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The influence of growth medium water chemistry, specifically carbon/nitrogen (C/N) molar ratios, on the characteristics and development of biofilms of the model microorganism Pseudomonas aeruginosa was investigated. C/N = 9 had a unique effect on biofilm composition as well as quorum sensing (QS) pathways, with higher concentrations of carbohydrates and proteins in the biofilm and a significant upregulation of the QS gene lasI in planktonic cells. The effect of C/N ratio on total attached biomass was negligible. Principal component analysis revealed a different behavior of most outputs such as carbohydrates and QS chemicals at C/N = 9, and pointed to correlations between parameters of biofilm formation and steady state distribution of cells and extracellular components. C/N ratio was also shown to influence organic compound utilization by both planktonic and sessile organisms, with a maximum chemical oxygen demand (COD) removal of 83% achieved by biofilms at C/N = 21. Planktonic cells achieved higher COD removal rates, but greater overall rates after six days occurred in biofilms. The development of a dual-species biofilm of P. aeruginosa and Nitrobacter winogradskyi was also influenced by C/N, with increase in the relative abundance of the slower-growing N. winogradskyi above C/N = 9. These results indicate that altering operational parameters related to C/N would be relevant for mitigating or promoting biofilm formation and function depending on the desired industrial application or treatment configuration.

Ensuring safe water supply for communities across the United States is a growing challenge due to aging infrastructure, impaired source water, strained community finances, etc. In 2019, about 6% of public water utilities in the U.S. had a health-based violation. Due to the high risk of exposure to various contaminants in drinking water, point-of-use (POU) drinking water treatment is rapidly growing in popularity in the U.S. and beyond. POU treatment technologies include various combinations of string-wound sediment filters, activated carbon, modified carbon, ion exchange and redox media filters, reverse osmosis membranes, and ultraviolet lamps depending on the contaminants of concern. While the technologies are well-proven, highly commoditized, and cost-effective, most systems offer little in the way of real-time performance monitoring or interactive technology like other smart home appliances (e.g., thermostats, smoke detectors, doorbells, etc.). Herein, we review water quality regulations and violations in the U.S. as well as state-of-the-art POU technologies and systems with an emphasis on their effectiveness at removing the contaminants most frequently reported in notices of violations. We conclude by briefly reviewing emerging smart water technologies and the needs for advances in the state-of-the-art technologies. The smartness of commercially available POU water filters is critiqued and a definition of smart water filter is proposed.

Conjugated polyaniline has shown anticorrosive, hydrophilic, antibacterial, pH-responsive, and pseudocapacitive properties making it of interest in many fields. However, in situ grafting of polyaniline without harsh chemical treatments is challenging. In this study, we report a simple, fast, and non-destructive surface modification method for grafting tetraaniline (TANI), the smallest conjugated repeat unit of polyaniline, onto several materials via perfluorophenylazide photochemistry. The new materials are characterized by nuclear magnetic resonance (NMR) and electrospray ionization (ESI) mass spectroscopy. TANI is shown to be covalently bonded to important carbon materials including graphite, carbon nanotubes (CNTs), and reduced graphene oxide (rGO), as confirmed by transmission electron microscopy (TEM). Furthermore, large area modifications on polyethylene terephthalate (PET) films through dip-coating or spray-coating demonstrate the potential applicability in biomedical applications where high transparency, patternability, and low bio-adhesion are needed. Another important application is preventing biofouling in membranes for water purification. Here we report the first oligoaniline grafted water filtration membranes by modifying commercially available polyethersulfone (PES) ultrafiltration (UF) membranes. The modified membranes are hydrophilic as demonstrated by captive bubble experiments and exhibit extraordinarily low bovine serum albumin (BSA) and Escherichia coli adhesions. Superior membrane performance in terms of flux, BSA rejection and flux recovery after biofouling are demonstrated using a cross-flow system and dead-end cells, showing excellent fouling resistance produced by the in situ modification.

Herein, we report on the performance of a hybrid organic-ceramic hydrophilic pervaporation membrane applied in a vacuum membrane distillation operating mode to desalinate laboratory prepared saline waters and a hypersaline water modeled after a real oil and gas produced water. The rational for performing &ldquo, pervaporative distillation&rdquo, is that highly contaminated waters like produced water, reverse osmosis concentrates and industrial have high potential to foul and scale membranes, and for traditional porous membrane distillation membranes they can suffer pore-wetting and complete salt passage. In most of these processes, the hard to treat feed water is commonly softened and filtered prior to a desalination process. This study evaluates pervaporative distillation performance treating: (1) NaCl solutions from 10 to 240 g/L at crossflow Reynolds numbers from 300 to 4800 and feed-temperatures from 60 to 85 &deg, C and (2) a real produced water composition chemically softened to reduce its high-scale forming mineral content. The pervaporative distillation process proved highly-effective at desalting all feed streams, consistently delivering &lt, 10 mg/L of dissolved solids in product water under all operating condition tested with reasonably high permeate fluxes (up to 23 LMH) at optimized operating conditions.

The separation performance, energy demand, and operating costs of electro-coagulation (EC) are compared to conventional chemical coagulation for oil&ndash, water separation using a simulated oil- and gas-produced water matrix. An iron-based chemical coagulant and sacrificial iron electrodes are evaluated. Effluent turbidity, chemical oxygen demand (COD), total organic carbon (TOC), and oil and grease (O&amp, G) removal were determined for various coagulant concentrations and reaction times and current densities. Chemical coagulation produced superior turbidity removal when scaled by the total iron dose. At lower iron doses (&lt, 500 mg/L), chemical coagulation yielded better COD, turbidity, and O&amp, G removal. However, chemical coagulation was unable to effectively remove contaminants to meet the offshore discharge limit of 29 ppm O&amp, G. At higher iron doses, EC was more effective at removing COD and O&amp, G. The energy consumption of EC was found to be much higher even when factoring in the energy of production, transporting, and mixing of chemical coagulants, but the overall cost of EC was approximately half the cost of chemical coagulation, and more effective at O&amp, G removal.

There is approximately 508.7 million cubic meters (3.2 million barrels) of oilfield-produced water generated per year across the oil fields of California. While less than 2% of this produced water receives advanced treatment for beneficial reuse, changing regulations and increasing scarcity of freshwater resources is expected to increase the demand for beneficial reuse. This paper reviews onshore-produced water quality across California, relevant standards and treatment objectives for beneficial reuse, identifies contaminants of concern, and treatment process design considerations. Lastly, we evaluate the capital and operating costs of an integrated membrane system for treating produced water based on data from a field pilot conducted in the coastal region of California.

The growth of mineral crystals on surfaces is a challenge across multiple industrial processes. Membrane-based desalination processes, in particular, are plagued by crystal growth (known as scaling), which restricts the flow of water through the membrane, can cause membrane wetting in membrane distillation, and can lead to the physical destruction of the membrane material. Scaling occurs when supersaturated conditions develop along the membrane surface due to the passage of water through the membrane, a process known as concentration polarization. To reduce scaling, concentration polarization is minimized by encouraging turbulent conditions and by reducing the amount of water recovered from the saline feed. In addition, antiscaling chemicals can be used to reduce the availability of cations. Here, we report on an energy-efficient electrophoretic mixing method capable of nearly eliminating CaSO4 and silicate scaling on electrically conducting membrane distillation (ECMD) membranes. The ECMD membrane material is composed of a percolating layer of carbon nanotubes deposited on porous polypropylene support and cross-linked by poly(vinyl alcohol). The application of low alternating potentials (2 Vpp,1Hz) had a dramatic impact on scale formation, with the impact highly dependent on the frequency of the applied signal, and in the case of silicate, on the pH of the solution.

Herein, we report on a mechanism of inorganic fouling observed in a pilot-scale anaerobic membrane bioreactor (AnMBR) treating high strength leachate from domestic food waste. Long-term operation (around 700 days) of the AnMBR encountered frequent, sudden irreversible fouling events driven by biologically induced mineral scaling which required intense chemical cleaning to recover membrane permeability. Mineral scale formation occurred on the surface and within pores of 100 kDa ultrafiltration (UF) membranes. The UF membrane rejected phosphorus, calcium and magnesium up to 97%, 92% and 60%, respectively, which suggests that these ions either precipitated ahead of the UF membranes and existed in a colloidal state and/or precipitated and were retained within UF membrane pores. Microscopic and spectroscopic analyses combined with geochemical modeling confirmed hydroxyapatite, dolomite and struvite were the prevailing mineral precipitates coming from the methanogenic digester; these minerals were embedded in the cake layer and found within membrane pores. Geochemical modeling suggests that slower-growing minerals such as dolomite might precipitate within the membrane pore structures possibly causing membrane pore constriction and/or blocking. Combined use of HOCl (to oxidize and remove organic matter) and citric acid (to dissolve minerals and chelate divalent ions) proved the most effective cleaning regime to recover membrane permeability.

Membrane distillation (MD) is a membrane-based thermal desalination process capable of treating hypersaline brines. Standard MD systems rely on preheating the feed to drive the desalination process. However, relying on the feed to carry thermal energy is limited by a decline of the thermal driving force as the water moves across the membrane, and temperature polarization. In contrast, supplying heat directly into the feed channel, either through the membrane or other channel surfaces, has the potential of minimizing temperature polarization, increasing single-pass water recoveries, and decreasing the number of heat exchangers in the system. When solar thermal energy can be utilized, particularly if the solar heat is optimally delivered to enhance water evaporation and process performance, MD processes can potentially be improved in terms of energy efficiency, environmental sustainability, or operating costs. Here we describe an MD process using layered composite membranes that include a high-thermal-conductivity layer for supplying heat directly to the membrane-water interface and the flow channel. The MD system showed stable performance with water flux up to 9 L/m2/hr, and salt rejection >99.9% over hours of desalinating hypersaline feed (100 g/L NaCl). In addition to bench-scale system, we developed a computational fluid dynamics model that successfully described the transport phenomena in the system.

Microplastics are continuously released into the terrestrial environment from sources where they are used and produced. These microplastics accumulate in soils, sediments, and freshwater bodies, and some are conveyed via wind and water to the oceans. The concentration gradient between terrestrial inland and coastal regions, the factors that influence the concentration, and the fundamental transport processes that could dynamically affect the distribution of microplastics are unclear. We analyzed microplastic concentration reported in 196 studies from 49 countries or territories from all continents and found that microplastic concentrations in soils or sediments and surface water could vary by up to eight orders of magnitude. Mean microplastic concentrations in inland locations such as glacier (191 n L−1) and urban stormwater (55 n L−1) were up to two orders of magnitude greater than the concentrations in rivers (0.63 n L−1) that convey microplastics from inland locations to water bodies in terrestrial boundary such as estuaries (0.15 n L−1). However, only 20% of studies reported microplastics below 20 μm, indicating the concentration in these systems can change with the improvement of microplastic detection technology. Analysis of data from laboratory studies reveals that biodegradation can also reduce the concentration and size of deposited microplastics in the terrestrial environment. Fiber percentage was higher in the sediments in the coastal areas than the sediments in inland water bodies, indicating fibers are preferentially transported to the terrestrial boundary. Finally, we provide theoretical frameworks to predict microplastics transport and identify potential hotspots where microplastics may accumulate.

Herein, loose nanofiltration membranes were prepared using non-solvent induced phase separation (NIPS) method. In NIPS, the non-solvent controls the morphology of the skin layer of the asymmetric membranes formed, while the solvent tunes the morphology of the lower layer. The membranes were made from polyethersulfone in n-methyl pyrrolidone (NMP) with the addition of dicarboxylic acids (glutaric acid, azelaic acid). Aliphatic alcohols (1-butanol, 1-octanol) were added to the solvent to tailor the skin layer pore morphology. Cross-sectional electron microscope images revealed the acids created nano-voids and shorter micro-voids. The addition of alcohols extended the micro-voids and improved symmetry. Pore size distribution results showed that the addition of the alcohols did indeed reduce the pore size as hypothesised. The performance of the modified polyethersulfone membranes was greatly improved in terms of pure water flux and salt passage without sacrificing the dye rejection. The loose nanofiltration membranes prepared in this study showed good dye/salt separation capability compared to most of the results reported in literature. The membranes were compacted with de-ionised water at an applied pressure of 4 bar for 5 h and rejections tests were done at 2 bar. It is hereby reported that the membranes achieved a high salt passage (Na2SO4 rejection varying between

Transport through composite membranes is strongly influenced by the morphologies of both the porous support membrane and overlying selective thin-film (i.e., active layer). Recently, the occurrence of water-filled voids within the active layer has been suggested in the literature; however, their effects on transport are uncertain. Here, we theoretically consider, through numerical modeling, the effect that liquid filled-voids have on the transport of water and solutes through supported thin-film morphologies. Specifically, we evaluated the effect of volume void fraction, void size, and relative location of the voids within the active layer with respect to both surface roughness features and the pores of the support. Transmission electron microscopy image analysis was used to obtain evidence supporting the existence of voids in two commercial brackish and seawater reverse osmosis membranes; the volume fraction of the active layer the voids occupied was determined to be about 30% for both membranes. Our calculations show that, for films with a constant polymer volume, a rough film containing voids is more permeable than an equivalent, homogeneous flat film, due to the creation of shorter paths for diffusion, not due to increased surface area, though the latter is shown to correlate positively with permeability when no base-film exists under the void. Results further illustrate the importance of void position within the thin-film, indicating that even with a significant void fraction, the presence of an underlying polymer base-film negatively impacts the permeability. Voids created closer to the bottom of the active layer will increase membrane permeability. Conversely, results show that even at significant void fractions, voids located closer to the top of the active layer negatively impact the permeability. Variations in the proportion of the active layer overlaying the voids will impact the flux distribution along the membrane, and may be used to reduce flux ‘hotspots’, which may enhance localized concentration polarization and fouling propensity. A strategy for creating high permeability membranes with relatively even flux distributions may include a combination of a rough film with a reduced base thickness, and with thicker regions of the film aligned with the support pore locations. Understanding the role of the voids in determining the transport properties of the membranes provides motivation for controlling their formation.

Application of forward osmosis (FO) membrane to microalgae cultivation processes enables concentration of microalgae and nutrients with low energy consumption. To understand fouling characteristics of FO membrane in concentration of microalgae culture, we studied flux decline, flux recovery by cleaning, and foulants characteristics, in different membrane orientation of active-layer-facing-feed-solution (AL-FS) and active-layer-facing-draw-solution (AL-DS) modes. Batch concentration of Chlorella vulgaris was conducted with a cellulose-triacetate FO membrane. Rapid flux decline and lower flux recovery was observed in AL-DS mode because of inner-membrane fouling including internal pore clogging, adsorption and internal concentration polarization in the support layer. A proportion of polysaccharides in extracellular polymeric substances to soluble microbial products were larger in chemical cleaning effluent than physical one in AL-DS mode, although those were not significantly different in AL-FS mode. Excitation-emission matrix analysis revealed that proteins and humic-like substances were also possible irreversible foulants both in AL-DS and AL-FS modes.

The controlled mixing of streams with different salinity is a potential route for clean and renewable base-load power generation. Here, a comprehensive process model has been developed for pressure-retarded osmosis (PRO) accounting for full-scale system losses such as viscous dissipation, external mass transfer and equipment efficiency. Also, an existing model for reverse electro-dialysis (RED) is adapted to account for analogous full-scale system losses. The models are used to predict practical power densities and process efficiencies. The projected power density for PRO (using best available membranes) is much lower than generally predicted by extrapolation of experimental data. For example, a power density of 4 W/m 2 extrapolated from laboratory experiments actually yielded negative power at full-scale. The maximum power density for PRO is doubled as the hydraulic energy recovery (HER) efficiency is increased from 90% to 99%. Furthermore, the operating pressure, load voltage, and crossflow velocities typically applied in laboratory studies appear much too high to be practical in full-scale PRO and RED systems. Notably, RED systems exhibit a lower system size required for achieving a given degree of mixing, compared with PRO. For both processes, maximum energy efficiency does not occur at thermodynamic equilibrium due to hydraulic losses. Finally, maximum power density appears to be an inadequate parameter for assessing full-scale PRO/RED process feasibility because both processes could produce the same maximum power density, yet exhibit different power outputs and efficiencies and system sizes.

The effects of single and combined fouling by sodium alginate, latex and Al 2 O 3 on membrane performance in terms of permeate flux, salt rejection and rejection of the pharmaceutical carbamazepine were evaluated in a laboratory-scale cross-flow filtration unit. Fouling resulted in different extents in permeate flux, salt rejection and carbamazepine rejection over time. Combined fouling resulted in larger flux declines, and the influence of Ca 2+ addition on flux was pronounced. In contrast, the influence of combined fouling and Ca 2+ addition on salt and carbamazepine rejection was limited. Several hypotheses were tested to assess the influence of fouling on carbamazepine rejection. Relating observed rejection results to the solution-diffusion model revealed insight in whether the effect of fouling on rejection was mainly flux-driven or not. For most foulants, rejection declined less than what was predicted as a function of flux by the solution-diffusion model, indicating that CECP is not the main mechanism responsible for the decline in rejection upon fouling, especially not for latex fouling layers (regardless of the presence of Ca 2+ ). This was corroborated by CECP modelling data. Solute–membrane interaction energies revealed that carbamazepine had higher affinity for the foulants than for the clean membrane surface. As such, it could be hypothesised that for most fouling layers, the relatively small decrease in carbamazepine rejection was mainly due to the decline in flux and the formation of a dense fouling layer on the membrane surface, which had some rejection properties.

In this study, three nonwoven fabrics were used as supports to form thin film composite membranes for forward osmosis (FO) applications. Lignin additive was added to the polysulfone layer in two different concentrations to increase the porosity of the substructure. The fabrics were characterized in terms of their Frazier permeability, tortuosity, porosity, thickness, structural parameter and capillary pressure. It was found that the fabric tortuosity and thickness had strong negative correlations with FO water flux, while fabric porosity had a strong positive correlation. The fabric capillary pressure was found to be indicative of how well the polysulfone layer adhered to the fabric layer. The membrane structural parameter of the fabric, unsupported and supported polysulfone layers were measured and compared using a “resistance-in-series” model. Although seepage of the casting solution into the fabric layer was physically observed, the addition of the individual structural parameters of the layers offered a good approximation of the composite membrane structural parameter. Membrane structural parameters calculated for fabric supported composite membranes using reverse osmosis (RO) permeability parameters and FO/RO established transport equations were much larger than structural parameters obtained from physical measurements. The difference may be due to compaction of composite membranes in reverse osmosis experiments, casting solution seepage partially plugging the upper layers of the support fabric and other non-idealities not captured in the established FO/RO transport equations.

A novel poly(amide-urethane@imide) reverse osmosis (RO) composite membrane with chlorine-tolerant property was prepared on a polysulfone supporting film through two-step interfacial polymerization. The crosslinking agent – 5-choroformyloxyisophaloyl chloride (CFIC) was first reacted with 4-methyl-phenylenediamine (MMPD) via interfacial polymerization to get the nascent poly(amide-urethane) base membrane (CFIC–MMPD) without curing treatment. Then the resultant base membrane contacted again with the second aqueous solution containing functional secondary amine – N,N′-dimethyl-m-phenylenediamine (DMMPD) to obtain the poly(amide-urethane@imide) TFC RO membrane (MMPD–CFIC@CFIC–DMMPD). X-ray photoelectronic spectroscopy (XPS) was combined with attenuated total reflectance infrared (ATR-IR) to verify that the ultrathin polyimide film (CFIC–DMMPD) has been successfully grafted on the surface of the MMPD–CFIC base membrane. The images of scanning electronic microscopy (SEM) and atomic force microscope (AFM) showed that the poly(amide-urethane@imide) membrane has much smoother, more hydrophilic surface than the poly(amide/imide-urethane) membrane (MMPD/DMMPD–CFIC) prepared by conventional one-step interfacial polymerization of CFIC and composite MMPD/DMMPD. However, the permeation experiment revealed that the poly(amide-urethane@imide) membrane has a slight loss in both salt rejection and water flux than the poly(amide/imide-urethane) membrane and conventional commercialized polyamide membrane (MPD–TMC), but exhibits better chlorine-tolerant property due to the introduction of ultrathin polyimide film (CFIC–DMMPD) on the outmost surface of the TFC RO membrane, and the combination of IR and XPS analyses shows a good agreement with the chlorine exposure results of membranes.

The combination of a photochemical (UV) and electrochemical (EL) process led to enhanced degradation of dissolved organic matter in reverse osmosis (RO) concentrate produced from municipal wastewater. Treatment by UV and EL alone resulted in 25% and 35% removal of dissolved organic carbon (DOC) after 5 h, respectively. However, the hybrid process (UVEL) degraded more than 80% of DOC after the same treatment time. Fluorescence excitation–emission matrix spectroscopy and size exclusion chromatography suggest simultaneous and cooperative degradation of backbone aliphatic bonds by UV and aromatic ring cleavage by EL within the UVEL process. Overall, UVEL treatment led to efficient and non-selective degradation of dissolved organics over a wide range of molecular weights. Further, energy consumption and halogenated by-product formation (typically a limiting factor for the application of oxidation technology) were reduced in the UVEL process relative to the UV and EL processes, respectively.

This study was aimed at investigating the effect solution total ionic strength, divalent ion concentration (Ca2+ and Mg2+) and membrane structural properties on the fouling propensity of alginate. The fouling reversibility of the resulting fouling layer was also determined through the use of ultrapure water and salt solutions as cleaning agents. Sodium alginate was used as a model foulant to represent extracellular polymeric substance (EPS) that are present in seawater and wastewater. In order to understand the influence of all possible interactions the membrane was tested using solutions of two ionic strengths (0.1 M and 0.5 M) with varying concentrations of calcium and magnesium ions. Experimental results suggested that membrane orientation had an impact on fouling behavior since the membrane fouled more easy when operated in PRO mode than in FO mode. There was severe permeate flux decline in PRO mode mainly due to the calcium–alginate complexes blocking the pores in the support layer. The interfacial free energies obtained from advanced contact angle measurements correlated strongly with the rates of membrane fouling and further predicted the membrane fouling trends. Initial adhesion of alginate particles on the membrane surface was dictated by the chemical interactions between the membrane and alginate. It was also found that once the membrane surface is covered with the foulant, fouling becomes less sensitive to the changes in hydrodynamic conditions (permeation drag and cross-flow velocity) but rather depends on the foulant–foulant interactions. The resulting fouling layer was easily removed by shear force resulting from increased cross-flow velocity during membrane cleaning.

This paper reports on the effects of lignin, polyvinyl pyrrolidone and polyethylene glycol as additives to polysulfone ultrafiltration membranes prepared by nonsolvent induced phase separation. The focus is on the mechanical and thermal properties of the resultant membranes. Differential scanning calorimetry (DSC) and thermogravimetric analysis were used to probe the thermal properties, while an Instron tensile tester was used to characterise the mechanical properties. Morphological studies indicate that the porosity of the bottom sub-layer increased with the use of each additive, suggesting that coagulation in the sub-layer differed from that of the top layer. Membranes fabricated using lignin were thermally stable as the residue at 800 °C increased from 13% to 44%, suggesting interaction of lignin with the polymer. The increase in free fractional volume was confirmed by DSC thermograms as the glass transition temperature decreased considerably after incorporating the additives. Generally, the modulus and tensile strength decreased after the introduction of the additives. These results offer new insight into the use of an emerging, cheap and readily available natural additive (lignin) compared to traditional synthetic additives in membrane formation.

Herein, we review mechanisms and models of solute transport relevant to nanofiltration (NF), reverse osmosis (RO), and forward osmosis (FO) membrane separation processes. We first consider state of the art polymeric NF, RO, and FO membrane properties and how these properties influence water and solute transport. Next, we critically review classical models (i.e., pore flow, solution-diffusion, and Nernst–Planck) and discuss the shortcomings of each, particularly focusing on their inability to explain fundamental relationships between water/solute transport and membrane properties, such as free volume, crystallinity, extent of swelling, and the presence of filler materials in mixed matrix/nanocomposite membranes. We then review modern structure–performance models that attempt to relate water/solute transport to quantifiable membrane structure and solute/water/polymer interactions. Finally, we consider both classical and modern mass transfer models that describe external, internal, and enhanced concentration polarization – all of which strongly influence water/solute transport through NF, RO, and FO membranes.

Hybridization of a UV-C photoreactor with an electrochemical cell led to the discovery of a distinctive synergistic mechanism for the degradation and mineralization of phenol when free chlorine-producing anodes were utilized in the presence of chloride. After 6 h, photochemical (UV) treatment resulted in 29% phenol mineralization and electrochemical (EL) treatment resulted in 35% and 52% mineralization using boron-doped diamond (BDD) and ruthenium oxide on titanium (DSA-Cl 2 ) anodes, respectively. However, the photo-assisted electrochemical (UVEL) process removed 88% and 96% of total organic carbon (TOC) after 6 h with BDD and DSA-Cl 2 anodes, respectively. The hybrid UVEL process generated highly reactive hydroxyl and chlorine radicals by the photolysis of in situ electrogenerated free chlorine. As a result, the UVEL treatment produced fewer chlorinated by-products compared to EL alone. UVEL with DSA-Cl 2 had the highest TOC removal after 6 h (96%), one of the highest mineralization rates (0.38 h −1 ), and the lowest energy demand per order TOC removed (E EO = 104 kW h m −3 order −1 ) without any residual toxicity after dechlorination. Generally, conventional advanced oxidation processes (UV/O 3 and UV/H 2 O 2 ) were most effective at mineralization up to 50%, but UVEL appeared more cost effective for mineralization beyond 75%.

The effects of feed solution ionic strength, pH and divalent cation content on NF/RO membrane structure and performance were elucidated experimentally and fitted with a modified solution–diffusion transport model that describes polyamide thin film free volume through an effective pore radius and structure factor. All the membranes tested became more hydrophilic and swollen with increasing feed solution ionic strength, pH, and divalent cation concentrations. Generally, water permeabilities of all three membranes decreased with ionic strength and divalent cation content, but increased with pH. For RO membranes, neutral solute rejection decreased with pH and divalent cation content, but increased with ionic strength and the salt rejection remained independent with water chemistry except for very low pH of 3; for a NF membrane, solute rejection was more sensitive to water chemistry and neutral solute rejection decreased with ionic strength and pH, but increased with divalent cation content. The results presented herein provide new insight into the fundamental relationship between changes in NF/RO membrane structure and performance. Ultimately, these new insights may be useful in selection of already commercial or design of new NF/RO membranes for removal of chemicals of emerging concern in water treatment.

Nanoporous membranes represent a possible route towards more precise particle and macromolecular separations, which are of interest across many industries. Here, we explored membranes with vertically-aligned nanopores formed from a poly(isoprene-b-styrene-b-4 vinyl pyridine) (ISV) triblock terpolymer via a hybrid self-assembly/nonsolvent induced phase separation process (S-NIPS). ISV concentration, solvent composition, and evaporation time in the S-NIPS process were varied to tailor ordering of the selective layer and produce enhanced water permeability. Here, water permeability was doubled over previous versions of ISV membranes. This was achieved by increasing volatile solvent concentration, thereby decreasing the evaporation period required for self-assembly. Fine-tuning was required, however, since overly-rapid evaporation did not yield the desired pore structure. Transport models, used to relate the in-situ structure to the performance of these materials, revealed narrowing of pores and blocking by the dense region below. It was shown that these vertically aligned nanoporous membranes compare favorably with commercial ultrafiltration membranes formed by NIPS and track-etching processes, which suggests that there is practical value in further developing and optimizing these materials for specific industrial separations.

Membrane formation by nonsolvent induced phase inversion was directly observed using light microscopy. Polysulfone (PSf) was used as a model polymer while 1-methyl-2-pyrrolidinone (NMP), N,N-dimethylformamide (DMF), water and glycerol were used as model solvents and nonsolvents. Direct observation and kinetic analyses suggest finger-like macrovoids formed by convective flow of nonsolvent into the polymer–solvent solution; convective flow arose from interfacial energy gradients at the polymer solution–nonsolvent interface. Convective nonsolvent flow into the polymer solution was hindered by the formation of surface skin layers or viscous gel layers within the polymer solution film. Viscous gel layers were often formed when using a poor nonsolvent, poor solvent, or an insufficient supply of a good nonsolvent. Greater viscous hindrance resulted in membranes with shorter or no finger-like macrovoids. Large finger-like macrovoids propagated only when nonsolvent convective flows into the polymer solution film exceeded viscous hindrance forces, i.e., when a good solvent, ample supply of good nonsolvent, and polymer solution of relatively lower viscosity were used.

Fouling of various kinds continues to limit membrane-based desalination and water treatment. Fouling is commonly countered through chemical cleaning of membrane elements, resulting in process downtime, membrane degradation and increased operation costs. Recent studies suggest that reversing permeate flux through RO membranes by dosing a slug of high salinity feedwater may offer an effective, chemical-free cleaning method. Herein, seawater RO membranes were fouled using alginic acid as a model seawater foulant and cleaned by osmotic backwashing with draw solutions of different salt concentration and chemistries. Flux recovery by osmotic backwashing was comparable with chemical cleaning (using caustic and a chelating agent); both recovered more flux than physical cleaning (rinsing with DI water). In particular, results illustrate the importance of combining chemical and physical mechanisms, the former contributing to ‘loosening’ of the foulant layer, and the latter facilitating its removal through fluid shear, enhanced by the presence of an osmotic backflow. Hence, osmotic backwashing may offer the potential for in-line, ‘low-chemical’ RO membrane cleaning, which would minimize discharge of cleaning chemicals to the environment and their impacts on RO membranes. Numerical simulations of the osmotic backwash cycle illustrate important time-scales and mass transfer limitations governing osmotic backwashing, through which operational insight may be obtained. The model offers a possible theoretical approach for optimization of RO membrane cleaning by osmotic backwashing.

This paper discusses the solute and structural properties of polysulfone (PSf)/β-cyclodextrin (β-CD) polyurethane (PU) mixed-matrix membranes. Relative to a commercial PSf membrane, β-CD polyurethane (β-CDPU) was blended with PSf at concentration levels of 0–10% to prepare mixed-matrix membranes using a convectional phase-inversion technique. The surface morphology and the porous structure were evaluated by scanning electron microscopy (SEM). Dynamic mechanical analysis was used to determine the mechanical stability (stiffness) of the membranes: mixed-matrix membranes (MMMs) were found to be mechanically stable even at elevated temperatures (30–350 °C). Pure water sorption results show a Fickian diffusion mode mechanism for the PSf membrane ( n =0.50), PSf/5% β-CDPU shows an anomalous transport mechanism ( n =0.80) while the PSf/8 %β-CDPU and PSf/10% β-CDPU membranes followed a non-Fickian diffusion mode ( n =1.1). Pure water permeability and glucose rejection characteristics were carried out using a cross-flow system. These results reveal that pure water and solute permeability increase with an increase in pressure. The hydrophilicity and surface energy of the MMMs were determined using a sessile-drop (contact-angle) method. Mixed-matrix PSf/β-CDPU membranes were found to be more hydrophilic (

Transport through composite membranes is influenced by the permeability and selectivity of the coating film and also by the skin layer pore morphology of the underlying porous support; however, the previous published research considered coating films with uniform thickness. Herein, we employed a numerical model to probe the impacts of coating film morphology on: (1) coating film permeability, (2) composite permeability, and (3) local permeate flux distribution. For the geometries modeled, coating film roughness can result in higher permeability provided that the mass of coating film is redistributed to produce both thinner and thicker cross-sections. On the other hand, permeability decreases when rough features are placed over a constant base film thickness. Further, rough coating films can exacerbate or dampen permeate flux ‘hot spots’ that appear over support membrane pores, depending on their relative orientation; however, dampening morphologies exhibit lower overall permeability even when the support membrane ‘solid phase’ is highly water-permeable. The presented theoretical results offer further insights into the fundamental challenges in designing high flux, fouling resistant RO membranes.

The effects of the support membrane pore size and porosity on diffusive transport through composite membranes have been investigated theoretically. Both 3D and 2D models were developed to mechanistically describe the relationship between support membrane pore structure, support material permeability, coating film thickness and the resulting composite membrane permeability; in addition, an analytical model was developed as an approximate, but more convenient approach for assessing trends of composite membrane transport. Model results suggest the choice of support is increasingly important as thin film permeability increases (i.e., less dense or thinner). For fixed coating film permeability, changes to support membrane pore structure create practically important changes to observed water flux and salt rejection by nanofiltration, brackish water reverse osmosis (RO), and seawater RO membranes. The diffusivity of the permeating species in the microporous phase of the support material may also contribute to the overall permeability of the composite membrane. Finally, a systematic numerical study suggests, for the first time, that the local permeate water flux through composite membranes is dictated by support membrane pore morphology, creating localized high flux “hot spots” with potentially high fouling and scaling propensity.

Permeation drag is the predominant cause for particle deposition onto filtration membranes, and it is known that at close approach to the membrane surface this force may greatly exceed the Stokes drag in an unbounded fluid. Herein, the hydrodynamic interaction between a sphere and a permeable wall is re-visited within the framework of the lubrication approximation with the goal of deriving an analytical solution. A closed-form analytical solution is found, based on a perturbation expansion in terms of the scaled permeability, which is considered a small parameter. Numerical calculations of the drag force on the sphere agree perfectly with numerical results available in the literature, as do analytical model results within a range of validity which is affected by the particle size and membrane permeability. Specifically, the presented calculations have been framed in the context of the low permeabilities and colloidal particle sizes representative of commercial membrane separations in current use. Results illustrate that for reverse osmosis and nanofiltration membranes, the hydrodynamic interaction is practically identical to that of an impermeable wall, while for ultrafiltration membranes the drag is substantially reduced; an analogous trend is observed for increasing particle sizes. The approximate solution derived herein offers a simple and direct means of performing hydrodynamic force calculations in particle–membrane systems.

Engineered osmosis (EO) is a membrane based separation technology with applications to sustainable energy, resource recovery, and water production. Still emerging, EO utilizes energy stored as chemical potential (osmotic pressure) to generate power or purify water, but the lack of membranes with suitable water flux, solute rejection, mechanical strength, and chemical stability has limited EO development. In this study, we attempt to address low water flux by proposing a novel thin film composite membrane for EO. This TFC membrane comprises an electrospun polymeric nanofiber support layer and a polyamide skin layer formed by in situ polymerization. The best nanofiber supported-polyamide composite membranes exhibited two to five times higher flux with up to 100 times lower salt flux than a standard commercial forward osmosis membrane. These results suggest that electrospun nanofiber supported polyamide composite membranes may enable applications like forward osmosis where internal concentration polarization is the performance-limiting factor. More research is needed to establish the applicability of this new membrane design for engineered osmosis applications involving harsh chemical environments and elevated mechanical pressures.

Interfacial composite membranes were prepared by dip-coating poly(vinyl alcohol) hydrogels on polysulfone ultrafiltration support membranes. Ultra-thin poly(vinyl alcohol) films were cast using multi-step coating procedure with dilute poly(vinyl alcohol) aqueous solutions and stabilized by a novel in situ cross-linking technique using five different cross-linking agents. A previously developed film casting technique allowed a constant film thickness of 200–300 nm to be maintained while varying cross-linking degree and cross-linking agent. The effects of crosslinking on the molecular structure, separation performance, and interfacial properties of poly(vinyl alcohol)–polysulfone composite membranes were probed experimentally and with molecular dynamic simulations. Higher degrees of cross-linking correlated strongly with lower PVA film crystallinity and decreased hydrophilicity. Experimentally determined solvent and solute permeability data correlated almost perfectly with molecular dynamics simulated fractional free volumes of the cross-linked poly(vinyl alcohol) membranes, demonstrating the importance of polymer free volume ( i.e. , steric exclusion and hindered diffusion) in solvent and solute transport through nanofiltration membranes and suggesting that predictive, in silico design of cross-linked PVA coating films may be practical.

A new high-pressure optical membrane module was developed to enable direct visual observation of bacterial deposition onto reverse osmosis (RO) membranes under practical seawater desalination operating conditions. The new optical membrane module withstands pressures up to 8.3 MPa (1200 psi) while allowing high transmission of UV and visible light. Computational fluid dynamic analyses of the optical module suggest practically relevant cross-flow hydrodynamic conditions exist through the viewing area of the optical window. Bacterial deposition rates and patterns were investigated for a live marine bacterium on two commercial seawater RO membranes operated at different permeate fluxes both with and without a commercial feed spacer present in the flow channel. These proof-of-concept results suggest the new device may prove valuable for laboratory studies designed to elucidate the effects of seawater RO membrane system parameters (e.g., permeate flux, cross-flow, membrane properties, spacer designs, etc.) on bacterial adhesion and removal. Future extensions of this innovation may include studies of novel seawater RO membrane materials, optimization of membrane cleaning, or using the device as an ex situ fouling detector at a full-scale seawater desalination plant.

This publication is based on the work supported in part by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST), in addition to the UCLA California NanoSystems Institute (CNSI) and NanoH 2 O Inc. Additional financial support for MTMP was provided by the UCLA Cota Robles Fellowship and the UCLA Faculty Women's Club Russell and Sallie O'Neill Memorial Scholarship, and for JMN by the Environmental Engineers for the Future funding program.

The authors describe a novel high-throughput screening platform that provides rapid, reliable, quantitative assessment of biofilm formation and removal on engineered surfaces. Unlike traditional biofilm assays based on plate readers, this assay platform is based on high-content screening, which allows for multiplexing to simultaneously quantify the number of bacterial adhesions per unit area and the viability of adhered cells using fluorescent dye combinations. This platform is fully automated and has a throughput of more than 10,000 wells per day. The authors used this platform to examine the influence of different assay buffer systems on bacterial adhesion, viability, and removal on cross-linked polyvinyl alcohol coating films synthesized directly onto the bottoms of 384-well plates. The results indicated that water chemistry, bacteria cell type, and film chemistry combine to govern biofilm formation. In general, both reversible and irreversible bacterial adhesion increased with the extent of cross-linking in coating films, which correlates strongly with coating film cross-linking degree and hydrophobicity, which is closely related. The high-throughput platform offers a powerful tool for rapid evaluation of fouling-resistant coating films in addition to elucidation of fundamental mechanisms governing bacterial adhesion.

Composite nanofiltration membranes were prepared by coating poly(vinyl alcohol) hydrogels on polysulfone ultrafiltration support membranes. Ultra-thin and defect-free poly(vinyl alcohol) hydrogels were cast using multi-step coating procedure with dilute PVA aqueous solutions and novel in situ cross-linking. The combined Spiegler–Kedem–film theory model was used to extract water permeability, solute permeability, reflection coefficients, and mass transfer coefficients for the composite membranes. Transport of water and salt ions through PVA coating films was dramatically influenced by feed solution pH and counter-ion valence as well as PVA molecular weight, concentration, and extent of cross-linking. Characterization of PVA coating film thickness, extent of cross-linking, surface thermodynamic properties, and crystallinity were used to explain differences in observed transport properties of the composite membranes.

Herein, we present the findings of a study employing contact angle measurements to systematically probe the impacts of solution chemistry (pH, ionic strength, ion valence, etc.) on surface charge, zeta potential, wettability, and hydrophilicity of a commercial polyamide RO membrane. Surface charge density, ionization fraction, and apparent dissociation constants were determined from contact angle titrations and converted to surface (zeta) potentials via the Grahame equation. Contact angle derived zeta potentials qualitatively agreed with zeta potentials independently determined from streaming potential measurements across a range of ionic strengths and pH values, although quantitative differences were significant. Contact angles of polar and apolar non-aqueous liquids were combined with aqueous contact angle titrations to quantify the influence of electrolyte pH, ionic strength, and ionic composition on surface acid–base functionality, wettability, and hydrophilicity. The polyamide membrane used in this study became more electron donor functionalized, more wetting, and less hydrophobic with increasing pH, salinity, and divalent cation content in the electrolyte. These results demonstrate, for the first time, a unified approach to characterize interfacial charge, electro-kinetic, and acid–base properties of polyamide composite RO membranes using a single analytical instrument.

Maximizing mass transfer and minimizing hydraulic losses in spiral wound elements is critical for designing effective and efficient reverse osmosis (RO) and nanofiltration (NF) processes. Herein we describe a multi-scale modeling approach, which links microscopic and macroscopic transport phenomena in spiral wound elements. Model simulations elucidate the impacts of feed spacer geometry on full-scale RO/NF system performance considering four representative water treatment scenarios: (1) RO membranes used to desalt ocean water, (2) low-pressure RO membranes used to desalt brackish water, (3) ultra-low pressure RO membranes used to purify wastewater, and (4) NF membranes used to soften a hard, fresh water. According to model simulations, feed spacer geometry had little impact on mass transfer; hence, engineering spacers to improve concentration polarization, trans-membrane osmotic pressure, or product water quality may prove difficult and yield limited benefits. In contrast, thinner filaments spread further apart significantly reduced hydraulic losses with negligible impacts to mass transfer. In addition, a few non-circular filament shapes produced even lower hydraulic losses, which might prove beneficial for RO/NF treatment of low salinity waters where hydraulic losses through spiral wound elements contribute significantly to the total process energy consumption. In high salinity waters, improved spacer designs may not significantly reduce energy consumption because hydraulic losses through spiral wound elements are relatively small.