Patent Application
20240391797
Widespread use of perfluoroalkyl substances and/or polyfluoroalkyl substances (“PFAS”). in manufacturing processes, consumer goods, and firefighting foams has directly contributed to contamination of municipal drinking water supplies at concentrations significantly exceeding recommended exposure levels. The use of aqueous film-forming foams (AFFF) for firefighting training has particularly contributed to the water contamination problem. PFAS show high toxicity, even in the low parts per trillion (ppt) range, and the stability of the C-F bond means that many PFAS are perpetually stable in the environment.
Current remediation methods for PFAS-impacted sites primarily include (a) filtration of PFAS from drinking water and (b) remediation of PFAS in contaminated soils. The most commonly used filtration technologies include PFAS adsorption with granulated activated carbon (GAC) or ion exchange resins (IXR). Soil remediation may involve soil washing followed by filtration with GAC or IXR. All filtration and fixation technologies serve to capture, but not destroy, PFAS molecules. End-of-life disposal with complete defluorination (cleaving the C—F bonds) is needed to eliminate the risk of subsequent environmental re-contamination, or future liability.
For highly contaminated sites or water supplies, the use of regenerable adsorbent media (i.e., regenerable IXR) is advantageous for reducing overall project costs. In the IXR or GAC regeneration process, a fluid is used to remove adsorbed contaminants from the surface of solid IXR or GAC particles. This regeneration fluid may contain methanol and NaCl, among other compositions. After regeneration, the contaminant-loaded regeneration fluid may be distilled for recycling of the solvent (e.g. methanol), leaving a “still bottom” in need of disposal. These still bottoms typically contain high quantities of NaCl, total organic carbon (TOC), and environmental contaminants (e.g. PFAS). Destruction of IXR still bottoms or GAC regeneration byproducts is a significant technical challenge.
Other PFAS capture and/or concentration technologies can be used to separate PFAS from soil or water, which also produce a PFAS-rich byproduct. These include reverse osmosis (RO) or nanofiltration (NF) which produce a reject brine, in situ or ex situ foam fractionation (producing a foam fractionate), soil washing (producing soil wash water), thermal desorption (producing a condensate stream), or some combination. The destruction challenge also applies to these remediation byproducts.
Several technologies have been investigated as general PFAS destruction processes, including electrochemical oxidation over boron-doped diamonds, sonochemical destruction, high-temperature incineration, alkaline hydrolysis, plasma treatment, supercritical water oxidation, and others. However, few destructive technologies have robustly demonstrated the ability to consistently and completely break all C-F bonds, and several are known to produce short-chain PFAS as treatment products. One issue with processes conducted at ambient pressures is the off-gassing of low molecular weight (MW) fluorocarbons, which can volatilize and escape the reaction environment. While most of the aforementioned technologies have been demonstrated to destroy perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), few have been demonstrated to achieve complete mineralization.
Alkaline hydrolysis is an effective process for neutralizing or destroying several hazardous wastes, including chemical warfare agents (CWAs), polychlorinated biphenyls (PCBs) and perfluoroalkyl and polyfluoroalkyl substances (PFAS). Alkaline hydrolysis occurs within the subcritical liquid phase of water (typically T=100-374° C., P=0.1-50 MPa) amended with a suitable base, such as NaOH, KOH, LiOH, NH4OH, and/or CaOH2. Alkaline conditions promote decomposition mechanisms for many compounds and contaminants of interest.
This disclosure is related to a continuous hydrothermal alkaline reactor system and method for the treatment of contaminated environmental remediation and industrial wastewater treatment byproducts, including, but not limited to, adsorbent regeneration byproducts; which may include ion exchange resin (IXR) regeneration brine, IXR regeneration still bottoms, granular activated carbon (GAC) regeneration fluid, GAC regeneration still bottoms, RO reject brine, foam fractionate, soil wash water, thermal desorption condensate, wet scrubber wastewater, and others. These feedstocks contain a high concentration of the compound(s) targeted for capture by the adsorbent media, such as perfluoroalkyl and polyfluoroalkyl substances (PFAS), 1′4-Dioxane, other environmental contaminants, or other substances. The continuous hydrothermal alkaline reactor system facilitates the complete and effective breakdown of environmental contaminants which exist in high concentrations in these and other feedstocks.
In one embodiment, a method for destroying perfluoroalkyl and/or polyfluoroalkyl substances includes introducing a liquid byproduct including a perfluoroalkyl and/or polyfluoroalkyl substance to a reactor; hydrolyzing in the reactor under alkaline conditions the perfluoroalkyl and/or polyfluoroalkyl substance in the byproduct; and producing a continuous stream of product from the reactor, wherein the byproduct is selected from:
In one embodiment, a method for destroying a contaminant in a byproduct from an adsorbent media regeneration or reactivation process includes introducing a byproduct from an adsorbent media regeneration or reactivation process to a reactor; and hydrolyzing in the reactor under alkaline conditions a contaminant in the byproduct, wherein the byproduct is a liquid selected from:
In one embodiment, both methods may include mixing the byproduct with an alkaline amendment before the reactor.
In one embodiment, both methods may use an alkaline amendment from NaOH, KOH, LiOH, NH4OH, Ca(OH)2 or a combination thereof.
In one embodiment, both methods may introduce the byproduct and an aqueous alkaline solution separately through a first inlet and a second inlet to the reactor.
In one embodiment, both methods may be used to destroy a contaminant that is selected from a perfluoroalkyl compound, a polyfluoroalkyl compound, perfluorooctanesulfonate, perfluorooctanoic acid, 1′4-dioxane, a polycholorinated biphenyl, a hydrocarbon, and a volatile organic carbon, or a combination thereof.
In one embodiment, in the second method, an absorbent media in the absorbent media regeneration or reactivation process is granular activated carbon or an ion exchange resin.
In one embodiment, both methods may include cooling an effluent leaving the reactor to produce a liquid effluent.
In one embodiment, both methods may include cooling the effluent with the byproduct before introducing to the reactor.
In one embodiment, both methods may include introducing a neutralizing agent to the liquid effluent to adjust pH of the liquid. In one embodiment, both methods may include HCl or H2SO4 as the neutralizing agent.
In one embodiment, both methods may include adding a calcium salt to the liquid effluent to produce precipitates, wherein the precipitates include CaF2 or CaSO4 or both.
In one embodiment, both methods may include controlling temperature and pressure within the reactor to undergo hydrolysis of the contaminant.
In one embodiment, both methods may include measuring one or more parameters of the liquid effluent including a concentration of the contaminant in the liquid effluent, a concentration of destruction byproducts such as F— ion concentration, or the pH of the liquid effluent, or a combination thereof.
In one embodiment, a system for destruction of a contaminant in a byproduct includes a reactor configured for continuous flow through the reactor; at least one pump has an inlet connected to a reservoir containing a byproduct with a contaminant, and an outlet of the at least one pump is connected to an inlet to the reactor; a heater to control internal temperature of the reactor; a pressure regulator to control internal pressure of the reactor; a heat exchanger to cool reactor effluent, wherein the byproduct is a liquid selected from:
In one embodiment, the heat exchanger is a recuperative heat exchanger that cools the reactor effluent with the byproduct.
In one embodiment, the byproduct further includes an alkaline amendment mixed in before the reactor.
In one embodiment, the pressure regulator is placed after an outlet from the reactor.
In one embodiment, the system further comprises a separator placed after the pressure regulator to separate liquid in the reactor effluent.
In one embodiment, the system further comprises an acid reservoir containing neutralizing acid, wherein the acid reservoir is configured to introduce the neutralizing acid to the separated liquid.
In one embodiment, the system further comprises a reagent reservoir containing a reagent, wherein the reagent reservoir is configured to introduce the reagent to the separated liquid to cause precipitation of reaction products.
In one embodiment, the system further comprises a second pump having an inlet connected to a reservoir containing an alkaline solution, wherein an outlet of the second pump is connected to the inlet of the reactor.
In one embodiment, the byproduct is a liquid selected from a wet scrubber used to capture contaminants in the emission stream of incinerators, rotary kilns or other thermal destructive processes.
In one embodiment, a method for destruction of a contaminant in a byproduct includes introducing a byproduct with a contaminant into a reactor configured for continuous flow through an interior of the reactor; maintaining a temperature from 200° C. to 400° C. throughout a length of the interior of the reactor; maintaining a pressure above 22 MPa in the interior of the reactor; introducing a byproduct containing a contaminant to the reactor; introducing an alkaline solution to the reactor to achieve an overall loading from 0.01 M to 20 M OH−; allowing the byproduct to undergo hydrolysis in the reactor; and producing a continuous stream of product from the reactor.
In one embodiment, the overall loading is from 5 M to 20 M OH−.
In one embodiment, the contaminant is selected from a perfluoroalkyl compound, a polyfluoroalkyl compound, perfluorooctanesulfonate, perfluorooctanoic acid, 1′4-dioxane, a polycholorinated biphenyl, a hydrocarbon, and a volatile organic carbon, or a combination thereof.
In one embodiment, a concentration of the contaminant in the product is less than or equal to 0.01% of a concentration of the contaminant in the byproduct.
In one embodiment, the byproduct is a liquid from an adsorbent media regeneration or reactivation process, wherein the liquid byproduct is,
In one embodiment, the byproduct is selected from:
In one embodiment, an interior of the reactor is a metal alloy having at least 50% Ni by weight or a stainless steel.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The foregoing aspects and many of the attendant advantages of this disclosure will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
Of the above destruction technologies, this disclosure determines that alkaline hydrolysis when carried out continuously is particularly advantageous for processing adsorbent regeneration byproducts as (i) methanol is stable and thus could be recovered post-processing, (ii) salts remain fully soluble and do not cause issues with precipitation and scale buildup, and (iii) the alkaline hydrolysis process can destroy PFAS and other contaminants with greater than 99.99% destruction efficiencies and without the production of unwanted byproducts. A hydrolysis reaction is a decomposition reaction in which the contaminant to be destroyed (e.g. PFAS) reacts with at least water. Hereafter, “PFAS” is intended to refer to one or more perfluoroalkyl substance and/or one or more polyfluoroalkyl substance.
The herein described system includes a continuous hydrothermal alkaline reactor designed to process liquid byproducts under alkaline conditions. The byproducts contain perfluoroalkyl and/or polyfluoroalkyl substances generated by processes, such as adsorbent regeneration processes, ozone foam fractionate processes, thermal treatments of soil or spent sorbents, aqueous film-forming foams, reverse osmosis reject brine, nanofiltration reject brine, wet scrubbers associated thermal destructive processes, and the like. In one embodiment, the continuous hydrothermal alkaline reactor is operated at temperature and pressure conditions in the range of 200 to 400° C. and 0.1 to 50 MPa, where the primary working fluid and reaction medium is water.
An example of a continuous reactor system 100 is illustrated in
In one embodiment, the two pumps may be used in parallel, where the first pump 110 pumps the influent liquid byproduct and a second pump 112 pumps the alkaline amendment solution. In one embodiment, the two pump outlet flows are mixed downstream to create an overall desired alkaline concentration. In one embodiment, the influent liquid byproduct line and the influent alkaline amendment line each have a separate inlet into the reactor 124.
In one embodiment, after the high pressure pumps 110, 112, both the influent liquid byproduct line and the influent alkaline amendment line can include pressure meters 106, 108. In one embodiment, both the influent liquid byproduct line and the influent alkaline amendment line can pass through respective heaters 114, 116. In one example, the effluent product line from the reactor can be used to preheat both the influent byproduct and the influent alkaline amendment in preheaters 114, 116. In one embodiment, after the preheaters 114, 116, both the influent liquid byproduct line and the influent alkaline amendment line can include temperature sensors 118, 120, such a thermocouples.
In one embodiment, the influent liquid byproduct line and the influent alkaline amendment line are premixed to a desired alkaline concentration before entering the reactor 124, and both liquid byproduct and alkaline amendment are introduced as a mixture through a single inlet in the reactor 124. Premixing the liquid byproduct and the alkaline amendment allows the use of a single pump and reduces the instrumentation and one preheater. The premixing can take place in a reservoir upstream of the pump.
In one embodiment, the reactor 124 includes a cylindrical hollow vessel that is closed on both ends with the exception for any inlets for the influent lines and outlet for the effluent product line. The reactor 124 is used for containing the compound destruction reactions at the desired temperature and pressure, and for the desired reaction residence time. In one embodiment, the reactor 124 is preferably insulated to prevent heat loss to the environment.
The reactor 124 vessel is adequately designed to withstand the chemical compositions, temperatures, and pressures described in this disclosure. In one embodiment, the reactor 124 vessel can include instrumentation 122 to measure internal temperature and pressure at any point along the length of the vessel 124 or before or after the vessel 124. In one embodiment, the reactor 124 vessel is devoid of interior baffles or other interior flow modifying structures. In one embodiment, the reactor 124 vessel includes one or more heaters (not shown) for bringing the reacting mixture to the desired operating temperatures. In one embodiment, the heater(s) may be electrical heaters (e.g. band heaters, wrap heaters, cartridge heaters, radiant heaters, immersion heaters, strip heaters, furnace). In one embodiment, the heater(s) may be a burner. In one embodiment, the heater(s) may be a fluidized sand bath or similar.
In one embodiment, the reactor 124 vessel, particularly the interior of the reactor vessel is made of a predominantly nickel-containing alloy (i.e., equal to or greater than 50% Ni by weight), such as alloys designated as Inconel®, Hastelloy®, and the like. In one embodiment, the reactor 124 vessel, particularly, the interior of the reactor vessel is made of stainless steel alloys.
In one embodiment, the reactor outlet line includes a temperature sensor 126, such as a thermocouple.
In one embodiment, the reactor outlet line includes a heat exchanger 128 for cooling the reacting mixture. In one embodiment, the heat exchanger 128 is preferably a recuperative heat exchanger to heat the influent flows flowing into the reactor 124, while cooling the fluid flowing out of the reactor 124. In one embodiment, the heat exchanger 128 and reactor 124 may be one single, combined vessel.
In one embodiment, the reactor outlet line is directed to the preheaters 114 and 116 to preheat the influent liquid byproduct and the alkaline amendment prior to their introduction to the reactor 124. In one embodiment, the heat exchanger 128 may be optional when the preheaters 114, 116 remove sufficient heat from the product rendering the heat exchanger 128 unnecessary.
In one embodiment, the reactor outlet line includes a back-pressure regulator 130. The back-pressure regulator 130 can be a throttling valve, capillary tube, or similar device that is used for reducing the pressure of the outgoing flow to ambient pressures while maintaining the internal pressure of the reacting environment within the reactor 124 vessel.
In one embodiment, a vapor-liquid separator 138 is used after the depressurization device 130. The vapor can be discharged through a separate outlet from the liquid. The vapor can be collected and disposed of through filtration or incineration, for example. The liquid effluent leaving the separator 138 may be further treated prior to disposal.
In one embodiment, the continuous hydrothermal alkaline reactor system 100 includes an acid reservoir 114 containing an acid, such as hydrochloric acid (HCl) or sulfuric acid (H2SO4). The pump 132 is used to introduce a neutralizing acid (e.g. HCl) to the liquid effluent in the reactor outlet line in order to buffer the pH to near-neutral (between pH=4 and 10) after reaction, cooling, and depressurization.
In one embodiment, after the introduction of the acid, the reactor product line is connected to a liquid collection vessel 136. The liquid collection vessel 136 is used for containing the liquid effluent prior to discharge.
In one embodiment, additional reagents may be added to the collected liquid before, within, or after the liquid collection vessel 136 to precipitate reaction products. For example, the use of CaCl2, Ca(OH)2 or similar can be used to form and precipitate CaF2 (or similar insoluble fluorides) for collection and disposal.
In one embodiment, the continuous hydrothermal alkaline reactor system may also provide for pressure relief, such as a rupture disc, pressure relief valve, or similar device that is used to prevent over-pressurization of the reactor vessel 124.
In one embodiment, temperature-sensing devices, such as thermocouple(s) 118, 120, 122, and 126 are positioned before and after the reactor 124 and along the length of the reactor to measure the reacting flow temperature at one or several locations.
In one embodiment, pressure gauges, pressure sensors, or similar devices are used to measure the internal pressure at one or several locations.
In one embodiment, a control and data acquisition system (not shown) is used to monitor and control the operating parameters based on one or more of the instrumentation, including temperature and pressure sensors.
In one embodiment, the collected liquid may be monitored for pH and/or ion concentrations via an immersion probe.
In one embodiment, the collected liquid may be periodically sampled and analyzed for concentrations of the original contaminant in the influent.
In one embodiment, the continuous hydrothermal alkaline reactor system 100 may be mounted on or in a trailer, a pallet, or within a shipping container to allow the system 100 to be transported and deployed at a site.
In one embodiment, the continuous hydrothermal alkaline reactor system 100 may be contained within a safety enclosure to ensure operator safety. The safety enclosure may be ventilated to prevent off-gassing of harmful chemicals in the event of a reactor leak. The ventilation system may include an air filtration system (e.g. carbon, electrostatic precipitator) to prevent release of harmful gases to the environment in the event of a reactor leak.
Features of the method of
In block 202, liquid byproducts containing one or more perfluoroalkyl and/or polyfluoroalkyl substances are selected from one or more of the following feedstocks.
In one embodiment, any liquid contaminated with PFAS having a total level about or above 100 ppb is a suitable feedstock for the method in
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
In one embodiment, the liquid byproduct in the method of
Embodiments of liquid byproducts include contaminants. Contaminants can include one or more of the following, perfluoroalkyl substances and polyfluoroalkyl substances (PFAS), perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA), 1′4-Dioxane, polychlorinated biphenyls (PCBs), hexafluoropropylene oxide dimer acid (HFPO-DA), hydrocarbons, volatile organic carbons (VOCs), and combinations thereof.
In one embodiment, the liquid byproduct used as reactor feedstock in the method of
In one embodiment, the liquid byproduct is a brine containing water, 20% wt. or less of a salt or base, and 1% wt. or less of the contaminant.
In one embodiment, the liquid byproduct is a solution containing 50 to 90 vol % of an alcohol, 10 to 50 vol % of water, 1 to 5 wt % of a salt or a base, and the contaminant.
In one embodiment, the liquid byproduct is a brine containing about 1 to 20 wt % salt or base (e.g. NaCl) and about 0.01 to 1 wt % of the adsorbed contaminant (still bottoms).
In one embodiment, the liquid byproduct is a solution containing an alcohol, a salt or base, and the adsorbed contaminant (regeneration fluid).
Embodiments of liquid byproducts can include one or more alcohols. In one embodiment, the alcohol is methanol. Embodiments of liquid byproducts can include one or more salts and bases. In one embodiment, the salt or the base is sodium chloride (NaCl).
Embodiments of adsorbed contaminants present on the adsorbent media, such as ion exchange resins or granular activated carbon, may include perfluoroalkyl substances and polyfluoroalkyl substances (PFAS), perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA), 1′4-Dioxane, a polychlorinated biphenyls (PCBs), hexafluoropropylene oxide dimer acid (HFPO-DA), hydrocarbons, volatile organic carbons (VOCs), and combinations thereof.
Referring to
In
In one embodiment, the OH− overall loading is from 0.01 to 5 M. “M” refers to molarity in moles per liter (mol/L). Overall loading means the concentration in the reactor (i.e., after mixing with the feedstock and/or other influent streams). In one embodiment, the OH− overall loading is from 5 M to 10 M or even higher. In one embodiment, the OH overall loading is from 5 M to 20 M. In one embodiment, the amount of alkaline amendment is sufficient to have an overall loading of OH greater than 5 M. The level of 5 M OH can drive rapid reactions. In one embodiment, an overall loading greater than 0.01 M OH is used to destroy perfluorocarboxylic acids. In one embodiment, an overall loading greater than 1 M OH is used to destroy perfluorosulfonic acids.
In
In one embodiment, a heater may be used to adjust the internal reactor temperature. Heaters include, but are not limited to, electrical heaters (for example, band heaters, wrap heaters, cartridge heaters, radiant heaters, immersion heaters, strip heaters, and furnaces), burners, fluidized sand bath, and the like.
In
In on embodiment, the internal pressure within the pressure 124 vessel is regulated by a back-pressure regulator, such as a throttling valve, capillary tube, or similar device that is used for reducing the pressure of the outgoing flow to ambient pressures while maintaining the internal pressure of the reacting environment within the reactor vessel
In
Referring to block 206 of
In one embodiment, one or more parameters of the liquid effluent in the reactor product is analyzed. Parameters that may be measured include the concentration of the contaminant in the liquid effluent to determine the destruction efficiency of the contaminant for disposal, the concentration of destruction byproducts such as F− ion concentration, and the pH of the liquid effluent, or a combination thereof.
In one embodiment, the destruction of the contaminant using the continuous hydrothermal alkaline reactor produces a concentration of the contaminant in the liquid effluent product that is less than or equal to 0.01% of a concentration of the contaminant in the influent feedstock byproduct In one embodiment, the PFAS levels in a continuous reactor effluent is at or below 70 ng/L total PFAS. For example, from a starting concentration of 100 ug/L to 10 mg/L this translates to an overall reduction in PFAS concentration of greater than 99.99% to greater than 99.9999%. In one embodiment, there is an associated production of fluoride corresponding to the initial PFAS concentration in the feedstock (e.g., 99.99% to 99.9999% defluorination efficiency). In one embodiment, the reactor output can be adjusted to neutral pH between 4 and 10, through the use of the acid for pH adjustment.
In block 314, a heat exchanger can be used to cool the product effluent from the reactor. In one embodiment, the heat exchanger is a recuperative heat exchanger that preheats the influent streams, such as the influent liquid byproduct feedstock, the solution of the alkaline amendment, or both. When the liquid byproduct and the alkaline amendment are not pre-mixed prior to the reactor, there can be two heat exchangers to heat each of the influent streams.
In block 316, the product effluent may be introduced into a vapor-liquid separator. In the vapor-liquid separator, the product effluent after the heat exchanger is provided with the space for allowing the separation of any non-condensable vapors or volatile gases. The non-condensable vapors or volatile gases will be vented usually from the top of the separator, and the liquid effluent will be collected in the bottom portion, which may then be further processed.
In block 318, the liquid effluent is neutralized by adding a neutralizing agent. In one embodiment, the neutralizing agent is an acid, such as aqueous hydrochloric acid (HCl). In one embodiment, the pH of the liquid effluent after neutralizing is in the range of 4 to 10.
In block 320, precipitation may be used to extract fluoride or sulfates from the liquid effluent. For example, the use of the reagent CaCl2, Ca(OH)2 or similar can be used to form and precipitate CaF2 or CaSO4 or both for collection and disposal.
Experimental Apparatus and Procedures. A continuous, tubular reactor can be used to evaluate the effect of system configuration and flow profiles on PFAS destruction rates. A process flow diagram (PFD) of the continuous hydrothermal alkaline reactor system is shown in
Reagents. Ion exchange resin still bottoms are provided from an industrial partner, with approximate characteristics of ˜10 wt % NaCl, and ˜1000 ppm total PFAS. NaOH (>97 wt %, Fisher Scientific) is used for reagent preparation. HCl (36.5-38.0 wt %, Millipore Sigma) is used for pH buffering post-treatment.
Data Collection and Analysis. Samples are collected in HDPE sample containers after treatment. HCl is added to samples to buffer the pH to between 5 and 7, as confirmed by pH strips. The dilution effect of HCl addition is factored into correcting the measured effluent characteristics. The solution is then filtered to remove any solid precipitates. Untreated and treated IXR still bottoms are analyzed for 26 PFAS analytes via commercial LC-MS/MS. Samples are also measured for fluoride ion concentration using a handheld fluoride ion-selective electrode (ISE).
Experimental Conditions. The continuous reactor can be operated at a constant internal temperature of 350° C., and residence times of 15, 30, 60, 90, and 120 min. Internal pressure is held at 22 MPa. The overall loading of NaOH is maintained at 5 M.
Over 1 gallon of sample from the FTP at Fairbanks International Airport was collected for feasibility testing in the continuous reactor of
Samples were processed in the continuous reactor at 350° C., 25 MPa, residence times from 2.5 to 30 min, and NaOH loadings from 0.1 to 5 M. The reactor was flushed with deionized (DI) water between each experiment to minimize cross-contamination. One sample was collected during reactor flushing to quantify baseline PFAS levels in the effluent, and one sample was collected without heating or pressurizing the reactor, to quantify PFAS loss within the system due to adsorption. About 60 mL of sample was collected for each processing condition. Three samples run at 5 M-NaOH loading were collected for analysis of DRO and RRO levels after continuous hydrothermal alkaline hydrolysis.
After product collection, samples were buffered to a near-neutral pH through the addition of 36 to 38.5% HCl solution. Samples were then sent for analysis via commercial LC-MS/MS analysis of 28 PFAS analytes. Three samples were analyzed for DRO and RRO concentrations via methods AK102 and AK103. PFAS levels in the effluent were determined by correcting for dilution by HCl.
Results from the analysis of all treated and untreated samples are summarized in Tables S1 to S4.
As shown in
Roughly, the observed PFOS destruction kinetics in the continuous system is about 10 times faster than PFOS destruction in stainless steel batch reactors with 5 M-NaOH loading. However, this drops to an about 1.6× rate increase at 1 M-NaOH loading. This suggests that continuous reactors are much more sensitive to NaOH concentration.
Diesel range organics (DRO) and residual range organics (RRO) are long-chain hydrocarbon co-contaminants, present at sites where hydrocarbon fuels have been used. Both DRO and RRO are present in the FTP water, at average levels of 18.2 and 7.81 mg/L respectively.
As shown in Table S4, continuous hydrothermal alkaline hydrolysis treatment for 5, 15, and 30 minutes led to some reduction in both DRO and RRO. DRO was reduced by 50.8 to 78.0%, while RRO was reduced by 75.6 to 81.2% during tests. Previous work of Wu et al. in batch hydrothermal reactors has shown that some hydrocarbons are unstable under hydrothermal alkaline hydrolysis conditions, while some smaller hydrocarbons, such as methanol, are completely stable under hydrothermal alkaline hydrolysis conditions. Likely, some constituents in the DRO/RRO matrices are stable under continuous hydrothermal alkaline hydrolysis conditions, and there appears to be a limit in total treatment efficacy for these co-contaminants. Overall, the process managed to bring DRO and RRO levels closer to the discharge limits.
PFOA
6,750
414,120
PFOS
1,300,000
1,045,450
DRO (mg/L)
18.2
Not Analyzed
RRO (mg/L)
7.81
Not Analyzed
PFOA
4,111
PFOS
860,000
1,040,300
1,111,000
1,212,000
80,300
PFOS
522,613
670,283
440,917
409,673
PFOS
2,255
1,287
2,309
1,951
3,708
1,416
DRO (mg/L)
Not Analyzed
4.00
Not Analyzed
Not Analyzed
8.95
7.31
RRO (mg/L)
Not Analyzed
1.47
Not Analyzed
Not Analyzed
1.91
1.86
While illustrative embodiments have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the disclosure.
This application claims the benefit of U.S. Provisional Application No. 63/137,879, filed on Jan. 15, 2021, herein expressly incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/012214 | 1/13/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63137879 | Jan 2021 | US |
