Natural organic matter (NOM) can influence the toxicity and speciation of chromium (Cr) in subsurface through redox reactions and complexation. Under anoxic conditions, NOM can be reduced by ...microorganisms or geochemical reductants, and the reduced NOM (NOMred) represents a large reservoir of organic matter observed in anoxic sediments and water. While the current body of work has established the kinetic of Cr(VI) reduction by oxidized NOM (NOMox) under oxic conditions, much less is known about the rates and mechanisms of Cr(VI) reduction triggered by NOMred under anoxic conditions and the colloidal properties of the reaction products. This study provided new information regarding the NOMred-mediated Cr(VI) reduction and colloidal stability of reduced Cr(III) particles over a wide range of environmentally relevant anoxic conditions. We show that under dark anoxic conditions reduced humic acid (HAred) moieties (e.g., quinone) can quickly reduce Cr(VI) to Cr(III), and the reduced Cr(III) can subsequently complex with carboxyl groups of HA leading to the formation of stable HA-Cr(III) colloids. Rates of Cr(VI) reduction by HAred are 3–4 orders of magnitude higher than those by oxidized HA (HAox) due primarily to the higher reducing capacity of HAred. The stable HA-Cr(III) colloids are formed across a range of HA concentrations (8–150 mg C/L) and pH conditions (6–10) with hydrodynamic diameter in the range of 210–240 nm. Aberration-corrected scanning transmission electron microscopy (Cs-STEM) and X-ray photoelectron spectroscopy (XPS) confirmed that the particles are composed of HA-Cr(III). The high colloidal stability of HA-Cr(III) particles could be attributed to the enhanced electrosteric stabilization effect from free and adsorbed HA, which decreased particle aggregation. However, the presence of divalent cations (Ca2+ and Mg2+) promoted particle aggregation at pH 6. These new findings are valuable for our fundamental understanding of the fate and transport of Cr in organic-rich anoxic environments, which also have substantial implications for the development and optimization of subsurface Cr sequestration technology.
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•Reduced NOM can effectively reduce Cr(VI) at pH 5–9 under anoxic conditions.•Rate of Cr(VI) reduction occurred on a time scale of minutes.•Reduced Cr(III) can complex with NOM to form NOM-Cr(III) colloids.•NOM-Cr(III) colloids were stable due to strong electrostatic interactions.•The presence of high Ca2+ and Mg2+ concentrations suppressed colloid formation.
•Main mechanisms of NF method and their relevant parameters are summarized.•The removal efficiencies of EDCs and PhACs under various conditions are reported.•The negative and positive influence of ...NOM on the pollutant removal are discussed.•The full-scale applications of NF built for organic removal are summarized.•Main drawbacks of NF applications for organic matter removal are pointed out.
Nanofiltration (NF) has been increasingly applied in municipal water treatment plants because it has a high removal rate of organic pollutants while simultaneously reserving certain amounts of minerals that are beneficial for drinking water. Endocrine-disrupting compounds (EDCs) and pharmaceuticals (PhACs) are two groups of the most detrimental and ubiquitous emerging organic compounds present in natural waters and are not effectively removed by conventional treatments. NF has proven to be a promising technology in removing EDCs and PhACs if membrane materials and operational conditions are appropriately applied. This paper outlines the removal efficiencies and mechanisms of EDCs and PhACs by NF based on the analysis of properties of the compounds and membranes as well as some important impact factors. The factors (pH, ionic strength and divalent cations) with a significant impact on the configuration of organic pollutants and membranes are summarized. In particular, the influences of natural organic matter (NOM), which play a vital role in NF applications, on the removal of pollutants and membrane fouling are discussed in detail. Furthermore, the models, including extended Derjaguin-Landau-Verwery-Overbeek (XDLVO) theory, applied in the prediction of membrane fouling are introduced as well. Finally, the typical cases of NF treatment plants as well as the corresponding details are summarized. The main drawbacks and expectations in membrane applications are also investigated.
Microplastics (MPs) have been recognized as transport vectors for micropollutants in the natural water environment and the food web; therefore, the sorption behavior of contaminant on MPs has ...recently gained an increased attention. However, a consensus has not yet been reached and information about the adsorption of water contaminants on real MPs remains elusive. Herein, we raise the question of “Should we continue using pure polymers as surrogates for real MPs?” This first systematic study compared the adsorption of multiple micropollutants (i.e. a pesticide, a pharmaceutical, and perfluoroalkyl substances (PFAS)) on a large set of MPs (i.e. 20 well-characterized MPs) and kaolin. Material characterizations results showed various physicochemical and compositional differences between real and pure MPs. Pure polymers had lower normalized uptake values than real MPs in most cases. This was attributed to the surface roughness and/or the presence of fillers (e.g. talc and glass fiber) in real samples. Further, preloaded MPs with natural organic matter (NOM) showed an increased uptake of micropollutants due to forming a complex with NOM and/or co-sorption. These findings indicate that employing real MPs in research studies is critical for obtaining environmentally meaningful results, and the evaluation of MPs sorption behavior without NOM preloading can result in a significant underestimation for their actual values. We also provided an outlook the key areas for further investigations.
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•Real MPs have heterogeneous compositions and contain additives and fillers.•MPs exhibited fast sorption kinetics (<24 h).•NOM preloading on MPs increased their adsorption affinity towards micropollutants.•Real MPs show different sorption behavior from pure polymers.•Results from studies on pure polymers shouldn't be generalized for all MPs.
Due to their submerged and cryptic lifestyle, the vast majority of fungal species are difficult to observe and describe morphologically, and many remain known to science only from sequences detected ...in environmental samples. The lack of practices to delimit and name most fungal species is a staggering limitation to communication and interpretation of ecology and evolution in kingdom Fungi. Here, we use environmental sequence data as taxonomical evidence and combine phylogenetic and ecological data to generate and test species hypotheses in the class Archaeorhizomycetes (Taphrinomycotina, Ascomycota). Based on environmental amplicon sequencing from a well-studied Swedish pine forest podzol soil, we generate 68 distinct species hypotheses of Archaeorhizomycetes, of which two correspond to the only described species in the class. Nine of the species hypotheses represent 78% of the sequenced Archaeorhizomycetes community, and are supported by long read data that form the backbone for delimiting species hypothesis based on phylogenetic branch lengths.Soil fungal communities are shaped by environmental filtering and competitive exclusion so that closely related species are less likely to co-occur in a niche if adaptive traits are evolutionarily conserved. In soil profiles, distinct vertical horizons represent a testable niche dimension, and we found significantly differential distribution across samples for a well-supported pair of sister species hypotheses. Based on the combination of phylogenetic and ecological evidence, we identify two novel species for which we provide molecular diagnostics and propose names. While environmental sequences cannot be automatically translated to species, they can be used to generate phylogenetically distinct species hypotheses that can be further tested using sequences as ecological evidence. We conclude that in the case of abundantly and frequently observed species, environmental sequences can support species recognition in the absences of physical specimens, while rare taxa remain uncaptured at our sampling and sequencing intensity.
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•Faster NOM reaction with •OH than SO4•− was examined using FTICR MS.•NOM reactivity towards SO4•− was highly electron density-dependent.•Reactivity to •OH was co-shaped by ...aromaticity, molecular size and composition.•SO4•− reaction occurred slower through electron transfer and decarboxylation.••OH reacted faster through radical addition and H-abstraction.
The higher scavenging capacity of natural organic matter (NOM) to hydroxyl radical (•OH) than sulfate radical (SO4•−) has been long-acknowledged. However, the difference in reactivity and the influence of initial characteristics, especially at the molecular-level, remain unaddressed. In this study, the reactivities of different NOM isolates to •OH and SO4•− were compared based on the determined second-order rate constants following the depletion of UV254-absorbing moieties. Three NOM isolates with varying characteristics were selected to investigate the influence of initial characteristics on their reactivities. With the identified reactive molecules using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), the distinct reactivity between the radicals and the influence of the initial characteristics were illustrated. The reactivity towards SO4•− was dominated by the electron density of the molecules (i.e., double bond equivalent (DBE)), while that of •OH was also shaped by molecular size (i.e., m/z) and composition (i.e., N- or S-incorporation). The examination on the exclusively reactive molecules (accounting for 10–20%) reflected a preferred H-abstraction by •OH and decarboxylation by SO4•−. Moreover, the analysis on the shared reactive molecules (80–90%) based on the UV254 versus electron-donating capacity (EDC) dependency revealed a prevalent •OH addition while single electron transfer to SO4•−. The different reaction rates associated with the proposed transformation pathways supported the observed higher reactivity of NOM to •OH than SO4•−.
This study compared effects of pH, ionic strength and complexation with Mg2+ on the chromophores and fluorophores of aquatic and terrestrial NOM exemplified by the standard isolates Suwannee River ...fulvic and humic acid (SRFA and SRHA) and Pahokee Peat fulvic and humic acids (PPFA and PPHA) provided by the International Humic Substance Society (IHSS). The intensity of the differential spectra of the NOM isolates increased monotonically with pH. These spectra comprised contributions of similar chromophore systems associated with the carboxylic and phenolic moieties. The intensity of SRFA and PPFA fluorescence changed non-monotonically vs. pH indicating that the deprotonation of the phenolic fluorophores decreased their emission yields. Examination of the effects of pH on the slopes of the log-transformed absorbance of NOM showed that the influence of deprotonation on the conformations of PPFA and PPHA molecules was less prominent than those for SRFA but not dissimilar to those of SRHA. Changes of the differential spectra and spectral slopes showed that Mg2+/PPFA and Mg2+/PPHA complexation was more effected by electrostatic interactions while the involvement of phenolic groups was notable for SRFA. The observed trends highlight similarities and differences in the properties of the chromophores and fluorophores in the standard isolates of soil and aquatic NOM. These results necessitate further systematic comparison of the properties of NOM isolates and those of unaltered NOM.
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The effects of a model natural organic matter (NOM) on the transport of Hg(II) into diffusive gradient in thin-film devices (DGTs) was evaluated in order to better understand their ability to measure ...colloidal Hg species in porewater. The presence of NOM significantly reduced the diffusivity of the Hg(II) species and the reduction was dependent upon NOM to Hg(II) ratio. This relationship was modeled by determining the Hg(II) partition coefficients (Kd) of size fractionated NOM obtained by ultrafiltration and estimating the Hg diffusivity through the DGT for the different NOM size fractions across a range of Hg-NOM ratios. The estimated diffusivities were consistent with experimental observations of uptake into the DGT. Overall, this study indicated that Hg(II) associated with NOM passes into a DGT, however the transport is slowed in accordance with the diffusivity of the NOM to which the Hg(II) is associated. Thus, the Hg—NOM association and complex diffusivities need to be considered when relating DGT uptake to Hg porewater concentration. The results also suggest that Hg(II) associated with colloidal or larger particles of negligible diffusivity are unlikely to contribute significantly to DGT measurements.
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•Accurate interpretation of porewater Hg(II) concentrations by DGTs is needed.•Diffusion parameters were determined for labile Hg species and associated with NOM.•NOM-dominated porewater systems reduce average Hg diffusivity by a factor of 2–5.•Ultrafiltration can be used to determine apparent Hg binding to different size NOM.•A model of size dependent diffusivity describes apparent Hg diffusivity in DGTs.
Gravity-driven membrane (GDM) filtration has been investigated for almost 10 years. The technology is characterized not only by relatively lower transmembrane pressures which can be achieved by ...gravity (extremely low energy consumption), but also by the phenomenon of flux stabilization: A biofilm is allowed to form on the membrane and a stabilization of flux occurs which is related to biological processes within the biofilm layer on the membrane. This enables stable operation during a year or longer without any cleaning or flushing. Initially, the technology was developed mainly for household drinking water treatment, but in the meantime, the research and application has expanded to the treatment of greywater, rainwater, and wastewater as well as the pretreatment of seawater for desalination. This review covers the field from the rather fundamental research on biofilm morphology and microbial community analysis to the impact of feedwater composition, process parameters and organic removal performance. Not only household applications, but also for community-scale treatment and full-scale applications are discussed. In addition, the application potential is highlighted in comparison to conventional ultrafiltration. Finally, an overall assessment is illustrated and the research and development needs are identified.
•Flux stabilization in gravity-driven UF has first been reported in 2010.•Many papers have described this process for water and wastewater treatment.•Mechanisms of biofilm formation and fouling have been studied.•Improved removal of dissolved compounds has been reported.•Total costs can be lower than conventional UF, depending on the scale of application.
The mechanisms governing interactions among various natural organic matter (NOM) fractions and the subsequently impact on ultrafiltration process have not been systematically studied. In this work, ...bovine serum albumin (BSA), humic acid (HA), sodium alginate (SA) were applied as model NOM to explore the influence of the interactions among NOM on ultrafiltration process. Results indicated that tryptophan-like fluorescence fraction was the dominant reaction fraction of HA to react with SA and BSA. Different interactions among model NOM not only changed the interception order of fluorescence fractions by ultrafiltration from fulvic acid-like, humic-like and tryptophan-like in BSA/HA mixture to tryptophan-like, humic-like and fulvic acid-like in BSA/HA/SA/kaolin mixture, but also remarkably influence the membrane fouling behavior. In BSA/HA mixture, new-generated aggregates with molecular weight (MW) of 10 kDa could not pass though ultrafiltration membrane and mainly contributed to chemical reversible fouling. In BSA/HA/SA mixture, SA simultaneously reacted with BSA and HA to generate aggregates with larger MW which could be washed down by physical cleaning. In BSA/HA/SA/kaolin mixture, the aggregates with MW of 10 kDa and chemical reversible fouling were disappeared due to the adsorption role of kaolin. These findings could further improve our understanding regarding membrane fouling mechanisms of raw water with different components.
We present a summary of part of the phytogeographic results described in the author’s PhD thesis. In this case, we characterise and validate several syntaxa of subsaline meadows in the
nom. corr. ...alliance (class.
) in Catalonia (incl. NE Spain and SE France) and in other regions of the Western Mediterranean (N Algeria, Languedoc and Provence). In total, we study six syntaxa in geobotanical terms, based on synthetic tables and factor analyses of correspondence published previously in the thesis: one alliance (
), two associations and three subassociations (
subass.
, subass.
, subass.
;
).
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