Wastewater treatment method

Abstract

To provide a wastewater treatment method capable of stably treating persistent organic wastewater containing 1,4-dioxane, which is a persistent organic substance generated in the process of ethylene oxide production, with low energy load.SOLUTION: A wastewater treatment method is a method in which persistent organic wastewater containing 1,4-dioxane is subjected to biological treatment using activated sludge, and in which the hydraulic residence time in the biological treatment is 4 days or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a wastewater treatment method. [Background technology]

[0002] 1,4-dioxane is known as a persistent organic substance, and is acutely toxic, chronically toxic, and carcinogenic. Therefore, strict regulations are imposed on wastewater standards for 1,4-dioxane. Specifically, the wastewater standard value for 1,4-dioxane for public water bodies and groundwater environments was set at 0.05 mg / L or less in 2009. Furthermore, the wastewater standard value for 1,4-dioxane for general wastewater was set at 0.5 mg / L or less in 2010.

[0003] 1,4-Dioxane is used industrially as a solvent for organic synthesis reactions together with various solvents. 1,4-Dioxane is also a by-product in the production of ethylene oxide using naphtha as a raw material. 1,4-Dioxane is a stable substance in its natural state and has been considered difficult to biodegrade. However, in recent years, methods for treating wastewater containing 1,4-dioxane have been disclosed, for example, in Patent Documents 1 and 2.

[0004] Patent Document 1 discloses a method for treating wastewater by adding decomposing bacteria (microorganisms) to the wastewater using a wastewater treatment device equipped with a biological treatment tank, a separation membrane module, and a culture tank. Patent Document 2 discloses a wastewater treatment system that includes a biological treatment tank that performs biological treatment using activated sludge containing 1,4-dioxane-degrading bacteria, and that is configured so that a nitrification inhibitor is added to the wastewater. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-65081 [Patent Document 2] Japanese Patent Application Publication No. 2017-154107 Summary of the Invention [Problem to be solved by the invention]

[0006] The methods described in Patent Documents 1 and 2 are bioaugmentation methods in which microorganisms cultured externally are introduced into a contaminated environment to purify the environment. This requires the maintenance and management of the microorganisms introduced from the outside, which poses a problem of difficulty. Another problem with bioaugmentation is that if microorganisms are eradicated in activated sludge, it is virtually impossible to back up or restore them. Furthermore, the methods described in Patent Documents 1 and 2 are treatment systems that combine biological treatment and AOP (Advanced Oxidation Process), which poses a problem of a large energy load.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wastewater treatment method that can stably treat persistent organic wastewater containing 1,4-dioxane, a persistent organic substance generated in the process of producing ethylene oxide, with a reduced energy load. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention proposes the following means. The wastewater treatment method of the present invention is a method for biologically treating wastewater containing refractory organic matter containing 1,4-dioxane using activated sludge containing a soluble iron(II) monooxygenase gene and 1,4-dioxane-degrading bacteria, wherein the hydraulic retention time in the biological treatment is set to 4 days or more, and the soluble iron(II) monooxygenase gene is introduced at a concentration of 4.2 × 10 6 Activated sludge containing more than (copies / mL) As it happens Biological treatment In the biological treatment, the 1,4-dioxane-degrading bacteria contained in the activated sludge are determined to comprise 1,4-dioxane-degrading bacteria that include at least Mycrobacterium and Pseudonocardia, based on sequence analysis of the base sequences of polymerase chain reaction amplification products using the Greengenes database and the Silva Living Tree database, as the proportion of 1,4-dioxane-degrading bacteria in the total number of bacteria.

[0009] According to this invention, biological treatment of wastewater containing persistent organic matter, including 1,4-dioxane, can be carried out without the need for maintenance and management of microorganisms contained in activated sludge and with a reduced energy load.

[0010] The present invention In the wastewater treatment method of the above, the concentration of the seed sludge in the mixture of the seed sludge and the wastewater containing hardly decomposable organic matter can be set to 8000 mg / L or more. In the wastewater treatment method of the present invention, by setting the hydraulic retention time to 8 days or more, the soluble iron (II) monooxygenase gene can be expressed at a concentration of 6.0 × 10 7 Activated sludge containing more than (copies / mL) As it happens Biological treatment is preferred.

[0011] According to the present invention, biological treatment of wastewater containing persistent organic matter containing 1,4-dioxane can be carried out more efficiently without the need for maintenance and management of microorganisms contained in activated sludge and with a reduced energy load.

[0012] In addition, in the mixed liquid of the persistent organic wastewater containing 1,4-dioxane and the activated sludge, The aforementioned Soluble iron(II) monooxygenase gene or The aforementioned The number of 1,4-dioxane-degrading bacteria may also be increased.

[0013] According to this invention, by increasing the number of soluble iron(II) monooxygenase genes that decompose 1,4-dioxane or 1,4-dioxane-decomposing bacteria, the decomposition efficiency of 1,4-dioxane is improved, thereby making it possible to reduce the energy load.

[0014] In the wastewater treatment method, the temperature at which the persistently decomposable organic wastewater containing 1,4-dioxane is biologically treated may be 30°C or higher and 35°C or lower.

[0015] According to the present invention, the decomposition of 1,4-dioxane by microorganisms is promoted within the above temperature range, and therefore the decomposition efficiency of 1,4-dioxane can be improved.

[0016] In the wastewater treatment method, the 1,4-dioxane-containing persistent organic wastewater and treated water produced by biological treatment of the 1,4-dioxane-containing persistent organic wastewater may be separated.

[0017] According to this invention, only the treated water is separated and recovered, while the activated sludge and the microorganisms contained therein remain in the biological treatment tank. Therefore, it is possible to carry out biological treatment of persistent organic wastewater containing 1,4-dioxane without the need for maintenance such as adding microorganisms. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a wastewater treatment method that can stably treat persistent organic wastewater containing 1,4-dioxane, a persistent organic substance generated in the process of producing ethylene oxide, with a reduced energy load. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram showing a schematic configuration of a wastewater treatment device used in a wastewater treatment method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] [Wastewater treatment method] An embodiment of a wastewater treatment method according to the present invention will now be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing a general configuration of a wastewater treatment device used in the wastewater treatment method according to an embodiment of the present invention.

[0021] The wastewater treatment method according to this embodiment is a wastewater treatment method in which persistent organic wastewater containing 1,4-dioxane is biologically treated using activated sludge, and the hydraulic retention time in the biological treatment is set to 4 days or more. As shown in FIG. 1, a wastewater treatment device 10 used in the wastewater treatment method according to this embodiment includes a biological treatment tank 11, a separation means 12, and a filtration pump 13.

[0022] The biological treatment tank 11 contains the 1,4-dioxane-containing persistent organic wastewater to be treated. In the biological treatment tank 11, activated sludge is used to biologically treat the 1,4-dioxane-containing persistent organic wastewater. Biological treatment is a method of treating organic matter contained in wastewater by using microorganisms to decompose the organic matter. The microorganisms used in the wastewater treatment method according to this embodiment are aerobic microorganisms that can survive only under conditions in which oxygen is present in the air or water.

[0023] A first conduit 14 is connected to the biological treatment tank 11 for introducing into the biological treatment tank 11 the hardly decomposable organic wastewater containing 1,4-dioxane to be treated.

[0024] The separation means 12 separates the hardly decomposable organic wastewater present in the biological treatment tank 11 from the treated water produced by the biological treatment of the hardly decomposable organic wastewater. The separation means 12 is not particularly limited as long as it can separate the hardly decomposable organic wastewater from the treated water, and examples thereof include a separation membrane, a centrifuge, etc. An example of the separation membrane is a hollow fiber.

[0025] A second conduit 15 is connected to the separating means 12 for recovering the treated water and taking it out of the biological treatment tank 11 .

[0026] The filtration pump 13 sucks and recovers the treated water separated by the separation means 12 . The filtration pump 13 is provided midway along the second conduit 15 .

[0027] The wastewater treatment method according to this embodiment will be described. First, the persistent organic wastewater containing 1,4-dioxane (hereinafter sometimes abbreviated as "persistent organic wastewater") is introduced from a storage tank (not shown) storing the persistent organic wastewater into the biological treatment tank 11 via the first conduit 14. The wastewater containing hardly decomposable organic matter stored in the storage tank is first introduced into a flow rate adjusting tank (not shown), where the flow rate is adjusted to a predetermined value, and then introduced into the biological treatment tank 11.

[0028] Before introducing the persistent organic wastewater into the biological treatment tank 11, seed activated sludge is introduced into the biological treatment tank 11. The seed activated sludge is used for biologically treating the chemical oxygen demand (COD) components of the persistent organic wastewater. This sludge contains at least one of a soluble iron(II) monooxygenase gene (hereinafter referred to as "SDIMO gene") and 1,4-dioxane-degrading bacteria.

[0029] The amount of seed sludge to be charged into the biological treatment tank 11, i.e., the concentration of the seed sludge in the mixture of seed sludge and persistent organic wastewater, is preferably 8000 mg / L or more, and more preferably 10000 mg / L or more. The upper limit of the seed sludge concentration may be 20000 mg / L or less, or 18000 mg / L or less. If the seed sludge concentration is equal to or higher than the lower limit, it is believed that 1,4-dioxane-degrading microorganisms will be adequately secured. On the other hand, if the seed sludge concentration is equal to or lower than the upper limit, it is believed that 1,4-dioxane will be adequately biologically treated, and problems such as membrane clogging will not occur.

[0030] Next, a predetermined amount of persistent organic wastewater is introduced into the biological treatment tank 11, and then air is sent to the persistent organic wastewater using an aeration device to aerate the persistent organic wastewater and activate the activated sludge in the biological treatment tank 11. This decomposes the persistent organic wastewater. That is, the microorganisms contained in the activated sludge activated by aeration decompose 1,4-dioxane and other organic matter contained in the persistent organic wastewater, producing treated water.

[0031] Here, the treated water refers to the liquid obtained by solid-liquid separation of the wastewater in the biological treatment tank 11.

[0032] Examples of aeration devices include a diffuser type (bubble type) device in which diffuser plates and diffuser pipes are installed in the biological treatment tank 11 and compressed air is sent to the diffuser plates and diffuser pipes, and a surface aeration type device in which a water wheel or impeller is installed in the biological treatment tank 11 and mechanical agitation is performed using the water wheel or impeller.

[0033] In the wastewater treatment method according to this embodiment, the hydraulic retention time (HRT) is set to 4 days or more. Although the longer the hydraulic retention time (HRT), the better in terms of improving the treatment capacity of 1,4-dioxane, a longer hydraulic retention time (HRT) would increase the capacity of the biological treatment tank, so a realistic value is about 4 days.

[0034] The hydraulic retention time (HRT) is the time that the persistent organic wastewater introduced into the biological treatment tank 11 remains in the biological treatment tank 11. In the wastewater treatment method according to this embodiment, the hydraulic retention time (HRT) is expressed by the following formula (1). HRT (days) = (Volume of biological treatment tank) / (Treatment amount of persistent organic wastewater) (1)

[0035] If the hydraulic retention time (HRT) is less than four days, the biodegradation effect of 1,4-dioxane will not be realized. This phenomenon occurs because microorganisms decompose the relatively easily degradable organic substances first in the wastewater containing persistent organic matter. 1,4-dioxane is a difficult organic substance to decompose in the wastewater containing persistent organic matter, and is targeted for degradation after the decomposition of the easily degradable organic substances has progressed.

[0036] In the wastewater treatment method according to this embodiment, the sludge retention time (SRT) is set to 80 days or more, preferably 90 days or more, and more preferably 100 days or more. The upper limit of the sludge retention time (SRT) may be 120 days or less, or may be 110 days or less.

[0037] The sludge retention time (SRT) is the average retention time of activated sludge in the biological treatment tank 11 until it is withdrawn as excess sludge. In the wastewater treatment method according to this embodiment, the sludge retention time (SRT) is expressed by the following formula (2).

[0038] SRT (days) = (biological treatment tank capacity) × (average MLSS concentration) / ((excess sludge volume) × (SS concentration in excess sludge) + (amount of refractory organic wastewater) × (SS concentration in treated water)) (2)

[0039] MLSS is an abbreviation for Mixed Liquor Suspended Solids. In other words, MLSS refers to the concentration of organic matter and the like contained in the mixed liquor in the biological treatment tank 11. In the wastewater treatment method according to this embodiment, the MLSS concentration is expressed by the following formula (3).

[0040] MLSS concentration = {((amount of persistent organic wastewater introduced into the biological treatment tank) / day) × (SS concentration of persistent organic wastewater introduced into the biological treatment tank) + ((amount of returned sludge) / day) × (SS concentration of returned sludge))} ÷ {((amount of persistent organic wastewater introduced into the biological treatment tank) / day) + ((amount of returned sludge) / day)} (3)

[0041] SS is an abbreviation for suspended solids. SS is also called suspended solids. In the industrial wastewater testing method specified in JIS K 0102, the measurement method for SS is specified as "suspended solids."

[0042] If the sludge retention time (SRT) is less than 80 days, the maintenance and management of microorganisms contained in activated sludge is required in the biological treatment of wastewater containing persistent organic matter, including 1,4-dioxane, and the energy load is also large.

[0043] In the wastewater treatment method according to this embodiment, it is preferable to increase the SDIMO gene or 1,4-dioxane-decomposing bacteria contained in the activated sludge in a mixed liquid of the activated sludge and persistent organic wastewater containing 1,4-dioxane, which is introduced into the biological treatment tank 11. In the biological treatment tank 11, means (method) for increasing the SDIMO gene and 1,4-dioxane-degrading bacteria contained in the activated sludge are to extend the hydraulic retention time (HRT) or the sludge retention time (SRT).

[0044] The SDIMO gene and 1,4-dioxane-degrading bacteria degrade 1,4-dioxane. Therefore, increasing the SDIMO gene or 1,4-dioxane-degrading bacteria improves the decomposition efficiency of 1,4-dioxane, thereby further reducing the energy load in the wastewater treatment method according to this embodiment.

[0045] In the wastewater treatment method according to this embodiment, the temperature at which the persistently decomposable organic wastewater is biologically treated in the biological treatment tank 11 is preferably 30°C or higher and 35°C or lower. If the temperature at which persistently decomposable organic wastewater is biologically treated is within the above range, the decomposition of 1,4-dioxane by microorganisms is promoted, thereby improving the efficiency of decomposition of 1,4-dioxane.

[0046] In the wastewater treatment method according to this embodiment, it is preferable to separate the persistent organic wastewater and treated water produced by the biological treatment of the persistent organic wastewater contained in the biological treatment tank 11 using a separation means 12. Specifically, the separation means 12 arranged in the biological treatment tank 11 is sucked by a filtration pump 13, thereby filtering a mixed liquid containing activated sludge, persistent organic wastewater, and treated water, and the filtrate is transferred as treated water to a treatment water tank (not shown). By separating the persistent organic wastewater from the treated water, only the treated water is separated and collected, while the activated sludge and the microorganisms contained therein remain in the biological treatment tank 11. Therefore, the persistent organic wastewater containing 1,4-dioxane can be biologically treated without the need for maintenance such as adding microorganisms.

[0047] According to the wastewater treatment method of this embodiment, wastewater containing persistent organic matter, including 1,4-dioxane, can be treated stably and with a reduced energy load. [Example]

[0048] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0049] [Example] Activated sludge seed sludge was first introduced into the biological treatment tank of a wastewater treatment system as shown in Figure 1. The amount of seed sludge introduced into the biological treatment tank, i.e., the seed sludge concentration in the mixture of seed sludge and raw water (refractory organic wastewater) was 10,000 mg / L. The seed sludge used was activated sludge for biologically treating the COD components of the wastewater, and contained the SDIMO gene and 1,4-dioxane-degrading bacteria. Then, 158 to 173 L / day of raw water with a biochemical oxygen demand (BOD) of 1100 to 1700 mg / L, a chemical oxygen demand (COD) of 1700 to 1900 mg / L, and a 1,4-dioxane content of 18 to 23 mg / L was introduced into the biological treatment tank. After introducing raw water into the biological treatment tank, air was sent to the mixture of raw water and seed sludge using an aeration device to aerate the mixture and promote decomposition of the mixture. In the biological treatment of wastewater, it is common to extract a certain amount of sludge from the biological treatment tank, but in this example, sludge extraction was not performed in order to actively increase the sludge retention time (SRT).

[0050] Aeration was continued while the sludge retention time (SRT) and hydraulic retention time (HRT) were varied. After a specified sludge retention time (SRT) had elapsed and after a specified hydraulic retention time (HRT) had elapsed, the mixed liquor in the biological treatment tank was sampled, and the biochemical oxygen demand (BOD, unit: mg / L), chemical oxygen demand (COD, unit: mg / L), 1,4-dioxane content (unit: mg / L), SDIMO gene content (copies / mL), and the proportion of 1,4-dioxane-degrading bacteria in the total bacterial population (unit: %) were measured. BOD and COD were measured based on JIS K0102:2019 "Testing Methods for Industrial Wastewater." 1,4-Dioxane content was measured based on JIS K0125:2016 "Testing Methods for Volatile Organic Compounds in Industrial Water and Wastewater."

[0051] The content of SDIMO genes and the proportion of 1,4-dioxane-degrading bacteria in the total bacterial population were measured using next-generation sequencing analysis technology. Next-generation sequencing analysis uses a next-generation sequencer to analyze the base sequence of PCR (Polymerase Chain Reaction) amplified products, for example, to decipher the base sequence of the DNA of microorganisms contained in a sample. Next-generation sequencers are also called massively parallel sequencers or novel sequencers. They are provided by sequencer vendors and brands such as Illumina, IonTorrent, Roche 454, PacBio RS, and SOLiD. The estimation of closely related species was carried out using a 16S rRNA gene sequence database (hereinafter referred to as the "database"). There are several databases available, but here we used a database called "Greengenes" that contains sequence information for unisolated cultured bacteria, and a database called "Silva Living Tree" that contains sequence information for isolated bacteria only.

[0052] The DNA for analysis was extracted using the environmental DNA extraction kit "Extrap Soil DNA Kit Plus ver.2 (Nippon Steel Sumikin Environmental Corporation)." DNA extraction using the DNA extraction kit involves the following steps (1) to (5) in order: (1) cell disruption (bead beating), (2) protein removal, (3) purification using magnetic beads, (4) DNA elution, and (5) quantification using real-time PCR.

[0053] (1) For cell disruption, a bead-type tissue and cell disrupter, the FastPrep FP100A (MP Biomedicals), is used. The bead-type tissue and cell disrupter effectively disrupts tissues and cells by rapidly moving a microtube containing special disrupting beads up and down. 0.5 mL of sample, extraction buffer, and lysis solution are added to the bead tube, and bead-beating is performed for, for example, 30 to 45 seconds. After bead-beating, the sample in the bead tube is centrifuged, and the supernatant is collected.

[0054] (2) To remove proteins, PP solution is added to the supernatant collected by cell disruption, and the mixture is centrifuged, after which the supernatant is collected.

[0055] (3) In magnetic bead purification, MBs solution (magnetic beads for DNA recovery) and binding solution are added to the supernatant collected from protein removal and stirred. After stirring, magnetic collection is performed and the supernatant is discarded. After discarding the supernatant, washing solution is added, and stirring and magnetic collection are performed again, and the supernatant is discarded. Finally, an aqueous ethanol solution is added, and stirring and magnetic collection are performed again, and the supernatant is discarded.

[0056] (4) For DNA elution, after purification with magnetic beads and air drying, an elution solution (TE Buffer or sterile Milli-Q water) is added and heated at 65°C for 5 to 10 minutes. After magnetic collection, the supernatant is collected.

[0057] (5) Real-time PCR quantification quantifies the number of 16S rRNA genes and SDIMO genes in eubacteria. Real-time PCR is a method for monitoring and analyzing amplification products produced by polymerase chain reaction (PCR) in real time. In real-time PCR, a calibration curve is created using serially diluted known amounts of DNA, plotting the threshold cycle (Ct value) at which a certain amount of amplification product is achieved in the exponential region of PCR amplification on the horizontal axis and the initial amount of DNA on the vertical axis. Then, using a sample with an unknown concentration, the Ct value is determined under the same conditions as for the known amount of DNA. The amount of DNA in the sample is then determined from the calibration curve for the known amount of DNA and the Ct value for the sample with the unknown concentration. Note that when monitoring with real-time PCR, a fluorescent reagent is used.

[0058] Using the values ​​obtained by the above measurements, the removal rates of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and 1,4-dioxane were calculated according to the following formulas (4) to (6). Biochemical oxygen demand (BOD) removal rate = (Biochemical oxygen demand (BOD) in the mixed liquor after biological treatment) / (Biochemical oxygen demand (BOD) in the mixed liquor before biological treatment) × 100 (%) (4) Chemical oxygen demand (COD) removal rate = (Chemical oxygen demand (COD) in the mixed liquor after biological treatment) / (Chemical oxygen demand (COD) in the mixed liquor before biological treatment) × 100 (%) (5) 1,4-dioxane removal rate = (1,4-dioxane content in the mixed solution after biological treatment) / (1,4-dioxane content in the mixed solution before biological treatment) × 100 (%) (6)

[0059] In addition, the rate of increase in the content of the SDIMO gene was calculated according to the following formula (7). Increase rate of SDIMO gene content = (SDIMO gene content in the mixed solution after biological treatment) / (SDIMO gene content in the mixed solution before biological treatment) × 100 (%) (7)

[0060] The results are shown in Table 1. In Table 1, (A) is Mycrobacterium, (B) is Pseudonocardia, (C) is Rhodococcus, and (D) is Afipia.

[0061] [Table 1]

[0062] At a sludge retention time (SRT) of 40 days, biochemical oxygen demand (BOD) removal was 94%, chemical oxygen demand (COD) removal was 90%, and 1,4-dioxane removal was 15%. The number of SDIMO genes was not measured at this time point. Furthermore, analysis of the Greengene database, which contains sequence information for unisolated cultured bacteria, revealed that Mycrobacterium accounted for 4.9% and Pseudonocardia for 0.2%, with no Rhodococcus detected. Analysis of the Silva Living Tree database, which contains sequence information for previously isolated strains, revealed that Mycrobacterium accounted for 4.9%, Pseudonocardia for 0.2%, and no Afipia detected.

[0063] Under the condition of 60 days of sludge retention time (SRT), the removal rates of biochemical oxygen demand (BOD) were 99%, chemical oxygen demand (COD) were 97%, and 1,4-dioxane were 52%. The number of SDIMO genes was 4.2 × 10 6 copies / mL. Furthermore, the composition ratio of 1,4-dioxane-degrading bacterial genera in Greengene was Mycrobacterium at 0.2%, Pseudonocardia at 0.2%, and Rhodococcus at 0.1%. In Silva Living Tree, the composition ratios were Mycrobacterium at 0.2%, Pseudonocardia at 0.2%, and Afipia was not detected.

[0064] Under the condition of 110 days of sludge retention time (SRT), the removal rates of biochemical oxygen demand (BOD) were 99%, chemical oxygen demand (COD) were 97%, and 1,4-dioxane were 56%. The number of SDIMO genes was 6.0 × 10 7 The ratio of 1,4-dioxane-degrading bacteria was 1.0% for Mycrobacterium, 5.2% for Pseudonocardia, and no Rhodococcus was detected in Greengene. The ratio of 1,4-dioxane-degrading bacteria was 1.0% for Mycrobacterium, 5.2% for Pseudonocardia, and 0.1% for Afipia in Silva Living Tree.

[0065] hydraulic Residence time ( H Under the condition of 2 days (RT), the removal rate of biochemical oxygen demand (BOD) was 94%, the removal rate of chemical oxygen demand (COD) was 90%, and the removal rate of 1,4-dioxane was 15%.

[0066] hydraulic Residence time ( H Under 4-day RT conditions, the biochemical oxygen demand (BOD) removal rate was 99%, the chemical oxygen demand (COD) removal rate was 97%, and the 1,4-dioxane removal rate was 52%. The number of SDIMO genes was 4.2 × 10 6 copies / mL.

[0067] hydraulic Residence time ( H Under 8 days of RT, the biochemical oxygen demand (BOD) removal rate was 99%, the chemical oxygen demand (COD) removal rate was 98%, and the 1,4-dioxane removal rate was 89%. The number of SDIMO genes was 6.0 × 10 7 copies / mL.

[0068] In the examples, the sludge retention time (SRT) increased daily because the sludge was not extracted. Also, in the examples, the hydraulic retention time (HRT) was gradually increased during the course of the experiment. The SDIMO gene expression increased with increasing sludge retention time (SRT) from 40 to 110 days and hydraulic retention time (HRT). The composition ratio of known decomposing bacteria showed a decrease in Mycrobacterium, but an increase in Pseudonocardia, Rhodococcus, and Afipia. According to the literature (Ji-Hyun Nam, Jey-R S. Ventura, Ick Tae Yeom, Yongwoo Lee, Deokjin Jahng, Structural and Kinetic Characteristics of 1,4-Dioxane-Degrading Bacterial Consoria Containing the Phylum TM7, J. Microbiaol. Biotechnol. (2016), 26(11)), microorganisms possessing the SDIMO gene are said to have the ability to degrade 1,4-dioxane. It is thought that as the sludge retention time (SRT) is extended, the absolute number of 1,4-dioxane-degrading bacteria increases and the composition of decomposing bacteria becomes suitable for the sludge retention time (SRT) and hydraulic retention time (HRT) environment. [Explanation of symbols]

[0069] 10 Wastewater treatment equipment 11 Biological treatment tank 12 Separation means 13 Filtration pump 14 1st conduit 15 Second conduit

Claims

1. A wastewater treatment method for biologically treating persistent organic wastewater containing 1,4-dioxane using activated sludge containing a soluble iron(II) monooxygenase gene and 1,4-dioxane-degrading bacteria, wherein the hydraulic retention time in the biological treatment is set to 4 days or more; The soluble iron(II) monooxygenase gene was transformed into 4.2 × 10 ６ (copies / mL) or more of activated sludge, The wastewater treatment method is characterized in that, in the biological treatment, the 1,4-dioxane-degrading bacteria contained in the activated sludge are 1,4-dioxane-degrading bacteria that include at least Mycrobacterium and Pseudonocardia, as determined by sequence analysis using the Greengenes database and sequence analysis using the Silva Living Tree database of the base sequences of polymerase chain reaction amplification products as the composition of the 1,4-dioxane-degrading bacteria out of the total number of bacteria.

2. 2. The wastewater treatment method according to claim 1, wherein the concentration of the seed sludge in the mixture of the seed sludge and the wastewater containing hardly decomposable organic matter is set to 8000 mg / L or more.

3. By setting the hydraulic retention time to 8 days or more, the soluble iron (II) monooxygenase gene can be expressed at a rate of 6.0 × 10 ７ 3. The wastewater treatment method according to claim 1, wherein the biological treatment is carried out so as to obtain activated sludge containing at least 1000 mg of urea per ...

4. The wastewater treatment method according to any one of claims 1 to 3, wherein the soluble iron(II) monooxygenase gene or the 1,4-dioxane-decomposing bacteria is increased in a mixed liquid of the 1,4-dioxane-containing persistent organic wastewater and the activated sludge.

5. The wastewater treatment method according to any one of claims 1 to 4, wherein the temperature at which the persistent organic wastewater containing 1,4-dioxane is biologically treated is 30°C or higher and 35°C or lower.

6. The wastewater treatment method according to any one of claims 1 to 5, characterized in that the persistent organic wastewater containing 1,4-dioxane and treated water produced by biological treatment of the persistent organic wastewater containing 1,4-dioxane are separated.

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