Removal Of Perfluorooctane Sulfonate Research Articles

Synthesis of magnetic chitosan biopolymeric spheres and their adsorption performances for PFOA and PFOS from aqueous environment

Due to numerous applications and excellent environmental stability, long-chain perfluorinated chemicals (PFCs) are ubiquitous in water across the world and adversely affect the living organisms. Thus, this study focused on the mitigation of the most frequently used long-chain PFCs namely perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) from water using reduced graphene oxide modified zinc ferrite immobilized chitosan beads (rGO-ZF@CB) as an adsorbent. The results from the adsorption isotherm and kinetic studies revealed that the adsorption data fitted well to the Langmuir and the pseudo-second-order models. According to the Langmuir isotherm, the rGO-ZF@CB possessed the maximum adsorption capacity of 16.07 mg/g for PFOA and 21.64 mg/g for PFOS. Both the electrostatic attractions and hydrophobic interactions have driven the removal of PFOA and PFOS by prepared rGO-ZF@CB. Eventually, the rGO-ZF@CB could be considered as an efficient adsorbent for the effective removal of PFOA and PFOS molecules from the aqueous environment.

Adsorption behavior of perfluorooctanesulfonate (PFOS) onto activated spent coffee grounds biochar in synthetic wastewater effluent

Improved understanding of human health risks, environmental persistence, and widespread dispersion of per- and polyfluoroalkyl substances (PFAS) has driven ongoing development of stringent regulations for these compounds in water. Char materials produced from agricultural food waste have recently been explored as alternatives to granular activated carbon for PFAS removal in water. Herein, spent coffee grounds (SCG) were pyrolyzed, activated with alkaline hydroxide, and evaluated for perfluorooctanesulfonate (PFOS) adsorption. At environmentally-relevant PFOS concentrations, pyrolyzed SCG showed minimal PFOS removal while activated SCG removed 9.9%–99.6% of PFOS depending on activation conditions. SCGKOH (produced from a 1:1 mass ratio of pyrolyzed SCG and potassium hydroxide) had a maximum adsorption capacity of 43.4 mg/g compared to Filtrasorb® F300 activated carbon (55.7 mg/g) and a wood-based fly ash char (79.5 mg/g). All adsorbents display non-linear pseudo first-order adsorption behavior with rate constants of 0.414 h−1, 0.062 h−1, 0.090 h−1 for fly-ash biochar, SCGKOH and F300, respectively. Additionally, PFOS removal by all adsorbents decreased in the presence of simulated effluent organic matter. SCGKOH presents an exciting alternative to existing commercial char adsorbents. The widely available feedstock and low-input production process could make this material a viable water treatment option for resource-constrained communities.

Perfluorooctane sulfonate decreases the performance of a sequencing batch reactor system and changes the sludge microbial community

The existence of perfluorooctane sulfonate (PFOS) in large quantities threatens environment biosafety. However, the fate of PFOS in a sequencing batch reactor (SBR) system and its influence in system has not yet been revealed. In this study, the fate and behavior of PFOS in an SBR processing system were investigated. Mass balance analyses revealed that PFOS removal was mainly through adsorption. After the reactors were run for 20 days, the PFOS (100 mg/L) removal rate was only 28%. Under the influence of PFOS, the removal rates of chemical oxygen demand (COD) and ammonia nitrogen dropped rapidly from 92, 98% to 23, 35% in the 20th day of system operation, respectively, while, accumulation of nitrite and nitrate was reduced. Compared with the control group, PFOS stimulates microorganisms to secrete more soluble microbial products (SMP) and extracellular polymeric substances (EPS). The adsorption of PFOS and EPS causes sludge bulking and decreases settling. The richness and diversity of microorganisms decreased significantly, affecting the system’s removal of COD and ammonia nitrogen. Therefore, the SBR system is not suitable for treating wastewater containing PFOS. It is necessary to remove PFOS through pretreatment to reduce its impact on the SBR system.

Polyacrylonitrile fiber functionalized with fluorous hyperbranched polyethylenimine for selective removal of perfluorooctane sulfonate (PFOS) in firefighting wastewaters

Perfluorooctane sulfonate (PFOS) is a well-known persistent organic pollutant in water systems, especially in firefighting wastewaters. It is highly desirable to develop new adsorbents that can remove PFOS efficiently and selectively from firefighting wastewaters. In this work, polyacrylonitrile (PAN) fiber was functionalized by adding fluorous hyperbranched polyethylenimine (F-PEI) under hydrothermal conditions, generating a series of fluorous PAN-g-F-PEI fibers. Compared with the fiber without perfluoroalkyl chains, the existence of perfluoroalkyl chains significantly shortened the equilibrium adsorption time. Lowering solution pH and increasing the F-PEI content were two more efficient ways to improve the maximum equilibrium adsorption capacity. The introduction of enough perfluoroalkyl chains into the fiber effectively suppressed the adverse effect of zwitterionic surfactants, nonionic surfactants and organic solvents on the PFOS removal efficiency, and also alleviated the adverse effect of anionic surfactants. The PAN-g-F-PEI fiber with the largest amount of perfluoroalkyl chains could efficiently and selectively remove PFOS from the firefighting wastewaters containing a high concentration of PFOS and the residual PFOS concentration could reach below 10 ng/L, satisfying the standard of the U.S. Environmental Protection Agency. Moreover, after adsorption, PAN-g-F-PEIs could be easily regenerated by methanol washing and reused for five times without pronounced loss of adsorption capacity.

Electrochemical Oxidation of Perfluorooctanesulfonate by Magnéli Phase Ti4O7 Electrode in the Presence of Trichloroethylene

This study examined the degradation of perfluorooctanesulfonate (PFOS) in electrochemical oxidation (EO) processes in the presence of trichloroethylene (TCE). The EO experiment was performed in a gas-tight reactor using Magnéli phase titanium suboxide (Ti4O7) as the anode. The experimental data demonstrated that 75% of PFOS (2 μM) was degraded at 10 mA/cm2 current density in 30 min without TCE present in the solution, while the presence of 76 μM TCE apparently inhibited the degradation of PFOS, reducing its removal down to 53%. Defluorination ratio suggested that PFOS was significantly mineralized upon EO treatment, and it appeared to be not influenced by the presence of TCE. The respective pseudo-first order rate constants (kobs) of PFOS removal were 0.0471 and 0.0254 min-1 in the absence and presence of TCE. The degradation rates of both PFOS and TCE increased with current density rising from 2.5 to 20 mA/cm2. In the presence of TCE, chloride, chlorate, and perchlorate were formed that accounted for 79.7 %, 5.53%, and 1.51% of the total chlorine at 60 min. This work illustrates the promise of the Magnéli phase Ti4O7 electrode based electrochemical oxidation technology for degrading per- and polyfluoroalkyl substances (PFASs) and co-contaminants in groundwaters.

Mechanistic insights into fast adsorption of perfluoroalkyl substances on carbonate-layered double hydroxides

Layered double hydroxide (LDH) with the metal composition of Cu(II)Mg(II)Fe(III) was prepared as an adsorbent for fast adsorption of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA). 84% of PFOS and 48% of PFOA in relation to the equilibrium state were adsorbed in the first minutes of contact with 0.1 g/L of suspended µm-sized LDH particles. The adsorption mechanisms of PFOS and PFOA on the CuMgFe-LDH were interpreted. Hydrophobic interactions were primarily responsible for the adsorption of these compounds in accordance with the different adsorption affinities of long-chain (C8, Kd = 105 L/kg) and short-chain (C4, Kd = 102 L/kg) perfluorinated carboxylic acids. PFOA adsorption on CuMgFe-LDH was strongly suppressed under alkaline conditions while PFOS uptake was only slightly affected in the pH range from 4.3 to 10.7, indicating a significant role of electrostatic interactions for PFOA adsorption. The adsorption of PFOS and PFOA was rather insensitive to competition by monovalent anions. The previously reported ‘memory effect’ of calcined CuMgFe-LDH for sorption of organic anions was not confirmed in the present study. Spent CuMgFe-LDH could be easily regenerated by extraction with 50 vol% methanol in water within 1 h and maintained a high PFOS removal in subsequent usage cycles.

Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor

A bench-scale plasma reactor was used to degrade poly- and perfluoroalkyl substances (PFAS) in landfill leachate samples obtained from three different locations. In the leachate samples before treatment, five long-chain, six short-chain perfluoroalkyl acids (PFAAs) and eight PFAA precursors were detected in a wide concentration range (~102 to 105 ng/L; total oxidizable precursors (TOP) ~106 ng/L). The concentration of perfluorooctane sulfonate (PFOS) plus perfluorooctanoic acid (PFOA) ranged between 2000 and 3000 ng/L. Plasma-based water treatment of 500 mL samples resulted in faster removal rates for longer-chain than shorter chain length PFAAs. Both PFOS and PFOA were removed to below United States Environmental Protection Agency’s (USEPA’s) health advisory concentration level (HAL) concentrations (<70 ng/L) in 10–75 min; 90% PFOA and PFOS removal was achieved in 10 min. Long-chain and short-chain PFAAs were removed by >99.9% and 10–99.9%, respectively. The removal rate constant (kPFOA+PFOS) for combined PFOA and PFOS ranged between 0.20 and 0.34 min-1. Overall, 60 ± 2% of the TOP concentration and 34 ± 2% of the TOC were removed. No effect of non-PFAS co-contaminants (e.g., total initial organic carbon concentration ~2000 mg/L) on the degradation efficiency was observed. Short-chain PFAA removal efficacy was enhanced by adding a cationic surfactant (cetrimonium bromide). Overall, the results indicate that plasma-based technology may be a viable technology for the treatment of PFAS-contaminated landfill leachates.

Enhanced sorption of perfluorooctane sulfonate and perfluorooctanoate by hydrotalcites

Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are recalcitrant compounds that are toxic to humans and ecosystems. Hydrotalcite-like compounds have emerged as promising PFOS and PFOA sorbents due to their high anion exchange capacity and high specific surface area. In this study, hydrotalcite (HT) compounds were intercalated with nitrate and carbonate ions (HT-CO 3 and HT-NO 3 ) and their specific surface area and particle aggregate size modified by treatment with acetone (AHT-CO 3 and AHT-NO 3 ). Sorption experiments with AHT-NO 3 indicated that sorption equilibrium was reached faster with PFOS (< 5 min) compared to PFOA (< 20 min), and that sorption capacity for PFOS (1,610.0 mg/g) was substantially higher compared to PFOA (909.0 mg/g). The sorption yields are explained by anion exchange occurring at higher PFOS and PFOA concentrations, along with surface adsorption, and by PFOS having a higher affinity for the HT interlayer. In comparison to AHT-NO 3 , PFOS and PFOA sorption by AHT-CO 3 was slower (equilibration times ≥ 20 min) and the maximum capacities were generally lower, because anion exchange is hindered by the affinity of the carbonate ion for the HT interlayer. As such, surface adsorption dominated across a large PFOS and PFOA concentration range (up to 2,000 mg/L). The presence of non-ionic species (trichloroethylene) did not affect the sorption capacity, while alkaline pH conditions and the presence of other anionic species (dodecyl sulfate) reduced the sorption capacity of AHT compounds towards PFOS and PFOA. Compared to untreated HT compounds, acetone treated HT exhibited improved sorption properties towards PFOA and PFOS removal from groundwater, particularly AHT-CO 3 . Overall, AHT compounds outperform activated carbon sorbents in terms of PFOA and PFOS sorption kinetics and capacities, thus could be promising new sorbents for PFAS removal from contaminated waters. • Acetone-treated hydrotalcites (AHT) show modified physical properties. • Nitrate-intercalated AHT show fast equilibration time (<1 h) towards PFOS and PFOA. • The maximum sorption uptake for PFOS is 1,610 mg/g by nitrate-intercalated AHT. • XPS and other techniques are used to evaluate the sorption mechanism. • Alkaline pH and other anions impact the sorption capacity of PFOS and PFOA by AHT.

Organically functionalized bentonite for the removal of perfluorooctane sulfonate, phenanthrene and copper mixtures from wastewater

The co-occurrence of a wide range of hydrophobic and hydrophilic contaminants with contrasting physicochemical properties in wastewaters makes practical remediation a challenge. Applications of ion exchangers such as clays are an environmentally friendly option in a cleanup strategy. However, clays often require chemical functionalization to adsorb non-polar contaminants. In this study, the most readily available low-cost Iranian bentonite was modified with Arquad® 2HT-75 (IBA) and further tailored with palmitic acid (IBAP) in order to prepare effective adsorbents. They were used for the removal of perfluorooctane sulfonate (PFOS), phenanthrene (PHE) and copper ions (Cu2+) both in single (S) and binary (B) contaminant conditions in simulated and real wastewater. The IB showed a large affinity for Cu2+ in both single (qmax: 43.43 mg/L) and binary (qmax: 43.95 mg/L) systems. Adsorption of PFOS and PHE was dramatically enhanced by the functionalized clays IBA (KF (PFOS): 11.1 and KF (PHE): 9.65 mg (1-n) Ln g−1) and IBAP (KF (PFOS): 10.2 and KF (PHE): 16.68 mg (1-n) Ln g−1). The co-occurrence of PFOS or PHE with Cu2+ enhanced their adsorption onto clays indicating that Cu2+ can form bridges between clays and PFOS or PHE in different mechanism to increase adsorption of PFOS or PHE in binary solutions. The surface-tailored organoclay IBAP showed great potential for the complete removal of PFOS, PHE and 86.6% of Cu2+ from real wastewater, which is usually considered challenging.

Perfluorooctane sulfonate removal by metal-organic frameworks (MOFs): Insights into the effect and mechanism of metal nodes and organic ligands

The metal–organic frameworks (MOFs) with different metal nodes and organic ligands have been prepared and used to remove perfluorooctane sulfonate (PFOS) from water. The results show that among three metal nodes of the MIL-53(Al), MIL-53(Fe) and MIL-101(Cr), MIl-53(Al) exhibit the best PFOS adsorption performance owing to the combined action of the highest unsaturated metal active sites and the smallest pore size. MIL-53(Al)-terephthalic acid (BDC), MIL-53(Al)-dimethyl 2,6-naphthalene dicarboxylate (NDC) and MIL-53(Al)-biphenyl-4,4′-dicarboxylic acid (BPDC) differs from the length of the organic ligand and MIL-53(Al)-BPDC achieves superior PFOS adsorption performance. We propose that longer organic ligand will contribute to larger 1D channel window and provide more PFOS entry. Adsorption kinetics shows that the experimental values can be well fitted to pseudo-second-order model, indicating that chemical adsorption demonstrate in the adsorption process. Besides, the existence of Fe3+ ions in MOFs/PFOS system could improve PFOS removal because of the bridging and interaction between Fe3+ ions and the PFOS molecule, which is confirmed by the density functional theory (DFT) calculation. These optimized MOFs are hopeful adsorbents to remove PFOS from water in a sustainability perspective.

Removal, distribution and plant uptake of perfluorooctane sulfonate (PFOS) in a simulated constructed wetland system

A vertical-flow constructed wetland (VFCW) was used to treat simulated domestic sewage containing perfluorooctane sulfonate (PFOS). The removal rate of PFOS in the domestic sewage was 93%–98%, through soil adsorption and plant uptake, suggesting that VFCWs can remove PFOS efficiently from wastewater. The removal of PFOS in the VFCW was dependent on soil adsorption and plant uptake; moreover, the percentage of soil adsorption was 61%–89%, and was higher than that of the plants uptake (5%–31%). The absorption capacity of Eichhornia crassipes (E. crassipes) (1186.71 mg/kg) was higher than that of Cyperus alternifolius (C. alternifolius) (162.77 mg/kg) under 10 mg/L PFOS, and the transfer factor of PFOS in E. crassipes and C. alternifolius was 0.04 and 0.58, respectively, indicating thatPFOS is noteasilytranslocatedto leaves fromroots of wetland plants; moreover, uptake of PFOS by E. crassipes was more than that of C. alternifolius because the biomass of E. crassipes was more than that of C. alternifolius and the roots of E. crassipes can take up PFOS directly from wastewater while C. alternifolius needs to do so via its roots in the soil. The concentration of 10 mg/L PFOS had an obvious inhibitory effect on the removal rate of total nitrogen, total phosphorus, chemical oxygen demand, and ammonia nitrogen in the VFCW, which decreased by 15%,10%,10% and 12%, respectively. Dosing with PFOS in the wastewater reduced the bacterial richness but increased the diversity in soil because PFOS stimulated the growth of PFOS-tolerant strains.

In situ soil flushing to remediate confined soil contaminated with PFOS- an innovative solution for emerging environmental issue

PerFluoroOctane Sulfonate (PFOS), is a toxic anthropogenic chemical that has been produced and gradually released into the environment for the past seven decades. An accurate audit of global PFOS contamination and contaminated sites are yet to be published. The available technologies to remediate PFOS contaminated soil are limited and often basic strategies such as temporary soil containment are adopted as immediate measures to manage the contaminated sites. In this study, the in situ soil flushing technique is assessed for its capacity to remediate soil contaminated with PFOS. A complete treatment process with several operation units was proposed such as solvent flushing, ground water pumping, solvent recovery and water treatment for PFOS. Potential solvents were identified and it was observed that more than 98% PFOS removal could be attained by flushing with five bed volumes of 50% ethanol. In addition, the study investigated thirteen commercially available filter materials and identified PFA694E, K6362, MP 62, Amberlite IRA 67 and Dowexoptopore V493 as suitable to eliminate PFOS with competitive PFOS adsorption characteristics. The proposed method can be recommended to remediate PFOS in recognised contaminated soils, such as those at defence sites. Furthermore, a contaminated site with favourable characteristics to implement the suggested method was identified in Australia and described in this paper.

Electrochemical Destruction of per- and Polyfluoroalkyl Substances (PFAS) in Complex Solution Matrices

Per- and Polyfluoroalkyl substances (PFAS) are a group of manmade chemicals which are persistent in the environment and have shown to be toxic to human health. They have accumulated in drinking water, groundwater, and wastewater around the globe for over six decades. Although the production of some chain lengths has ceased, remediation is critical. Current remediation techniques include adsorbents such as granular activated carbon (GAC) and Ion exchange (IX) columns. GAC is merely used to adsorb the PFAS, but struggles with capturing shorter chains and requires regeneration with incineration.1 IX has shown improvement in its ability to capture all PFAS chain lengths, and can be regenerated with a solution comprised of a salt or base and an alcohol.1 This regenerate solution desorbs all of the PFAS from the resin into a smaller concentrated solution of roughly a few hundred gallons. This solution is typically comprised of PFAS in the parts per million (ppm) range.2 These concentrated PFAS solutions can lead to further contamination of the environment through discharge of landfill leachate to wastewater treatment plants from landfill disposal. Due to the high salinity, low volume, and high concentration of PFAS in IX regenerate solutions, electrochemical oxidation is a promising treatment technology to destroy the PFAS and remove the chance of future human exposure.This study employs a boron-doped diamond (BDD) on niobium (Nb) electrode stack to investigate the role that current density has in the electrochemical destruction of PFAS in a complex solution matrix. The electrode stack was comprised of two anode plates sandwiched in between three cathode plates. This entire stack was then placed into a constantly stirred reactor comprised of 750 ml of solution. A constant current density of 50 mA/cm2 was investigated initially for a total of 12 hours. In order to save on energy consumption, further studies used a combined current density approach. This involved applying 50 mA/cm2 for only the first hour of the test before lowering the current density to 5 mA/cm2 for the remaining 11 hours. Multiple literature IX regenerate solutions were simulated and spiked with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS).3–6 Multiple samples were taken over the course of the oxidation experiments and sent for PFAS analysis using the Environmental Protection Agency’s (EPA) modified 537 method. Additional process parameters were monitored over time including the pH, voltage, temperature, and the reduction in chemical oxygen demand (COD) and ammonia depending on the simulated regenerate solution used. Further analysis showed a significant reduction in energy with a minimal additional amount of PFAS remaining in the initial combined current density study compared to the traditional constant current density approach. 1. Woodard, S., Berry, J. & Newman, B. Ion exchange resin for PFAS removal and pilot test comparison to GAC. Remediation 27, 19–27 (2017).2. Liang, S., Pierce, R. “David”, Lin, H., Chiang, S. Y. D. & Huang, Q. “Jack”. Electrochemical oxidation of PFOA and PFOS in concentrated waste streams. Remediation 28, 127–134 (2018).3. Conte, L., Falletti, L., Zaggia, A. & Milan, M. Polyfluorinated Organic Micropollutants Removal from Water by Ion Exchange and Adsorption. in CHEMICAL ENGINEERING TRANSACTIONS 43, (2015).4. Zaggia, A., Conte, L., Falletti, L., Fant, M. & Chiorboli, A. Use of strong anion exchange resins for the removal of perfluoroalkylated substances from contaminated drinking water in batch and continuous pilot plants. Water Res. 91, 137–146 (2016).5. Chularueangaksorn, P., Tanaka, S., Fujii, S. & Kunacheva, C. Regeneration and reusability of anion exchange resin used in perfluorooctane sulfonate removal by batch experiments. J. Appl. Polym. Sci. 130, 884–890 (2013).6. Deng, S., Yu, Q., Huang, J. & Yu, G. Removal of perfluorooctane sulfonate from wastewater by anion exchange resins: Effects of resin properties and solution chemistry. Water Res. 44, 5188–5195 (2010).

Adsorption of perfluorooctane sulfonate on carbonized poly-melamine-formaldehyde sponge

In this study, we developed a simple carbonized poly-melamine-formaldehyde sponge (CMF) acting as an adsorbent for adsorbing perfluorooctane sulfonate (PFOS) from the waste poly-melamine-formaldehyde (MF) sponge. The PFOS removal by the developed adsorbent was comprehensively investigated using batch adsorption, including kinetics, isotherm, ionic strength and ionic type and pH edge. PFOS adsorption kinetics followed a pseudo-second-order kinetic model, and reached equilibrium within 3 min. The adsorption isotherm was well described by the Freundlich model, as well as by the Langmuir model at a low initial concentration. The adsorption capacity gradually decreased with the increase of pH, and it was up to 216.4 μg/g even at pH 12.1. However, the adsorption capacity increased with the increase in ionic strength. Furthermore, the co-existing ions and small organic acids also promoted the PFOS adsorption on CMF sponge to different extents. Both the hydrophobic interaction and electrostatic attraction played an important role on adsorption, as well as chemical interaction and hydrogen bonding from spectroscopic results.

Calcination of hydrotalcite to enhance the removal of perfluorooctane sulfonate from water

Perfluorinated compounds (PFCs), due to their thermal and chemical stability and broad usage in industry, have been detected in surface and ground water. As emerging compounds, their fate in the environment and removal from water attracted great attention in the last 10 years. In this study, we evaluated the performance of calcinated hydrotalcite (CHT) for the removal of PFCs using perfluorooctane sulfonate (PFOS) as an example. Our results showed that CHT can sorb up to 1.4 times of its mass for PFOS and the removal was fast, with equilibrium being achieved in 30 min. The PFOS removal was less sensitive to pH in pH 4–11 range. At low loading levels, only small fractions of CHT were intercalated by PFOS and the 3R polytype of hydrotalcite (HT) was largely maintained. As the PFOS uptake increased beyond 300 mg/g, intercalation of PFOS took place. The structure of HT changed to 1 layer stacking beyond 600 mg/g. Electrostatic interaction was responsible for the PFOS uptake at low loading levels and hydrophobic interaction started to play a role among PFOS molecules as its loading level increased. Crystalline PFOS decomposed at 513 °C, but its decomposition temperature decreased to 443 °C once sorbed on CHT, due to the breakdown of HT at about 390 °C. The CHT was regeneratable after calcination of PFOS-saturated HT at 450 °C for 3 h with the full PFOS removal capacity restored. The finding from this study showed the superior feature of using CHT for the removal of PFCs over other methods.

Adsorption of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) from water using leaf biomass (Vitis vinifera) in a fixed-bed column study.

Adsorption of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) onto modified activated carbons (AC-H3PO4) produced from leaf biomass of Vitis vinifera leaf litter in a fixed bed column experiment was investigated in this study. The column bed was packed with the produced activated carbons in a uniform particle size of ˃ 64μm. Experimental parameters including the initial concentration of the solution, column bed height, the mass of adsorbent and flow rate were optimized to establish the best adsorption efficiency parameters for the system. Breakthrough and saturated time were estimated from the column fixed bed experimental data and analysed using the Adam-Bohart, Thomas model, and Yoon-Nelson models. Maximum sorption capacities of produced activated carbon ACH3PO4 based on Thomas model were 159.61 and 208.64mg/g for PFOA and PFOS, respectively. The results indicated the breakthrough and saturated time of the system increased concurrently with the increase in bed height and initial concentrations, while an increase in flow rate enhanced fractional bed utilization (FBU) efficiency of the column. Thomas and Yoon-Nelson model best describe the prediction of breakthrough data and sorption behaviour of PFOA and PFOS indicating suitability of AC-H3PO4 column design. Findings suggest that agro based adsorbent is a good alternative to non-ago based adsorbent. The surface characteristics of the phosphoric acid modified activated carbons AC-H3PO4 affirmed the removal of PFOA and PFOS from the contaminated water.

Evaluating perfluorooctanesulfonate oxidation in permanganate systems.

Permanganate (PM) has shown to be able to oxidize a range of organic contaminants including perfluorooctane sulfonate (PFOS). However, mechanisms of PFOS removal by PM have been questioned. To provide clarity to what may be happening to PFOS in PM systems, here we evaluated the ability of PM on PFOS destruction by conducting studies similar to previous studies that reported PFOS destruction which included PM solutions and PM combined with persulfate (PS). We also evaluated if addition of various soluble catalysts could enhance PM's potential to breakdown PFOS. We observed no PFOS destruction by PM. We also show that the F- and SO42- generation reported in a published study as evidence that PM was breaking bonds in PFOS were found below or not significantly higher than reported limits of quantitation and that SO42- impurities in technical PM approach the reported SO42- levels. For PM-PS systems, heterogeneous PFOS distribution was observed when subsampling reaction vessels at different depths and "salting-out" of PFOS was evident. In addition, subsequent sonication and filtering of the samples led to the apparent disappearance of most of the PFOS, which was an artifact arising from the behavior of PFOS aggregates or potential hemi-micelle formation. Given these findings, addition of salts may have application for collecting or concentrating PFOS and other PFAAs in a remediation or water treatment strategy.

Degradation of a persistent organic pollutant perfluorooctane sulphonate with Ti/SnO2–Sb2O5/PbO2-PTFE anode

Abstract PbO2-poly tetra fluoro ethylene (PTFE) coating anode was prepared through electrodeposition method, which involved the use of scanning electron microscope, linear sweep voltammetry, contact angle, and accelerated life test. Degradation of perfluorooctane sulfonate (PFOS) with Ti/PbO2 and Ti/SnO2–Sb2O5/PbO2-PTFE anodes was performed. Operating parameters, including initial concentration of PFOS, current density, and initial pH value were evaluated. Experimental results indicated that Ti/SnO2–Sb2O5/PbO2-PTFE had longer lifespan (46.5 h) than Ti/PbO2 anode (3.5 h). The hydrophobic property of PbO2 was substantially improved after the addition of PTFE. Hydrophilic Ti/PbO2 with the contact angle of 45.4° was transformed into hydrophobic Ti/SnO2–Sb2O5/PbO2-PTFE with a contact angle of 130.9°. The electrochemical performance was also enhanced after PTFE particles were added into PbO2 electrodeposition coating. The oxygen evolution potential was increased by 0.32 V, and removal ratios of PFOS had increased from 53.5% to 89% after addition of PTFE. When initial PFOS concentration varied from 100 mg/L to 300 mg/L, PFOS removal ratios increased with the initial concentration. High current density favored the high PFOS removal ratio and the defluorination ratio. Low pH profited the degradation of PFOS. However, alkaline atmosphere had detrimental effect to the PFOS desulfonation. Intermediate products of PFOS degradation were identified with liquid chromatography system coupled with a triple-stage quadruple mass spectrometer. Moreover, mechanisms of PFOS degradation were proposed.

Degradation of Perfluorooctanesulfonate by Reactive Electrochemical Membrane Composed of Magnéli Phase Titanium Suboxide.

This study investigated the degradation of perfluorooctanesulfonate (PFOS) in a reactive electrochemical membrane (REM) system in which a porous Magnéli phase titanium suboxide ceramic membrane served simultaneously as the anode and the membrane. Near complete removal (98.30 ± 0.51%) of PFOS was achieved under a cross-flow filtration mode at the anodic potential of 3.15 V vs standard hydrogen electrode (SHE). PFOS removal efficiency during the REM operation is much greater than that of the batch operation mode under the same anodic potential. A systematic reaction rate analysis in combination with electrochemical characterizations quantitatively elucidated the enhancement of PFOS removal in REM operation in relation to the increased electroactive surface area and improved interphase mass transfer. PFOS appeared to undergo rapid mineralization to CO2 and F-, with only trace levels of short-chain perfluorocarboxylic acids (PFCAs, C4-C8) identified as intermediate products. Density functional theory (DFT) simulations and experiments involving free radical scavengers indicated that PFOS degradation was initiated by direct electron transfer (DET) on anode to yield PFOS free radicals (PFOS•), which further react with hydroxyl radicals that were generated by water oxidation and adsorbed on the anode surface (•OHads). The attack of •OHads is essential to PFOS degradation, because, otherwise, PFOS• may react with water and revert to PFOS.

Electrooxidation of short and long chain perfluorocarboxylic acids using boron doped diamond electrodes

This study investigates electrooxidation of short (C3-C6) and long (C7-C-18) chain perfluorocarboxylic acids (PFCAs) including perfluorooctane sulfonate (PFOA) using Si/BDD electrode. The effect of operational parameters (supporting electrolyte type, applied current density, and initial pH) were explored for PFOA removal. At the optimized conditions, 74% TOC removal and 37% defluorination ratio were gained for 10 mg L-1 of PFOA solution which evidences that the shorter chain PFCAs were formed. The PFOA degradation pathway followed one direct electron transfer from PFOA molecule to anode surface. Then two different degradation pathways were proposed. The first proposed degradation mechanism involved the reaction of perfluoroheptyl radical and hydroxyl radical, the release of HF and hydrolysis. The second mechanism involved the reaction between perfluoroheptyl radical and O2, formation of C7F15O and perfluorohexyl radical with releasing COF2. The removal of short- (C3-C6) and long-chain PFCAs (C7-C18) was also characterized. More than 95% of removal efficiency was gained for all long-chain PFCAs, excluding C7. The removal ratios of short-chain PFCAs (C3-C6) were 39%, 41%, 66% and 70% for C3, C4, C5 and C6, respectively. Contrary to long-chain PFCAs, chain-length dependence for short-chain PFCAs were observed. Defluorination ratio of short-chain PFCAs was only 45% signifying that defluorination partially occurred. Water matrix did not significantly affect the degradation of short-chain PFCAs in deionized water (DI), river water and secondary effluent of a wastewater treatment plant (WWTP). In contrast, defluorination ratio of long-chain PFCAs was noticeably affected by water matrix with the order of DI water > WWTP effluent > river water.