Effects of microbial activity on perfluorinated carboxylic acids (PFCAs) generation during aerobic biotransformation of fluorotelomer alcohols in activated sludge

Occurrence, fate, and remediation for per-and polyfluoroalkyl substances (PFAS) in sewage sludge: A comprehensive review

Addressing per-and polyfluoroalkyl substances (PFAS) contamination is an urgent environmental concern. While most research has focused on PFAS contamination in water matrices, comparatively little attention has been given to sludge, a significant by-product of wastewater treatment. This critical review presents the latest information on emission sources, global distribution, international regulations, analytical methods, and remediation technologies for PFAS in sludge and biosolids from wastewater treatment plants. PFAS concentrations in sludge matrices are typically in hundreds of ng/g dry weight (dw) in developed countries but are rarely reported in developing and least-developed countries due to the limited analytical capability. In comparison to water samples, efficient extraction and cleaning procedures are crucial for PFAS detection in sludge samples. While regulations on PFAS have mainly focused on soil due to biosolids reuse, only two countries have set limits on PFAS in sludge or biosolids with a maximum of 100 ng/g dw for major PFAS. Biological technologies using microbes and enzymes present in sludge are considered as having high potential for PFAS remediation, as they are eco-friendly, low-cost, and promising. By contrast, physical/chemical methods are either energy-intensive or linked to further challenges with PFAS contamination and disposal. The findings of this review deepen our comprehension of PFAS in sludge and have guided future research recommendations.

Occurrence of per- and polyfluorinated alkyl substances in wastewater treatment plants in Northern Italy

Wastewater treatment plants are known to be relevant input sources of per- and polyfluoroalkyl substances (PFAS) in the aquatic environment. This study aimed to investigate the occurrence, fate, and seasonal variability of twenty-five PFAS in four municipal wastewater treatment plants (WWTP A, B, C, and D) surrounding the city of Milan (Northern, Italy). Composite 24-h wastewater samples were collected in July and October 2021 and May and February 2022 from influents and effluents of the four WWTPs. PFAS were detected at concentrations ranging between 24.1 and 66.9 μg L-1 for influent and 13.4 and 107 μg L-1 for effluent wastewater samples. Perfluoropentanoic acid was the most abundant (1.91-30.0 μg L-1) in influent samples, whereas perfluorobutane sulfonic acid predominated (0.80-66.1 μg L-1) in effluent samples. In sludge, PFOA was detected in plant A at concentrations in the range of 96.6-165 ng kg-1 dw in primary sludge samples and 98.6-440 ng kg-1 dw in secondary treatment sludge samples. The removal efficiency of total PFAS varied between 6 % and 96 %. However, an increase of PFAS concentrations was observed from influents to effluents for plant D (during July and October), plant A (during October and May), and plant C (during May) indicating that biotransformation of PFAS precursors can occur during biological treatments. This was supported by the observed increase in concentrations of PFOA from primary to secondary treatment sludge samples in plant A. Moreover, the plant operating at shorter hydraulic retention times (plant D) showed lower removal efficiency (<45 %). Seasonal variation of PFAS in influent and effluent appears rather low and more likely due to pulse release instead of seasonal factors.

Structural insights into hydrolytic defluorination of difluoroacetate by microbial fluoroacetate dehalogenases

Fluorine forms the strongest single bond to carbon with the highest bond dissociation energy among natural products. However, fluoroacetate dehalogenases (FADs) have been shown to hydrolyze this bond in fluoroacetate under mild reaction conditions. Furthermore, two recent studies demonstrated that the FAD RPA1163 from Rhodopseudomonas palustris can also accept bulkier substrates. In this study, we explored the substrate promiscuity of microbial FADs and their ability to defluorinate polyfluorinated organic acids. Enzymatic screening of eight purified dehalogenases with reported fluoroacetate defluorination activity revealed significant hydrolytic activity against difluoroacetate in three proteins. Product analysis using liquid chromatography-mass spectrometry identified glyoxylic acid as the final product of enzymatic DFA defluorination. The crystal structures of DAR3835 from Dechloromonas aromatica and NOS0089 from Nostoc sp. were determined in the apo-state along with the DAR3835 H274N glycolyl intermediate. Structure-based site-directed mutagenesis of DAR3835 demonstrated a key role for the catalytic triad and other active site residues in the defluorination of both fluoroacetate and difluoroacetate. Computational analysis of the dimer structures of DAR3835, NOS0089, and RPA1163 indicated the presence of one substrate access tunnel in each protomer. Moreover, protein-ligand docking simulations suggested similar catalytic mechanisms for the defluorination of both fluoroacetate and difluoroacetate, with difluoroacetate being defluorinated via two consecutive defluorination reactions producing glyoxylate as the final product. Thus, our findings provide molecular insights into substrate promiscuity and catalytic mechanism of FADs, which are promising biocatalysts for applications in synthetic chemistry and bioremediation of fluorochemicals.

An overview on human exposure, toxicity, solid-phase microextraction and adsorptive removal of perfluoroalkyl carboxylic acids (PFCAs) from water matrices

Perfluoroalkyl carboxylic acids (PFCAs) are sub-class of perfluoroalkyl substances commonly detected in water matrices. They are persistent in the environment, hence highly toxic to living organisms. Their occurrence at trace amount, complex nature and prone to matrix interference make their extraction and detection a challenge. This study consolidates current advancements in solid-phase extraction (SPE) techniques for the trace-level analysis of PFCAs from water matrices. The advantages of the methods in terms of ease of applications, low-cost, robustness, low solvents consumption, high pre-concentration factors, better extraction efficiency, good selectivity and recovery of the analytes have been emphasized. The article also demonstrated effectiveness of some porous materials for the adsorptive removal of the PFCAs from the water matrices. Mechanisms of the SPE/adsorption techniques have been discussed. The success and limitations of the processes have been elucidated.

Predicting microbial community compositions in wastewater treatment plants using artificial neural networks

BACKGROUND

Activated sludge (AS) of wastewater treatment plants (WWTPs) is one of the world's largest artificial microbial ecosystems and the microbial community of the AS system is closely related to WWTPs' performance. However, how to predict its community structure is still unclear.

RESULTS

Here, we used artificial neural networks (ANN) to predict the microbial compositions of AS systems collected from WWTPs located worldwide. The predictive accuracy R²_1:1 of the Shannon-Wiener index reached 60.42%, and the average R²_1:1 of amplicon sequence variants (ASVs) appearing in at least 10% of samples and core taxa were 35.09% and 42.99%, respectively. We also found that the predictability of ASVs was significantly positively correlated with their relative abundance and occurrence frequency, but significantly negatively correlated with potential migration rate. The typical functional groups such as nitrifiers, denitrifiers, polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), and filamentous organisms in AS systems could also be well recovered using ANN models, with R²_1:1 ranging from 32.62% to 56.81%. Furthermore, we found that whether industry wastewater source contained in inflow (IndConInf) had good predictive abilities, although its correlation with ASVs in the Mantel test analysis was weak, which suggested important factors that cannot be identified using traditional methods may be highlighted by the ANN model.

CONCLUSIONS

We demonstrated that the microbial compositions and major functional groups of AS systems are predictable using our approach, and IndConInf has a significant impact on the prediction. Our results provide a better understanding of the factors affecting AS communities through the prediction of the microbial community of AS systems, which could lead to insights for improved operating parameters and control of community structure. Video Abstract.

Biotransformation of 8:2 Fluorotelomer Alcohol in Soil from Aqueous Film-Forming Foams (AFFFs)-Impacted Sites under Nitrate-, Sulfate-, and Iron-Reducing Conditions

The environmental fate of per- and polyfluoroalkyl substances (PFAS) in aqueous film-forming foams (AFFFs) remains largely unknown, especially under the conditions representative of natural subsurface systems. In this study, the biotransformation of 8:2 fluorotelomer alcohol (8:2 FTOH), a component of new-generation AFFF formulations and a byproduct in fluorotelomer-based AFFFs, was investigated under nitrate-, iron-, and sulfate-reducing conditions in microcosms prepared with AFFF-impacted soils. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and high-resolution mass spectrometry (HRMS) were employed to identify biotransformation products. The biotransformation was much slower under sulfate- and iron-reducing conditions with >60 mol % of initial 8:2 FTOH remaining after ∼400 days compared to a half-life ranging from 12.5 to 36.5 days under nitrate-reducing conditions. Transformation products 8:2 fluorotelomer saturated and unsaturated carboxylic acids (8:2 FTCA and 8:2 FTUA) were detected under all redox conditions, while 7:2 secondary fluorotelomer alcohol (7:2 sFTOH) and perfluorooctanoic acid (PFOA) were only observed as transformation products under nitrate-reducing conditions. In addition, 1H-perfluoroheptane (F(CF₂)₆CF₂H) and 3-F-7:3 acid (F(CF₂)₇CFHCH₂COOH) were identified for the first time during 8:2 FTOH biotransformation. Comprehensive biotransformation pathways for 8:2 FTOH are presented, which highlight the importance of accounting for redox condition and the related microbial community in the assessment of PFAS transformations in natural environments.

Removing nutrients from wastewater by constructed wetlands under perfluoroalkyl acids stress

Constructed wetlands (CWs) are often used to treat wastewater discharged from wastewater treatment plants (WWTPs), while emerging contaminants (such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)) have been commonly discovered in WWTPs. However, no research has examined whether PFOA/OS (i.e. PFOA and PFOS) affects the performance of CW. Therefore, this study compared the nutrient removal efficiencies of four CWs with varied configurations under PFOA/OS and no PFOA/OS stress conditions. We found that CW containing plants or/and iron-carbon had higher removal efficiency for nutrients (except NH₄⁺-N) than conventional CW in stable operation under wastewater without PFOA/OS. Plants or/and iron increased the nutrient removal efficiency by plant uptake, chemical reaction, and co-precipitation of iron hydroxides. In contrast, the iron-carbon inhibited the nitrification of nitrifying bacteria by consuming dissolved oxygen, converting NO₃^--N to NH₄⁺-N. Although the removal efficiencies of nutrients by CWs differed after introducing PFOA/OS, the removal order was consistent with those before adding PFOA/OS. Plants or/and iron-carbon effectively increased CWs' resistance to PFOA/OS loading and toxicity, and the function of iron-carbon was superior to the plants. In addition, PFOA/OS reduced the abundances of microbes Hydrogenophaga, Pseudomonas, Sphingomonas, Nitrospira, and Candidatus_Accumulibacter that contributed to nutrient removal.

Removal of perfluoroalkyl acids and dynamic succession of biofilm microbial communities in the decomposition process of emergent macrophytes in wetlands

Perfluoroalkyl acids (PFAAs) are emerging contaminants that pose significant environmental and health concerns. Water-sediment-macrophyte residue systems were established to clarify the removal efficiency of PFAAs, explore possible removal pathways, and profile the dynamic succession of biofilm microbial communities in the decomposition process. These systems were fortified with 12 PFAAs at three concentration levels. Iris pseudacorus and Alisma orientale were selected as the decomposing emergent macrophytes. The removal rates in the treatments with residues of I. pseudacorus (IP) and A. orientale (AO) were 34.4% to 88.9% and 36.5% to 89.9%, respectively, which were higher than those in the control groups (CG) (30.3% to 86.9%), suggesting that decomposition could alter the removal of PFAAs. Sediment made the greatest contributions (preloaded 14.5% to 77.8% of PFAAs in IP, 14.3% to 78.2% in AO, and 27.4% to 71.9% in CG). PFAAs could also be removed by macrophyte residue sorption (0.0190% to 13.0% in IP and 0.016% to 15.6% in AO) and bioaccumulation of residual biofilm (the contributions of biofilm microbes and their extracellular polymeric substances were 0.0110% to 3.93% and 0.918% to 34.4%, respectively, in IP and 0.0141% to 4.65% and 1.49% to 34.1%, respectively, in AO). Significant correlations were observed between sediment/residue adsorption and bioaccumulation of biofilm microbes, and were significantly correlated with perfluoroalkyl chain length (p < 0.05). The dynamic succession of residual biofilm microbial communities was investigated. The largest difference was found at the preliminary stage. The most similar communities were found in AO on day 70 (with specific genera Macellibacteroides and WCHB1-32) and in IP on day 35 (with specific genera Aeromonas and Flavobacterium). This study is useful to understand the removal of PFAAs during the decomposition process, providing further assistance in removing PFAAs during the life cycle of macrophytes in wetlands.

Per- and polyfluoroalkyl substances in the environment

Over the past several years, the term PFAS (per- and polyfluoroalkyl substances) has grown to be emblematic of environmental contamination, garnering public, scientific, and regulatory concern. PFAS are synthesized by two processes, direct fluorination (e.g., electrochemical fluorination) and oligomerization (e.g., fluorotelomerization). More than a megatonne of PFAS is produced yearly, and thousands of PFAS wind up in end-use products. Atmospheric and aqueous fugitive releases during manufacturing, use, and disposal have resulted in the global distribution of these compounds. Volatile PFAS facilitate long-range transport, commonly followed by complex transformation schemes to recalcitrant terminal PFAS, which do not degrade under environmental conditions and thus migrate through the environment and accumulate in biota through multiple pathways. Efforts to remediate PFAS-contaminated matrices still are in their infancy, with much current research targeting drinking water.

Removal of perfluoroalkyl acids (PFAAs) in constructed wetlands: Considerable contributions of submerged macrophytes and the microbial community

The broad application of perfluoroalkyl acids (PFAAs) has attracted global concern regarding their adverse environmental effects. The possible removal processes of PFAAs in constructed wetlands were excavated and quantified using two typical submerged macrophytes (rooted Potamogeton wrightii and rootless Ceratophyllum demersum). Our results showed that 33.59-88.99% of PFAAs could be removed via not only sediment sorption or phytoextraction but also by the bioaccumulation of microbiota. The sediment acts as a vital sink for PFAAs, preloading 23.51-50.09% and 16.65-52.18% of PFAAs in treatments with P. wrightii (Pw1) and C. demersum (Cd1), respectively. C. demersum showed a better capacity to accumulate PFAAs (0.91-32.03%) than P. wrightii (<10%). Considerable PFAAs were observed to be distributed in microbes, underlining the non-negligible role of microbiota in bioaccumulating PFAAs. The contributions of planktonic microbes, biofilm microbes, and extracellular polymeric substances in biofilms were 0.39-20.96%, 0.03-7.95%, and 0.39-14.15% in Pw1 and 0.23-15.68%, 0.01-15.68%, and 0.53-26.77% in Cd1, respectively. The adsorption/uptake was significantly correlated with the perfluoroalkyl chain length (p<0.05), except for the uptake of biofilms in C. demersum. Furthermore, PFAAs and submerged macrophytes could decrease the richness of microbiota but increase the relative abundance of some strains in Betaproteobacteriales, Sphingomonadales, and Cytophagales. Our results were helpful for understanding the removal processes of PFAAs in constructed wetlands and their linkages with PFAA properties, thus further providing insight into the management and removal of emerging organic contaminants.

Occurrence and dissipation mechanism of organic pollutants during the composting of sewage sludge: A critical review

Sewage sludge contains various classes of organic pollutants, limiting its land application. Sludge composting can effectively remove some organic pollutants. This review summarizesrecent researches on concentration changes and dissipation of different organic pollutants including persistent organic pollutants during sludge composting, and discusses their dissipation pathways and the current understanding on dissipation mechanism. Some organic pollutants like PAHs and phthalates were removed mainly through biodegradation or mineralization, and their dissipation percentages were higher than those of PCDD/Fs and PCBs. Nevertheless, some recalcitrant organic pollutants could be sequestrated in organic fractions of sludge mixtures, and their levels and ARG abundance even increased after sludge composting in some studies, posing potential risks for land application. This review demonstrated that microbial community and their corresponding degradation for organic pollutants were influenced by different pollutants, bulking agents, composting methods and processes. Further research perspectives on removing organic pollutants during sludge composting were highlighted.

Biotransformation of perfluoroalkyl acid precursors from various environmental systems: advances and perspectives

Perfluoroalkyl acids (PFAAs) are widely used in industrial production and daily life because of their unique physicochemical properties, such as their hydrophobicity, oleophobicity, surface activity, and thermal stability. Perfluorosulfonic acids (PFSAs) and perfluorocarboxylic acids (PFCAs) are the most studied PFAAs due to their global occurrence. PFAAs are environmentally persistent, toxic, and the long-chain homologs are also bioaccumulative. Exposure to PFAAs may arise directly from emission or indirectly via the environmental release and degradation of PFAA precursors. Precursors themselves or their conversion intermediates can present deleterious effects, including hepatotoxicity, reproductive toxicity, developmental toxicity, and genetic toxicity. Therefore, exposure to PFAA precursors constitutes a potential hazard for environmental contamination. In order to comprehensively evaluate the environmental fate and effects of PFAA precursors and their connection with PFSAs and PFCAs, we review environmental biodegradability studies carried out with microbial strains, activated sludge, plants, and earthworms over the past decade. In particular, we review perfluorooctyl-sulfonamide-based precursors, including perfluroooctane sulfonamide (FOSA) and its N-ethyl derivative (EtFOSA), N-ethyl perfluorooctane sulfonamido ethanol (EtFOSE), and EtFOSE-based phosphate diester (DiSAmPAP). Fluorotelomerization-based precursors are also reviewed, including fluorotelomer alcohols (FTOH), fluorotelomer sulfonates (FTSA), and a suite of their transformation products. Though limited information is currently available on zwitterionic PFAS precursors, a preliminary review of data available for 6:2 fluorotelomer sulfonamide betaine (FTAB) was also conducted. Furthermore, we update and refine the recent knowledge on biotransformation strategies with a focus on metabolic pathways and mechanisms involved in the biotransformation of PFAA precursors. The biotransformation of PFAA precursors mainly involves the cleavage of carbon-fluorine (C-F) bonds and the degradation of non-fluorinated functional groups via oxidation, dealkylation, and defluorination to form shorter-chained PFAAs. Based on the existing research, the current problems and future research directions on the biotransformation of PFAA precursors are proposed.

A critical review of modeling Poly- and Perfluoroalkyl Substances (PFAS) in the soil-water environment

Due to their health effects and the recalcitrant nature of their CF bonds, Poly- and Perfluoroalkyl Substances (PFAS) are widely investigated for their distribution, remediation, and toxicology in ecosystems. However, very few studies have focused on modeling PFAS in the soil-water environment. In this review, we summarized the recent development in PFAS modeling for various chemical, physical, and biological processes, including sorption, volatilization, degradation, bioaccumulation, and transport. PFAS sorption is kinetic in nature with sorption equilibrium commonly quantified by either a linear, the Freundlich, or the Langmuir isotherms. Volatilization of PFAS depends on carbon chain length and ionization status and has been simulated by a two-layer diffusion process across the air water interface. First-order kinetics is commonly used for physical, chemical, and biological degradation processes. Uptake by plants and other biota can be passive and/or active. As surfactants, PFAS have a tendency to be sorbed or concentrated on air-water or non-aqueous phase liquid (NAPL)-water interfaces, where the same three isotherms for soil sorption are adopted. PFAS transport in the soil-water environment is simulated by solving the convection-dispersion equation (CDE) that is coupled to PFAS sorption, phase transfer, as well as physical, chemical, and biological transformations. As the physicochemical properties and concentration vary greatly among the potentially thousands of PFAS species in the environment, systematic efforts are needed to identify models and model parameters to simulate their fate, transport, and response to remediation techniques. Since many process formulations are empirical in nature, mechanistic approaches are needed to further the understanding of PFAS-soil-water-plant interactions so that the model parameters are less site dependent and more predictive in simulating PFAS remediation efficiency.

First report on the sources, vertical distribution and human health risks of legacy and novel per- and polyfluoroalkyl substances in groundwater from the Loess Plateau, China

In this study, legacy and novel per and polyfluoroalkyl substances (PFASs) were measured in groundwater samples collected from the Loess Plateau of China to understand their occurrence, sources and health risks. The total concentration of PFASs ranged from 2.78 to 115 ng/L, with perfluorooctanoic acid (PFOA) as the dominant compound. Many emerging PFASs, including 6:2 fluorotelomer sulfonates (FTS), 6:2 chlorinated polyfluorinated ether sulfonic acid (Cl-PFESAs), ammonium 4,8-dioxa-3H-perfluorononanoate (ADONA), and hexafluoropropylene oxide (HFPO) homologues were frequently detected in 96.7-100% of the samples. Multiple source apportionment analyses indicated that the PFASs in the groundwater mainly originated from industrial activities, but in rural areas, agricultural activities also contributed. The total oxidizable precursor (TOP) assay indicated that there were substantial unknown precursors of perfluoroalkyl acids (PFAAs) in the groundwater samples. The total concentration of PFASs decreased with the well depth, while the PFAA-precursors displayed contrasting vertical profile trends, which might be due to the suppressed microbial transformation in the groundwater. The potential human health risk caused by PFAS exposure via drinking groundwater in the Loess Plateau was low, except for one site that was close to the industry bases.

Structure Database and In Silico Spectral Library for Comprehensive Suspect Screening of Per- and Polyfluoroalkyl Substances (PFASs) in Environmental Media by High-resolution Mass Spectrometry

Per and polyfluoroalkyl substances (PFASs) are an important class of organic pollutants. Many diverse PFASs are used in commerce and most are not amenable to conventional targeted chemical analysis due to lack of reference standards. Therefore, methods for elucidating the chemical structure of previously unreported or unexpected PFASs in the environment rely extensively on high-resolution mass spectrometry (HRMS). High-throughput structure identification by HRMS is hindered by a lack of PFAS molecular databases and tandem mass spectral libraries. Here, we report a new approach for generating an environmentally relevant PFAS molecular database constructed from curated structure lists and biotic/abiotic in silico predicted transformation products. Further, we have generated a predicted tandem mass spectral library using computational mass spectrometry tools. Results demonstrate the utility of the generated database and approach for identifying PFASs in HRMS-enabled suspect- and nontarget screening studies.

Degradation and effect of 6:2 fluorotelomer alcohol in aerobic composting of sludge

Perfluoroalkyl carboxylates (PFCAs) is toxic to the environment and human health. However, the degradation characteristics of fluorotelomer alcohols (FTOHs), precursors of PFACAs biodegradation, in the sludge during aerobic composting remain unclear. In this study, the degradation characteristics of 6:2 FTOH in sewage sludge by composting were researched and the influences of 6:2 FTOH on the composting process and microbial communities of the sludge were evaluated. After 52 days of composting, 6:2 FTOH retained only 0.73% of its original concentration, and its half-life was less than 1 d; 6:2 FTOH was degraded finally to perfluorohex unsaturated acid, perfluoropentanoic acid, 5:3 polyfluorinated acid (FTCA), 4:3 FTCA, and perfluorobutanoic acid through two pathways; and 6:2 FTCA and 6:2 fluorotel unsaturated acid were the intermediate products. Notably, dosing with 6:2 FTOH affected the composting process of sewage sludge. Additionally, 50 mg/kg 6:2 FTOH resulted in a decrease in the microbial richness and diversity of sludge compost. When compared with the compost without 6:2 FTOH, the proportion of Proteobacteria had increased, and the proportion of Firmicutes had decreased as the concentration of 6:2 FTOH increased. The negative effect of a dosage of 50 mg/kg 6:2 FTOH was more obvious than the effect of other treatments. This study expanded our understanding of the risk of sludge contaminated by 6:2 FTOH being used as a fertilizer after composting.

Aerobic degradation of 4-fluoroaniline and 2,4-difluoroaniline: performance and microbial community in response to the inocula

In this study, a distinct inoculum was investigated as an isolated variable within sequencing batch reactors via a comparison of the 4-fluoroaniline (4-FA) or 2,4-difluoroaniline (2,4-DFA) removal amounts. The inocula were derived from a treatment plant for treating pharmaceutical wastewater plus a small amount of municipal sewage (PMS), a treatment plant for treating fluoridated hydrocarbon wastewater (FHS), and a treatment plant for treating the comprehensive wastewater in an industrial park (CIS). There were slight differences among the degradation patterns of the 4-FA for the three inocula, whether during the enrichment period or the high concentration shock period. In contrast, it was observed that the degradation efficiency of 2,4-DFA initially varied with the inocula. The FHS-derived inoculum was determined to be optimal, exhibiting the earliest degradation reaction only after an acclimation of 7 days had the highest degradation rate constant of 0.519 h^-1, and had the fastest recovery time of three weeks after high concentration shock. Additionally, compared with the PMS-derived inoculum, the CIS-derived inoculum exhibited an earlier degradation reaction within three weeks, and a higher microbial diversity, but a lower shock resistance and degradation rate constant of 0.257 h^-1. High-throughput sequencing demonstrated that each final consortium was different in composition, and the microbial consortia developed well on the inoculum and substrate. In comparison of the similarity among the three 2,4-DFA enrichment cultures, the higher similarity (63.9-70.0%) among three final consortia enriching with 4-FA was observed. The results indicated that the inoculum played an important role in the degradation of FAs and the microbial bacterial communities of final consortia, and the effect extent might well depend on the fluorinated level of FAs.

Anammox reactor exposure to thiocyanate: Long-term performance and microbial community dynamics

Anaerobic ammonium oxidation (anammox) is an autotrophic denitrification process that has broad application potential for treating coking wastewaters. The present study estimated the effects of thiocyanate (SCN^-), a common pollutant in coking wastewaters, on anammox processes and microbial communities in anammox reactors for over two years of continuous exposure. The addition of SCN^- (from 50 to 200 mg L^-1) showed negative effects on the denitrification performance of the anammox reactors. In SCN^--dosed reactors, increased effluent ammonium concentrations indicated the occurrence of SCN^--based biodegradation processes. Microbial analysis revealed that the anammox species almost disappeared in the reactor dosed with SCN^- at over 100 mg L^-1. Instead, an abundance of chemolithoautotrophic bacteria belonging to the Thiobacillus genus demonstrated a linear increase with SCN^- addition. The competition between anammox species and SCN^--degrading microorganisms was expected to dominate the inhibition effects of SCN^- addition on the performance of anammox reactors.

Aerobic biotransformation of fluorotelomer compounds in landfill leachate-sediment

Consumer products containing fluorotelomer polymers are a source of fluorotelomer compounds to the environment following their disposal at landfills. The fate and transformation of fluorotelomer compounds are unknown in landfill leachates. This study investigates the aerobic biotransformation of 8:2 fluorotelomer alcohol (FTOH) and 6:2 fluorotelomer sulfonate (FTS) in landfill leachate-sediment microcosms using batch tests. Spiked 8:2 FTOH, 6:2 FTS and their known biotransformation products were quantified in sediment-leachate and headspace over 90 days under aerobic conditions. 8:2 FTOH and 6:2 FTS biotransformation was slow (half-life >>30 d) in landfill leachate-sediment microcosm, suggesting persistence of fluorotelomer compounds under the conditions investigated. Significant volatilization (>20%) of 8:2 FTOH was observed in the microcosm headspace after 90 days. C6 - C8 and C4 - C6 perfluorocarboxylic acids (PFCAs) were the most abundant products for 8:2 FTOH and 6:2 FTS, respectively. PFCAs accounted for 4-9 mol% of the initially spiked parent compounds at 90 days. Perfluorooctanoic acid (PFOA) was the single most abundant product of 8:2 FTOH (>2.8 mol% at 90 days). The unaccounted mass (20 to 35 mol%) of the initially spiked parent compounds indicated formation of fluorotelomer intermediates and sediment-bound residue. Overall the findings suggest that aerobic biotransformation of fluorotelomer compounds acts as a secondary source of long- and short-chain (≤C7) PFCAs in the environment. Partitioning of semi-volatile fluorotelomer compounds (e.g., 8:2 FTOH) to the gas-phase indicates possible long-range transport and subsequent release of PFCAs in pristine environments. Short-chain fluorotelomer replacements (e.g., 6:2 FTS) result in a higher abundance of short-chain PFCAs in landfill leachate. Future research is needed to understand the long-term exposure effects of short-chain PFCAs to humans, aquatic life and biota.

Formation of perfluorocarboxylic acids from 6:2 fluorotelomer sulfonate (6:2 FTS) in landfill leachate: Role of microbial communities

Fluorotelomer compounds in landfill leachate can undergo biotransformation under aerobic conditions and act as a secondary source of perfluorocarboxylic acids (PFCAs) to the environment. Very little is known about the role of various microbial communities towards fluorotelomer compounds biotransformation. Using an inoculum prepared from the sediment of a leachate collection ditch, 6:2 fluorotelomer sulfonate (6:2 FTS) biotransformation experiments were carried out. Specific substrates (i.e., glucose, ammonia) and ammonia-oxidizing inhibitor (allylthiourea) were used to produce two experimental runs with heterotrophic (HET) growth only and heterotrophic with ammonia-oxidizing and nitrite- oxidizing bacteria (HET + AOB + NOB). After 10 days, ∼20% of the spiked 6:2 FTS removal was observed in HET + AOB + NOB, compared to ∼7% under HET condition. Higher 6:2 FTS removal in HET + AOB + NOB likely resulted from ammonia monooxygenase enzyme that catalyzes the first step of ammonia oxidation. The HET + AOB + NOB condition also showed higher PFCA (C4-C6) formation (∼2% of initially spiked 6:2 FTS), possibly due to higher overall bioactivity. Microbial community analysis through 16s rRNA sequencing confirmed that Proteobacteria and Bacteroidetes were the most abundant phyla (>75% relative abundance) under all experimental conditions. High abundance of Actinobacteria (>17%) was observed under the HET + AOB + NOB condition on day 7. Since Actinobacteria can synthesize a wide range of enzymes including monooxygenases, they likely play an important role in 6:2 FTS biotransformation and PFCA production.

Harnessing fluoroacetate dehalogenase for defluorination of fluorocarboxylic acids: in silico and in vitro approach

Widely distributed fluorocarboxylic acids have aroused worldwide environmental concerns due to its toxicity, persistence, and bioaccumulation. Enzyme-based eco-friendly biodegradation techniques have become increasingly important in treating fluorocarboxylic acids. Here we utilized in silico and in vitro approaches to investigate the defluorination mechanism of fluoroacetate dehalogenase (FAcD) toward monofluoropropionic acids at atomic-level. The experimentally determined k_cat and k_M for defluorination of 2-fluoropropionic acid are 330 ± 60 min^-1 and 6.12 ± 0.13 mM. The in silico results demonstrated positive/negative correlations between activation barriers and structural parameters (e.g. distance and angle) under different enzymatic conformations. We also screened computationally and tested in vitro (enzyme assay and kinetic study) the catalytic proficiency of FAcD toward polyfluoropropionic acids and perfluoropropionic acids which are known to be challenging for enzymatic degradation. The results revealed potential degradation activity of FAcD enzyme toward 2,3,3,3-tetrafluoropropionic acids. Our work will initiate the development of a new "integrated approach" for enzyme engineering to degrade environmentally persistent fluorocarboxylic acids.

Biotransformation of polyfluoroalkyl substances by microbial consortia from constructed wetlands under aerobic and anoxic conditions

The wide application of 6:2 fluorotelomer sulfonate (6:2 FTS) and its precursors results in their ubiquitous occurrence in the environment. This study investigated the biotransformation of 6:2 FTS using fresh slurries collected from constructed wetland under aerobic and anoxic conditions. Biotransformation rates of 6:2 FTS was extremely slow under both aerobic and anoxic conditions. The analysis of transformation products showed that less than 0.7 mol% of initial concentration of 6:2 FTS was biotransformed under anoxic conditions. Effects of 6:2 FTS on the shifts in microbial community in wetland slurry during aerobic and anoxic transformation were evaluated using 16S rRNA gene amplicon sequencing. Under aerobic conditions, 6:2 FTS altered the microbial community structure, in which Methylocaldum (Gamma-proteobacteria) became the predominant genus after being exposed to 6:2 FTS. This means that Methylocaldum appears to have higher tolerance to 6:2 FTS and seems to be potential 6:2 FTS-degrading bacteria. Under anoxic transformation, only the genus Methanomethylovorans (Euryarchaeota) was increased remarkably in wetland slurry exposed to 6:2 FTS.

Biotransformation of Sulfluramid (N-ethyl perfluorooctane sulfonamide) and dynamics of associated rhizospheric microbial community in microcosms of wetland plants

Although the use of Sulfluramid (N-ethyl perfluorooctane sulfonamide (N-EtFOSA)) has been restricted by the Stockholm Convention, it is still frequently detected in the environmental matrices and in use in some countries. Employing constructed wetlands as treatment systems requires understanding of the biodegradation process in the rhizosphere and the effect of contaminants on the microbes of wetlands. This study aimed to investigate the interactions between the microbial community and N-EtFOSA under aerobic and anaerobic conditions. Aerobic biotransformation of N-EtFOSA occurred with a half-life of 0.51 day and yielded 85.1 mol% PFOS of after 91 days. Kinetic modelling revealed that cleavage of the SN was the rate-limiting degradation step. Biotransformation was not observed under anaerobic and anoxic conditions, suggesting that N-EtFOSA is recalcitrant to biodegradation without dissolved oxygen. Under aerobic condition, the presence of N-EtFOSA and its biotransformation products decreased the microbial richness and diversity and exerted selective pressure on the microbial community. Enrichment of Methylocaldum was significant (49%) in the presence of N-EtFOSA compared to unexposed conditions (11%), suggesting that Methylocaldum is relatively tolerant to N-EtFOSA and potentially degrading N-EtFOSA. Under anaerobic conditions, the microbial richness and diversity were not significantly altered by the presence of N-EtFOSA. Only Methanomethylovorans increased significantly in the spiked microcosm (30% vs. 20%). These findings provide knowledge for comprehending the contribution of N-EtFOSA to other PFASs in various environmental conditions, information about microbial community changes in response to PFASs and robust microbial species which can degrade N-EtFOSA in the environment.

Anaerobic biodegradation of 8:2 fluorotelomer alcohol in anaerobic activated sludge: Metabolic products and pathways

The anaerobic biodegradability and metabolic pathways of 8:2 fluorotelomer alcohol (8:2 FTOH) were investigated in anaerobic activated sludge. The biodegradation was well described by a double exponential decay model. 8:2 FTOH was biodegraded to poly- and perfluorinated metabolites with the release of fluoride ion. All polyfluorinated metabolites were intermediate metabolic products and could be further transformed to other metabolites, while perfluorinated metabolites were terminal products. 2H-perfluoro-2-decenoic acid (8:2 FTUA) and perfluorooctanoic acid (PFOA) were verified as the most abundant poly- and perfluorinated metabolites, respectively. Two shorter-chain perfluorinated metabolites, perfluoropentanoic acid (PFPeA) and perfluorobutyric acid (PFBA), were first reported in the biodegradation of 8:2 FTOH. However, the total molar recovery of 8:2 FTOH decreased with increasing incubation time, indicating that there might be some unknown metabolites. Thus, the anaerobic biodegradation pathways were proposed as follows: 8:2 FTOH was oxidized to 8:2 FTUA and 2-perfluorooctyl ethanoic acid (8:2 FTCA) via 2-perfluorooctyl acetaldehyde (8:2 FTAL), and then 8:2 FTUA and 8:2 FTCA were further transformed to 1-perfluoroheptyl ethanol (7:2 sFTOH) via 3-perfluoroheptyl propionic acid (7:3 acid) or/and 3-perfluoroheptyl acrylic acid (7:3 Uacid), and eventually 7:2 sFTOH was further biodegraded to PFOA and other perfluorocarboxylates containing less than eight carbons.

Enhanced generation of perfluoroalkyl carboxylic acids (PFCAs) from fluorotelomer alcohols (FTOHs) via ammonia-oxidation process

With the phase-out of persistent, bioaccumalative, and toxic perfluoroalkyl carboxylic acids (PFCAs), it is needed to explore the potential release of PFCAs from precursors being emitted into the environment. Biotransformation of fluorotelomer alcohols (FTOHs) via biological processes in wastewater treatment plants (WWTPs) leads to discharge of PFCAs into receiving waters. However, the commonly existed microbial activity that can impact on FTOHs biodegradation in WWTPs remains unclear. The objective of present research was to explore the relationship between ammonia-oxidation process and the enhanced PFCAs generation from FTOHs biodegradation under aerobic activated sludge. The obtained results indicate that the cometabolism process performed by nitrifying microorganisms (NMs) was responsible for enhanced PFCAs generation. Among NMs, the ammonia-oxidation bacteria that can express non-specific enzyme of ammonia monooxygenases resulted in the enhanced PFCAs generation from FTOHs. Meanwhile, the different addition amount of ammonia contributed to different defluorination efficiency of FTOHs. The present study further correlated the enhanced PFCAs generation from FTOHs biodegradation with ammonia-oxidation process, which can provide practical information on effective management of PFCAs generation in WWTPs.

Fate of perfluorooctanoic acid (PFOA) in sewage sludge during microwave-assisted persulfate oxidation treatment

The fate of perfluorooctanoic acid (PFOA) has been investigated for an emerging sludge treatment technique using microwave heating-assisted persulfate (PS) oxidation. The effect of heating temperature (20, 50, and 70 °C) and PS dose (PS1: 0.01; PS2: 0.1; PS3: 0.2 g/g wet sludge) was studied in sludge spiked with PFOA at an environmentally relevant concentration (200 ng/g wet weight). Control degradation experiments using spiked sludge without PS addition and background sludge (no PFOA spike) with PS addition were also conducted at each temperature. Sludge samples were analyzed for eight perfluorocarboxylic acids (PFCAs) (C4 - C11) using LC-MS/MS. At 20 °C (PS2 dose), minimal (~ 5%) removal of the spiked PFOA was observed after 72 h, suggesting the need for elevated treatment temperature. For the same PS dose (0.1 g /g sludge), treatment at 50 and 70 °C showed a decrease in PFOA concentration with increasing temperature, with ~ 28 and ~ 42% removal following 4 h of treatment. No significant increase in degradation was observed for the highest dose (PS3) after 2 h, possibly indicating self-scavenging of PS at high dosage. Due to the low initial spiking concentration of PFOA and low extraction recovery, all shorter-chain PFCAs (< C8), the degradation products of PFOA, were below quantification limits in all sludge samples.