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==Supercritical Water Oxidation (SCWO)==
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==PFAS Destruction by Ultraviolet/Sulfite Treatment==  
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Supercritical water oxidation (SCWO) is a single step [[Wikipedia: Wet oxidation | wet oxidation]] process that transforms organic matter into water, carbon dioxide and, depending on the waste undergoing treatment, an inert mineral solid residue. The process is highly effective and can treat a variety of wet wastes without dewatering. The SCWO technology allows for the complete destruction of persistent and toxic organic contaminants such as [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | perfluoroalkyl and polyfluoroalkyl substances (PFAS)]], [[1,4-Dioxane | 1,4-dioxane]], and many more.  
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The ultraviolet (UV)/sulfite based reductive defluorination process has emerged as an effective and practical option for generating hydrated electrons (''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'' ) which can destroy [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) | PFAS]] in water. It offers significant advantages for PFAS destruction, including significant defluorination, high treatment efficiency for long-, short-, and ultra-short chain PFAS without mass transfer limitations, selective reactivity by hydrated electrons, low energy consumption, low capital and operation costs, and no production of harmful byproducts. A UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor">Haley and Aldrich, Inc. (commercial business), 2024. EradiFluor. [https://www.haleyaldrich.com/about-us/applied-research-program/eradifluor/ Comercial Website]</ref>) has been demonstrated in two field demonstrations in which it achieved near-complete defluorination and greater than 99% destruction of 40 PFAS analytes measured by EPA method 1633.
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
 
<div style="float:right;margin:0 0 2em 2em;">__TOC__</div>
  
 
'''Related Article(s):'''
 
'''Related Article(s):'''
  
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* [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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*[[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)]]
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* [[PFAS Transport and Fate]]
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*[[PFAS Ex Situ Water Treatment]]
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* [[Chlorinated Solvents]]
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*[[PFAS Sources]]
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*[[PFAS Treatment by Electrical Discharge Plasma]]
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*[[Supercritical Water Oxidation (SCWO)]]
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*[[Photoactivated Reductive Defluorination - PFAS Destruction]]
  
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'''Contributor(s):''' [[Kobe Nagar]] and [[Dr. Marc Deshusses]]
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'''Contributors:''' John Xiong, Yida Fang, Raul Tenorio, Isobel Li, and Jinyong Liu
  
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'''Key Resource(s):'''
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'''Key Resources:'''
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*Defluorination of Per- and Polyfluoroalkyl Substances (PFAS) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management<ref name="BentelEtAl2019">Bentel, M.J., Yu, Y., Xu, L., Li, Z., Wong, B.M., Men, Y., Liu, J., 2019. Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management. Environmental Science and Technology, 53(7), pp. 3718-28. [https://doi.org/10.1021/acs.est.8b06648 doi: 10.1021/acs.est.8b06648]&nbsp; [[Media: BentelEtAl2019.pdf | Open Access Article]]</ref>
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*Treatment of municipal sewage sludge in supercritical water: A review<ref name="Qian2016">Qian, L., Wang, S., Xu, D., Guo, Y., Tang, X., and Wang, L., 2016. Treatment of municipal sewage sludge in supercritical water: A review. Water Research, 89, pp. 118-131. [https://doi.org/10.1016/j.watres.2015.11.047 DOI: 10.1016/j.watres.2015.11.047]&nbsp;&nbsp; Free download from: [https://www.researchgate.net/profile/Shuzhong-Wang/publication/284563832_Treatment_of_Municipal_Sewage_Sludge_in_Supercritical_Water_a_Review/links/5d9b63b6299bf1c363fef63e/Treatment-of-Municipal-Sewage-Sludge-in-Supercritical-Water-a-Review.pdf ResearchGate]</ref>.
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*Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies<ref>Liu, Z., Chen, Z., Gao, J., Yu, Y., Men, Y., Gu, C., Liu, J., 2022. Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies. Environmental Science and Technology, 56(6), pp. 3699-3709. [https://doi.org/10.1021/acs.est.1c07608 doi: 10.1021/acs.est.1c07608]&nbsp; [[Media: LiuZEtAl2022.pdf | Open Access Article]]</ref>
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*Destruction of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment<ref>Tenorio, R., Liu, J., Xiao, X., Maizel, A., Higgins, C.P., Schaefer, C.E., Strathmann, T.J., 2020. Destruction of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment. Environmental Science and Technology, 54(11), pp. 6957-67. [https://doi.org/10.1021/acs.est.0c00961 doi: 10.1021/acs.est.0c00961]</ref>
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*Supercritical Water Oxidation – Current Status of Full-scale Commercial Activity for Waste Destruction<ref name="Marrone2013">Marrone, P.A., 2013. Supercritical Water Oxidation – Current Status of Full-scale Commercial Activity for Waste Destruction. Journal of Supercritical Fluids, 79, pp. 283-288. [https://doi.org/10.1016/j.supflu.2012.12.020 DOI: 10.1016/j.supflu.2012.12.020]&nbsp;&nbsp; Author’s manuscript available from: [https://semspub.epa.gov/work/06/9545963.pdf US EPA]</ref>.
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*EradiFluor<sup>TM</sup><ref name="EradiFluor"/>
  
 
==Introduction==
 
==Introduction==
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Supercritical water oxidation (SCWO) is an [[Wikipedia: Advanced oxidation process | advanced oxidation process]] that holds enormous potential for the treatment of a wide range of organic wastes, in particular concentrated wet wastes in slurries such as biosolids, sludges, agricultural wastes, chemical wastes with recalcitrant chemicals such as [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)| perfluoroalkyl and polyfluoroalkyl substances (PFAS)]], and many more. SCWO relies on the unique reactivity and transport properties that occur when an aqueous waste stream is brought above the critical point of water (374&deg;C and 218 atm, or 704&deg;F and 3200 psi, see phase diagram in Figure 1). [[Wikipedia: Supercritical fluid |  Supercritical water]] is a dense single phase with transport properties similar to those of a gas, and solvent properties comparable to those of a non-polar solvent<ref name="Tassaing2002">Tassaing, T., Danten, Y., and Besnard, M., 2002. Infrared spectroscopic study of hydrogen bonding in water at high temperature and pressure. Journal of Molecular Liquids, 101(1-3), pp. 149-158.  [https://doi.org/10.1016/S0167-7322(02)00089-2 DOI: 10.1016/S0167-7322(02)00089-2]</ref>. Oxygen is fully soluble in supercritical water, resulting in extremely rapid and complete oxidation of all organics to carbon dioxide, clean water (that can be reused), and some non-leachable inorganic salts.  
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The hydrated electron (''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'' ) can be described as an electron in solution surrounded by a small number of water molecules<ref name="BuxtonEtAl1988">Buxton, G.V., Greenstock, C.L., Phillips Helman, W., Ross, A.B., 1988. Critical Review of Rate Constants for Reactions of Hydrated Electrons, Hydrogen Atoms and Hydroxyl Radicals (⋅OH/⋅O-) in Aqueous Solution. Journal of Physical and Chemical Reference Data, 17(2), pp. 513-886. [https://doi.org/10.1063/1.555805 doi: 10.1063/1.555805]</ref>. Hydrated electrons can be produced by photoirradiation of solutes, including sulfite, iodide, dithionite, and ferrocyanide, and have been reported in literature to effectively decompose per- and polyfluoroalkyl substances (PFAS) in water. The hydrated electron is one of the most reactive reducing species, with a standard reduction potential of about −2.9 volts. Though short-lived, hydrated electrons react rapidly with many species having more positive reduction potentials<ref name="BuxtonEtAl1988"/>.  
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For SCWO to be economical, the heat from the oxidation reaction is recovered and used in part to heat the influent stream, while the excess heat can be converted to electricity. Depending on the concentration of waste in the feedstock, SCWO reactors can be operated autothermally, i.e., no outside input of heat is required. Typical reaction times are in the order of 2-10 seconds, resulting in SCWO systems that are quite compact compared to other technologies (see Table 1). The process does not generate harmful by-products such as nitrogen oxides (NOx) or Sulfur oxides (SOx), carbon monoxide (CO), or odors<ref Name="Bermejo">Bermejo, M.D. and Cocero, M.J., 2006. Supercritical water oxidation: A technical review. AIChE Journal, 52(11) pp. 3933-3951. [https://doi.org/10.1002/aic.10993 DOI: 10.1002/aic.10993]</ref>. Typically, if present, ammonia and organic nitrogen in the waste undergoing treatment are converted to nitrogen gas, while phosphorous precipitates as phosphates and can be recovered. When [[Wikipedia: Halogen | halogen]] containing contaminants are treated (e.g., [[Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)| PFAS]]), halogen-carbon bonds are generally broken and [[Wikipedia: Halide | halide]] anions are released in solution (e.g., F- when treating PFAS or Cl- when treating [[Wikipedia: Trichloroethylene | trichloroethene (TCE)]] and [[Wikipedia: Tetrachloroethylene | tetrachloroethene (PCE)]]). 
 
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==Advantages and Disadvantages==
 
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There are many advantages to SCWO treatment. SCWO is a destructive treatment in that the compounds treated are mineralized to simple elements or harmless molecules (e.g., water and carbon dioxide) rather than just being transferred to another medium. Another advantage is the absence of reaction by-products, incompletely oxidized contaminants or unreacted harmful oxidants (e.g., ozone). SCWO is an extremely rapid and effective reaction (typical reaction times are in the order of 5-10 seconds) making it possible to build systems that are very compact and have a high throughput. SCWO is also a very clean process. The highly oxidizing environment makes it possible to effectively treat all sorts of organic contaminants, often recalcitrant to other processes, with very high (>99%) destruction efficiencies. This includes treatment of trace contaminants, slurries of biosolids, waste oil, food wastes, plastics, or emerging contaminants such as PFAS or 1,4-dioxane. Also, the relatively moderate temperatures (380-600&deg;C) compared to other destructive technologies such as incineration, combined with the presence of supercritical water prevent the formation of NOx and SOx compounds. Lastly, SCWO treatment does not require drying of the waste, and both liquids and slurries can be treated using SCWO.
 
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There are several disadvantages to SCWO treatment. First, a significant amount of energy needs to be expended to bring the oxidant and the waste undergoing treatment to the critical point of water. Although a large fraction of this energy can be efficiently recovered in heat exchangers, compensating for heat losses constrains SCWO to the treatment of concentrated wastes with sufficient organic content for the exothermic oxidation reaction to provide the necessary heat. Typically, a minimum calorific content of around 2 MJ/kg (which generally corresponds to a chemical oxygen demand of about 120-150 g/L) is needed for autothermal operation. For more dilute streams, external heating or supplementation of fuel (diesel, alcohol, waste oil, etc.) can be implemented, but it can rapidly become cost prohibitive. Thus, SCWO is currently not economical for very large volumes (>50,000 gallon/day) of very dilute waste streams. A second limitation is related to the pumping of the waste. Because the process is conducted at high pressure (240 bars or 3500 psi), positive displacement pumps are required. This limits SCWO to liquids and slurries that can be pumped. Waste streams that contain excessive grit or abrasive materials, and soils cannot currently be processed using SCWO.
 
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The many appealing benefits of supercritical water processing have stimulated engineers and entrepreneurs to invest significant efforts and resources in the development of the technology. Today, after roughly 30 years of development, commercial deployment is on the horizon<ref name="Marrone2013"/>. Technical challenges that have slowed down commercial deployment of SCWO are linked to the complex nature of a high-pressure, high-temperature process. Critical issues include reactor materials selection to resist corrosion (typically high nickel alloys are used), reactor designs and construction to withstand the corrosive nature of the reactive mass, dealing with highly exothermic reactions at high pressure and high temperature, plugging of the reactor by minerals deposits, and energy recovery for autothermal operation. Another challenge was the unrealistic goal of some companies entering the SCWO market to produce power from waste streams (often wastewater sludge) at a competitive cost (3-5 cents/kWh). This was not feasible with the available technology, which led to several business failures.
 
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The value proposition of treating recalcitrant wastes using SCWO is markedly different, especially in today’s context of increasing liability for trace levels of emerging contaminants such as PFAS. SCWO may prove to be the optimal treatment technology for many highly concentrated aqueous waste streams.  
 
  
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==State of the Art==
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Among the electron source chemicals, sulfite (SO<sub>3</sub><sup>2−</sup>) has emerged as one of the most effective and practical options for generating hydrated electrons to destroy PFAS in water. The mechanism of hydrated electron production in a sulfite solution under ultraviolet is shown in Equation 1 (UV is denoted as ''hv, SO<sub>3</sub><sup><big>'''•-'''</big></sup>'' is the sulfur trioxide radical anion):
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Relatively few large scale SCWO systems exist. Researchers at Duke University ([http://sanitation.pratt.duke.edu/community-treatment/about-community-treatment-project Deshusses lab]) have designed and built a prototype pilot-scale SCWO system housed in a standard 20-foot shipping container (Figure 2). This project was funded by the Reinvent the Toilet program of the [https://www.gatesfoundation.org/ Bill and Melinda Gates Foundation]. The pilot system is a continuous process designed to treat 1 ton of sludge per day at 10-20% dry solids content. The unit has been undergoing testing at Duke since early 2015. The design includes moderate preheating of the waste slurry, followed by mixing with supercritical water (~600&deg;C) and air, which serves as the oxidant. This internal mixing rapidly brings the waste undergoing treatment to supercritical conditions thereby minimizing corrosion and the risks of waste charring and associated reactor plugging. The organics in the sludge are rapidly oxidized to CO<sub>2</sub>, while the heat of oxidation is recovered to heat the influent waste. The reactor is a single tubular reactor. The high supercritical fluid velocity in the system helps with controlling mineral salts deposition in the reactor. The system is well instrumented, and operation is controlled using a supervisory control and data acquisition (SCADA) system with historian software for trends analysis and reporting of key performance indicators (e.g., temperatures and pressures, pollutant destruction). Experiments conducted with this pilot plant have shown effective treatment of a wide variety of otherwise problematic wastes such as primary, secondary and digested sludge slurries, landfill leachate (see Figure 3), animal waste, and co-contaminants including waste oil, food wastes, and plastics. The results are consistent with other SCWO studies and show very rapid treatment of all wastes with near complete conversion (often >99.9%) of organics to CO<sub>2</sub>. Total nitrogen and phosphorous removal are generally over 95% and 98%, respectively. Emerging contaminants such as pharmaceuticals, [[Perfluoroakyl and Polyfluoroalkyl Substances (PFAS) |PFAS]], [[1,4-Dioxane | 1,4-dioxane]] and [[Wikipedia: Microplastics | microplastics]] are also treated with destruction generally exceeding 99%.
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</br>
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::<big>'''Equation 1:'''</big>&nbsp;&nbsp; [[File: XiongEq1.png | 200 px]]
  
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Early projections for treatment costs (Capital Expenditures + Operating Expenditures) for slurries are in the range of $12 to $90 per ton (or $0.04 to $0.37 per gallon) depending on system scale and contaminant concentration, with a majority of the cost coming from amortizing the equipment. These cost projections make SCWO treatment very competitive compared to other treatment technologies for high-strength wastes. When treating large volumes of water, combining SCWO with another technology (e.g., nanofiltration, reverse osmosis, or adsorption onto GAC) should be considered so that only the concentrated brines or spent sorbent are treated using SCWO, thereby increasing the cost effectiveness of the overall treatment.
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The hydrated electron has demonstrated excellent performance in destroying PFAS such as [[Wikipedia:Perfluorooctanesulfonic acid | perfluorooctanesulfonic acid (PFOS)]], [[Wikipedia:Perfluorooctanoic acid|perfluorooctanoic acid (PFOA)]]<ref>Gu, Y., Liu, T., Wang, H., Han, H., Dong, W., 2017. Hydrated Electron Based Decomposition of Perfluorooctane Sulfonate (PFOS) in the VUV/Sulfite System. Science of The Total Environment, 607-608, pp. 541-48. [https://doi.org/10.1016/j.scitotenv.2017.06.197 doi: 10.1016/j.scitotenv.2017.06.197]</ref> and [[Wikipedia: GenX|GenX]]<ref>Bao, Y., Deng, S., Jiang, X., Qu, Y., He, Y., Liu, L., Chai, Q., Mumtaz, M., Huang, J., Cagnetta, G., Yu, G., 2018. Degradation of PFOA Substitute: GenX (HFPO–DA Ammonium Salt): Oxidation with UV/Persulfate or Reduction with UV/Sulfite? Environmental Science and Technology, 52(20), pp. 11728-34. [https://doi.org/10.1021/acs.est.8b02172 doi: 10.1021/acs.est.8b02172]</ref>. Mechanisms include cleaving carbon-to-fluorine (C-F) bonds (i.e., hydrogen/fluorine atom exchange) and chain shortening (i.e., [[Wikipedia: Decarboxylation | decarboxylation]], [[Wikipedia: Hydroxylation | hydroxylation]], [[Wikipedia: Elimination reaction | elimination]], and [[Wikipedia: Hydrolysis | hydrolysis]])<ref name="BentelEtAl2019"/>.
  
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==SCWO for the Treatment of PFAS and AFFF==
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==Process Description==
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Several reports have indicated that PFAS can be treated using SCWO<ref name="Kucharzyk2017">Kucharzyk, K.H., Darlington, R., Benotti, M., Deeb, R. and Hawley, E., 2017. Novel treatment technologies for PFAS compounds: A critical review. Journal of Environmental Management, 204(2), pp. 757-764.  [https://doi.org/10.1016/j.jenvman.2017.08.016 DOI: 10.1016/j.jenvman.2017.08.016]&nbsp;&nbsp; Manuscript available from: [https://www.researchgate.net/profile/Katarzyna_kate_Kucharzyk/publication/319125507_Novel_treatment_technologies_for_PFAS_compounds_A_critical_review/links/5a06590b4585157013a3be77/Novel-treatment-technologies-for-PFAS-compounds-A-critical-review.pdf ResearchGate]</ref>. Several runs treating biosolids known to contain PFAS as well as dilutions of pure [[Wikipedia: Firefighting foam | aqueous film forming foam (AFFF)]] have also been conducted with the Duke SCWO system. Typical results are shown in Table 2. They indicate very effective treatment performance, with for example 110,000 ng/L PFOS in the feed reduced to 0.79 ng/L in the effluent, and many other PFAS reduced to below their detection limits. No HF was found in the effluent gas, and all the fluorine from the destroyed PFAS was accounted for as fluoride in the effluent water. These results show the ability of the SCWO process to destroy PFAS to levels well below the EPA health advisory levels of 70 ng/L for PFOS and PFOA. The [https://www.serdp-estcp.org/ Environmental Security Technology Certification Program (ESTCP)] project number [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/ER20-5350/ER20-5350 ER20-5350]<ref name="Deshusses2020">Deshusses, M.A., 2020. Supercritical Water Oxidation (SCWO) for Complete PFAS Destruction. Environmental Security Technology Certification Program (ESTCP) Project number ER20-5350. [https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/ER20-5350/ER20-5350 Project website]</ref> launched in June 2020 will assess the technical feasibility of using supercritical water oxidation (SCWO) for the complete destruction of PFAS in a variety of relevant waste streams and will evaluate the cost effectiveness of the treatment.
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A commercial UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>) includes an optional pre-oxidation step to transform PFAS precursors (when present) and a main treatment step to break C-F bonds by UV/sulfite reduction. The effluent from the treatment process can be sent back to the influent of a pre-treatment separation system (such as a [[Wikipedia: Foam fractionation | foam fractionation]], [[PFAS Treatment by Anion Exchange | regenerable ion exchange]], or a [[Reverse Osmosis and Nanofiltration Membrane Filtration Systems for PFAS Removal | membrane filtration system]]) for further concentration or sent for off-site disposal in accordance with relevant disposal regulations. A conceptual treatment process diagram is shown in Figure 1. [[File: XiongFig1.png | thumb | left | 600 px | Figure 1: Conceptual Treatment Process for a Concentrated PFAS Stream]]<br clear="left"/>
  
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==Advantages==
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A UV/sulfite treatment system offers significant advantages for PFAS destruction compared to other technologies, including high defluorination percentage, high treatment efficiency for short-chain PFAS without mass transfer limitation, selective reactivity by ''e<sub><small>aq</small></sub><sup><big>'''-'''</big></sup>'', low energy consumption, and the production of no harmful byproducts. A summary of these advantages is provided below:
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*'''High efficiency for short- and ultrashort-chain PFAS:''' While the degradation efficiency for short-chain PFAS is challenging for some treatment technologies<ref>Singh, R.K., Brown, E., Mededovic Thagard, S., Holson, T.M., 2021. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. Journal of Hazardous Materials, 408, Article 124452. [https://doi.org/10.1016/j.jhazmat.2020.124452 doi: 10.1016/j.jhazmat.2020.124452]</ref><ref>Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S., Holson, T.M., 2020. Removal of Poly- and Per-Fluorinated Compounds from Ion Exchange Regenerant Still Bottom Samples in a Plasma Reactor. Environmental Science and Technology, 54(21), pp. 13973-80. [https://doi.org/10.1021/acs.est.0c02158 doi: 10.1021/acs.est.0c02158]</ref><ref>Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M., Mededovic Thagard S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly- and Perfluoroalkyl Substances in Groundwater. American Chemical Society’s Environmental Science and Technology (ES&T) Water, 1(3), pp. 680-87. [https://doi.org/10.1021/acsestwater.0c00170 doi: 10.1021/acsestwater.0c00170]</ref>, the UV/sulfite process demonstrates excellent defluorination efficiency for both short- and ultrashort-chain PFAS, including [[Wikipedia: Trifluoroacetic acid | trifluoroacetic acid (TFA)]] and [[Wikipedia: Perfluoropropionic acid | perfluoropropionic acid (PFPrA)]]. 
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*'''High defluorination ratio:''' As shown in Figure 3, the UV/sulfite treatment system has demonstrated near 100% defluorination for various PFAS under both laboratory and field conditions.
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*'''No harmful byproducts:''' While some oxidative technologies, such as electrochemical oxidation, generate toxic byproducts, including perchlorate, bromate, and chlorate, the UV/sulfite system employs a reductive mechanism and does not generate these byproducts.
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*'''Ambient pressure and low temperature:''' The system operates under ambient pressure and low temperature (<60°C), as it utilizes UV light and common chemicals to degrade PFAS. 
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*'''Low energy consumption:''' The electrical energy per order values for the degradation of [[Wikipedia: Perfluoroalkyl carboxylic acids | perfluorocarboxylic acids (PFCAs)]] by UV/sulfite have been reduced to less than 1.5 kilowatt-hours (kWh) per cubic meter under laboratory conditions. The energy consumption is orders of magnitude lower than that for many other destructive PFAS treatment technologies (e.g., [[Supercritical Water Oxidation (SCWO) | supercritical water oxidation]])<ref>Nzeribe, B.N., Crimi, M., Mededovic Thagard, S., Holsen, T.M., 2019. Physico-Chemical Processes for the Treatment of Per- And Polyfluoroalkyl Substances (PFAS): A Review. Critical Reviews in Environmental Science and Technology, 49(10), pp. 866-915. [https://doi.org/10.1080/10643389.2018.1542916 doi: 10.1080/10643389.2018.1542916]</ref>.
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*'''Co-contaminant destruction:''' The UV/sulfite system has also been reported effective in destroying certain co-contaminants in wastewater. For example, UV/sulfite is reported to be effective in reductive dechlorination of chlorinated volatile organic compounds, such as trichloroethene, 1,2-dichloroethane, and vinyl chloride<ref>Jung, B., Farzaneh, H., Khodary, A., Abdel-Wahab, A., 2015. Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation. Journal of Environmental Chemical Engineering, 3(3), pp. 2194-2202. [https://doi.org/10.1016/j.jece.2015.07.026 doi: 10.1016/j.jece.2015.07.026]</ref><ref>Liu, X., Yoon, S., Batchelor, B., Abdel-Wahab, A., 2013. Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) – Effects of reagents and pH. Chemical Engineering Journal, 215-216, pp. 868-875. [https://doi.org/10.1016/j.cej.2012.11.086 doi: 10.1016/j.cej.2012.11.086]</ref><ref>Li, X., Ma, J., Liu, G., Fang, J., Yue, S., Guan, Y., Chen, L., Liu, X., 2012. Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process. Environmental Science and Technology, 46(13), pp. 7342-49. [https://doi.org/10.1021/es3008535 doi: 10.1021/es3008535]</ref><ref>Li, X., Fang, J., Liu, G., Zhang, S., Pan, B., Ma, J., 2014. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Research, 62, pp. 220-228. [https://doi.org/10.1016/j.watres.2014.05.051 doi: 10.1016/j.watres.2014.05.051]</ref>.
  
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[[File: revOsmosisPlant.png | thumb | 500px | Figure 1.  A RO municipal drinking water plant in Arizona]]  
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==Limitations==
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Several environmental factors and potential issues have been identified that may impact the performance of the UV/sulfite treatment system, as listed below. Solutions to address these issues are also proposed.
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*Environmental factors, such as the presence of elevated concentrations of natural organic matter (NOM), dissolved oxygen, or nitrate, can inhibit the efficacy of UV/sulfite treatment systems by scavenging available hydrated electrons. Those interferences are commonly managed through chemical additions, reaction optimization, and/or dilution, and are therefore not considered likely to hinder treatment success.
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*Coloration in waste streams may also impact the effectiveness of the UV/sulfite treatment system by blocking the transmission of UV light, thus reducing the UV lamp's effective path length. To address this, pre-treatment may be necessary to enable UV/sulfite destruction of PFAS in the waste stream. Pre-treatment may include the use of strong oxidants or coagulants to consume or remove UV-absorbing constituents.
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*The degradation efficiency is strongly influenced by PFAS molecular structure, with fluorotelomer sulfonates (FTS) and [[Wikipedia: Perfluorobutanesulfonic acid | perfluorobutanesulfonate (PFBS)]] exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.
  
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{| class="wikitable" style="float:right; margin-left:10px;"
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==State of the Practice==
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|+ Table 1. Comparison of SCWO with other thermal technologies
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[[File: XiongFig2.png | thumb | 500 px | Figure 2. Field demonstration of EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> for PFAS destruction in a concentrated waste stream in a Mid-Atlantic Naval Air Station: a) Target PFAS at each step of the treatment shows that about 99% of PFAS were destroyed; meanwhile, the final degradation product, i.e., fluoride, increased to 15 mg/L in concentration, demonstrating effective PFAS destruction; b) AOF concentrations at each step of the treatment provided additional evidence to show near-complete mineralization of PFAS. Average results from multiple batches of treatment are shown here.]]
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[[File: XiongFig3.png | thumb | 500 px | Figure 3. Field demonstration of a treatment train (SAFF + EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>) for groundwater PFAS separation and destruction at an Air Force base in California: a) Two main components of the treatment train, i.e. SAFF and EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>; b) Results showed the effective destruction of various PFAS in the foam fractionate. The target PFAS at each step of the treatment shows that about 99.9% of PFAS were destroyed. Meanwhile, the final degradation product, i.e., fluoride, increased to 30 mg/L in concentration, demonstrating effective destruction of PFAS in a foam fractionate concentrate. After a polishing treatment step (GAC) via the onsite groundwater extraction and treatment system, all PFAS were removed to concentrations below their MCLs.]] 
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! Technology
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The effectiveness of UV/sulfite technology for treating PFAS has been evaluated in two field demonstrations using the EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> system. Aqueous samples collected from the system were analyzed using EPA Method 1633, the [[Wikipedia: TOP Assay | total oxidizable precursor (TOP) assay]], adsorbable organic fluorine (AOF) method, and non-target analysis. A summary of each demonstration and their corresponding PFAS treatment efficiency is provided below.
−
! SCWO
+
*Under the [https://serdp-estcp.mil/ Environmental Security Technology Certification Program (ESTCP)] [https://serdp-estcp.mil/projects/details/4c073623-e73e-4f07-a36d-e35c7acc75b6/er21-5152-project-overview Project ER21-5152], a field demonstration of EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was conducted at a Navy site on the east coast, and results showed that the technology was highly effective in destroying various PFAS in a liquid concentrate produced from an ''in situ'' foam fractionation groundwater treatment system. As shown in Figure 2a, total PFAS concentrations were reduced from 17,366 micrograms per liter (µg/L) to 195 µg/L at the end of the UV/sulfite reaction, representing 99% destruction. After the ion exchange resin polishing step, all residual PFAS had been removed to the non-detect level, except one compound (PFOS) reported as 1.5 nanograms per liter (ng/L), which is below the current Maximum Contaminant Level (MCL) of 4 ng/L. Meanwhile, the fluoride concentration increased up to 15 milligrams per liter (mg/L), confirming near complete defluorination. Figure 2b shows the adsorbable organic fluorine results from the same treatment test, which similarly demonstrates destruction of 99% of PFAS.
−
! SCWG
+
*Another field demonstration was completed at an Air Force base in California, where a treatment train combining [https://serdp-estcp.mil/projects/details/263f9b50-8665-4ecc-81bd-d96b74445ca2 Surface Active Foam Fractionation (SAFF)] and EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was used to treat PFAS in groundwater. As shown in Figure 3, PFAS analytical data and fluoride results demonstrated near-complete destruction of various PFAS. In addition, this demonstration showed: a) high PFAS destruction ratio was achieved in the foam fractionate, even in very high concentration (up to 1,700 mg/L of booster), and b) the effluent from EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/> was sent back to the influent of the SAFF system for further concentration and treatment, resulting in a closed-loop treatment system and no waste discharge from EradiFluor<sup><small>TM</small></sup><ref name="EradiFluor"/>. This field demonstration was conducted with the approval of three regulatory agencies (United States Environmental Protection Agency, California Regional Water Quality Control Board, and California Department of Toxic Substances Control).
−
! HTL/HTC
 
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! WAO
 
−
|-
 
−
| Temperature || >380&deg;C || >380&deg;C || 250-300&deg;C || 150-320&deg;C
 
−
|-
 
−
| Pressure || >240 bar || >240 bar || 40-200 bar || 10-200 bar
 
−
|-
 
−
| Oxidant || Required || None || None || Required
 
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|-
 
−
| Reaction time || 2-10 sec. || 40-90 sec. || 30 min. to 2 hr.s || 30 min. to 3 hr.s
 
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|-
 
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| Corrosion potential || Moderate to high || Moderate || Low || Low to moderate
 
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|-
 
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| Risk of reactor plugging || Moderate to high || High || High || Low
 
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|-
 
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| Reaction || Exothermic || Endothermic || Endothermic || Exothermic
 
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|-
 
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| Useable products || CO<sub>2</sub> + clean H<sub>2</sub>O + heat + minerals || Syngas (H<sub>2</sub> + CH<sub>4</sub> + CO) || Biocrude/Biochar || Possible H<sub>2</sub>O, volatile fatty acids
 
−
|-
 
−
| By-products || None || Tars, phenols, recalcitrant N, contaminated water || Tars, phenols, recalcitrant N, contaminated water ||Tars, phenols, recalcitrant N, contaminated water
 
−
|-
 
−
| Fate of feedstock N, if any || N<sub>2</sub> gas || NH<sub>4</sub><sup>+</sup> in liquid effluent || NH<sub>4</sub><sup>+</sup> in liquid effluent + N in (by)-products || NH<sub>4</sub><sup>+</sup> in liquid effluent + N in (by)-products
 
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|-
 
−
| colspan="3" style="background:white;" | Notes: SCWG = supercritical water gasification. HTL/HTC = [[Wikipedia: Hydrothermal liquefaction | hydrothermal liquefaction]]/carbonization. WAO = wet air oxidation
 
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|}
 
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<br clear="left" />
 
  
 
==References==
 
==References==
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<references />
 
<references />
  
 
==See Also==
 
==See Also==

Latest revision as of 11:33, 29 January 2026

PFAS Destruction by Ultraviolet/Sulfite Treatment

The ultraviolet (UV)/sulfite based reductive defluorination process has emerged as an effective and practical option for generating hydrated electrons (eaq- ) which can destroy PFAS in water. It offers significant advantages for PFAS destruction, including significant defluorination, high treatment efficiency for long-, short-, and ultra-short chain PFAS without mass transfer limitations, selective reactivity by hydrated electrons, low energy consumption, low capital and operation costs, and no production of harmful byproducts. A UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluorTM[1]) has been demonstrated in two field demonstrations in which it achieved near-complete defluorination and greater than 99% destruction of 40 PFAS analytes measured by EPA method 1633.

Related Article(s):

Contributors: John Xiong, Yida Fang, Raul Tenorio, Isobel Li, and Jinyong Liu

Key Resources:

  • Defluorination of Per- and Polyfluoroalkyl Substances (PFAS) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management[2]
  • Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies[3]
  • Destruction of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment[4]
  • EradiFluorTM[1]

Introduction

The hydrated electron (eaq- ) can be described as an electron in solution surrounded by a small number of water molecules[5]. Hydrated electrons can be produced by photoirradiation of solutes, including sulfite, iodide, dithionite, and ferrocyanide, and have been reported in literature to effectively decompose per- and polyfluoroalkyl substances (PFAS) in water. The hydrated electron is one of the most reactive reducing species, with a standard reduction potential of about −2.9 volts. Though short-lived, hydrated electrons react rapidly with many species having more positive reduction potentials[5].

Among the electron source chemicals, sulfite (SO32−) has emerged as one of the most effective and practical options for generating hydrated electrons to destroy PFAS in water. The mechanism of hydrated electron production in a sulfite solution under ultraviolet is shown in Equation 1 (UV is denoted as hv, SO3•- is the sulfur trioxide radical anion):

Equation 1:   XiongEq1.png

The hydrated electron has demonstrated excellent performance in destroying PFAS such as perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA)[6] and GenX[7]. Mechanisms include cleaving carbon-to-fluorine (C-F) bonds (i.e., hydrogen/fluorine atom exchange) and chain shortening (i.e., decarboxylation, hydroxylation, elimination, and hydrolysis)[2].

Process Description

A commercial UV/sulfite treatment system designed and developed by Haley and Aldrich (EradiFluorTM[1]) includes an optional pre-oxidation step to transform PFAS precursors (when present) and a main treatment step to break C-F bonds by UV/sulfite reduction. The effluent from the treatment process can be sent back to the influent of a pre-treatment separation system (such as a foam fractionation, regenerable ion exchange, or a membrane filtration system) for further concentration or sent for off-site disposal in accordance with relevant disposal regulations. A conceptual treatment process diagram is shown in Figure 1.

Figure 1: Conceptual Treatment Process for a Concentrated PFAS Stream


Advantages

A UV/sulfite treatment system offers significant advantages for PFAS destruction compared to other technologies, including high defluorination percentage, high treatment efficiency for short-chain PFAS without mass transfer limitation, selective reactivity by eaq-, low energy consumption, and the production of no harmful byproducts. A summary of these advantages is provided below:

  • High efficiency for short- and ultrashort-chain PFAS: While the degradation efficiency for short-chain PFAS is challenging for some treatment technologies[8][9][10], the UV/sulfite process demonstrates excellent defluorination efficiency for both short- and ultrashort-chain PFAS, including trifluoroacetic acid (TFA) and perfluoropropionic acid (PFPrA).
  • High defluorination ratio: As shown in Figure 3, the UV/sulfite treatment system has demonstrated near 100% defluorination for various PFAS under both laboratory and field conditions.
  • No harmful byproducts: While some oxidative technologies, such as electrochemical oxidation, generate toxic byproducts, including perchlorate, bromate, and chlorate, the UV/sulfite system employs a reductive mechanism and does not generate these byproducts.
  • Ambient pressure and low temperature: The system operates under ambient pressure and low temperature (<60°C), as it utilizes UV light and common chemicals to degrade PFAS.
  • Low energy consumption: The electrical energy per order values for the degradation of perfluorocarboxylic acids (PFCAs) by UV/sulfite have been reduced to less than 1.5 kilowatt-hours (kWh) per cubic meter under laboratory conditions. The energy consumption is orders of magnitude lower than that for many other destructive PFAS treatment technologies (e.g., supercritical water oxidation)[11].
  • Co-contaminant destruction: The UV/sulfite system has also been reported effective in destroying certain co-contaminants in wastewater. For example, UV/sulfite is reported to be effective in reductive dechlorination of chlorinated volatile organic compounds, such as trichloroethene, 1,2-dichloroethane, and vinyl chloride[12][13][14][15].

Limitations

Several environmental factors and potential issues have been identified that may impact the performance of the UV/sulfite treatment system, as listed below. Solutions to address these issues are also proposed.

  • Environmental factors, such as the presence of elevated concentrations of natural organic matter (NOM), dissolved oxygen, or nitrate, can inhibit the efficacy of UV/sulfite treatment systems by scavenging available hydrated electrons. Those interferences are commonly managed through chemical additions, reaction optimization, and/or dilution, and are therefore not considered likely to hinder treatment success.
  • Coloration in waste streams may also impact the effectiveness of the UV/sulfite treatment system by blocking the transmission of UV light, thus reducing the UV lamp's effective path length. To address this, pre-treatment may be necessary to enable UV/sulfite destruction of PFAS in the waste stream. Pre-treatment may include the use of strong oxidants or coagulants to consume or remove UV-absorbing constituents.
  • The degradation efficiency is strongly influenced by PFAS molecular structure, with fluorotelomer sulfonates (FTS) and perfluorobutanesulfonate (PFBS) exhibiting greater resistance to degradation by UV/sulfite treatment compared to other PFAS compounds.

State of the Practice

Figure 2. Field demonstration of EradiFluorTM[1] for PFAS destruction in a concentrated waste stream in a Mid-Atlantic Naval Air Station: a) Target PFAS at each step of the treatment shows that about 99% of PFAS were destroyed; meanwhile, the final degradation product, i.e., fluoride, increased to 15 mg/L in concentration, demonstrating effective PFAS destruction; b) AOF concentrations at each step of the treatment provided additional evidence to show near-complete mineralization of PFAS. Average results from multiple batches of treatment are shown here.
Figure 3. Field demonstration of a treatment train (SAFF + EradiFluorTM[1]) for groundwater PFAS separation and destruction at an Air Force base in California: a) Two main components of the treatment train, i.e. SAFF and EradiFluorTM[1]; b) Results showed the effective destruction of various PFAS in the foam fractionate. The target PFAS at each step of the treatment shows that about 99.9% of PFAS were destroyed. Meanwhile, the final degradation product, i.e., fluoride, increased to 30 mg/L in concentration, demonstrating effective destruction of PFAS in a foam fractionate concentrate. After a polishing treatment step (GAC) via the onsite groundwater extraction and treatment system, all PFAS were removed to concentrations below their MCLs.

The effectiveness of UV/sulfite technology for treating PFAS has been evaluated in two field demonstrations using the EradiFluorTM[1] system. Aqueous samples collected from the system were analyzed using EPA Method 1633, the total oxidizable precursor (TOP) assay, adsorbable organic fluorine (AOF) method, and non-target analysis. A summary of each demonstration and their corresponding PFAS treatment efficiency is provided below.

  • Under the Environmental Security Technology Certification Program (ESTCP) Project ER21-5152, a field demonstration of EradiFluorTM[1] was conducted at a Navy site on the east coast, and results showed that the technology was highly effective in destroying various PFAS in a liquid concentrate produced from an in situ foam fractionation groundwater treatment system. As shown in Figure 2a, total PFAS concentrations were reduced from 17,366 micrograms per liter (µg/L) to 195 µg/L at the end of the UV/sulfite reaction, representing 99% destruction. After the ion exchange resin polishing step, all residual PFAS had been removed to the non-detect level, except one compound (PFOS) reported as 1.5 nanograms per liter (ng/L), which is below the current Maximum Contaminant Level (MCL) of 4 ng/L. Meanwhile, the fluoride concentration increased up to 15 milligrams per liter (mg/L), confirming near complete defluorination. Figure 2b shows the adsorbable organic fluorine results from the same treatment test, which similarly demonstrates destruction of 99% of PFAS.
  • Another field demonstration was completed at an Air Force base in California, where a treatment train combining Surface Active Foam Fractionation (SAFF) and EradiFluorTM[1] was used to treat PFAS in groundwater. As shown in Figure 3, PFAS analytical data and fluoride results demonstrated near-complete destruction of various PFAS. In addition, this demonstration showed: a) high PFAS destruction ratio was achieved in the foam fractionate, even in very high concentration (up to 1,700 mg/L of booster), and b) the effluent from EradiFluorTM[1] was sent back to the influent of the SAFF system for further concentration and treatment, resulting in a closed-loop treatment system and no waste discharge from EradiFluorTM[1]. This field demonstration was conducted with the approval of three regulatory agencies (United States Environmental Protection Agency, California Regional Water Quality Control Board, and California Department of Toxic Substances Control).

References

  1. ^ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Haley and Aldrich, Inc. (commercial business), 2024. EradiFluor. Comercial Website
  2. ^ 2.0 2.1 Bentel, M.J., Yu, Y., Xu, L., Li, Z., Wong, B.M., Men, Y., Liu, J., 2019. Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management. Environmental Science and Technology, 53(7), pp. 3718-28. doi: 10.1021/acs.est.8b06648  Open Access Article
  3. ^ Liu, Z., Chen, Z., Gao, J., Yu, Y., Men, Y., Gu, C., Liu, J., 2022. Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies. Environmental Science and Technology, 56(6), pp. 3699-3709. doi: 10.1021/acs.est.1c07608  Open Access Article
  4. ^ Tenorio, R., Liu, J., Xiao, X., Maizel, A., Higgins, C.P., Schaefer, C.E., Strathmann, T.J., 2020. Destruction of Per- and Polyfluoroalkyl Substances (PFASs) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photoreductive Treatment. Environmental Science and Technology, 54(11), pp. 6957-67. doi: 10.1021/acs.est.0c00961
  5. ^ 5.0 5.1 Buxton, G.V., Greenstock, C.L., Phillips Helman, W., Ross, A.B., 1988. Critical Review of Rate Constants for Reactions of Hydrated Electrons, Hydrogen Atoms and Hydroxyl Radicals (⋅OH/⋅O-) in Aqueous Solution. Journal of Physical and Chemical Reference Data, 17(2), pp. 513-886. doi: 10.1063/1.555805
  6. ^ Gu, Y., Liu, T., Wang, H., Han, H., Dong, W., 2017. Hydrated Electron Based Decomposition of Perfluorooctane Sulfonate (PFOS) in the VUV/Sulfite System. Science of The Total Environment, 607-608, pp. 541-48. doi: 10.1016/j.scitotenv.2017.06.197
  7. ^ Bao, Y., Deng, S., Jiang, X., Qu, Y., He, Y., Liu, L., Chai, Q., Mumtaz, M., Huang, J., Cagnetta, G., Yu, G., 2018. Degradation of PFOA Substitute: GenX (HFPO–DA Ammonium Salt): Oxidation with UV/Persulfate or Reduction with UV/Sulfite? Environmental Science and Technology, 52(20), pp. 11728-34. doi: 10.1021/acs.est.8b02172
  8. ^ Singh, R.K., Brown, E., Mededovic Thagard, S., Holson, T.M., 2021. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. Journal of Hazardous Materials, 408, Article 124452. doi: 10.1016/j.jhazmat.2020.124452
  9. ^ Singh, R.K., Multari, N., Nau-Hix, C., Woodard, S., Nickelsen, M., Mededovic Thagard, S., Holson, T.M., 2020. Removal of Poly- and Per-Fluorinated Compounds from Ion Exchange Regenerant Still Bottom Samples in a Plasma Reactor. Environmental Science and Technology, 54(21), pp. 13973-80. doi: 10.1021/acs.est.0c02158
  10. ^ Nau-Hix, C., Multari, N., Singh, R.K., Richardson, S., Kulkarni, P., Anderson, R.H., Holsen, T.M., Mededovic Thagard S., 2021. Field Demonstration of a Pilot-Scale Plasma Reactor for the Rapid Removal of Poly- and Perfluoroalkyl Substances in Groundwater. American Chemical Society’s Environmental Science and Technology (ES&T) Water, 1(3), pp. 680-87. doi: 10.1021/acsestwater.0c00170
  11. ^ Nzeribe, B.N., Crimi, M., Mededovic Thagard, S., Holsen, T.M., 2019. Physico-Chemical Processes for the Treatment of Per- And Polyfluoroalkyl Substances (PFAS): A Review. Critical Reviews in Environmental Science and Technology, 49(10), pp. 866-915. doi: 10.1080/10643389.2018.1542916
  12. ^ Jung, B., Farzaneh, H., Khodary, A., Abdel-Wahab, A., 2015. Photochemical degradation of trichloroethylene by sulfite-mediated UV irradiation. Journal of Environmental Chemical Engineering, 3(3), pp. 2194-2202. doi: 10.1016/j.jece.2015.07.026
  13. ^ Liu, X., Yoon, S., Batchelor, B., Abdel-Wahab, A., 2013. Photochemical degradation of vinyl chloride with an Advanced Reduction Process (ARP) – Effects of reagents and pH. Chemical Engineering Journal, 215-216, pp. 868-875. doi: 10.1016/j.cej.2012.11.086
  14. ^ Li, X., Ma, J., Liu, G., Fang, J., Yue, S., Guan, Y., Chen, L., Liu, X., 2012. Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process. Environmental Science and Technology, 46(13), pp. 7342-49. doi: 10.1021/es3008535
  15. ^ Li, X., Fang, J., Liu, G., Zhang, S., Pan, B., Ma, J., 2014. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Research, 62, pp. 220-228. doi: 10.1016/j.watres.2014.05.051

See Also

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