second stage. Two movable polyvinyl chloride separator plates were installed to separate the first and second stages of the ITUA reactor, and a permeation hole of less than approximately 1 mm was provided between the two separator plates to prevent the permeation of the green tuff and granular sludge. The granular sludge was stored at 4°C under anaerobic conditions for 4 months before the start of this test. The volume of the inlet tank was 20 L and the hydraulic retention time (HRT) was maintained at 24 h.

[0040] Characteristics of TA / DMT Wastewater In this example, the TA production wastewater treated by the TA production wastewater treatment method of the present invention was prepared according to Table 1 below. Because this wastewater simulates the addition of DMT production wastewater to TA production wastewater, hereafter this wastewater will be referred to as TA / DMT wastewater. The operational phases of this treatment method were divided into phases 1 to 27, and the components and substrate concentrations of the TA / DMT wastewater were adjusted for each phase. Starting from phase 3.5 (day 164), green tuff granules were loaded into the first stage of the ITUA reactor. In phases 3, 3.5, 9 to 17, and 25 to 27, ethylene glycol was added to the TA / DMT wastewater as a biostimulation to activate the anaerobic symbiotic bacteria and methanogenic archaea in the granular sludge loaded into the second stage of the reactor. The aromatic compound substrate was dissolved in tap water using a hot-plate magnetic stirrer (ASHS-1HP, AS ONE). Inorganic chemicals (g / L: Na ２ SO ４ ,0.24;MgSO ４ ,0.21;CaCl ２ -2H ２ O, 0.15; KCl, 0.30; KH ２ P.O. ４ , 0.15;NH ４ Cl, 0.11) and minerals (mg / L: FeSO ４ -7H ２ O, 7.0; CoCl ２ -6H ２ O, 0.17; ZnSO ４ -7H ２ O, 0.15; H ３ BO ３ ,0.060;MnCl ２ -4H ２ O, 0.42; NiCl ２ -6H ２ O, 0.040; CuCl ２ -2H ２ O, 0.027; Na ２ MoO ４ -2H ２ 0.025) was added to the TA / DMT wastewater. The pH of the TA / DMT wastewater was adjusted to approximately 7.0 with 2 M HCl and 2 M NaOH. Table 1. Composition of influent TA / DMT wastewater used in this study

[0041] Analytical Methods: For routine analysis, the wastewater before treatment (influent wastewater) in the inlet tank of the ITUA reactor and the treated wastewater that had passed through the reactor (effluent wastewater) were collected. pH and biogas production were measured on-site. pH was measured using a pH meter (HM-30P, DKK-TOA). Biogas production was detected using a wet gas meter (W-NK-0.5B, Shinagawa). Total solids (TS) and volatile organic solids (TVS) were measured by heating 20 mL of influent and effluent wastewater, respectively, at 105°C for 24 hours and 600°C for 30 minutes in an oven. Total COD and soluble COD concentrations were analyzed by the potassium dichromate method using a spectrophotometer (HACH, DR1900, USA) and COD2 reagent HR TNT (HACH, HACH1227). The soluble COD concentration was measured using samples filtered through a 0.22 μm filter. The COD concentrations of various organic acids and aromatic compounds were calculated by determining the theoretical oxygen demand from the equation for complete oxidation when various compounds react with oxygen. ４ , CO ２ , N ２ , H ２Biogas components were measured in phases 3.5-27 using a gas chromatograph (GC-2014, Shimadzu) equipped with a thermal conductivity detector and a SHINCARBON-ST50 / 80 stainless steel column, 4.0 m x 3.0 mm (ID). The column temperature was 130°C, and the inlet / detector temperature was 150°C. The aromatic compound concentrations (terephthalic acid, isophthalic acid, orthophthalic acid, p-toluic acid, and benzoic acid) in the influent and effluent wastewater were measured in phases 6-27 using an ACQUITY UPLC H-Class system equipped with an ACQUITY UPLC BEH C18 (1.7 μm, 2.1 x 100 mm) column and a PDA detector (270 nm) (Nihon Waters). The flow rate was 0.4 ml / min, the column temperature was 35°C, and the solvents were 20% methanol (A), 100% methanol (B), and 1.0% formic acid (C). The gradients were A:B:C = 80:10:10 (0-5.0 min), A:B:C = 30:60:10 (5.0-8.0 min), and A:B:C = 80:10:10 (8.0-10 min). Volatile fatty acids (VFAs) in the influent and effluent wastewaters were analyzed using a Prominence HPLC system (Shimadzu Corporation) equipped with a Shim-pack Fast-OA column (100 mm long, 7.8 mm inner diameter, 5 μm columns, two in series) and a conductivity detector (6-27 phase). Solvent A (5 mM p-toluenesulfonic acid) and solvent B (5 mM p-toluenesulfonic acid, 20 mM Bis-Tris, 0.1 mM EDTA) were purchased from Shimadzu (Organic Acid High-Speed ​​Analysis Mobile Phase Reagent Set, Shimadzu). The flow rates of pumps A and B were 0.8 ml / min, and the column temperature was 40°C.

[0042] Results Start-up of an Internal Two-Stage Upflow Anaerobic (ITUA) Reactor In phases 1 and 2, the first stage of the reactor was not yet filled with green tuff granules, and the second stage was filled with granular sludge. The reactors were operated for a total of 32 days with simple TA / DMT wastewater of 1,380 mg COD / L and 2,170 mg COD / L, respectively (Tables 1 and 2). However, the total COD removal efficiency was unstable, less than 70% (Table 2). Therefore, in phase 3, formate and ethylene glycol were added to enhance the physiological activity of the granular sludge. Although the total COD removal efficiency improved to 78.9% in phase 3, the reactor performance remained stable due to the high organic matter removal rate (6.6 kg COD / m). ３ This result did not reach the results of our previous study (Non-Patent Document 22), which achieved a COD removal efficiency of 88.6% (total COD removal efficiency) and 89.6% (soluble COD removal efficiency). Therefore, to further improve the organic matter removal efficiency, green tuff granules were packed into the first stage of the ITUA reactor starting from Phase 3.5 (Day 164). In Phase 3.5, a total COD removal efficiency of 88.6% and a soluble COD removal efficiency of 89.6% were achieved, demonstrating that the green tuff granules packed into the first stage of the ITUA reactor are effective in enhancing TA wastewater treatment. Because the ITUA reactor performed well in Phase 3.5, ethylene glycol was removed from the TA / DMT wastewater from Phases 4 to 8 (Table 1), increasing the influent COD concentration from 2,690 mg / L to 7,110 mg / L (Table 2). The ITUA reactor without ethylene glycol achieved a high total COD removal efficiency of 87.0–93.5% in phases 4–8, allowing 7,110 mg COD / L. Table 2 Summary of organic loading and COD concentration in the internal two-stage upflow anaerobic (ITUA) reactor

[0043] Effect of biostimulation and internal two-stage treatment To further evaluate the effect of the ITUA reactor and biostimulation of the present invention, ethylene glycol was added again to the influent wastewater of the TA / DMT wastewater in phases 9 to 17, increasing the set COD concentration from 9,010 to 14,292 mg / L (Table 1). Phase 15 (organic loading rate [OLR]: 9.96 kg COD / m ３ / d), total COD and soluble COD removal efficiencies of over 90% were achieved, but in phases 16 and 17, the OLR was 12.3 kg COD / m ３ / d and 11.2 kg COD / m ３ / d, resulting in a decline in the performance of the ITUA reactor (Table 2 and Figure 2). During these phases, high concentrations of p-toluic acid (710 mg COD / L in Phase 16 and 777 mg COD / L in Phase 17), isophthalic acid (433 and 448 mg COD / L), orthophthalic acid (294 and 296 mg COD / L), and terephthalic acid (233 and 203 mg COD / L) remained in the effluent wastewater from the ITUA reactor (Figure 3). Among the components of TA production wastewater, p-toluic acid is known to be the most difficult to degrade under anaerobic conditions (Non-Patent Document 22). Therefore, promoting the degradation of p-toluic acid is an important step toward more efficient treatment of TA production wastewater.

[0044] Considering wastewater treatment on a plant scale, it is more preferable to limit the amount of biostimulation added to the treatment of TA production wastewater. ３ / d) to Phase 23 (11.4 kg COD / m ３ / d), the addition of formic acid and ethylene glycol to the influent wastewater was stopped. In the ITUA reactor without biostimulation, the OLR was 9.4 kg COD / m ３ / d (Phase 22) allowed for an overall COD removal efficiency of 92% with a residual aromatic compound concentration of less than 600 mg COD / L (Figure 3). Phase 23 reduced the OLR to 11.4 kg COD / m ３ / d, the total COD removal efficiency dropped significantly to less than 80%. Therefore, in Phase 24, a low concentration of formate (100 mg COD / L) was added to the influent wastewater. As a result, the organic matter removal rate (9.9 kg COD / m ３ / d) and total COD removal efficiency (81±2%) improved from Phase 23 (Figure 2), but aromatic compounds, including p-toluic acid, were still present in the effluent wastewater at approximately 1,900 mg COD / L. To further improve the performance of the ITUA reactor, 500 mg COD / L of ethylene glycol was added to the influent wastewater in Phase 25, resulting in a 5.2% increase in total COD removal efficiency from Phase 24. Furthermore, the residual aromatic compound concentration in the effluent wastewater decreased to approximately 720 mg COD / L, indicating that the addition of ethylene glycol activated anaerobic symbiotic bacteria and methanogenic archaea for aromatic compound degradation. The total COD removal efficiency was 11.9 kg COD / m ３ In phase 26 of 12,500 mg COD / L influent, the total COD removal efficiency dropped to 83.4%, with high levels of aromatic compounds remaining. For methane gas production, a linear relationship (R ２ = 0.937), the methane conversion was 84.6% (Figure 4). This was comparable to that of a UASB reactor for TA / DMT wastewater treatment (Non-Patent Document 22) and a two-stage UASB system for treating TA production wastewater containing acetic acid, benzoic acid, and terephthalic acid (Non-Patent Document 6).

[0045] Comparison of aromatic compound removal rates in different phases revealed a clear positive effect of biostimulation (Figure 5). When comparing the removal rates of terephthalic acid, isophthalic acid, orthophthalic acid, and p-toluic acid between phases 8 and 9, and phases 23, 24, and 25, where the aromatic compound concentration in TA / DMT wastewater was the same, the aromatic compound removal rates in the phase 9 with both ethylene glycol and formic acid were 7–8% higher than those in the phase 8 with formic acid alone. At high OLR, the aromatic compound removal rates in the phase 24 with formic acid addition were 1–4% higher than those in the phase 24 without formic acid addition. The addition of ethylene glycol (phase 25) further increased the aromatic compound removal rates by 8–24%. These results clearly demonstrate that the addition of biostimulation is an effective approach to improve the degradation of phthalate ester isomers and p-toluic acid in methanogenic bioreactors.

[0046] During the 1,026-day operation period of the ITUA reactor, the average organic matter removal rate that showed the highest value in each phase was 11.0±0.6 kg COD / m in Phase 25. ３ / d, and the organic matter removal rate (5.8-22.5 kg COD / m) obtained with the conventional external two-stage reactor system ３ / d) (Non-Patent Documents 6, 16 and 18). Regarding the aromatic compound removal efficiency, the results of the previous study by the present inventors (6.6 kg COD / m) showed the highest organic matter removal rate compared to the single anaerobic bioreactors treating TA production wastewater reported so far (excluding processes treating wastewater containing only TA and those in which TA decomposition within the process has not been confirmed). ３ / d), which was 1.67 times higher than that of the non-patent literature 6, 26 and 27. Incidentally, the organic matter removal rate was the highest (22.5 kg COD / m ３In a previous study using a two-stage UASB reactor system, the feed wastewater contained only terephthalic acid, benzoic acid, and acetic acid (Non-Patent Document 6). The combination of the ITUA reactor system and biostimulation of the present invention demonstrated treatment capacities equal to or greater than those of the previous external two-stage system. Furthermore, it was demonstrated that the combination of the ITUA reactor system and biostimulation of the present invention can stably treat more complex TA production wastewater, i.e., wastewater containing 36 mM acetic acid, 9 mM benzoic acid, and 5.5-8.6 mM of aromatic compounds such as p-toluic acid and terephthalic acid (Figure 3 and Table 1). As described above, the combination of the ITUA reactor system and biostimulation of the present invention can avoid the irreversible inhibitory effect of acetic acid / benzoic acid on the degradation of aromatic compounds in TA production wastewater and significantly improve the treatment efficiency of TA production wastewater without excessively increasing the treatment process.

[0047] In general, two-stage anaerobic digestion (AD) systems, consisting of two tanks connected in series and vertically, offer many advantages over simple single-stage systems, including increased methane production, high organic load treatment, and better organic matter removal rates (Non-Patent Document 28). Two-stage anaerobic digestion systems are also considered suitable for overcoming the inhibitory effects on methane production caused by the accumulation of volatile fatty acids and the presence of complex substrates such as lipids and proteins (Non-Patent Document 29). However, single-stage systems are far more common than two-stage systems due to their lower installation costs and operational simplicity (Non-Patent Documents 28, 30). The newly demonstrated reactor design integrates the two stages into a single reactor, eliminating the need for separate monitoring and operation of two-stage wastewater treatment systems. By combining the advantages of both single-stage and two-stage systems, the AD system overcomes the problems inherent in each of the previous technologies. Furthermore, because the biostimulation substrates formic acid and ethylene glycol are discharged as wastewater or waste products during the production of DMT and PET (Non-Patent Documents 8, 10, 22, 31, 32), this disclosure provides a technology that enables both (i) highly efficient TA / DMT wastewater treatment and (ii) combined treatment of wastewater species from different sources, which is expected to further simplify wastewater treatment facilities and reduce costs.

Claims

1. A method for treating terephthalic acid (TA) production wastewater, comprising: (A) subjecting the TA production wastewater to anaerobic biological wastewater treatment by the action of methanogenic archaea and anaerobic symbiotic bacteria to decompose the organic matter in the TA production wastewater; and (B) adding alkylene glycol to the TA production wastewater one or more times during the process of the anaerobic biological wastewater treatment in (A).

2. The method according to claim 1, wherein the alkylene glycol is ethylene glycol.

3. The method according to any one of claims 1 or 2, further comprising, before the step (A), a step of adding dimethyl terephthalate (DMT) production wastewater to the TA production wastewater.

4. The method according to claim 3, wherein the TA production wastewater contains one or more aromatic compounds selected from the group consisting of orthophthalic acid, benzoic acid, terephthalic acid, isophthalic acid, and p-toluic acid, and their salts and esters.

5. The method according to claim 1, wherein the methanogenic archaea and anaerobic symbiotic bacteria are subjected to anaerobic biological wastewater treatment in a state aggregated in granular sludge.

6. The method according to claim 1, wherein the methanogenic archaea includes one or more archaea selected from the group consisting of archaea of the genera Methanobacterium, Methanolinea, Methanoregula, Methanothrix, Methanomethylvorans, and Methanomassiliicoccus.

7. The method according to claim 1, wherein the anaerobic symbiotic bacteria includes one or more bacteria selected from the group consisting of bacteria of the genera Syntrophus, Syntrophorhabdus, and Pelotomaculum.

8. The method according to claim 1, further comprising, before the step (A), a step of adjusting the components of the TA production wastewater.

9. The method according to claim 5, wherein the step (A) includes: 1) a step of providing an internal two-stage upflow anaerobic reactor, where the internal two-stage upflow anaerobic reactor includes a lower tank (the first stage) and an upper layer (the second stage), and the space between the first stage and the second stage is partitioned by a separation plate, and the bottom of the first stage is provided with a wastewater inlet and the upper part of the second stage is provided with a wastewater outlet, and the first stage is filled with an inorganic carrier having the activity of removing fatty acids and benzoic acids, and the second stage is filled with granular sludge in which methanogenic archaea and anaerobic symbiotic bacteria are aggregated, and the separation plate does not allow the inorganic carrier and the granular sludge to pass through but allows the wastewater to pass through; 2) a step of injecting the TA production wastewater into the reactor of step 1) through the wastewater inlet; 3) a step of sequentially passing the wastewater injected in step 2) through the inorganic carrier in the first stage of the reactor and the granular sludge in the second stage; and 4) a step of recovering the treated wastewater that has passed through the reactor in step 3) through the wastewater outlet.

10. The method according to claim 9, wherein the inorganic carrier is green tuff.

11. The method according to claim 9, wherein the injection of the wastewater in step 2) and the passage of the wastewater in the reactor in step 3) are driven by a pump, and the injection rate and the passage rate are adjusted under the control of the pump.

12. The method according to claim 9, further including a step of measuring the organic composition of the TA production wastewater injected into the reactor in step 2) and the residual organic composition of the treated wastewater recovered in step 4), and comparing the results to monitor the efficiency of the wastewater treatment in the method.

13. The method according to claim 12, wherein the operating conditions of the wastewater treatment method are adjusted according to the results of the monitoring, and the adjustment of the operating conditions includes adjusting the composition of the wastewater, adjusting the reactor, or adjusting the passage rate of the wastewater in the reactor.

14. The method according to claim 13, wherein the adjustment of the composition of the wastewater is the adjustment of the addition amount of DMT production wastewater or alkylene glycol to the wastewater.

15. A method for producing methane from the TA production wastewater, which is further configured to include a step of recovering methane generated by the decomposition of organic matter in the TA production wastewater in addition to the method according to any one of claims 1 to 14.