SYSTEM AND METHOD FOR CONTINUOUS METABOLISM OF 1,4-DIOXANE

Abstract

Bioreactors and associated methods are provided herein including bioreactors capable of treating water contaminated with 1,4-dioxane. In certain embodiments, a bioreactor is disclosed and may include an adsorbent layer with a biofilm capable of metabolizing 1,4-dioxane and a screen disposed downstream of the adsorbent layer configured to retain detached biofilm.

Claims

1. A bioreactor system comprising: a housing having an inlet and an outlet; at least one adsorbent layer which (i) comprises a biofilm comprising microbes capable of metabolizing 1,4-dioxane and (ii) is contained with the housing; and a first screen positioned downstream from the at least one adsorbent layer, wherein the first screen is configured to retain within the bioreactor any of the biofilm that becomes detached from the at least one adsorbent layer, and wherein the housing is configured to receive through the inlet a flow of an influent comprising water contaminated with 1,4-dioxane and the bioreactor is configured to be operated in a manner effective to discharge an effluent from the outlet, which effluent comprises water contaminated with 1,4-dioxane in an amount of less than 0.5 μg/L.

2. The bioreactor system of claim 1, further comprising a second screen positioned upstream from the at least one adsorbent layer.

3. The bioreactor system of claim 1, wherein the at least one adsorbent layer comprises a bed of adsorbent particles.

4. The bioreactor system of claim 1, wherein the bioreactor is configured to be operated in an up-flow mode.

5. The bioreactor system of claim 1, wherein the bioreactor is configured to be operated in a down-flow mode.

6. The bioreactor system of claim 1, further comprising a pump in fluid communication with the inlet. 7 The bioreactor system of claim 1, which is configured to be operated to produce an empty bed contact time from about 30 minutes to about 720 minutes.

8. A method of reducing 1,4-dioxane content in water from a water source, the method comprising: flowing water from a water source as an influent into the bioreactor system of claim 1, wherein the influent has a first concentration of 1,4-dioxane; and collecting treated water discharged as an effluent from the bioreactor system, wherein the bioreactor system is operated such that the effluent has a second concentration of 1,4-dioxane that is lower than the first concentration of 1,4-dioxane.

9. The method of claim 8, wherein the first concentration of 1,4-dioxane is less than 25 μg/L.

10. The method of claim 8, wherein the first concentration of 1,4-dioxane is between 0.5 μg/L and 25 μg/L.

11. The method of claim 8, wherein the first concentration of 1,4-dioxane is about 25 μg/L.

12. The method of claim 11, wherein the bioreactor system is operated to produce an empty bed contact time from about 30 minutes to about 720 minutes.

13. The method of claim 8, wherein the second concentration of 1,4-dioxane is less than 0.5 μg/L.

14. The method of claim 8, wherein the first concentration of 1,4-dioxane is about 25 μg/L and the second concentration of 1,4-dioxane is less than 0.5 μg/L.

15. The method of claim 8, wherein the bioreactor system is operated to produce an empty bed contact time from about 30 minutes to about 720 minutes.

16. The method of claim 8, wherein the at least one adsorbent layer of the bioreactor system comprises a bed of adsorbent particles.

17. The method of claim 16, wherein the absorbent particles comprise AmberSorb™ 560, HiSiv 3000, Zeolite HSZ-Alumina, and/or Zeolite HSZ-Clay.

18. The method of claim 8, wherein the bioreactor system is operated at conditions to selectively enrich 1,4-dioxane-metabolizing microbes that are able to degrade 1,4-dioxane to below 0.5 μg/L.

19. A method of reducing 1,4-dioxane content in water, the method comprising: providing the bioreactor system of claim 1; enriching, via an influent, the biofilm within the bioreactor system, which biofilm comprises 1,4-dioxane-metabolizing microbes; removing the biofilm from the bioreactor system; and then injecting the biofilm into a contaminated site, wherein injecting the biofilm into the contaminated site results in in-situ remediation of the contaminated site through bioaugmentation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The detailed description is set forth with respect to the accompanying drawings. The use of the same reference numerals may indicate similar or identical items. Various embodiments may utilize elements and/or components other than those illustrated in the drawings, and some elements and/or components may not be present in various embodiments. Elements and/or components in the figures are not necessarily drawn to scale.

[0012] FIG. 1 depicts a bioreactor in accordance with one or more embodiments of the present disclosure.

[0013] FIG. 2 depicts a bioreactor system in accordance with one or more embodiments of the present disclosure.

[0014] FIG. 3 depicts a bioreactor system in accordance with one or more embodiments of the present disclosure.

[0015] FIG. 4 depicts experimental results of 1,4-dioxane removal in seven different reactors.

[0016] FIG. 5 depicts experimental results of 1,4-dioxane removal in five different bioreactors.

DETAILED DESCRIPTION

[0017] New and improved bioreactors for reducing 1,4-dioxane concentration in a water source have been developed. In particular, the inability for bioreactors to effectively reduce 1,4-dioxane content in a water source may be remedied by incorporating a screen for retaining detached biofilm. Without intending to be bound by any particular theory, it is believed that the environmentally relevant concentration of 1,4-dioxane in a given water source, although greater than the health-based reference level of 0.35 μg/L, is nonetheless too low to induce/maintain growth of microbes capable of metabolically oxidizing 1,4-dioxane. By incorporating a screen configured to retain the biofilm that naturally detaches from the adsorbent layer in a bioreactor, it has been unexpectedly discovered that the 1,4-dioxane content in a given water source may be effectively reduced.

[0018] As used herein, a “water source” refers to any water source contaminated by 1,4-dioxane, such as groundwater, drinking water, wastewater, landfill leachate, and the like. In some embodiments, these terms are used interchangeably. For example, “groundwater” and “drinking water” may refer to the same source of water. In other words, any source of water that is contaminated by 1,4-dioxane may be treated using the bioreactors and methods disclosed herein.

[0019] As used herein, a “biofilm” refers to an agglomeration of microbial colonies adhered to a surface such as an adsorbent.

[0020] As used herein, the “environmentally relevant” concentration of 1,4-dioxane is on the order of about 0.5 μg/L to about 100 μg/L, such as around 25 μg/L.

[0021] As used herein, the “health-based reference level” for 1,4-dioxane refers to the United States Environmental Protection Agency health advisory level, based on a 1-in-10.sup.6 cancer risk, of 0.35 μg/L.

[0022] As used herein, an “adsorbent layer” refers to a layer or surface configured to permit growth and/or attachment of a biofilm.

[0023] Throughout this disclosure, various aspects may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0024] As used herein, the term “about” with reference to dimensions refers to the dimension plus or minus 10%.

Bioreactors for Reducing 1,4-dioxane content in Water

[0025] In some embodiments, a bioreactor is provided including at least one adsorbent layer comprising a biofilm (thereon/therein) and a screen positioned downstream from the at least one adsorbent layer configured to retain detached biofilm ejected from the at least one adsorbent layer. In some embodiments, the biofilm comprises microbes capable of metabolizing 1,4-dioxane. Without intending to be bound by any particular theory, it is believed that a screen designed to “catch” or retain biofilm that detaches or sloughs off the adsorbent layers increases the lifetime of the biofilm itself and improves 1,4-dioxane removal.

[0026] In some embodiments, the bioreactor is operated in an up-flow mode. Operating a bioreactor in “up-flow” mode refers to passing contaminated water upward though the filtration means within the bioreactor. In other embodiments, the bio reactor is operated in a down-flow mode.

[0027] In some embodiments, the empty bed contact time is between about 30 minutes and about 720 minutes. As used herein, the “empty bed contact time” (EBCT), also called the “empty bed retention time,” refers to the amount of time the contaminated water is in contact with the adsorbent. The EBCT depends on the concentration of the contaminant to be removed and the specific surface area of the adsorptive medium. Without intending to be bound by any particular theory, it is believed that the EBCT has a linear, positive correlation with the influent 1,4-dioxane concentration, and a linear, negative correlation with the surface area of the adsorptive medium. Thus, a middle-ground EBCT exists for a given adsorptive medium surface area. It is believed that this medium empty bed retention time is desired for maximizing the efficiency of the 1,4-dioxane removal using a given bioreactor. EBCT may be calculated according to Formula I:

[00001]$\begin{array}{cc}EBCT=\frac{\mathrm{Bed}\mathrm{Volume}\left({\mathrm{ft}}^3\right)\times 7.48\mathrm{Gallons}/{\mathrm{ft}}^3}{\mathrm{Flow}\mathrm{Rate}(\mathrm{gallons}/\min )}& \mathrm{Formula}I\end{array}$$\mathrm{Empty}\mathrm{Bed}\mathrm{Contact}\mathrm{Time}$

[0028] In some embodiments, the bioreactor has an influent in the form of water contaminated with 1,4-dioxane. In some embodiments, the concentration of 1,4-dioxane is less than or about 25 μg/L, for example between 0.50 μg/L and 100 μg/L. Without intending to be bound by any particular theory, it is believed that a medium concentration of 1,4-dioxane in the influent, such as around 25 μg/L, contributes to an improved removal of 1,4-dioxane from the influent, and therefore a more successful bioreactor.

[0029] In some embodiments, the bioreactor has an effluent in the form of water contaminated with 1,4-dioxane. As a result of the metabolic oxidation of 1,4-dioxane by the microbes in the biofilm within the bioreactor, the effluent has a concentration of 1,4-dioxane of less than 0.5 μg/L or about 0.5 μg/L.

[0030] FIG. 1 depicts an exemplary bioreactor 100 in accordance with the present disclosure. Bioreactor 100 is depicted as accepting an influent 102 at a lower position of the bioreactor 100, and discharging an effluent 104 at an upper position of the bioreactor 100. In this way, bioreactor 100 is depicted in an “up-flow” mode. In some embodiments, a bioreactor may accept an influent at an upper position of the bioreactor and discharge an effluent at a lower position of the bioreactor so that the bioreactor is in a “down-flow” mode. In other embodiments, the bioreactor may be configured for lateral flow of the influent and/or the effluent, such as to accept an influent at a side position of the bioreactor. Any suitable configuration of bioreactor and influent/effluent streams may be used depending on the needs of the application, and the decision to depict only the “up-flow” configuration is in the interest of brevity only and is not intended to be limiting.

[0031] Bioreactor 100 includes an adsorbent layer 106. Adsorbent layer 106 includes an adsorbent material and a microbial inoculum. Suitable adsorbent materials include those known in the art. In some embodiments, the adsorbent material is one or more of AmberSorb™ 560, HiSiv 3000, Zeolite HSZ-Alumina, Zeolite HSZ-Clay, and Granular Activated Carbon. In some embodiments, the microbial inoculum, also referred to as a biofilm because it is in the form of a microbial “film” on the surface of the adsorbent particles, includes microbes capable of metabolizing 1,4-dioxane. In some embodiments, the column material 106 is in the form of a fluidized bed of particles of the adsorbent material.

[0032] Bioreactor 100 includes screens 108a and 108b. Screen 108a is depicted in FIG. 1 as being positioned downstream from the adsorbent layer 106 and screen 108b is depicted as being positioned upstream from the adsorbent layer 106. The screens are configured to ensure the microbial inoculum remains within the bioreactor and continues to metabolize 1,4-dioxane. Suitable screens are characterized by having a plurality of openings, each opening having a size smaller than the size of the adsorbent particles present within the bioreactor. For example, suitable screens may have a plurality of openings having a size (e.g., diameter, or largest dimension) of at least 0.001 mm.

Methods for Reducing 1,4-dioxane Content in a Water Source

[0033] Methods for reducing 1,4-dioxane content in a water source are also disclosed herein. In some embodiments, the method includes providing a bioreactor as disclosed herein. The method may include supplying the water source to the bioreactor as influent and collecting treated water exiting the bioreactor as effluent. In some embodiments, the influent has a first concentration of 1,4-dioxane and the effluent has a second concentration of 1,4-dioxane that is lower than the first concentration.

[0034] In another embodiment, a method includes providing a bioreactor as disclosed herein and supplying the bioreactor with contaminated water as the influent. Passing contaminated water through the bioreactor enriches the biofilm with the influent. Without intending to be bound by any particular theory, it is believed that removal of 1,4-dioxane from the contaminated water results in growth of microbes on the biofilm through this “enrichment” process.

[0035] In some embodiments, the enriched biofilm is removed from the reactor. The removed enriched biofilm may then be injected into a contaminated water source, which may be the same or another water source as that being treated in the bioreactor. Without intending to be bound by any particular theory, it is believed that the 1,4-dioxane-metabolizing microbes in the enriched biofilm, when injected into a contaminated water source, acts to remediate the contaminated site in-situ through bioaugmentation.

[0036] The invention may be further understood with reference to the following non-limiting examples.

Example 1: Bench Trial of Bioreactor

[0037] A bioreactor was constructed as described herein, and as illustrated in FIGS. 1-2, and charged with influent corresponding to groundwater. FIG. 2 depicts a bioreactor system 200 including an influent source 202, a pump 204, a bioreactor 100, and an effluent 206. The concentration of 1,4-dioxane in the influent was approximately 25 μg/L. The concentration of 1,4-dioxane in the treated water was measured to be less than 0.5 μg/L, which represents the detection limit of the measuring equipment available.

Example 2: Comparison of Adsorbents

[0038] Bioreactors were constructed as described herein, and as illustrated in FIGS. 1-3. FIG. 3 depicts a bioreactor system 300 including an influent source vessel 202 configured to deliver influent to each of the five bioreactors 100. A pump 204 was used to drive the influent to/through the bioreactors. Each bioreactor 100 had an effluent collection vessel 206. Each bioreactor included a column charged with a different adsorbent. The adsorbents used are listed in Table 1 along with the height of the absorbent in the column and the weight of adsorbent used. As described above, the surface area of the adsorbent is determinative of the adsorbent's effectiveness. Thus, Table 1 also details the specific surface area of each adsorbent.

TABLE-US-00001 TABLE 1 Adsorbents tested Height Weight Specific surface in column in column Adsorbent Type Area (m.sup.2/g) (mm) (g) Ambersorb ™ 560 ~450 45 10.8 Zeolite HSZ - Alumina 310~340 45 11.9 Zeolite HSZ - Clay ~310 45 12.0 Granular Activated Carbon ~600 45  8.9 (GAC) HiSiv 3000 ~300 45 12.3

[0039] Each of the AmberSorb™ 560, HiSiv 3000, Zeolite HSZ-Alumina, and Zeolite HSZ-Clay were acquired from Geosyntec Consultants, Boca Raton, Fla., USA. All adsorbents were washed with deionized water before being loaded into the reactor.

[0040] Each reactor was operated in an up-flow mode, with influent passing upwards through the reactor. Each reactor included a screen above the adsorbent to prevent adsorbents from being carried out of the reactors by the water flow. The screen happened to also retain any biomass that detached from the surface of the adsorbents. The accumulated detached biomass caught by the screen unexpectedly helped to remove additional 1,4-dioxane.

[0041] Each reactor was tested under four different empty bed contact times (EBCT) and four different influent flow rates; the different operating conditions are referred to as Phase 1, 2, 3 and 4. Each bioreactor was operated for 1,4-dioxane removal with an influent concentration of 25 μg/L and an EBCT of 1.5 hours for Phase 1, 3 hours for Phase 2, 0.75 hours for Phase 3, and 1.5 hours for Phase 4. The influent was charged into the adsorbent column using a pump configured to operate at a flow rate of 0.2 mL/min for Phase 1, 0.1 mL/min for Phase 2, 0.4 mL/min for Phase 3, and 0.2 mL/min for Phase 4.

[0042] Two abiotic columns (Ambersorb™ 560 and GAC) were used as controls and were introduced during Phase 4.

[0043] The influent for the experiment was a simulated contaminated water prepared by adding a 1,4-dioxane stock solution (100 mg/L) to a nitrate mineral medium.

[0044] As the source of inoculation, biomass from previous kinetics experiments in the lab was used. Biomass from the kinetic experiment was shaken and then transferred to centrifuge tubes, which were centrifuged for 10 minutes. The supernatant was removed, and nitrate mineral medium was added to wash the pellet without resuspending cells. This process was repeated to further wash the biomass. Then the pellet was resuspended in 60 mL of nitrate mineral medium. Duplicate 1.5 mL samples of the mixed biomass were collected and stored at a −20° C. refrigerator. Afterwards, the five bioreactors were inoculated by adding 10 mL biomass to each reactor and mixing the biomass with the absorbents. The reactors stood for 24 hours and then were continuously fed with the nitrate mineral medium that contained 1,4-dioxane at 25 μg/L. All the reactors were covered with aluminum foil to prevent algae growth.

[0045] Samples were taken every one or two weeks from the influent bottle and the five biotic effluent bottles (one effluent bottle for each bioreactor/each adsorbent). Each sample was filtered with a 0.45 μm filter immediately following sampling. The 1,4-dioxane measurement was carried out using Gas Chromatography-Mass Spectrometry (GC-MS) combined with solid phase microextraction (SPME). Biomass samples were taken from all reactors when reactors reached steady state at stages 2 and 3. DNA was extracted from eleven samples, including the inoculum, five reactors in stage 2, and five reactors in stage 3.

[0046] The results of the 1,4-dioxane removal for each reactor is depicted in FIG. 4. All five bioreactors successfully removed 1,4-dioxane to below the detection limit in the first three phases. In each Phase, the Ambersorb™ 560 was the most effective. This represented the first biological reactors to metabolically remove 1,4-dioxane to below the detection limit of 0.5 μg/L, which is close to the health-based reference level of 0.35 μg/L, when operated at a continuous flow mode and a steady state.

[0047] As shown in FIG. 4, each of the abiotic columns, introduced in Phase 4, quickly reached a steady state in Phase 4 and were unable to remove any additional 1,4-dioxane. This was expected because the abiotic columns did not include microbial inoculum, so the 1,4-dioxane removal capabilities were limited.

[0048] FIG. 5 depicts the relative abundance of microbial groups in microbial communities in the five columns at Day 0 (in the influent), Phase 2 steady state (“S2”), and Phase 3 steady state (“S3”). The abundances of Methyloversatilis, Other Rhodocyclaceae, Dechloromonas, and Sulfuritalea significantly decreased from the inoculum to Phases 2 and 3. On the other hand, most of the other groups in FIG. 5 were enriched in at least one of the columns for at least one of the two phases. Among them, Dokdonella and Mycobacterium are well-known as 1,4-dioxane degraders. The abundances of these 1,4-dioxane degraders depended on the phase and adsorbent type: e.g., the relative abundance of Mycobacterium in steady state 2 was 2.7% for Alumina, 8.8% for Clay, 7.6% for GAC, 16.6% for Hisiv, and the lowest for AmberSorb™ 560.

[0049] The first key factor in the success of the bioreactors is the operating condition that combines low influent 1,4-dioxane concentration (˜25 μg/L) and a medium empty bed contact time (EBCT=0.75-3.0 hours). The combined condition helped the reactors to selectively enrich 1,4-dioxane-metabolizing microbes that are able to degrade 1,4-dioxane to below the health-based reference level. The 1,4-dioxane concentration that was used in the influent (˜25 μg/L) is environmentally relevant; the 1,4-dioxane concentrations in the vast majority of groundwater are less than tens of μg/L.

[0050] A medium EBCT is also critical to the success of the reactors. While a too large EBCT leads to inadequate substrate (food) for microbial growth, a too small EBCT leads to high 1,4-dioxane concentration in the reactor and the reactor effluent.

[0051] The second key factor in the bioreactor success was the screen above the adsorbent in each reactor.

[0052] The reactors described herein can be directly used to treat drinking water sources that are contaminated by 1,4-dioxane. The reactors can also be used to enrich microorganisms that can metabolize 1,4-dioxane at environmentally relevant concentrations. The enriched microorganisms can then be injected through bioaugmentation into groundwater for in-situ bioremediation of sites contaminated by 1,4-dioxane.

[0053] While the disclosure has been described with reference to a number of embodiments, it will be understood by those skilled in the art that the disclosure is not limited to such embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not described herein, but which are commensurate with the spirt and scope of the disclosure. Conditional language used herein, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, generally is intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements or functional capabilities. Additionally, while various embodiments of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure it not to be seen as limited by the foregoing described, but is only limited by the scope of the appended claims.