Nitrate removal from contaminated groundwater by micellar-enhanced ultrafiltration using a polyacrylonitrile membrane with a hydrogel-stabilized ZIF-L layer.

Contamination of groundwater by nitrate from intensive agriculture is a serious problem globally. Excessive fertilization has led to nitrate contamination of the Coastal Aquifer in Israel. Here we report the efficient removal of nitrate from contaminated groundwater by micellar-enhanced ultrafiltration (MEUF) using a specially tailored membrane. Graft polymerization with hydrophilic poly(methacrylate) and incorporation of porous zeolitic imidazole framework ZIF-L nanoparticles imparted antifouling properties to the membrane. The resulting modified membrane showed high water permeance (82.2 ± 1.7 L·m-2·h-1·bar-1). The efficiency of nitrate removal by MEUF was tested using cetylpyridinium chloride as a surfactant in nitrate-contaminated groundwater collected from the Coastal Aquifer of Israel. The membrane reduced nitrate levels from 40-70 to levels of 6.8-29.5 mg·L-1, depending on the groundwater composition; further reduction to 6.1-24.1 mg·L-1 with complete surfactant rejection was achieved via two-stage membrane filtration, which showed high permeate flux (between 32.1 ± 0.9 and 45.9 ± 0.6 L·m-2·h-1) at 2 bar. The membrane maintained stable separation performance during multiple cycles, and the flux recovery ratio was >93 %. Nitrate concentrations fell well below the acceptable limit for drinking water, allowing the treated water to be used without restriction. Overall, the membrane has the potential to allow efficient removal by MEUF of nitrate from contaminated groundwater.

Distinct Antifouling Mechanisms on Different Chain Densities of Zwitterionic Polymers.

Antifouling polymer coating surfaces are used in widespread industries applications. Zwitterionic polymers have been identified as promising materials in developing polymer coating surfaces. Importantly, the density of the polymer chains is crucial for acquiring superior antifouling performance. This study introduces two different zwitterionic polymer density surfaces by applying molecular modeling tools. To assess the antifouling performance, we mimic static adsorption test, by placing the foulant model bovine serum albumin (BSA) on the surfaces. Our findings show that not only the density of the polymer chain affect antifouling performance, but also the initial orientation of the BSA on the surface. Moreover, at a high-density surface, the foulant either detaches from the surface or anchor on the surface. At low-density surface, the foulant does not detach from the surface, but either penetrates or anchors on the surface. The anchoring and the penetrating mechanisms are elucidated by the electrostatic interactions between the foulant and the surface. While the positively charged ammonium groups of the polymer play major role in the interactions with the negatively charged amino acids of the BSA, in the penetrating mechanism the ammonium groups play minor role in the interactions with the contact with the foulant. The sulfonate groups of the polymer pull the foulant in the penetrating mechanism. Our work supports the design of a high-density polymer chain surface coating to prevent fouling phenomenon. Our study provides for the first-time insights into the molecular mechanism by probing the interactions between BSA and the zwitterion surface, while testing high- and low-densities polymer chains.

Glycidyl and Methyl Methacrylate UV-Grafted PDMS Membrane Modification toward Tramadol Membrane Selectivity.

Pharmaceutical wastewater pollution has reached an alarming stage, as many studies have reported. Membrane separation has shown great performance in wastewater treatment, but there are some drawbacks and undesired byproducts of this process. Selective membranes could be used for pollutant investigation sensors or even for pollutant recovery. The polydimethylsiloxane (PDMS) membrane was first tested on separated and mixed antibiotic (ATB) water solutions containing sulfamethoxazole (SM), trimethoprim (TMP), and tetracycline (TET). Then, the bare and ultra-violet grafted (UV-grafted) PDMS membranes (MMA-DMAEMA 10, GMA-DMAEMA 5, and GMA-DMAEMA 10) were tested in tramadol (TRA) separation, where the diffusion coefficient was evaluated. Finally, the membranes were tested in pertraction with a mixture of SM, TMP, TET, and TRA. The membranes were characterized using the following methods: contact angle measurement, FTIR, SEM/EDX, and surface and pore analysis. The main findings were that TET was co-eluted during mixed ATB pertraction, and GMA-DMAEMA 5 was found to selectively permeate TRA over the present ATBs.

Modified Single-Walled Carbon Nanotube Membranes for the Elimination of Antibiotics from Water.

The hydrophilic and hydrophobic single-walled carbon nanotube membranes were prepared and progressively applied in sorption, filtration, and pertraction experiments with the aim of eliminating three antibiotics-tetracycline, sulfamethoxazole, and trimethoprim-as a single pollutant or as a mixture. The addition of SiO2 to the single-walled carbon nanotubes allowed a transparent study of the influence of porosity on the separation processes. The mild oxidation, increasing hydrophilicity, and reactivity of the single-walled carbon nanotube membranes with the pollutants were suitable for the filtration and sorption process, while non-oxidized materials with a hydrophobic layer were more appropriate for pertraction. The total pore volume increased with an increasing amount of SiO2 (from 743 to 1218 mm3/g) in the hydrophilic membranes. The hydrophobic layer completely covered the carbon nanotubes and SiO2 nanoparticles and provided significantly different membrane surface interactions with the antibiotics. Single-walled carbon nanotubes adsorbed the initial amount of antibiotics in less than 5 h. A time of 2.3 s was sufficient for the filtration of 98.8% of sulfamethoxazole, 95.5% of trimethoprim, and 87.0% of tetracycline. The thicker membranes demonstrate a higher adsorption capacity. However, the pertraction was slower than filtration, leading to total elimination of antibiotics (e.g., 3 days for tetracycline). The diffusion coefficient of the antibiotics varies between 0.7-2.7 × 10-10, depending on the addition of SiO2 in perfect agreement with the findings of the textural analysis and scanning electron microscopy observations. Similar to filtration, tetracycline is retained by the membranes more than sulfamethoxazole and trimethoprim.

Silica Fouling in Reverse Osmosis Systems-Operando Small-Angle Neutron Scattering Studies.

We present operando small-angle neutron scattering (SANS) experiments on silica fouling at two reverse osmose (RO) membranes under almost realistic conditions of practiced RO desalination technique. To its realization, two cells were designed for pressure fields and tangential feed cross-flows up to 50 bar and 36 L/h, one cell equipped with the membrane and the other one as an empty cell to measure the feed solution in parallel far from the membrane. We studied several aqueous silica dispersions combining the parameters of colloidal radius, volume fraction, and ionic strength. A relevant result is the observation of Bragg diffraction as part of the SANS scattering pattern, representing a crystalline cake layer of simple cubic lattice structure. Other relevant parameters are silica colloidal size and volume fraction far from and above the membrane, as well as the lattice parameter of the silica cake layer, its volume fraction, thickness, and porosity in comparison with the corresponding permeate flux. The experiments show that the formation of cake layer depends to a large extent on colloidal size, ionic strength and cross-flow. Cake layer formation proved to be a reversible process, which could be dissolved at larger cross-flow. Only in one case we observed an irreversible cake layer formation showing the characteristics of an unstable phase transition. We likewise observed enhanced silica concentration and/or cake formation above the membrane, giving indication of a first order liquid-solid phase transformation.

Redox condition of saline groundwater from coastal aquifers influences reverse osmosis desalination process.

Reverse osmosis (RO) seawater desalination is a widely applied technological process to supply potable water worldwide. Recently, saline groundwater (SGW) pumped from beach wells in coastal aquifers that penetrate beneath the freshwater-seawater interface is considered as a better alternative water source to RO seawater desalination as it is naturally filtered within the sediments which reduces membrane fouling and pre-treatment costs. The SGW of many coastal aquifers is anoxic - and thus, in a low redox stage - has elevated concentrations of dissolved manganese, iron and sulfides. We studied the influence of the SGW redox stage and chemistry on the performance - permeate flux and fouling properties - of RO desalination process. SGWs from three different coastal aquifers were sampled and characterized chemically, and RO desalination experiments were performed under inert and oxidized conditions. Our results show that all three aquifers have anoxic saline groundwater and two of them have intensive anaerobic oxidation of organic matter. Two aquifers were found to be in the denitrification stage or slightly lower and the third one in the sulfate reduction stage. Our results indicate that the natural redox stage of SGWs from coastal aquifers affects the performance of RO desalination. All SGW types showed better RO performance over seawater desalination. Furthermore, air oxidation of the SGW was accompanied with pH elevation, which increased the membrane fouling. Hence, keeping the feed water unexposed to atmospheric conditions for maintaining the natural reducing stage of the SGW is crucial for low fouling potential. The observed benefits of using naturally reduced SGW in RO desalination have significant implications for reduction in overall process costs.

The effects of long-term saline groundwater pumping for desalination on the fresh-saline water interface: Field observations and numerical modeling.

This study tests for the first time the long-term effects of pumping saline groundwater (SGW) as feed for a desalination plant on a coastal aquifer. Field measurements combined with 3D modeling of the hydrological conditions were conducted to examine the effects of SGW pumping on the aquifer system. The plant is next to the city of Almeria (South East Spain) and has been operating since 2006. It uses multiple beach wells along the shore to draw SGW from beneath the fresh-saline water interface (FSI) of the Andarax coastal aquifer. The long-term impact of the intensive pumping on the aquifer was assessed by electrical conductivity profiles in three observation wells during 12 years of pumping. The FSI deepened with continuous pumping, reaching a decrease of ~50 m in the observation well closest to the pumping wells. A calibrated three-dimensional numerical model of the Andarax aquifer replicates the freshening of the aquifer due to the continuous pumping, resulting in a salinity decrease of ~16% in the vicinity of the wells. The salinity decrease stabilizes at 17%, and the model predicts no further significant decrease in salinity for additional 20 years. Submarine groundwater discharge is lowered due to the SGW pumping and ~19,000,000 m3 of freshwater has not lost to the sea during the 12 years of pumping with a rate of ~1,100,000 m3 yr-1 after 6 years of pumping. After pumping cessation, hydrostatic equilibrium would take about 20 years to recover. This work presents the complex dynamics of the FSI due to the SGW pumping for desalination in the first real long-term scenario. It shows by combining field work and numerical modeling, a significant freshening of the aquifer by pumping SGW, emphasizing an additional advantage and the effectiveness of this use as a negative hydraulic barrier against seawater intrusion.

Morphology of Thin Film Composite Membranes Explored by Small-Angle Neutron Scattering and Positron-Annihilation Lifetime Spectroscopy.

The morphology of thin film composite (TFC) membranes used in reverse osmosis (RO) and nanofiltration (NF) water treatment was explored with small-angle neutron scattering (SANS) and positron-annihilation lifetime spectroscopy (PALS). The combination of both methods allowed the characterization of the bulk porous structure from a few Å to µm in radius. PALS shows pores of 4.5 Å average radius in a surface layer of about 4 m thickness, which become 40% smaller at the free surface of the membranes. This observation may correlate with the glass state of the involved polymer. Pores of similar size appear in SANS as closely packed pores of 6 Å radius distributed with an average distance of 30 Å. The main effort of SANS was the characterization of the morphology of the porous polysulfone support layer as well as the fibers of the nonwoven fabric layer. Contrast variation using the media H2O/D2O and supercritical CO2 and CD4 identified the polymers of the support layers as well as internal heterogeneities.

Mixed Nanosheet Membranes Assembled from Chemically Grafted Graphene Oxide and Covalent Organic Frameworks for Ultra-high Water Flux.

2D graphene oxide (GO) membranes attract great attention because of their ultrathin thickness and superior molecular sieving ability, but their low flux and instability in aqueous environments are still the major challenges for practical applications. In this study, we designed hybrid nanosheets from chemically grafted GO and covalent organic frameworks (COFs) as building blocks to fabricate mixed nanosheet membranes. The covalent triazine framework (CTF), a triazine-based COF, is exfoliated into nanosheets and then reacted with GO to form the GO-CTF hybrid nanosheets, which are then assembled into GO-CTF mixed nanosheet membranes. The GO-CTF membranes show a layered configuration of ca. 32 nm thickness. The incorporation of CTF nanosheets inappreciably changes the interlayer distance of GO-CTF membranes, ensuring high rejections to organic dyes (>90%); meanwhile, the CTF nanosheets afford extra through-plane channels that significantly shorten the water transport pathway. The GO-CTF membranes exhibit a water flux of 226.3 L m-2 h-1 bar-1, more than 12-fold higher than pure GO membranes. Besides, the strong chemical bonds between GO and COF render the GO-CTF membranes notably enhanced stability. Grafting of porous nanosheets onto nonporous nanosheets to acquire hybrid nanosheets as building blocks opens a new avenue to the fabrication of 2D membranes with promising application potential.

Surface-Induced Silica Scaling during Brackish Water Desalination: The Role of Surface Charge and Specific Chemical Groups.

Silica scaling of membranes used in reverse osmosis desalination processes is a severe problem, especially during the desalination of brackish groundwater due to high silica concentrations. This problem limits the water supply in inland arid and semiarid regions. Here, we investigated the influence of surface-exposed organic functional groups on silica precipitation and scaling. A test solution simulating the mineral content of brackish groundwater desalination brine at 75% recovery was used. The mass and chemical composition of the precipitated silica was monitored using a quartz crystal microbalance, X-ray photoelectron spectroscopy, and infrared spectroscopy, showing that surfaces with positively charged groups induced rapid silica precipitation, and the rate of silica precipitation followed the order -NH2 ∼ -N+(CH3)3 > -NH2/-COOH > -H2PO3 ∼ -OH > -COOH > -CH3. Force vs distance AFM measurements showed that the adhesion energy between a silica colloid glued to AFM cantilever and the studied surfaces increased as the surface charge changed from negative to positive. Thus, for the first time direct measurements of molecular forces and specific chemical groups that govern silica scaling during brackish water desalination is reported here. The influence of the different functional groups and the effect of the surface charge on silica precipitation that were found here can be used to design membranes that resist silica scaling in membrane-based desalination processes.

The effect of pumping saline groundwater for desalination on the fresh-saline water interface dynamics.

Over the past few decades, seawater desalination has become a necessity for freshwater supply in many countries worldwide, particularly in arid and semi-arid regions. One potentially high-quality feed water for desalination is saline groundwater (SGW) from coastal aquifers, which has lower fouling propensity than seawater. This study examines the effect of pumping SGW from a phreatic coastal aquifer on fresh groundwater, particularly on the dynamics of the fresh-saline water interface (FSI). Initially, we constructed a 3D finite-element model of a phreatic coastal aquifer by using the FEFLOW software, which solves the coupled variable density groundwater flow and solute transport equations. Then, we compared and validated the results of the model to those of a field-scale pumping test. The model indicates that pumping SGW from a coastal aquifer freshens the aquifer and rehabilitates parts that were salinized due to seawater intrusion - an effect that increases with increasing pumping rate. In addition, when simultaneously pumping fresh groundwater further inland and SGW from below the FSI, the freshening effect is less pronounced and the salinity of the aquifer is more stable. In line with the results of the model, the field experiment revealed that salinity in the observation well decreases over the course of pumping. Taken together, our findings demonstrate that, in addition to providing a high-quality source feed water for desalination, pumping SGW does not salinize the aquifer and even rehabilitates it by negating the effect of seawater intrusion. These findings are important for planning shoreline desalination facilities and for managing arid coastal regions with lack of water supply and over exploited aquifers.

Humanin Nanoparticles for Reducing Pathological Factors Characteristic of Age-Related Macular Degeneration.

BACKGROUND: Humanin is a novel neuronal peptide that has displayed potential in the treatment of Alzheimer's Disease through the suppression of inflammatory IL-6 cytokine receptors. Such receptors are found throughout the body, including the eye, suggesting its other potential applications. Age-related Macular Degeneration (AMD) is the leading cause of blindness in the developing world. There is no cure for this disease, and current treatments have several negative side effects associated with them, making finding other treatment options desirable. OBJECTIVE: In this study, the potential applications in treating AMD for a more potent humanin derivative, AGA-HNG, were studied. METHODS: AGA-HNG was synthesized and encapsulated in chitosan Nanoparticles (NPs), which were then characterized for their size, Encapsulation Efficiency (EE), and drug release. Their ability to suppress VEGF secretion and protect against oxidative apoptosis was studied in vitro using ARPE-19 cells. The chitosan NPs exhibited similar anti-VEGF properties and oxidative protection as the free protein while exhibiting superior pharmaceutical characteristics including biocompatibility and drug release. RESULTS: Drug-loaded NPs exhibited a radius of 346nm with desirable pharmacokinetic properties including a stable surface charge (19.5 ± 3.7 mV) and steady drug release capacity. AGA-HNG showed great promise in mediating apoptosis in hypoxic cells. They were also able to significantly reduce VEGF expression in vitro with reduced cellular toxicity compared to the free drug. CONCLUSION: The ability of this drug delivery system to reduce retinal apoptosis with desirable pharmacokinetic and biocompatible properties makes this a promising therapeutic option for AMD.

Grafted Polymer Coatings Enhance Fouling Inhibition by an Antimicrobial Peptide on Reverse Osmosis Membranes.

Bacterial biofilms that are formed on surfaces are highly detrimental to many areas of industry and medicine. Seawater desalination by reverse osmosis (RO) suffers from biofilm growth on the membranes (biofouling), which limits its widespread use because biofouling decreases water permeance and necessitates module cleaning and replacement, leading to increased economic and environmental costs. Antimicrobial peptides (AMPs) bound covalently to RO membranes inhibit biofilm growth and might delay membrane biofouling. Here we examined how various hydrophilic membrane coatings composed of zwitterionic, neutral, positively charged, and poly(ethylene glycol) (PEG)-grafted polymers affected the biocidal activity and the biofilm inhibition of a covalently bonded AMP on RO membranes. AMP magainin-2 was linked by the copper-catalyzed azide-alkyne cycloaddition reaction to a series of RO membranes that were grafted with different methacrylate polymers. Surface characterization by infrared spectroscopy, X-ray photoelectron spectroscopy, and water drop contact angle gave evidence of successful RO modifications, and zeta potential analysis reflected the increase in surface charge due to the linked, positively charged peptide. All AMP-modified membranes inhibited Pseudomonas aeruginosa growth compared to unmodified membranes, and the grafted methacrylic polymers did not significantly interfere with the peptide activity. On the other hand, membranes coated with zwitterionic and other acrylate polymers including AMP attachment inhibited biofilm growth more than either the AMP or the polymer coating alone. This enhancement led to ∼20% less biofilm biovolume on the membrane surfaces. The combination of antimicrobial coatings with polymer coatings known to resist fouling might aid future designs of surface coatings susceptible to biofilm growth.

An environmentally-friendly chitosan-lysozyme biocomposite for the effective removal of dyes and heavy metals from aqueous solutions.

Developing efficient and cost-effective adsorbents for removing heavy metals and dyes from water streams is of utmost importance as prolonged human and animals consumption might lead to adverse health effects. In the present study, an environmentally-friendly bio-composite of a polysaccharide with a protein was prepared, by conjugating chitosan to lysozyme using glutaraldehyde as a crosslinker. We investigated the utility of this chitosan-lysozyme biocomposite (CLC) as an adsorbent for the removal of methyl orange (MO) dye and hexavalent chromium (Cr(VI)) ions from aqueous solutions. CLC showed excellent removal of MO and Cr(VI) along with concurrent removal of other heavy metals such as Cd(II) and Ni(II) ions from aqueous mixtures. The maximum adsorption capacities of CLC for MO and Cr(VI) were as high as 435 and 216 mg g-1, respectively. This study demonstrates the potential use of conjugated biopolymers such as chitosan and lysozyme for water treatment applications.

Synergy on Surfaces: Anti-Biofouling Interfaces Using Surface-Attached Antimicrobial Peptides PGLa and Magainin-2.

The synergistic effect of antimicrobial compounds is an important phenomenon that can increase the potency of treatment and might be useful against the formation of biofilms on surfaces. A strong inhibition of microbial viability on surfaces can potentially delay the development of biofilms on treated surfaces, thereby enhancing the performance of water-purification technologies and medical devices, for example, to prevent hospital-acquired infections. However, the synergistic effects of surface-immobilized antimicrobial peptides (AMPs) have not yet been reported. Here, we demonstrate the synergistic antimicrobial effects of the AMPs PGLa and magainin-2 on modified reverse-osmosis (RO) membranes. These AMPs are known to act synergistically in the free state, but their antimicrobial synergistic effects have not yet been reported in a surface-immobilized state. The AMPs were functionalized with alkyne linkers and covalently attached to RO membranes modified with azides, using a click chemistry reaction. The resulting RO membranes showed reduced contact angles, indicating increased wettability. X-ray photoelectron spectroscopy confirmed the presence of the two peptides on the membranes via changes in the amounts of carbon, oxygen, and sulfur, which led to an increased S/C ratio, probably because of the sulfur present in the methionine residue of the peptides. The synergistic activity was measured with the free peptides in solution and covalently bound on RO membrane surfaces by observing increased leakage of 5(6)-carboxyfluorescein from large unilamellar vesicles. The synergistic antimicrobial activity against Pseudomonas aeruginosa was observed using surface-activity assays, where the AMP-modified RO membranes showed an effective inhibition of P. aeruginosa biofilm growth, as compared with unmodified membranes. An enhanced activity of antimicrobials on surfaces might lead to potent antimicrobial surfaces, which could result in more fouling-resistant water-treatment membranes.

Ink-Jet Printing-Assisted Modification on Polyethersulfone Membranes Using a UV-Reactive Antimicrobial Peptide for Fouling-Resistant Surfaces.

Antimicrobial peptides (AMPs) are promising candidates for surface coatings to control biofilm growth on water treatment membranes because of their broad activity and the low tendency of bacteria to develop resistance to AMPs. However, general and convenient surface modification methods are limited, and a deeper understanding of the antimicrobial mechanism of action is needed for surface-attached AMPs. Here, we show a method for covalently attaching AMPs on porous ultrafiltration membranes using ink-jet printing and provide insight into the mode of action for the covalently tethered peptide RWRWRWA-(Bpa) (Bpa, 4-benzophenylalanine) against Pseudomonas aeruginosa. AMP-coated ultrafiltration membranes showed surface antibacterial activity and reduced biofilm growth. Fluorescence microscopy analysis revealed that the modified surfaces could cause cell membrane disruption, which was seen by live uptake of propidium iodide stain, and scanning electron microscopy images showed compromised cell membranes of attached bacteria. This study indicated that the mode of action of covalently tethered AMPs was similar to that of freely soluble AMPs. The deeper understanding of the mode of action of AMPs covalently attached to surfaces could lead to a more rational approach for designing surfaces with antibacterial activity.

Hexavalent chromium ion and methyl orange dye uptake via a silk protein sericin-chitosan conjugate.

Sericin, a protein waste product of the silk industry, was crosslinked with chitosan, and a chitosan-sericin conjugate (CS) was prepared, characterized and used to remove hexavalent chromium (Cr(vi)) ions and methyl orange (MO) dye from aqueous solutions. The CS was shown to effectively remove Cr(vi) ions and MO dye at maximum adsorption capacities (Langmuir) of 139 mg g-1 for Cr(vi) ions and 385 mg g-1 for MO dye. Moreover, the adsorption of both Cr(vi) ions and MO dye was highly pH dependent and varied under different experimental conditions. Cr(vi) ion and MO dye uptake by the CS was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry analysis. Additionally, XPS analysis of the Cr(vi)-loaded CS revealed that Cr(vi) was reduced to the less toxic Cr(iii). The CS was shown not only to be highly amenable to regeneration, but also to be able to effectively remove MO dye and Cr(vi) ions from a binary mixture.

Calcium phosphate scaling during wastewater desalination on oligoamide surfaces mimicking reverse osmosis and nanofiltration membranes.

Desalinated domestic wastewater is an indispensable water resource in arid regions; however, its recovery can be limited by calcium phosphate scaling and fouling of the membrane. Here we investigated calcium phosphate mineralization on oligoamide surfaces that mimics reverse osmosis (RO) and nanofiltration (NF) membrane surfaces. We used a solution that simulates desalination of secondary treated domestic wastewater effluents for calcium phosphate mineralization experiments with oligoamide-coated gold surfaces. Attenuated total reflection-Fourier transform infrared spectroscopy and energy dispersive spectrometry showed that calcium phosphate and carbonate precipitated on RO mimetic surfaces. The rate of precipitation on oligoamide sensors was monitored by a quartz crystal microbalance, showing that scaling was more intense on the RO than the NF mimetic surface and that excessive carboxyl functional groups on both surfaces promoted scaling. Filtration experiments of similar solutions with commercial membranes showed that scaling was more intense on the RO membranes than on the NF membranes, which supported the results obtained with the oligoamide model surfaces. The results of this study can be implemented in developing RO and NF membranes to prevent calcium phosphate scaling and consequently lower water-treatment costs of domestic wastewater treatment.

Biopolymer-induced calcium phosphate scaling in membrane-based water treatment systems: Langmuir model films studies.

Biofouling and scaling on reverse osmosis (RO) or nanofiltration (NF) membranes during desalination of secondary and tertiary effluents pose an obstacle that limits the reuse of wastewater. In this study we explored the mineral scaling induced by biopolymers originated from bacterial biofilms: bovine serum albumin (BSA), fibrinogen, lysozyme and alginic acid, as well as an extracts of extracellular polymeric substances (EPS) from bio-fouled RO membranes from wastewater treatment facility. Mineralization studies were performed on Langmuir films of the biopolymers deposited at the interface of a solution simulating RO desalination of secondary-treated wastewater effluents. All studied biopolymers and EPS induced heterogeneous mineralization of mainly calcium phosphate. Using IR spectroscopy coupled with systematic quantitative analysis of the surface pressure versus molecular-area isotherms, we determined the mineralization tendencies of the biopolymers to be in the order of: fibrinogen>lysozyme>BSA>alginic acid. The biopolymers and EPS studied here were found to be accelerators of calcium-phosphate mineralization. This study demonstrates the utilization of Langmuir surface-pressure area isotherms and a model solution in quantitatively assessing the mineralization tendencies of various molecular components of EPS in context of membrane-based water treatment systems.

Saline Groundwater from Coastal Aquifers As a Source for Desalination.

Reverse osmosis (RO) seawater desalination is currently a widespread means of closing the gap between supply and demand for potable water in arid regions. Currently, one of the main setbacks of RO operation is fouling, which hinders membrane performance and induces pressure loss, thereby reducing system efficiency. An alternative water source is saline groundwater with salinity close to seawater, pumped from beach wells in coastal aquifers which penetrate beneath the freshwater-seawater interface. In this research, we studied the potential use of saline groundwater of the coastal aquifer as feedwater for desalination in comparison to seawater using fieldwork and laboratory approaches. The chemistry, microbiology and physical properties of saline groundwater were characterized and compared with seawater. Additionally, reverse osmosis desalination experiments in a cross-flow system were performed, evaluating the permeate flux, salt rejection and fouling propensities of the different water types. Our results indicated that saline groundwater was significantly favored over seawater as a feed source in terms of chemical composition, microorganism content, silt density, and fouling potential, and exhibited better desalination performance with less flux decline. Saline groundwater may be a better water source for desalination by RO due to lower fouling potential, and reduced pretreatment costs.