Surface-modified activated carbon for reducing backwashing frequency during microparticle filtration

Abstract

This specification provides a method for reducing the backwash frequency required in water treatment facilities, including using surface-modified activated carbon. A method for preparing the surface-modified activated carbon is also provided. The preparation method may include a step of oxidizing the activated carbon with a chemical oxidant, whereby surface functionalization of the activated carbon may occur.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of priority of U.S. Provisional Patent Application No. 63 / 369,285, filed Jul. 25, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] Field The present disclosure generally relates to activated carbon for water treatment. More specifically, the present disclosure relates to the preparation of modified activated carbon for water treatment that reduces backwash frequency and thereby improves the efficiency of filtration plants.

[0003] Background Water treatment systems are an essential technology for modern society, and water treatment facilities have long benefited from technological improvements. Numerous studies have been conducted to improve the effectiveness and efficiency of water treatment systems, and new filtration materials and device designs have made it possible to remove undesirable components from municipal and industrial water supplies. The filtration materials used vary depending on the contaminants to be removed and the end use of the water source.

[0004] Activated carbon is known in the art as an effective water treatment medium. Generally, activated carbon obtained from organic raw materials such as coal, coconut shells, peat, wood, etc. can remove many contaminants from water by adsorption. By using activated carbon with different particle sizes and other filter components, various contaminants such as dissolved organic compounds, chlorine, hydrogen sulfide, bacteria, and other undesirable components can be removed. Methods for manufacturing activated carbon are known in the art and most commonly involve thermal activation or chemical activation. During manufacture, activated carbon may be prepared to have specific physical properties such as different pore sizes and surface areas, along with different chemical compositions. Since these factors affect the performance of the resulting activated carbon filter, there is a strong desire to develop preparation methods that can control these variables.

[0005] Activated carbon filters can be reused for water filtration if proper maintenance is carried out. Backwashing is a maintenance strategy for reusable filter materials. It is used to remove the fine particles accumulated in the filter, prevent filter failure, and minimize the growth of microorganisms in the filter. Usually, backwashing involves taking the filter offline and flowing clean water through the filter in the direction opposite to the normal flow to remove particles that may clog the filter. The frequency of backwashing varies depending on the type of filter and the level of contaminants removed in the water treatment process. Backwashing is a preventive maintenance procedure necessary to extend the operating time of the filter, but it requires a temporary stoppage of the water treatment process and leads to water waste.

[0006] Reducing the backwashing frequency has many advantages, such as increasing the production capacity of the filtration plant and reducing the water wasted in the backwashing process. Methods for reducing the backwashing frequency include increasing the particle size and decreasing the uniformity coefficient, but both will reduce the particle removal efficiency during the water treatment process. Balancing the reduction of backwashing frequency and maintaining the high efficiency of the filter material is extremely important for the operation of water treatment facilities.

Summary of the Invention

[0007] In some aspects, the technology described herein relates to a method for modifying the surface of activated carbon, which includes a step of contacting activated carbon with a chemical oxidizing agent to produce surface-modified activated carbon.

[0008] In some aspects, the technology described herein relates to a method in which the activated carbon is contacted with a chemical oxidizing agent at a temperature of about 300°C to about 700°C.

[0009] In some aspects, the technology described herein relates to a method in which the activated carbon is contacted with a chemical oxidizing agent at a temperature of about 350°C to about 500°C.

[0010] In some embodiments, the technology described herein relates to a method in which the chemical oxidant is selected from the group consisting of air, oxygen, ozone, nitric acid, peroxide, peracid, perborate, persulfate, perchlorate, and combinations thereof.

[0011] In some embodiments, the technology described herein relates to a method in which the chemical oxidant is gaseous.

[0012] In some embodiments, the technology described herein relates to a method in which the chemical oxidant is air.

[0013] In some embodiments, the technology described herein relates to a method in which the chemical oxidant is oxygen.

[0014] In some embodiments, the technology described herein relates to a method in which activated carbon is contacted with a chemical oxidant at a flow rate of about 2.5 to about 50 liters per minute.

[0015] In some embodiments, the technology described herein relates to a method in which activated carbon is contacted with a chemical oxidant for a time of about 5 minutes to about 3 hours.

[0016] In some embodiments, the technology described herein relates to a method in which the contact between the activated carbon and the chemical oxidant is carried out in a rotary kiln.

[0017] In some embodiments, the technology described herein relates to a method in which the rotary kiln has a rotational speed of about 1 to about 10 revolutions per minute.

[0018] In some embodiments, the technology described herein relates to a method of preparing activated carbon such that the surface of the activated carbon is oxidized and functional groups are generated on the surface of the activated carbon.

[0019] In some embodiments, the technology described herein relates to a method in which the functional groups include carboxyl groups, phenol groups, or combinations thereof.

[0020] In some embodiments, the techniques described herein relate to a method in which a functional group can be deprotonated in an aqueous solution, inducing an overall net negative charge on the surface of activated carbon.

[0021] In some embodiments, the techniques described herein relate to a method for preparing modified activated carbon that, when used in water filtration, requires no more than 15 backwash cycles to treat 10,000 gallons of water with 0.9 gallons of the modified activated carbon.

[0022] In some embodiments, the techniques described herein relate to a method that includes contacting activated carbon with a chemical oxidizing agent.

[0023] In some embodiments, the techniques described herein relate to a method in which the activated carbon is contacted with a chemical oxidizing agent at a temperature from about 300 °C to about 700 °C.

[0024] In some embodiments, the techniques described herein relate to a method in which the chemical oxidizing agent is selected from the group consisting of air, oxygen, ozone, nitric acid, peroxides, peracids, perborates, persulfates, perchlorates, and combinations thereof.

[0025] In some embodiments, the techniques described herein relate to a method in which the activated carbon is contacted with the chemical oxidizing agent at a flow rate from about 2.5 liters per minute to about 50 liters per minute.

[0026] In some embodiments, the techniques described herein relate to a method in which the activated carbon is contacted with the chemical oxidizing agent for a time from about 5 minutes to about 3 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Aspects, features, advantages, and benefits of the embodiments described herein will become apparent with reference to the following description, the appended claims, and the accompanying drawings:

[0028]

Figure 1

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present disclosure is not limited to the specific systems, devices, and methods described. The terms used herein are for the purpose of describing particular versions or embodiments only and are not intended to limit the scope.

[0030] In the present disclosure, an example of oxidizing the surface of activated carbon will be described. In the following description, for the purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments. It will be apparent to those skilled in the art that the embodiments can be practiced without these specific details without departing from the scope and spirit of the present disclosure.

[0031] Activated carbon can be obtained from any known source such as bituminous coal, sub-bituminous coal, lignite, anthracite, wood, peat, nut shells, pits, coconuts, babassu nuts, macadamia nuts, dendena nuts, peach pits, cherry pits, olive pits, walnut shells, wood, bagasse, rice husks, corn husks, wheat husks, polymers, resins, petroleum pitch, other carbonaceous materials (e.g., extruded pellets), or any combination thereof, but is not limited thereto. The raw materials of activated carbon used as described herein are not particularly limited.

[0032] Activated carbon can be formed by processes well-known in the art, such as carbonization and activation or direct activation. For example, raw materials such as wood, nut shells, coal, pitch, etc. can be oxidized and devolatilized with steam and / or gasified carbon dioxide to form a pore structure in the carbonaceous material, thereby forming adsorption sites. The oxidation and devolatilization treatment may include, for example, chemical treatment with dehydrating chemicals such as phosphoric acid, boric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, or any combination thereof. The method for preparing activated carbon as used herein is not particularly limited.

[0033] The surface of the activated carbon can be oxidized during manufacture to functionalize the activated carbon surface with functional groups such as carboxyl groups, phenol groups, or combinations thereof that can be deprotonated in an aqueous solution, resulting in a net negative charge on the carbon surface. Without wishing to be bound by theory, the negative surface charge allows the particles captured during water treatment to penetrate deeper into the activated carbon bed, enabling more of the activated carbon bed to participate in the filtration process, thereby improving the overall particle filtration capacity of the system.

[0034] When oxidized activated carbon is used in water treatment, fewer backwash cycles are required compared to unmodified activated carbon. Oxidized activated carbon requires 14 backwash cycles per 10,000 gallons of treated water, while unmodified activated carbon requires 18 backwash cycles per 10,000 gallons. Without wishing to be bound by theory, it is believed that the net negative surface charge and the resulting charge repulsion are aspects that enable the reduction of backwashing, as activated carbon prepared to have a net positive surface charge required 24 backwashes per 10,000 gallons. Reducing the frequency of backwash cycles increases the operating time of the treatment system and reduces the amount of water used compared to when frequent backwashing is required.

[0035] The figure shows the difference in the required backwash cycles among untreated activated carbon, activated carbon treated to have a net negative surface charge, and activated carbon treated to have a net positive surface charge. As shown in the figure, the 12x40 nitrided activated carbon with a net positive surface charge had more backwash cycles per gallon of treated water than the 12x4 or 8x30 untreated activated carbon. Conversely, the 8x30 oxygenated activated carbon with a net negative surface charge required fewer backwash cycles than the untreated activated carbon.

[0036] Oxidation of the activated carbon can be achieved by contacting the activated carbon with any number of chemical oxidizing agents including, but not limited to, air, oxygen, ozone, nitric acid, peroxides, peracids, perborates, persulfates, and perchlorates. The disclosed compositions can be oxidized at a temperature from about 300°C to about 700°C, or in some embodiments, from about 350°C to about 500°C. For example, the activated carbon may be oxidized at any temperature within any range formed by about 300°C, about 350°C, about 400°C, about 450°C, about 500°C, about 550°C, about 600°C, about 650°C, about 700°C, or any value preceding it.

[0037] Activated carbon can be oxidized in a time ranging from about 5 minutes to about 3 hours. For example, the activated carbon can be oxidized at any time within any range formed by, for example, about 5 minutes, about 10 minutes, about 15 minutes, about 20 minutes, about 25 minutes, about 30 minutes, about 35 minutes, about 40 minutes, about 45 minutes, about 50 minutes, about 55 minutes, about 1 hour, about 1.5 hours, about 2 hours, about 2.5 hours, about 3 hours, or any value formed by any of the preceding values. The oxidation may be carried out using a gas stream of an oxidizing agent having a flow rate ranging from about 2.5 liters per minute to about 50 liters per minute (lpm), for example, about 2.5 lpm, about 5 lpm, about 10 lpm, about 15 lpm, about 20 lpm, about 25 lpm, about 30 lpm, about 35 lpm, about 40 lpm, about 45 lpm, about 50 lpm, or any value within any range formed by any of the preceding values. The oxidation can be carried out in a rotary kiln having a rotational speed ranging from about 1 revolution per minute (rpm) to about 10 rpm, for example, about 1 rpm, about 2 rpm, about 3 rpm, about 4 rpm, about 5 rpm, about 6 rpm, about 7 rpm, about 8 rpm, about 9 rpm, about 10 rpm, or any value within any range formed by any of the preceding values.

[0038] The modified activated carbon disclosed herein may be useful in water treatment without wishing to be bound by theory. Water treatment may include any water treatment process known to those skilled in the art, including but not limited to the removal of contaminants or desirable components.

[0039] In some embodiments, a method for preparing modified activated carbon is provided such that when used in water treatment, no more than 15 backwash cycles are required to treat 10,000 gallons of water with 0.9 gallons of modified activated carbon. The preparation method can include any of the steps of the methods disclosed herein, such as contacting the activated carbon with a chemical oxidizing agent.

[0040] In some embodiments, a method for modifying the surface of activated carbon is provided, which includes contacting the activated carbon with a chemical oxidizing agent to produce surface-modified activated carbon.

[0041] In some embodiments, the activated carbon is contacted with a chemical oxidizing agent at a temperature of from about 300 °C to about 700 °C.

[0042] In some embodiments, the activated carbon is contacted with a chemical oxidizing agent at a temperature of from about 350 °C to about 500 °C.

[0043] In any of the above embodiments, the chemical oxidizing agent is selected from the group consisting of air, oxygen, ozone, nitric acid, peroxide, peracid, perborate, persulfate, perchlorate, and combinations thereof.

[0044] In any of the above embodiments, the chemical oxidizing agent is gaseous.

[0045] In any of the above embodiments, the chemical oxidizing agent is air.

[0046] In any of the above embodiments, the chemical oxidizing agent is oxygen.

[0047] In any of the above embodiments, the activated carbon is contacted with the chemical oxidizing agent at a flow rate of from about 2.5 liters per minute to about 50 liters per minute.

[0048] In any of the above embodiments, the activated carbon is contacted with the chemical oxidizing agent for a time of from about 5 minutes to about 3 hours.

[0049] In any of the above embodiments, the contact between the activated carbon and the chemical oxidizing agent is carried out in a rotary kiln.

[0050] In any of the above embodiments, the rotary kiln has a rotational speed of from about 1 revolution per minute to about 10 revolutions per minute.

[0051] A method is provided for preparing activated carbon such that the surface of the activated carbon is oxidized and functional groups are generated on the surface of the activated carbon.

[0052] In some embodiments, the functional groups include carboxyl groups, phenol groups, or combinations thereof.

[0053] In any of the above embodiments, the functional group can be deprotonated in an aqueous solution to induce an overall net negative charge on the surface of the activated carbon.

[0054] When used for water treatment, there is provided a method for preparing modified activated carbon that requires no more than 15 backwash cycles to treat 10,000 gallons of water with 0.9 gallons of the modified activated carbon.

[0055] In some embodiments, the method includes contacting the activated carbon with a chemical oxidizing agent.

[0056] In any of the above embodiments, the activated carbon is contacted with the chemical oxidizing agent at a temperature of from about 300 °C to about 700 °C.

[0057] In any of the above embodiments, the chemical oxidizing agent is selected from the group consisting of air, oxygen, ozone, nitric acid, peroxides, peracids, perborates, persulfates, perchlorates, and combinations thereof.

[0058] In any of the above embodiments, the activated carbon is contacted with the chemical oxidizing agent at a flow rate of from about 2.5 to about 50 liters per minute.

[0059] In any of the above embodiments, the activated carbon is contacted with the chemical oxidizing agent for a time of from about 5 minutes to about 3 hours.

[0060] One of ordinary skill in the art will understand that the term "air" represents the typical composition of ambient air, including a mixture of gaseous nitrogen, oxygen, carbon dioxide, and other gases. One of ordinary skill in the art will understand that "air" is not limited to a precise composition and that variations in the composition of air that may occur due to changes in elevation are also included within the scope of the present disclosure.

[0061] In the foregoing detailed description, reference is made to the accompanying drawings, which form a part hereof. The illustrative embodiments set forth in the detailed description, the drawings, and the claims are not meant to be limiting. Other embodiments may be used and other changes may be made without departing from the spirit or scope of the subject matter presented herein. Aspects of the present disclosure can be arranged, substituted, combined, separated, and designed in a variety of different configurations as generally described herein and illustrated in the figures, all of which are readily understood to be explicitly contemplated herein.

[0062] The present disclosure is not limited to the specific embodiments described in this application, which are intended as examples of various aspects. Without departing from its spirit and scope, as will be apparent to those skilled in the art, many modifications and variations can be made. Functionally equivalent methods and apparatuses within the scope of the present disclosure will be apparent to those skilled in the art from the foregoing description in addition to those enumerated herein. Such modifications and variations are intended to be included within the scope of the appended claims. The present disclosure is limited only by the terms of the appended claims and the full scope of equivalents to such claims. It is understood that the present disclosure is not limited to a particular method, reagent, compound, composition, or biological system, and that these may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0063] Regarding the use of substantially any plural and / or singular terms herein, one of ordinary skill in the art can translate from plural to singular and / or from singular to plural as appropriate for the context and / or application. For clarity, various singular / plural permutations may be explicitly set forth herein.

[0064] As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Nothing in this disclosure shall be construed as an admission that the embodiments described in this disclosure have any right to antedate such disclosure by virtue of prior invention. As used herein, the term "comprising" means "including, but not limited to".

[0065] In general, it will be understood by those of skill in the art that the terms used herein, and particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "including" should be interpreted to mean "including but not limited to", the term "having" should be interpreted to mean "having at least", the term "includes" should be interpreted to mean "including but not limited to", etc.). Various compositions, methods, and apparatuses are described with the term "comprising" (interpreted to mean "including, but not limited to") various components or steps, but the compositions, methods, and apparatuses can "consist essentially of" or "consist of" the various components and steps, and such terms should be interpreted to define essentially closed groups of members. Those of skill in the art will further understand that where a specific number of introduced claim recitations is intended, such intent will be explicitly recited in the claim, and where no such recitation is present, no such intent exists.

[0066] For example, for the sake of understanding, the following appended claims may include introductory phrases such as "at least one" and "one or more" to introduce the claim recitations. However, the use of such phrases should not be construed to mean that the introduction of a claim recitation by the indefinite article "a" or "an" limits the particular claim containing the introduced claim recitation to embodiments that contain only one such recitation. Even if the same claim contains an introductory phrase such as "one or more" or "at least one" and an indefinite article such as "a" or "an" (wherein, for example, "a" and / or "an" should be construed to mean "at least one" or "one or more"), the same holds true for the definite article used to introduce the claim recitation.

[0067] As used herein, the term "about" means plus or minus 10% of the numerical value in which it is used. Thus, about 50% means in the range of 45% to 55%.

[0068] In addition, even when a specific number of the introduced claims is explicitly recited, one of ordinary skill in the art would recognize that such a recitation should be construed to mean at least the recited number (e.g., a mere recitation of "two recitations" without other qualifying language means at least two recitations, or two or more recitations). Further, when a phraseology similar to "at least one of A, B, and C, etc." is used, generally, such a construction is intended in the sense that one of ordinary skill in the art would understand the phraseology (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, a system having A alone, B alone, C alone, a system having A and B together, a system having A and C together, a system having B and C together, and / or a system having A, B, and C together, etc.). When a convention similar to "at least one of A, B, or C, etc." is used, generally, such a construction is intended in the sense that one of ordinary skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, a system having A alone, B alone, C alone, a system having A and B together, a system having A and C together, a system having B and C together, and / or a system having A, B, and C together, etc.). It will be understood by one of ordinary skill in the art that substantially any disjunctive and / or phraseology presenting two or more alternative terms in any of the specification, claims, or drawings is to be understood as contemplating the possibility of including one of the terms, any of the terms, or both terms. For example, the phrase "A or B" would be understood to include the possibilities of "A" or "B", or "A and B".

[0069] In addition, when a feature or aspect of the present disclosure is described from the perspective of a Markush group, one of ordinary skill in the art would recognize that the present disclosure is also described from the perspective of any individual member of the Markush group or a subgroup of the members.

[0070] As will be understood by those skilled in the art, all ranges disclosed herein include, for all purposes, such as for the purpose of providing a written description, any possible sub-ranges and combinations of such sub-ranges. It can be readily recognized that each of the recited ranges is such that it can be fully described and enabled to be broken down into at least half, one third, one fourth, one fifth, one tenth, etc. of the same range. By way of non-limiting example, each range discussed herein can be readily broken down into a lower third, a middle third, an upper third, etc. Also, as will be understood by those skilled in the art, all language such as "up to", "at least", etc. includes the recited number and refers to a range that can be subsequently broken down into sub-ranges as described above. Finally, as will be understood by those skilled in the art, a range includes its individual members. Thus, for example, a group having 1 to 3 cells refers to a group having 1, 2, or 3 cells. Similarly, a group having 1 to 5 cells refers to a group having 1, 2, 3, 4, or 5 cells, etc.

[0071] Various alternatives, modifications, variations, or improvements that are not currently foreseen or anticipated may subsequently be made by those skilled in the art, and each of these is also intended to be encompassed by the disclosed embodiments.

Claims

1. A method for modifying the surface of activated carbon, the method comprising the step of contacting the activated carbon with a chemical oxidizing agent to produce a surface-modified activated carbon.

2. The method according to claim 1, wherein the activated carbon is contacted with the chemical oxidizing agent at a temperature of from about 300 °C to about 700 °C.

3. The method according to claim 1, wherein the activated carbon is contacted with the chemical oxidizing agent at a temperature of from about 350 °C to about 500 °C.

4. The method according to claim 1, wherein the chemical oxidizing agent is selected from the group consisting of air, oxygen, ozone, nitric acid, peroxide, peracid, perborate, persulfate, perchlorate, and combinations thereof.

5. The method according to claim 1, wherein the chemical oxidizing agent is gaseous.

6. The method according to claim 1, wherein the chemical oxidizing agent is air.

7. The method according to claim 1, wherein the chemical oxidizing agent is oxygen.

8. The method according to claim 1, wherein the activated carbon is contacted with the chemical oxidizing agent at a flow rate of from about 2.5 to about 50 liters per minute.

9. The method according to claim 1, wherein the activated carbon is contacted with the chemical oxidizing agent for a time of from about 5 minutes to about 3 hours.

10. The method according to claim 1, wherein the contact between the activated carbon and the chemical oxidizing agent is carried out in a rotary kiln.

11. The method according to claim 10, wherein the rotary kiln has a rotational speed of from about 1 to about 10 revolutions per minute.

12. A method for preparing activated carbon such that functional groups are generated on the surface of the activated carbon by oxidizing the surface of the activated carbon.

13. The method according to claim 12, wherein the functional groups include carboxyl groups, phenol groups, or combinations thereof.

14. The method according to claim 12, wherein the functional groups are deprotonated in an aqueous solution and can induce a net negative charge on the surface of the activated carbon as a whole.

15. A method for preparing a modified activated carbon which, when used in water treatment, requires no more than 15 backwash cycles to treat 10,000 gallons of water with 0.9 gallons of the modified activated carbon.

16. The method according to claim 15, wherein the method comprises the step of contacting the activated carbon with a chemical oxidizing agent.

17. The method according to claim 16, wherein the activated carbon is contacted with the chemical oxidant at a temperature of from about 300 °C to about 700 °C.

18. The method according to claim 16, wherein the chemical oxidant is selected from the group consisting of air, oxygen, ozone, nitric acid, peroxide, peracid, perborate, persulfate, perchlorate, and combinations thereof.

19. The method according to claim 16, wherein the activated carbon is contacted with the chemical oxidant at a flow rate of from about 2.5 to about 50 liters per minute.

20. The method according to claim 16, wherein the activated carbon is contacted with the chemical oxidant for a time of from about 5 minutes to about 3 hours.

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