Patent Publication Number: US-2022227644-A1

Title: Systems and methods of removing per- and polyfluoroalkyl substances (pfas) with calcium oxide

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of U.S. Provisional Application No. 63/139,499, filed Jan. 20, 2021, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to systems and methods for removing per- and polyfluoroalkyl substances (PFAS), and more specifically to systems and methods for removing PFAS using calcium oxide to produce calcium fluoride. 
     BACKGROUND 
     Per- and polyfluoroalkyl substances (PFAS) include more than 3,000 chemicals, each of which is characterized by a strong carbon-fluoride bond. This carbon-fluoride bond allows many PFAS to be resistant to grease, oil, water, and heat. Thus, PFAS have been used for decades in the production of stain- and water-resistant fabrics and carpeting, cleaning products, paints, cookware, food packaging, fire-fighting foams, and other such products. 
     However, because the carbon-fluoride bond of PFAS is so strong, the half-life of per-and polyfluoroalkyl substances is considerably long. These chemicals have even earned the nickname “forever chemicals” due to their long half-lives and inability to easily breakdown. Further, because PFAS are so prevalent in commercial products and processes and their half-lives are so long, the environment has become increasingly contaminated by PFAS over the years. This environmental contamination is especially concerning due to the adverse health effects attributed to PFAS, which can include kidney damage, immune system impairment, increased cholesterol levels, changes in liver enzymes, decreased vaccine response in children, low birth rates and birth defects, increased risk of some cancers, and reproductive issues, just to name a few. 
     SUMMARY OF THE DISCLOSURE 
     As explained above, PFAS have been used for decades in numerous different industries to produce various grease-, oil-, water-, and/or heat-resistant products. Due to the high levels of environmental contamination and numerous adverse health effects attributed to PFAS, there is a need to find a method of treating contamination sites to eliminate the PFAS that has accumulated over the years. However, developing such methods have been particularly challenging due to the strong carbon-fluoride bond of PFAS. This strong carbon-fluoride bond makes it very difficult to break down the PFAS into less toxic chemicals. 
     Accordingly, provided herein are systems and methods for removing PFAS with calcium oxide (CaO). When one or more PFAS reacts with CaO, it produces calcium fluoride, carbon dioxide, and water. These products, including calcium fluoride, are significantly less toxic than the products of known PFAS removal processes (e.g., sodium fluoride, lithium fluoride, iron fluoride). Thus, the systems and methods for PFAS removal provided herein achieve processes that effectively break down PFAS to produce less toxic substances. By treating PFAS contamination sites using the systems and methods provided herein, PFAS can be effectively removed to protect local communities from PFAS&#39;s adverse health effects. 
     In some embodiments, provided is a method of removing per- and polyfluoroalkyl substances (PFAS) from a contaminated stream, the method comprising: collecting a contaminated stream comprising one or more PFAS; concentrating the one or more PFAS of the contaminated stream to achieve a concentrated stream having greater than or equal to 0.01 wt. % PFAS; and removing the one or more PFAS of the concentrated stream by heating the concentrated stream in the presence of calcium oxide to produce calcium fluoride. 
     In some embodiments of the method, the contaminated stream comprises 1×10−7 to 5×10−3 wt. % PFAS. 
     In some embodiments of the method, the concentrated stream has less than or equal to 10 wt. % PFAS. 
     In some embodiments of the method, the contaminated stream comprises groundwater. 
     In some embodiments of the method, concentrating the one or more PFAS comprises routing the contaminated stream through a separation system. 
     In some embodiments of the method, the separation system comprises one or more of a filtration process, ion exchange process, distillation process, a chromatography process, or an evaporation process. 
     In some embodiments of the method, the separation system comprises an ion exchange column comprising resin. 
     In some embodiments of the method, concentrating the one or more PFAS of the contaminated stream comprises routing the contaminated stream through an ion exchange column comprising resin. 
     In some embodiments of the method, concentrating the one or more PFAS of the contaminated stream comprises regenerating the resin of the ion exchange column with methanol to produce an ion exchange outlet stream comprising the one or more PFAS and methanol. 
     In some embodiments of the method, concentrating the one or more PFAS of the contaminated stream comprises distilling methanol from the ion exchange outlet stream comprising the one or more PFAS and methanol. 
     In some embodiments of the method, concentrating the one or more PFAS of the contaminated stream comprises diluting the one or more PFAS of the ion exchange outlet stream with water to produce the concentrated stream. 
     In some embodiments of the method, removing the one or more PFAS of the concentrated stream by heating the concentrated stream in the presence of calcium oxide to produce calcium fluoride comprises heating the concentrated stream to 450-900 degrees Celsius. 
     In some embodiments of the method, the method comprises capturing residual one or more PFAS using granulated activated carbon. 
     In some embodiments, a per- and polyfluoroalkyl substance (PFAS) removal system is provided, the system comprising: a separation system comprising an inlet feed stream comprising one or more PFAS and an outlet concentrated stream comprising the one or more PFAS, wherein the outlet concentrated stream has a PFAS concentration greater than that of the inlet feed stream; and a furnace configured to receive the outlet concentrated stream and heat the outlet concentrated stream in the presence of calcium oxide (CaO) to remove the one or more PFAS and produce calcium fluoride. 
     In some embodiments of the system, the inlet feed stream comprises a contaminated stream having 1×10−7 to 5×10×3 wt. % PFAS. 
     In some embodiments of the system, the inlet feed stream comprises groundwater. 
     In some embodiments of the system, the outlet concentrated stream has greater than or equal to 0.01 wt. % PFAS. 
     In some embodiments of the system, the outlet concentrated stream has less than or equal to 10 wt. % PFAS. 
     In some embodiments of the system, the separation system comprises one or more of a filtration process, ion exchange process, distillation process, a chromatography process, or an evaporation process. 
     In some embodiments of the system, the separation system comprises an ion exchange column comprising resin. 
     In some embodiments of the system, the ion exchange column comprises an ion exchange outlet stream comprising the one or more PFAS and methanol. 
     In some embodiments of the system, the separation system comprises a distillation system configured to distill the methanol off the ion exchange outlet stream comprising the one or more PFAS and methanol. 
     In some embodiments of the system, the separation system comprises a dilution system configured to dilute the ion exchange outlet stream with water. 
     In some embodiments of the system, the outlet concentrated stream comprises water. 
     In some embodiments of the system, the furnace is configured to heat the outlet concentrated stream to 450-900 degrees Celsius. 
     In some embodiments of the system, the system comprises a granulated activated carbon tank configured to capture residual one or more PFAS from the furnace. 
     In some embodiments, any one or more of the features, characteristics, or elements discussed above with respect to any of the embodiments may be incorporated into any of the other embodiments mentioned above or described elsewhere herein. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates a PFAS removal process, according to some embodiments; 
         FIG. 2  illustrates a PFAS removal process, according to some embodiments; and 
         FIG. 3  illustrates a method of removing PFAS from a PFAS-contaminated stream, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Described below are exemplary embodiments of PFAS removal systems and methods. As explained above, PFAS has been used in commercial products for decades due in part to their non-stick and stain-resistant characteristics. However, because PFAS have such long half-lives (i.e., due to the particularly strong carbon-fluoride bond), they have leached into soil column and accumulated in the groundwater to contaminate the environment over the years. This is particularly concerning due to the adverse health risks associated with PFAS (i.e., kidney damage, immune system impairment, increased cholesterol levels, changes in liver enzymes, decreased vaccine response in children, low birth rates and birth defects, increased risk of some cancers, and reproductive issues, just to name a few). 
     Many PFAS treatment systems and methods known in the art remove PFAS and form other toxic substances. Thus, these systems and methods just replace one toxic chemical (a PFAS) with another toxic chemical (e.g., sodium fluoride, lithium fluoride, iron fluoride). However, the PFAS removal systems and methods provided herein treat one or more PFAS with calcium oxide (CaO) to remove the one or more PFAS and form calcium fluoride, carbon dioxide, and water, instead. Each of these products (i.e., calcium fluoride, carbon dioxide, and water) are less toxic than the products of known PFAS treatment systems and methods (e.g., sodium fluoride, lithium fluoride, iron fluoride). 
     The systems and methods described herein are configured to remove PFAS from a contaminated stream. PFAS, as used herein, may include any one or more of the following substances: AFFF, perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), GenX, perfluorobutane sulfonic acid (PFBS), perfluoropentanesulfonic acid (PFPS), perfluorohexane sulfonic acid (PFHxS), perfluoroheptanesulfonic acid PFHpS), perfluorononanesulfonic acid (PFNS), or perfluorodecanesulfonic acid (PFDS). 
     PFAS streams that may be treated by the PFAS removal systems provided herein can include groundwater, collected fire suppression foam (e.g., AFFF), water from natural bodies of water (e.g., creeks, rivers), soil, sediments, concentrated PFAS aqueous streams, PFAS ion exchange resins regeneration waste streams, fire suppression solutions stored in structures (Hangars, etc.) and firefighting equipment. 
     Prior to removing the PFAS from the contaminated stream, the stream may be treated to remove other contaminates in the stream. This pretreatment may include for example, separation methods, concentration methods, filtration methods (e.g., granulated activated carbon), distillation methods, for removing excess water, soil, minerals, solvents, sediments, and/or debris from the contaminated stream. Pretreatment methods may also include dilution methods for diluting concentrated PFAS of a concentrated PFAS stream to a suitable concentration for removal (i.e., CaO treatment). 
     The pretreated stream including PFAS can then be fed to a furnace comprising a calcium oxide source to remove the PFAS from the stream and produce calcium fluoride. The waste stream from this removal process is calcium fluoride, water, and carbon dioxide. The calcium fluoride can be disposed at municipal landfills after demonstration (toxicity characteristic leaching procedure (TCLP) analysis) of not being a RCRA hazardous waste. The water and carbon dioxide can be released into the atmosphere. In some embodiments, the carbon dioxide can be passed through an aqueous solution of calcium oxide at room temperature to form calcium carbonate to be landfilled. 
     Provided below are PFAS removal systems and methods for removing PFAS from a contaminated stream. The PFAS removal systems provided include systems that include a PFAS separation system and systems that do not include a PFAS separation system. Each are described in detail below. 
     PFAS Removal Systems 
     Described herein are systems for removing PFAS from contamination sites by treating the PFAS of a contaminated stream with calcium oxide (CaO) to produce calcium fluoride, carbon dioxide, and water.  FIG. 1 , which is described in detail below, depicts a system for removing a PFAS from a concentrated feed stream (i.e., a feed stream having a PFAS concentration suitable for calcium oxide treatment). In some embodiments, PFAS removal systems may include a PFAS separation system for separating PFAS from a dilute contaminated stream to form a concentrated PFAS stream that may then be treated with calcium oxide to remove the PFAS. For example,  FIG. 2  depicts a system having both a PFAS separation system (i.e., to form a concentrated PFAS stream for calcium oxide treatment) as well as a PFAS removal system (i.e., for treating a PFAS contaminated stream with calcium oxide). Note that the PFAS separation system is optional and is dependent upon the PFAS source material (i.e., the PFAS concentration of the PFAS source material). Below, both a PFAS removal system without a PFAS separation system (i.e., that depicted in  FIG. 1 ) as well as a PFAS removal system including a PFAS separation system (i.e., that depicted in  FIG. 2 ) are described. 
       FIG. 1  illustrates a PFAS removal process, according to some embodiments. As shown in  FIG. 1 , the input stream  102  comprises aqueous film-forming foam (AFFF) stockpile. AFFF is frequently used in the military to rapidly extinguish hydrocarbon fuel fires. However, over years of AFFF use, it has contaminated the environment and caused significant health concerns. 
     In some places, residual AFFF has been collected and contained in stockpiles. In these cases, the PFAS of the PFAS-contaminated stream (e.g., a stream comprising AFFF and water) does not need to be concentrated (i.e., by a PFAS separation system), since the concentration of the stockpile is suitable for calcium oxide treatment as-is. Accordingly, input stream  102  may already have a PFAS concentration suitable for PFAS removal (and not require concentration or other pretreatment). In some embodiments, input stream  102  may comprise any one or more PFAS. AFFF is only one example. 
     In some embodiments, the concentration of input stream  102  is 0.1-10, 1-8, or 1-5 wt. % PFAS. In some embodiments, the concentration of input stream  102  is less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 wt. % PFAS. In some embodiments, the concentration of input stream  102  is greater than or equal to 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 wt. % PFAS. 
     As shown in the Figure, input stream  102  is fed into furnace  104 . In some embodiments, input stream  102  may be fed into furnace  104  using air. Furnace  104  may be a muffle furnace. Furnace  104  may also be any kiln or heated oven. Furnace  104  comprises CaO source  106 , such as a CaO cartridge. In some embodiments, a CaO cartridge may include CaO pellets that can allow for a fast and easy flow. However, a CaO cartridge comprising CaO pellets exclusively may result in a less than acceptable PFAS reaction (e.g., 90%). Thus, in some embodiments, a CaO cartridge may include CaO pellets mixed with silica sand. The CaO pellets mixed with silica sand may significantly increase the reactive surface area while still exhibiting an acceptable flow rate (e.g., 1-4 cubic feet per minute through a 4 inch inside diameter cartridge). 
     CaO source  106  is configured to react with the one or more PFAS of input stream  102 . In some embodiments, system  100  may comprise a single furnace  104 . In some embodiments, system  100  may comprise more than one furnace  104 , such as two, three, four, five, six, or more furnaces  104 . In some embodiments, two or more furnaces  104  may be connected in series. In some embodiments, two or more furnaces  104  may be connected in parallel. In some embodiments, three or more furnaces  104  may be connected in a combination of series and parallel. 
     In some embodiments, system  100  may be a batch process. In some embodiments, system  100  may be a continuous process. In some embodiments of a batch process, system  100  may be configured to process input stream  102  in quantities of 0.1-1,000, 50-500, or 100-500 L. In some embodiments, system  100  may be configured to process input stream  102  in quantities of less than or equal to 1,000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 50, 10, 11, or 0.5 L. In some embodiments, system  100  may be configured to process input stream  102  in quantities of greater than or equal to 0.1, 0.5, 1, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, or 900 L. 
     In some embodiments of a continuous process, input stream  102  may enter furnace  104  at flow rates of 0.1 to 10 or 2 to 5 gallons per minute (GPM). In some embodiments, input stream  102  may enter furnace  104  at flow rates less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 GPM. In some embodiments, input stream  102  may enter furnace  104  at flow rates greater than or equal to 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 GPM. 
     Once the one or more PFAS have sufficiently reacted with CaO source  106 , some of the CaO is converted to calcium fluoride (CaF 2 ). Other products of the PFAS-CaO reaction (i.e., water and carbon dioxide) are released from furnace  104  in outlet stream  108 . In some embodiments, these products are released into the atmosphere. In some embodiments, the carbon dioxide may be bubbled through a calcium hydroxide solution to capture the carbon dioxide and avoid the release of greenhouse gases. In some embodiments, about 0.25 pounds of carbon dioxide is generated for each pound of PFAS mineralized. In some embodiments, about 66 liters of carbon dioxide is generated at 25° C. per pound of PFAS mineralized. 
     In some embodiments, systems provided herein include methods of capturing residual PFAS in the event not all PFAS is converted to CaF 2 , water, and carbon dioxide. For example, one such method may include tank  110 . As shown in the Figure, tank  110  includes granular activated carbon and sodium hydroxide. In the event not all PFAS reacts and some remains, it can be collected in tank  110  and disposed of as toxic waste, or extracted and recycled through the system. In some embodiments, tank  110  may comprise an alcohol. In some embodiments, system provided herein may comprise more than one tank  110 . For example, one tank  110  may comprise an alcohol, and a second tank  110  may comprises a hydroxide (e.g., sodium hydroxide, calcium hydroxide). 
     In some embodiments, to effectively react the PFAS and CaO, furnace  104  may be heated to 200-1500, 400-1000, or 500-800 degrees Celsius. In some embodiments, furnace  104  may be heated to less than or equal to 1500, 1200, 1000, 800, 600, 500, 400, or 300. In some embodiments, furnace  104  may be heated to greater than or equal to 200, 300, 400, 500, 600, 800, 1000, or 1200 degrees Celsius. In some embodiments, furnace  104  may comprise heating coils to maintain the desired temperature throughout the duration of the reaction. In some embodiments, furnace  104  operates at atmospheric pressure. 
     As explained above, the PFAS of input stream  102  can react with CaO under certain conditions to produce water, carbon dioxide, and CaF 2 . For example, Table 1 below shows an example reaction, including the Gibbs free energy of each reactant, each product, and of the complete reaction. 
     
       
         
           
               
               
               
               
            
               
                   
               
               
                   
                 Reactants 
                 Products 
                 Total  
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 2 
                 15 
                 7 
                 15  
                 16 
                 1  
                 ΔG 
               
               
                   
                 C 8 HF 15 O 2   
                 CaO 
                 O 2   
                 CaF 2   
                 CO 2   
                 H 2 O 
                 (kJ/mol) 
               
               
                   
               
               
                 ΔG 
                 −12,400 
                 −9049.5 
                 0 
                 −17,634 
                 −6310.4 
                 −237 
                 −2731.9 
               
               
                 (kJ/mol) 
               
               
                   
               
            
           
         
       
     
     In some embodiments, the energy required to operate the system and evaporate the regeneration waste is 300-1500 or 500-1000 Kcal/L of waste. In some embodiments, the energy required to operate the system and evaporate the regeneration waste is less than or equal to 1500, 1200, 1000, 800, or 500 Kcal/L of waste. In some embodiments, the energy required to operate the system and evaporate the regeneration waste is greater than or equal to 300, 500, 800, 1000, or 1200 Kcal/L of waste. 
     In some embodiments, the PFAS-CaO reaction may run to 80-100%, 85-99%, 90-99%, or 90-95% completion. In some embodiments, the PFAS-CaO reaction may run to less than or equal to 100%, 99%, 95%, 90%, or 85% completion. In some embodiments, the PFAS-CaO reaction may run to greater than or equal to 80%, 85%, 90%, 95%, or 99% completion. 
       FIG. 2  illustrates a system  200  comprising PFAS removal process  214  as well as a PFAS separation system  212  for concentrating the PFAS of a feed stream to form a concentrated PFAS stream suitable for calcium oxide treatment, according to some embodiments. Specifically, the process shown in  FIG. 2  includes a PFAS separation system  212  for concentrating one or more PFAS of a contaminated stream to more effectively remove the one or more PFAS from the contaminated stream. Once the PFAS is concentrated by PFAS separation system  212 , it may be removed by PFAS removal system  214 . Each component of both the PFAS separation system  212  and PFAS removal system  214  are explained below. 
     As explained above and depicted in  FIG. 2 , some systems described herein may include a PFAS separation system, such as PFAS separation system  212  of  FIG. 2 . In some embodiments, PFAS separation system  212  can include contaminated stream  216 , ion exchange system  218 , concentrated stream  220 , distillation system  222 , and dilution system  224 . 
     In some embodiments, contaminated stream  216  is obtained from groundwater. For example, PFAS can leech into a soil column and get washed down and dissolve into the groundwater. The PFAS then migrates with the groundwater in a contamination plume. To mitigate the contamination, wells can be installed near a downstream end of the contamination plume to extract contaminated groundwater and prevent it from migrating any further. To remediate a contamination plume, well can be installed closer to the contamination source area to pump the groundwater out from the source area and treated (e.g., using PFAS removal systems provided herein). Thus, contaminated stream  216  may be obtained from a well installed near a PFAS contamination source. 
     PFAS separation system  212  is configured to receive contaminated stream  216  (e.g., obtained from a contamination plume) comprising one or more PFAS and produce a concentrated stream  220  with the one or more PFAS, such that the PFAS concentration of concentrated stream  220  is greater than that of the input contaminated stream  216 . In some embodiments, the concentration of contaminated stream  216  is 1×10 −7  to 5×10 −3  wt. % PFAS. In some embodiments, the concentration of contaminated stream  216  is less than or equal to 5×10 −3 , 1×10 −3 , 1×10 −4 , 1×10 −5 , or 1×10 −6  wt. % PFAS. In some embodiments, the concentration of contaminated stream is greater than or equal to 1×10 −7 , 1×10 −6 , 1×10 −5 , 1×10 −4 , or 1×10 −3  wt. % PFAS. In some embodiments, contaminated stream  216  comprises contaminated groundwater. In some embodiments, contaminated stream  216  may comprise soil and sediment. 
     Separation system  212  is configured to concentrate the PFAS of contaminated stream  216  to achieve a concentrated stream  202  having a PFAS concentration suitable for CaO treatment (i.e., of PFAS removal system  214 ). In some embodiments, PFAS separation system  212  may include one or more of a filtration process, ion exchange process, distillation process, a chromatography process, an evaporation process, an extraction process, a heating process, a solvent extraction process, and/or a concentration process. 
     In some embodiments, separation system  212  comprises ion exchange system  218 . Ion exchange system  218  may comprise resin. Ion exchange system  218  may comprise two input streams: contaminated stream  216  comprising PFAS and a regeneration substance stream. Ion exchange system  218  may comprises two output streams: a PFAS-free effluent stream and a PFAS-methanol stream  220 . A PFAS-free effluent stream is formed after the PFAS of input contaminated stream  216  exchanges with components of the resin. Methanol may be used as a regeneration substance to regenerate the resin and remove the PFAS from the resin. After regeneration, PFAS-methanol stream  220  is produced. 
     In some embodiments, separation system  212  may include one, two, three, four, or more ion exchange systems  218 . In some embodiments, two or more ion exchange systems  212  may be connected in series or in parallel. In some embodiments, three or more ion exchange systems  212  may be connected in a combination of series and parallel. 
     In some embodiments, PFAS separation system  212  may be a batch process. In some embodiments, PFAS separation system  212  may be a continuous process. In some embodiments of a batch process, PFAS separation system  212  may be configured to process input contaminated stream  216  in quantities of 0.1-1,000, 50-500, or 100-500 L. In some embodiments, PFAS separation system  212  may be configured to process input contaminated stream  216  in quantities of less than or equal to 1,000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 50, 10, 11, or 0.5 L. In some embodiments, PFAS separation system  212  may be configured to process input contaminated stream  216  in quantities of greater than or equal to 0.1, 0.5, 1, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, or 900 L. 
     In some embodiments of a continuous process, input contaminated stream  216  may enter ion exchange system  218  at flow rates of 2 to 20 gallons per minute (GPM) per ion exchange unit. In some embodiments, input contaminated stream  216  may enter ion exchange system  218  at flow rates of less than or equal to 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, or 3 GPM per ion exchange unit. In some embodiments, input contaminated stream  216  may enter ion exchange system  218  at flow rates of greater than or equal to 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 GPM per ion exchange unit. 
     In some embodiments, PFAS-methanol stream  220  may be treated prior to removing the PFAS. For example,  FIG. 2  includes distillation system  222  and dilution system  224  configured to distill the methanol of PFAS-methanol stream  220  and dilute the PFAS to a suitable concentration, respectively. A concentrated stream  202  is formed after the output PFAS stream of ion exchange  218  (e.g., PFAS-methanol stream  220 ) has been treated by distillation system  222  and dilution system  224 . 
     Once the PFAS is concentrated (e.g., by PFAS separation system  212  of  FIG. 2  to form concentrated stream  202 ), the contaminated stream (i.e., concentrated stream  202 ) is treated by PFAS removal system  214  to remove the PFAS. In some embodiments, PFAS removal system can include inlet feed  202 , furnace  204 , CaO source  206 , outlet  208 , and residual PFAS collection  210 . 
     Concentrated stream  202  includes any or all of the features of input stream  102  described above with reference to  FIG. 1 . For example, concentrated stream may have a concentration of 0.1-10, 1-8, or 1-5 wt. % PFAS. In some embodiments, the concentration of concentrated stream  202  is less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 wt. % PFAS. In some embodiments, the concentration of concentrated stream  202  is greater than or equal to 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 wt. % PFAS. 
     After passing through PFAS separation system  212 , one or more PFAS may be removes by PFAS removal system  214 . PFAS removal system  214  may include concentrated stream  202 , furnace  204 , CaO source  206 , byproduct outlet  208 , and tank  210 . 
     Concentrated stream  202  may be routed to furnace  204  comprising calcium oxide (CaO) source, such as CaO source  206 . In some embodiments, furnace  204  may include any or all features of furnace  104  of  FIG. 1 . In some embodiments, CaO source  206  may include any or all features of CaO source  106  of  FIG. 1 . 
     In some embodiments, furnace  204  may be a muffle furnace, kiln, or gas furnace. In some embodiments, PFAS removal system  214  may comprise a single furnace  204 . In some embodiments, PFAS removal system  214  may comprise more than one furnace  204 , such as two, three, four, five, six, or more furnaces  204 . In some embodiments, two or more furnaces  204  may be connected in series. In some embodiments, two or more furnaces  204  may be connected in parallel. In some embodiments, three or more furnaces  204  may be connected in a combination of series and parallel. 
     In some embodiments, PFAS removal system  214  may be a batch process. In some embodiments, PFAS removal system  214  may be a continuous process. In some embodiments of a batch process, PFAS removal system  214  may be configured to process input stream  202  in quantities of 0.1-1,000, 50-500, or 100-500 L. In some embodiments, PFAS removal system  214  may be configured to process input stream  202  in quantities of less than or equal to 1,000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 50, 10, 11, or 0.5 L. In some embodiments, PFAS removal system  214  may be configured to process input stream  202  in quantities of greater than or equal to 0.1, 0.5, 1, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, or 900 L. 
     In some embodiments of a continuous process, the concentrated input stream  202  may enter furnace  204  at flow rates of 0.1 to 10 gallons per minute (GPM) per furnace unit. In some embodiments, concentrated input stream  202  may enter furnace  204  at flow rates less than or equal to 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5 GPM per furnace unit. In some embodiments, concentrated input stream  202  may enter furnace  204  at flow rates greater than or equal to 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, or 9 GPM per furnace unit. 
     Furnace  204  may be configured to heat concentrated stream  202 , allowing one or more PFAS of concentrated stream  202  to react with the CaO of CaO source  206 . Furnace  204  may be heated to any of the temperatures provided above with reference to furnace  104  of  FIG. 1 . After reacting, the CaO of CaO source  206  is replaced with calcium fluoride (CaF 2 ). Periodically, CaO source  206  will need to be replaced, since the CaO is replaced with CaF 2  as more PFAS is treated and removed. In some embodiments, CaO source  206  may include a cartridge. 
     Byproducts of the PFAS-CaO reaction (described above with respect to  FIG. 1  and shown in Table 1) are released from furnace  204  to the atmosphere and can include water and carbon dioxide. In some embodiments, PFAS removal system  214  can include a capture system such as tank  210  to capture any residual PFAS that does not react with the CaO of CaO source  206 . In some embodiments, tank  210  may comprise granular activated carbon and sodium hydroxide. Tank  210  may include any or all features of tank  110  of  FIG. 1 . 
     Methods of Removing PFAS from a Contaminated Stream 
     Also provided herein are methods of removing PFAS from a PFAS-contaminated stream. For example,  FIG. 3  illustrates a method  300  of removing per- and polyfluoroalkyl substances (PFAS) from a contaminated stream, according to some embodiments. Described below are methods that include separating (i.e., concentrating) PFAS from a contaminated stream (i.e., at step  304 ) and removing the PFAS from the contaminated stream (i.e., at step  306 ). 
     At step  302 , method  300  includes collecting a contaminated stream (e.g., contaminated stream  216  of  FIG. 2 ) comprising one or more PFAS. In some embodiments, the contaminated stream comprising one or more PFAS may include contaminated groundwater and/or contaminated soil. The contaminated stream may first be concentrated or separated. For example, the contaminated stream may be routed through a separation system (e.g., PFAS separation system  212  of  FIG. 2 ) configured to produce a concentrated PFAS stream (e.g., concentrated stream  202  of  FIG. 2 ). 
     At step  306 , the concentrated PFAS stream may be treated by a PFAS removal system (e.g., PFAS removal system  214  of  FIG. 2 , system  100  of  FIG. 1 ). For example, the PFAS of the concentrated PFAS stream may be removed by heating the concentrated stream in the presence of calcium oxide, producing calcium fluoride, water, and carbon dioxide. 
     Examples 
     In a stainless-steel container, 50 milliliters of a 1000 mg/L solution of perfluorooctanoic acid (PFOA) in methanol was mixed with 51 mg calcium oxide (CaO). The container was placed in a 65 degrees Celsius water bath to remove the methanol, producing a 101 mg powdered mixture of CaO and PFOA. 
     To cause the PFOA to react with the CaO to produce calcium fluoride (CaF 2 ), the container was placed in a muffle furnace at 400° C. The time durations tested for thermal treatment include 10, 20, 30 and 60 minutes. The maximum reaction pressure was less than 50 psig. A complete stoichiometric reaction yields residuals of 71 mg. 
     After the reaction, any unreacted PFOA was separated by rinsing the residuals with 100 mL methanol and separating the residuals from the methanol rinse using glass fiber filtration/and or centrifuge. The solids are treated with 100 ml of 0.1 N HCL to remove all CaO and leave behind CaF 2  which is dried at 150 C and weighed to confirm stoichiometric completion of the reaction. Both the filtrate and the residuals were stored in borosilicate glass vials at 4 degrees Celsius for GC/MS/MS confirmation analysis. 
     The foregoing description sets forth exemplary systems, methods, techniques, parameters, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure but is instead provided as a description of exemplary embodiments. 
     Although the description herein uses terms first, second, etc. to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another. 
     For any of the structural and functional characteristics described herein, methods of determining these characteristics are known in the art.