Increase In Membrane Resistance Research Articles

Organic fouling and floc transport in capillaries

Coagulation and adsorption are two widely recommended pretreatments to ultrafiltration (UF) membranes. Optimal concentrations of ferric chloride and powdered activated carbon (PAC) are reducing membrane fouling and increasing the retention of the organic matter. Intuitive pretreatment may result in either increased fouling or in low retention of organic matter. In addition, the inside-out capillaries might become partially plugged by the formed flocs. The understanding of the fouling mechanisms in inside-out capillaries is therefore a challenging and much practically needed task. We investigated the fouling using an unique setup with separate measurements of flux and retention of organic matter in five segments of a 1.5-m long multibore capillary. The high coagulant doses resulted in average 90% humic acid retention and in severe fouling. The use of powdered activated carbon at higher pH also contributed to severe increases in membrane resistance. As the filtration progressed, the dead-end part of the capillary (far from the feed) gradually became clogged with flocs.

Chemical and mechanical degradation of sulfonated poly(sulfone) membranes in vanadium redox flow batteries

A sulfonated poly(sulfone) (S-Radel®) membrane with high proton conductivity and low vanadium ion permeability showed high initial performance in a vanadium redox flow battery (VRFB) but suffered mechanical and chemical degradation during charge/discharge cycling. The S-Radel membrane showed different degradation behavior in flow cell cycling and ex-situ vanadium ion immersion tests. When the membrane was immersed in aqueous V5+ solution, the sample cracked into small pieces, but did not degrade to any measurable extent in V4+ solution. During charge/discharge cycling in the VRFB cell, the membrane underwent internal delamination, preferentially on the side of the membrane that faced the positive electrode. A vanadium-rich region was observed near the membrane surface that experienced delamination and Raman spectroscopic analysis of the degraded surface indicated a slightly depressed 1026 cm−1 band corresponding to a loss in the sulfonate SO2 stretch intensity. Even though the S-Radel membrane underwent severe mechanical damage during the flow cell cycling, significant chemical degradation was not obvious from the spectroscopic analyses. For the VRFB containing an S-Radel membrane, an increase in membrane resistance caused an abnormal voltage depression during the discharge cycle. The reversible increase in membrane resistance and severe mechanical degradation of the membrane during cycling may be attributed to repeated formation and dissolution of particles inside the membrane. The mechanical stresses imposed by the particles coupled with a small amount of chemical degradation of the polymer by V5+ ions, are likely degradation mechanisms of the S-Radel membrane in VRFBs under high state-of-charge conditions.

The influence of low power microwave on the properties of DPPC vesicles

The effect of microwave exposure on liposome at non-thermal level are studied. Dipalmitoyl phosphatidylcholine (DPPC) liposomes were exposed to 950 MHz at power densities of 2.5 mW/cm 2, which is equivalent to specific absorption rate (SAR) of 0.238 W/K. The interaction of microwave with liposomes was investigated by membrane solubilization measurements using a non-ionic detergent, octylglucoside (OG), as well as Fourier transform infrared (FTIR) spectroscopy and flow activation energy measurements. The amount of detergent needed to completely solubilize the liposomal membrane was increased after exposure of liposomes to microwave irradiation, indicating an increased membrane resistance to the detergent and hence a change in the natural membrane permeation properties. In the analysis of FTIR spectra the symmetric and antisymmetric CH 2 (at 2070 cm −1) band and the C O (at 1640 cm −1) stretching bands were investigated after liposomal exposure to microwave irradiation. It is clearly shown from the flow activation energy measurements, that low-power microwave induce changes in the liposomes deformability (decreases the liposome fluidity and increases the liposome rigidity). Finally it could be concluded that low-power microwave of 950 MHz induced structural and functional changes in liposomes as a membrane model system.

Removal and recovery of nutrients by ion exchange from high rate membrane bio-reactor (MBR) effluent

In this study a membrane bioreactor (MBR) with ion-exchange as post-treatment was investigated for organic removal and nutrient recovery. The MBR was operated at a short HRT of 4h in order to mainly remove organic carbon. This was followed by an ion-exchange process to remove and later recover the nitrogen and phosphorus from the MBR effluent. The increase in membrane resistance was reduced by 90% (from 0.061 to 0.006m-1d-1) when the air scouring rate was increased from 0.5 to 1.5m3/m2membrane areah. The organic removal rate in terms of DOC was 85–90%. The bio-polymer in the molecular weight range of 24,500Da was retained by the membrane of the MBR while humic type substances and lower molecular organic matter (molecular weight of 360–60Da) were not effectively removed by the membrane. The ion-exchange process effectively removed the nutrients from the effluent of the MBR. The retention of PO43− and NO3− by the two ion-exchange columns in series was 85% and 95% respectively. Over 95–98% phosphate and nitrate recovery was obtained during regeneration of columns with 1% NaCl of 20 bed volumes. This integrated process can remove pollutants and at the same time recover nutrients and thus open a new source for nitrogen and phosphorous.

Correlation of structural differences between Nafion/polyaniline and Nafion/polypyrrole composite membranes and observed transport properties

Polyaniline/Nafion and polypyrrole/Nafion composite membranes, prepared by chemical polymerization, are studied by scanning electron microscopy, infrared and nuclear magnetic resonance spectroscopy. Differences in vanadium ion diffusion through the membranes and in the membranes’ area specific resistance are linked to analytical observations that polyaniline and polypyrrole interact differently with Nafion. Polypyrrole, a weakly basic polymer, binds less strongly to the sulfonic acid groups of the Nafion membrane. Infrared spectroscopy results suggest that the hydrophobic polymer aggregates in the center of the Nafion channel rather than attaching to the hydrophilic walls containing sulfonic acid groups. This results in a drastically elevated membrane resistance and only slightly decreased vanadium ion diffusion compared to a Nafion membrane. Polyaniline, on the other hand, polymerizes along the sides of the Nafion pores and on the membrane surface, binding tightly to the sulfonic acid groups of Nafion, polyaniline's greater basicity possibly causing the difference in polymerization behavior. This leads to a more effective reduction in vanadium ion transport across the polyaniline/Nafion membranes and the increase in membrane resistance is less severe. The performance of selected polypyrrole/Nafion composite membranes is tested in a static vanadium redox cell. Increased coulombic efficiency, compared to a cell employing a pure Nafion membrane, further confirms the reduced vanadium ion transport through the composite membranes.

Correlation between fouling propensity of soluble extracellular polymeric substances and sludge metabolic activity altered by different starvation conditions

Soluble extracellular polymeric substances (EPSs) cause membrane fouling in membrane bioreactors (MBRs), correlated with MBR sludge characteristics. Effects of F/M ratios on the evolution of soluble EPSs, fouling propensity of supernatants, and sludge metabolic activity were measured in this study in a two-period sequencing batch reactor (SBR). The experimental results show that fouling propensity was directly correlated with soluble-EPS concentration and composition. Sludge that had entirely lost active cells by long-term starvation released 64.4 ± 0.9 mg/L of humic acids, which caused a rapid increase in membrane resistance (40.67 ± 2.24 × 10 11 m −1) during fouling tests. During short-term starvation, induced by incubation at a normal to low F/M ratio of 0.05 d −1, sludge can use previously secreted utilization-associated products (UAPs) to maintain endogenous respiration. Therefore, the strategies of accumulating sludge and prolonging sludge retention time in MBRs may create long-term starvation and promote membrane fouling.

In situ embedment and growth of anhydrous and hydrated aluminum oxide particles on polyvinylidene fluoride (PVDF) membranes

Surface modification of polyvinylidene fluoride (PVDF) membranes was successfully performed by doping anhydrous and hydrated aluminum oxide particles (γ-alumina, boehmite and gibbsite) through in situ particle embedment and subsequent crystal growth under a hydrothermal environment. The approach of particle embedment involves the dispersion of anhydrous or hydrated aluminum oxide particles in the water phase during PVDF membrane precipitation, and the result was found to strongly depend on the change of free energy in particle–membrane interaction. The embedment of γ-alumina nanoparticles is thermodynamically favorable, but the embedment of boehmite or gibbsite particles is less favorable, especially when using hydrophilic polyvinylpyrrolidone (PVP) additive within the membrane cast solution. The approach of 105°C hydrothermal treatment initiates the growth of gibbsite on embedded γ-alumina nanoparticles, and the treatment duration determines the coverage of gibbsite particles on PVDF membrane. The overall hydrophilicity of membranes increases with the embedment of γ-alumina and the growth of gibbsite. An increase of membrane resistance was not observed with γ-alumina embedment, but the excessive growth of gibbsite particles may reduce membrane permeability. The Escherichia coli attachment result shows that the surface doping of aluminum oxide particles can greatly reduce E. coli adhesion to the membrane surface, suggesting the positive effect on the reduction of bio-fouling. The success of this PVDF membrane modification method has also provided a promising strategy to manipulate the surface property of other polymer membranes by inorganic materials.

PVDF-TiO2coated microfiltration membranes: preparation and characterization

Organic fouling and biofouling pose a significant challenge to the membrane filtration process. Photocatalysis-membrane hybrid system is a novel idea for reducing these membranes fouling however, when <TEX>$TiO_2</TEX> photocatalyst nanoparticles are used in suspension, catalyst recovery is not only imposes an extra step on the process but also significantly contributes to increased membrane resistance and reduced permeate flux. In this study, <TEX>$TiO_2$</TEX> photocatalyst has been immobilized by coating on the microfiltration (MF) membrane surface to minimize organic and microbial fouling. Nano-sized <TEX>$TiO_2$</TEX> was first synthesized by a sol-gel method. The synthesized <TEX>$TiO_2$</TEX> was coated on a Poly Vinyl Difluoride (PVDF) membrane (MF) surface using spray coating and dip coating techniques to obtain hybrid functional composite membrane. The characteristics of the synthesized photocatalyst and a functional composite membrane were studied using numerous instruments in terms of physical, chemical and electrical properties. In comparison to the clean PVDF membrane, the <TEX>$TiO_2$</TEX> coated MF membrane was found more effective in removing methylene blue (20%) and E-coli (99%).

Immature brains don't need GABA to get ‘hyper’‐excited

Immature brains don't need GABA to get ‘hyper’‐excited

On the resistances of membrane, diffusion boundary layer and double layer in ion exchange membrane transport

Membrane resistances are often measured under direct current conditions using a standard 0.5 M NaCl characterization solution, although several electro-membrane processes (e.g. reverse electrodialysis, electrodialysis, fuel cells, microbial fuel cells and membrane capacitive deionization) operate in a much lower concentration range (<0.1 M NaCl). Our work reveals that at lower concentrations, the membrane resistance as measured under direct current conditions becomes strongly concentration dependent and strongly increases with decreasing concentration. The overall resistance measured under direct current conditions however, does not only include the pure membrane resistance but also takes the interfacial ionic charge transfer through the double layer and diffusion boundary layer effects into account. Because direct current methods do not allow discriminating between these individual resistances, we applied electrochemical impedance spectroscopy (EIS), which uses an alternating current, to analyze resistance phenomena in ion exchange membranes under different hydrodynamic conditions and at different temperatures. The results clearly show that the increase in membrane resistance with decreasing concentration as measured in direct current experiments is the consequence of the strong increase in resistance of the diffusion boundary layer with decreasing concentration. This also explains the strong effect of the flow rate on the resistance. At higher concentrations, the pure membrane resistance starts to dominate the resistance as measured by direct current measurements, although also the diffusion boundary layer resistance still plays a considerable role.

Slow Excitation of Cultured Rat Retinal Ganglion Cells by Activating Group I Metabotropic Glutamate Receptors

As in many CNS neurons, retinal ganglion cells (RGCs) receive fast synaptic activation through postsynaptic ionotropic receptors. However, the potential role of postsynaptic group I metabotropic glutamate receptors (mGluRs) in these neurons is unknown. In this study we first demonstrated that the selective group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) increased intracellular calcium concentration in neurons within the ganglion cell layer of the rat retina. This prompted us to use an immunopanned-RGC and cortical astroglia coculture preparation to explore the effect of group I mGluR activation on the electrophysiological properties of cultured RGCs. Using perforated patch-clamp recordings in current-clamp configuration, we found that application of DHPG increased spontaneous spiking and depolarized the resting membrane potential of RGCs. This boosting effect was attributed to an increase in membrane resistance due to blockade of a background K(+) conductance. Further experiments showed that the group I mGluR-sensitive K(+) conductance was not blocked by 3 mM Cs(+), but was sensitive to acidification. Pharmacological studies indicated that the effect of DHPG on RGCs was mediated by the mGluR1 rather than the mGluR5 receptor subtype. Our results suggest a facilitatory role for group I mGluR activation in modulating RGC excitability in the mammalian inner retina.

Surface modification of nanofiltration membrane for reduction of membrane fouling

Membrane fouling is a major drawback to any membrane system. Fouling reduces the membrane flux either temporarily or permanently. Unfortunately, it is impossible to produce zero-fouling membranes but minimization of membrane fouling can be done efficiently. Membrane surface modification is one of the most often used methods to increase membrane resistance to fouling. The three major parameters that affect the membrane fouling are hydrophilicity, surface charge and surface roughness. Besides that, some researchers also suggest that two other parameters which should be taken into account are chemical composition and porosity. In this study, the first three major parameters mentioned above only are considered as contributing to fouling. Usually, these three parameters are characterized by three different techniques (hydrophilicity by contact angle measurement, surface roughness by atomic force microscopy (AFM) and surface charge by zeta potential). This study concentrates on characterising effect of surface roughness alone. Commercial polyethersulfone (PES) nanofiltration membranes with and without surface modification were characterized and humic acid was chosen as the foulants.

Biophysical studies on chitosan-coated liposomes

Liposomes have been used as delivery vehicles for stabilizing drugs, overcoming barriers to cellular and tissue uptake, and for directing their contents toward specific sites in vivo. Chitosan is a biological macromolecule derived from crustacean shells and has several emerging applications in drug development, obesity control, and tissue engineering. In the present work, the interaction between chitosan and dipalmitoyl phosphatidylcholine (DPPC) liposomes was studied by transmission electron microscopy (TEM), zeta potential, solubilization using the nonionic detergent octylglucoside (OG), as well as Fourier transform infrared (FTIR) spectroscopy and viscosity measurements. The coating of DPPC liposomes by a chitosan layer was confirmed by electron microscope images and the zeta potential of liposomes. Coating of liposome by chitosan resulted in an increase in liposomal size by addition of a layer of 92 +/- 27.1 nm. The liposomal zeta potential became increasingly positive as chitosan concentration increased from 0.1 to 0.3% w/v, then it held at a relatively constant value. The amount of detergent needed to completely solubilize the liposomal membrane was increased after coating of liposomes with chitosan, indicating an increased membrane resistance to the detergent and hence a change in the natural membrane permeation properties. In the analysis of FTIR spectra of DPPC, the symmetric and antisymmetric CH(2) (at 2,800-3,000 cm(-1)) bands and the C=O (at 1,740 cm(-1)) stretching band were investigated in the absence and presence of the chitosan. It was concluded that appropriate combining of the liposomal and chitosan characteristics might be utilized for the improvement of the therapeutic efficacy of liposomes as a drug delivery system.

Reverse Current Pulse Method To Restore Uniform Concentration Profiles in Ion-Selective Membranes. 2. Comparison of the Efficiency of the Different Protocols

The membrane potential of ion-selective electrodes is measured at zero current in traditional potentiometric analysis. Recently, pulsed potentiometric methods have gained importance. In pulsed potentiometric methods, the voltage measured at the end of a current pulse is usually the analytical signal. The applied current alters the concentration profiles inside the sensing membrane. For reproducible voltage measurements the original concentration profiles must be restored in the membrane between current pulses. The simplest restoration method is the zero-current relaxation. Unfortunately, the zero-current method is very slow, which limits the frequency of measurements. In analytical practice the controlled voltage restoration method is most commonly used, but the controlled voltage method has no adequate theoretical description. This paper presents a finite element model of the controlled voltage method to predict its efficiency. The model demonstrates for the first time that increasing membrane resistance decreases the efficiency of this restoration method. The model allows estimating the necessary restoration time for voltage errors below an acceptable threshold value and provides guidance for minimizing the voltage error. The efficiency of the controlled voltage method is compared to the reverse current pulse restoration method discussed in part 1 of this set of papers. It is found that the reverse current restoration method is simpler, requires shorter restoration times (i.e., it allows higher measurement frequency), and it has 4 and 10 times smaller voltage errors compared to the controlled voltage method. These theoretical results are confirmed experimentally. The only limitation of the reverse current pulse restoration method is that it cannot be used with membranes containing a background electrolyte (R(+)R(-)) but no excess lipophilic cation exchanger (R(-)). However, lipophilic cation exchanger can often be added to the membrane to reduce restoration times by allowing the reverse current pulse method to be used.

Impedance study of membrane dehydration and compression in proton exchange membrane fuel cells

Abstract Electrochemical impedance spectroscopy (EIS) is used to measure drying and rehydration in proton exchange membrane fuel cells running under load. The hysteresis between forward and backward acquisition of polarization curves is shown to be largely due to changes in the membrane resistance. Drying tests are carried out with hydrogen and simulated reformate (hydrogen and carbon dioxide), and quasi-periodic drying and rehydration conditions are studied. The membrane hydration state is clearly linked to the high-frequency arc in the impedance spectrum, which increases in size for dry conditions indicating an increase in membrane resistance. Changes in impedance spectra as external compression is applied to the cell assembly show that EIS can separate membrane and interfacial effects, and that changes in membrane resistance dominate. Reasons for the presence of a capacitance in parallel with the membrane resistance are discussed.

Investigation of dynamic driving cycle effect on performance degradation and micro-structure change of PEM fuel cell

Degradation of PEMFC performance under dynamic loading cycling situation was studied by simulating automotive working conditions. A protocol of driving cycle was set up. Each driving cycle was consisting of six different periods. The performance of the fuel cell during driving cycle periods was represented by time-dependent voltage profiles. Polarization curves, measured in regular intervals, revealed a changed degradation rate in different operation periods. A rapid degradation of performance could be observed after 280 h of operation. In contrast to the starting conditions of the MEA, the degradation of membrane and dissolution and aggregation of catalysts were clearly visible at the end of testing. Furthermore, after 370 h of testing, Pt was not uniformly dispersed in the catalysts layer and some also scattered in the membrane. Cracks and gaps appeared in the catalyst layer. This change of micro-structure corresponded to the loss of electro-chemical active area of the MEA and the increased membrane resistance and charge transfer resistance.

Comparison of numerical simulations of barrier membranes with impermeable flakes

Steady-state permeation through membranes filled with impermeable flakes has been simulated numerically using a three-dimensional finite element solver. These numerical results are compared to other published numerical results and the equations that are commonly used to estimate the increased membrane resistance. We discuss the conditions for which these equations fail to give good predictions and why. In comparison with other numerical results, predictions of barrier function by the published Monte Carlo simulations are of variable quality in both two and three dimensions. We present a rationale for layer independence of the results and the implications this has on both the design of membranes and how many layers are needed to produce a layer-independent result.

Application of chemical precipitation and membrane bioreactor hybrid process for piggery wastewater treatment

This study was conducted to investigate the chemical precipitation (CP) and membrane bioreactor (MBR) hybrid process for the treatment of piggery wastewater. Average removal efficiencies for BOD, COD and turbidity in CP process were 64.3%, 77.3% and 96.4%, respectively. CP process had a moderate effect on NH 3–N removal (40.4%) which improved up to 98.2% mainly due to nitrification and filtration processes in MBR. The average removal efficiencies of BOD, COD and turbidity in MBR were 99.5%, 99.4% and 99.8%, respectively. Monod equation was used to explain the microbial activities in terms of specific growth rate. The specific growth rate of bacteria in aeration tank (N-batch) and anoxic tank (D-batch) were 0.013 and 0.005 d −1 with a biomass yield of 0.78 and 0.43 mg MLSS produced/mg COD utilized, respectively. Microorganisms from the N-batch and D-batch showed a low-level of nitrifying and moderate-level of denitrifying capabilities which were 1.08 mg NH 3–N/(g MLVSS.h) and 2.82 mg NO 3–N/(g MLVSS.h), respectively. Carbohydrates were the main component in extracellular polymeric substance (EPS) compounds that could be attached to the membrane surface easily and led to membrane biofouling. The increase of MLSS, EPS and sludge viscosity concentration, decrease of sludge floc size and incomplete chemical cleaning procedure resulted in the increase of membrane resistance. Total membrane resistance increased from 3.19 × 10 12 m −1 to 5.43 × 10 14 m −1.

Distribution of two-pore-domain potassium channels in the adult rat vestibular periphery

Constitutively active background or “leak” two-pore-domain potassium (K +) channels (Kcnk family), as defined by lack of voltage and time dependency are central to electrical excitability of cells by controlling resting membrane potential and membrane resistance. Inhibition of these channels by several neurotransmitters, e.g. glutamate, or acetylcholine, induces membrane depolarization and subsequent action potential firing as well as increases membrane resistance amplifying responses to synaptic inputs. In contrast, their opening contributes to hyperpolarization. Because of their central role in determining cellular excitability and response to synaptic stimulation, these channels likely play a role in the differential effects of vestibular efferent neurons on afferent discharge. Microarray data from previous experiments showed Kcnk 1, 2, 3, 6, 12 and 15 mRNA in Scarpa’s ganglia. Real-time RT-PCR showed Kcnk 1, 2, 3, 6, 12 and 15 mRNA expression in Scarpa’s ganglia and Kcnk 1, 2, 3, 6, 12 but not 15 mRNA expression in the crista ampullaris. We studied the distribution of two-pore-domain potassium channels K 2P1.1, 2.1, 3.1 and 6.1 like immunoreactivity (corresponding to Kcnk genes 1, 2, 3 and 6) in the vestibular periphery. K 2P1.1 (TWIK 1) immunoreactivity was detected along nerve terminals, supporting cells and blood vessels of the crista ampullaris and in the cytoplasm of neurons of the Scarpa’s ganglia. K 2P2.1 (TREK 1) immunoreactivity was detected in nerve terminals and transitional cells of the crista ampullaris, in the vestibular dark cells and in neuronal fibers and somata of neurons of Scarpa’s ganglia. K 2P3.1 (TASK 1) immunoreactivity was detected in supporting cells and transitional cells of the crista ampullaris, in vestibular dark cells and in neuron cytoplasm within Scarpa’s ganglia. K 2P6.1 (TWIK 2) immunoreactivity was detected in nerve terminals, blood vessels hair cells and transitional cells of the crista ampullaris and in the somata and neuron fibers of Scarpa’s ganglia.

Synaptic effects of low molecular weight components from Chilean Black Widow spider venom

α-Latrotoxin is the principal component of the venom from the euroasiatic Black Widow spider and has been studied for its pharmacological use as a synaptic modulator. Interestingly, smaller molecular weight fractions have been found to be associated with this toxin, but their cellular actions have not been studied in detail. The venom from the Chilean Black Widow spider ( Latrodectus mactans) does not produce α-latrotoxin, however it does contain several small polypeptides. We have recently demonstrated cellular effects of these peptides at the synaptic level using whole-cell patch clamp techniques. Purified venom from the glands of L. mactans was studied in 12 DIV rat hippocampal neuronal cultures. Venom at a concentration of 10 nM was able to decrease neuronal conductance thereby increasing membrane resistance. This effect on the passive properties of the neurons induced a change in action potential kinetics simulating the action of classic potassium channel blockers. These changes produced an increase in spontaneous synaptic activity in rat hippocampal cultures in the presence of the venom in a concentration- and time-dependent manner. These results indicate that venom from Chilean spider L. mactans is capable of increasing cell membrane resistance, prolonging the action potential and generating an increase in synaptic activity demonstrating an interesting pharmacological effect of these low molecular weight fragments.