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An increasing demand for freshwater inspires further understanding of the mechanism of water diffusion in reverse-osmosis membranes for the development of high-performance membranes for desalination. Water diffusion has a close relationship with the structural and dynamical characteristics of hydrogen bonds, which is not well-understood for the confining environment inside the polyamide membrane at the molecular level. In this work, an atomistic model of a highly cross-linked polyamide membrane was built with an equilibrated mixture of m-phenylenediamine and trimesoyl chloride monomers. The structure and dynamics of water in the regions from the bulk phase to the membrane interior were investigated by molecular dynamics simulations. Explicit hydrogen bond criteria were determined for hydrogen-bonding analysis. The local distribution and orientation of water reveal that the hydrogen-bonding affinity of the hydrophilic functional groups of polymers inhibits water diffusion inside the membrane. The affinity helps to produce percolated water channels across the membrane. The hydrogen-bonding structures of water in different regions indicate dehydration is required for the entry of water into the polyamide membrane, which dominates water flux across the membrane. This paper not only deepens the understanding of the structure and dynamics of water confined in the polyamide membrane but also stimulates the future work on high-performance reverse-osmosis membranes. [ABSTRACT FROM AUTHOR]

Reverse osmosis and nanofiltration are highly adopted, growing technologies that are used to remove salts and other small molecules in water treatment. Both of these technologies primarily use cross-linked polyamide membranes to achieve the desired separation. Many novel nanoporous materials are being developed as alternatives or complements to polyamides, including graphene, graphene oxide, block copolymers, liquid crystals, aquaporins, and other biologically inspired molecular channels. This article evaluates each of these technologies by (i) reviewing the current progress in each area, (ii) identifying key needs for immediate research, and (iii) evaluating considerations for commercial development. The economic benefits of these technologies in reverse osmosis applications are further reviewed to help frame the expected commercial value proposition. [ABSTRACT FROM AUTHOR]

The top polyamide layer of composite reverse osmosis (RO) membranes has a fascinatingly complex structure, yet nanoscale nonuniformities inherently present in polyamide layer may reduce selectivity, e.g., for boron rejection. This study examines improving selectivity by in situ "caulking" such nonuniformities using concentration polarization-enhanced graft-polymerization with a surfactant added to the reactive solution. The surfactant appears to enhance both polarization (via monomer solubilization in surfactant micelles) and adherence of graft-polymer to the membrane surface, which facilitates grafting and reduces monomer consumption. The effect of surfactant was particularly notable for a hydrophobic monomer glycidyl methacrylate combined with a nonionic surfactant Triton X-100. With Triton added at an optimal level, close to critical micellization concentration (CMC), monomer gets solubilized and highly concentrated within micelles, which results in a significantly increased degree of grafting and uniformity of the coating compared to a procedure with no surfactant added. Notably, no improvement was obtained for an anionic surfactant SDS or the cationic surfactant DTAB, in which cases the high CMC of surfactant precludes high monomer concentration within micelles. The modification procedure was also up-scalable to membranes elements and resulted in elements with permeability comparable to commercial brackish water RO elements with superior boric acid rejection. [ABSTRACT FROM AUTHOR]

Ozonation followed by biological activated carbon (O3/BAC) is being considered as a key component of reverse osmosis-free advanced treatment trains for potable wastewater reuse. Using a laboratory-scale O3/BAC system treating two nitrified wastewater effluents, this study characterized the effect of different ozone dosages (0-1.0 mg O3/mg dissolved organic carbon) and BAC empty bed contact times (EBCT; 15-60 min) on the formation after chlorination or chloramination of 35 regulated and unregulated halogenated disinfection byproducts (DBPs), 8 N-nitrosamines, and bromate. DBP concentrations were remarkably similar between the two wastewaters across O3/BAC conditions. Ozonation increased bromate, TCNM, and N-nitrosodimethylamine, but ozonation was less significant for other DBPs. DBP formation generally decreased significantly with BAC treatment at 15 min EBCT, but little further reduction was observed at higher EBCT where low dissolved oxygen concentrations may have limited biological activity. The O3/BAC-treated wastewaters met regulatory levels for trihalomethanes (THMs), haloacetic acids (HAAs), and bromate, although N-nitrosodimethylamine exceeded the California Notification Level in one case. Regulated THMs and HAAs dominated by mass. When DBP concentrations were weighted by measures of their toxic potencies, unregulated haloacetonitriles, haloacetaldehydes, and haloacetamides dominated. Assuming toxicity is additive, the calculated DBP-associated toxicity of the O3/BAC-treated chloraminated effluents were comparable or slightly higher than those calculated in a recent evaluation of Full Advanced Treatment trains incorporating reverse osmosis. [ABSTRACT FROM AUTHOR]

The development of reliable criteria for determining the onset of scaling of sparingly soluble salts on reverse osmosis desalination membranes is of great practical significance. Calcium carbonate, which is dealt with in this study, is a commonly encountered membrane scale compound. Reliable modeling and simulation tools of the reverse osmosis operation (accounting for onset and development of scaling) are very important for process optimization, aiming to reduce the effects of scaling and to minimize the use of antiscalants; such comprehensive modeling requires knowledge of key scaling parameters. In recent years a procedure has been developed to extract these parameters by employing a facile testing procedure, involving a small pressurized dead-end filtration cell. Using such a stirred test cell, the conditions are much closer to the actual reverse osmosis desalination process, compared to those in a non-agitated cell. Here, a detailed model of the testing process is developed and a procedure for estimating the scaling parameters is presented, by employing available relevant data. The results of the present work confirm the previous suggestion that fluid agitation in the test cell leads to an improved scaling parameter estimation procedure. [ABSTRACT FROM AUTHOR]

Increasingly strict constraints on the boron concentration for safe drinking and irrigation water present a tremendous challenge for the design of seawater reverse osmosis (RO) desalination systems. This work presents an optimization study of a seawater reverse osmosis RO network with permeate split (PS) design under boron concentration restrictions. Front part permeates with better quality and higher flux are sent directly to the product, and back part permeates are reprocessed in pass 2 with high pH value. The irreversible thermodynamic model is employed to describe the membrane transport behavior of boron. Constraints for the system flow and operation conditions are added to guarantee safe operating of the RO system. Both single-product and two-product RO systems are optimized for different types of feed seawater. Results show that the PS design is mainly dominated by the boron constraints, while the system recovery is mainly controlled by the feed salt concentration. Due to the upper bound of pH for pass 2, PS design could be introduced for pass 2 to improve the boron rejection. For a two-product output system, the permeates from both RO pass 1 and pass 2 could be split and sent to different products. In general, PS design could offer lower water cost, lower energy consumption, and smaller system size compared with normal design. Not only the operation conditions but also the flow structure of the RO system should be adjusted according to both membrane fouling and degradation with time. [ABSTRACT FROM AUTHOR]

Groundwater is becoming an increasingly important drinking water source. However, the use of groundwater for potable purposes can lead to chronic human exposure to geogenic contaminants, for example, uranium. Nanofiltration (NF) and reverse osmosis (RO) processes are used for drinking water purification, and it is important to understand how contaminants interact with membranes since accumulation of contaminants to the membrane surface can lead to fouling, performance decline and possible breakthrough of contaminants. During the current study laboratory experiments were conducted using NF (TFC-SR2) and RO (BW30) membranes to establish the behavior of uranium across pH (3-10) and pressure (5-15 bar) ranges. The results showed that important determinants of uranium-membrane sorption interactions were (i) the uranium speciation (uranium species valence and size in relation to membrane surface charge and pore size) and (ii) concentration polarization, depending on the pH values. The results show that it is important to monitor sorption of uranium to membranes, which is controlled by pH and concentration polarization, and, if necessary, adjust those parameters controlling uranium sorption. [ABSTRACT FROM AUTHOR]

The water-energy nexus continues to gain traction around the world, because of the inherent merits in simultaneously considering both resources. In this paper, a systematic procedure is developed for maximizing the benefits of this interdependent relationship, when coupled with industrial processes exhibiting a net surplus of heat energy. The presented methodology utilizes a total site analysis to first screen the process for power and water generation potential. In addition to process water streams, seawater desalination is considered as an additional resource. Based on this analysis, heat integration is carried out to capture the options for steam production for process requirements, thermal desalination of seawater, and power production. For the power generation system, a turbine network is developed, whereas, for the water desalination system, a hybrid multieffect distillation-reverse osmosis (MED-RO) system is utilized. A superstructure is constructed to embed the various configurations, and the associated optimization formulation is solved to obtain an optimal process that economically balances the need for water and power. A case study is solved to evaluate several scenarios for developing water and energy strategies for a gas-to-liquids (GTL) process in a region with various demands, as well as power and water exportation restrictions. [ABSTRACT FROM AUTHOR]

While single-layer nanoporous graphene (NPG) has shown promise as a reverse osmosis (RO) desalination membrane, multilayer graphene membranes can be synthesized more economically than the single-layer material. In this work, we build upon the knowledge gained to date toward single-layer graphene to explore how multilayer NPG might serve as a RO membrane in water desalination using classical molecular dynamic simulations. We show that, while multilayer NPG exhibits similarly promising desalination properties to single-layer membranes, their separation performance can be designed by manipulating various configurational variables in the multilayer case. This work establishes an atomic-level understanding of the effects of additional NPG layers, layer separation, and pore alignment on desalination performance, providing useful guidelines for the design of multilayer NPG membranes. [ABSTRACT FROM AUTHOR]

Swelling of the active layer of reverse osmosis (RO) membranes has an important effect on permeate water flux. The effects of organic- and biofouling on the swelling of the RO membrane active layer and the consequent changes of permeate flux are examined here. A cross-linked aromatic oligoamide film that mimics the surface chemistry of an RO polyamide membrane was synthesized stepwise on gold-coated surfaces. Foulant adsorption to the oligoamide film and its swelling were measured with a quartz crystal microbalance, and the effects of fouling on the membrane's performance were evaluated. The foulants were extracellular polymeric substances (EPS) extracted from fouled RO membranes and organic compounds of ultrafiltration permeate (UFP) from a membrane bioreactor used to treat municipal wastewater. The adsorbed foulants affected the swelling of the cross-linked oligoamide film differently. EPS had little effect on the swelling of the oligoamide film, whereas UFP significantly impaired swelling. Permeate flux declined more rapidly under UFP fouling than it did under EPS. Foulant adsorption was shown to diminish swelling of the aromatic oligoamide surfaces. Among the already known RO membrane fouling mechanisms, a novel RO fouling mechanism is proposed, in which foulant-membrane interactions hinder membrane swelling and thus increase hydraulic resistance. [ABSTRACT FROM AUTHOR]

Thepresent work is focused on three main aims. The first one is the comparisonof commercial polyamide (BE from Woongjin Chemical) and celluloseacetate (CE from GE Osmonics) reverse osmosis membranes when appliedto the ultrapurification of aqueous hydrogen peroxide solutions. Thesecond one is the search for possible advantages of combination ofboth types of membranes, which show quite different characteristics,under a hybrid cascade configuration. The results demonstrated thatthe employment of only polyamide membrane cascades is more competitivethan hybrid systems for this application. The third one is the analysisof the influence of the product quality over the optimal economiccascades. The polyamide membrane systems were then formulated addingproduct quality metrics to economic criteria to afford a bicriterianonlinear programming (NLP) problem. The Pareto solutions to the multiobjectiveproblem were generated via the epsilon constraint method. On the onehand, maximum economic profit solutions corresponded with the configurationsapplying bypass. On the other hand, maximum quality solutions wereobtained by low recovery rates (specifically in the last stages ofthe cascade). [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is an emerging desalination technology that uses low-grade heat to drive water vapor across a micro-porous hydrophobic membrane. Currently, little is known about the bio-films that grow on MD membranes. In this study, we use estuarine water collected from Long Island Sound in a bench-scale direct contact MD system to investigate the initial stages of biofilm formation. For comparison, we studied biofilm formation in a bench-scale reverse osmosis (RO) system using the same feedwater. These two membrane desalination systems expose the natural microbial community to vastly different environmental conditions: high temperatures with no hydraulic pressure in MD and low temperature with hydraulic pressure in RO. Over the course of 4 days, we observed a steady decline in bacteria concentration (nearly 2 orders of magnitude) in the MD feed reservoir. Even with this drop in planktonic bacteria, significant biofilm formation was observed. Biofilm morphologies on MD and RO membranes were markedly different. MD membrane biofilms were heterogeneous and contained several colonies, while RO membrane biofilms, although thicker, were a homogeneous mat. Phylogenetic analysis using nextgeneration sequencing of 16S rDNA showed significant shifts in the microbial communities. Bacteria representing the orders Burkholderiales, Rhodobacterales, and Flavobacteriales were most abundant in the MD biofilms. On the basis of the results, we propose two different regimes for microbial community shifts and biofilm development in RO and MD systems. [ABSTRACT FROM AUTHOR]

Recentadvances in the development of nanoporous graphene (NPG)hold promise for the future of water supply by reverse osmosis (RO)desalination. But while previous studies have highlighted the potentialof NPG as an RO membrane, there is less understanding as to whetherNPG is strong enough to maintain its mechanical integrity under thehigh hydraulic pressures inherent to the RO desalination process.Here, we show that an NPG membrane can maintain its mechanical integrityin RO but that the choice of substrate for graphene is critical tothis performance. Using molecular dynamics simulations and continuumfracture mechanics, we show that an appropriate substrate with openingssmaller than 1 μm would allow NPG to withstand pressures exceeding57 MPa (570 bar) or ten times more than typical pressures for seawaterRO. Furthermore, we demonstrate that NPG membranes exhibit an unusualmechanical behavior in which greater porosity may help the membranewithstand even higher pressures. [ABSTRACT FROM AUTHOR]

As reverse osmosis (RO) and nanofiltration polyamide membranes become increasingly used for water purification, prediction of pollutant transport is required for membrane development and process engineering. Many popular models use hindered transport theory (HTT), which considers a spherical solute moving through an array of fluid-filled rigid cylindrical pores. Experiments and molecular dynamic simulations, however, reveal that polyamide membranes have a distinctly different structure of a "molecular sponge", a network of randomly connected voids widely distributed in size. In view of this disagreement, this study critically examined the validity of HTT by directly measuring diffnsivities of several alcohols within a polyamide film of commercial RO membrane using attenuated total reflection-FTIR. It is found that measured diffusivities deviate from HTT predictions by as much as 2-3 orders of magnitude. This result indicates that HTT does not adequately describe solute transport in desalination membranes. As a more adequate alternative, the concept of random resistor networks is suggested, with resistances described by models of activated transport in "soft" polymers without a sharp size cutoff and with a proper address of solute partitioning. [ABSTRACT FROM AUTHOR]

A pilot system was designed and constructed to evaluate reverse osmosis (RO) energy reduction that can be achieved using pressure-retarded osmosis (PRO). The RO-PRO experimental system is the first known system to utilize energy from a volume of water transferred from atmospheric pressure to elevated pressure across a semipermeable membrane to prepressurize RO feedwater. In other words, the system demonstrated that pressure could be exchanged between PRO and RO subsystems. Additionally, the first experimental power density data for a RO-PRO system is now available. Average experimental power densities for the RO-PRO system ranged from 1.1 to 2.3 W/m². This is higher than previous river-to-sea PRO pilot systems (1.5 W/m²) and closer to the goal of 5 W/m² that would make PRO an economically feasible technology. Furthermore, isolated PRO system testing was performed to evaluate PRO element performance with higher cross-flow velocities and power densities exceeding 8 W/m² were achieved with a 28 g/L NaCl draw solution. From this empirical data, inferences for future system performance can be drawn that indicate future RO-PRO systems may reduce the specific energy requirements for desalination by ~1 kWh/m³. [ABSTRACT FROM AUTHOR]

We studied the volume-averaged chlorine (Cl) uptake into the bulk region of the aromatic polyamide active layer of a reverse osmosis membrane upon exposure to free chlorine. Volume-averaged measurements were obtained using Rutherford backscattering spectrometry with samples prepared at a range of free chlorine concentrations, exposure times, and mixing, rinsing, and pH conditions. Our volume-averaged measurements complement previous studies that have quantified Cl uptake at the active layer surface (top ≈7 nm) and advance the mechanistic understanding of Cl uptake by aromatic polyamide active layers. Our results show that surface Cl uptake is representative of and underestimates volume-averaged Cl uptake under acidic conditions and alkaline conditions, respectively. Our results also support that (i) under acidic conditions, N-chlorination followed by Orton rearrangement is the dominant Cl uptake mechanism with N-chlorination as the rate-limiting step; (ii) under alkaline conditions, N-chlorination and dechlorination of N-chlorinated amide links by hydroxyl ion are the two dominant processes; and (iii) under neutral pH conditions, the rates of N-chlorination and Orton rearrangement are comparable. We propose a kinetic model that satisfactorily describes Cl uptake under acidic and alkaline conditions, with the largest discrepancies between model and experiment occurring under alkaline conditions at relatively high chlorine exposures. [ABSTRACT FROM AUTHOR]

Severaltheorems are presented and proved analytically for normalized specificenergy consumption (NSEC) in single- or multistage spiral-wound seawaterreverse osmosis (RO) desalination with or without brine energy recovery.It is shown that a spiral-wound RO unit employing an infinite numberof RO stages and interstage booster pumps is essentially equivalentto a fully reversible RO process in terms of NSEC if the energy inthe brine can be fully recovered. Without energy recovery, the minimumof NSEC decreases monotonically from 4 to 3.1462 and the correspondingoptimal recovery increases monotonically from 50% to 68.22% as thenumber of RO stages increases from 1 to infinity. NSEC decreases monotonicallyas the number of stages or the energy recovery device (ERD) efficiencyincreases. An effective way to reduce NSEC in seawater RO is to usean ERD at low recoveries and a multistage design with interstage boosterpumps at high recoveries. A combination of the two methods would bringNSEC toward its lowest theoretical limit, but the capital cost shouldalso be taken into account. Brine recirculation does not reduce NSECbecause of an increase in feed salinity. [ABSTRACT FROM AUTHOR]

Reverse osmosis (RO) membrane fouling is not a static state but a dynamic phenomenon. The investigation of fouling kinetics and dynamics of change in the composition of the foulant mass is essential to elucidate the mechanism of fouling and foulant-foulant interactions. The aim of this work was to study at a lab scale the fouling process with an emphasis on the changes in the relative composition of foulant material as a function of operating time. Fouled membrane samples were collected at 8 h, and 1, 2, and 4 weeks on a lab-scale RO unit operated in recirculation mode. Foulant characterization was performed by CLSM, AFM, ATR-FTIR, pyrolysis GC-MS, and ICP-MS techniques. Moreover, measurement of active biomass and analysis of microbial diversity were performed by ATP analysis and DNA extraction, followed by pyro-sequencing, respectively. A progressive increase in the abundance of almost all the foulant species was observed, but their relative proportion changed over the age of the fouling layer. Microbial population in all the membrane samples was dominated by specific groups/species belonging to Proteobacteria and Actinobacteria phyla; however, similar to abiotic foulant, their relative abundance also changed with the biofilm age. [ABSTRACT FROM AUTHOR]

The effect of different water treatments such as ultrafiltration (UF) and reverse osmosis (RO) on dissolved organic matter (DOM) is still unknown. Electrospray ionization Fourier transform orbitrap mass spectrometry has been used to provide valuable information of marine DOM evolution through a desalination process on a molecular scale. In the present manuscript, the characterization of four real composite water samples from a desalination pilot plant installed in the coast of Barcelona (Spain) has been carried out. The sampling was performed on each point of the pilot plant: raw seawater (RSW), UF effluent, brine RO and permeate RO. The mass spectra of the different samples show several thousand peaks, however for the present screening study, only the mass range m/z 200-500 and the main signals in this mass range (relative intensities ⩾1%) have been considered. The analysis of RSW and UF samples reveal that there is little effect on DOM by the UF pilot. However, when the water is treated on the RO an important change on DOM has been observed. The recurring periodical patterns found in RSW and UF are lost in Permeate RO sample. Compounds with more aliphatic character, with higher H/C ratio (H/Cav 1.72) are present in the Permeate and some of them have been tentatively identified as fatty acids. [ABSTRACT FROM AUTHOR]

The cost of dilute ethanol purificationis a significant componentof the overall cost for fuel grade ethanol production through fermentationor other biological routes. In this study, we consider bioethanolpurification to the fuel grade in a closed system of photobioreactors(PBRs) that produce a dilute (0.5–5 wt %) ethanol solution,and where the water is recycled back to the reactors after separation.To reduce the energy consumption and hence the cost of dilute ethanolpurification, a reverse osmosis (RO) membrane process is introducedas a potential pretreatment in order to purify ethanol–watermixtures to an intermediate concentration. The pretreated mixtureis separated across the azeotropic point to the fuel grade by a hybriddistillation-membrane-pervaporation (D-PV) process. A superstructureof the overall separation process is formulated in the General AlgebraicModeling System (GAMS) environment as a mixed-integer nonlinear programming(MINLP) problem and optimized to minimize the total separation cost.The problem is posed with a constraint on the minimum ethanol recoveryby the overall system. For dilute feeds, the steam used in the distillationreboiler dominates both the energy and the cost of the overall system.Installing the RO system reduces the steam usage at the expense oflarger capital investment in membrane modules, which has been foundto be optimal for dilute feeds below 3 wt % ethanol. The optimal numberof membrane stages and the feed location of individual RO moduleschange at different feed concentrations and ethanol recoveries. Theoptimal process design results in a higher ethanol recovery by themain hybrid separation unit compared to the RO membrane process dueto the high capital cost of an RO system to achieve a high recovery.Developing a cheaper RO membrane may further reduce the separationcost and may expand an optimal dilute feed concentration range. [ABSTRACT FROM AUTHOR]

Calcium phosphate scale formationon reverse osmosis (RO) membranesis one of the main limitations on cost-effective desalination of domesticwastewater worldwide. It has been shown that organic agents affectmineralization. In this study, we explored mineralization in the presenceof two biofilm-relevant organic compounds, the proteins bovine serumalbumin (BSA) and lysozyme, in a simulated secondary effluent (SSE)solution using small-angle neutron scattering (SANS), and appliedthe results to analyses of mineral precipitation in RO desalinationof secondary effluents of wastewater. The two proteins are prominentmembers of bacterial extracellular polymeric substances (EPSs), formingbiofilms that are frequently associated with RO-membrane fouling duringwastewater desalination. Laboratory experiments showed that both proteinsin SSE solution are involved in complex mineralization processes.Only small portions of both protein fractions are involved in mineralizationprocesses, whereas most of the protein fractions remain as monomersin solution. Contrast variation showed that composite particles ofmineral and protein are formed instantaneously to a radius of gyrationof about 300 Å, coexisting with particles of about μm size.After about one day, these large particles start to grow again atthe expense of the 300 Å particles. The volume fraction of the300 Å particles is of the order of 2 × 10–4, which is too large to represent calcium phosphate such as hydroxyapatiteas the only mineral present. Considering the data of mineral volumefraction obtained here as well as the solubility product of possiblemineral polymorphs in the SSE solution, we suggest the formation ofprotein-mineral particles of hydroxyapatite and calcium carbonateduring scale formation. [ABSTRACT FROM AUTHOR]

The results of this study reveal a strong linear correlation (R² = 0.95) between the rejections of boron and N-nitrosodimethylamine (NDMA) by six different reverse osmosis (RO) membranes, suggesting that boron can be used as a surrogate for NDMA rejection. This proposal is based on the premise that the rejection of both boric acid and NDMA is governed by steric hindrance and that they have similar molecular dimensions. The concept proposed here is shown to be valid at pH 8 or below where boron exists as the neutral boric acid species and NDMA is also a neutral solute. Observed changes in the rejections of these two species, as a function of permeate fluxes and feed solution temperatures, were also almost identical. Boron rejection increased from 21 to 79%, and the correlation coefficient of the linear regression between boron and NDMA rejections was 0.99 as the permeate flux increased from 5 to 60 L m-2 h-1. Similarly, a linear correlation between boron and NDMA rejections was observed as the feed solution temperature increased from 10 to 40 °C. This linear correlation was also validated in a tertiary treated effluent matrix. [ABSTRACT FROM AUTHOR]

Aromatic phenols represent an important class of endocrine-disrupting and toxic pollutants, many of which (e.g., bisphenol A and substituted phenols) are known to be insufficiently removed by reverse osmosis (RO) and nanofiltration polyamide membranes that are widely used for water purification. In this study, the mechanism of phenol transport across the polyamide layer of RO membranes is studied using model phenolic compounds hydroquinone (HQ) and its oxidized counterpart benzoquinone (BQ). The study employs filtration experiments and two electrochemical techniques, impedance spectroscopy (EIS) and chronoamperometry (CA), to evaluate the permeability of an RO membrane SWC1 to these solutes in the concentration range 0.1-10 mM. In addition, combination of the permeability data with EIS results allows separately estimating the average diffusivity and partitioning of BQ and HQ. All methods produced permeability of the order 10-7 to 10-6 m s-1 that decreased with solute concentration, even though the permeability obtained from filtration was consistently lower. The decrease of permeability with concentration could be related to the nonlinear convex partitioning isotherm, in agreement with earlier measurements by FTIR. The diffusivity of HQ and BQ was estimated to be of the order 10-15 m² s-1 and partitioning coefficient of the order 10. The high affinity of phenols toward polyamide and their high uptake may change membrane characteristics at high concentration of the solute. EIS results and hydraulic permeability indeed showed that permeability to ions and water significantly decreases with increasing concentration of organic solute. [ABSTRACT FROM AUTHOR]

This work focuses on optimal operation of brackish waterreverse osmosis (BWRO) plants employing multitrains which have differentservice times and membrane permeability parameters. A nonlinear optimizationproblem, based on a previously developed comprehensive RO model thataccounts for characteristic curves of booster pumps driving the ROtrains and pressure drop along each RO train, is formulated and solvedto minimize the overall specific energy consumption (SEC) while maintainingthe same overall water production. A 16–17% reduction in SECis possible by optimizing production allocations among all trainsas well as operating conditions within the normal pump operating rangein each train. It is shown that optimizing each train individually(without optimizing production allocations) could yield a higher SEC. [ABSTRACT FROM AUTHOR]

We report on the efficient removal of heavy metal ions from simulated wastewater with a nanostructured assembly. The nanoassembly was obtained via direct assembling the performed anisotropic layered double hydroxide nanocrystals (LDH-NCs) onto the surface of carbon nanospheres (labeled as LDH-NCs@CNs). It was found that the maximum adsorption capacity of the nanoassembly toward Cu2+ was ∼19.93 mg g-1 when the initial Cu2+ concentration was 10.0 mg L-1, displaying a high efficiency for the removal of heavy metal ions. The Freundlich adsorption isotherm was applicable to describe the removal processes. Kinetics of the Cu2+ removal was found to follow pseudo-second-order rate equation. Furthermore, the as-prepared building unit of the assembly, including LDH-NCs, CNs, and the assembly, as well as Cu2+-adsorbed assembly, were carefully examined by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), nitrogen sorption measurements, and X-ray photoelectron spectroscopy (XPS). Based on the characterization results, a possible mechanism of Cu2+ removal with the assembly of LDH-NCs@CNs was proposed. Comparison experiments show that the adsorption capacity of the resulting LDH-NCs@CNs assembly was much higher than its any building unit alone (CNs or LDH-NCs), exhibiting the deliberation of the assembly on water decontamination. This work provides a very efficient, fast and convenient approach for exploring promising nanoassembly materials for water treatment. [ABSTRACT FROM AUTHOR]

The application of reverse osmosis (RO) in water intended for reuse is promising for assuring high water quality. However, one significant disadvantage is the need to dispose of the RO retentate (or reject water). Studies focusing on Pharmaceutical and Personal Care Products (PPCPs) have raised questions concerning their concentrations in the RO retentate. Advanced oxidation processes (AOPs) are alternatives for destroying these compounds in retentate that contains high concentration of effluent organic matter (EfOM) and other inorganic constituents. Twenty-seven PPCPs were screened in a RO tetentate using solid phase extraction (SPE) and UPLC-MS/MS, and detailed degradation studies for 14 of the compounds were obtained. Based an the absolute hydroxyl radical (HO) reaction rate constants for individual pharmaceutical compounds, and that of the RO retentate (EfOM and inorganic constituents), it was possible to model their destruction. Using excitation-emission matrix (EEM) fluorescence spectroscopy, the HO oxidation of the EfOM could be observed through decreases in the retentate fluorescence. The decrease in the peak normally associated with proteins correlated well with the removal of the pharmaceutical compounds. These results suggest that fluorescence may be a suitable parameter for monitoring the degradation of PPCPs by AOPs in RO retentates. [ABSTRACT FROM AUTHOR]

Herein we report on the formation and characterization of pure polyamide thin film composite (TFC) and zeolite—polyamide thin film nanocomposite (TFN) reverse osmosis (RO) membranes. Four different physical—chemical post-treatment combinations were applied after the interfacial polymerization reaction to change the molecular structure of polyamide and zeolite—polyamide thin films. Both TFC and TFN hand-cast membranes were more permeable, hydrophilic, and rough than a commercial seawater RO membrane. Salt rejection by TFN membranes was consistently below that of hand-cast TFC membranes; however, two TFN membranes exhibited 32 g/L NaCl rejections above 99.4%, which was better than the commercial membrane under the test conditions employed. The nearly defect-free TFN films that produced such high rejections were achieved only with wet curing, regardless of other post-treatments. Polyamide films formed in the presence of zeolite nanoparticles were less cross-linked than similarly cast pure polyamide films. At the very low nanoparticle loadings evaluated, differences between pure polyamide and zeolite—polyamide membrane water and salt permeability correlated weakly with extent of cross-linking of the polyamide film, which suggests that defects and molecular-sieving largely govern transport through zeolite—polyamide thin film nanocomposite membranes. [ABSTRACT FROM AUTHOR]

The article presents an experiment involving the synthesis of various shapes and sizes of nanoprismatic silver nanoparticles (AgNPs). It enumerates various chemicals required, including sodium citrate tribasic dihydrate, hydrogen peroxide, and sodium borohydride, along with water purified through reverse osmosis. It also outlines the procedures and results, emphasizing on the aspects of changing colors which can be seen through ultraviolet (UV)-vis spectroscopy.

Designing tailored block copolymers represents a viable strategy for building polymer membranes with fruitful combinations of properties, such as the high ionic or small molecule conductivity and high mechanical strength needed for applications such as fuel cells and reverse-osmosis water purification. Here we present a systematic study of water transport and morphological alignment in a class of poly(arylene ether sulfone) hydrophilic−hydrophobic multiblock copolymer membranes and compare these with Nafion 212. Multiaxis pulsed-field-gradient NMR yields diffusion anisotropy, the ratio of diffusion coefficients measured both in plane (D∥) and through plane (D⊥), as a function of water uptake and block lengths. As block mass increases, diffusion anisotropy exhibits an increasing dependence on water uptake, in contrast to Nafion 212, where diffusion is isotropic and displays no dependence on water uptake. 2H NMR spectroscopy on absorbed D2O further probes membrane alignment modes. Both types of measurements corroborate uniformly ordered planar structures oriented through the membrane plane in accordance with a lamellar morphology previously observed locally with microscopy. The combination of these two measurements also provides insights into average defect distributions. [ABSTRACT FROM AUTHOR]

We have demonstrated in this work the prospect of dual-layer polybenzimidazole-polyethersulfone (PBI-PES) nanofiftration (NF) hollow fiber membranes in the forward osmosis (FO) process for water production: The state-of-the-art for dual- layer membrane fabrication via coextrusion technology could produce the resultant membrane consisting of an ultrathin selective skin, fully porous water channels underneath, and a microporous sponge-like support structure. Together with its sharp pore size distribution and self-charged PBI selective membrane surface, the dual-layer hollow fiber forward osmosis membrane can achieve a water flux as high as 33.8 L·m-2hr-1 and a salt flux less than 1.0 g·m-2·hr-1 at room temperature of 23 °C using 5M MgCI2 as the draw solution. A comprehensive literature review of previous efforts on identifying suitable membranes and appropriate draw solutions in the FO process for water production and seawater desalination have also been conducted. It shows that the water fluxes of the dual-layer hollow fiber FO membrane developed in this work utilizing MgCI2 as the draw solutions generally surpasses those FO processes utilizing RO membranes and is comparable to most FO processes using commercial FO membrane and employing other salts or sugar instead of MgCI2 as the draw solutions. [ABSTRACT FROM AUTHOR]

Perfluorooctane sulfonate (PFOS) is an emergent contaminant of substantial environmental concerns. In this study, reverse osmosis (RO) and nanofiltration (NF) membranes were used to remove this toxic and persistent compound from PFOS-containing wastewater. Five RO membranes and three NF membranes were tested at a feed concentration of 10 ppm PFOS over 4 days, and the PFOS rejection and permeate flux performances were systematically investigated. PFOS rejection was well correlated to sodium chloride rejection. The rejection efficiencies for the RO membranes were >99%, and those for the NF membranes ranged from 90–99%. Improvement in PFOS rejection, together with mild flux reduction (<16%), was observed at longer filtration time. Such shifts in rejection and flux performance were probably due to the increased PFOS accumulation at longer duration, as shown by X-ray photoelectron spectroscopy and liquid chromatograph and tandem mass spectrometry results. A fraction of PFOS molecules might be entrapped in the polyamide layer of the composite membranes, which hindered the further passage of both water and other PFOS molecules. In a similar fashion, PFOS rejection and fouling were enhanced for greater initial flux and/or applied pressure, where PFOS accumulation was promoted probably due to increased hydrodynamic permeate drag. Flux reduction was also shown to correlate to membrane roughness, with the rougher membranes tend to experience more flux reduction than the smoother ones. [ABSTRACT FROM AUTHOR]

The aromatic region of two-dimensional heteronuclear ¹H, 13C NMR spectra of natural organic matter and related materials (e.g., ¹H and 13C chemical shifts ranging from approximately 5 to 10 and 80 to 140 ppm, respectively) is highly complex and difficult to interpret using conventional approaches. In principle, this region of the NMR spectrum should be amenable to detailed analysis, because the effects of many common substituents on the chemical shifts of aromatic carbon and hydrogen are well documented. This paper describes the development of a model for prediction of substitution patterns in aromatic rings by increment analysis (SPARIA). In the forward mode, SPARIA is used to predict the chemical shifts of ¹H and 13C on aromatic moieties containing every possible combination of eight common substituents that are likely to be representative of substituents on aromatic moieties in natural organic matter. The accuracy of SPARIA in the forward mode is evaluated for 29 aromatic compounds (100 peaks) by comparison of predicted chemical shifts for ¹H and 13C with experimental values and with predictions of commercially available software for prediction of NMR spectra. The most important development in this paper is the inverse mode that is built into SPARIA. Given chemical shifts for ¹H and 13C (such as may be obtained from a two-dimensional, heteronuclear NMR spectrum), the inverse mode of SPARIA calculates all possible combinations of the eight selected substituents that yield chemical shifts within a specified window of chemical shift for both ¹H and 13C. Both the distribution of possible substitution patterns and simple descriptive statistics of the distribution are thus obtained. The inverse mode of SPARIA has been tested on the 29 aromatic compounds (100 peaks) that were used to evaluate its forward mode, and the dependence of the inverse process on the size of the chemical shift window has been evaluated. Finally, the inverse mode of SPARIA has been applied to selected peaks from the two-dimensional heteronuclear HSQC spectrum of a sample of natural organic matter that was isolated by reverse osmosis from the Suwannee River in southeastern Georgia. [ABSTRACT FROM AUTHOR]

Perfluorooctane sulfonate (PFOS) and related substances are persistent, bioaccumulative, and toxic, and thus of substantial environmental concern. PFOS is an essential photolithographic chemical in the semiconductor industry with no substitutes yet identified. The industry seeks effective treatment technologies. The feasibility of using reverse osmosis (RO) membranes for treating semiconductor wastewater containing PFOS has been investigated. Commercial RO membranes were characterized in terms of permeability, salt rejection, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and membrane surface zeta potential (streaming potential measurements). Filtration tests were performed to determine the membrane flux and PFOS rejection. Over a wide range of feed concentrations (0.5 – 1500 ppm), the RO membranes generally rejected 99% or more of the PFOS. Rejection was better for tighter membranes, but was not affected by membrane zeta potential. Flux decreased with increasing PFOS concentration. While the flux reduction was severe for a loose RO membrane probably due to its higher initial flux, very stable flux was maintained for tighter membranes. At a very high feed concentration (about 500 ppm), all the membranes exhibited an identical stable flux. Isopropyl alcohol, present in some semiconductor wastewaters, had a detrimental effect on membrane flux. Where present it needs to be removed from the wastewater prior to using RO membranes. [ABSTRACT FROM AUTHOR]

Long-alkyl chain functionalized poly(propylene imine) dendrimer, poly(ethylene imine) hyperbranched polymer, and β-cyclodextrin derivatives, which are completely insoluble in water, have the property of encapsulating organic pollutants from water. Ceramic porous filters can be impregnated with these compounds resulting in hybrid organic/ inorganic filter modules. These hybrid filter modules were tested for the effective purification of water, by continuous filtration experiments, employing a variety of water pollutants. It has been established that polycyclic aromatic hydrocarbons (PAHs) can be removed very efficiently (more than 95%), and final concentrations of several ppb (μg/L) are easily obtained. Representatives of the pollutant group of trihalogen methanes (THMs), monoaromatic hydrocarbons (BTX), and pesticides (simazine) can also be removed (>80%), although the filters are saturated considerably faster in these cases. [ABSTRACT FROM AUTHOR]

Examines the rejection characteristics of nitrogen compounds on membranes. Explanation of nitrogen compound rejection through the extended Nernst-Planck model; Impact of electromigration on the reaction; Implications for reverse osmosis water purification efficiency.