Effect of Spacer Configuration on the Characteristics of FO Membranes: Alteration of Permeation Characteristics by Membrane Deformation and Concentration Polarization.

Membrane deformation is a significant problem in osmotically driven membrane processes, as it restricts practical operating conditions and reduces overall process performance due to unfavorable alteration of membrane permeation characteristics. In this respect, a spacer plays a crucial role, as it dictates the form and extent of membrane deformation in association with concentration polarization (CP), which is also influenced by spacer-induced hydrodynamic behavior near the membrane surface. These two roles of spacers on membrane permeation characteristics are inherently inseparable with the coexistence of hydraulic and osmotic pressures. Here, we suggest a novel analytical method to differentially quantify the proportions of effective osmotic pressure drop caused by membrane deformation and CP. Furthermore, we tested two different FO membranes with three different spacer configurations to define and discuss different forms of membrane deformation and their effects on membrane permeation characteristics. The differential analysis revealed the effect of spacer configuration on effective osmotic pressure drop in membrane deformation (up to ∼201% of variation) is much greater than that in CP (up to ∼20.1% of variation). In addition, a combined configuration of a feed spacer and tricot spacer demonstrated its ability of mitigating membrane deformation with lower selectivity loss and channel pressure drop under pressurization.

Antibacterial rGO-CuO-Ag film with contact- and release-based inactivation properties.

To reduce the high operational costs of water treatment because of membrane biofouling, next-generation materials are being developed to counteract microbial growth. These modern anti-biofouling strategies are based on new membrane materials or membrane surface modifications. In this study, antimicrobial films comprising rGO, rGO-CuO, rGO-Ag, and rGO-CuO-Ag were synthesized, evaluated, and tested for potential biofouling control using Pseudomonas aeruginosa PAO1 as the model bacterium. The combined rGO-CuO-Ag film displayed enhanced reduction (10-log reduction) in biofouling in comparison to the rGO film (control), followed by the rGO-Ag film (8-log reduction) and rGO-CuO film (0-log reduction). This demonstrated that the use of mixed antimicrobial agents is more effective in reducing biofouling than that of a single agent. The rGO-CuO-Ag film exhibited consistent, controlled, and moderate release of silver (Ag) ions. The release of Ag ions produced a long-lasting antimicrobial effect. These results underscore the potential applications of combined antimicrobial surface-based agents in practice and further research.

Implications of Chemical Reduction Using Hydriodic Acid on the Antimicrobial Properties of Graphene Oxide and Reduced Graphene Oxide Membranes.

The antimicrobial properties of graphene-based membranes such as single-layer graphene oxide (GO) and modified graphene oxide (rGO) on top of cellulose ester membrane are reported in this study. rGO membranes are made from GO by hydriodic acid (HI) vapor treatment. The antibacterial properties are tested after 3 h contact time with selected model bacteria. Complete bacterial cell inactivation is found only after contact with rGO membranes, while no significant bacterial inactivation is found for the control i) GO membrane, ii) the mixed cellulose ester support, and the iii) rGO membrane after additional washing that removes the remaining HI. This indicates that the antimicrobial effect is neither caused by the graphene nor the membrane support. The antimicrobial effect is found to be conclusively linked to the HI eliminating microbial growth, at concentrations from 0.005%. These findings emphasize the importance of caution in the reporting of antimicrobial properties of graphene-based surfaces.

Tunable Ion Sieving of Graphene Membranes through the Control of Nitrogen-Bonding Configuration.

Graphene-oxide (GO) membranes with notable ionic-sieving properties have attracted significant attention for many applications. However, the swelling and unstable nanostructure of GO laminates in water results in enlarged interlayer spacing and a low permeation cut-off, limiting their applicability for water purification and desalination. Herein, we propose novel nitrogen-doped graphene (NG) membranes for use in tunable ion sieving that are made via facile fabrication by a time-dependent N-doping technique. Doping reaction time associated variation in atomic content and bonding configurations strongly contributed to the nanostructure of NG laminates by yielding narrower interlayer spacing and a more-polarized surface than GO. These nanostructural features subsequently allowed ion transport through the combined mechanisms of size exclusion and electrostatic interaction. The stacked NG membranes provided size-dependent permeability for hydrated ions and improved ion selectivity by 1-3 orders of magnitude in comparison to that of a GO membrane. For ions small enough to move through the interlayer spacing, the ion permeation is determined by electrostatic properties of NG membranes with the type of N configuration, especially polarized pyridinic N. Due to these properties, the NG membrane functioned as an unconventionally selective graphene-based membrane with better ion sieving for water purification.

Removal behaviors and fouling mechanisms of charged antibiotics and nanoparticles on forward osmosis membrane.

Fouling and rejection mechanisms of both charged antibiotics (ABs) and nanoparticles (NPs) were determined using a negatively-charged polyamide thin film composite forward osmosis (FO) flat sheet membrane. Two types of ABs and NPs were selected as positively and negatively charged foulants at pH 8. The ABs did not cause significant membrane fouling, but the extent of fouling and rejection changed based on the electrostatic attraction or repulsion forces. The addition of opposite charged AB and NP resulted in a decline of the membrane flux by 11.0% but a 6.5% AB average rejection efficiency improvement. On the other hand, mixing of like-charged ABs and NPs generated repulsive forces that improved average rejection efficiency about 5.5% but made no changes in the membrane flux. In addition, NPs and ABs were mixed and tested at various concentrations and pH levels to rectify the behavior of ABs. The aggregate size and removal efficiency were observed to vary with the change in the electron double layer of the mixture. It can help to make the strategy to control the ABs in the FO process and consequently it enables the FO process to produce environmentally safe effluent.

Forward Osmosis Membranes under Null-Pressure Condition: Do Hydraulic and Osmotic Pressures Have Identical Nature?

Forward osmosis (FO) membranes fall into the category of nonporous membranes, based on the assumption that water and solute transport occur solely based on diffusion. The solution-diffusion (S-D) model has been widely used in predicting their performances in the coexistence of hydraulic and osmotic driving forces, a model that postulates the hydraulic and osmotic driving forces have identical nature. It was suggested, however, such membranes may have pores and mass transport could occur both by convection (i.e., volumetric flow) as well as by diffusion assuming that the dense active layer of the membranes is composed of a nonporous structure with defects which induce volumetric flow through the membranes. In addition, the positron annihilation technique has revealed that the active layers can involve relatively uniform porous structures. As such, the assumption of a nonporous active layer in association with hydraulic pressure is questionable. To validate this assumption, we have tested FO membranes under the conditions where hydraulic and osmotic pressures are equivalent yet in opposite directions for water transport, namely the null-pressure condition. We have also established a practically valid characterization method which quantifies the vulnerability of the FO membranes to hydraulic pressure.

Correlation Between Quorum Sensing Signal Molecules and Pseudomonas aeruginosa's Biofilm Development and Virulency.

Bacteria, when adhered to a substratum, can form biofilms. Nevertheless, many factors dictate biofilm formation and virulence factor production, including a response by the bacteria to their surroundings. This system is referred to as Quorum sensing (QS) also known as cell-cell communication. Pseudomonas aeruginosa is an infection causing agent in immune-compromised patients, it uses acyl-homoserine lactone (AHL) to coordinate its QS systems. In this work, the connection between some members of AHL produced by P. aeruginosa PAO1 and its biofilm development and the production of virulence factor was investigated. It was discovered that N-butanoyl-homoserine lactone (C4-HSL) and N-hexanoyl-L-homoserine lactone (C6-HSL) perform a more consequential and eminent function in the biofilm maturation and virulence factor production while N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL) plays a role in biofilm initiation. Because QS has been reported to be required for biofilm development and pathogenesis of P. aeruginosa, the results of this work have great importance and significance for the design of strategies for the control and prevention of biofilms.

Tumor necrosis factor α-converting enzyme inhibitor attenuates lipopolysaccharide-induced reactive oxygen species and mitogen-activated protein kinase expression in human renal proximal tubule epithelial cells.

Tumor necrosis factor-α (TNFα) and the angiotensin system are involved in inflammatory diseases and may contribute to acute kidney injury. We investigated the mechanisms by which TNFα-converting enzyme (TACE) contributes to lipopolysaccharide (LPS)-induced renal inflammation and the effect of TACE inhibitor treatment on LPS-induced cellular injury in human renal proximal tubule epithelial (HK-2) cells. Mice were treated with LPS (10 mg/kg, i.p.) and HK-2 cells were cultured with or without LPS (10 µg/ml) in the presence or absence of a type 1 TACE inhibitor (1 µM) or type 2 TACE inhibitor (10 µM). LPS treatment induced increased serum creatinine, TNFα, and urinary neutrophil gelatinase-associated lipocalin. Angiotensin II type 1 receptor, mitogen activated protein kinase (MAPK), and TACE increased, while angiotensin-converting enzyme-2 (ACE2) expression decreased in LPS-induced acute kidney injury and LPS-treated HK-2 cells. LPS induced reactive oxygen species and the down-regulation of ACE2, and these responses were prevented by TACE inhibitors in HK-2 cells. TACE inhibitors increased cell viability in LPS-treated HK-2 cells and attenuated oxidative stress and inflammatory cytokines. Our findings indicate that LPS activates renin angiotensin system components via the activation of TACE. Furthermore, inhibitors of TACE are potential therapeutic agents for kidney injury.

Cleaning efficacy of hydroxypropyl-beta-cyclodextrin for biofouling reduction on reverse osmosis membranes.

In this study, an environmentally friendly compound, hydroxypropyl-beta-cyclodextrin (HP-ß-CD) was applied to clean reverse osmosis (RO) membranes fouled by microorganisms. The cleaning with HP-ß-CD removed the biofilm and resulted in a flux recovery ratio (FRR) of 102%. As cleaning efficiency is sometimes difficult to determine using flux recovery data alone, attached bacterial cells and extracellular polymeric substances (EPS) were quantified after cleaning the biofouled membrane with HP-ß-CD. Membrane surface characterization using scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) and atomic force microscopy (AFM) confirmed the effectiveness of HP-ß-CD in removal of biofilm from the RO membrane surface. Finally, a comparative study was performed to investigate the competitiveness of HP-ß-CD with other known cleaning agents such as sodium dodecyl sulfate (SDS), ethylenediaminetetraacetic acid (EDTA), Tween 20, rhamnolipid, nisin, and surfactin. In all cases, HP-ß-CD was superior.

Physicochemical interactions between rhamnolipids and Pseudomonas aeruginosa biofilm layers.

This study investigated the physicochemical interactions between a rhamnolipid biosurfactant and a biofilm layer. A concentration of 300 µg mL(-1) of rhamnolipids, which is around the critical micelle concentration value (240 µg mL(-1)), showed great potential for reducing biofilm. The surface free energy between the rhamnolipids and biofilm layer decreased, as did the negative surface charge, due to the removal of negatively charged humic-like, protein-like, and fulvic acid-like substances. The carbohydrate and protein concentrations composed of extracellular polymeric substances decreased by 31.6% and 79.6%, respectively, at a rhamnolipid concentration of 300 µg mL(-1). In particular, rhamnolipids can interact with proteins, leading to a reduction of the N source and amide groups on the membrane. For carbohydrates, the component ratio of glucosamine was decreased, but the levels of glucose and mannose that form the majority of the carbohydrates remained unchanged. To our knowledge, the present study is the first attempt at studying the interactions of the two phases of rhamnolipids and the biofilm layer, and as such is expected to clarify the mechanism by which rhamnolipids lead to a reduction in biofilm.

Use of rhamnolipid biosurfactant for membrane biofouling prevention and cleaning.

Rhamnolipids were evaluated as biofouling reducing agents in this study. The permeability of the bacterial outer membrane was increased by rhamnolipids while the growth rate of Pseudomonas aeruginosa was not affected. The surface hydrophobicity was increased through the release of lipopolysaccharides and extracellular polymeric substances from the outer cell membrane. Rhamnolipids were evaluated as agents for the prevention and cleaning of biofilms. A high degree of biofilm detachment was observed when the rhamnolipids were used as a cleaning agent. In addition, effective biofilm reduction occurred when rhamnolipids were applied to various species of Gram-negative bacteria isolated from seawater samples. Biofilm reduction using rhamnolipids was comparable to commercially available surfactants. In addition, 20% of the water flux was increased after rhamnolipid treatment (300 µg ml(-1), 6 h exposure time) in a dead-end filtration system. Rhamnolipids appear to have promise as biological agents for reducing membrane biofouling.

Effect of initial salt concentrations on cell performance and distribution of internal resistance in microbial desalination cells.

Microbial desalination cells (MDCs) are modified microbial fuel cells (MFCs) that concurrently produce electricity and desalinate seawater, but adding a desalination compartment and an ion-exchange membrane may increase the internal resistance (Ri), which can limit the cell performance. However, the effects of a desalination chamber and initial NaCl concentrations on the internal resistances and the cell performances (i.e. Coulombic efficiency (CE), current and power density) of MDCs have yet to be thoroughly explored; thus, the cell performance and Ri distributions of MDCs having different initial concentrations and an MFC having no desalination chamber were compared. In the MDCs, the current and power density generation increased from 2.82 mA and 158.2 mW/m2 to 3.17 mA and 204.5 mW/m2 when the initial NaCl concentrations were increased from 5 to 30 g/L, as a consequence of the internal resistances decreasing from 2432.0 to 2328.4 Ω. And even though the MFC has a lower Ri than the MDCs, lower cell performances (current: 2.59 mA; power density: 141.6 mW/m2 and CE: 62.1%) were observed; there was no effect of improved junction potential in the MFC. Thus, in the MDCs, the higher internal resistances due to the addition of a desalination compartment can be offset by reducing the electrolyte resistance and improving the junction potential at higher NaCl concentrations.

Comparative pyrosequencing analysis of bacterial community change in biofilm formed on seawater reverse osmosis membrane.

The change in bacterial community structure induced by bacterial competition and succession was investigated during seawater reverse osmosis (SWRO) in order to elucidate a possible link between the bacterial consortium on SWRO membranes and biofouling. To date, there has been no definitive characterization of the microbial diversity in SWRO in terms of distinguishing time-dependent changes in the richness or abundance of bacterial species. For bacterial succession within biofilms on the membrane surface, SWRO using a cross-flow filtration membrane test unit was operated for 5 and 100h, respectively. As results of the pyrosequencing analysis, bacterial communities differed considerably among seawater and the 5 and 100 h samples. From a total of 33,876 pyrosequences (using a 95% sequence similarity), there were less than 1% of shared species, confirming the influence of the operational time factor and lack of similarity of these communities. During SWRO operation, the abundance of Pseudomonas stutzeri BBSPN3 (GU594474) belonging to gamma-Proteobacteria suggest that biofouling of SWRO membrane might be driven by the dominant influence of a specific species. In addition, among the bacterial competition of five bacterial species (Pseudomonas aeruginosa, Bacillus sp., Rhodobacter sp., Flavobacterium sp., and Mycobacterium sp.) competing for bacterial colonization on the SWRO membrane surfaces, it was exhibited that Bacillus sp. was the most dominant. The dominant influences ofPseudomonas sp. and Bacillus sp. on biofouling during actual SWRO is decisive depending on higher removal efficiency of the seawater pretreatment.

Sulfonated graphene oxide-based pervaporation membranes inspired by a tortuous brick and mortar structure for enhanced resilience against silica scaling and organic fouling.

A novel tortuous brick-and-mortar structure utilizing intercalation of polyvinyl alcohol (PVA) on sulfonated graphene oxide (SGO) membranes was specifically tailored for brine treatment by pervaporation to ensure excessive resistance to silica scaling and organic fouling, as well as ultrafast water transport without compromising salt rejection. The synthesized SGO membrane showed a smoother surface morphology, improved zeta potential, and a higher hydration capacity than the graphene oxide (GO) membrane. Further intercalation of PVA through glutaraldehyde (GA) crosslinking, confirmed by Fourier transform infrared spectroscopy and X-ray diffraction analysis, conferred increased cohesiveness, and the SGO-PVA-GA membrane was therefore able to withstand ultrasonication tests without any erosion of the coating layer. According to a pervaporative desalination test, the SGO-PVA-GA membrane exhibited 62 kg m-2 h-1 of permeate flux, with an extraordinary salt rejection of 99.99% for a 10 wt% NaCl feed solution at 65 °C. The 72 h organic fouling, silica scaling, and combined fouling and scaling tests proved that the SGO-PVA-GA membrane sustains a stable flux with less scaling and fouling than the GO-PVA-GA membrane, attributable to dense surface negative charges and great hydration capacities caused by sulfonic acid. Thus, the SGO-PVA-GA membrane offers superlative advantages for long-term brine treatment by pervaporation, related to its ability to withstand silica scaling and organic fouling.

Fabrication and Performance Evaluation of a Cation Exchange Membrane Using Graphene Oxide/Polyethersulfone Composite Nanofibers.

Ion exchange membranes, especially cation exchange membranes (CEMs), are an important component in membrane-based energy generation and storage because of their ability to transport cations via the electrochemical potential gradient while preventing electron transport. However, developing a CEM with low areal resistance, high permselectivity, and stability remains difficult. In this study, electrospun graphene oxide/polyethersulfone (GO/PES) composite nanofibers were prepared with varying concentrations of GO. To fabricate a CEM, the pores of the electrospun GO/PES nanofiber substrates were filled with a Nafion ionomer. The pore-filled PES nanofiber loaded with 1% GO revealed a noticeable improvement in hydrophilicity, structural morphology, and mechanical properties. The 1% GO/PES pore-filled CEM was compared to a Nafion membrane of a varying thickness and without a nanofiber substrate. The CEM with a nanofiber substrate showed permselectivity of 85.75%, toughness of 111 J/m3, and areal resistance of 3.7 Ω cm2, which were 12.8%, 4.3 times, and 4.0 times better, respectively, than those of the Nafion membrane at the same thickness. The development of a reinforced concrete-like GO/PES nanofiber structure containing stretchable ionomer-enhanced membrane surfaces exhibited suitable areal resistance and reduced the thickness of the composite membrane without compromising the mechanical strength, suggesting its potential application as a cation exchange membrane in electrochemical membrane-based systems.

RASSF1A and ERCC1 expression levels might be predictive of prognosis in advanced, recurrent, and metastatic squamous cell carcinoma of the head and neck treated with docetaxel and cisplatin.

BACKGROUND: The purpose of this study was to test the hypothesis that the immunohistochemical expression of ERCC1 and RASSF1A would predict both response to and survival after docetaxel and cisplatin combination chemotherapy in inoperable or recurrent head and neck squamous cell carcinoma. PATIENTS AND METHODS: A total of 54 patients were treated with frontline systemic chemotherapy composed of docetaxel (60 mg/m(2)) and cisplatin (65 mg/m(2)), every 3 weeks for up to 6 cycles. The expression levels of ERCC1 and RASSF1A were evaluated in the available 36 prechemotherapy samples. RESULTS: The overall objective response rate was 35% (complete remission 12% and partial remission 23%). The median progression-free survival and overall survival (OS) times were 5.0 months (95% confidence interval (CI), 3.7-6.4 months) and 24.2 months (95% CI, 3.5-45.0 months), respectively. The status of low ERCC1 and high RASSF1A expression was an independent favorable prognostic factor for OS in multivariate analysis (p = 0.043; hazard ratio, 7.224; 95% CI, 1.060-49.217). Toxicities were comparable with those of previously reported trials. CONCLUSIONS: Less intensive doses of cisplatin and docetaxel are active but not effective in reducing toxicity. Also, both ERCC1 and RASSF1A might be useful prognostic markers in this regimen.

Proapoptotic effect of a micropollutant (tris-(2-chloroethyl)-phosphate) at environmental level in primary cultured renal proximal tubule cells.

Being a typical micropollutant, tris-(2-chloroethyl)-phosphate (TCEP) is often found in aquatic environments. However, the potential effects of TCEP at environmental concentrations on apoptotic mechanisms are mostly unknown. Thus, the purpose of this study is to investigate the apoptotic regulatory protein expression of TCEP at environmental concentration in primary cultured renal proximal tubule cells (PTCs). The results show that TCEP at 0.01 and 1 mg L(-1) significantly increased the phosphorylation of c-Jun-NH2-terminal kinase (JNK) (135.5 and 138.0% of the control, respectively), and significantly decreased the expression of Bcl-2 and cIAP-2 at all tested concentrations, except for a slight decrease of Bcl-2 at 0.01 mg L(-1). In addition, TCEP significantly increased the expression of caspase-3 at all three concentrations (132.6, 172.6 and 167.9% of the control, respectively) and caspase-9 at 1 and 10 mg L(-1) (128.3 and 144.5% of the control, respectively). Furthermore, TCEP increased the apoptotic cell population in a flow cytometry analysis. In conclusion, environmental TCEP might have a dose-dependent proapoptotic effect with a decrease of DNA synthesis and cell number in primary cultured renal PTCs.

Spatial distribution and viability of nitrifying, denitrifying and ANAMMOX bacteria in biofilms of sponge media retrieved from a full-scale biological nutrient removal plant.

The spatial distribution and activities of nitrifying and denitrifying bacteria in sponge media were investigated using diverse tools, because understanding of in situ microbial condition of sponge phase is critical for the successful design and operation of sponge media process. The bacterial consortia within the media was composed of diverse groups including a 14.5% Nitrosomonas spp.-like ammonia oxidizing bacteria (AOB), 12.5% Nitrobacter spp.-like nitrite oxidizing bacteria (NOB), 2.0% anaerobic ammonium-oxidizing (ANAMMOX) bacteria and 71.0% other bacteria. The biofilm appeared to be most dense in the relatively outer region of the media and gradually decreased with depth, but bacterial viabilities showed space-independent feature. The fluorescent in situ hybridization results revealed that AOB and NOB co-existed in similar quantities on the side fragments of the media, which was reasonably supported by the microelectrode measurements showing the concomitant oxidation of NH(4) (+) and production of NO(3) (-) in this zone. However, a significantly higher fraction of AOB was observed in the center than side fragment. As with the overall biofilm density profile, the denitrifying bacteria were also more abundant on the side than in the center fragments. ANAMMOX bacteria detected throughout the entire depth offer another advantage for the removal of nitrogen by simultaneously converting NH(4) (+) and NO(2) (-) to nitrogen gas.

Nitrification and denitrification using biofilters packed with sulfur and limestone at a pilot-scale municipal wastewater treatment plant.

A pilot-scale municipal wastewater treatment plant composed of a fixed film activated sludge (IFAS) system with sulfur-limestone autotrophic denitrification (SLAD) was operated for a year and the influence of different operational factors was investigated. Nitrification efficiency was found to be above 91% at temperatures above 25 degrees C even at short hydraulic residence times (HRTs), but declined to 51 +/- 2% when the temperature dropped to 22 +/- 3 degrees C. The minimum HRT (HRT(min)) to achieve nitrification efficiency > 90% was found to be 12 h at temperatures above 25 degrees C. Denitrification efficiencies were found to be 89% and 79% at a nitrate loading of 0.36 kg NO3(-)-N m(-3) d(-1) and at 0.18 kg NO3(-)-N m(-3) d(-1), respectively. The minimum empty bed residence time (EBRT) to achieve denitrification efficiency above 80% without methanol addition was 3 h at a nitrate loading rate of 0.27-0.38 kg NO3(-)-N m(-3) d(-1). The amount of nitrate removed as a function of the sulfate formed was found to be 0.188 g NO3(-)-N/g SO4(2-). The nitrate load removed by the biofilter as a function of the alkalinity consumed was found to be very close to the theoretical stoichiometric value. The application of the pilot plant was proven to be feasible and the performance of the SLAD system, especially with respect to the minimum EBRT to achieve denitrification efficiency above 80%, the maximum denitrification rate and performance at temperatures below 10 degrees C. To achieve a nitrification efficiency above 90% in the IFAS system, temperature changes and the minimum HRT were found to be the most influential operational parameters.