JP7822121B2 - Wastewater treatment method - Google Patents

Description

The present invention relates to a wastewater treatment method.

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 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 for 1,4-dioxane for general wastewater was set at 0.5 mg/L or less in 2010.

1,4-dioxane is used industrially as a solvent for organic synthesis reactions, along with various other solvents. It is also a by-product of the ethylene oxide production process using naphtha as a raw material. 1,4-dioxane is a stable substance in its natural state, and biological decomposition has been considered difficult. However, in recent years, methods for treating wastewater containing 1,4-dioxane have been disclosed, such as those described in Patent Documents 1 and 2.

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.

JP 2018-65081 A Japanese Patent Application Laid-Open No. 2017-154107

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 external sources, which can be difficult. Another issue with bioaugmentation is that if microorganisms are eradicated in activated sludge, it is virtually impossible to back them 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 significant energy burden.

The present invention was made in consideration of the above circumstances, and aims to provide a wastewater treatment method that can stably treat persistent organic wastewater containing 1,4-dioxane, a persistent organic substance generated in the ethylene oxide production process, with a low energy load.

In order to solve the above problems, the present invention proposes the following means.
The wastewater treatment method of the present invention biologically treats 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 biological treatment is carried out with a hydraulic retention time of 4 days or more and to produce activated sludge containing 4.2 x ¹⁰ (copies/mL) or more of the soluble iron(II) monooxygenase gene. In the biological treatment, the 1,4-dioxane-degrading bacteria contained in the activated sludge are determined to comprise 1,4-dioxane-degrading bacteria of at least Mycrobacterium and Pseudonocardia as the proportion of 1,4-dioxane-degrading bacteria in the total bacterial population, as determined by sequence analysis of the nucleotide sequences of polymerase chain reaction amplification products using the Greengenes database and the Silva Living Tree database.

This invention makes it possible to biologically treat wastewater containing persistent organic matter, including 1,4-dioxane, without the need to maintain and manage the microorganisms contained in activated sludge and with a reduced energy load.

In the wastewater treatment method of the present invention , the concentration of the seed sludge in the mixture of the seed sludge and the persistently decomposable organic wastewater can be set to 8000 mg/L or more.
In the wastewater treatment method of the present invention, it is preferable to carry out biological treatment so as to obtain activated sludge containing 6.0 × 10 ⁷ (copies/mL) or more of the soluble iron(II) monooxygenase gene by setting the hydraulic retention time to 8 days or more.

This invention makes it possible to more efficiently biologically treat wastewater containing persistent organic matter, including 1,4-dioxane, without the need to maintain and manage the microorganisms contained in activated sludge and with a reduced energy load.

Furthermore, the soluble iron(II) monooxygenase gene or the 1,4-dioxane-decomposing bacteria may be increased in a mixed liquid of the 1,4-dioxane-containing persistent organic wastewater and the activated sludge.

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 efficiency of 1,4-dioxane decomposition is improved, thereby reducing the energy load.

In addition, in the above wastewater treatment method, the temperature at which the persistent organic wastewater containing 1,4-dioxane is biologically treated may be 30°C or higher and 35°C or lower.

According to this invention, the decomposition of 1,4-dioxane by microorganisms is promoted within the above temperature range, thereby improving the decomposition efficiency of 1,4-dioxane.

Furthermore, in the above wastewater treatment method, the 1,4-dioxane-containing persistent organic wastewater and the treated water produced by biological treatment of the 1,4-dioxane-containing persistent organic wastewater may be separated.

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. This means that biological treatment of persistent organic wastewater containing 1,4-dioxane can be carried out without the need for maintenance such as adding microorganisms.

The present invention provides a wastewater treatment method that can stably treat persistent organic wastewater containing 1,4-dioxane, a persistent organic substance generated in the ethylene oxide production process, with a reduced energy load.

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.

[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 the general configuration of a wastewater treatment device used in the wastewater treatment method according to an embodiment of the present invention.

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 in the biological treatment, the hydraulic retention time 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 separating means 12 , and a filtration pump 13 .

The biological treatment tank 11 contains the wastewater containing persistent organic matter, which is the target of treatment, and contains 1,4-dioxane. In the biological treatment tank 11, activated sludge is used to biologically treat the wastewater containing persistent organic matter, which contains 1,4-dioxane.
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 only survive under conditions in which oxygen is present in the air or water.

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

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.

A second conduit 15 is connected to the separation means 12 to collect treated water and remove it from the biological treatment tank 11.

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 .

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 .

Before introducing the persistent organic wastewater into the biological treatment tank 11, seed activated sludge is added to 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 the "SDIMO gene") and 1,4-dioxane-degrading bacteria.

The amount of seed sludge to be charged into the biological treatment tank 11, i.e., the concentration of the seed sludge in the mixed liquid of seed sludge and persistent organic wastewater, is preferably 8,000 mg/L or more, and more preferably 10,000 mg/L or more. The upper limit of the seed sludge concentration may be 20,000 mg/L or less, or 18,000 mg/L or less.
If the seed sludge concentration is equal to or higher than the above-mentioned 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 above-mentioned upper limit, it is believed that 1,4-dioxane will be adequately biologically treated, and problems such as membrane clogging will not occur.

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. In other words, 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.

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

Examples of aeration devices include aeration (bubble) devices that install aeration plates and aeration pipes in the biological treatment tank 11 and send compressed air to the aeration plates and aeration pipes, and surface aeration devices that install a water wheel or impeller in the biological treatment tank 11 and use the water wheel or impeller to perform mechanical agitation.

In the wastewater treatment method according to this embodiment, the hydraulic retention time (HRT) is set to four days or more. Furthermore, the longer the hydraulic retention time (HRT), the better in terms of improving the treatment capacity for 1,4-dioxane. However, since a longer hydraulic retention time (HRT) would increase the capacity of the biological treatment tank, a realistic setting is around four days.

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) = (biological treatment tank capacity) / (treatment amount of persistent organic wastewater) (1)

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 first decompose the relatively easily degradable organic substances in the wastewater containing persistent organic matter. 1,4-dioxane is in the difficult-to-decompose category in wastewater containing persistent organic matter, and is targeted for degradation after the decomposition of the easily degradable organic substances has progressed.

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 110 days or less.

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 equation (2):

SRT (days) = (biological treatment tank capacity) x (average MLSS concentration) / ((excess sludge volume) x (SS concentration in excess sludge) + (amount of persistent organic wastewater) x (SS concentration in treated water)) (2)

MLSS is an abbreviation for mixed liquor suspended solids. In other words, MLSS refers to the concentration of organic matter and other substances 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):

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

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

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

In the wastewater treatment method according to the present 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 persistently decomposable 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).

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

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 the wastewater containing persistent organic matter is biologically treated is within the above range, the decomposition of 1,4-dioxane by microorganisms is promoted, and the efficiency of decomposition of 1,4-dioxane can be improved.

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.

The wastewater treatment method according to this embodiment allows for stable treatment of persistent organic wastewater containing 1,4-dioxane with a reduced energy load.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples.

[Example]
Activated sludge seed sludge was previously charged into the biological treatment tank of a wastewater treatment device as shown in Figure 1. The amount of seed sludge charged into the biological treatment tank, i.e., the seed sludge concentration in the mixed liquid of the seed sludge and raw water (wastewater containing persistent organic matter) was 10,000 mg/L. Activated sludge for biologically treating the COD components of the wastewater was used as the seed sludge, and this sludge contained the SDIMO gene and 1,4-dioxane-degrading bacteria.
Thereafter, 158 L/day to 173 L/day of raw water having a biochemical oxygen demand (BOD) of 1100 mg/L to 1700 mg/L, a chemical oxygen demand (COD) of 1700 mg/L to 1900 mg/L, and a 1,4-dioxane content of 18 mg/L 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).

Aeration was continued while the sludge retention time (SRT) and hydraulic retention time (HRT) were changed. After a predetermined sludge retention time (SRT) had elapsed and after a predetermined 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 count (unit: %) in the mixed liquor 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."

The content of the SDIMO gene and the proportion of 1,4-dioxane-degrading bacteria in the total number of bacteria were measured using next-generation sequencing analysis technology.
Next-generation sequencing analysis involves using a next-generation sequencer to perform sequence analysis of the base sequence of a PCR (Polymerase Chain Reaction) amplification product, 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, new-type sequencers, etc. Next-generation sequencers are provided by sequencer vendor 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 on unisolated cultured bacteria, and a database called "Silva Living Tree" that contains sequence information only on isolated bacteria.

The DNA extraction kit for analysis, "Extrap Soil DNA Kit Plus ver. 2 (manufactured by Nippon Steel & Sumikin Environmental Corporation)," was used. To extract DNA using the DNA extraction kit, the following steps (1) to (5) are carried out 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.

(1) For cell disruption, a bead-type tissue/cell disruptor, the FastPrep FP100A (manufactured by MP Biomedicals), is used. The bead-type tissue/cell disruptor effectively disrupts tissues and cells by rapidly moving a microtube containing special disruption 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.

(2) To remove proteins, PP solution is added to the supernatant collected by cell disruption, followed by centrifugation, and the supernatant is collected.

(3) In magnetic bead purification, MBs solution (magnetic beads for DNA recovery) and binding solution are added to the supernatant collected during 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.

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

(5) Quantification using real-time PCR 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 cycle number (threshold cycle; Ct value) at which a certain amount of amplification product is reached 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 of unknown concentration, the Ct value is determined under the same conditions as for the known amount of DNA, and the amount of DNA in the sample is measured from the calibration curve for the known amount of DNA and the Ct value for the sample of unknown concentration. Note that when monitoring using real-time PCR, a fluorescent reagent is used.

Using the values obtained by the above measurements, the removal rate of biochemical oxygen demand (BOD), the removal rate of chemical oxygen demand (COD), and the removal rate of 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)

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)

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

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

Under the condition of a sludge retention time (SRT) of 60 days, 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 x 10 ⁶ copies/mL. Furthermore, in the composition ratio of 1,4-dioxane-degrading bacterial genera, the analysis results for Greengene showed that Mycrobacterium was 0.2%, Pseudonocardia was 0.2%, and Rhodococcus was 0.1%. The analysis results for Silva Living Tree showed that Mycrobacterium was 0.2%, Pseudonocardia was 0.2%, and Afipia was not detected.

Under the condition of a sludge retention time (SRT) of 110 days, 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 56%. The number of SDIMO genes was 6.0 x 10 ⁷ copies/mL. Furthermore, in the composition ratio of 1,4-dioxane-degrading bacteria, the analysis results for Greengene showed that Mycrobacterium was 1.0%, Pseudonocardia was 5.2%, and Rhodococcus was not detected. The analysis results for Silva Living Tree showed that Mycrobacterium was 1.0%, Pseudonocardia was 5.2%, and Afipia was 0.1%.

At a hydraulic retention time ( HRT ) of 2 days, 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%.

Under the condition of a hydraulic retention time ( HRT ) of 4 days, the removal rate of biochemical oxygen demand (BOD) was 99%, the removal rate of chemical oxygen demand (COD) was 97%, and the removal rate of 1,4-dioxane was 52%. The number of SDIMO genes was 4.2 x ¹⁰ copies/mL.

Under the condition of a hydraulic retention time ( HRT ) of 8 days, the removal rate of biochemical oxygen demand (BOD) was 99%, the removal rate of chemical oxygen demand (COD) was 98%, and the removal rate of 1,4-dioxane was 89%. The number of SDIMO genes was 6.0 x ¹⁰ copies/mL.

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 increasing hydraulic retention time (HRT). The composition ratio of known decomposing bacteria showed a decrease in the proportion of Mycrobacterium, but the proportions of Pseudonocardia, Rhodococcus, and Aphipia tended to increase. Literature (Ji-Hyun Nam, Jey-R S. Ventura, Ick Tae Yeom, Yongwoo Lee, Deokjin Jahng, Structural and Kinetic Characteristic of 1,4-Dioxane-Degrading Bacterial Consoria Containing the Phylum TM7, J. Microbial. Biotechnol. (2016), 26(11)) indicates that microorganisms having the SDIMO gene are capable of decomposing 1,4-dioxane. It is thought that the absolute number of 1,4-dioxane-decomposing bacteria increased with the extension of the sludge retention time (SRT), resulting in a composition of decomposing bacteria suited to the sludge retention time (SRT) and hydraulic retention time (HRT) environments.

10 wastewater treatment device 11 biological treatment tank 12 separation means 13 filtration pump 14 first conduit 15 second conduit

Claims (6)

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;
biological treatment to produce activated sludge containing 4.2 x 10 ⁶ (copies/mL) or more of the soluble iron (II) monooxygenase gene ;
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. 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. The wastewater treatment method according to claim 1 or 2, characterized in that the hydraulic retention time is set to 8 days or more, thereby carrying out biological treatment to produce activated sludge containing 6.0 x ¹⁰⁷ (copies/mL) or more of the soluble iron(II) monooxygenase gene. 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 bacterium 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 claim 1 , 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. 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.