Fluoride removal from coal mining water using novel polymeric aluminum modified activated carbon prepared through mechanochemical process.

Defluoridation of coal mining water is of great significance for sustainable development of coal industry in western China. A novel one-step mechanochemical method was developed to prepare polymeric aluminum modified powder activated carbon (PAC) for effective fluoride removal from coal mining water. Aluminum was stably loaded on the PAC through facile solid-phase reaction between polymeric aluminum (polyaluminum chloride (PACl) or polyaluminum ferric chloride (PAFC)) and PAC (1:15 W/W). Fluoride adsorption on PACl and PAFC modified PAC (C-PACl and C-PAFC) all reached equilibrium within 5 min, at rate of 2.56 g mg-1 sec-1 and 1.31 g mg-1 sec-1 respectively. Larger increase of binding energy of Al on C-PACl (AlF bond: 76.64 eV and AlFOH bond: 77.70 eV) relative to that of Al on C-PAFC (AlF bond: 76.52 eV) explained higher fluoride uptake capacity of C-PACl. Less chloride was released from C-PACl than that from C-PAFC due to its higher proportion of covalent chlorine and lower proportion of ionic chlorine. The elements mapping and atomic composition proved the stability of Al loaded on the PAC as well as the enrichment of fluoride on both C-PACl and C-PAFC. The Bader charge, formation energy and bond length obtained from DFT computational results explained the fluoride adsorption mechanism further. The carbon emission was 7.73 kg CO2-eq/kg adsorbent prepared through mechanochemical process, which was as low as 1:82.3 to 1:8.07 × 104 compared with the ones prepared by conventional hydrothermal methods.

Determination of total reducible organofluorine in PFAS-impacted aqueous samples based on hydrated electron defluorination.

Per- and polyfluoroalkyl substances (PFASs) is a large group of thousands of anthropogenic chemicals. Recently, measurement of total organic fluorine (TOF) to reflect the total PFASs has been recommended in limits and advisories. In this study, a total reducible organofluorine (TROF) assay is developed based on hydrated electron (eaq-) conversion of PFASs into inorganic fluorine combined with ion chromatograph, which is a common and widespread instrument. The eaq- is generated in UV/sulfite system with alkaline condition, and the concentration of TROF (CF_TROF) is the difference of fluoride concentration before and after assay. Method validation uses perfluorooctanesulfonic acid, perfluorooctanoic acid and their main alternatives, and F- recoveries are 76.6%-101%, except for perfluorobutanesulfonic acid (48.5%). Method application of TROF assay uses industrial surfactant products and fluorochemical industry-contaminated water, meanwhile, target PFAS analysis and total oxidizable precursors (TOP) assay are concurrently conducted. Concentrations of PFASs detected in target analysis and TOP assay were converted to fluorine equivalents concentrations (CF_Target and CF_TOP). ∑CF_Target and ∑CF_TOP account for 0.80%-36% of CF_TROF in industrial samples, 0.12%-54% in environmental water and 9.7%-14% in wastewater. The TROF assay can be used to initially judge whether PFASs contamination occurred near a hotspot with known sources. The CF_TROF could infer the extent of PFAS contamination in PFAS-impacted samples and estimate the fraction of uncharacterized PFAS.

Degradation of OBS (Sodium p-Perfluorous Nonenoxybenzenesulfonate) as a Novel Per- and Polyfluoroalkyl Substance by UV/Persulfate and UV/Sulfite: Fluorinated Intermediates and Treatability in Fluoroprotein Foam.

Sodium p-perfluorous nonenoxybenzenesulfonate (OBS) is a novel fluorosurfactant used as the alternative to perfluorooctanesulfonic acid (PFOS) in several applications such as fire-fighting foams and chemical enhanced oil recovery ("EOR") in China, with the annual production capacity of about 3,500 t. Here, for the first time, we investigated the degradability of OBS under the conditions of UV/persulfate (UV/PS) and UV/sulfite (UV/SF) as typical redox processes. A higher reaction rate (1.05 min-1) and total organic carbon (TOC) reduction (46.9%) but a low defluorination rate (27.6%) along with the formation of a series of fluorinated intermediates were found in UV/PS, while a high defluorination rate (87.7%) was realized in UV/SF. In particular, a nontargeted workflow using high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC/Q-TOF-MS) was established to detect fluorinated intermediates. Combined with the theoretical calculation, the distinctive degradation pathways in both oxidation and reduction processes were proposed. The degradation mechanism of OBS in UV/SF was proposed to be H/F exchange and subsequent HF elimination. Furthermore, the diluted OBS-based fluoroprotein (FP) foam was used to investigate the degradation of OBS, which confirms the treatability using the redox approach. This work provides insights into the degradability of OBS, fluorinated intermediate search, and proper treatment of related contamination.

Role of hydrogenated moiety in redox treatability of 6:2 fluorotelomer sulfonic acid in chrome mist suppressant solution.

6:2 Fluorotelomer sulfonic acid (6:2 FTS) is used as alternative to perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) for different purposes such as chrome mist suppressant (CMS) and active ingredient in fire-fighting foams. In this study, degradability of 6:2 FTS under ultraviolet/persulfate (UV/PS) and ultraviolet/sulfite (UV/SF), which are typical technologies for advanced oxidation and reduction, were investigated respectively. Due to the hydrogenated moiety, 6:2 FTS was decomposed completely by UV/PS within 10 min, forming a mixture of short-chain perfluoroalkyl carboxylic acids with variable chain length (2-7 carbon atoms). Such oxidation products account for > 50% organofluorine of 6:2 FTS unmineralized portion. 6:2 FTS degradability under reductive UV/SF system was dramatically slowed down by the hydrogenated moiety, which lowered electron affinity and, consequently, reactivity with aqueous electron (eaq‾) produced by UV/SF. Fluorine mass balance showed that degradation intermediates were almost negligible: most of decomposed 6:2 FTS fluorine was converted to fluoride. A real 6:2 FTS-based CMS solution prepared from a commercial product was also tested. Both types of treatment were effective and in good agreement with the trends observed for tests with sole 6:2 FTS. Moreover, experimental results highlighted a remarkable amount of identifiable (like 4:2 FTS, 8:2 FTS and other per-/polyfluoroalkyl substances) and unidentifiable components in the CMS mixture. Indeed, fluoride concentration under UV/SF (73.8 mg/L) and UV/PS (44.9 mg/L) treatment were both higher than the estimated total concentration (<23 mg/L, according to 6:2 FTS concentration). Results strongly suggest that an oxidation pretreatment followed by reduction might be a better way to degrade and defluorinate 6:2 FTS and other precursors with non-fluorinated moieties, rather than employing single reduction or oxidation technology.

Determination of total oxidizable precursors in foam surfactants and foam contaminated water based on UV-activated persulfate oxidation.

In this study, ultraviolet (UV)-activated persulfate under alkaline condition was developed as an alternative Total Oxidizable Precursor (TOP) assay to convert per- and polyfluoroalkyl substances (PFASs) precursors into detectable perfluoroalkyl acids (PFAAs). The conventional heat-based TOP assay takes 6 h at 85 °C, which is time consuming and may lose the volatile PFASs. Shorter time treatment would be beneficial to promote the analysis efficiency of the samples. We here report the UV-based TOP method as faster replacement of conventional heat-based TOP assay. The 6:2 fluorotelomer sulfonate (FTS), 8:2 FTS, and perfluorooctanesulfonamide (FOSA) achieved nearly complete conversion (with the molar yield of PFAAs of 97.2%-109.9%) at 60 min. This new UV-based TOP assay was then applied to 23 industry samples, and the results are comparable with the heat-based TOP assay. The perfluoroalkyl carboxylic acids (PFCAs) concentrations of 23 samples before and after normal TOP assay were 0-4290 mg L-1 and 438-77,420 mg L-1, respectively. The PFCAs after 60 min UV-based TOP assay was 310-81,881 mg L-1. The QuotientMol of 21 samples were 0.71-1.28, the QuotientMol of other two samples were 1.45 and 1.68, this probably due to the loss of volatile precursors during heat-based TOP assay. The UV-based TOP assay is an efficient, reliable and faster alternative to the conventional heat-based TOP assay.

Occurrence and variations of pharmaceuticals and personal-care products in rural water bodies: A case study of the Taige Canal (2018-2019).

A systematic monitoring campaign of pharmaceuticals and personal-care products (PPCPs) was performed in the Taige Canal basin, which is located in a rural area of the Yangtze River Delta. A total of 55 out of 61 monitored PPCPs were detected, with concentrations up to 647 ng/L. The maximum concentrations of 75% of monitored antibiotics and 80% of non-antibiotics were above the median values of previously reported maximum concentrations in China, indicating that the basin is heavily contaminated. It is estimated that the PPCP mass flow of the Taige Canal (0.06-0.58 kg/day) entering into Lake Taihu is similar to that of the influent of a wastewater treatment plant. Analysis of the seasonal variation shows that, during the wet season, the average total concentration of sulfonamides was 8 and 11 times that of the normal season and dry season, respectively. The concentration of sulfachlorpyridazine accounted for 40.37% of total antibiotics, suggesting heavy pollution from the animal-breeding industry in this area. The PPCP mass flow rates observed in 2019 were lower than those of 2018 in the same season, and this interannual variation is mainly attributable to water pollution controls in the watershed. Combined analysis of ordination and clustering indicates that the distribution of PPCPs in the Taige Canal is affected by the confluence with Yong'an River and human activities such as water pollution control. Water-sediment distribution analysis demonstrates that the sediment-water distribution coefficients of quinolone and macrolide were higher than those of sulfonamide, lincosamide and chloramphenicol.

Mechanochemical degradation of perfluorohexane sulfonate: Synergistic effect of ferrate(VI) and zero-valent iron.

Perfluorohexane sulfonate (PFHxS) has been newly recommended to be added into the Stockholm Convention on persistent organic pollutants (POPs). As one of the major perfluoroalkyl pollutants, its long half-time in human serum and neurotoxicity are cause for significant concern. Although mechanochemical degradation has been evaluated as a promising ecofriendly technology to treat pollutants, the extraordinary stability of poly- and perfluoroalkyl substances (PFASs) raises harsh requirements for co-milling reagents. In the present study, zero-valent iron (ZVI) and ferrate(VI) were for the first time used as the co-milling reagents to degrade PFHxS. When ZVI and ferrate(VI) were used alone, both the degradation and defluorination efficiencies were low. However, after milling at the optimum ratio (ferrate(VI):ZVI = 1:2) for 4 h, the synergistic effect of ZVI and ferrate(VI) resulted in almost complete degradation (100%) and defluorination (95%). Two points can account for this excellent performance: (1) the mechanochemical energy input in the system initiates and prominently promotes related reactions; and (2) the active species generated from the reactions among ZVI, ferrate(VI) and other high-valent iron species will accelerate the process of electron transfer. The sulfonate group comprises the favorable attack sites, as corroborated by both the identified intermediates and quantum chemical calculations. The homolysis of the C-S bond is not only the triggering step, but also the rate-limiting step. In summary, the present work confirms the feasibility and underlying mechanism of the ZVI-ferrate(VI) co-milling system to defluorinate PFHxS, which might be a promising technology to treat PFASs in solid wastes.

Role of SiF groups in enhancing interfacial reaction of Fe-MCM-41 for pollutant removal with ozone.

Heterogeneous catalytic ozonation had met the bottlenecks when treating low concentration but high toxic pollutants: (i) the low mass transfer efficiency of ozone and pollutants to hydrophilic catalyst; (ii) the negative impact of coexisted water matrixes. Herein, to enhance the mass transfer efficiency of reactants toward hydrophilic Fe-MCM-41 as well as enhance the interfacial reaction, the fluoride planting Fe-MCM-41 (F-Fe-MCM-41) was synthesized and employed as catalyst in catalytic ozonation for nitrobenzene (NB). Both NB and TOC removal were promoted in F-Fe-MCM-41/O3 with 99.0 % NB removal in 60 min and 88.6 % TOC removal in 120 min, which were superior to the degradation efficiency by O3 and Fe-MCM-41/O3. FTIR, EPR, Mössbauer spectra, 29Si NMR, 19F NMR et al verified that the replacement of non-reactive silanols (-Si-OH) of Fe-MCM-41 with SiF groups could enhance its hydrophobicity, Lewis acidity and mass transfer effect. Comparative characterizations, experiments and theoretical calculations verified that interfacial reaction played the major role over liquid phase reaction for NB degradation in F-Fe-MCM-41/O3. Moreover, the strengthened interfacial reaction also reduced the OH scavenging effect of water matrix, such as humic acid and carbonate. The interfacial adjustment method proposed in this study provided a novel insight into catalyst design and water treatment process.

Removal of F-53B as PFOS alternative in chrome plating wastewater by UV/Sulfite reduction.

Chrome mist suppressants are key chemicals used in the chrome plating industry to reduce exposure of workers by inhalation to airborne chromic acid pollution. Perfluoroalkyl sulfonated compounds are excellent mist suppressants, thanks to their chemical stability and surface activity. Therefore, despite mounting evidence for their persistence, bioaccumulation and toxicity, it is likely that such chemicals will continue to be used for the foreseeable future because of their importance and lack of alternatives. The present study is aimed at assessing the feasibility of advanced reduction as an effective technology to treat chrome plating industry wastewater. In particular, wastewater containing a chlorinated polyfluorinated ether sulfonate (i.e. F-53B), an alternative to perfluorooctanesulfonate (PFOS) used to prepare chrome mist suppressant in China, was treated by UV-activated sulfite. Results demonstrates that in ultrapure water F-53B can be easily degraded within 1 min-much faster than PFOS. Stoichiometric fluoride recovery was also achieved, confirming significant defluorination of the pollutant. Such superior reducibility was due to the presence of chlorine atoms, as corroborated by quantum chemical calculations. F-53B degradation was also achieved in chrome plating industrial wastewater, which yielded results were slower than those achieved in the laboratory nonetheless obtained complete abatement within 60 min. These results suggest that the proposed advanced reduction process is one of the safest options to control PFAS discharge in the environment and reduce the related risks to ecosystems.

Mineralization of salicylic acid via catalytic ozonation with Fe-Cu@SiO2 core-shell catalyst: A two-stage first order reaction.

Mesoporous Fe-Cu@SiO2 core-shell catalyst was synthesized and assessed for its catalytic activity in the ozonation of salicylic acid (SA). The synthesized catalyst was characterized by XRD, TEM, SEM, XPS, H2-TPR, etc. Fe-Cu@SiO2 exhibited a regular spherical shape and had the surface area at 1216 m2 g-1. The wrapping of metal components and their strong interaction prevented metal leaching. Fe-Cu@SiO2 showed the highest activity for SA mineralization when compared with Fe@SiO2 and Cu@SiO2. In Fe-Cu@SiO2/O3, 88% TOC was removed, which was 2.5 times as much as that in sole ozonation. SA degradation efficiency in Fe-Cu@SiO2/O3 increased with initial pH. O3, ·OH and H2O2 were the main reactive oxygen species accounting for SA mineralization. Due to their scavenging effect of ·OH, NH4+, NO3- and humic acids would inhibit the degradation efficiency of Fe-Cu@SiO2/O3. Acidic sites, oxygen vacancies and the Fe-Cu(I/II) electron transfer were responsible for ozone decomposition and ·OH generation. SA mineralization proceeded through the ·OH mechanism. Moreover, SA mineralization in O3 and Fe-Cu@SiO2/O3 both exhibited a two-stage pseudo first-order kinetics (stage I: 0-45 min; stage II: 45-120 min). The degradation intermediates were detected to investigate the reaction pathway. ORP and EEM were used to monitor the degradation process. Great difference was found for carboxylic acids accumulation in O3 and Fe-Cu@SiO2/O3. The accelerated removal of oxalic acid and humic acid-like intermediates were responsible for the two-stage pseudo first-order kinetics.

Degradation of PFOA Substitute: GenX (HFPO-DA Ammonium Salt): Oxidation with UV/Persulfate or Reduction with UV/Sulfite?

Hexafluoropropylene oxide dimer acid (HFPO-DA, ammonium salt with trade name: GenX) has been recently detected in river water worldwide. There are significant concerns about its persistence, and potential adverse effects to the biota. In this study, the degradability of GenX by typical advanced redox technologies (UV/persulfate and UV/sulfate) is investigated. Results demonstrate that <5% GenX is oxidized after 3 h in UV/persulfate system, which is much lower than ∼27% for PFOA. In comparison, GenX can be readily degraded and defluorinated by hydrated electron (eaq-) generated by UV/sulfite system. Specifically, GenX is not detectable after 2 h, and >90% of fluoride ion is recovered 6 h later. This is attributed to the accumulation and subsequent degradation of CF3CF2COOH and CF3COOH, which are stable intermediates of GenX degradation. Mechanistic investigations suggest that the etheric bond in the molecule is a favorable attack point for the eaq-. Such finding is corroborated by quantum chemical calculations. The side CF3- at the α-carbon probably acts as an effective barrier that prevents GenX from being cleaved by SO4-• or OH• at its most sensible point (i.e. the carboxyl group). This study illustrates that reduction by UV/sulfite might be a promising technology to remove GenX from contaminated water.

Vertical distribution of microbial communities in soils contaminated by chromium and perfluoroalkyl substances.

Both Bacteria and Archaea are important players in soil biogeochemical cycles. Both chromium (Cr) and perfluoroalkyl substances (PFASs) are widely present in soil environment. However, the depth-related distribution of microbial community in soils contaminated by Cr or/and PFASs remains unknown. Hence, the present study applied quantitative PCR assay and Illumina MiSeq sequencing to investigate the vertical variations of archaeal and bacterial communities in soils (0.5-12.5m depth) contaminated by chrome plating waste and the potential effects of Cr and PFASs. Both bacterial and archaeal communities displayed the remarkable depth-related changes of abundance (2.16×107-5.05×109 and 4.95×105-2.56×108 16S rRNA gene copies per gram dry soil respectively for Bacteria and Archaea), diversity (bacterial and archaeal Shannon diversity indices of 5.06-6.34 and 2.91-4.61, respectively) and structure. However, at each soil depth, bacterial community had higher abundance, richness and diversity than archaeal community. Soil bacterial communities were mainly composed of Proteobacteria, Chloroflexi, Actinobacteria and Firmicutes, and archaeal communities were dominated by Thaumarchaeota and unclassified Archaea. Moreover, microbial abundance and richness increased with increasing perfluorohexane sulfonate (PFHxS) content. Microbial abundance was correlated to total Cr, and archaeal richness was correlated to total Cr and Cr(IV). In addition, total Cr might be a key determinant of soil microbial community structure.