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.

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.

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 μm 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.

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.

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.

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.

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.

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.

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 dye from aqueous solutions.

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.

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.

Attachment of antimicrobial peptides to reverse osmosis membranes by Cu(i)-catalyzed 1,3-dipolar alkyne–azide cycloaddition

Optimized polymer membrane surface modification with antimicrobial properties.

Humanin Derivatives Inhibit Necrotic Cell Death in Neurons

Humanin and its derivatives are peptides known for their protective antiapoptotic effects against Alzheimer's disease. Herein, we identify a novel function of the humanin-derivative AGA(C8R)-HNG17 (namely, protection against cellular necrosis). Necrosis is one of the main modes of cell death, which was until recently considered an unmoderated process. However, recent findings suggest the opposite. We have found that AGA(C8R)-HNG17 confers protection against necrosis in the neuronal cell lines PC-12 and NSC-34, where necrosis is induced in a glucose-free medium by either chemohypoxia or by a shift from apoptosis to necrosis. Our studies in traumatic brain injury models in mice, where necrosis is the main mode of neuronal cell death, have shown that AGA(C8R)-HNG17 has a protective effect. This result is demonstrated by a decrease in a neuronal severity score and by a reduction in brain edema, as measured by magnetic resonance imaging (MRI). An insight into the peptide's antinecrotic mechanism was attained through measurements of cellular ATP levels in PC-12 cells under necrotic conditions, showing that the peptide mitigates a necrosis-associated decrease in ATP levels. Further, we demonstrate the peptide's direct enhancement of the activity of ATP synthase activity, isolated from rat-liver mitochondria, suggesting that AGA(C8R)-HNG17 targets the mitochondria and regulates cellular ATP levels. Thus, AGA(C8R)-HNG17 has potential use for the development of drug therapies for necrosis-related diseases, for example, traumatic brain injury, stroke, myocardial infarction, and other conditions for which no efficient drug-based treatment is currently available. Finally, this study provides new insight into the mechanisms underlying the antinecrotic mode of action of AGA(C8R)-HNG17.

Diminished swelling of cross-linked aromatic oligoamide surfaces revealing a new fouling mechanism of reverse-osmosis membranes

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.

Small-angle neutron scattering studies of mineralization on BSA coated citrate capped gold nanoparticles used as a model surface for membrane scaling in RO wastewater desalination

Bovine serum albumin (BSA) coated on citrate capped gold nanoparticles (BSA-GNPs) was exposed to a simulated wastewater effluent (SSE) in order to study the mineralization and thereby mimic scaling at biofouled membranes of reverse osmosis (RO) wastewater desalination plants. RO is a leading technology of achieving freshwater quality as it has the capability of removing both dissolved inorganic salts and organic contaminants from tertiary wastewater effluents. The aim was to better understand one of the major problems facing this technology which is fouling of the membranes, mainly biofouling and scaling by calcium phosphate. The experiments were performed using the small-angle neutron scattering (SANS) technique. The nanoparticles, GNPs, stabilized by the citrate groups showed 30 Å large particles having a homogeneous distribution of gold and citrate with a gold volume fraction of the order of 1%. On the average two BSA monomers are grafted at 2.4 GNPs. The exposed BSA-GNPs to SSE solution led to immediate mineralization of stable composite particles of the order of 0.2 μm diameter and a mineral volume fraction between 50% and 80%. The volume fraction of the mineral was of the order of 10(-5), which is roughly 3 times larger but an order of magnitude smaller than the maximum possible contents of respectively calcium phosphate and calcium carbonate in the SSE solution. Considering the extreme low solubility product of calcium phosphate, we suggest total calcium phosphate and partially (5-10%) calcium carbonate formation in the presence of BSA-GNPs.

Effect of organic Matter on RO Membrane Scaling in Wastewater Desalination

Biofouling and scaling are major limitations of membrane-based desalination techniques. In particular scaling by calcium phosphate on reverse osmosis (RO) membranes limits the desalination efficiency of secondary wastewater effluents. The exploration of biofilm formation and of scaling is the topic of our research. Our particular interest is the effect of components representing the biofilm on calcium mineralization at a molecular level using the experimental technique of small-angle neutron scattering (SANS). To this end we are studying the formation of calcium minerals in a model solution simulating a secondary waste water effluent (SSE) [1] after adding biopolymers as single molecules or as grafted at gold nanoparticles. The latter experiment should simulate mineralization at surfaces such as membranes. SANS is a promising tool in this field as was demonstrated on similar studies in the related field of biomineralization [2]. We will present data showing the process of mineralization in SSE solutions stimulated by some relevant proteins (BSA, lysozyme) and polysaccharides (alginic acid, chitosan) using stopped-flow technique in combination with classical as well as with focusing ultra-small SANS techniques [3]. This work was funded by the Ministry of Science, Culture and Sport (MOST) and the Bundesministerium für Bildung und Forschung (BMBF).

Effects of biological molecules on calcium mineral formation associated with wastewater desalination as assessed using small-angle neutron scattering

Calcium phosphate scale formation on reverse osmosis (RO) membranes is one of the main limitations on cost-effective desalination of domestic wastewater worldwide. It has been shown that organic agents affect mineralization. In this study, we explored mineralization in the presence of two biofilm-relevant organic compounds, the proteins bovine serum albumin (BSA) and lysozyme, in a simulated secondary effluent (SSE) solution using small-angle neutron scattering (SANS), and applied the results to analyses of mineral precipitation in RO desalination of secondary effluents of wastewater. The two proteins are prominent members of bacterial extracellular polymeric substances (EPSs), forming biofilms that are frequently associated with RO-membrane fouling during wastewater desalination. Laboratory experiments showed that both proteins in SSE solution are involved in complex mineralization processes. Only small portions of both protein fractions are involved in mineralization processes, whereas most of the protein fractions remain as monomers in solution. Contrast variation showed that composite particles of mineral and protein are formed instantaneously to a radius of gyration of about 300 Å, coexisting with particles of about μm size. After about one day, these large particles start to grow again at the expense of the 300 Å particles. The volume fraction of the 300 Å particles is of the order of 2 × 10(-4), which is too large to represent calcium phosphate such as hydroxyapatite as the only mineral present. Considering the data of mineral volume fraction obtained here as well as the solubility product of possible mineral polymorphs in the SSE solution, we suggest the formation of protein-mineral particles of hydroxyapatite and calcium carbonate during scale formation.

Studying the role of common membrane surface functionalities on adsorption and cleaning of organic foulants using QCM-D

Adsorption of organic foulants on nanofiltration (NF) and reverse osmosis (RO) membrane surfaces strongly affects subsequent fouling behavior by modifying the membrane surface. In this study, impact on organic foulant adsorption of specific chemistries including those in commercial thin-film composite membranes was investigated using self-assembled monolayers with seven different ending chemical functionalities (-CH(3), -O-phenyl, -NH(2), ethylene-glycol, -COOH, -CONH(2), and -OH). Adsorption and cleaning of protein (bovine serum albumin) and polysaccharide (sodium alginate) model foulants in two solution conditions were measured using quartz crystal microbalance with dissipation monitoring, and were found to strongly depend on surface functionality. Alginate adsorption correlated with surface hydrophobicity as measured by water contact angle in air; however, adsorption of BSA on hydrophilic -COOH, -NH(2), and -CONH(2) surfaces was high and dominated by hydrogen bond formation and electrostatic attraction. Adsorption of both BSA and alginate was the fastest on -COOH, and adsorption on -NH(2) and -CONH(2) was difficult to remove by surfactant cleaning. BSA adsorption kinetics was shown to be markedly faster than that of alginate, suggesting its importance in the formation of the conditioning layer. Surface modification to render -OH or ethylene-glycol functionalities are expected to reduce membrane fouling.

Effect of surface-exposed chemical groups on calcium-phosphate mineralization in water-treatment systems

Calcium-phosphate-scale formation on reverse osmosis (RO) membranes is a major limiting factor for cost-effective desalination of wastewater. We determined the effects of various organic chemical groups found on membrane surfaces on calcium-phosphate scaling. Langmuir films exposing different functional groups were equilibrated with a solution simulating the ionic profile of secondary effluent (SSE). Surface pressure-area (Langmuir) isotherms combined with ICP elemental analyses of the interfacial precipitate suggested acceleration of calcium-phosphate mineralization by the surface functional groups in the order: PO(4) > COOH ∼ NH(2) > COOH:NH(2) (1:1) > OH > ethylene glycol. Immersion of gold-coated silicon wafers self-assembled with different alkanethiols in SSE solution showed formation of a hydroxyapatite precipitate by X-ray diffraction and ATR-IR analysis. Data showed diverse influences of functional groups on mineralization, implying low calcium-phosphate scaling for uncharged surfaces or surfaces coated with both positively and negatively charged groups. This information is valuable for understanding scaling processes, and for designing of novel low-scaling membranes for water desalination.

The effects of peptides with estrogen-like activity on cell proliferation and energy metabolism in human derived vascular smooth muscle cells

Hormone replacement therapy (HRT) for post-menopausal symptoms in diabetes is associated with increased risk of coronary heart disease and stroke. Therefore, there is a need for new HRT with no adverse effects on diabetic post-menopausal women. We developed peptides as potential estrogen mimetic compounds and now we evaluated the effects of the most efficacious peptide; hexapeptide estrogen-mimetic peptide 1 (EMP-1) (VSWFFE) in comparison to estrogen (E(2)) and peptides with weak activity A44 (KAWFFE) and A45 (KRAFFE) on modulation of cell proliferation of vascular smooth muscle cells (VSMC) growing in normal (ng) or high glucose (hg) concentrations. In ng EMP-1-like E(2) inhibited cell proliferation at high concentration, and stimulated at low concentration. EMP-1 did not affect E(2) stimulation of DNA, but inhibited E(2) inhibition of cell proliferation at high concentration. All effects by the combination of EMP-1 and E(2) were abolished at hg. A44-stimulated cell proliferation at all concentrations and A45 had no effect. When A44 was co-incubated with E(2) at both concentrations, DNA synthesis was stimulated, but abolished at hg. A45 abolished E(2) stimulation and inhibition of cell proliferation at both glucose concentrations. All peptides tested except A45-stimulated CK-specific activity at both glucose concentrations. In hg A44 stimulation of DNA was unaffected as well as its inhibition by EMP-1. EMP-1 and A44 similar to E(2)-stimulated MAPK activity in ng or hg, suggesting similar mechanism of action. The results presented here suggest that EMP-1 provided it acts similarly in vivo can replace E(2) for treatment of post-menopausal women in hyperglycemia due to diabetes.

Restrain of bone growth by estrogen-mimetic peptide-1 (EMP-1): a micro-computed tomographic study

Estrogen has a key role in the regulation of skeletal growth and maintenance of bone mass. Recently, we developed peptides having estrogen-like activity as potential estrogen-based new drugs. The aim of the present study was to evaluate the influence of long-term administration of the most efficacious of these peptides, the hexapeptide EMP-1 (VSWFFE), on bone mass and development. EMP-1 was injected daily to ovariectomized (OVX) and intact young, sexually mature female mice for 10 weeks. Whole femora, including the cartilaginous growth plates were analyzed by micro-computed tomography (microCT). We found that peptide EMP-1 restrains bone growth in OVX mice: it inhibited dramatically bone longitudinal growth (40%), and decreased femoral diaphyseal diameter. Peptide EMP-1 had no effect on bone growth in normal mice, and did not influence the OVX-induced bone loss. We then developed a new microCT methodology to evaluate uncalcified and calcified growth plate parameters. In the OVX mice, peptide EMP-1 reduced volume and thickness of the uncalcified growth plate, a possible cause for the inhibition of bone longitudinal growth. Peptide EMP-1 may be used as a lead compound for the development of drugs to treat acromegalic patients.

Design, synthesis, and evaluation of peptides with estrogen-like activity

Currently used antiestrogenic drugs against hormone-dependent breast cancer, and estrogenic drugs used in treatment of osteoporosis, are associated with risk factors. Therefore, there is a strong need to develop selective estrogen receptor modulators with better tissue selectivity. In a recent study (Peptides, 2002, Vol. 3, 573-580), we used a monoclonal antibody to estradiol (mAb-E2) to screen a phage-display peptide library. We identified a 15-mer peptide (peptide H5) that recognizes mAb-E2 (IC(50) 1 microM) and estrogen receptor (ER)alpha (IC(50) 500 microM) but not ERbeta, and displays estrogen-like activity in vitro and in vivo. In this study, we designed and prepared peptides based on peptide H5, which possess improved estrogenic activity, by evaluating their binding to mAb-E2 and to ERs. Initially, we determined the minimal binding sequence of peptide H5 capable of binding mAb-E2 and ER. Subsequently, systematic single-residue replacements of the minimal sequence, followed by multiple-residue replacements, yielded hexa- and heptapeptides with increased affinities to mAb-E2 and to ER. The most promising peptides, VSWFFE (EMP-1) and VSWFFED (EMP-2) (EMP: estrogen-mimetic peptide), bind mAb-E2 with high affinity (IC(50) of 6 and 30 nM, respectively), recognize ERs with increased affinity (IC(50) of 100 microM for ERalpha, and 100-250 microM for ERbeta), and possess estrogenic activity in vivo. The short peptides described in this study may be used as potential lead compounds for developing new ER ligands.

Design and synthesis of peptides that bind alpha-bungarotoxin with high affinity and mimic the three-dimensional structure of the binding-site of acetylcholine receptor

Alpha-bungarotoxin (alpha-BTX) is a highly toxic snake neurotoxin that binds to acetylcholine receptor (AChR) at the neuromuscular junction, and is a potent inhibitor of this receptor. In the following we review multi-phase research of the design, synthesis and structure analysis of peptides that bind alpha-BTX and inhibit its binding to AChR. Structure-based design concomitant with biological information of the alpha-BTX/AChR system yielded 13-mer peptides that bind to alpha-BTX with high affinity and are potent inhibitors of alpha-BTX binding to AChR (IC(50) of 2 nM). X-Ray and NMR spectroscopy reveal that the high-affinity peptides fold into an anti-parallel beta-hairpin structure when bound to alpha-BTX. The structures of the bound peptides and the homologous loop of acetylcholine binding protein, a soluble analog of AChR, are remarkably similar. Their superposition indicates that the toxin wraps around the binding-site loop, and in addition, binds tightly at the interface of two of the receptor subunits and blocks access of acetylcholine to its binding site. The procedure described in this article may serve as a paradigm for obtaining high-affinity peptides in biochemical systems that contain a ligand and a receptor molecule.

The binding site of acetylcholine receptor: from synthetic peptides to solution and crystal structure

Our group has been employing short synthetic peptides, encompassing sequences from the acetylcholine receptor (AChR) alpha-subunit for the analysis of the binding site of the AChR. A 13-mer peptide mimotope, with similar structural motifs to the AChR binding region, was selected by alpha-bungarotoxin (alpha-BTX) from a phage-display peptide library. The solution structure of a complex between this library-lead peptide and alpha-BTX was solved by NMR spectroscopy. On the basis of this NMR study and on structure-function analysis of the AChR binding site, and in order to obtain peptides with higher affinity to alpha-BTX, additional peptides resulting from systematic residue replacement in the lead peptide were designed and characterized. Of these, four peptides, designated high-affinity peptides (HAPs), homologous to the binding region of the AChR, inhibited the binding of alpha-BTX to the AChR with an IC(50) of 2 nM. The solution and crystal structures of complexes of alpha-BTX with HAP were solved, demonstrating that the HAP fits snugly to alpha-BTX and adopts a beta-hairpin conformation. The X-ray structures of the bound HAP and the homologous loop of the acetylcholine binding protein (AChBP) are remarkably similar. Their superposition results in a model indicating that alpha-BTX wraps around the receptor binding-site loop and, in addition, binds tightly at the interface of two of the receptor subunits, where it inserts a finger into the ligand-binding site. Our proposed model explains the strong antagonistic activity of alpha-BTX and accommodates much of the biochemical data on the mode of interaction of alpha-BTX with the AChR.