Nontarget Analysis and Comprehensive Characterization of Iodinated Polyfluoroalkyl Acids in Wastewater and River Water by LC-HRMS with Cascade Precursor-Ion Exclusions and Algorithmic Approach.

Poly- and perfluoroalkyl acids (PFAAs) are a large family of widespread contaminants of worldwide concern and well-known as "forever chemicals". Direct emission of PFAAs from the fluorochemical industry is a crucial source of PFAA pollutants in the environment. This study implemented nontarget analysis and comprehensive characterization for a category of new PFAA contaminants, i.e., iodinated PFAAs (IPFAAs), in fluorochemical industry wastewater and relevant contaminated river water by liquid chromatography-high-resolution mass spectrometry with a cascade precursor ion exclusion (PIE) strategy and in-house developed data extraction and processing algorithms. A total of 26 IPFAAs (including 2 isomers of an IPFAA) were found and identified with tentative molecular structures. Semiquantification of the IPFAAs was implemented, and the total concentrations of IPFAAs were 0.16-285.52 and 0.15-0.17 µg/L in wastewater and river water, respectively. The high concentrations in association with the predicted ecotoxicities and environmental behaviors demonstrate that these IPFAAs are worthy of more concern and further in-depth research. The cascade PIE strategy along with the data extraction and processing algorithms can be extended to nontarget analysis for other pollutants beyond IPFAAs. The nontarget identification and characterization outcomes provide new understanding on the environmental occurrence and pollution status of IPFAAs from a comprehensive perspective.

An electrocoagulation and electrooxidation treatment train to remove and degrade per- and polyfluoroalkyl substances in aqueous solution.

This study examined the feasibility of a novel treatment train that combines electrocoagulation (EC) with electrooxidation (EO) treatment to remove and degrade per- and polyfluoroalkyl substances (PFASs) from water. Electrocoagulation with a zinc anode could effectively remove PFASs from water, and long-chain PFASs (C7-C10) tended to have a higher removal rate. Foam was generated when a relatively high current density (>1 mA cm-2) was applied to a relatively high PFAS concentration (each PFAS > 0.1 µM) during EC, which promoted the separation of PFASs from the bulk solution, especially for long-chain PFASs. Isotherm-like adsorption results indicated that competitive adsorption on floc occurred between PFASs when no foam was produced in a solution containing 10 different PFASs. Acid dissolution methods could recover and concentrate 10 PFASs in controlled volumes from both the floc and the foam, and it was also successfully applied in groundwater collected from a contaminated site. The concentrated PFASs in the acid solutions were efficiently destructed using EO treatment with a Ti4O7 anode at 10 mA cm-2, and no supplement of electrolyte was needed for the floc dissolved solution. This electrochemical-based process can economically separate, concentrate and destroy PFASs in groundwater and wastewater.

Electrochemical inactivation of bacteria with a titanium sub-oxide reactive membrane.

A reactive electrochemical membrane (REM) system was developed with titanium suboxide microfiltration membrane serving as the filter and the anode, and was examined to inactivate Escherichia coli (E. coli) in water at various current densities. After passing through the membrane filter, the concentration of E. coli decreased from 6.46 log CFU/mL to 0.18 log CFU/mL. The REM operation and effects, including membrane pressure, anode potential, protein leakage, and cell morphology, were characterized under different treatment conditions. It was found that several mechanisms, including membrane filtration, external electrical field influence, and direct oxidation, functioned in concert to lead to bacteria removal and inactivation, and direct oxidation likely played the major role. As revealed by scanning electron microscope and extracellular protein analysis, high current density and voltage caused severe cell damage that resulted in partial or complete cell disintegration. The removal of a model virus, bacteriophage MS2, was also investigated at the current density of 10 mA cm-2 and achieved 6.74 log reduction compared to the original concentration (1011 PFU/mL). In addition to illustration of mechanisms, this study may provide a potentially promising approach that is suitable for decentralized treatment to meet dispersed water disinfection needs.

Laccase induced degradation of perfluorooctanoic acid in a soil slurry.

Perfluorooctanoic acid (PFOA) can induce undesirable effects to humans and animals and has thus attracted much attention from the public and scientific communities in recent years. Extensive studies have been devoted to exploring PFOA degradation in aqueous phase, while information for that in soil is rather limited. Understanding the transformation of PFOA in soil is important in developing strategies to assess and manage its environmental fate. In this study, we have demonstrated that PFOA can be effectively degraded by enzyme catalyzed oxidative humification reactions (ECOHRs) with a natural organic material, soybean meal, as the mediator. In the presence of soybean meal and laccase, PFOA was degraded 24% in water after 36 days, 40% in soil slurry after 140 days. The water extract of soybean meal contained high concentrations of natural organic mediators and multivalent metal ions, both of which were essential to PFOA degradation by ECOHRs. The ECOHR degradation products of PFOA in soil were identified to be partially fluorinated organic compounds, and the molecular features of the products suggest that the degradation mechanism involves free radical chain reaction processes, which was initiated by direct free radical attacks on the CC bonds in perfluoroalkyl acids.

A reactive electrochemical filter system with an excellent penetration flux porous Ti/SnO2-Sb filter for efficient contaminant removal from water.

Tubular porous Ti/SnO2-Sb filters with excellent penetration flux (∼61.94 m3 m-2 h-1 bar-1) and electrochemical activity were prepared by a sol-gel method using low-cost porous titanium filters as the substrates. The porous Ti/SnO2-Sb filters were used as anodic reactive electrochemical membranes to develop reactive electrochemical filter systems, by combining membrane filtration technology with the electrooxidation process, for water treatment. A convection-enhanced rate constant of 4.35 × 10-4 m s-1 was achieved for Fe(CN)6 4- oxidation, which approached the kinetic limit and is the highest reported in an electrochemical system. The electrooxidative performance of the reactive electrochemical filter system was evaluated with 50 mg L-1 rhodamine B (RhB). The results showed that the reactive electrochemical filter system in flow-through mode resulted in an 8.6-fold enhancement in RhB oxidation as compared to those in flow-by mode under the same experimental conditions. A normalized rate constant of 5.76 × 10-4 m s-1 for RhB oxidation was observed at an anode potential of 3.04 V vs. SCE, which is much higher than that observed in a reactive electrochemical filter system with carbon nanotubes and/or Ti4O7 (1.7 × 10-5-1.4 × 10-4 m s-1). The electrical energy per order degradation (EE/O) for RhB was as low as 0.28 kW h m-3 in flow-through mode, with a relatively short residence time of 9.8 min. The overall mineralization current efficiency (MCE) was calculated to be 83.6% with ∼99% RhB removal and ∼51% TOC removal. These results illustrate that this reactive electrochemical filter system is expected to be a promising method for water treatment.

Degradation of sulfadimethoxine catalyzed by laccase with soybean meal extract as natural mediator: Mechanism and reaction pathway.

Natural laccase-mediator systems have been well recognized as an eco-friendly and energy-saving approach in environmental remediation, whose further application is however limited by the high cost of natural mediators and relatively long treatment time span. This study evaluated the water extract of soybean meal, a low-cost compound system, in mediating the laccase catalyzed degradation of a model contaminant of emerging concern, sulfadimethoxine (SDM), and demonstrated it as a promising alternative mediator for soil and water remediation. Removal of 73.3% and 65.6% was achieved in 9 h using soybean meal extract (SBE) as the mediating system for laccase-catalyzed degradation of sulfadimethoxine at the concentration of 1 ppm and 10 ppm, respectively. Further degradation of sulfadimethoxine was observed with multiple SBE additions. Using SBE as mediator increased the 9-h removal of SDM at 1 ppm initial concentration by 52.9%, 49.4%, and 36.3% in comparison to the system mediated by 1-Hydroxybenzotriazole (HBT), p-Coumaric acid (COU) and 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) (ABTS), respectively. With the detection of stable coupling products formed with radical scavenger (5,5-Dimethyl-1-pyrroline N-oxide, DMPO), three phenolic compounds (vanillin, apocynin, and daidzein) in SBE were confirmed to serve as mediators for Trametes versicolor laccase. Reaction pathways were proposed based on the results of High Resolution Mass Spectrometry. SO2 excursion happened during SDM transformation, leading to elimination of antimicrobial activity. Therefore, as a natural, phenol rich, and affordable compound system, the future application of SBE in wastewater and soil remediation is worth exploring.

Factors controlling the rate of perfluorooctanoic acid degradation in laccase-mediator systems: The impact of metal ions.

This study investigated the factors that regulated the degradation of perfluorooctanoic acid (PFOA) in laccase-catalyzed oxidative humification reactions with 1-hydroxybenzotriazole (HBT) as a mediator. The reaction rates were examined under conditions with key factors varied, including initial PFOA concentrations, laccase and HBT dosages, and the ionic contents of the reaction solutions. The PFOA degradation followed pseudo-first order kinetics, and the rate constants (k) were similar for the high (100 µmol L-1) and low (1.00 µmol L-1) initial PFOA concentrations, respectively at 0.0040 day-1 (r2 = 0.98) and 0.0042 day-1 (r2 = 0.86) under an optimum reaction condition tested in this study. The metal ions contained in the reaction solution appeared to have a strong impact on PFOA degradation. Differential UV-Vis spectrometry revealed that Cu2+ can complex with PFOA, which plays an essential role to enable PFOA degradation, probably by bridging the negatively charged PFOA and laccase, so that the free radicals of HBT that are released from laccase can reach and react with PFOA. It was also found that Fe3+ plays a similar role as Cu2+ to enable PFOA degradation in the laccase-HBT reaction system. In contrast, Mg2+ and Mn2+ cannot complex with PFOA under the investigated conditions, and do not enable PFOA degradation in the laccase-HBT system. Fluoride and partially fluorinated compounds were detected as PFOA degradation products using ion chromatography and high resolution mass spectrometry. The structures of the products suggest the reaction pathways involving free-radical initiated decarboxylation, rearrangement, and cross-coupling.

Transformation of 17ß-estradiol in humic acid solution by ε-MnO2 nanorods as probed by high-resolution mass spectrometry combined with (13)C labeling.

Steroidal estrogens (SEs), widespread in aquatic systems, have a potential to disrupt the endocrine system of wildlife species and humans. In our experiments, the performance of ε-MnO2 nanorods in transforming 17ß-estradiol (E2) was investigated, and the effect of humic acid (HA) on the reaction behaviors was systematically characterized. Reconfiguration of humic molecules was also investigated by high-performance size exclusion chromatography (HPSEC). Results indicated that ε-MnO2 nanomaterials ensured efficient removal of E2 from the aqueous solution. The presence of HA hindered the transformation of E2, while enhanced the cross-coupling between E2 and humic molecules. In particular, we used a mixture of un-labeled E2 and (13)C3-labeled E2 at a 1: 1 set ratio (w/w) to probe the reaction products via high-resolution mass spectrometry (HRMS). The combination of HRMS and (13)C3-labeling revealed the intermediate products including estrone (E1), and hydroxylated, quinone-like, and ring-opened species, as well as E2 dimer and trimer. More importantly, possible cross-coupling products between E2 and HA were also identified. A reaction mechanism including two-electron oxidation and single-electron oxidation was proposed. The applied analytical approach using HRMS along with (13)C3-labeling for reaction-product identification is crucial to understanding the role of HA in the transformation of SEs.