Evaluation of In Vitro Antimicrobial, Cytotoxic, Thrombolytic, and Antiarthritic Property of Different Parts of Bari Orchid.

Many different herbal extracts have historically been utilized to treat microbe-induced infections, injuries, cancer, thrombosis, and arthritis. The purpose of this study was to determine the antibacterial, cytotoxic, in vitro thrombolytic, and in vitro antiarthritic properties of ethanolic extracts of stem and seed of Bari orchid 1 (BO) plant. This orchid plant was developed by the Bangladesh Agriculture Research Institute (BARI) in Gazipur. Fourteen microbes were employed in the antimicrobial investigation, and samples of orchids were compared to ciprofloxacin as a reference. The BO/seed extract was found to possess more antibacterial activity. The lethality test of brine shrimps was used to assess the LC50 values. The BO/stem extract exhibited a higher cytotoxicity potential, in comparison to the BO/seed extract. Two concentrations (1000 and 100 ppm) and two incubation times (24 hours and 1.5 hours) were used to assess the thrombolytic activity of the extracts. Regarding the thrombolytic effect, the BO/stem extract has demonstrated greater promise. Furthermore, the herbal extract's antiarthritic activity was investigated at four different concentrations, and the results were evaluated in comparison with those of diclofenac sodium. When comparing BO/stem extract to other extracts, the greatest values for protein denaturation were obtained.

Exploring the biomedical competency of gamma-radiation aided hydroxyapatite and its composite fabricated with nano-cellulose and chitosan.

The well-known biomaterial Ca-hydroxyapatite (Hap) in its pristine form holds the top ranking position in the field of biomedical research and extensive investigation is continuing across the globe to enhance its competency. Hence, having the intention to introduce superior physiognomies (e.g. cytotoxicity, haemocompatibility, and bioactivity coupled with antimicrobial and antioxidant activity) in Hap, in this research work, we exposed Hap to 200 kGy γ-radiation. As a result, γ-radiated Hap exhibited extreme antimicrobial (more than 98%) and moderate (∼34%) antioxidant properties. On the other hand, cytotoxicity and haemocompatibility of γ-radiated Hap were in good agreement with the ISO 10993-5 and ISO 10993-4 standards respectively. Since, bone and joint infections as well as degenerative disorders e.g. osteoarthritis, osteomyelitis, bone injury, and spinal problems have emerged as serious issues and urge a remedial way out, application of γ-radiated Hap could be a promising solution in this regard.

Reuse of gamma-ray irradiated textile wastewater: implications on the growth of Capsicum frutescens plant.

This investigation concentrates on the possibility of using gamma radiation for the decomposition of organic pollutants in textile wastewater and reuse as irrigation water. The wastewater sample was irradiated at four different absorbed doses of 3, 5, 8, and 10 kilo Gray (kGy). After irradiation at 8-10 kGy, physicochemical parameters, i.e., pH, turbidity, EC, total suspended solids (TSS) and total dissolved solids (TDS), have decreased sharply and approached to the expected value recommended by Department of Environment (DoE), Bangladesh. At 10 kGy absorbed dose, 59.0 % biological oxygen demand (BOD5) and 71.6 % chemical oxygen demand (COD) removal has been achieved, accelerating the enhancement in biodegradability index (BOD5/COD). Ammonium and total nitrogen have improved up to 87.0 % and 94.5 % after irradiation at 10 kGy doses. Subsequently, the treated textile wastewater samples were reused to grow Capsicum frutescens plants to inspect the fertility responses. When Capsicum plants were nourished by textile wastewater irradiated at 8-10 kGy, increased values were observed in the plant morphological parameters such as dry masses of the fruits (from 2.25 to 3.02 g), moisture content (from 91.35 to 92.62%), root length (from 13.21 to 16.56 cm), average plant height (from 2.42 to 4.07 cm/week), average number of leaves (from 14 to 16 nos./week), and total number of fruits (from 25 to 40 nos.) in comparison to those plants nourished by simply water and raw wastewater. The elemental analysis confirmed that negligible amounts of heavy metals were found in Capsicum fruits at higher absorbed doses. In contrast, helpful macro and micronutrients for plant production were raised to sufficient levels at 8-10 kGy, which can be the optimum doses for gamma irradiation to treat textile wastewater for maintaining sustainable water resources.

Nitrogen and organic load removal from anaerobically digested leachate using a hybrid electro-oxidation and electro-coagulation process.

This study evaluated the performance of an integrated electrochemical process, which simultaneously utilizes electro-oxidation (EO) and electro-coagulation (EC) methods while removing organic and nitrogen loads from high-strength leachate obtained from anaerobic digesters. A bipolar arrangement of the aluminum electrode, sandwiched between a monopolar boron-doped diamond anode and stainless-steel cathode, integrates EC and EO into a single reactor. This arrangement demonstrated an enhancement of 33%, 27%, and 24% in removal capacity for ammonia nitrogen (AN), total Kjeldahl nitrogen (TKN), and total nitrogen, respectively, when compared to just EO at 0.8 A current intensity after 24 h. Increasing the current intensity from 0.4 A to 1.0 A enhanced the organic nitrogen and AN removal. Chemical oxygen demand (COD) exhibited initial faster removal kinetics with higher current intensities and eventually reached 95%-98% removal for intensities of 0.6 A or higher. Additional removal for AN, TKN were also observed with increasing current intensity. Lowering the pH further expedited the COD removal kinetics. Reducing and maintaining the pH at 4, 6, and 8 by dosing of hydrochloric acid (HCl) resulted in the 100% removal of AN and TKN from the integrated system in 6, 8, and 20 h, respectively. Accelerated removal of COD and the enhanced removal of AN and TKN through pH control could be linked to the formation of active chlorine species in bulk solution. The integrated system offered lower energy consumption than EO due to oxidation on the additional anodic surface of the bipolar electrode, as well as the adsorption-precipitation of contaminants in aluminum flocs.

A photo-Fenton nanocomposite ultrafiltration membrane for enhanced dye removal with self-cleaning properties.

Membrane fouling is an ongoing challenge in the membrane filtration process. Herein, a photocatalytic membrane comprising a reactive layer was fabricated by engineering partially reduced graphene oxide/Ag nanoparticles/MIL-88A (prGO/Ag/M88A, pGAM) photocatalysts on the PVDF substrate membranes. Benefiting from the high conductivity of prGO and the surface plasmon resonance (SPR) effect of Ag nanoparticles (Ag NPs), the photo-sensitivity of the prGO/Ag/M88A is significantly enhanced. Compared to the membrane in the dark condition, the pGAM membrane displayed an enhanced dye removal efficiency (∼99.7%) and significantly improved permeability (∼189 L·m-2·h-1 bar-1) towards dye contaminants based on the synergistic filtration/photo-Fenton processes. Significantly, the membrane retained high perm-selectivity after 10 cyclic runs (183 L·m-2·h-1 bar-1 of permeability and 98.1% of dye removal), and its nano-channel structure did not collapse under high pressure (0.1-0.4 MPa). The membrane also exhibits antifouling properties with a high water flux recovery of more than 90%. In addition, the pGAM membrane exhibited a high MB degradation efficiency (∼90%) when it is directly used as a photocatalyst in the photo-Fenton system. The mechanism of the self-cleaning is also proposed through quenching experiments. The results of this study demonstrate that this self-cleaning membrane has huge promise for membrane anti-fouling and wastewater remediation.

Processing High-Solid and High-Ammonia Rich Manures in a Two-Stage (Liquid-Solid) Low-Temperature Anaerobic Digestion Process: Start-Up and Operating Strategies.

Globally, livestock and poultry production leads to total emissions of 7.1 Gigatonnes of CO2-equiv per year, representing 14.5% of all anthropogenic greenhouse gas emissions. Anaerobic digestion (AD) is one of the sustainable approaches to generate methane (CH4) from manure, but the risk of ammonia inhibition in high-solids AD can limit the process. Our objective was to develop a two-stage (liquid-solid) AD biotechnology, treating chicken (CM) + dairy cow (DM) manure mixtures at 20 °C using adapted liquid inoculum that could make livestock farming more sustainable. The effect of organic loading rates (OLR), cycle length, and the mode of operation (particularly liquid inoculum recirculation-percolation mode) was evaluated in a two-stage closed-loop system. After the inoculum adaptation phase, aforementioned two-stage batch-mode AD operation was conducted for the co-digestion of CM + DM (Total Solids (TS): 48-51% and Total Kjeldahl Nitrogen (TKN): 13.5 g/L) at an OLR of 3.7-4.7 gVS/L.d. Two cycles of different cycle lengths (112-d and 78-d for cycles 1 and 2, respectively) were operated with a CM:DM mix ratio of 1:1 (w/w) based on a fresh weight basis. Specific methane yield (SMY) of 0.35 ± 0.11 L CH4g/VSfed was obtained with a CH4 concentration of above 60% for both the cycles and Soluble Chemical Oxygen Demand (CODs) and volatile solid (VS) reductions up to 85% and 60%, respectively. For a comparison purpose, a similar batch-mode operation was conducted for mono-digestion of CM (TS: 65-73% and TKN: 21-23 g/L), which resulted in a SMY of 0.52 ± 0.13 L CH4g/VSfed. In terms of efficiency towards methane-rich biogas production and ammonia inhibitions, CM + DM co-digestion showed comparatively better quality methane and generated lower free ammonia than CM mono-digestion. Further study is underway to optimize the operating parameters for the co-digestion process and to overcome inhibitions and high energy demand, especially for cold countries.

Fouling and wetting in the membrane distillation driven wastewater reclamation process - A review.

Fouling and wetting of membranes are significant concerns that can impede the widespread application of the membrane distillation (MD) process during high-salinity wastewater reclamation. Fouling, caused by the accumulation of undesirable materials on the membrane surface and pores, causes a decrease in permeate flux. Membrane wetting, the direct permeation of the feed solution through the membrane pores, results in reduced contaminant rejection and overall process failure. Lately, the application of MD for water recovery from various types of wastewaters has gained increased attention among researchers. In this review, we discuss fouling and wetting phenomena observed during the MD process, along with the effects of various mitigation strategies. In addition, we examine the interactions between contaminants and different types of MD membranes and the influence of different operating conditions on the occurrence of fouling and wetting. We also report on previously investigated feed pre-treatment options before MD, application of integrated MD processes, the performance of fabricated/modified MD membranes, and strategies for MD membrane maintenance during water reclamation. Energy consumption and economic aspects of MD for wastewater recovery is also discussed. Throughout the review, we engage in dialogues highlighting research needs for furthering the development of MD: the incorporation of MD in the overall wastewater treatment and recovery scheme (including selection of appropriate membrane material, suitable pre-treatment or integrated processes, and membrane maintenance strategies) and the application of MD in long-term pilot-scale studies using real wastewater.

Zwitterion-Functionalized Graphene Oxide Incorporated Polyamide Membranes with Improved Antifouling Properties.

In this study, zwitterionic polymer poly(sulfobetaine methacrylate) (PSBMA) functionalized graphene oxide (GO) nanocomposites (GO-PSBMA) were synthesized and incorporated into the active layer of a polyamide membrane to improve its water perm-selectivity and fouling-resistant properties. GO-PSBMA nanocomposite contained covalently tethered PSBMA brushes on GO sheets, which were grown by activators regenerated by the electron transfer-atom transfer radical polymerization technique via the "graft-from" strategy. The grafting of zwitterionic PSBMA partially neutralized the surface charge of GO and increased its dispersibility in organic solvent. The incorporation of the GO-PSBMA-1h nanocomposite in the active layer of the polyamide membrane significantly improved surface hydrophilicity of the membrane and reduced its charge density. A near twofold increase in water permeation flux, with the nonsignificant change in MgSO4 and NaCl rejection, was achieved after the incorporation of 0.3 wt % of GO-PSBMA-1h in the membrane casting solution. With an improved water affinity, the fabricated nanocomposite membrane exhibited a near 80% reduction in bacterial ( Escherichia coli) attachment in comparison to the control membrane, even after 48 h of culture. In a crossflow filtration test, the nanocomposite membrane exhibited less of a reduction in the flux associated with bovine serum albumin fouling and salt ion scaling. The results demonstrated that incorporating zwitterionic polymer-decorated GO in the polyamide skin layer is a promising method to fabricate thin film nanocomposite membranes with improved water flux and fouling resistance.

Crossflow electrochemical filtration for elimination of ibuprofen and bisphenol a from pure and competing electrolytic solution conditions.

For the first time, a crossflow electrochemical filtration system containing multiwalled carbon nanotubes (MWNTs) blended with buckypaper as a flat sheet dual membrane electrode was investigated for the removal of two contaminants of emerging concern, Ibuprofen and Bisphenol A. Breakthrough experiments revealed that a crossflow configuration could be highly efficient in eliminating both contaminants at applied DC potentials of 2 and 3 V over an extended period, from pure salt electrolyte as well as from synthetic secondary wastewater effluent. The shear flow provided consistent surface coverage resulting in excellent sorption performance. The long residence time of the two contaminants within the membrane (18.3 s) was sufficient enough to allow for almost complete degradation of phenolic aromatic products and quinoid rings and the resulting formation of aliphatic carboxylic acids, which was more evident at a higher applied potential (3 V). The formation of the non-toxic aliphatic carboxylic acids is a clear indication of the superior electrochemical performance of the crossflow mode over the dead-end flow-through system. Moreover, this study provides an in-depth understanding of different factors such as filter surface area and residence time that can greatly affect the removal of the contaminants considered.

pH-sensitive and magnetically separable Fe/Cu bimetallic nanoparticles supported by graphene oxide (GO) for high-efficiency removal of tetracyclines.

Nanoscale zero-valent iron (nZVI) has been recognized as one of the most promising materials for the removal of a wide range of pharmaceuticals in water; however, aggregation and instability of nZVI in aqueous media reduces its efficacy. In this study, graphene oxide (GO) supported nZVI/copper bimetallic-nanoparticles (BNPs) were fabricated for high-efficiency removal of tetracyclines (TCs). In comparison to pure nZVI, the addition of Cu to the nano-adsorbents enhanced the efficacy of TC removal by 13%. The GO supporter mitigated the aggregation of BNPs and reduced the dissolution of metal nanoparticles, thereby demonstrating a higher working efficacy than Fe/Cu BNPs, even over five consecutive runs. At the optimal condition (pH 5-7, [TCs]: [Fe/Cu-GO] = 1:2.5 w/w), the Fe/Cu-GO nanocomposite showed near-complete (∼100%) TCs-removal within 15 min. The adsorption of TCs by Fe/Cu-GO fits the Freundlich model, with an adsorption capacity of 201.9 mg g-1. The Fe/Cu-GO nanocomposite showed pH-dependent assembly behavior to potentially recycle GO at a pH > 9 condition to generate new nanoparticles. The high removal efficiency of TCs, combining with high stability and easy separation performance in the aqueous environment, makes Fe/Cu-GO nanocomposites a promising material for treating latent antibiotics in water.

Bacteriophage-based strategies for biofouling control in ultrafiltration: In situ biofouling mitigation, biocidal additives and biofilm cleanser.

The ability of bacteriophages to infect and destroy specific bacteria makes them promising antimicrobial agents in industrial processes. In this study, potential strategies of bacteriophage-facilitated biofouling control during membrane ultrafiltration (UF) were investigated through use of the model T4 bacteriophage and the model host bacterium, Escherichia coli. In the dead-end filtration mode, phages were immobilized on the membrane surface to serve as biocidal agents and inhibit the propagation of bacteria in situ. After 6 h of filtration, a 36% flux reduction was observed for the T4-functionalized membrane in comparison to 71% for the non-functionalized membrane. Surface modification of the membrane using O2 plasma treatment resulted in increased numbers of bound phage and enhanced biofouling resistance of the membrane. Introducing the phage into the feed of a cross-flow filtration system effectively mitigated the water flux reduction of the membrane caused by bacterial growth. By modifying the concentration of phage additives, the growth of bacteria was delayed, inhibited, or eliminated. Phage treatment changed the structure of biofilms on the membrane surface and facilitated in situ biofilm cleaning. A 20% greater recovery in water flux was observed for the biofilm-contaminated membrane following phage-assisted cleaning when compared to the membrane cleaned via a physical washing process. Taken together, these results show that bacteriophage assisted anti-biofouling strategies have the potential to mitigate biofouling in membrane processes in an environmentally friendly manner.

Removal of bisphenol A by electrochemical carbon-nanotube filter: Influential factors and degradation pathway.

Bisphenol A is a chemical with hazardous health effects that is largely used in the manufacture of extensively used products including adhesives, plastics, powder paints, thermal paper and paper coatings, and epoxy resin, and is reported to exist in nature in an accumulative manner. In this study, both pristine and boron-doped multiwalled carbon nanotubes (MWNTs) were employed as filtration and electrochemical filtration materials, resulting in a significant removal of bisphenol A with identical performance for both MWNTs types. It was shown that the presence of salt is not critical for the greatest contaminant removal efficiency, likely due to the vital role of other electroactive species (e.g. reactive oxygen species). Near complete removal of 1 mg L-1 bisphenol A at 2 and 3 V of applied DC potentials was achieved, indicating that the electrochemical filtration process is voltage dependent at both 2 and 3 V. Increasing the residence time by 7.4 fold (from 2.0 to 14.9 s) resulted in a significant removal of bisphenol A and its toxic byproducts, up to 424 min of electrochemical filtration time at 3 V of applied potential. Based on these results, electrochemical filtration using MWNTs is considered a promising technology for the removal of the accumulative bisphenol A and the reduction of its hazardous effects in waters.

Cysteamine- and graphene oxide-mediated copper nanoparticle decoration on reverse osmosis membrane for enhanced anti-microbial performance.

In this work, copper nanoparticles (CuNPs) were decorated onto the polyamide RO membranes via in-situ reduction for biofouling mitigation. To increase CuNPs loading and improve anti-microbial properties of the membrane, cysteamine (Cys) and graphene oxide (GO), which contain different functional groups with high metal affinity, were applied as bridging agents between CuNPs and membrane surface via covalent bonding. The functionalization of Cys and GO linkers on membrane was confirmed by XPS and SEM analysis. By applying the linkers, the loading quantity of copper, in particular on Cys-modified membrane, was significantly improved and the particle size of CuNPs appeared smaller and had more uniform distribution. The GO medium increased the hydrophilicity of CuNP-decorated membranes, leading to an increase in water permeation with minor impact on membrane's salt rejection. Bacterial inactivation of the Cys-Cu- and GO-Cu-functionalized membranes was over 25% higher than that of the bare CuNP-coated surface, indicating enhanced bacterial inactivation benefiting from the application of linkers. After a CuNPs' release test, the membranes modified with Cys and GO retained larger quantities of CuNPs and showed better antimicrobial performance than that of bare CuNP-modified membranes. The successful regeneration of CuNPs after their depletion demonstrated the modified membranes' potential for long-term application.

Spray- and spin-assisted layer-by-layer assembly of copper nanoparticles on thin-film composite reverse osmosis membrane for biofouling mitigation.

Copper nanoparticles (CuNPs) have long been considered as highly effective biocides; however, the lack of suitable methods for loading CuNPs onto polymeric membranes is recognized as being one of the primary reasons for the limited research concerning their application in membrane industries. A highly efficient spray- and spin-assisted layer-by-layer (SSLbL) method was developed to functionalize the TFC polyamide RO membranes with controllable loading of CuNPs for biofouling control. The SSLbL method was able to produce a uniform bilayer of polyethyleneimine-coated CuNPs and poly(acrylic) acid in less than 1 min, which is far more efficient than the traditional dipping approach (25-60 min). The successful loading of CuNPs onto the membrane surface was confirmed by XPS analysis. Increasing the number of bilayers from 2 to 10 led to an increased quantity of CuNPs on the membrane surface, from 1.75 to 23.7 µg cm(-2). Multi-layer coating exhibited minor impact on the membrane water permeation flux (13.3% reduction) while retaining the original salt rejection ability. Both static bacterial inactivation and cross-flow filtration tests demonstrated that CuNPs could significantly improve anti-biofouling property of a polyamide membrane and effectively inhibit the permeate flux reduction caused by bacterial deposition on the membrane surface. Once depleted, CuNPs can also be potentially regenerated on the membrane surface via the same SSLbL method.

Electrochemical efficacy of a carboxylated multiwalled carbon nanotube filter for the removal of ibuprofen from aqueous solutions under acidic conditions.

This study provides insight into the efficiency of a functionalized multiwalled carbon nanotube filter for the removal of an anti-inflammatory drug, ibuprofen, through conventional filtration and electrochemical filtration processes. A comparison was made between carboxylated multiwalled carbon nanotubes (MWNTs-COOH) and pristine multiwalled carbon nanotubes (MWNTs) in order to emphasize the enhanced performance of MWNTs-COOH for the removal of ibuprofen using an electrochemical filtration process under acidic conditions. Ibuprofen-removal trials were evaluated based on absorbance values obtained using a UV/Vis spectrophotometer, and possible degradation products were identified using liquid chromatography mass spectrometry (LC-MS). The results exhibited near complete removal of ibuprofen by MWNTs-COOH at lower applied potentials (2 V), at lower flow rates, and under acidic conditions, which can be attributed to the generation of superoxides and their active participation in simultaneous degradation of ibuprofen, and its by-products, under these conditions. At higher applied potential (3 V), the possible participation of both bulk indirect oxidation reactions, and direct electron transfer were hypothesized for the removal behavior over time (breakthrough). At 3 V under acidic conditions, near 100% removal of the target molecule was achieved and was attributed to the enhanced generation of electroactive species toward bulk chemical reactions and a possible contribution from direct electron transfer under these conditions. The degradation by-products of ibuprofen were effectively removed by allowing longer residence time during the filtration process. Moreover, the effect of temperature was studied, yet showed a non-significant effect on the overall removal process.

Electrospun novel super-absorbent based on polysaccharide-polyvinyl alcohol-montmorillonite clay nanocomposites.

A novel super-absorbent material was fabricated by electrospinning the natural polysaccharide pullulan (PULL) with polyvinyl alcohol (PVA) and montmorillonite (MMT) clay to form nonwoven webs, which were then heat treated. Transmission electron microscopy (TEM) micrographs, X-ray diffraction (XRD) patterns, and Fourier transform infrared (FTIR) analysis of the novel super-absorbent nanofibers suggest the coexistence of PULL, PVA, and MMT through the exfoliation of MMT layers in the super-absorbent nanofiber composite. The heat-treated PULL/PVA/MMT webs loaded with 5 wt% MMT electrospun nanofibers exhibited a water absorbency of 143.42 g g(-1) in distilled water and a water absorbency of 39.75 g g(-1) in a 0.9 wt% NaCl solution. Under extremely dry conditions, the PULL/PVA/MMT webs exhibited the ability to retain 43% distilled water and 38% saline water after being exposed to the atmosphere for one week. The heat treatment improved the crystallinity of the electrospun PULL/PVA/MMT super-absorbent webs and thus made the webs highly stable in aqueous environments. Overall, the addition of MMT resulted in improved thermal stability and mechanical properties and increased the water absorbency of the PULL/PVA/MMT composite.

Modeling phosphorus removal and recovery from anaerobic digester supernatant through struvite crystallization in a fluidized bed reactor.

The cost associated with the disposal of phosphate-rich sludge, the stringent regulations to limit phosphate discharge into aquatic environments, and resource shortages resulting from limited phosphorus rock reserves, have diverted attention to phosphorus recovery in the form of struvite (MAP: MgNH4PO4·6H2O) crystals, which can essentially be used as a slow release fertilizer. Fluidized-bed crystallization is one of the most efficient unit processes used in struvite crystallization from wastewater. In this study, a comprehensive mathematical model, incorporating solution thermodynamics, struvite precipitation kinetics and reactor hydrodynamics, was developed to illustrate phosphorus depletion through struvite crystal growth in a continuous, fluidized-bed crystallizer. A thermodynamic equilibrium model for struvite precipitation was linked to the fluidized-bed reactor model. While the equilibrium model provided information on supersaturation generation, the reactor model captured the dynamic behavior of the crystal growth processes, as well as the effect of the reactor hydrodynamics on the overall process performance. The model was then used for performance evaluation of the reactor, in terms of removal efficiencies of struvite constituent species (Mg, NH4 and PO4), and the average product crystal sizes. The model also determined the variation of species concentration of struvite within the crystal bed height. The species concentrations at two extreme ends (inlet and outlet) were used to evaluate the reactor performance. The model predictions provided a reasonably good fit with the experimental results for PO4-P, NH4-N and Mg removals. Predicated average crystal sizes also matched fairly well with the experimental observations. Therefore, this model can be used as a tool for performance evaluation and process optimization of struvite crystallization in a fluidized-bed reactor.

Control of biofouling on reverse osmosis polyamide membranes modified with biocidal nanoparticles and antifouling polymer brushes.

Thin-film composite (TFC) polyamide reverse osmosis (RO) membranes are prone to biofouling due to their inherent physicochemical surface properties. In order to address the biofouling problem, we have developed novel surface coatings functionalized with biocidal silver nanoparticles (AgNPs) and antifouling polymer brushes via polyelectrolyte layer-by-layer (LBL) self-assembly. The novel surface coating was prepared with polyelectrolyte LBL films containing poly(acrylic acid) (PAA) and poly(ethylene imine) (PEI), with the latter being either pure PEI or silver nanoparticles coated with PEI (Ag-PEI). The coatings were further functionalized by grafting of polymer brushes, using either hydrophilic poly(sulfobetaine) or low surface energy poly(dimethylsiloxane) (PDMS). The presence of both LBL films and sulfobetaine polymer brushes at the interface significantly increased the hydrophilicity of the membrane surface, while PDMS brushes lowered the membrane surface energy. Overall, all surface modifications resulted in significant reduction of irreversible bacterial cell adhesion. In microbial adhesion tests with E. coli bacteria, a normalized cell adhesion in the range of only 4 to 16% on the modified membrane surfaces was observed. Modified surfaces containing silver nanoparticles also exhibited strong antimicrobial activity. Membranes coated with LBL films of PAA/Ag-PEI achieved over 95% inactivation of bacteria attached to the surface within 1 hour of contact time. Both the antifouling and antimicrobial results suggest the potential of using these novel surface coatings in controlling the fouling of RO membranes.

Electrochemical carbon-nanotube filter performance toward virus removal and inactivation in the presence of natural organic matter.

The performance of an electrochemical multiwalled carbon nanotube (EC-MWNT) filter toward virus removal and inactivation in the presence of natural organic matter was systematically evaluated over a wide range of solution chemistries. Viral removal and inactivation were markedly enhanced by applying DC voltage in the presence of alginate and Suwannee River natural organic matter (SRNOM). Application of 2 or 3 V resulted in complete (5.8 to 7.4 log) removal and significant inactivation of MS2 viral particles in the presence of 5 mg L(-1) of SRNOM or 1 mg L(-1) of alginate. The EC-MWNT filter consistently maintained high performance over a wide range of solution pH and ionic strengths. The underlying mechanisms of enhanced viral removal and inactivation were further elucidated through EC-MWNT filtration experiments using carboxyl latex nanoparticles. We conclude that enhanced virus removal is attributed to the increased viral particle transport due to the applied external electric field and the attractive electrostatic interactions between the viral particles and the anodic MWNTs. The adsorbed viral particles on the MWNT surface are then inactivated through direct surface oxidation. Minimal fouling of the EC-MWNT filter was observed, even after 4-h filter runs with solutions containing 10 mg L(-1) of natural organic matter and 1 mM CaCl(2). Our results suggest that the EC-MWNT filter has a potential for use as a high performance point-of-use device for the removal of viruses from natural and contaminated waters with minimal power requirements.

Electrochemical multiwalled carbon nanotube filter for viral and bacterial removal and inactivation.

Nanotechnology has potential to offer solutions to problems facing the developing world. Here, we demonstrate the efficacy of an anodic multiwalled carbon nanotube (MWNT) microfilter toward the removal and inactivation of viruses (MS2) and bacteria (E. coli). In the absence of electrolysis, the MWNT filter is effective for complete removal of bacteria by sieving and multilog removal of viruses by depth-filtration. Concomitant electrolysis during filtration results in significantly increased inactivation of influent bacteria and viruses. At applied potentials of 2 and 3 V, the electrochemical MWNT filter reduced the number of bacteria and viruses in the effluent to below the limit of detection. Application of 2 and 3 V for 30 s postfiltration inactivated >75% of the sieved bacteria and >99.6% of the adsorbed viruses. Electrolyte concentration and composition had no correlation to electrochemical inactivation consistent with a direct oxidation mechanism at the MWNT filter surface. Potential dependent dye oxidation and E. coli morphological changes also support a direct oxidation mechanism. Advantages of the electrochemical MWNT filter for pathogen removal and inactivation and potential for point-of-use drinking water treatment are discussed.