Method for treating methanol-containing wastewater

Abstract

A method for treating methanol-containing wastewater is provided in which the methanol is anaerobically treated, the method being characterized by adding a C2-C4 organic nitrogen (which is not an amino acid). The organic nitrogen is, for example, at least one selected from among TMAH, trimethylamine, and dimethylamine.

Description

Method for treating wastewater containing methanol

[0001] The present invention relates to a method for treating methanol-containing wastewater, and more particularly to a method for anaerobic treatment of methanol-containing wastewater.

[0002] One method for treating methanol-containing wastewater is to subject it to anaerobic treatment. Patent Document 1 describes a method for treating methanol-containing wastewater by mesophilic methane fermentation using an upflow anaerobic sludge bed process (UASB process), in which acetic acid or an acetic acid-producing substance is supplied to the raw water at the start of the process.

[0003] Patent Document 2 describes a method of pretreating raw water to adjust the methanol concentration within a predetermined range and then treating it by the UASB method. Patent Document 3 describes a method of treating methanol-containing wastewater by the UASB method using a carrier supporting methane fermentation bacteria.

[0004] Japanese Patent Laid-Open No. 4-310294 Japanese Patent Laid-Open No. 2012-239954 Japanese Patent Laid-Open No. 2019-107609

[0005] Anaerobic treatment requires nitrogen as one of the nutrient sources for anaerobic microorganisms, and conventionally, urea or ammonium salts have been added as this nitrogen component. In Patent Document 1, ammonium chloride is used.

[0006] When methanol is anaerobically treated, yeast is sometimes added as a nutrient to stabilize the treatment and increase the decomposition rate, but nutrients such as yeast are expensive.

[0007] An object of the present invention is to provide a method for treating methanol-containing wastewater that can stabilize the anaerobic treatment of methanol without using expensive nutrients.

[0008] The present inventors have found that when methanol-containing wastewater is subjected to anaerobically treating the wastewater, adding organic nitrogen having 2 to 4 carbon atoms (excluding amino acids), such as TMAH, which is contained in wastewater from the electronics industry, to the methanol-containing wastewater stabilizes the anaerobic treatment and also increases the decomposition rate.

[0009] The present invention is based on this finding and has the following gist.

[0010] [1] A method for treating methanol-containing wastewater by anaerobically treating methanol, characterized in that organic nitrogen having 2 to 4 carbon atoms (excluding amino acids) is added.

[0011] [2] The method for treating methanol-containing wastewater according to [1], wherein the organic nitrogen is at least one of TMAH, trimethylamine, and dimethylamine.

[0012] [3] The method for treating methanol-containing wastewater according to [1] or [2], wherein the organic nitrogen is added in an amount of 250 to 800 mg-N / L in terms of N equivalent, or in an amount of 1 to 25% in terms of the weight ratio of the N equivalent to methanol.

[0013] [4] The method for treating methanol-containing wastewater according to any one of [1] to [3], wherein the anaerobic treatment is a UASB method, an MBR method, or a carrier method.

[0014] [5] Methanol removal load is 0.1 kg-COD in the case of the UASB method Ｃｒ / kg-VSS / d or less, in the case of the MBR process, 0.15 kg-COD Ｃｒ / kg-VSS / d or less, the organic nitrogen is added.

[0015] [6] The method for treating methanol-containing wastewater according to [5], wherein TMAH is added as the organic nitrogen in an amount of 1 to 25 wt % of methanol.

[0016] By adding organic nitrogen with carbon numbers of 2 to 4 (excluding amino acids) such as TMAH, which is found in wastewater from the electronics industry, to the anaerobic treatment process for methanol-containing wastewater, the treatment becomes more stable and the decomposition rate increases, thereby increasing the volumetric load.

[0017] The reason for this is presumably that when the organic nitrogen is added to the anaerobic treatment process, methanogenic bacteria that can decompose the organic nitrogen (e.g., TMAH) become dominant, and the high methanol decomposition ability of these methanogenic bacteria increases the methanol decomposition rate.

[0018] 1 is a block diagram showing an example of an anaerobic treatment apparatus; and FIG. 2 is a block diagram showing another example of an anaerobic treatment apparatus.

[0019] The present invention will be described in further detail below.

[0020] In the method of the present invention, when methanol-containing wastewater is anaerobically treated, organic nitrogen having a carbon number of 2 to 4 (excluding amino acids) is added to the methanol-containing wastewater. This organic nitrogen may be added to the methanol-containing wastewater (raw water) or to the anaerobic treatment tank.

[0021] Examples of methanol-containing wastewater include wastewater from paper factories, chemical factories, etc. The methanol concentration in the methanol-containing wastewater supplied to the anaerobic treatment step is 0.2 to 20 wt %, preferably about 0.5 to 10 wt %, but is not limited thereto.

[0022] The methanol-containing wastewater may generally contain organic substances other than methanol.

[0023] The TOC concentration of the methanol-containing wastewater to be supplied to the anaerobic treatment step is preferably about 750 to 80,000 mg / L, particularly about 1,900 to 40,000 mg / L, but is not limited to this.

[0024] The proportion of methanol in the TOC is preferably 50 wt % or more, and particularly preferably 75 wt % or more.

[0025] Suitable organic nitrogen to be added to methanol-containing wastewater is tetramethylammonium hydroxide (TMAH) and alkylated organic nitrogen such as trimethylamine (TMA) and dimethylamine (DMA) produced during the decomposition process of TMAH.

[0026] TMAH has the chemical formula [(CH ３ ) ４ N] ＋ [OH] －TMAH is a quaternary ammonium compound expressed as follows. TMAH is widely used as a resist developer in semiconductor and liquid crystal factories, and is a substance found in the wastewater from these factories. TMA is a tertiary amine, and is a gas with a strong, foul odor at room temperature and pressure, so it is handled as an approximately 40% aqueous solution. Dimethylamine, which is produced during the decomposition process of TMAH, is a secondary amine and is highly soluble in water or alcohol. The aqueous solution is strongly alkaline.

[0027] As the organic nitrogen having 2 to 4 carbon atoms (excluding amino acids), an electronics wastewater containing TMAH may be used. When an electronics wastewater containing TMAH is used, it may be used as is, or may be concentrated or diluted before use. The TMAH concentration of the electronics wastewater added as a TMAH source is preferably about 0.5 to 25 wt %.

[0028] The amount of organic nitrogen added to the methanol-containing wastewater is preferably 250 to 800 mg / L, particularly 300 to 500 mg / L, in terms of N equivalent.

[0029] The ratio of the TOC-equivalent amount (mg / L) of the organic nitrogen to the TOC concentration (mg / L) of organic matter in the methanol-containing wastewater [organic nitrogen TOC-equivalent amount added] / [organic matter TOC concentration] is preferably about 10 to 50%, particularly about 10 to 25%. The organic nitrogen is preferably added so that the ratio of the N-equivalent concentration (wt%) of organic nitrogen to the methanol concentration (wt%) in the methanol-containing wastewater to which the organic nitrogen has been added (N / methanol) is about 1 to 25%, particularly about 1.5 to 10%.

[0030] The organic nitrogen may be added constantly or only when necessary depending on the anaerobic treatment status. When the activity of anaerobic treatment is high and the sludge load is high, for example, 0.3 kg-COD Ｃｒ When the nitrogen content is 1 / kg-VSS / d or more, it is preferable not to add the organic nitrogen.

[0031] In the present invention, the addition of urea or the like, which has been conventionally used as a nitrogen source, is not necessary, but may be added.

[0032] The anaerobic treatment method is preferably the UASB method, the MBR method (particularly the outer membrane type) or the carrier method.

[0033] Figure 1 shows a UASB-type anaerobic treatment system. Raw water (methanol-containing wastewater) flows upward through a UASB reactor 1 and undergoes anaerobically treatment while passing through a sludge blanket 1a. Biogas and treated water are extracted from the top of the reactor.

[0034] Figure 2 shows an anaerobic treatment apparatus using an external membrane MBR (membrane bioreactor). Raw water is supplied to an anaerobic treatment tank 2 and undergoes anaerobically treatment. The anaerobic treatment tank 2 is equipped with a stirring blade 2a, which stirs the inside of the tank. A portion of the liquid in the tank is sent via piping 3 and pump 4 to a raw liquid chamber 5a of a membrane separator 5 outside the tank. The anaerobic treatment tank 2 may be filled with a carrier.

[0035] Within the membrane separator 5, a raw liquid chamber 5a and a permeate chamber 5b are formed by a separation membrane 5m. A UF ​​membrane is preferably used as the membrane 5m. The permeate that permeates the membrane 5m is extracted from the permeate chamber 5b as treated water. The liquid that does not permeate the membrane 5m is returned to the anaerobic treatment tank 2 through a pipe 6.

[0036] In the case of the UASB method, the volume load is 8 kg-COD Ｃｒ / m ３ / d or more, preferably 10 kg-COD Ｃｒ / m ３ / d or more, more preferably 15 kg-COD Ｃｒ / m ３ It is preferable to apply it to the treatment of 30 kg-COD / day or more. Ｃｒ / m ３ / d or less, especially 25 kg-COD Ｃｒ / m ３ It is preferable that the ratio is 1 / d or less.

[0037] When treating using the UASB method, the methanol removal load is 0.1 kg-COD ＣｒWhen the treatment load drops to 1000 kJ / kg-VSS / d or less, it is preferable to add the organic nitrogen, and in particular, it is preferable to add TMAH in an amount of 1 to 25 wt %, particularly 1 to 12 wt %, and especially 1 to 5 wt % in terms of N relative to methanol, to recover the treatment load.

[0038] In the case of the UASB system, the addition of the organic nitrogen reduces the methanol removal load to 0.15 kg-COD. Ｃｒ / kg-VSS / d or more, especially 0.3kg-COD Ｃｒ / kg-VSS / d or more. In addition, the treatment operation can be started (the treatment operation can be started and then transitioned to a steady operation) even when the loading rate of the granules that decomposes methanol is low.

[0039] When treating using the MBR method, the volume load is 5 kg-COD Ｃｒ / m ３ / d or more, preferably 8 kg-COD Ｃｒ / m ３ / d or more, more preferably 10 kg-COD Ｃｒ / m ３ It is effective to apply it to anaerobic treatment at a temperature of 1 / d or more.

[0040] When treating with the MBR method, the methanol removal load is 0.15 kg-COD Ｃｒ When the nitrogen content drops to 1000 kJ / kg-VSS / d or less, it is preferable to add the organic nitrogen. In particular, it is preferable to add TMAH in an amount of 1 to 25 wt %, particularly 1 to 12 wt %, and especially 1 to 5 wt % in terms of N relative to methanol to restore the treatment load.

[0041] In the case of the MBR system, the addition of the above organic nitrogen reduces the methanol removal load to 0.25 kg-COD Ｃｒ / kg-VSS / d or more, especially 0.3kg-COD Ｃｒ / kg-VSS / d or more. In addition, treatment operation can be started even when there is only a small amount of sludge to decompose methanol.

[0042] As mentioned above, when the organic nitrogen is added to raw water or the anaerobic treatment tank, methanogenic bacteria capable of decomposing the organic nitrogen (e.g., TMAH) become dominant, and it is presumed that the high methanol decomposition ability of these methanogenic bacteria increases the methanol decomposition rate.

[0043] Examples of methanogenic bacteria to be prioritized include the genera Methanofastidiosum, Methanomethylovorans, Methanosarcina, Methanomassiliicoccus, and Methanomethylophilaceae.

[0044] By continuing the treatment with the addition of the organic nitrogen, it is preferable to make the total abundance ratio of the methanogenic bacteria to the total amount of anaerobic bacteria (the number of viable bacteria in 1 mL of liquid) 5% or more, particularly 20% or more.

[0045] Example 1 As shown in FIG. 1, the following simulated raw water was passed through a UASB reactor 1 under the following conditions, and the state of methanol treatment was observed.

[0046] <Raw water> 5000 mg / L of methanol and 500 mg / L of TMAH (N equivalent concentration: 500 x (14 / 91) = 76.9 mg / L) dissolved in pure water (N / methanol weight ratio: 500 x (14 / 91) / 5000 = 1.5 wt%). Temperature: 36°C, pH: 7.5

[0047] <UASB reactor> Tower volume: 4 L Sludge: Anaerobic sludge obtained by mixing anaerobic sludge collected from an anaerobic reactor treating wastewater containing methanol and anaerobic sludge collected from an anaerobic reactor treating food wastewater at a volume ratio of 1:4 Sludge concentration: MLSS 60,000 mg / L, MLVSS 48,000 mg / L Sludge filling rate: 60% Volume load: 5 kg-COD Ｃｒ / m ３ / d to 12 kg-COD Ｃｒ / m ３ / d over a period of 5 days. (The raw water flow rate is gradually increased from 2.76 L / d to 6.62 L / d over a period of 5 days.) Sludge load: 0.06 kg-COD Ｃｒ / kg-VSS / d to 0.16 kg-CODＣｒ / kg-VSS / d

[0048] <Results and Discussion> Volume load 5 kg - COD Ｃｒ / m ３ / d, the COD removal rate was 95% and the SS concentration in the treated water was 130 mg / L. Ｃｒ / m ３ / d, the COD removal rate was maintained at 95%, and the SS concentration in the treated water was also maintained at 130 mg / L.

[0049] The abundance ratio of the following five representative species of methanogens capable of TMAH decomposition in anaerobic bacteria increased as follows: Methanofastidiosum genus: increased from undetected to 0.08% Methanomethylovorans genus: increased from undetected to 23% Methanosarcina genus: increased from undetected to 5% Methanomassiliicoccus genus: increased from undetected to 2% Methanomethylophilaceae genus: increased from undetected to 0.03% Total of the above five species: increased from undetected to 30.1%

[0050] From this example, it was found that the addition of TMAH to raw water significantly increased the presence of methanogenic bacteria capable of decomposing TMAH, and increased the methanol decomposition rate.

[0051] Comparative Example 1 Treatment was carried out in the same manner as in Example 1, except that TMAH was not added to the raw water.

[0052] <Results and Discussion> Volume load 5 kg - COD Ｃｒ / m ３ On the fourth day, the volume load was increased to 10 kg-COD / day, and the COD removal rate was 95% and the SS concentration in the treated water was 130 mg / L. Ｃｒ / m ３ / d (water flow rate 5.52 L / d), the granules began to break down, the SS concentration in the treated water exceeded 300 mg / L, and the COD removal rate fell to 80%. Ｃｒ / m ３ It was not possible to increase the dose to / d.

[0053] None of the typical methanogens capable of TMAH decomposition (genera Methanofastidiosum, Methanomethylovorans, Methanosarcina, Methanomassiliicoccus, and Ethanomethylophilaceae) were detected even on the fourth day, indicating that the number of methanogens capable of TMAH decomposition did not increase.

[0054] Example 2 As shown in FIG. 2, simulated raw water described below was passed through an anaerobic treatment tank 2 connected to a membrane separator 5 installed outside the tank under the following conditions, and the state of methanol treatment was observed.

[0055] <Raw water> As in Example 1, 5000 mg / L of methanol and 500 mg / L of TMAH were dissolved in pure water. Temperature: 36°C, pH: 7.5

[0056] <Anaerobic treatment tank> Volume: 4 L Sludge: Anaerobic sludge collected from an anaerobic reactor decomposing methanol and anaerobic sludge collected from an anaerobic reactor treating food wastewater, mixed at a volume ratio of 1:9 Sludge concentration: MLSS 22,000 mg / L, MLVSS 20,000 mg / L Volume load: 2 kg-COD Ｃｒ / m ３ / d to 8 kg-COD Ｃｒ / m ３ / d (the raw water supply amount is gradually increased from 1.11 L / d to 4.44 L / d over two weeks). Sludge load: 0.09 kg-COD Ｃｒ / kg-VSS / d to 0.36 kg-COD Ｃｒ / kg-VSS / d

[0057] <Results and Discussion> The target load was achieved in two weeks. The COD removal rate in the second week was 95%.

[0058] The abundance ratio of five representative species of methanogens capable of TMAH decomposition in anaerobic bacteria increased as follows: Methanofastidiosum genus: increased from undetected to 0.05% Methanomethylovorans genus: increased from undetected to 10% Methanosarcina genus: increased from undetected to 2% Methanomassiliicoccus genus: increased from undetected to 1% Methanomethylophilaceae genus: increased from undetected to 0.02% Total of the above five species: increased from undetected to 13.1%

[0059] From Example 2, it was found that the addition of TMAH to raw water significantly increased the abundance of methanogenic bacteria capable of decomposing TMAH, thereby increasing the methanol decomposition rate.

[0060] Comparative Example 2 Experimental Conditions In parallel with Example 2, treatment was carried out in the same manner as in Example 2, except that TMAH was not added to the raw water.

[0061] <Results and Discussion> The target load was achieved in one month. The COD removal rate after one month was 95%.

[0062] None of the typical methanogens capable of decomposing TMAH (genera Methanofastidiosum, Methanomethylovorans, Methanosarcina, Methanomassiliicoccus, and Ethanomethylophilaceae) were detected even after one month, indicating that the number of methanogens capable of decomposing TMAH did not increase.

[0063] Example 3 Treatment was carried out under the same conditions as in Example 2, except that trimethylamine was used instead of TMAH in the simulated raw water (the trimethylamine concentration in the simulated raw water was 500 mg / L, the same as the TMAH concentration in Example 2).

[0064] <Results and Discussion> The target load was achieved in two weeks. After two weeks, the COD removal rate was 95%.

[0065] The abundance ratios of five representative species of methanogens capable of trimethylamine degradation in anaerobic bacteria increased as follows: Methanofastidiosum genus: increased from undetected to 0.03% Methanomethylovorans genus: increased from undetected to 8% Methanosarcina genus: increased from undetected to 2% Methanomassiliicoccus genus: increased from undetected to 0.8% Methanomethylophilaceae genus: increased from undetected to 0.02% Total of the above five species: increased from undetected to 10.9%

[0066] From Example 3, it was found that adding trimethylamine to raw water significantly increases the abundance of methanogenic bacteria capable of decomposing trimethylamine, thereby increasing the methanol decomposition rate.

[0067] Comparative Example 3 Experimental Conditions In parallel with Example 3, treatment was carried out in the same manner as in Example 3, except that trimethylamine was not added to the raw water.

[0068] <Results and Discussion> It took one month to achieve the target load. After one month, the COD removal rate was 95%.

[0069] None of the typical methanogens capable of decomposing trimethylamine (genera Methanofastidiosum, Methanomethylovorans, Methanosarcina, Methanomassiliicoccus, and Ethanomethylophilaceae) were detected even after one month, indicating that the number of methanogens capable of decomposing trimethylamine did not increase.

[0070] Example 4 Treatment was carried out under the same conditions as in Example 2, except that dimethylamine was used instead of TMAH in the simulated raw water (the dimethylamine concentration in the simulated raw water was 500 mg / L, the same as the TMAH concentration in Example 2).

[0071] <Results and Discussion> The target load was achieved in two weeks. After two weeks, the COD removal rate was 95%.

[0072] The abundance ratios of five representative species of methanogens capable of decomposing dimethylamine in anaerobic bacteria increased as follows: Methanofastidiosum genus: increased from undetected to 0.01% Methanomethylovorans genus: increased from undetected to 5% Methanosarcina genus: increased from undetected to 1% Methanomassiliicoccus genus: increased from undetected to 0.5% Methanomethylophilaceae genus: increased from undetected to 0.01% Total of the above five species: increased from undetected to 6.5%

[0073] From Example 4, it was found that the addition of dimethylamine to raw water significantly increased the abundance of methanogenic bacteria capable of decomposing dimethylamine, thereby increasing the methanol decomposition rate.

[0074] Comparative Example 4 Experimental Conditions In parallel with Example 4, treatment was carried out in the same manner as in Example 4, except that dimethylamine was not added to the raw water.

[0075] <Results and Discussion> It took one month to achieve the target load. After one month, the COD removal rate was 95%.

[0076] None of the representative methanogens capable of decomposing dimethylamine (genera Methanofastidiosum, Methanomethylovorans, Methanosarcina, Methanomassiliicoccus, and Ethanomethylophilaceae) were detected even after one month, indicating that the number of methanogens capable of decomposing dimethylamine did not increase.

[0077] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-136429 filed on August 24, 2023, and is incorporated by reference in its entirety.

[0078] 1 UASB reactor 1a sludge blanket 2 anaerobic treatment tank 2a stirring blade 5 membrane separator 5m separation membrane

Claims

1. A method for treating wastewater containing methanol, which involves anaerobically treating methanol, and which comprises adding organic nitrogen having a carbon number of 2 to 4 (excluding amino acids).

2. The method for treating methanol-containing wastewater according to claim 1, wherein the organic nitrogen is at least one of TMAH, trimethylamine, and dimethylamine.

3. The method for treating methanol-containing wastewater according to claim 1, wherein the organic nitrogen is added in an amount of 250 to 800 mg-N / L in terms of N.

4. The method for treating methanol-containing wastewater according to claim 1, wherein the organic nitrogen is added in an amount of 1 to 25% by weight in terms of the weight of the organic nitrogen converted into N and the weight of the methanol.

5. The method for treating methanol-containing wastewater according to claim 1, wherein the anaerobic treatment is a UASB method, an MBR method or a carrier method.

6. The anaerobic treatment is the UASB method, and the methanol removal load is 0.1 kg-COD Ｃｒ 2. The method for treating methanol-containing wastewater according to claim 1, wherein the organic nitrogen is added when the methanol-containing wastewater concentration is equal to or less than 100% by mass per day.

7. The anaerobic treatment is the MBR method, and the methanol removal load is 0.15 kg-COD Ｃｒ 2. The method for treating methanol-containing wastewater according to claim 1, wherein the organic nitrogen is added when the methanol-containing wastewater concentration is equal to or less than 100% by mass per day.

8. The method for treating methanol-containing wastewater according to claim 4 or 7, characterized in that TMAH is added as the organic nitrogen in an amount of 1 to 25 wt % of methanol in terms of N.

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