WO1995021794A1

WO1995021794A1 - Integrated adsorption/advanced oxidation fluidized bed reactor

Info

Publication number: WO1995021794A1
Application number: PCT/US1995/000621
Authority: WO
Inventors: Jeffrey S. Devine
Original assignee: Envirex, Inc.
Priority date: 1994-02-14
Filing date: 1995-01-17
Publication date: 1995-08-17
Also published as: AU1603795A

Abstract

A fluid, such as contaminated vapors or gases, or wastewater from industrial processes, contaminated ground water, a municipal wastewater stream or a municipal water supply (raw source water), is treated by passing the fluid through a bed (38) of particulate adsorbent material (42), capable of adsorbing contaminants from the fluid, preferably granular activated carbon (or GAC), whereby the bed is fluidized by the flow of the fluid and the contaminants are adsorbed on the adsorbent material as the fluid flows therethrough, and by introducing into the fluidized bed an oxidant such as UV-radiation, hydrogen peroxide, ozone, oxygen, Fenton's reagent, hydroxyl radicals, and mixtures thereof for oxidizing the contaminants adsorbed on the adsorbent material.

Description

INTEGRATED ADSORPTION/ADVANCED OXIDATION FLUIDIZED BED REACTOR BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method and apparatus for treating a fluid containing contaminants to oxidize those contaminants .

Reference to Prior Art Ultraviolet (or UV) enhanced oxidation processes have been used to treat contaminated fluids . The principles of conventional UV-enhanced oxidation processes are described in the following: U.S. Patent

No. 4,735,728 issued to Wemhoff; U.S. Patent No. 5,215,592 issued to Jackson; U.S. Patent No. 4,780,287 and 4,941,957 issued to Zeff; U.S. Patent No. 5,045,288 issued to Raupp; U.S. Patent No. 5,120,450 issued to Stanley; U.S. Patent No. 5,043,080 issued to Cater; and, PCT application No. 092/08544. Adsorption has also been used to treat contaminated fluids. The principles of conventional adsorption treatment processes are described in the following: U.S. Patent No. 5,198,001 issued to Kuebel; U.S. Patent No. 4,544,488 issued to O'Brien; and, U.S. Patent No. 4,624,789 issued to Fan.

Biological fluid bed reactors have also been used to treat contaminated fluids. The principles of conventional biological fluid bed treatment processes are described in the following: U.S. Patent No. 3,956,129 issued to Jeris; and, Hickey, R.F., et al, "Combined Biological Fluid Bed - Carbon Adsorption System For BTEX Contaminated Groundwater Remediation." These processes have several disadvantages . A primary disadvantage of the conventional UV-enhanced oxidation processes is that slow to oxidize organic contaminants, such as saturated organic contaminants, are not cost effectively treated. In particular, slow to oxidize organic contaminants require a sufficiently longer hydraulic retention time in order to achieve sufficient contact with the UV-radiation for oxidation of the contaminant to occur. As a result, the reactor size needed to achieve the necessary hydraulic retention time is prohibitively expensive.

Another major disadvantage of the conventional UV- enhanced oxidation processes is the cleaning requirement of the quartz sleeves which house the UV-lamps in the reactors . Quartz sleeves are used to protect the UV- lamps from direct contact with the water and contaminants. A film tends to accumulate on the sleeves which inhibits transmission of the UV-radiation to the fluid. Conventional UV-enhanced oxidation processes remove the film by periodic mechanical or chemical cleaning. For instance, complex mechanical wipers have been used to travel the length of the sleeves in order to wipe the sleeves clean. Mechanical cleaning processes add capital expense to the equipment and manual cleaning is operator intensive. Both are inefficient and may require shutting down the treatment system.

A primary disadvantage of conventional carbon adsorption treatment processes is that the organic contaminants are merely transferred from the fluid medium to the solid carbon medium. The contaminants themselves are not destroyed. Therefore, the contaminated carbon medium must then either be disposed of or regenerated. Disposal of the spent carbon can be costly.

A primary disadvantage of conventional biological fluid bed treatment processes is the production of biological sludge which may require additional handling and disposal.

Another major disadvantage of conventional biological fluid bed treatment processes is that such processes are limited to treating biodegradable contaminants. Therefore, there is a need for a cost effective and efficient method and apparatus for treating fluids containing a broad scope of contaminants, including organic contaminants which are slow to oxidize and not readily biodegraded. Examples of organic contaminants which are slow to oxidize and difficult to biodegrade include saturated chlorinated organic compounds such as trichloroethane (TCA), dichloroethane (DCA), and many other synthetic organic hydrocarbons .

SUMMARY OF THE INVENTION

The present invention provides a cost effective and efficient method and apparatus for treating fluids containing contaminants, especially contaminated vapors or gases, or wastewaters from industrial processes, contaminated ground waters, municipal wastewater streams and municipal water supplies (raw source waters), by passing the fluid through a bed of particulate adsorbent material capable of adsorbing contaminants from the fluid, preferably granular activated carbon (or GAC), whereby the bed is fluidized and the contaminants are adsorbed on the adsorbent material; and, by oxidizing the contaminants adsorbed on the adsorbent material.

One feature of the invention is the provision of a cost effective and efficient method and apparatus to polish and disinfect municipal wastewater streams and, for potable use, municipal water supplies (raw source waters) , including water contaminated with pesticides . Another feature of the invention is the reduction of operating costs and inefficiency of regeneration associated with conventional adsorption treatment processes by simultaneously regenerating the fluid bed of adsorbent material while treating the fluid containing contaminants . Another feature of the invention is the provision of a method and apparatus capable of effectively treating an expanded list of contaminants, including organic contaminants which are slow to oxidize (such as trichloroethane, dichloroethane, and other saturated organic compounds) by holding the slow to oxidize contaminants on the adsorbent material (such as GAC) until oxidation of the contaminant is complete; including contaminants which are non-biodegradable or difficult to biodegrade (such as trichloroethylene (TCE), perchloroethylene (PCE), pesticides and other synthetic organic compounds); and including other organic and inorganic contaminants, and organisms (such as bacteria, viruses, protozoa, and helminths). Another feature of the invention is the elimination of contaminated GAC media and biological sludge associated with carbon adsorption and biological fluid beds by destroying the contaminants rather than merely transferring the contaminants to a different medium. Another feature of the invention is the provision of more simple, smaller, and therefore less costly, reactors for treating fluids containing a broad scope of contaminants .

Another feature of the invention is the elimination of complex mechanical or chemical cleaning of the quartz sleeve protecting the UV-lamp by providing an inherent cleaning system. The invention provides scouring action of the fluidized bed of particulate material in the reactor to maintain the transparency of the quartz sleeve.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a fluid bed reactor embodying the invention and with portions broken away for clarity.

Figure 2 is a view similar to Figure 1 and showing an alternative embodiment of the invention. Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings . The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention provides a method and apparatus for treating fluids containing contaminants . The contaminants may be organic (including TCA, DCA, TCE, PCE, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), pesticides and trihalomethane (THM) precursors and other saturated hydrocarbons), inorganic (including cyanides and hydrogen sulfide), organisms (including various forms of bacteria, protozoa, viruses and helminths), or mixtures thereof. The invention is particularly useful for treating fluids containing organic contaminants . The fluids may be either a gas or a liquid. The invention is especially suitable for treating aqueous liquids such as wastewater from industrial processes (including those processes used by organic chemical manufacturers and users; petroleum refineries; petrochemical industries; wood treating operations; food and beverage companies; pulp and paper industries; pesticide manufacturers and users; and, explosive manufacturers and users), contaminated groundwaters, municipal wastewater streams and municipal water supplies (raw source waters). The invention is especially useful for polishing and disinfecting municipal wastewater streams and, for potable use, municipal water supplies (raw source waters). The invention is also useful for treating, for potable use, water contaminated with pesticides. The application of the invention to wastewater containing organic contaminants will be described below.

The wastewater is introduced into a suitable reactor containing a bed of particulate adsorbent material capable of adsorbing the organic contaminants from the wastewater, and capable of being fluidized by the flow of the fluid being treated. Suitable adsorbent materials include granular activated carbon (GAC), powdered activated carbon, activated alumina, mineral clay, zeolite, and mixtures thereof. Presently, GAC is preferred because of its superior adsorption and fluidization properties .

The particle size of the adsorbent material is not particularly critical and depends to a large degree upon the size of the reactor, the incoming flow rate of the wastewater, and the desired bed expansion, which will be described in detail below. For instance, for a given reactor size and bed expansion, the preferred particle size will be smaller at a low flow rate and larger at a high flow rate. For example, for a reactor which is 100mm in diameter and about 1 meter tall, a bed expansion of 100%, and a flow rate of 5 gpm, the preferred particle size for the adsorbent material is about 2mm to about 5mm (or about 4 to about 10 mesh).

The wastewater is introduced into the reactor in a manner to pass upwardly through the bed of adsorbent material thereby generating a fluidized bed. The term

"fluidized bed" as used herein refers to the flow of the fluid upwardly through the bed of adsorbent material at a velocity sufficient to buoy the adsorbent material, to counter the influence of gravity and to impart to the adsorbent material an appearance of movement within the bed expanded to a greater height than when no flow is passing through the bed. The extent of bed expansion can be about 10% to about 200%, and preferably about 50%. As the wastewater passes through the fluidized bed, organic contaminants in the wastewater are adsorbed on the adsorbent material thereby removing the organic contaminants from the fluid. The term "adsorbed" as used herein refers to the accumulation of contaminants on the outer or pore surface of the adsorbent material. An oxidant is introduced into the fluidized bed to oxidize the organic contaminants adsorbed on the adsorbent material and in the wastewater being treated. The term "oxidant" as used herein refers to any substance which oxidizes contaminants . The term "oxidize" as used herein refers to either direct photolysis by UV-radiation, or redox reactions with oxygen containing substances such as ozone, hydrogen peroxide, and/or hydroxyl radicals. Hydroxyl radicals are generated by the reaction of hydrogen peroxide and/or ozone with UV-radiation; in the reaction of ferrous ion with hydrogen peroxide (commonly known as Fenton's reagent) with or without UV-radiation; or, in the reaction of a solid metal photocatalyst such as titanium dioxide with UV-radiation. The term "oxidation" as used herein refers to the reaction of the contaminants with an oxidant to yield non-harmful or less harmful end products (for example, the reaction of organic contaminants with an oxidant to yield carbon dioxide, water, and miscellaneous salts).

The organic contaminants are oxidized by one of several pathways. Readily oxidizable contaminants may be adsorbed by the adsorbent material, or may immediately be oxidized in the fluid before being adsorbed on the adsorbent material. The readily oxidizable contaminants may be oxidized by direct photolysis by the UV-radiation or by hydrogen peroxide, ozone, or the hydroxyl radical. Slow to oxidize contaminants will be adsorbed by the adsorbent material and held in the reactor until the oxidation is complete by any of the pathways described above.

When ozone is used to oxidize the organic contaminants, the ozone is preferably pre-dissolved in the wastewater before being introduced into the reactor. Alternatively, ozone may be generated in the reactor by introducing oxygen into the reactor and exposing the oxygen to UV-radiation. When UV-radiation is used to oxidize the organic contaminants, the UV-radiation is preferably generated by a UV-lamp (or a number of UV-lamps commonly referred to as a bank of lamps). The UV-lamp (or bank of lamps) is selected to produce UV-radiation with a wavelength similar to the wavelength that is most absorbed by the contaminant or mixture of contaminants in the wastewater to be treated or is most absorbed by the chemical oxidant being employed. The UV-lamp (or bank of lamps) may be mounted on the outside of the reactor, or may be disposed within the reactor. In one preferred embodiment of the invention, a single elongated UV-lamp is centrally located within the fluidized bed of adsorbent material and extends through the height of the bed. This configuration allows the UV-radiation to fully penetrate the wastewater as it passes through the fluidized bed of adsorbent material. The UV-lamp is preferably mounted inside a protective tube of material transparent to UV-radiation to protect the UV-lamp from the wastewater and contaminants. Most preferably, a UV- transmissive quartz sleeve is used as the protective tube.

When a solid metal photocatalyst is used to generate the hydroxyl radicals, it is fluidized along with the adsorbent material making up the bed. The photocatalyst can be in the form of separate particles mixed and fluidized with the adsorbent material, or the photocatalyst can be impregnated onto GAC. Any suitable method of impregnation can be employed. If the photocatalyεt is impregnated onto GAC, and GAC also functions as the adsorbent material for adsorbing the organic contaminants from the wastewater being treated, then it is important that the adsorption properties of the GAC are not adversely inhibited by the amount of photocatalyst impregnated onto the GAC. Suitable photocatalysts for practicing the invention include titanium dioxide, which may be further enhanced by platinizing, or strontium titanate. The photocatalysts can be used separately or in mixtures. However, commercially available titanium dioxide is the most preferred.

Figure 1 shows a treatment system 10 for carrying out the process of the invention. The treatment system 10 can be used for treating liquids or gases. However, Figure 1 only shows treatment of a liquid, and, only treatment of wastewater will be described in detail.

The treatment system 10 includes a vertical cylindrical reactor 14 having an inside wall 22, a top portion 28, and a bottom portion 29. The reactor 14 further includes a base 30 and a top 34. The base 30 is connected to a drain 36 for emptying the reactor 14 when the treatment system 10 is shut down. The reactor 14 also includes a bed 38 of particulate adsorbent material 42 such as GAC, with or without a photocatalyst as described above.

The reactor 14 further includes a UV-lamp 46 mounted inside a quartz sleeve 50 which is centrally located inside the reactor 14 and is suspended from the top 34 of the reactor 14. The reactor 14 also includes a quartz sleeve centralizer 54. The quartz sleeve centralizer 54 includes three support members 56 (only two of which are shown in Fig. 1) evenly spaced around the quartz sleeve 50. Any suitable rigid material can be employed for the support members 56. The quartz sleeve centralizer 54 connects the quartz sleeve 50 to the inside wall 22 of the reactor 14 to stabilize the central location of the quartz sleeve 50 inside the reactor 14. The UV-lamp 46 is connected to a suitable power source (not shown) by way of wires 60.

Wastewater is introduced into the reactor 14 through an inlet 68 in the base 30. To obtain the desired fluidization of the bed 38 of adsorbent material 42, the incoming wastewater is pumped by a suitable pump 72 through an influent line 76 connected to the inlet 68. A series of distribution nozzles 80 connected to the inlet 68 distribute the flow of the incoming wastewater across the base 30 of the reactor 14 to provide a uniform fluidization of the bed 38 of adsorbent material 42.

Treated wastewater is withdrawn through an effluent line 84 in the top portion 28 of the reactor 14. Optionally, a portion of the treated wastewater can be recycled to the reactor 14 by way of a recycle line 88. The recycle line 88 is connected to a heat exchanger 92 for cooling the recycled treated wastewater. It may be necessary to use the option of recycling a portion of the treated wastewater if the flow rate of the incoming wastewater needed to achieve the desired fluidization is greater than the flow rate of the untreated wastewater alone. In such a circumstance, recycled treated wastewater flowing from the heat exchanger 92 is added to the incoming untreated wastewater by way of line 96 connected between the heat exchanger 92 and the influent line 76.

When hydrogen peroxide is used as an oxidant in accordance with one embodiment of the invention, it is introduced into the incoming wastewater by a suitable pump 100 in a feed line 104 connected between influent line 76 and a source of hydrogen peroxide (not shown). One or more chemicals for adjusting the pH of the incoming wastewater can be introduced by a suitable pump 108 in a feed line 112 connected between the influent line 76 and a source of pH adjusting chemicals) (not shown). Other additives for enhancing performance can be introduced into the incoming wastewater by a suitable pump 116 in a feed line 120 connected between the influent line 76 and a source of additives (not shown). When ozone is used as an oxidant, the treatment system 10 also includes an ozone system 124. The ozone system 124 includes a source of compressed air (not shown) connected to an ozone generator 128 by way of a feed line 132. Any suitable ozone generator can be employed. The ozone generator 128 produces an ozone/air mixture which contains about 2% by weight of ozone. The ozone/air mixture is introduced into the base 30 of the reactor 14 by way of a feed line 136 connected between the ozone generator 128 and the base 30 of the reactor 14. The ozone/air mixture flows into the bottom portion 29 of the reactor 14 through a fritted glass diffuser 138 for distributing the ozone/air mixture across the base 30 of the reactor 14. Any suitable diffuser may be employed. Alternatively, the ozone/air mixture can be pre-dissolved in the incoming wastewater by introducing it into the influent line 76 by way of feed line 140 illustrated by dashed lines, connected between the feed line 136 and the influent line 76. Alternatively, ozone may be generated in the reactor 14 by introducing oxygen directly into the reactor 14 where it is exposed to UV- radiation to produce ozone. In this embodiment, the oxygen is introduced into the base 30 of the reactor 14 through an oxygen feed line 144 illustrated by dashed lines, connected between a source of oxygen 148 and feed line 136. The oxygen flows into the bottom portion 29 of the reactor 14 through the diffuser 138.

Figure 2 shows an alternative arrangement of a treatment system 200 for carrying out the process of the invention. Treatment system 200 is used when the desired oxidant is the combination of hydrogen peroxide and a ferrous ion source, commonly referred to as Fenton's reagent. Components of the treatment system 200 common with those for treatment system 10 illustrated in Fig. 1 are designated by common reference numerals. As illustrated, the treatment system 200 does not include a source of UV-radiation, and includes a liquid containing ferrous ions, such as from ferrous sulfate, which is introduced into the incoming wastewater by a suitable pump 204 in a feed line 208 connected between the influent line 76 and a source of the liquid (not shown). The reaction of ferrous ion with hydrogen peroxide, with or without UV-radiation, produces hydroxyl radicals, so a source of UV-radiation may not be required for the treatment of some wastewaters . However, it should be understood that the treatment system 200 shown in Fig. 2 can include a source of UV-radiation when needed for wastewaters requiring large amounts of hydroxyl radicals to obtain the desired degree of treatment or for wastewaters containing mixtures of contaminants in which some constituents are readily destroyed by direct photolysis . Various features of the invention are set forth in the following claims.

Claims

C AIMS

1. A method for treating a fluid containing contaminants selected from the group consisting of organics, inorganics, organisms, and mixtures thereof, said method comprising the steps of : a) introducing the fluid into a reaction zone including a bed of particulate adsorbent material capable of adsorbing the contaminants from the fluid; b) passing the fluid through the bed of adsorbent material whereby the bed is fluidized and the contaminants in the fluid are adsorbed on the adsorbent material; c) introducing an oxidant into the fluidized bed for oxidizing the contaminants adsorbed on the adsorbent material.

2. The method according to claim 1, wherein the adsorbent material is selected from the group consisting of granular activated carbon, powder activated carbon, activated alumina, mineral clay, zeolite, and mixtures thereof .

3. The method according to claim 1, wherein the adsorbent material is granular activated carbon.

4. The method according to claim 1, wherein the fluid being treated is water.

5. The method according to claim 1, wherein step (c) includes introducing ultraviolet radiation into the bed.

6. The method according to claim 5, wherein the ultraviolet radiation is introduced into the bed by an ultraviolet lamp positioned within the fluidized bed of adsorbent material.

7. The method according to claim 6, wherein the ultraviolet lamp is located within a protective tube of material transparent to ultraviolet radiation.

8. The method according to claim 1, wherein step (c) includes introducing into the bed an oxidant selected from the group consisting of oxygen, ozone, hydrogen peroxide, hydroxyl radicals, Fenton's reagent and mixtures thereof.

9. The method according to claim 5, wherein step (c) further includes introducing into the reaction zone an oxidant selected from the group consisting of oxygen, ozone, hydrogen peroxide, hydroxyl radicals, Fenton's reagent, and mixtures thereof.

10. The method according to claim 5, wherein the bed of step (a) further includes a photocatalyst for oxidizing the contaminants in step (c) and is selected from the group consisting of titanium dioxide, platinized titanium dioxide, strontium titanate, and mixtures thereof.

11. The method according to claim 10, wherein the adsorbent material is granular activated carbon and the photocatalyst is impregnated thereon.

12. A method for treating an aqueous liquid containing contaminants selected from the group consisting of organics, inorganics, organisms, and mixtures thereof, said method comprising: a) introducing the liquid into a reaction zone including a bed of granular activated carbon; b) passing the liquid through the bed of granular activated carbon whereby the bed is fluidized and the contaminants in the liquid are adsorbed on the granular activated carbon; c) introducing into the fluidized bed ultraviolet radiation and an oxidant selected from the group consisting of oxygen, ozone, hydrogen peroxide, hydroxyl radicals, Fenton's reagent and mixtures thereof for oxidizing the contaminants adsorbed on the granular activated carbon.

13. The method according to claim 12, wherein the ultraviolet radiation is introduced into the fluidized bed by an ultraviolet lamp positioned within the fluidized bed.

14. The method according to claim 13, wherein the ultraviolet lamp is located within a protective tube of material transparent to ultraviolet radiation.

15. A method for treating an aqueous liquid containing contaminants selected from the group consisting of organics, inorganics, organisms, and mixtures thereof, said method comprising: a) introducing the liquid into a reaction zone including a bed of granular activated carbon; b) passing the liquid through the bed of granular activated carbon whereby the bed is fluidized and the contaminants in the liquid are adsorbed on the granular activated carbon; c) introducing into the fluidized bed an oxidant selected from the group consisting of oxygen, ozone, hydrogen peroxide, hydroxyl radicals, Fenton's reagent and mixtures thereof for oxidizing the contaminants adsorbed on the granular activated carbon.

16. A method for treating an aqueous liquid containing contaminants selected from the group consisting of organics, inorganics, organisms, and mixtures thereof, said method comprising: a) introducing the liquid into a reaction zone including a bed of granular activated carbon and titanium dioxide; b) passing the liquid through the bed whereby the bed is fluidized and the contaminants in the liquid are adsorbed on the granular activated carbon; c) introducing ultraviolet radiation into the fluidized bed for oxidizing the contaminants adsorbed on the granular activated carbon.

17. The method according to claim 16, wherein the titanium dioxide is impregnated onto the granular activated carbon.

18. An apparatus for treating a fluid containing contaminants selected from the group consisting of organics, inorganics, organisms, and mixtures thereof, said apparatus comprising: a reactor tank containing a bed of particulate adsorbent material which is capable of being fluidized by flow of the fluid being introduced into the reactor and which is capable of adsorbing contaminants from the fluid, and including an inlet for introducing the fluid into the reactor tank; and means for introducing an oxidant into the bed of adsorbent material for oxidizing the contaminants adsorbed on the adsorbent material.

19. The apparatus according to claim 18, wherein the adsorbent material is selected from the group consisting of granular activated carbon, powdered activated carbon, activated alumina, mineral clay, zeolite, and mixtures thereof.

20. The apparatus according to claim 18, wherein the adsorbent material is granular activated carbon.

21. The apparatus according to claim 18, wherein the means for introducing an oxidant includes a source of ultraviolet radiation.

22. The apparatus according to claim 21, wherein the source of ultraviolet radiation is an ultraviolet lamp positioned within the fluidized bed of adsorbent material.

23. The apparatus according to claim 22, wherein the ultraviolet lamp is located within a protective tube of material transparent to ultraviolet radiation.

24. The apparatus according to claim 18, wherein the means for introducing an oxidant includes a means for introducing an oxidant selected from the group consisting of oxygen, ozone, hydrogen peroxide, hydroxyl radicals, Fenton's reagent, and mixtures thereof.

25. The apparatus according to claim 21 further including a means for introducing an oxidant selected from the group consisting of oxygen, ozone, hydrogen peroxide, hydroxyl radicals, Fenton's reagent, and mixtures thereof.