Systems and methods for removing refractory organic compounds from water

Abstract

The present invention relates to a system and method for increasing the removal of PFAS and other persistent organic compound contaminants from water, particularly groundwater and drinking water, using submicron powdered activated carbon.

Description

[Technical field]

[0001] The present invention relates to systems and methods for removing refractory organic compounds, including perfluoroalkyl and polyfluoroalkyl materials, from water. In particular, the present invention relates to systems and methods for removing such contaminants from water using submicron powdered activated carbon in combination with ceramic membrane filtration. The present invention also relates to systems and methods for spent carbon concentration and removal. [Background technology]

[0002] Per- and polyfluoroalkyl substances ("PFAS"), such as perfluorooctane sulfate ("PFOS") and perfluorooctanoic acid ("PFOA"), including their precursors and related ranges, are compounds that are resistant to water and oil. They are man-made compounds that are used in a wide variety of industries, including carpeting, upholstery, and firefighting foams. However, such compounds are bioaccumulative and known carcinogens, and their removal from water, particularly groundwater and drinking water, is a significant environmental problem. Due to the strong fluorine-carbon bond, PFAS compounds are resistant to common treatment methods, including biological and chemical oxidation.

[0003] One of the more common methods of removing PFAS from water is the granular activated carbon ("GAC") or powdered activated carbon ("PAC") treatment system. As the name suggests, GAC uses granular activated carbon to remove a variety of contaminants, including organic recalcitrant compounds such as PFAS. In a typical GAC system, a tank contains the granular activated carbon and is of sufficient size to hold the water stream to be treated for a sufficient time for the contaminants to react with the GAC. During the reaction, PFAS and other organic compounds adhere to the surface of the granular activated carbon, i.e., they are adsorbed by the granular activated carbon.

[0004] After use, the adsorption of organic pollutant compounds declines to the point where the system fails. In other words, breakthrough is said to occur when the amount of pollutant adsorbed becomes less than the desired treatment requirement. At that point, a typical system must be shut down, the granular activated carbon removed, and properly rehabilitated. Depending on the pollutants filtered, the used GAC, especially those that have adsorbed PFAS, must be extracted and incinerated. Furthermore, the operating costs of GAC treatment are relatively high due to the rapid breakthrough of GAC systems and the need for frequent GAC regeneration and treatment. A relatively large plant footprint is also required for GAC treatment systems.

[0005] The ability of GAC to adsorb contaminants and the typical breakthrough time is related to the mean particle diameter ("MPD") of the carbon. In conventional GAC systems, the MPD is approximately 1,600 microns. Even in systems using PAC, the MPD of the PAC is greater than 45 microns. In both GAC and PAC, the adsorption of PFAS is facilitated by the porous structure of the carbon, including macropores, micropores, and mesopores. The primary adsorption mechanism depends on the size of the contaminant, with macropores and mesopores found to be the most important for PFAS removal. For both GAC and PAC, larger MPDs can limit access to the interior pores, leading to breakthrough despite the availability of surface area for adsorption deep within the carbon particle. As shown, larger MPDs result in shorter breakthrough times and increased carbon removal and disposal costs. Additionally, typical GAC systems do not effectively remove short chain length (i.e., 4, 6, and 7 carbon chain lengths) PFAS compounds.

[0006] Therefore, there is a need to increase the removal of PFAS and other difficult-to-remove organic compound contaminants from water, especially groundwater and drinking water. There is also a need to increase the breakthrough time of typical GAC filtration systems and reduce the burden and cost of waste disposal of used materials. In the present invention, it has been found that the use of submicron powdered activated carbon ("SPAC") and its smaller particle size provides a larger surface area and increased amount of mesopores, resulting in lower waste rates and faster adsorption, requiring less volume. SPAC is also effective in removing short-chain PFAS that are ineffective in known treatment methods. The larger surface area and improved access to mesopores and macropores provided by SPAC and the present invention have been shown to increase the adsorption of PFAS over that of GAC by more than 500 times for a given carbon content basis. Furthermore, the present invention provides thickening or concentration of used SPAC, reducing waste disposal costs. Summary of the Invention

[0007] Thus, the present invention retains the advantages of known PFAS removal systems and methods, and further provides novel features and advantages.

[0008] The objective of the present invention is to use submicron powdered activated carbon ("SPAC") to remove refractory organic compound contaminants from water, including PFAS, 1,4-dioxane, BTEX and many others.

[0009] It is another object of the present invention to provide an adsorption reactor, preferably a pressurized adsorption reactor, that provides sufficient residence time for the SPAC / water slurry to allow the SPAC to adsorb contaminants from the water influent to be treated.

[0010] An additional object of the present invention is to use a ceramic membrane filter, preferably a high velocity cross-flow ceramic membrane filter, to separate the filtered water from the contaminant-adsorbed SPAC and return a portion of the bulk liquid to the adsorption reactor.

[0011] A further object of the present invention is to increase the recovery and concentration of SPAC to reduce removal and disposal of spent SPAC.

[0012] It is yet an additional object of the present invention to retain the SPAC in a closed loop system as the treated water is separated from the SPAC using a high strength, high velocity cross-flow ceramic membrane filter and a feed-and-bleed type SPAC storage and recovery system.

[0013] It is yet another object of the present invention to flush and clean the membranes of a ceramic membrane filtration system while filtering treated water from SPAC and its adsorbed contaminants.

[0014] It is a still further object of the present invention to use a ceramic membrane filter to retain the SPAC within the system, thereby allowing the SPAC to continue removing soluble and persistent organic compounds, including PFAS.

[0015] It is yet another object of the present invention to reduce backwash frequency and backwash waste using a high velocity cross-flow ceramic membrane filter.

[0016] Yet a further object of the present invention is to maximize contaminant adsorption and reduce the use rate and disposal of SPACs.

[0017] Yet another object of the present invention is to concentrate spent SPAC to reduce the frequency and amount of removal and / or disposal.

[0018] In accordance with the object of the present invention, a method for removing contaminants from water is provided, which includes the steps of: adding submicron granular activated carbon (SPAC) to an influent stream of water to be treated; combining the SPAC with the water to be treated; introducing the mixture or slurry of SPAC and water into an adsorption reactor for treatment; allowing the mixture to be held in the adsorption reactor for a residence time sufficient for the SPAC to adsorb the contaminants in the water; and transferring the mixture or slurry from the adsorption reactor using a recycle pump to a high-rate ceramic membrane filter unit operating in cross-flow filtration, where the treated water is discharged as permeate and the SPAC slurry is returned to the adsorption reactor as retentate. The method may also include the steps of: removing a concentrate of the SPAC and adsorbed contaminants from the ceramic membrane filter via a concentrate line after the SPAC reaches breakthrough; and adding new SPAC to the influent stream of water to continue removing the contaminants. Further, in a preferred method, the SPAC and adsorbed contaminants are thickened for removal by stopping the influent flow to the adsorption reactor and continuing to operate the recycle pump until the retentate is thickened and then removed via a concentrate line for waste disposal. The membrane of the ceramic membrane filter has a nominal pore size barrier of approximately 0.1 microns. In a preferred method, the influent flow rate is 1 Qi, and the mixture of SPAC and influent is pumped from the adsorption reactor to the ceramic membrane filter at a rate of 10 times the influent flow rate (10 Qi). Also, preferably, the permeate is discharged from the ceramic membrane filter at a rate of 1 times the influent flow rate (1 Qi), and the retentate is returned to the adsorption reactor at a rate of Qr, where Qr is preferably 9 times the influent flow rate (9 Qi). Preferably, the SPAC has an average particle size of less than approximately 1 micron.

[0019] Also provided is a system for removing contaminants, including PFAS, from water.The system includes: a pressurized adsorption reactor in fluid communication with the influent line; a SPAC feed line in communication with the influent line for adding SPAC to the influent; an adsorption reactor receiving an influent stream of water to be treated and submicron powdered activated carbon ("SPAC"), the adsorption reactor having a capacity to hold the influent and the SPAC slurry for a sufficient retention time such that contaminants to be removed are adsorbed by the SPAC in the slurry; a slurry effluent line in communication with an outlet of the adsorption reactor and a recycle pump in the slurry effluent line; a cross-flow ceramic membrane filter in fluid communication with the slurry effluent line of the adsorption reactor; a recycle pump that transfers the contaminant-adsorbed SPAC at a high flow rate to a ceramic membrane filter unit which separates the treated water from the contaminant-adsorbed SPAC as a permeate; a pressurized adsorption reactor in fluid communication with the influent line; a SPAC feed line in communication with the influent line for adding SPAC to the influent; an adsorption reactor receiving an influent stream of water to be treated and submicron powdered activated carbon ("SPAC"), the adsorption reactor having a capacity to hold the influent and SPAC slurry for a sufficient retention time such that the contaminants to be removed are adsorbed by the SPAC in the slurry; a slurry effluent line connected to the outlet of the adsorption reactor and a recycle pump in the slurry effluent line; a cross-flow ceramic membrane filter in fluid communication with the slurry effluent line of the adsorption reactor; a recycle pump that transfers the contaminant-adsorbed SPAC at a high flow rate to a ceramic membrane filter unit which separates the treated water from the contaminant-adsorbed SPAC as a permeate; a permeate line in fluid communication with the ceramic membrane filter for removing the treated water as a permeate; a retentate line in fluid communication with the ceramic membrane filter and the adsorption reactor that returns the SPAC slurry to the influent line; and a concentrate line for removing the SPAC after breakthrough.A preferred system uses SPAC having an average particle size of less than about 1 micron, where the ceramic membrane filter has a nominal pore size barrier of about 0.1 micron. One embodiment of this system may include a SPAC delivery system in fluid communication with the influent line. Definition of inventor's terminology

[0020] The following terms, which may be used in the various claims and / or specification of this patent application, are intended to have their broadest meaning consistent with the requirements of law:

[0021] As used herein, "influent" or "influent stream" (also referred to as Qi) refers to the liquid (water or wastewater) to be treated that is introduced into the pollutant removal system.

[0022] As used herein, "permeate" or "filtrate" shall refer to the treated fluid or fluid stream following treatment by the contaminant removal system and separation of the SPAC from the contaminants adsorbed thereto.

[0023] As used herein, "retentate" or "retentate stream (Qr)" refers to the bulk liquid or slurry containing SPAC from which the "permeate" or "filtrate" has been removed.

[0024] As used herein, "SPAC" refers to submicron, or ultrafine, powdered activated carbon, preferably wood-based, and preferably having an average particle size of less than about 1 micron.

[0025] As used herein, "PFAS" refers to a broad range of per- or polyfluoroalkyl substances, including, for example, perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), as well as short-chain polyfluoroalkyl acids (PFAA) and their precursors. As used herein, PFAS may also generally refer to other difficult-to-remove organic compounds.

[0026] As used herein, "breakthrough" refers to a SPAC that is no longer capable of adsorbing sufficient levels of contaminants for the desired effective treatment.

[0027] Where alternative meanings are possible, the broadest meaning consistent with the understanding of one of ordinary skill in the art is intended in the specification or claims. All words used in the claims are intended to be used in accordance with grammar, trade and ordinary and customary usage of the English language. [Brief description of the drawings]

[0028] The stated and unstated objects, features and advantages of the present invention (sometimes used in the singular but not excluding the plural) will become apparent from the description and drawings set forth below, in which like reference numerals represent like elements in the various drawings.

[0029] [Figure 1] 1 is a schematic diagram of a basic form of a preferred contaminant removal system of the present invention;

[0030] [Diagram 2] 1 is a schematic diagram of a more comprehensive preferred contaminant removal system of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Set forth below are descriptions of what are presently believed to be the preferred embodiments or best representative examples of the invention as claimed. Future and current alternatives and embodiments to these and the preferred embodiments are contemplated. Any alternatives or variations that make insubstantial changes in function, purpose, structure or result are intended to be covered by the claims of this patent application.

[0032] A preferred PFAS removal system and method of the present invention is shown in its basic form in FIG. 1. The system includes an influent line 11, which introduces an influent stream of water to be treated (Qi) into the system. SPAC 12 is added to the influent (Qi) via SPAC feed line 13, typically using a carbon feed system or other means as described below. A mixer 14 may be optionally included to facilitate mixing the influent and SPAC 12, forming the bulk liquid or slurry to be treated. The slurry of SPAC 12 and influent is then transported by feed pump 16 through slurry feed line 15 to adsorption reactor 20. Feed pump 16 is sized to transport the influent stream and SPAC slurry at a design flow rate (Qi). Feed pump 16 transports the influent at Qi with the SPAC slurry via slurry feed line 15 to adsorption reactor 20.

[0033] In a preferred embodiment, the system and method uses wood-based SPAC12 with a mean particle diameter (MPD) of approximately less than 1 micron. The use of submicron powder particles provides a larger external surface area per unit mass and an increased amount of and access to mesopores contained in the particles, allowing for faster and more effective adsorption of contaminants. The use of submicron powder particles also allows for greater access to contaminants and lower use rates. As a result, it has been found to be particularly effective in removing short-chain PFAS.

[0034] SPAC12 is not currently considered to be a readily available material in good stock, as current demand is relatively low. However, it can be readily manufactured from GAC and / or PAC, of ​​which many manufacturers are known, as will be appreciated by those skilled in the art. Some known GAC / PAC manufacturers include Asbury Carbons, Nalco Waters, and Calgon Carbons. These and other GAC / PAC manufacturers also have milling processes available to manufacture SPAC. For example, Asbury Carbons has a readily available milling process that can manufacture SPAC from GAC or PAC with very short lead times. Thus, the source of SPAC of the present invention is readily available to one skilled in the art.

[0035] In a preferred embodiment, the SPAC12 will be manufactured and shipped to the processing site in a liquid slurry for ease of handling and end use. For example, a 10% slurry of 1 micron SPAC and water (100 grams carbon / liter) has been found to be desirable for use in the present invention. As described below, the initial SPAC12 slurry is further diluted to a working concentration with the influent water to be treated and transferred to the adsorption reactor 20. In a preferred embodiment where the SPAC slurry is 100 grams carbon / liter, the slurry is diluted to approximately 0.5-2 grams carbon / liter in the adsorption reactor 20. These concentrations are merely exemplary and not limiting.

[0036] The adsorption reactor 20 is a vessel in which, among other things, the water to be treated is in contact with the SPAC 12 or SPAC slurry for a sufficient time such that the PFASs can be adsorbed by the SPAC 12. The adsorption tank 20 serves as a reaction chamber for the SPAC 12 and the water to be treated such that the PFASs and other contaminants are adsorbed by the SPAC 12 in the adsorption tank 20. The adsorption reactor 20 provides a desired and / or designed residence time for the SPAC / influent slurry such that the PFASs and other contaminants can be adequately adsorbed by the SPAC 12.

[0037] In a preferred embodiment, the adsorption reactor 20 is sized to accommodate at least 10 times (10 Qi) the influent flow, as described below. It will be understood by those skilled in the art that the adsorption reactor 20 is also sized to provide a desired residence time to promote adsorption of PFAS and other contaminants by SPAC. The larger the adsorption reactor 20 is at a given flow rate, the longer the residence time it can provide. In a preferred embodiment, a residence time of 30-60 minutes at an influent flow rate (Qi) has been determined to be sufficient for the reaction between SPAC and PFAS in an influent having a typical influent of (Qi) of 100 gal (379 liters) / min. Other residence times may be sufficient, depending on the desired treatment parameters and influent flow. Thus, in a system with a Qi of 100 gal (379 liters) / min and a residence time in the adsorption reactor 20 of 1 hour, the adsorption reactor 20 must accommodate at least 6,000 gal (22.7 kiloliters).

[0038] The preferred adsorption reactor 20 of the present invention is a pressurized tank closed from the atmosphere. Baffles 21 (see FIG. 2) may be provided within the adsorption reactor 20 to prevent shortcuts. It will be understood by those skilled in the art that non-pressurized tanks may also be used; however, such tanks would have to be relatively tall and / or would require substantially greater energy requirements.

[0039] The SPAC adsorbs the PFAS and other contaminants in the adsorption reactor 20. After sufficient residence time in the adsorption reactor 20, the SPAC reacted slurry with the bulk liquid is then transported via the slurry effluent line 22 to the ceramic membrane filter unit 30 using a recycle pump 26. In a preferred embodiment, the recycle pump 26 is sized to transport ten times the influent flow (10 Qi) through the slurry effluent line 22 to the ceramic membrane filter 30.

[0040] The ceramic membrane filter unit 30 provides important unique functions of the present invention. First, the ceramic membrane filter 30 separates the SPAC and adsorbed contaminants from the treated liquid, which is discharged as clean permeate via permeate line 32. The ceramic membrane filter also returns the SPAC slurry to the adsorption reactor 20 for further processing of the influent, which reduces SPAC consumption. Third, the ceramic membrane filter 30 also serves to thicken and thicken the SPAC 12 after breakthrough or exhaustion, aiding in the disposal of the SPAC 12 without the need for complex additional equipment.

[0041] In a preferred embodiment, the ceramic membrane filter 30 has a nominal pore size barrier of 0.1 microns. This small pore size results in high permeability and reduced pressure drop through each membrane of the ceramic membrane filter 30. As will be appreciated by those skilled in the art, suitable ceramic membrane filters 30 are available from a number of manufacturers, including Aqua-Aerobic Systems, Inc. (see www.aqua-aerobic.com).

[0042] In a preferred embodiment, the ceramic membrane filter 30 is operated in a cross-flow filtration mode. Preferably, the recycle pump 26 delivers the SPAC / liquid slurry to the ceramic membrane filter 30 via the slurry effluent line 22 at 10 times the influent flow rate, i.e., 10Qi. The membrane of the ceramic membrane filter 30 separates the treated liquid from the SPAC and liquid slurry. The treated water is preferably discharged as permeate via the permeate line 32 at a flow rate approximately equal to the initial influent flow rate, Qi. The SPAC and bulk liquid not discharged as permeate are discharged from the ceramic membrane filter 30 as retentate (Qr) via the retentate line 36, preferably at 9 times the initial flow rate, i.e., 9Qi. The retentate is returned upstream of the adsorption reactor 20 either to the slurry feed line 15 or directly to the adsorption reactor 20. Notably, the return of the SPAC-containing retentate slurry increases the concentration of SPAC 12 in the adsorption reactor 20, thereby requiring less unused SPAC 12 to be added to the system. This also promotes enhanced PFAS adsorption by SPAC 12. The ceramic membrane filter 30 also includes a concentrate outlet 37, which is in fluid communication with a concentrate withdrawal line 38 for removing spent SPAC 12 after breakthrough.

[0043] Importantly, pumping 10 Qi of slurry into the ceramic membrane filter 30 at a high rate while removing only 1 Qi as permeate flushes fouling from the membrane 31 inside the ceramic membrane filter 30. This results in a clean membrane 31 and maintaining high permeability of the membrane 31. This also reduces the frequency of backwashing requirements. Passing the ceramic membrane filter 30 at a high rate further reduces the chance of biological growth, which helps maintain filtration efficiency and reduces the need for frequent backwashing or chemical adjustments. In a preferred embodiment, when 10 Q is pumped by the pump 26 to the ceramic membrane filter 30, 1 Qi is removed as permeate via the permeate line 32. As a result, 9 Q (9 Qr) is returned to the adsorption reactor 20 as retentate via the retentate line 36. It will be understood by those skilled in the art that these flow rates are exemplary and / or preferred, and that other flow rates may be used consistent with the present invention.

[0044] What has been described above is a basic system and method for removing PFAS using the SPAC, adsorption reactor 20 and ceramic membrane filter 30 of the present invention. Additionally, a more comprehensive system of the present invention is described herein by reference to Figure 2. A system and method for thickening and removal of SPAC is also described by reference to Figure 2, although thickening and removal are also part of the basic system shown in Figure 1.

[0045] As shown in FIG. 2, a SPAC feed system 40 is provided as an alternative to the direct feed of SPAC 12 to influent line 11 and the optional use of mixer 14. SPAC feed system 40 includes tank 41 and mixer 42, which mixes a SPAC slurry for use in the system. Specifically, in a preferred embodiment, a 10% SPAC slurry (e.g., 100 grams of carbon / liter) is added to tank 41 and mixed by mixer 42. The SPAC slurry is pumped from tank 41 through SPAC feed line 13 using SPAC feed pump 43 to influent line 11. The mixture or slurry is then pumped to adsorption reactor 20 via slurry feed line 15 using feed pump 16, preferably at a flow rate of Qi. In a preferred embodiment, the 10% SPAC concentration is diluted in adsorption reactor 20 to approximately 0.5-2 grams of carbon / liter. As shown in the schematic diagram, the preferred adsorption reactor 20 includes one or more baffles 21 to help prevent shortcuts. After sufficient residence time for the SPAC 12 to adsorb the contaminants, the bulk liquid is sent via the slurry effluent line 22 and recycle pump 26 to the ceramic membrane filter 30. Again, the preferred pumping rate is 10 Qi into the ceramic membrane filter 30 and the recycle pump 26 sized accordingly.

[0046] 1, the ceramic membrane filter 30 separates the permeate from the SPAC 12 and contaminants adsorbed thereto. The permeate is removed from the ceramic membrane filter 30 via a permeate line 32 at a flow rate of 1 Qi. However, in this embodiment, a permeate tank 50 is provided in fluid communication with the permeate line 32. The permeate from the ceramic membrane filter 30 is sent to the permeate tank 50 and may be removed as treated effluent via a permeate drain 52 or stored for use in backwashing as described hereinafter.

[0047] In the embodiment of FIG. 2, a backwash line 62 is in fluid communication with the permeate tank 50 for withdrawal of permeate for use in backwashing. A backwash pump 61 is also provided in the backwash line 62. The backwash line 62 is in fluid communication with a backwash tank 70, which in turn is in fluid communication with the permeate line 32 of the ceramic filter membrane unit 30. When backwashing is desired or required, permeate is pumped from the permeate tank 50 to the backwash tank 70 by the backwash pump 61. The permeate from the backwash tank 70 flows from the backwash line 62 to the permeate line 32, which is in fluid communication with the ceramic membrane filter 30. This reverses the flow through the ceramic membrane filter 30 to backwash the membrane 31, as described below.

[0048] An optional chemical tank 60 may also be provided. The chemical tank 60 is in fluid communication with a chemical feed line 65, which in turn is equipped with a chemical feed pump 64. The chemical feed line 65 is in turn in fluid communication with the backwash line 62. The chemical tank 60 holds a solution of chemicals that may be used when backwashing the membrane of the ceramic membrane filter 30. Such chemicals may include NaOCl and citric acid to help clean the membrane. As will be appreciated by those skilled in the art, other chemicals may be used. Thus, if a chemical is desired for use in backwashing, the chemical solution is pumped by the chemical feed pump 64 through the chemical feed line 65 into the permeate stream of the backwash line 62.

[0049] Additionally, an optional air supply 80 may be provided. The air supply 80 is in fluid communication with an air supply line 81. The air supply line 81 is in fluid communication with the backwash tank 70 and the retentate line 36. The air supply 80 may be provided in a specific system for use in backwashing. When backwashing is desired, the air supply 80 pressurizes the backwash tank 70 via the air supply line 81 until a pressure setpoint is reached, after which the air supply valve 83 closes. The backwash valve 63 is then opened, releasing pressurized permeate from the backwash tank 70 through the membrane filter 30 to help clean the membrane 31.

[0050] An important aspect of the present invention is the thickening, dewatering and removal of spent SPAC 12. A preferred system and method are described by reference to FIG. 2. For removal of PFAS and other organic contaminants, an influent flow at a flow rate of Qi is introduced at influent line 11 (e.g., 100 gal / min). Using SPAC feed pump 43, SPAC solution (e.g., 100 grams / liter of carbon) is pumped from SPAC tank 41 via SPAC feed line 13 through open SPAC feed valve 18. A slurry of influent and SPAC is pumped by feed pump 16 via slurry feed line 15 to adsorption tank 20. The slurry is pumped into adsorption reactor 20 at a flow rate of Qi. The SPAC 12 and influent slurry is retained in adsorption reactor 20 for a desired retention time, whereby PFAS and other contaminants are adsorbed into SPAC 12. The concentration of the SPAC12 slurry in the adsorption reactor 20 may typically be between 0.5 and 2 grams of carbon per liter.

[0051] The slurry of contaminant-loaded SPAC and bulk liquid is transferred from the adsorption reactor 20 to the ceramic membrane filter 30 for filtration. Specifically, the slurry is pumped using the recycle pump 26 through the slurry effluent line 22 through the open recycle valve 27 and into the ceramic membrane filter 30. As previously discussed, the recycle pump 26 is sized to pump 10 times the influent flow rate (10 Qi) into the ceramic membrane filter 30. The membrane of the ceramic membrane filter 30 separates the permeate from the SPAC / influent slurry.

[0052] Permeate leaves the ceramic membrane filter 30 via permeate line 32 and enters the permeate tank 50 where it may be removed via permeate removal line 52. Retentate leaves the ceramic membrane filter 30 through retentate line 36 and the open retentate valve 34 and is returned to the adsorption reactor 20. The retentate is returned to the adsorption reactor 20 at a flow rate of Qr, which is nine times the influent flow rate, or 9Qi. During a typical filtration run, the backwash pump 61 is stopped, the backwash valve 66 is closed, and the air supply valves 83 and 84 are closed.

[0053] As indicated, an important aspect of the present invention is the dewatering, thickening and removal of the spent SPAC 12 (and contaminants adsorbed thereto). When the SPAC reaches breakthrough, the influent flow to the system is stopped, the feed pump 16 is stopped and the SPAC feed valve 18 is closed. The recycle pump 26 continues to run, pumping the slurry from the adsorption reactor 20 at a rate of 10 Qi. During the dewatering process, the ceramic membrane filter 30 continues to pump the permeate at a rate of 1 Qi and the retentate continues to be returned to the adsorption reactor 20 at a rate of 9 Qi. After a period of time based on the size (retention time) of the adsorption reactor 20, the spent SPAC is dewatered and concentrated enough to be removed for disposal. The desired concentration of the SPAC 12 slurry when removed is, by way of example, 10 grams of carbon / liter. If the concentration is too high, it is difficult to remove from the system.

[0054] It should also be noted that when concentrating the retentate for removal after the influent flow Qi to the adsorption reactor 20 is stopped, in practice the permeate is typically not removed at the full 1Q flow rate desired for the overall process. Instead, the permeate is scaled down to less than 1Q so that the retentate is not too thickened or concentrated for effective removal from the system.

[0055] When backwashing of the membrane of the ceramic membrane filter 30 is required, the influent flow for dewatering is stopped. The recycle pump 26 is closed and the drain valve 59 is opened. The permeate valve 33 is closed and the backwash valves 63 and 66 are opened. The backwash pump 61 is started and the permeate is pumped from the permeate tank 50. The permeate flows through the backwash line 62 to the backwash tank 70. If desired, chemicals may be added to the permeate through the backwash line 62 via the chemical line 65. The permeate or chemically enhanced permeate flows from the backwash line 62 into the permeate line 32 in countercurrent to the permeate. The backwashed permeate passes through the ceramic membrane filter 30 in the opposite direction to filtration. The backwash liquid flows back to the slurry effluent line 22 and is removed through the open drain valve 59.

[0056] The above description is not intended to limit the meaning of the words used therein or the scope of the following claims which define the present invention. Rather, it is contemplated that there may be structural, functional or consequential modifications which are not substantive changes, and that all such non-substantial changes in the claimed invention are intended to be covered by the claims. Thus, while preferred embodiments of the present invention have been illustrated and described, it will be understood that changes and modifications can be made without departing from the claimed invention. Furthermore, although the term "claimed invention" or "invention" may be used in the singular form herein, it will be understood that there are multiple inventions which have been described and claimed.

[0057] Various features of the invention are set forth in the following claims.

Claims

1. 1. A method for removing PFAS from water, comprising the steps of: 1) adding submicron powdered activated carbon (SPAC) to the influent stream of water to be treated; 2) combining the SPAC with the water to be treated; 3) introducing the mixture of SPAC and water into an adsorption reactor for treatment; 4) maintaining the mixture in the adsorption reactor for a sufficient time for the SPAC to adsorb the PFAS in the water, with a residence time in the adsorption reactor of 30 to 60 minutes and a SPAC concentration of 0.5 to 2 grams of carbon / liter; and 5) transferring the mixture from the adsorption reactor using a recycle pump to a high rate ceramic membrane filter unit operating in cross-flow filtration, where the treated water is discharged as permeate and the SPAC is returned to the adsorption reactor as retentate, the flow rate of the water influent stream through a slurry feed line is 1Q, and the SPAC / influent mixture is pumped by the recycle pump from the adsorption reactor via a slurry effluent line to the high rate ceramic membrane filter unit at a flow rate 10 times that of the influent (10Q).

2. The method of claim 1, comprising the steps of: 1) removing a concentrate of the SPACs and adsorbed PFAS from the high velocity ceramic membrane filter unit via a concentrate line after the SPACs reach breakthrough; and 2) Adding fresh SPAC to the water influent stream to continue removing PFAS.

3. 2. The method of claim 1, wherein the permeate is discharged from the high velocity ceramic membrane filter unit at a flow rate of 1 times the influent flow rate and the retentate is returned to the adsorption reactor at a flow rate (9Q) of 9 times the influent flow rate.

4. The method of claim 3 , wherein the SPACs have an average particle size of less than 0.1 microns.

5. 3. The method of claim 2, wherein the SPACs and adsorbed PFAS are thickened for removal by stopping the influent flow to the adsorption reactor and continuing to operate the recycle pump until the retentate is thickened and then removed via the concentrate line for waste disposal.

6. 5. The method of claim 4, wherein the high rate ceramic membrane filter unit has a nominal pore size of 0.1 microns.

7. 1. A system for removing PFAS from water, the system comprising: 1) a pressurized adsorption reactor in fluid communication with an influent line, and a SPAC feed line in communication with the influent line for adding a SPAC to the influent, the adsorption reactor receiving an influent stream of water to be treated and submicron powdered activated carbon (SPAC), the adsorption reactor having a capacity to hold the influent and SPAC slurry for a sufficient retention time such that the PFAS to be removed are adsorbed by the SPAC in the slurry, the SPAC having a concentration of 0.5 to 2 grams carbon / liter; 2) a slurry effluent line connected to the outlet of the adsorption reactor and a recycle pump in the slurry effluent line; 3) a cross-flow ceramic membrane filter unit in fluid communication with the slurry effluent line of the adsorption reactor, wherein the recycle pump transfers the PFAS-adsorbed SPACs to the cross-flow ceramic membrane filter unit at a high flow rate, the cross-flow ceramic membrane filter unit separates treated water as a permeate from the PFAS-adsorbed SPACs, and wherein the flow rate of the water influent stream through a slurry feed line is 1Q, and a mixture of the SPACs and influent is pumped by the recycle pump from the adsorption reactor via the slurry effluent line to the ceramic membrane filter at a flow rate 10 times that of the influent (10Q); 4) a permeate line in fluid communication with the cross-flow ceramic membrane filter unit for removing the treated water as a permeate; 5) a retentate line in fluid communication with the cross-flow ceramic membrane filter unit and the adsorption reactor, which returns the permeate-removed SPAC slurry to the influent line; and 6) A concentrate line to remove SPACs after breakthrough.

8. The system of claim 7 , wherein the SPACs have an average particle size of less than 0.1 microns.

9. 9. The system of claim 8, wherein the cross-flow ceramic membrane filter unit has a nominal pore size of 0.1 microns.

10. The system of claim 9 including a SPAC supply system in fluid communication with the influent line.

11. 8. The system of claim 7, wherein the PFAS to be removed includes perfluoroalkyl and polyfluoroalkyl materials.

Images