Micropollutants in the aquatic environment pose a high risk to both environmental and human health. The photocatalytic degradation of steroid hormones in a flow-through photocatalytic membrane ...reactor under UV light (365 nm) at environmentally relevant concentrations (50 ng l–1 to 1 mg l–1) was examined using a polyethersulfone–titanium dioxide (PES–TiO2) membrane. The TiO2 nanoparticles (10–30 nm) were immobilized both on the surface and in the nanopores (220 nm) of the membrane. Water quality and operational parameters were evaluated to elucidate the limiting factors in the degradation of steroid hormones. Flow through the photocatalytic membrane increased contact between the micropollutants and ·OH in the pores. Notably, 80% of both oestradiol and oestrone was removed from a 200 ng l–1 feed (at 25 mW cm–2 and 300 l m–2 h–1). Progesterone and testosterone removal was lower at 44% and 33%, respectively. Increasing the oestradiol concentration to 1 mg l–1 resulted in 20% removal, whereas with a 100 ng l–1 solution, a maximum removal of 94% was achieved at 44 mW cm–2 and 60 l m–2 h–1. The effectiveness of the relatively well-known PES–TiO2 membrane for micropollutant removal has been demonstrated; this effectiveness is due to the nanoscale size of the membrane, which provides a high surface area and facilitates close contact of the radicals with the very small (0.8 nm) micropollutant at an extremely low, environmentally relevant concentration (100 ng l–1).A polyethersulfone–titanium dioxide membrane is demonstrated to be effective at micropollutant removal during the photocatalytic degradation of steroid hormones in a flow-through photocatalytic membrane reactor under UV light at environmentally relevant concentrations.
Nanofiltration (NF) membranes can retain micropollutants (MPs) to a large extent, even though adsorption into the membrane and gradual permeation result in breakthrough and incomplete removal. The ...permeation of MPs is investigated by examining the energy barriers (determined using the Arrhenius concept) for adsorption, intrapore diffusion, and permeation encountered by four different steroid hormones in tight and loose NF membranes. Results show that the energy barriers for steroid hormone transport in tight membrane are entropically dominated and underestimated because of the high steric exclusion at the pore entrance. In contrast, the loose NF membrane enables steroid hormones partitioning at the pore entrance, with a permeation energy barrier (from feed toward the permeate side) ranging between 96 and 116 kJ/mol. The contribution of adsorption and intrapore diffusion to the energy barrier for steroid hormone permeation reveals a significant role of intrapore diffusive transport on the obtained permeation energy barrier. Overall, the breakthrough phenomenon observed during the NF of MPs is facilitated by the low energy barrier for adsorption. Experimental evidence of such principles is relevant for understanding mechanisms and ultimately improving the selectivity of NF.
This study examined the feasibility of nanofiltration (NF) and reverse osmosis (RO) in treating challenging natural tropical waters containing high fluoride and natural organic matter (NOM). A total ...of 166 water samples were collected from 120 sources within northern Tanzania over a period of 16months. Chemical analysis showed that 81% of the samples have fluoride levels exceeding the WHO drinking guideline of 1.5mg/L. The highest fluoride levels were detected in waters characterized by high ionic strength, high inorganic carbon and on some occasions high total organic carbon (TOC) concentrations.
Bench-scale experiments with 22 representative waters (selected based on fluoride concentration, salinity, origin and in some instances organic matter) and 6 NF/RO membranes revealed that ionic strength and recovery affected fluoride retention and permeate flux. This is predominantly due to osmotic pressure and hence the variation of diffusion/convection contributes to fluoride transport. Different membranes had distinct fluoride removal capacities, showing different raw water concentration treatability limits regarding the WHO guideline compliance. BW30, BW30-LE and NF90 membranes had a feed concentration limit of 30–40mg/L at 50% recovery.
NOM retention was independent of water matrices but is governed predominantly by size exclusion. NOM was observed to have a positive impact on fluoride removal. Several mechanisms could contribute but further studies are required before a conclusion could be drawn.
In summary, NF/RO membranes were proved to remove both fluoride and NOM reliably even from the most challenging Tanzanian waters, increasing the available drinking water sources.
•Natural water sources sampled from northern Tanzania indicated high fluoride, inorganic carbon and NOM content.•Effects of operating conditions and water compositions on F and NOM removal by NF/RO were examined for many natural waters.•A positive effect of NOM on F retention is reported for these natural waters.
Comparison of nanofiltration characterization data from literature is challenging due to different hydrodynamics and system designs, which affect membrane retention. In this study, stirred cell (SC), ...micro and macro cross flow systems (micro and macro CF) with different configuration were used to measure salt and organic tracer retention. Minimal concentration polarization conditions were applied in order to:1)evaluate comparability of the systems for characterization of membrane pore radius and molecular-weight-cut-off,2)understand the impact of system configuration and operation on mass transfer,3)compare salt retention at laboratory scale with the retention of spiral wound module.
Results indicated that system dimension was the most important parameter to affect the mass transfer and the concentration of both salt and organic tracers on the membrane surface (Cm) in the macro CF system. Indeed, the higher channel length to width ratio of macro CF was related to reduced mass transfer and higher Cm. However, a comparability of the three systems was observed by operating at low flux (below 80 L/m2h) and higher cross flow velocity (above 0.4 m/s), where the lowest concentration polarization conditions were maintained. This is valid taking into account the variation of hydrodynamics (e.g. relation of Sherwood number and Reynolds range), which is intrinsically related to the different operation modes of dead end and cross flow. This study gives a novel contribution to improve the accuracy of membrane characterization methodologies and to identify suitable operative conditions for testing new membrane materials at small scale.
Display omitted
•Salt retention in micro CF is similar to SWM at minimal concentration polarization condition.•Larger scale (length) dimension in macro CF reduces mass transfer and retention.•Loose NF membrane retention is affected more by system design than tight membrane.•MWCO and pore radius estimated with organic tracer are comparable in all three systems.
Organic micropollutants such as estrogens occur in water in increasing quantities from predominantly anthropogenic sources. In water such micropollutants partition not only to surfaces such as ...membrane polymers but also to any other natural or treatment related surfaces. Such interactions are often observed as sorption in treatment processes and this phenomenon is exploited in activated carbon filtration, for example. Sorption is important for polymeric materials and this is used for the concentration of such micropollutants for analytical purposes in solid phase extraction. In membrane filtration the mechanism of micropollutant sorption is a relatively new discovery that was facilitated through new analytical techniques. This sorption plays an important role in micropollutant retention by membranes although mechanisms of interaction are to date not understood. This review is focused on sorption of estrogens on polymeric surfaces, specifically membrane polymers. Such sorption has been observed to a large extent with values of up to 1.2
ng/cm
2 measured. Sorption is dependent on the type of polymer, micropollutant characteristics, solution chemistry, membrane operating conditions as well as membrane morphology. Likely contributors to sorption are the surface roughness as well as the microporosity of such polymers. While retention—and/or reflection coefficient as well as solute to effective pore size ratio—controls the access of such micropollutants to the inner surface, pore size, porosity and thickness as well as morphology or shape of inner voids determines the available area for sorption. The interaction mechanisms are governed, most likely, by hydrophobic as well as solvation effects and interplay of molecular and supramolecular interactions such as hydrogen bonding, π-cation/anion interactions, π–π stacking, ion–dipole and dipole–dipole interactions, the extent of which is naturally dependent on micropollutant and polymer characteristics. Systematic investigations are required to identify and quantify both relative contributions and strength of such interactions and develop suitable surface characterisation tools. This is a difficult endeavour given the complexity of systems, the possibility of several interactions taking place simultaneously and the generally weaker forces involved.
Display omitted
► Sorption plays an important role in micropollutant retention by membranes. ► Measured sorption was up to 1.2
ng/cm
2 for estrogens. ► The internally accessible surface area of polymers is important. ► Material differences are attributed to a combination of hydrophobic and supramolecular interactions. ► Methodologies need to be developed to measure such interactions qualitatively and quantitatively.
The removal of the trace inorganic contaminants boron (B(OH)
4
−), fluoride (F
−) and nitrate (NO
3
−) from synthetic aqueous solutions containing organic matter using electrodialysis was ...investigated. The transport of the contaminants through the ion-exchange membranes was evaluated in relation to hydrated ionic radius, whereby a positive correlation was found in absence of organic matter. NO
3
−, with the smaller hydrated ionic radius and weaker hydration shell, was removed more effectively than F
−, which has a larger hydrated ionic radius and stronger hydration shell. The removal of F
− and NO
3
− was not significantly influenced by solution pH due to their pH independent speciation. However, the removal of boron was dependent on increasing solution pH and the degree of demineralization. Dissolved organic matter (humic acid, tannic acid and alginic acid) resulted in enhanced removal of boron and F
− as a result of the binding of F
− within the organic matter structure and complexation of boric acid (B(OH)
3) with carboxylate groups in the organic matter. Deposition of organic matter to the anion-exchange membranes was noted. Inorganic trace contaminant and organic matter membrane deposition influenced system performance in regards to an increase in stack resistance and decrease in removal and flux of total dissolved solids.
R-loops are DNA-RNA hybrids enriched at CpG islands (CGIs) that can regulate chromatin states
. How R-loops are recognized and interpreted by specific epigenetic readers is unknown. Here we show that ...GADD45A (growth arrest and DNA damage protein 45A) binds directly to R-loops and mediates local DNA demethylation by recruiting TET1 (ten-eleven translocation 1). Studying the tumor suppressor TCF21 (ref.
), we find that antisense long noncoding (lncRNA) TARID (TCF21 antisense RNA inducing promoter demethylation) forms an R-loop at the TCF21 promoter. Binding of GADD45A to the R-loop triggers local DNA demethylation and TCF21 expression. TARID transcription, R-loop formation, DNA demethylation, and TCF21 expression proceed sequentially during the cell cycle. Oxidized DNA demethylation intermediates are enriched at genomic R-loops and their levels increase upon RNase H1 depletion. Genomic profiling in embryonic stem cells identifies thousands of R-loop-dependent TET1 binding sites at CGIs. We propose that GADD45A is an epigenetic R-loop reader that recruits the demethylation machinery to promoter CGIs.
The transport of hydrated ions through narrow pores is important for a number of processes such as the desalination and filtration of water and the conductance of ions through biological channels. ...Here, molecular dynamics simulations are used to systematically examine the transport of anionic drinking water contaminants (fluoride, chloride, nitrate, and nitrite) through pores ranging in effective radius from 2.8 to 6.5 Å to elucidate the role of hydration in excluding these species during nanofiltration. Bulk hydration properties (hydrated size and coordination number) are determined for comparison with the situations inside the pores. Free energy profiles for ion transport through the pores show energy barriers depend on pore size, ion type, and membrane surface charge and that the selectivity sequence can change depending on the pore size. Ion coordination numbers along the trajectory showed that partial dehydration of the transported ion is the main contribution to the energy barriers. Ion transport is greatly hindered when the effective pore radius is smaller than the hydrated radius, as the ion has to lose some associated water molecules to enter the pore. Small energy barriers are still observed when pore sizes are larger than the hydrated radius due to re‐orientation of the hydration shell or the loss of more distant water. These results demonstrate the importance of ion dehydration in transport through narrow pores, which increases the current level of mechanistic understanding of membrane‐based desalination and transport in biological channels.
The critical role of ion hydration for determining anion selectivity in narrow pores is examined as a function of anion type, pore size, and surface charge. Ion transport is strongly hindered in narrow pores, due to the energetic expense of the required ion dehydration.
Vertically-aligned carbon nanotube (VaCNT) membranes allow water to conduct rapidly at low pressures and open up the possibility for water purification and desalination, although the ultralow viscous ...stress in hydrophobic and low-tortuosity nanopores prevents surface interactions with contaminants. In this experimental investigation, steroid hormone micropollutant adsorption by VaCNT membranes is quantified and explained via the interplay of the hydrodynamic drag and friction forces acting on the hormone, and the adhesive and repulsive forces between the hormone and the inner carbon nanotube wall. It is concluded that a drag force above 2.2 × 10
pN overcomes the friction force resulting in insignificant adsorption, whereas lowering the drag force from 2.2 × 10
to 4.3 × 10
pN increases the adsorbed mass of hormones from zero to 0.4 ng cm
. At a low drag force of 1.6 × 10
pN, the adsorbed mass of four hormones is correlated with the hormone-wall adhesive (van der Waals) force. These findings explain micropollutant adsorption in nanopores via the forces acting on the micropollutant along and perpendicular to the flow, which can be exploited for selectivity.
Glyphosate (GLY) is the most commonly used herbicide worldwide, and aminomethylphosphonic acid (AMPA) is one of its main metabolites. GLY and AMPA are toxic to humans, and their complex ...physicochemical properties present challenges in their removal from water. Several technologies have been applied to remove GLY and AMPA such as adsorption, filtration, and degradation with varied efficiencies. In previous works, an ultrafiltration membrane with permeate-side polymer-based spherical activated carbon (UF-PBSAC) showed the feasibility of removing uncharged micropollutants via adsorption in a flow-through configuration. The same UF-PBSAC was investigated for GLY and AMPA adsorption to assess the removal of charged and lower molecular weight micropollutants. The results indicated that both surface area and hydraulic residence time were limiting factors in GLY/AMPA adsorption by UF-PBSAC. The higher external surface of PBSAC with strong affinity for GLY and AMPA showed higher removal in a dynamic process where the hydraulic residence time was short (tens of seconds). Extending hydraulic residence times (hundreds of seconds) resulted in higher GLY/AMPA removal by allowing GLY/AMPA to diffuse into the PBSAC pores and reach more surfaces. Enhancement was achieved by minimising both limiting factors (external surface and hydraulic residence time) with a low flux of 25 L/m
.h, increased PBSAC layer of 6 mm, and small PBSAC particle size of 78 µm. With this configuration, UF-PBSAC could remove 98 % of GLY and 95 % of AMPA from an initial concentration of 1000 ng/L at pH 8.2 ± 0.2 and meet European Union (EU) regulation for herbicides (100 ng/L for individuals and 500 ng/L for total herbicides). The results implied that UF-PBSAC was able to remove charged micropollutants to the required levels and had potential for application in wastewater treatment and water reuse.
PDF
