REMOVAL OF CONTAMINANTS FROM A FLUID INVOLVING IN-SITU GENERATION OF ADSORPTION FILTRATION MEDIA OR REACTIVE COMPONENTS

Abstract

In one embodiment, a treatment system for removing dissolved contaminants (e.g., arsenic) from a contaminated fluid (e.g., water) utilizes in-situ generation of adsorption filtration media or reactive components. Corrosion materials (e.g., iron oxide complexes) that serve as the adsorption filtration media or reactive components are generated by supplying a flow of contaminated fluid, and injecting air, into a generator vessel containing pieces of an oxidizable source (e.g., zero-valent iron spheres). The pieces of the oxidizable source are agitated to release particulates of corrosion materials from their surface into solution with the contaminated fluid. Simultaneous to the ongoing generation of corrosion materials, dissolved contaminants in the contaminated fluid are adsorbed on the corrosion materials. New particulate compounds generated by adsorption of the dissolved contaminants on the corrosion materials precipitate from the solution, and are filtered out, thereby removing the contaminants, and yielding treated fluid (e.g., potable water).

Claims

1. A method for removing dissolved contaminants from a contaminated fluid using in-situ generation of adsorption filtration media or reactive components, comprising: supplying a flow of the contaminated fluid into a generator vessel that contains pieces of an oxidizable source; injecting air into the generator vessel; agitating the pieces of the oxidizable source in the generator vessel to cause the pieces to grind against each other to release particulates of corrosion materials from the surface of the pieces into solution with the contaminated fluid and to expose fresh portions of the pieces; generating corrosion materials within the generator vessel by reacting the particulates of corrosion materials with the contaminated fluid and oxygen from the injected air; simultaneous to the generating, adsorbing the dissolved contaminants in the contaminated fluid on the corrosion materials to generate particulate compounds; precipitating the particulate compounds generated by the adsorption of the dissolved contaminates on the corrosion materials; and filtering the particulate compounds to remove contaminants and yield treated fluid.

2. The method of claim 1, wherein the agitating is performed by magnetic fields operating upon the pieces of the oxidizable source.

3. The method of claim 1, wherein the agitating is performed by a recirculation flow incident upon the pieces of the oxidizable source.

4. The method of claim 1, wherein particulates of corrosion materials released from the pieces of the oxidizable source and the contaminated fluid are maintained in a solution within a mixing vessel by agitation, recirculation, concentration and/or mixing.

5. The method of claim 1, further comprising: heating the generator vessel.

6. The method of claim 1, wherein the filtering further comprises: passing the particulate compounds and fluid through a cartridge filter system.

7. The method of claim 1, wherein the filtering further comprises: passing the particulate compounds and fluid through a fixed bed system; and periodically refreshing the fixed bed system by creating a backflow to drag particles deposited in the fixed bed system to a backwash water storage tank.

8. The method of claim 1, wherein the dissolved contaminants comprise a form of arsenic.

9. The method of claim 8 wherein the form of arsenic comprises arsenite (As.sup.+3) or arsenate (As.sup.+5).

10. The method of claim 1, wherein the dissolved contaminants comprise a form of lead, selenium or aluminum.

11. The method of claim 1, wherein the dissolved contaminants comprise at least one contaminant selected from the group consisting of: uranium, mercury, cadmium, nickel, tin, chromium, zinc, cobalt, copper, thallium, molybdenum and antimony.

12. The method of claim 1, wherein the contaminated fluid is contaminated water and the treated fluid is potable water.

13. The method of claim 1, wherein the pieces of the oxidizable source comprise zero-valent iron spheres and the particulates of corrosion materials comprise iron oxide complexes.

14. A system for removing dissolved contaminants from a contaminated fluid using in-situ generation of adsorption filtration media or reactive components, comprising: a generator vessel configured to receive a flow of the contaminated fluid and pass the contaminated fluid over pieces of an oxidizable source; an air injector configured to inject air into the generator vessel to promote generation of corrosion materials by reaction of the pieces of the oxidizable source with the contaminated fluid and oxygen from the injected air; an agitation system configured to cause the pieces of the oxidizable source to grind against each other to release particulates of corrosion materials from the surface of the pieces of the oxidizable source into solution with the contaminated fluid, wherein particulates of corrosion materials adsorb the dissolved contaminants in the contaminated fluid to generate particulate compounds; and a filtration system configured to filter the particulate compounds to remove the dissolved contaminants and yield treated fluid.

15. The system of claim 14, wherein the agitation system comprises a magnetic field agitation device that uses magnetic fields to move the pieces of the oxidizable source.

16. The system of claim 14, wherein the agitation system comprises a recirculator pump that uses recirculation flow to move the pieces of the oxidizable source.

17. The system of claim 14, further comprising: a mixing vessel in which the particulates of corrosion materials released from the pieces of corrosion materials and the contaminated fluid are maintained in a solution by agitating, recirculating, concentrating and/or mixing to promote adsorption of the dissolved contaminants.

18. The system of claim 17, wherein the generator vessel is disposed internal to the mixing vessel.

19. The system of claim 14, wherein the filtration system is a cartridge filter system or a fixed bed system.

20. The system of claim 14, wherein the dissolved contaminants comprise a form of arsenic, the contaminated fluid is contaminated water and the treated fluid is potable water, the pieces of the oxidizable source comprise zero-valent iron spheres and the particulates of corrosion materials comprise iron oxide complexes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The description below refers to the accompanying drawings, of which:

[0023] FIG. 1 is a diagram of an example fluid treatment system for removing contaminants (e.g., arsenic as well as other dissolved metals, metalloids and non-metals contaminants) from a fluid (e.g., water) involving in-situ generation of filtration media/reactive components;

[0024] FIG. 2 is a graph indicating example amounts of corrosion materials produced from zero-valent iron when varying the content of dissolved oxygen, temperature, and an amount of sodium chloride in solution;

[0025] FIG. 3 is a layout diagram of a first embodiment of the example fluid treatment system of FIG. 1;

[0026] FIG. 4 is a layout diagram of a second embodiment of the example fluid treatment system of FIG. 1;

[0027] FIG. 5 is a layout diagram of a third embodiment of the example fluid treatment system of FIG. 1;

[0028] FIG. 6 is a graph showing experimental results of an example laboratory scale test system; and

[0029] FIG. 7 is a graph showing experimental results of an example intermediate scale test system.

DETAILED DESCRIPTION

Example Embodiments of Deployed Systems

[0030] FIG. 1 is a diagram 100 of an example fluid treatment system for removing contaminants (e.g., arsenic, as well as other dissolved metals, metalloids and non-metals contaminants) from a fluid (e.g., water) involving in-situ generation of filtration media/reactive components. The fluid treatment system 100 includes a mixing vessel 110, a fixed bed system 120, a treated fluid storage tank 130, a backwash fluid storage tank 140 and a telemetry control system (not shown). The mixing vessel 110 may include internally, or be coupled to an external generator vessel 150 and a recirculator pump 160. The generator vessel 150 includes an air injector 152, e.g., coupled to a compressor or other source of air (not shown) and a magnetic field agitation device 154. An optional heating apparatus 156 may also be provided.

[0031] In operation, contaminated fluid (e.g., contaminated water) 170 is fed to the fluid treatment system 100 via inflow pumps 180. The contaminated fluid flows into the generator vessel 150, which contains an oxidizable source (or sources) that constantly generate corrosion materials that serve as adsorbent filtration media or as reactive components for the system. In the embodiment shown in FIG. 1, the oxidizable source is zero-valent iron spheres, and the corrosion materials are iron oxide complexes, including lepidocrocite, magnetite, green rust, ferrate and bernalite, among other intermediate products produced as a result of corrosion of iron. However, it should be understood that the oxidizable source may alternatively be another material (such as carbon steel, carbon chrome steel, alumina ceramic, etc.) that oxidizes to produce the same, or different, corrosion materials. In the example shown, the generator vessel 150 operates to continuously generate corrosion materials from the oxidizable source because it promotes abrasion between piece (e.g., spheres) of the oxidizable source and supplies sufficient available oxygen. The abrasion is promoted by maximizing contact between the piece of the oxidizable source and agitating the pieces. Sufficient supplies of oxygen are ensured by injecting air into the generator vessel 150 through the air injector 152. The air injector 152 may include an air venturi injector and a diffuser or sparger.

[0032] More specifically, in an implementation that uses zero-valent iron spheres and contaminated water, the spheres are oxidized upon contact with the contaminated water and oxygen molecules from the injected air, generating corrosion materials on the surface of the spheres. The magnetic field agitation device 154 generates an intermittent movement of the spheres, while the recirculator pump 158 causes a recirculation flow upward (in opposite direction to gravity). Such operations may cause the spheres to grind against each other and rub against the walls and other internals of the generator vessel 150, releasing particulates of corrosion materials from the surface of the spheres into the contaminated water, and exposing fresh portions of the zero-valent iron. The recirculation flow in the generator vessel 150 may also cause the more buoyant particulates to flow out of the generator vessel 150 into the mixing vessel 110. The air injector 152 ensures sufficient oxygen molecules are available inside in the generator vessel 150 for a stable chemical reaction, so that the when fresh portions of the zero-valent iron spheres are exposed, they rapidly corrode to generate more corrosion material.

[0033] The particulates of corrosion materials and contaminated water pass into the mixing vessel 110. Both in the generator vessel 150 and in the larger mixing vessel 110 the corrosion materials operate as an adsorbent filtration media/reactive components, such that contaminants (e.g., arsenic) in the water are adsorbed on, or react with, active sites of the corrosion materials to form new particulate compounds. To promote such action, the particulates of corrosion materials and contaminated water are agitated, recirculated, concentrated and/or mixed, by operation of recirculator pump 158, a mechanical agitator or mixer (not shown), or as a byproduct of velocity gradients, inside the mixing vessel 110. In some implementations, such operation forms a solution (e.g., a homogenous solution) in which the corrosion materials are evenly distributed, to increase the chance that corrosion materials will meet and bond with contaminate particles.

[0034] The new compounds precipitate and are dragged by the flow of the fluid into a cartridge filter system and/or a fixed bed system 120. A cartridge filter system may include a sedimentation vessel and granular activated carbon (GAC) cartridge filters, manganese filters, polypropylene microfiber filters, and ceramic filter, among other types of filters. A fixed bed system 120 may include different layers of filtering media, such as manganese dioxide, charcoal, zeolite, and activated carbon, among others, and an automatic backwash system to clean the layers. The automatic backwash system may periodically create a backflow of water (e.g., from a treated fluid storage tank 130), to drag particles deposited in the fixed bed system 120 back to the backwash fluid storage tank 140 or other means of disposal. When not in backflow, clean water 190 flows from the filter bed system 120 to the treated water storage tank 130, to be consumed.

[0035] The speed of formation of corrosion materials in the generator vessel 150 from the oxidizable source (e.g., zero-valent iron spheres) is highly dependent on variables such as dissolved oxygen, temperature, agitation and abrasion. As described above, to enable generation of corrosion materials to be fast enough to support continuous operation, supplemental oxygen is supplied by the air injector 152. Further, in some embodiments, supplemental heat is supplied by heating apparatus 156.

[0036] FIG. 2 is a graph 200 indicating example amounts of corrosion materials produced from zero-valent iron when varying the content of dissolved oxygen, temperature, and an amount of sodium chloride in solution. The content of dissolved oxygen determines the nature of the oxides and oxy-hydroxides formed on the surface of zero-valent iron, and the type of the corrosion materials produced. Possible corrosion materials may cover a wide range, but in the presence of oxygen the main products are typically lepidocrocite, magnetite, green rust, ferrate and bernalite; compounds that have demonstrated a high affinity for adsorbing dissolved metals, metalloids and non-metals such as aluminum, arsenate, arsenite, cadmium, cobalt, chromium, copper, mercury, molybdenum, nickel, lead, antimony, selenium, tin, thallium, uranium, zinc, among others.

[0037] Corrosion is an electrochemical reaction. Increasing the temperature reduces oxygen solubility, increases the rate of oxygen diffusion to the metal surface, decreases the viscosity of water and increases the solution conductivity. In open systems, in which oxygen can be released from the system, corrosion will increase up to a maximum at 80° C. (175° K) where the oxygen solubility is 3 milligrams per liter (mg/L). Since the diffusion of oxygen to the metal surface has increased, more oxygen is available for the cathodic reduction process thus increasing the corrosion rate. Therefore, the corrosion rate of iron is increased by the increase in temperature by virtue of its effect on the oxygen solubility and oxygen diffusion coefficient. Such effects are demonstrated in FIG. 2.

[0038] FIG. 3 is a layout diagram of a first embodiment 300 of the example fluid treatment system of FIG. 1, showing, among other things, the generator vessel 150 arranged separate from the mixing vessel 150. In such an example, contaminated fluid (e.g., water) 170 enters the generator vessel 150 where it contacts with corrosion materials, which adsorb the dissolved contaminants. Some adsorption may occur in the generator vessel 150, and the resulting new compounds precipitate and are dragged by the flow of the fluid into the mixing vessel 110. Additional adsorption may occur in the mixing vessel 110, between particulates of corrosion materials that were dragged from the generator vessel 150 and any remaining contaminants in the fluid. Upon outflow from the mixing vessel 110, into the filter bed system 120, the new compounds are filtered out, letting clean fluid (e.g., clean water) pass to the treated fluid storage tank 130.

[0039] FIG. 4 is a layout diagram of a second embodiment 400 of the example fluid treatment system of FIG. 1, showing, among other things, the generator vessel 150 arranged internal from the mixing vessel 110.

[0040] FIG. 5 is a layout diagram of a third embodiment 500 of the example fluid treatment system of FIG. 1, showing, among other things, the generator vessel 150 arranged internal from the mixing vessel 110, and alternative arrangements for the introduction of air and filtration. In such configuration, air may be injected into a fluid supply line 510 leading from the recirculator pump 156 back to the mixing vessel 110. Further, filtration may be performed using a sedimentation vessel 520, a pair of granular activated carbon filters 530, 540 and a manganese filter 550.

Test Systems of Different Scales

[0041] The above describes techniques for removal of contaminants (e.g., arsenic, as well as other dissolved metals, metalloids and non-metals contaminants) from a fluid (e.g., water) involving in-situ generation of filtration media/reactive components have been experimentally tested using systems of different scales. A first, laboratory scale single pass test system (packed-bed filter) was built using the corrosion materials produced with carbon steel spheres of 1.000 degree, ⅛ inch diameter and with a composition of approximately 98% iron, 0.1-0.3% carbon, 0.3-1% manganese, less than 0.045% phosphorus, less than 0.5% sulfur and less than 0.3% silicon. The corrosion materials mentioned above were obtained by mixing 70 milliliters (ml) of deionized water and 16.3 grams of iron spheres in a 100 ml plastic receptacle. The receptacle was placed in a rotator at 30 revolutions per minute (RPM) for 24 hours. A procedure was used to simulate a fixed bed filter system consisting of building a filtration media cake (i.e. layer) with 25 milligrams of corrosion materials. Then, 100 ml of naturally occurring arsenic contaminated well water from a household in New Hampshire was passed through the filtration media cake five times (henceforth referred to as one cycle). The filtration media cake was rinsed with 100 ml of deionized water with a neutral pH after every cycle. After the last cycle, 100 ml of deionized water at a neutral pH, and solutions with pH 4 and pH 12, were passed through the filtration media cake to verify the arsenic particles were irreversibly captured within the filtration media cake (which they were). FIG. 6 is a graph 600 showing experimental results of an example laboratory scale test system, built according to the above description. As can be seen, the arsenic concentration drops from 100 ppb to less than 5 ppb. Such results were achieved in less than 4 minutes.

[0042] A second, intermediate scale test system was built capable of treating a continuous flow of 0.001 liters per second (L/s) of contaminated fluid. The system utilized corrosion materials produced from carbon steel spheres (as in the above discussed laboratory scale test system), a 9 liter (L) mixing tank, and a faucet filter to simulate a fixed bed filter system. The mixing tank was made of acrylic, and a generator vessel was placed inside. The faucet filter contained coconut shell activated carbon. The preparation of the system consisted of placing the generator vessel containing 121.41 grams (˜970 units) of the carbon steel spheres and 9 L of a synthetic contaminated aqueous solution with a concentration of 300 ppb of arsenic at 30° C. inside the mixing vessel, while injecting airflow of 0.2 L per second for a period of time of 5 to 20 minutes. Testing was performed using a pentavalent arsenate (As(V)) solution at a concentration of 1,000 milligrams (mg)/L and 0.1 molar (M) nitric acid (HNO.sub.3). The synthetic contaminated solution was prepared in the mixing tank by diluting 2.7 mL of As(V) solution in 9 L of potable water. Another contaminated solution was prepared in a 20 L drum diluting 6 mL of As(V) solution in 20 L of potable water. The electrochemical reaction with water and air and the rubbing, collisions and abrasion of the spheres with each other and the equipment internals released sufficient corrosion materials into the contaminated solution to remove the contaminants in a single pass. Testing showed that one sphere generated about 0.728 milligrams of corrosion materials. A continuous flow of contaminated solution passed through the whole system, with the contaminants being adsorbed by the corrosion materials inside the mixing tank. The contaminants and corrosions material were captured in the simulated fixed bed filter system (faucet filter). Testing was conducted to treat 29 L of synthetic contaminated solution. FIG. 7 is a graph 700 showing experimental results of an example intermediate scale test system, built according to the above description. As can be seen, the arsenic concentration drops from 300 ppb to less than 10 ppb in less than 20 minutes and it is kept below 10 ppb for the remainder of the test period.

[0043] A third, larger scale test system was built capable of treating a continuous flow of 3.79 liters per minute (L/m) of contaminated fluid. The system used a 60 L mixing vessel and a 28 L fixed bed filter system. The preparation of the system included placing 6.8 kilograms of the carbon steel spheres (having the characteristics discussed above in relation to the laboratory scale system), and 60 L of contaminated aqueous solution inside the mixing vessel while injecting airflow of 0.2 L/s. A continuous flow of contaminated fluid passed through the whole system. The contaminants were captured in a fixed bed filter system containing manganese dioxide, which is backwashed for 25 seconds 3 times per week with clean water. The backwash system was programmed to pump 1.6 L of clean water from a treated water storage tank through the fixed bed filter system in backward flow, leading to a backwash water storage tank.

Concluding Comments

[0044] It should be understood that various adaptations and modifications may be made to the above discussed systems and methods for removing contaminants from a fluid using in-situ generation of filtration media or reactive components. While various ones of the embodiments discussed above involve removing various forms of arsenic, it should be understood that the techniques are applicable to a wide variety of other dissolved metal, metalloid and non-metal contaminants, including aluminum, cadmium, cobalt, chromium, copper, mercury, molybdenum, nickel, lead, antimony, selenium, tin, thallium, uranium, and zinc, among others. Further, while various ones of the embodiments discussed above involve water as the fluid, it should be understood that the techniques are applicable to other types of liquids. Similarly, while it is discussed above that the techniques may be used to produce corrosion materials that function as adsorption filtration media or reactive components, it should be understood they may also produce materials that function as catalysts in the removal of contaminants Still further, it should be understood that systems employing the techniques may be constructed in any of a range of different capacities and sizes, including miniaturized sizes. Such systems may be positioned in any of a variety of locations between a fluid source (e.g., a water source, such as a well, reservoir, etc.) and a site where the fluid (e.g., water) is used. Above all, it should be understood that the above discussed systems and methods are meant to be taken only by way of example, and that the true scope of the invention is to be defined by the following claims.