The effective removal of micropollutants necessitates the use of dense membranes, such as thin-film composite (TFC) reverse osmosis (RO) and nanofiltration (NF) membranes. TFCs have a polyamide active layer interfacially polymerized on a support layer that is typically made of polysulfone (PSu) or polyethersulfone (PES). Retention by NF and RO is often incomplete because micropollutants are adsorbed to the polymer material and subsequently permeate via a combination of convection and diffusion, which evidences a breakthrough curve. When describing breakthrough phenomena, the role of the support membrane is commonly neglected, even though the adsorption in this layer can be significant. This work investigated the adsorption of steroid hormone micropollutants (17 beta-estradiol, E2) by fabricated and commercial PES ultrafiltration membranes with varying morphology. By increasing the coagulation bath temperature between 10 and 70 degrees C, the pure water permeability increased from 13 to 3800 L/m2 center dot h- 1 center dot bar- 1, and consequently, the average pore size rose from 12 to 191 nm. The fabricated membranes with smaller pore sizes showed higher E2 removal via adsorption which can be attributed to the higher internal surface area. The adsorbed mass of fabricated PES membranes (using dimethylformamide (coded as PDG) and N-methyl-2-pyrrolidone (coded as PNG) and PES (Istanbul Technical University (ITU), with nonwoven supports) varies from 0.30 to 0.60, 0.27-0.60 and 1-1.2 ng center dot cm- 2, respectively. These values are lower than the adsorbed masses with commercial Biomax (Millipore Inc.) membranes (0.5-2.0 ng center dot cm- 2). Ultrafiltration membranes used as support for composite membranes, nanofiltration or as filters in sample preparation benefit from lower micropollutant adsorption.

The Gambia River is a tidal and tropical river that covers 12 % of the area of The Gambia and is to date not harnessed for drinking water supply purposes. Previous investigation on water quality indicated that the upper regions, with permanent and pristine freshwater, would be well suited for drinking water supply. With seawater intrusion, however, the downstream tidal and saline region is expanding further inland, requiring desalination technologies. In the urban area near the river mouth, there is potential for water reuse, while addressing the increasing load of micropollutants (MPs) from the discharged wastewater effluents. Ultrafiltration (UF) could decrease the turbidity to ≤0.5 NTU with partial removal of dissolved organic carbon. During UF operation, transmembrane pressure increased due to fouling mainly caused by the high turbidity (up to 140 NTU) in the freshwater region. Nanofiltration/reverse osmosis (NF/RO) removed salinity and achieved the WHO recommendation for drinking water (< 1 g/L as TDS) in the tidal regions with salinities up to 4 g/L. MPs, with a total concentration of up to 26.3 μg/L for pesticides, 38.4 μg/L for pharmaceuticals, and 2.1 μg/L for hormones, were found in a wastewater treatment plant effluent discharged 500 m near the ocean. This led to water quality degradation of the nearby stream, connected to The Gambia River. NF/RO membranes were able to remove most of the MP to concentrations below the surface water guidelines. With an appropriate pretreatment to mitigate fouling, and thus reduce energy consumption and process overall cost, NF/RO technology is well suited for water supply from desalination of the tidal region of The Gambia River and municipal water reuse for non-potable purposes, such as irrigation.

In flow-through reactors, the photodegradation rate can be improved by enhancing contact and increasing the photocatalyst loading. Both can be attained with a higher surface-to-volume ratio. While previous studies focused on thin membranes (30 - 130 mu m) with small pore sizes of 20 - 650 nm, this work employed poly(tetrafluoroethylene) (PTFE) supports, of which pore sizes are in the order of 10 mu m, while the porosities and thicknesses are variable (22.5- 45.3 % and 0.2- 3 mm, respectively). These porous materials were anticipated to allow a higher loading of porphyrin photosensitisers and better light penetration for subsequent photodegradation of steroid hormone micropollutants via singlet oxygen (1O2) generation. The reactor surface refers to the surface within the PTFE pores, while the reactor volume is the total void space inside these pores. The surface-to-volume ratios between 105 and 106 m2/m3 are higher than those of typical microreactors (103 to 104 m2/m3). The weighted average light transmittance varied from 38 % with the thinnest and most porous support to 4.8 % with the thickest support. Good light penetration combined with minimal absorption by PTFE enhanced the light utilisation of the porphyrins when coated in the porous supports. Changes in the support porosity of the coated supports minimally affected steroid hormone removal, because the collision frequency in the very large pores remained relatively constant. However, varying the support thickness, porphyrin loading (0.3- 7.7 mu mol/g), and water flux (150- 3000 L/m2.h), hence the resulting hydraulic residence time, influenced the collision frequency and steroid hormone removal. Results showed that the supports did not outperform membranes most likely because the larger pore size in the former limited contact between the hormones and 1 O 2 . From photostability testing of the pristine supports, perfluoroalkyl substances (PFAS) released from the supports were found at 10- 300 ng/L concentrations during accelerated ageing. While PFAS formation was detectable, the quantities during water treatment operations would be extremely low. In summary, this study elucidates the capability and limitations of porous supports coated with photosensitisers to remove waterborne micropollutants.

Size fractionation of organic matter (OM) by asymmetric flow field-flow fractionation (FFFF) with ultrafiltration (UF) is limited by solute loss and peak resolution, particularly for low molecular weight fractions (<10 kDa). Nanofiltration (NF) with a molecular weight cut-off (MWCO) of <= 1 kDa can achieve significant OM retention and may improve OM fractionation. NF membranes with MWCOs ranging from 0.3 to 3 kDa were used to evaluate the retention and fractionation of nine OMs in the humic, polyphenol, biopolymer, and low molecular weight organic classes in stirred cell NF and FFFF. Membranes with an MWCO of 0.2-0.3 kDa (with a pure water permeability of 5-16 L.m(-2).h(-1).bar(-1)) with low OM interaction exhibited high peak recovery and resolution and hence improved OM fractionation. Loose NF (MWCO 3 kDa) exhibited a poor peak recovery because of a high OM loss due to both adhesion and permeation, particularly at high ionic strengths (>10 mM). A mixture of nine types of OM and natural organic matter samples from rivers, swamps and lakes achieved good fractionation with a 0.3 kDa (NF270) membrane at low ionic strength. The performance of NF for the analysis of OM and colloids in the smallest size range (<= 1 kDa MW) could be further improved by optimizing the salt composition of the mobile phase and by overcoming the pressure limitations of FFFF channels.

Biocatalytic degradation of micropollutants has been extensively explored in both batch and membrane reactors in mu g/L to mg/L concentrations and variable water compositions. The degradation of micropollutants by biocatalytic membranes at environmentally relevant concentrations of ng/L range found in natural surface water matrices has not yet been investigated, presumably because of the challenging concentration analysis. This study investigated the limitations of biocatalytic degradation of estradiol (E2) micropollutant at environmentally relevant concentrations by a biocatalytic membrane. The contributions of solute flux, hydraulic residence time (HRT) and water matrix composition on reaction kinetics, the apparent rate of disappearance (or reaction rate) and enzyme activity were examined. Two biocatalytic membranes were used: i) laccase entrapped in an ultrafiltration (UF) membrane support (namely UF-SNPs) and, ii) laccase covalently bound to the nanofiber matrix of a composite microfiltration (MF) membrane. The three main findings are reported. Firstly, the apparent rate of E2 disappearance decreases significantly by four orders of magnitude at a low micropollutant concentration of 0.1 mu g/L, resulting in undetectable degradation during filtration, irrespective of the biocatalytic membrane. Secondly, the solute mass transfer and HRT control the biocatalytic degradation through the membranes resulting in different E2 removal. For the UF-SNPs membrane, a removal of 31 % is achieved only by increasing the concentration to 3000 mu g/L and at a flux of 60 L/m2.h (HRT of 4.5 s) due to an increase in solute flux by an order of magnitude similar to the apparent rate of disappearance. In contrast, the nano-MF membrane is ineffective in achieving biocatalytic degradation regardless of E2 concentration, as the HRT is approximately seven times lower (0.6 s) than that of the UF-SNPs, and thus insufficient for E2 to reach the catalytic site. Thirdly, the composition of the aqueous matrix plays a crucial role in the control of laccase activity irrespective of the membrane. Indeed, laccase is inactivated predominantly by chloride ions in synthetic carbonate buffer, since the typical NaCl concentration is about two orders of magnitude higher than E2 concentration. This study highlights that the slower kinetics achieved in the biocatalytic UF-SNPs and MF membranes are ineffective in removing steroid hormone micropollutants at realistic concentrations in surface water matrices. Further research is suggested to accelerate the reaction kinetics at such low concentrations and prolong the residence time within the membrane.

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/m2.h, increased PBSAC layer of 6 mm, and small PBSAC particle size of 78 mu m. 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.

Cross-linkers employed to enhance cyclodextrin's (CD) stability and mechanical strength in composite polymers may additionally enhance micropollutant removal. The impact of cross-linker types on the interaction, removal, and uptake of steroid hormones (SHs) with cross-linked beta-cyclodextrin polymer (beta CDP) in functionalized composite nanofiber membranes (CNMs) was investigated. The primary objective of the study was to assess the efficiency of CNM cross-linking with triphenylolmethane triglycidyl ether (TMTE) and trimethylolpropane triglycidyl ether (TPTE) in eliminating SH, as compared to the extensively used epichlorohydrin (EP) that is recognized for its higher toxicity and epoxy-based structure. Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of the cross-linked beta CDP structure, while thermogravimetric analysis (TGA) validated the successful immobilization of beta CDP in nanofiber matrix membranes before and after filtration. The type of cross-linker influenced the uptake of SHs and their removal by the beta CD molecules during filtration. The highest SH removal was achieved with beta CD-EP and beta CD-TPTE, reaching 67 +/- 4 and 59 +/- 5%, with respective uptake values of 10.6 and 9.7 ng/cm2 at a flux of 600 L/m2h and using the nanofiber matrix thickness of 320 and 528 mu m. beta CD-TMTE exhibited the lowest removal (22 +/- 7%) and uptake (4.9 ng/cm2) due to the hindrance posed by its Y-shaped polymeric chain, which limited access to the beta CD cavity. Molecular dynamics simulations further supported these experimental findings, illustrating a more dispersed spatial distribution of SH molecules around the beta CD cavity when TPTE and TMTE were used as cross-linkers, in contrast to EP. In conclusion, triphenylphosphine glycidyl ether (TPTE) could be used as a potential alternative for EP in beta CDP CNMs, given the comparable efficacy in SH removal and uptake. This study highlights the significance of cross-linker selection for designing cyclodextrin-based materials applied to micropollutant removal from water.

Adsorption processes with carbon-based adsorbents have received substantial attention as a solution to remove uranium from drinking water. This study investigated uranium adsorption by a polymer-based spherical activated carbon (PBSAC) characterised by a uniformly smooth exterior and an extended surface of internal cavities accessible via mesopores. The static adsorption of uranium was investigated applying varying PBSAC properties and relevant solution chemistry. Spatial time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed to visualise the distribution of the different uranium species in the PBSAC. The isotherms and thermodynamics calculations revealed monolayer adsorption capacities of 28-667 mg/g and physical adsorption energies of 13-21 kJ/mol. Increasing the surface oxygen content of the PBSAC to 10 % enhanced the adsorption and reduced the equilibrium time to 2 h, while the WHO drinking water guideline of 30 mu gU/L could be achieved for an initial concentration of 250 mu gU/L. Uranium adsorption with PBSAC was favourable at the pH 6-8. At this pH range, uranyl carbonate complexes (UO2CO3(aq), UO2(CO3)22-, (UO2)2CO3(OH)3-) predominated in the solution, and the ToF-SIMS analysis revealed that the adsorption of these complexes occurred on the surface and inside the PBSAC due to intra-particle diffusion. For the uranyl cations (UO22+, UO2OH+) at pH 2-4, only shallow adsorption in the outermost PBSAC layers was observed. The work demonstrated the effective removal of uranium from contaminated natural water (67 mu gU/L) and meeting both German (10 mu gU/L) and WHO guideline concentrations. These findings also open opportunities to consider PBSAC in hybrid treatment technologies for uranium removal, for instance, from high-level radioactive waste.

Photocatalytic membrane reactors (PMRs) are a promising technology for micropollutant removal. Sunlight utilization and catalyst surface sites limit photodegradation. A poly(vinylidene fluoride) (PVDF) nanofiber composite membrane (NCM) with immobilized visible-light-responsive g-C3N4/Bi2MoO6 (BMCN) were developed. Photodegradation of steroid hormones with the PVDF-BMCN NCM was investigated with varying catalyst properties, operating conditions, and relevant solution chemistry under solar irradiation. Increasing CN ratio (0-65%) enhanced estradiol (E2) degradation from 20±10 to 75±7% due to improved sunlight utilization and photon lifetime. PVDF nanofibers reduced self-aggregation of catalysts. Hydraulic residence time and light intensity enhanced the photodegradation. With the increasing pH value, the E2 removal decreased from 84±4 to 67±7% owing to electrical repulsion and thus reduced adsorption between catalysts and E2. A removal of 96% can be attained at environmentally relevant feed concentration (100ng.L–1) with a flux of 60L.m-2.h-1, irradiance of 100mW.cm-2, and 1mg.cm-2 BMCN65 loading. This confirmed that heterojunction photocatalysts can enhance micropollutants degradation in PMRs.

Photocatalytic membrane (PCM) reactors are an emerging technology for the continuous elimination of micropollutants from water. PCM material and process properties define performance limitations. A collision theory framework was established to elucidate the limiting factors of steroid hormone micropollutant photodegradation inside the pores (200 nm) of a palladium-porphyrin-coated polytetrafluoroethylene (PTFE) PCM under simulated sunlight. The collision theory can describe the degree of photodegradation of 17 beta-estradiol (E2). The production of singlet oxygen reactive species was limited by light intensity (up to 14 mW cm- 2), porphyrin loading (up to 50 mu mol g-1), and membrane layer thickness (46 mu m, achieved via stacking thin membranes). Further increases in these parameters did not significantly enhance the removal of E2, because the quantity of singlet oxygen generated, and consequently the collision frequency, levelled off. Not all collisions result in photodegradation reaction. By reducing the reaction time via increasing the E2 molar flux, the rate of disappearance reached a threshold of 7 +/- 2 nmol L- 1 s-1. This is identified as the maximum effective collision frequency, implying that 11 % of the total collisions (64 +/- 5 nmol L- 1 s- 1) resulted in successful reaction. The study presents a novel framework based on collision theory to predict the fundamental mechanisms of and limitations to photodegradation in porphyrin-PTFE membranes, providing unprecedented insight into the performance constraints of diverse membrane reactors for advances in materials and process engineering.

Composite membranes incorporated with high-performance adsorbents are promising for uranium removal. The impact of speciation and ionic strength on uranium adsorption by zeolites was investigated in both static adsorption and composite membrane filtration. Zeolites with high Si/Al ratios exhibited the highest uranium adsorption capacity. Iron-modified zeolite, BEA-Fe30 completely removed uranium at a concentration of 0.6 g/L in static adsorption, with uranium uptake ranging from 125 to 130 μg/g at pH values between 6 and 12. At lower pH values, uptake decreased, dropping to 3 μg/g at pH 2. The increased uranium uptake between pH 6 and 12 is attributed to the formation of a ternary complex involving U(VI), carbonate, and Fe oxide surface (hydr)oxo sites. High ionic strength did not impact the adsorption of uranium. Additionally, PHREEQC modeling was employed to simulate uranium speciation and adsorption behavior under varying pH and ionic strength conditions, further validating experimental findings. Zeolite-loaded microfiltration/ultrafiltration (MF/UF) membranes achieved the WHO guideline of 30 μg/L uranium in the permeate, using less zeolite compared to static adsorption. With 0.25 g of zeolite, the MF/UF process achieved a uranium uptake of 699 μg/g, significantly higher than the 256 μg/g observed in static adsorption. However, uranium removal decreased with increased flow rates, suggesting mass transfer limitations during filtration. The study highlights the potential of composite membranes with high-performance zeolites for efficient uranium removal, contributing to advancements in water purification technologies and addressing environmental contamination.

The growing concern over micropollutants in aquatic ecosystems motivates the development of electrochemical membrane reactors (EMRs) as a sustainable water treatment solution. Nevertheless, the intricate interplay among adsorption/desorption, electrochemical reactions, and byproduct formation within EMR complicates the understanding of their mechanisms. Herein, the degradation of micropollutants using an EMR equipped with carbon nanotube membrane are investigated, employing isotope-labeled steroid hormone micropollutant. The integration of high-performance liquid chromatography with a flow scintillator analyzer and liquid scintillation counting techniques allows to differentiate hormone removal by concurrent adsorption and degradation. Pre-adsorption of hormone is found not to limit its subsequent degradation, attributed to the rapid adsorption kinetics and effective mass transfer of EMR. This analytical approach facilitates determining the limiting factors affecting the hormone degradation under variable conditions. Increasing the voltage from 0.6 to 1.2 V causes the degradation dynamics to transition from being controlled by electron transfer rates to an adsorption-rate-limited regime. These findings unravels some underlying mechanisms of EMR, providing valuable insights for designing electrochemical strategies for micropollutant control. Pervasive micropollutants in aquatic environments pose significant threats to global water supply safety. Here, authors achieved permeate concentrations below the detection limit (2.5 ng/L) using a CNT-based electrochemical membrane, with the contributions of adsorption and degradation distinguished.

Strontium (Sr) removal from water is required because excessive naturally occurring Sr exposure is hazardous to human health. Climate and seasonal changes cause water quality variations, in particular quality and quantity of organic matter (OM) and pH, and such variations affect Sr removal by nanofiltration (NF). The mechanisms for such variations are not clear and thus OM complexation and speciation require attention. Sr removal by NF was investigated with emphasis on the role of OM (type and concentration) and pH (2-12) on possible removal mechanisms, specifically size and/or charge exclusion as well as solute -solute interactions. The filtration results show that the addition of various OM (10 types) and an increase of OM concentration (2-100 mgC.L-1) increased Sr removal by 10-15%. The Sr -OM interaction was enhanced with increasing OM concentration, implying enhanced size exclusion via Sr -OM interaction as the main mechanism. Such interactions were quantified by asymmetric flow field -flow fractionation (FFFF) coupled with an inductively coupled plasma mass spectrometer (ICP-MS). Both extremely low and high pH increased Sr removal due to the enhanced charge exclusion and SrOM interactions. This work elucidated and verified the mechanism of OM and pH on Sr removal by NF membranes.

Cyclodextrins (CD) entrapped in nanofiber composite membranes are potential selective adsorbing materials to remove steroid hormone (SHs) micropollutants from water. This study aims to elucidate the role of CD macrocyclic host type on the SHs inclusion complexation and uptake in filtration. Three CD types (α, β, and γ) are cross-linked with epichlorohydrin to form polymers (αCDP, βCDP and γCDP) and entrapped into a nanofiber composite membrane by electrospinning. TGA analysis confirmed the CD entrapment into the nanofiber without loss of CD molecules during filtration. The CD type plays a dominant role in controlling the removal of different SHs. A similar removal (range 33 to 50 %) was observed with αCDP, irrespective of the SH type. In contrast, removal and uptake dependent on SH type were observed for β and γCDP, with the highest removal of 74 % for progesterone, followed by estradiol (46 %) and estrone (27 %) and the lowest removal of 3 % for testosterone. Molecular dynamic (MD) simulation revealed a stronger and more stable complex formed with βCDP, as demonstrated by: i) the closer spatial distribution of SH molecules from the βCDP cavity and, ii) the quantum chemistry calculations of the lower de-solvation energy (+6.0 kcal/mol), which facilitates the release of water molecules from interacting interface of CD molecule and hormone. Regarding γCDP, the highest de-solvation energy (+8.3 kcal/mol) poses an energetic barrier, which hinders the formation of the inclusion complex. In the case of αCDP, a higher interaction energy (-8.9 kcal/mol) compared to βCDP (-4.9 kcal/mol) was obtained, despite the broader spatial distribution observed from the MD simulation attributed to a dominant hydrogen bonding interaction with the OH primary groups on the external surface cavity. The findings highlight the relevance of the CD type in designing selective adsorbing membranes for steroid hormone micropollutant uptake. Experimental results and MD simulation suggest that βCD is the most suitable CD type for steroid hormone uptake, due to a more stable and stronger inclusion complexation than α and γCD.

Calcium (Ca)-enhanced organic matter (OM) fouling of nanofiltration (NF) membranes leads to reduced flux during desalination and requires frequent cleaning. Fouling mechanisms are not fully understood, which limits the development of targeted fouling control methods. This study employed synchrotron-based X-ray fluorescence (XRF) and X-ray absorption near-edge structure (XANES) spectroscopy to quantify the spatial distribution and mass of Ca deposition as well as changes in the Ca coordination environment characteristic of specific fouling mechanisms, respectively. Bench-scale filtration experiments were performed using feed solutions containing Ca and ten different types of organic matter (OM), as well as the common scalants, calcium carbonate (CaCO3) and calcium sulfate (CaSO4). Osmotic backwash (OB) was performed at regular intervals for fouling control. Ca-OM aggregation resulted in greater flux decline and lower flux recovery during OB than Ca conditioning of membranes followed by filtration of feed solution with OM. Linear combination fitting (LCF) of XANES absorption spectra from fouled membranes indicated that Ca-OM aggregation preferentially occurred for OM types that exhibited both high carboxylic group and negative charge density. Consequently, these OM types exhibited greater deposition of Ca and TOC on the membrane surface when compared to other OM types. For the coexistence of scalants and OM, Ca speciation within the fouling layer was characteristic of both Ca bound to the membrane (i.e. potential bridging, charge screening) as well as Ca-OM aggregation and deposition mechanisms, while a range of crystal polymorphs were observed to occur simultaneously. XRF and XANES represent powerful tools for the elucidation of NF fouling mechanisms by quantification of Ca deposition as well as Ca speciation. Fouling control methods should target OM types with high carboxyl group density and negative charge to neutralize or eliminate interactions with Ca.

Directly coupled photovoltaic-powered nanofiltration/reverse osmosis is a sustainable and cost-effective solution to brackish water desalination in remote areas. Intermittent operation of the system may cause physical membrane damage and loss of membrane integrity. The potential causes of integrity loss during intermittency include the sudden spontaneous restart process, frequent shut-down events, and osmotic backwash (OB) cleaning with controlled permeate backpressure. A bench-scale crossflow system powered by a solar array simulator was used to perform periodic fluctuation on filtration experiments that in this case cause intermittency. A wide range of feed pressure increase rates (0.17 to 2 bar/s) during the start-up process, up to 1000 shut-down events, and additional permeate backpressure up to 4 bar to enhance OB were applied. Results show that no significant membrane performance deterioration was observed at the highest feed pressure increase rate (2 bar/s), and when the shut-down event number increased to 1000 implying the robustness of NF/RO membranes and spontaneous OB cleaning. When increasing permeate backpressure to 2-4 bar to enhance the OB process, membrane integrity loss of both membranes was observed. This demonstrates the reliability and robustness towards fluctuations, intermittency, and spontaneous OB cleaning in a directly coupled photovoltaic-powered nanofiltration/reverse osmosis system if permeate backwash is avoided.

Estimation of membrane molecular weight cut off (MWCO) in the range between ultrafiltration (UF) and nanofiltration (NF) is challenging because retention is not controlled only by size exclusion. This review provides an experimental and theoretical overview of the membrane MWCO in the range from UF to loose NF (from 500 to 0.7 kDa) to evaluate the significance of membrane MWCO on predicting retention of organic solutes when approaching NF pore structure. The experimental section includes filtration of: i) organic tracers with different molecular weights (MW) and properties, such as polyethylene glycol (PEG) and oligosaccharides, and ii) natural organic matter (e.g. humic acid, alginic acid, Tanzanian and Australian organic matter) in the MWCO range between UF and NF, at minimal concentration polarization. The role of molecule structure, size exclusion and charge shielding when filtering organic solutes is elucidated. The molecular structure of uncharged organic tracers plays a major role on MWCO estimation, especially for loose NF membranes, where oligosaccharides are retained more effectively compared to PEG tracers of similar MW. The MWCO determined by PEG filtration and estimated from the pore radius distribution are consistent in the UF range from 1 to 500 kDa, indicating major contribution of size exclusion. Conversely, MWCO of loose NF membranes determined with PEG tracers is overestimated. Charged organics, such as humic acid (1.5 kDa < MW < 3 kDa), shows retention between 60 and 80 % for UF membrane MWCO below 30 kDa (pore radius < 14 nm) and full retention by loose NF (pore radius below 1.4 nm). This is explained with an interplay of size exclusion and charge shielding in the pore. This review can assist in the selection of the organic tracer and operating conditions for membrane MWCO determination between UF and NF, elucidating the relevance of membrane MWCO in organic matter retention.

Experimental water research lacks clear methodology to estimate experimental error. Especially when natural waters are involved, the characterization tools bear method-specific artifacts while the varying environmental conditions prevent regular repeats. This tutorial review identifies common mistakes, and proposes a practical procedure to determine experimental errors at the example of membrane filtration. Statistical analysis is often applied to an insufficient number of repeated measurements, while not all error sources and contributions are considered. This results in an underestimation of the experimental error. Variations in relevant experimental parameters need to be investigated systematically, and the related errors are quantified as a half of the variation between the max and min values when standard deviation is not applicable. Error of calculated parameters (e.g. flux, pollutant removal and mass loss) is estimated by applying error propagation, where weighing contributions of the experimental parameters are considered. Appropriate judgment and five-time repetition of a selected experiment under identical conditions are proposed to validate the propagated experimental error. For validation, the five repeated data points should lie within the estimated error range of the error bar. The proposed error evaluation procedure is adaptable in experimental water research and intended for researchers to identify the contributing factors of an experimental error and carry out appropriate error quantification and validation. The most important aim is to raise awareness of the necessity to question error methodology and reproducibility of experimental data, to produce and publish high quality research.

Glyphosate (GLY) is the most commonly used herbicide worldwide, and aminomethylphosphonic acid (AMPA) is its main metabolite. Their occurrence in ground and surface waters causes diseases in humans, while complex physico-chemical properties hinder detection and effective removal. Polymer-based spherical activated carbon (PBSAC) can adsorb many micropollutants efficiently and, hence, overcome the shortfalls of conventional treatment methods. The static adsorption of a mixture of GLY and AMPA by PBSAC was investigated with varying PBSAC properties and relevant solution chemistry. The results show that PBSAC can remove 95% GLY and 57% AMPA from an initial concentration of 1 µg/L at pH 8.2. PBSAC properties (size, activation level, and surface charge) have a strong influence on herbicide removal, where surface area plays a key role. Low to neutral pH favors non-charge interactions and results in good adsorption, while higher temperatures equally enhance GLY/AMPA adsorption by PBSAC. The work demonstrated the effective removal of GLY to meet the European guideline concentration (0.1 µg/L), while AMPA could not be removed to the required level.

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 −3 pN overcomes the friction force resulting in insignificant adsorption, whereas lowering the drag force from 2.2 × 10 −3 to 4.3 × 10 −4 pN increases the adsorbed mass of hormones from zero to 0.4 ng cm −2 . At a low drag force of 1.6 × 10 −3 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.