WO2002047786A1

WO2002047786A1 - Groundwater remediation

Info

Publication number: WO2002047786A1
Application number: PCT/US2001/047985
Authority: WO
Inventors: William B. Kerfoot
Original assignee: K-V Associates, Inc.
Priority date: 2000-12-13
Filing date: 2001-12-11
Publication date: 2002-06-20
Also published as: CA2431176A1

Abstract

In general, the invention features a cartridge for use in a water remediation system. The cartridge includes an ion-exchange resin and a resin holder that contains the resin. The resin holder has an upper segment having water-permeable walls, a middle segment with substantially water-impermeable walls, and a lower segment having inward-facing or bottom-facing, substantially water-permeable walls. The invention also features a method for water remediation. The method includes the steps of: disposing an air-sparging system into a water bed contaminated with one or more radioactive or toxic ionic compound (e.g., TcO4-, Pb?2+, Ni2+, Cd2+, AsO4-¿, ClO¿4-?, ClO3-, BrO4-, BrO3-, or Zn?2+¿), the air-sparging system including a pump and a cartridge having an ion-exchange resin and a resin holder that contains the resin, the resin holder having an upper segment having water-permeable walls, and a lower segment having substantially water-impermeable walls; and operating the pump to draw water from the water bed through the walls of the upper segment of the resin holder, through the resin, and through an exit at the bottom of the cartridge.

Description

BACKGROUND OF THE INVENTION

The invention relates generally to water remediation systems. There is a recognized need for methods and devices for remediation of, for example, ground and surface water contaminated with radioactive or toxic metal ions, including both anions and cations. For example, the radionuclide technetium-99 (Tc₉ ) is produced during uranium enrichment processes. The groundwater on sites that carry out such processes can be contaminated with Tc₉₉ ions (e.g., TcO₄ ^"). On these or other sites, other metal ions (e.g., arsenic anions, sodium or potassium cations) or organic compounds (e.g., volatile halogenated hydrocarbons such as perchloroethene, PCE, trichloroethene, TCE, dichloroethene, DCE, or vinyl chloride) may also be present.

Unlike organic compounds, undesirable metals and ions are not generally broken down to simpler materials in groundwater. While some success has been achieved through the use of sequestering agents such as iron filings to precipitate, adsorb, or trap toxic or radioactive contaminants under selective pH conditions, these agents do not allow for removal of the contaminants, only sequestration. The contaminants remain present at the remediation site and may even be resolubilized so as to reenter the water if the pH is perturbed.

SUMMARY OF THE INVENTION In general, the invention features a cartridge for use in a water remediation system. The cartridge includes an ion-exchange resin and a resin holder that contains the resin. The resin holder has an upper segment having water-permeable walls, a middle segment with substantially water-impermeable walls, and a lower segment having inward-facing or bottom-facing, substantially water-permeable walls. The ion-exchange resin can be, for example, in the form of beads or a woven or non-woven fabric. The ion-exchange resin can, for example, have a K value for TcO₄ ^" ions greater than about 10,000 milliequivalents per gram resin as 24 h I- (or 20,000 milliliters per gram 24h K ). For example, the ion-exchange resin can include a bifunctional anion-exchange resin having two quaternary ammonium groups selected from the group consisting of triethylammonium, fripropyl-immonium, and trihexylammonium (e.g., a "biquat" resin).

The resin holder can, for example, have vertical segments having a water permeability greater than about 0.5 gal/min/ft² surface area (e.g., greater than 1, 2, 5, 10, 20, 50, or 100 or more gal/min/ft² surface area). The lower segment of the resin holder can, for example, have exit screens having a water permeability greater than about 0.5 gal/min/ft² surface area (e.g., greater than 1, 2, 5, 10, 20, 50, or 100 or more gal/min/ft² surface area).

The invention also features a method for water remediation. The method includes the steps of: disposing an air-sparging system into a water bed contaminated with one or more radioactive or toxic ionic compounds (e.g., TcO₄ ^", Pb²⁺, Ni²⁺, Cd²⁺, AsO₄ ^", ClO₄ ^", ClO₃ ^", BrO \ BrO₃ ^", or Zn²⁺), the air-sparging system including a pump and a cartridge having an ion-exchange resin and a resin holder that contains the resin, the resin holder having an upper segment having water-permeable walls, and a lower segment having substantially water-impermeable walls; and operating the pump to draw water from the water bed through the walls of the upper segment of the resin holder, through the resin, and through an exit at the bottom of the cartridge.

The method can also include the step of sparging the water with a gas such as ozone (e.g., via emission through microporous bubblers). In some cases, the groundwater bed can also be contaminated with a volatile organic compound such as PCE, TCE, DCE, or vinyl chloride.

The method can also include the step of providing an oxic environment for the cartridge (e.g., by sparging the water with ozone at a rate that results in bubbles of ozone gas taking between one and ten hours to travel through the water to the upper segment of the resin holder).

The invention provides several advantages. For example, the cartridges of the invention have high hydraulic permeability (e.g., about 20 gallons/minute) and long useful lifetimes (up to 12 months or longer). The resins contained within the cartridges can be prepared in a variety of formats, including beads and woven or nonwoven fabrics. The resins have high K values (e.g., 24 h K_d greater than about 20,000 ml/g (or about 7,900 ml/mEq); where Ka= TcO₄ ^" (mg sorbed/g (or mEq) resin)/TcO₄ ^"(mg in solution/ml liquid)). The new cartridges also allow remediation of water over large distances. For example, when used in conjunction with a microporous diffusion apparatus such as K-N Associates, Inc.'s C-Sparger^® system, a cartridge with a screen length of 10-15 feet can be used to clean groundwater of both organic and ionic contaminants in a radius of up to 80 feet of more, thus allowing million-fold or greater concentration of contaminants into a removable cartridge for appropriate disposal. Because the cartridges are replaceable, they can be used to remove trapped contaminants from the remediation sites. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a resin cartridge/recirculating sparging well.

FIG. 2 is a cross-sectional view of the detail of the pump and resin cartridge shown in FIG. 1.

FIG. 3 is a plot of the breakthrough curves, representing the ratio between effluent TcO₄ ^" concentration and inlet TcO₄ ^" concentration (C/C₀) vs. bed volume, for the synthetic resin RO-02-119 (Δ) and Purolite A-520 (o) resin using PGDP groundwater. FIG. 4 is a cross-sectional view of a resin cartridge/recirculating sparging well that includes a PNC lock stopper.

FIG. 5 is a cross-sectional view of a segment of a resin cartridge of FIG. 2.

DETAILED DESCRIPTION

The techniques described below use removable, replaceable cartridges that can be used in the remediation of water contaminated with metals or other ionic contaminants. The cartridges can be used, for example, in conjunction with a microporous diffusion apparatus as described in U.S. Patent Nos. 5,855,775 and 6,083,407, incorporated herein by reference in their entirety, to additionally decompose organic halogenated volatile organic compounds (HNOCs) in situ. The technique includes water that is pumped through a replaceable cartridge containing an adsorbable material that is not biologically decomposable to remove contaminants, either independently or together with, for example, ozone sparging. Referring to FIGS. 1 and 4, systems that include a resin cartridge for removal of radioactive contaminants are shown. Detail of a cartridge is shown in FIG. 2. The cartridges can be made in various formats. In one format, the cartridge includes a resin holder and a resin. The resin holder can be made of various materials, including polyvinyl chloride (PNC) and stainless steel. The resin can be in the form of, for example, beads or a fabric (e.g., a nonwoven fabric or a woven fabric). The resin generally includes an adsorbable surface such as an ion-exchange material (e.g., Dowex or Reillex resins). The cartridge traps, but generally does not destroy, contaminants present in the water or another liquid to be decontaminated. The cartridge also includes at least one inlet screen, which can be integral with the walls of the resin holder, and an outlet. The outlet can also include a screen. As explained in more detail below, the cartridge can be segmented to increase purification efficiency.

For removal of radioactive ions such as Tc₉₉, Gilbert Brown and co-workers at Oak Ridge National Laboratory discovered that ion-exchange resins that include a polychloromethylstyrene backbone cross-linked with divinylbenzene (DVB) and aminated with two different trialkylamines (e.g., hexylamine and tripropylamine or triethylamine) to provide bifunctional quaternary ammonium surfaces are particularly effective (Gu et al., Environ. Sci. Technol, 34:1075-1080, 2000, incorporated herein by reference in its entirety). Examples of suitable resins thus include, Brown's resins NP- 02- 165, RO-02-61 , and NP-02-217, which each have trihexylammonium and tripropylarnmonium groups, and biquat resin (having trihexylammonium and triethylammonium sites). Such bifunctional resins are available from Purolite as A530 and D3696. While possibly less effective, monofunctional ammonium resins such as Purolite A520 can also be suitable for use in the new cartridges. The properties of the resins can be tailored to specific needs. According to Gu et al., for example, the longer chain alkylammonium groups in their biquat resins (e.g., trihexylammonium) provide selectivity, while the shorter chain groups (e.g., triethylammonium) provide for unproved reaction kinetics. They found that resin selectivity for TcO ^" sorption increased with the radius of the immobilized alkyl chain length of the quaternary ammonium groups on resin beads and a concomitant decrease in exchange capacity and rate. They also found that because TcO₄ ^" is larger than has a lower hydration energy than most anions encountered in groundwater, there is a chemical bias toward exchanging TcO₄ ^" preferentially over the other anions, and that this bias can be enhanced by chemical modification of the resin, including altering the size and shape of the cationic exchange sites and polymer cross-linking density.

Microporous diffusion apparatuses are used to inject ozone gas microbubbles or coated microbubbles to decompose halogenated ethylene and ethane compounds. Compounds such as trichloroethene (TCE) are effectively removed from aqueous solution (e.g., ground water) or from fraction bound (i.e., adsorbed) soil particles. Ozone sparging can be used as an active groundwater remedial technology to aggressively oxidize volatile organic compounds (NOCs) in groundwater at the source area, along the core of a plume, or as a reactive wall installation for containment purposes.

The apparatus releases micron-sized bubbles through microporous diffusers or a bubble chamber that normally rise in aqueous solutions, inducing secondary circulation eddies. At the core of the recirculation well, and presumably at the plume of contaminated groundwater, a two-wellscreen unit serves as a bubble chamber, producing small bubbles in intermittent pulses, which, with a delay, segregate fine bubbles from larger bubbles. A small submersible pump then pushes the fine bubble-containing fluid into the geological formation that contains the contaminants (e.g., the surrounding soil). The pump withdraws from the top wellscreen to create a small vertical circulating system. The pump shown in FIG. 2 includes a submersible intake, side water ducts, a motor, and a discharge element leading into a packer.

As shown in FIGS. 1 and 2, a resin cartridge containing a column of exchange resin is placed above the pump. Water entering the top, or inlet screen of the cartridge passes through the resin column and into the central water duct before being pumped through the lower, or outlet screen. The column can, for example, be made of a resin that removes TcO₄ ^" and other anions, or Na⁺ and other cations from the water. The arrangement shown in FIG. 4 includes a PVC lock stopper below the pump in place of the packer.

The systems shown in FIGS. 1 and 4 include two microporous diffusion apparatuses. The lower apparatus create bubbles that move horizontally through the formation due to the deflection provided by a bentonite or grout barrier above the second apparatus. The barrier extends out into the formation (not shown), generally at least about 10 feet, and often as much as 40 feet. The upper apparatus is used to create very fine bubbles that stay within the well column. The system of FIG. 4 also includes a flow deflector on one side of the upper apparatus.

The microporous diffusion apparatuses can be operated in a pulsed mode, a continuous mode, or a semi-continuous mode. In the pulsed mode, the lower apparatus is activated briefly, followed by a brief activation of the upper apparatus, which is then followed by activation of the pump. This three-step cycle is repeated over and over. In the continuous mode, both apparatuses and the pump are operated continuously. In the semi-continuous mode, the upper apparatus and pump are operated continuously, while the lower apparatus is cycled on and off. The system shown in FIG. 1 includes an outdoor panel enclosure that includes a gas generator, a compressor, electric power lines, zone control, pump control, and a timer. Gas feed lines from the zone control lead to a well box and the microporous diffusion apparatuses.

In addition to removing TCE and other organic compounds from the formation and groundwater, ozone sparging can increase the effectiveness of the resin cartridges. The resins described above for removal of radioactive materials operate best under oxic conditions. Ozone sparging provides conditions conducive to trapping of radioactive ions. At too high of concentrations, however, ozone can damage the resins, so active ozone should not be allowed to enter the top screen of the cartridge. Accordingly, the ozone flow rate is adjusted so that the bubbles take a minimum of one hour, and more preferably about 10 hours, to travel from the upper diffusion apparatus to the top screen. The bentonite installation used as a barrier prevents the ozone from the lower diffusion apparatus from reaching the top screen at too high of a concentration.

The control of the rate of flow can be important in the combined sparging/resin adsorption methods. The system can be operated in a pulse-mode, to provide semicontinuous purification, or can provide continuous feed of water and microbubbles. The rate of flow and the spatial separation of the wellscreens determines the radius of capture and circulation. A flow rate of 20 gpm provides a radius of capture of over 80 feet. All water in the region defined by this radius passes through the ion-exchange media at least once during the travel time across the cylinder formed by the area of influence (AOI). A greater flow rate can expand the radius and area of influence. A greater separation of the screens can also provide a greater radius of influence.

The bubble zone can then be enlarged from 80 feet with a likely extension of flow from a secondary induced gyre flow to over 100 feet. For ion exchange resin adsorption, a replaceable resin is held in a cartridge that can be slipped into the well after an inflatable packer is placed as a barrier between the intake wellscreen and the outflow wellscreen. The cartridge can, for example, include an upper portion having screen walls that allow water to flow in, and a lower portion with solid walls. As shown in FIG. 2, the upper portion of the cartridge can be, for example, about ten feet long and made up of multiple segments, each, for example, 1.5 to 2 feet long and 5 to 6 inches in diameter. The bottom portion of the cartridge shown in FIG. 2 is five feet long. Water flows in through the wellscreen on the sides of the top portion and exits through a bottom opening (i.e., towards the inner cylinder that runs the length of the cartridge and allows tubes carrying ozone/air to the inwell water tubes to inflate the packer, and electrical supply to the pump).

FIG. 5 depicts a single 1.5-foot segment. Inlet water flows into the top portion of each segment through a screened opening ("screen") opposite the wellscreen, then moves vertically 1 to 1.5 feet before exiting through an inward-facing lower screen at the bottom of the segment, towards the center of the cylinder. The use of a segmented system is advantageous in that the surface area of the exit screens increases as the number of segments increases, providing more flow volume at less resistance.

The combined ozone sparging/resin adsorption systems are suitable, for example, for simultaneous removal of ions (e.g., TcO₄ ^") and NOCs (e.g., TCE). Thus, for example, the cartridge can contain a biquat resin as described above. Table 1 provides a comparison of bed volume at breakthough for seven different resins, with a bed volume of 94 ml and a flow rate of 2 gal/min ft.

Table 1

An 8-month long trial was completed with a 5.25" diameter column, 12" in length. After pumping 600,000 bed volumes (840,000 gallons) through the column, the column was analyzed. The top 1/3 of the column indicated breakthrough, the middle 1/3 showed 20% capacity depleted, and the bottom 1/3 showed only limited depletion. The hydraulic conductivity of the resin was about 1000 ft/day, the flow capacity was about 20 g/min/ft², and the particle size was 0.42 mm. The expanded capacity of the biquat resin allows for a four-fold increase in capacity and a rapid absorption rate, enabling complete absorption in only 12-15 seconds residence time.

The acceptable range of adsorption capacity and residence time versus cylinder diameter is presented in Table 2. All cartridges tested were 15 ft long, had a 0.25" gap, and a one inch conduit diameter.

Table 2

The resin adsorption shown in FIG. 3 and Table 1 using groundwater from the Paducah Gas Diffusion Plant (PGDP) Site corresponds to a flow of 840,000 gallons during 8 months. Only 50% of the bed capacity was exhausted during an 8-month throughput. The rapid adsorption and high capacity can allow a cartridge containing the biquat resin to be used for 6 months or longer in a mid-plume region before removal or regeneration, allowing the system to be reasonably cost-effective. Use of the other resins in Table 1 would require replacing the cartridge more often, perhaps every month.

The process and apparatus thus provide removable and replaceable filtration cartridges for water remediation and methods of using the cartridges. The cartridges allow rapid and efficient removal of radioactive ions (e.g., Tc₉₉ ions), toxic metal ions (e.g., arsenic, sodium, potassium ions), non-metallic ions (e.g., bromates, perbromates, chlorates, or perchlorates) and volatile organic compounds (e.g., trichloroethene). Unlike existing methods that enable only sequestration of contaminants, the new methods allow the trapped contaminants to be removed from the remediation site altogether.

Other embodiments are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A cartridge for use in a water remediation system, the cartridge comprising: an ion-exchange resin and a resin holder that contains the resin, the resin holder having an upper segment having water-permeable walls, a middle segment with substantially water-impermeable walls, and a lower segment having inward-facing or bottom-facing substantially water-permeable walls.

2. The cartridge of claim 1, wherein the ion-exchange resin is in the form of beads.

3. The cartridge of claim 1 , wherein the ion-exchange resin is in the form of a fabric.

4. The cartridge of claim 1, where the ion-exchange resin has a K value for TcO₄ ^" ions greater than about 10,000 milliequivalents per gram resin as 24 h K_<*.

5. The cartridge of claim 1, wherein the ion-exchange resin comprises a bifunctional anion- exchange resin having two quaternary ammonium groups selected from the group consisting of triethylammonium, tripropylammonium, and trihexylammonium.

6. The cartridge of claim 1, wherein the resin holder has a vertical segment that has a water permeability greater than about 1 gal/min/ft² surface area.

7. The cartridge of claim 1, wherein the lower segment of the resin holder has exit screens that have a water permeability greater than about 5 gal/min/ft² surface area.

8. A method for water remediation, the method comprising: disposing an air-sparging system into a groundwater bed contaminated with one or more radioactive or toxic ionic compounds, the air-sparging system including a pump and a cartridge having an ion-exchange resin and a resin holder that contains the resin, the resin holder having an upper segment having water-permeable walls, and a lower segment having substantially water-impermeable walls; and operating the pump to draw water from the groundwater bed through the walls of the upper segment of the resin holder, through the resin, and through an exit at the bottom of the cartridge.

9. The method of claim 8, wherein the groundwater bed is contaminated with TcO ^' ions.

10. The method of claim 8, further comprising sparging the water with a gas.

11. The method of claim 10, wherein the gas is ozone.

12. The method of claim 10, wherein the gas is emitted through microporous bubblers.

13. The method of claim 11 , wherein the groundwater bed is contaminated with TcO₄ ^" and a volatile organic compound.

14. The method of claim 11, wherein the groundwater bed is contaminated with TcO ^" and PCE, TCE, DCE, or vinyl chloride.

15. The method of claim 11, wherein the groundwater bed is contaminated with perchlorate and PCE, TCE, DCE, or vinyl chloride.

16. The method of claim 11, wherein the groundwater bed is contaminated with one or more heavy metals and PCE, TCE, DCE, or vinyl chloride.

17. The method of claim 11 , wherein the groundwater bed is contaminated with AsO₄ ^" and PCE, TCE, DCE, or vinyl chloride.

18. The method of claim 11, further comprising providing an oxic environment for the cartridge.

19. The method of claim 18, wherein the oxic environment is provided by sparging the water at a rate that results in bubbles of ozone gas taking between one and ten hours to travel through the water to the upper segment of the resin holder.