Dioxane-degrading bacteria-immobilized carrier, biodegradation treatment method, and biodegradation treatment apparatus

Abstract

An object is to provide a degrading bacteria-immobilized carrier on which a 1,4-dioxane-degrading bacterium is supported, as well as a biodegradation treatment method for organic compounds, and a biodegradation treatment apparatus, both using this carrier. As a means for achieving the object, a degrading bacteria-immobilized carrier comprising a porous carrier and a 1,4-dioxane-degrading bacterium supported on the porous carrier, as well as a biodegradation treatment method for organic compounds, and a biodegradation treatment apparatus, both using this carrier, are provided.

Claims

1. A 1,4-dioxane-degrading bacteria-immobilized carrier comprising: a porous carrier; and a 1,4-dioxane-degrading bacterium immobilized on the porous carrier, wherein the porous carrier is hydrophobic and has a specific surface area of 3,000 m.sup.2/m.sup.3 or greater but no greater than 60,000 m.sup.2/m.sup.3, pores of the porous carrier have an average diameter of 20 μm or greater but no greater than 2,000 μm, and the 1,4-dioxane-degrading bacteria is of a Pseudonocardia species.

2. The 1,4-dioxane-degrading bacteria-immobilized carrier according to claim 1, characterized in that the 1,4-dioxane-degrading Pseudonocardia species is strain N23 that has been deposited under Accession No. NITE BP-02032.

3. A method for manufacturing the 1,4-dioxane-degrading bacteria-immobilized carrier of claim 1, comprising introducing the porous carrier to a liquid culture medium while culturing therein the 1,4-dioxane-degrading bacteria bacterium.

4. A biodegradation treatment method comprising contacting water contaminated with an organic compound with the 1,4-dioxane-degrading bacteria-immobilized carrier of claim 1.

5. The biodegradation treatment method according to claim 4, characterized in that the organic compound contains a cyclic ether.

6. The biodegradation treatment method according to claim 4, characterized in that the organic compound contains at least one compound selected from the group consisting of 1,4-dioxane, 1,3-dioxolane, 2-methyl-1,3-dioxolane, and tetrahydrofuran.

7. The biodegradation treatment method according to claim 4, characterized by being a fed-batch process.

8. The biodegradation treatment method according to claim 4, characterized by being a continuous process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 A diagram showing how the dioxane concentration in wastewater changes over time during the continuous process in Experiment 2.

MODE FOR CARRYING OUT THE INVENTION

(2) The present invention is explained in detail below.

(3) The degrading bacteria-immobilized carrier proposed by the present invention comprises a porous carrier and a 1,4-dioxane-degrading bacterium supported on the porous carrier.

(4) Porous Carrier

(5) A porous carrier is a granular and solid carrier having multiple holes inside the carrier, and is different from a general fibrous carrier. The shape of the porous carrier is not limited in any way and may be, for example, a cube shape, rectangular solid shape, hexagonal prism, or other polygonal prism shape, cylindrical shape, or spherical shape, for example. A cube shape or rectangular solid shape is preferred for ease of manufacturing of the carrier.

(6) The carrier size of the porous carrier is not limited in any way, but it is preferably 1 mm.sup.3 or greater but no greater than 1,000 mm.sup.3, or more preferably in a range of 100 mm.sup.3 or greater but no greater than 1,000 mm.sup.3. If the carrier size of the porous carrier is smaller than 1 mm.sup.3, the screen separating the carrier may be clogged; if it exceeds 1,000 mm.sup.3, on the other hand, the specific surface area may decrease to a point where the degrading bacterium can no longer be retained sufficiently. It should be noted that the carrier size of the porous carrier refers to the average value of volume, of at least 10 carriers, calculated according to their shape based on the values measured thereabout using a caliper, microscope, etc.

(7) The average diameter of the holes in the porous carrier is not limited in any way, but one whose average hole diameter is in a range of 20 μm or greater but no greater than 2,000 μm may be used, for example. If the average diameter of the holes is smaller than 20 μm, the air permeability of the carrier may drop, resulting in lower flowability. If the average diameter of the holes exceeds 2,000 μm, on the other hand, fixing of the degrading bacterium may become difficult. It should be noted that the average diameter of the holes in the porous carrier refers to the average value of the opening diameters, measured with a caliper, microscope, etc., of at least 30 hole openings that are present on the carrier surface.

(8) Preferably the specific surface area of the porous carrier per specific volume of carrier is 3,000 m.sup.2/m.sup.3 or greater but no greater than 60,000 m.sup.2/m.sup.3. If the specific surface area is smaller than 3,000 m.sup.2/m.sup.3, the degrading bacterium may not be retained sufficiently. If the specific surface area is greater than 60,000 m.sup.2/m.sup.3, on the other hand, the carrier may lift and flow out of the treatment tank easily. The specific surface area is more preferably 4,000 m.sup.2/m.sup.3 or greater but no greater than 55,000 m.sup.2/m.sup.3, or yet more preferably 4,500 m.sup.2/m.sup.3 or greater but no greater than 50,000 m.sup.2/m.sup.3. It should be noted that the specific surface area of the porous carrier can be calculated according to the BET gas adsorption method using nitrogen gas.

(9) Preferably the porosity of the porous carrier is 50% or higher but no higher than 99%. If the porosity of the porous carrier is lower than 50%, the attached quantity of degrading bacterium may become insufficient. If the porosity exceeds 99%, on the other hand, the air permeability of the carrier may drop, resulting in lower flowability.

(10) The porosity of the porous carrier is calculated using the formula below, by measuring the specific gravity of the subject carrier:
Porosity (%)={1−(Specific gravity/True specific gravity)}×100

(11) Specific gravity: Measured value of specific gravity of the subject carrier

(12) True specific gravity: Specific gravity of the subject carrier material (Literature value, such as 1.20 in the case of polyurethane)

(13) For the porous carrier, any material may be used without limitation and, for example, a sponge made of polyurethane resin, polyethylene, polypropylene, or other polyolefin resin, polyester resin, cellulose resin, vinyl chloride, etc., or gel made of polyvinyl alcohol, alginic acid, polyethylene glycol, etc., may be used. In particular, a porous carrier made of a hydrophobic material is preferred, as it provides an excellent property of attaching the degrading bacterium. This is probably because the degrading bacterium forms a biofilm constituted by a hydrophobic viscous substance, although its composition is unknown. Here, a hydrophobic carrier refers to a carrier that will not sediment in deionized water within 24 hours of being introduced thereto, while a hydrophilic carrier refers to a carrier that will sediment in deionized water within 24 hours of being introduced thereto. Such hydrophobic materials include polyurethane resins, polyethylene, polypropylene, and other polyolefin resins, polyester resins, and cellulose resins.

1,4-dioxane-Degrading Bacterium

(14) The degrading bacterium used under the present invention is not limited in any way, and those belonging to the Mycobacterium sp., Pseudonocardia sp., Afipia sp., Rhodococcus sp., Flavobacterium sp., Methylosinus sp., Burkholderia sp., Ralstonia sp., Cordyceps sp., Xanthobacter sp., Acinetobacter sp., etc., may be used. Among these, those belonging to the Mycobacterium sp. or Pseudonocardia sp. are preferred. Also, while any of constitutive assimilating bacteria, inducible assimilating bacteria, and co-metabolic bacteria may be used, assimilating bacteria are preferred because they require no inducing substance, and constitutive assimilating bacteria are more preferred because they need not be acclimated.

(15) Specific examples include Pseudonocardia sp. N23, Mycobacterium sp. D11, Pseudonocardia sp. D17, Mycobacterium sp. D6, Pseudonocardia dioxanivorans CB1190, Afipia sp. D1, Mycobacterium sp. PH-06, Pseudonocardia benzenivorans B5, Flavobacterium sp., Pseudonocardia sp. ENV478, Pseudonocardia tetrahydrofuranoxydans K1, Rhodococcus ruber T1, Rhodococcus ruber T5, Methylosinus trichosporium OB3b, Mycobacterium vaccae JOB5, Burkholderia cepacia G4, Pseudomonas mendocina KR1, Pseudonocardia tetrahydrofuranoxydans K1, Ralstonia pickettii PKO1, Rhodococcus sp. RR1, Acinetobacter Baumannii DD1, Rhodococcus sp. 219, Pseudonocardia antarctica DVS 5a1, Cordyceps sinensis A, Rhodococcus aetherivorans JCM14343, etc. Among these, Pseudonocardia sp. N23, which is a constitutive assimilating bacterium of excellent degrading ability, is preferred.

(16) Pseudonocardia sp. N23 (hereafter referred to as “strain N23”) has been internationally deposited, effective Apr. 10, 2015, with the National Institute of Technology and Evaluation's Patent Microorganisms Depositary (NPMD) (2-5-8 Kazusakamatari, Kisarazu-shi, Chiba, Japan (Postal Code 292-0818)) under Accession No. NITE BP-02032.

(17) Strain N23 is Gram positive and catalase positive. Strain N23 has the highest 1,4-dioxane maximum specific degradation rate among the constitutive 1,4-dioxane-degrading bacteria reported to date, the value of which is equal to or greater than the corresponding rates of inducible 1,4-dioxane-degrading bacteria. Also, strain N23 can degrade 1,4-dioxane to an extremely low concentration of 0.017 mg/L or below, and treat 1,4-dioxane of as high a concentration as approx. 5,200 mg/L.

(18) Degrading Bacteria-Immobilized Carrier

(19) How the 1,4-dioxane-degrading bacterium should be supported on the porous carrier to manufacture the degrading bacteria-immobilized carrier proposed by the present invention, is not limited in any way; however, a method whereby a porous carrier is introduced to a liquid culture medium in which the 1,4-dioxane-degrading bacterium is being cultured, is simple and convenient.

(20) The method for culturing the 1,4-dioxane-degrading bacterium is not limited in any way, but since 1,4-dioxane-degrading bacteria have lower proliferation potential compared to other microorganisms (hereinafter referred to as “bacteria”), normal culturing methods are likely to cause bacterial contamination. Accordingly, preferred is the culturing method that uses a culture medium containing diethylene glycol (Patent Literature 2), or, if the degrading bacterium is strain N23, the culturing method that uses a culture medium containing at least one type selected from 1,4-dioxane, glyoxylic acid, glycolic acid, ethylene glycol, diethylene glycol, 1,4-butane diol, 1-butanol, tetrahydrofuran, glucose, and acetic acid (Patent Literature 3), each proposed by the inventors of the present invention.

(21) The degrading bacteria-immobilized carrier proposed by the present invention may also be obtained by introducing the porous carrier into an aeration tank in which biodegradation treatment of the organic compound using the 1,4-dioxane-degrading bacterium is already underway. In this case, preferably the porous carrier is introduced in the organic-compound biodegradation treatment step in the fed-batch process mentioned below, in order to prevent outflow of the degrading bacterium.

(22) Biodegradation Treatment Method and Biodegradation Treatment Apparatus

(23) The biodegradation treatment method and biodegradation treatment apparatus proposed by the present invention are characterized in that an organic compound is biodegradation-treated using a degrading bacteria-immobilized carrier comprising a porous carrier and a 1,4-dioxane-degrading bacterium supported on the porous carrier.

(24) The target of biodegradation treatment may be, for example, groundwater, factory effluent or other contaminated water, or contaminated soil at an illegal damping site, each containing organic compounds. It should be noted that, when purifying contaminated soil, the soil is washed with water beforehand to change to water phase the target organic compound to be treated, so as to treat the soil as contaminated water.

(25) Under the biodegradation treatment method and biodegradation treatment apparatus proposed by the present invention, not much of the dioxane-degrading bacterium flows out with the wastewater following the biodegradation treatment because the degrading bacterium is fixed to the carrier, and consequently the concentration of the degrading bacterium in the treatment tank can be kept at a high level. As a result, the capacity of the treatment tank in which biodegradation treatment is performed can be reduced.

(26) The organic compound to be biodegradation-treated is not limited in any way so long as it is an organic compound that can be degraded, or used as a carbon source, by the 1,4-dioxane-degrading bacterium. Examples include 1,4-dioxane, 1,3-dioxolane, 2-methyl-1,3-dioxolane, tetrahydrofuran and other cyclic ethers, ethylene glycol, diethylene glycol, 1,4-butane diol, and the like.

(27) The biodegradation treatment method using the degrading bacteria-immobilized carrier proposed by the present invention is not limited in any way, but it may be implemented by, for example, a so-called “fed-batch process” in which (1) a biodegradation treatment step targeting the organic compound in contaminated water, (2) a draining step in which the degrading bacteria-immobilized carrier is settled out and only the supernatant of treated water is drained, and (3) a contaminated water introduction step in which new contaminated water is introduced, are repeated in the order of (1).fwdarw.(2).fwdarw.(3).fwdarw.(1).fwdarw. . . . , or by a continuous process in which equal amounts of contaminated water and treated water are introduced upstream/drained downstream continuously. In a fed-batch process, the biodegradation treatment rate can be kept at a high level because the initial contaminant concentration in the aeration tank is high. In a continuous process, an existing wastewater treatment facility can be used as is.

(28) Under the biodegradation treatment method and biodegradation treatment apparatus proposed by the present invention, the porous carrier quantity relative to the aeration tank capacity is in a range of preferably 5% or more but no more than 50%, or more preferably 10% or more but no more than 40%, to the water to be treated based on apparent volume. If this porous carrier quantity is less than 5%, the quantity of dioxane-degrading bacterial bodies may become insufficient; if the porous carrier quantity is more than 50%, on the other hand, the flowability of the porous carrier may drop.

EXAMPLES

(29) The present invention is explained more specifically in detail below by citing examples and a comparative example; it should be noted, however, that the present invention is not limited to the following examples.

Experiment 1: Fed-Batch Process

(30) Well water was adjusted to contain 1,000 mg/L of 1,4-dioxane, 20 mg/L of ammonium sulfate in nitrogen concentration, and 5 mg/L of potassium dihydrogen phosphate in phosphorous concentration, for use as test water.

(31) The following three types of porous carriers were used:

(32) Carrier A: Polyurethane porous carrier. Hydrophobic. Cube shape (7-mm square).

(33) Average diameter of holes: 525 μm (measured values: 500 to 550 μm)

(34) Specific surface area: 5,000 m.sup.2/m.sup.3

(35) Porosity: 95.0%

(36) Carrier B: Polyurethane porous carrier. Hydrophilic. Cube shape (10-mm square).

(37) Average diameter of holes: 1,500 μm (measured values: 1,000 to 2,000 μm)

(38) Specific surface area: 1,000 m.sup.2/m.sup.3

(39) Porosity: 96.5%

(40) Carrier C: Polyvinyl alcohol porous carrier. Hydrophilic. Cube shape (7-mm square).

(41) Average diameter of holes: 80 μm (measured values: 70 to 90 μm)

(42) Specific surface area: 46,000 m.sup.2/m.sup.3

(43) Porosity: 89%

(44) It should be noted that the specific surface areas of the carriers were calculated according to the BET gas adsorption method using nitrogen gas, using a high-precision fully automated gas adsorption apparatus (apparatus name: BELSORP36, manufactured by BEL Japan Inc. (current name: MicrotracBEL Corp.)).

(45) For the 1,4-dioxane-degrading bacterium, strain N23 was used.

(46) Strain N23 was cultured for 2 weeks using an MGY culture medium (Malt Extract: 10 g/L, Glucose: 4 g/L, Yeast Extract: 4 g/L, pH: 7.3). This culture solution was centrifuged for 3 minutes at 10,000×g and 4° C. for harvesting, and then washed twice using an inorganic salt culture medium (composition of culture medium: K.sub.2HPO.sub.4: 1 g/L, (NH.sub.4).sub.2SO.sub.4: 1 g/L, NaCl: 50 mg/L, MgSO.sub.4.7H.sub.2O: 200 mg/L, FeCl.sub.3:10 mg/L, CaCl.sub.2): 50 mg/L, pH: 7.3), and the resulting bacterial bodies were used.

Example 1

(47) The test water was added to a reaction column of 2.2 L in volumetric capacity, to approx. one-third the volumetric capacity. To carrier A that had been weighed to 30% in apparent volume with respect to the volumetric capacity of the reaction column, strain N23 (inoculated solution washed/adjusted using 0.85% saline solution (bacterial body concentration 2,000 mg/L)) was added by 0.1 L and blended under light agitation, after which all remaining quantity was added to the reaction column. The reaction column was filled up with the test water, and then aerated at room temperature (21 to 22° C.) from below the reaction column for 48 hours at 1.0 L/min, to obtain a degrading bacteria-immobilized carrier.

(48) Next, the aeration was stopped for 1 hour to let the degrading bacteria-immobilized carrier to sediment. One half the quantity of the supernatant was discarded and replaced with fresh test water, after which aeration was performed for 24 hours at 1.0 L/min.

(49) Now, the test water comprises well water to which 1,4-dioxane, etc., have been added, and almost the entire quantity of total organic carbons (TOC) present in the test water are derived from dioxane. Accordingly, the TOC concentration in the treated water was measured over time using a total organic carbon analyzer (TOC-LCPN model, manufactured by Shimadzu Corporation) and the equivalent values obtained through the conversion formula below were used to evaluate the dioxane concentrations (equivalent), while the rates of decrease in dioxane were obtained based on the value of initial dioxane concentration (equivalent):
Conversion formula: Dioxane concentration (equivalent)(mg/L)=TOC concentration (mg/L)/0.545

Example 2

(50) Same as Example 1, except that carrier B was used.

Example 3

(51) Same as Example 1, except that carrier C was used.

Comparative Example 1

(52) A control produced in the same manner as Example 1, except that neither a porous carrier nor strain N23 was added and only aeration was performed.

(53) Visual Observation

(54) Examples 2 and 3 that used hydrophilic carriers B and C were agitated by aeration and began flowing inside the reaction column immediately after the start of aeration. However, bacterial bodies were not seen as infiltrating into the holes in the porous carrier.

(55) In Example 1 that used hydrophobic carrier A, on the other hand, the carrier remained suspended and did not flow up or down immediately after the start of aeration.

(56) After 48 hours, it was confirmed that strain N23 was attached to all of carriers A to C. In addition, the carrier was also confirmed flowing in Example 1, having blended with the water.

(57) Rate of Decrease in Dioxane

(58) The rates of decrease in dioxane from the start, in Examples 1 to 3 and Comparative Example 1, are shown in Table 1.

(59) TABLE-US-00001 TABLE 1 Rate of decrease in dioxane (%) Comparative Example 1 Example 2 Example 3 Example 1 Treatment period (h) Initial concentration 939 949 949 1004 mg/L  3 4.7 4.3 2.0 3.9  6 9.2 9.3 6.0 4.8 24 12.9 13.4 3.9 11.3 48 25.3 20.3 20.3 16.6 Replacement of test water Initial concentration 800 866 870 983 mg/L 18 36.5 20.8 14.1 6.7

(60) In Examples 1 to 3, dioxane decreased at higher rates than in Comparative Example 1, confirming that dioxane was degraded by strain N23. In particular, Example 1 using hydrophobic carrier A that had not flowed due to poor blending with the test water at the start of aeration, exhibited excellent dioxane degradability and recorded the highest rate of decrease in dioxane after 48 hours.

(61) Although strain N23 was added by equal quantities in Examples 1 to 3, the dioxane-degrading activity was significantly different between Example 1 and Examples 2 and 3. This suggests that the degrading bacterium fixed to a hydrophobic porous carrier would demonstrate higher degrading activity than the degrading bacterium fixed to a hydrophilic porous carrier.

Experiment 2: Continuous Process

(62) The apparatus used in Experiment 1 above was employed as is to perform a continuous process. The experiments conducted in the same manner as Examples 1 to 3 and Comparative Example 1 using the same apparatus, are referred to as Examples 2-1 to 2-3 and Comparative Example 2-1, respectively.

(63) Well water was adjusted to contain 500 mg/L of 1,4-dioxane, 20 mg/L of ammonium sulfate in nitrogen concentration, and 5 mg/L of potassium dihydrogen phosphate in phosphorous concentration, for use as simulated wastewater.

(64) A continuous process, which involved aeration at 1.0 L/min with this simulated wastewater passed from the top side to the bottom side of the reaction column at a flow rate of 1.2 mL/min (1,4-dioxane loading: 0.37 to 0.42 kg/m.sup.3/day), was performed for 25 days.

(65) Once a day, approx. 15 mL of treated water was collected with a syringe from the top part of the reaction column and filtered through a filtration paper (No. 5C), and then evaluated for 1,4-dioxane concentration in the same manner as in Experiment 1 above. It should be noted that the samples collected on day 20 onward were measured for dioxane concentration using a headspace gas chromatograph mass spectrometer (GC/MS-QP2010 PLUS, TURBOMATRIX HS40, manufactured by Shimadzu Corporation; hereinafter referred to as “GC/MS”), to determine accurate values.

(66) How the dioxane concentration changed over time is shown in FIG. 1. It should be noted that, in FIG. 1, outlined plot marks represent GC/MS-measured values of dioxane.

(67) The treatment performance stabilized the fastest in Example 2-1, with the water quality of treated water stabilizing in around 10 days. This was followed by Example 2-3, where the water quality of treated water stabilized in around 2 weeks. In Examples 2-1 and 2-3, the GC/MS-measured dioxane concentration values ranged from 0.5 to 3 mg/L, corresponding to removal rates of 95% or higher. In Example 2-2, on the other hand, there was little improvement in dioxane removal performance, and the removal rate remained at 40% or so.

(68) When the attachment condition of strain N23 was checked visually after the experiment, the surface color of hydrophobic carrier A used in Example 2-1 had changed from yellow to dark orange, while that of hydrophilic carrier C used in Example 2-3 had changed from white to light brown, confirming that large quantities of strain N23 were attached to the carriers. Also, in Example 2-3, it took a longer time for the water quality to stabilize than in Example 2-1. The reason for this is suspected that, although the carrier used in Example 2-3 is hydrophilic and thus its attaching performance and degrading activity with respect to strain N23 were initially poor, it subsequently attached more strain N23 as the hydrophobic viscous substance produced by strain N23 provided footholds, and eventually demonstrated performance equivalent to what was achieved in Example 2-1 where a hydrophobic carrier was used. On the other hand, carrier B used in Example 2-2 did attach strain N23 but hardly changed its surface color and the attached quantity was small. It is suspected that carrier B demonstrated poor performance of attaching the dioxane-degrading bacterium due to its small specific surface area of 1,000 m.sup.2/m.sup.3 and large hole diameters.