Initial Membrane Permeability Research Articles

Nanofiltration applied to the landfill leachate treatment and preliminary cost estimation.

The leachate treatment by nanofiltration (NF) process has received much attention over the last two decades. Previous studies focused on the investigation of the technical feasibility of NF. However, there are a limited number of works that examined leachate treatment costs. On the other hand, in a landfill management system, the economic component is an imperative factor for the decisions of all operations. Thereby, this work aimed to investigate the technical feasibility and economic parameters involved in a full-scale NF plant for the treatment of leachate previously treated by the physicochemical process. The average quality of the pre-treated leachate was 2258 ± 230 mg L-1 chemical oxygen demand (COD) and 821 ± 86 mg L-1 humic substances (HS). NF was performed using a bench-scale filtration module with commercial polymeric membranes SR100 and NP030. At the end of each filtration, a cleaning protocol was applied to recover the initial membrane permeability. The concentration of recalcitrant compounds, expressed as HS, was reduced to 84 ± 8 mg L-1 in the permeate, and COD complies with the wastewater discharge standards imposed by local legislation. The capital costs for a full-scale NF was estimated at MUS$ 0.772, and specific total cost, treated leachate per volume unit, has been estimated at US$ 8.26 m-3.

Impact of intermittent operation on reverse osmosis membrane fouling for brackish groundwater desalination systems

Solar powered reverse osmosis systems are a promising technology for remote communities facing water insecurity. These systems are often operated intermittently with extended shutdown periods to reduce energy storage requirements and system cost. This article experimentally evaluates the effect of intermittent operation on membrane fouling with brackish groundwater. Lab-scale results show that the use of anti-scalant during operation and a rinse with clean water before shutting down the system results in high membrane permeability, above 70% of the initial membrane permeability after seven days of operation. Without rinsing, the lab-scale results showed the membrane permeability dropped to less than 50% of the initial permeability. Membrane autopsy using scanning electron microscopy for mineral deposits and adenosine triphosphate for quantifying biofouling revealed the fewest deposits when anti-scalant and a rinse were performed. To show scalability, pilot-scale studies were conducted and showed similar permeability declines and fouling structures in membrane autopsy. These results will help inform the advancement of reliable solar powered reverse osmosis systems for remote areas.

Influence of triphenyltetradecylphosphonium bromide on the Na+-Li+- countertransport rate in the erythrocyte membrane in patients with genetically different permeability of cell membranes to sodium

Aim. To study the influence of triphenyltetradecylphosphonium bromide [(PPh)3P+C14H29] Br- on the cell membranes permeability to Na+ by determining the rate of Na+-Li+-counter transport in erythrocyte membrane depending on it’s variable initial condition. Methods. Blood samples of 10 healthy volunteers with different Na+-Li+-counter transport rate distribution in erythrocyte membrane were analyzed: I quartile (5 subjects) - low permeability, III quartile (5 subjects) - moderately high permeability. Results. Na+-Li+-counter transport rate change in erythrocyte membrane under the influence of triphenyltetradecylphosphonium bromide depends on genetically determined initial membrane permeability. In subjects belonging to III quartile of Na+-Li+-counter transport the initial membrane permeability is high, and after administration of 0.001 and 0.005 μM concentrations of [(PPh)3P+C14H29] Br- membrane permeability to Na+ increased. In subjects belonging to I quartile of Na+-Li+-counter transport (low initial permeability) [(PPh)3P+C14H29] Br- did not alter membrane permeability to Na+. Conclusion. Triphenyltetradecylphosphonium bromide increases erythrocyte membrane permeability to Na+ in subjects belonging to III quartile of Na+-Li+-counter transport and dose not influence subjects belonging to I quartile of Na+-Li+-counter transport.

Numerical investigations of the effect of non-uniform membrane permeability on deposit formation and filtration process

Spatial variations of cake thickness along flat-sheet membranes were previously evidenced from filtration experiments [J. Mendret, C. Guigui, P. Schmitz, C. Cabassud and P. Duru, An optical method for in situ characterization of fouling during filtration, AIChE Journal, 53 (2007) 2265–2274.]. Neither gravity effects nor pressure drop in channel could explain these unexpected variations. Therefore a theoretical model was developed to investigate growth of a cake on a non-uniform permeability membrane. The model considers two dimensional flow of a particle suspension in a rectangular channel with one porous wall under suction. Cake growth is assumed to be proportional to local filtration velocity. Its macroscopic properties are prescribed from empirical power laws obtained from the aforementioned experiments. A finite element method using mesh deformation was adopted to solve the governing equations of the problem, i.e., the coupled Navier-Stokes and Darcy Brinkman equations, to simulate a complete filtration run. Comparisons between simulations and experiments are in good agreement. Then a careful analysis of the numerical results reveals a non-uniform initial filtration velocity along the porous wall which rapidly becomes uniform. On the contrary, a non-uniform cake thickness still remains after a long time of filtration which profile is similar to the initial membrane permeability profile. Moreover increase of the transmembrane pressure significantly reduces the time necessary to recover a uniform behaviour of the filter.

Evaluation of backwash efficiency, definition of remaining fouling and characterisation of its contribution in irreversible fouling: Case of drinking water production by air-assisted ultra-filtration

Abstract In ultra-filtration or micro-filtration plants the commonly used method for fouling characterisation is based on an analysis of easily measurable process parameters such as membrane permeability. The results presented in this paper are included in a research project aiming to optimize membrane plant operation for drinking water production with a backwash procedure using air and water flow in dead-end ultra-filtration using inside-out hollow-fibres. Experiments on both semi-industrial and laboratory scale pilot plants were first performed with a clay suspension for different filtration conditions and backwash procedures. A comparison of backwash efficiency assessed by initial permeability recovery and by mass balances on particles was performed. From these experiments, it can be pointed out that: - Permeability at the beginning of the filtration cycle is constant whatever the backwash procedures (with or without air). However this cannot be considered as a criterion of good backwash efficiency, because of the following results. - Mass balances on backwash waters show that, despite total permeability recovery, some particles remain on the membrane surface, creating a so-called “remaining particulate fouling”. In addition, the quantity of particles remaining on the membrane surface is influenced by backwash parameters and procedure. Air injection during backwash enhances particle removal. So this study demonstrates that there is remaining particulate fouling after backwash in spite of total permeability recovery. This remaining particulate fouling depends on both filtration and backwash conditions and might contribute to the long-term fouling. Indeed, experiments with natural surface water showed that the long-term decrease in initial membrane permeability (i.e. permeability at the beginning of each filtration cycle) was mainly due to the particles remaining at the end of a classical backwash and only slightly due to irreversible fouling by natural organic matter adsorption. In contrast, when the backwash procedure was hydraulically enhanced by air injection, the remaining particulate fouling was significantly lowered and the long-term decrease in membrane permeability was mainly due to irreversible fouling phenomena, which leads to an increase in process runtime.

Development of reactive thin film polymer brush membranes to prevent biofouling

In an effort to reduce biofouling and enhance membrane cleaning and flux recovery, a positively charged polymer was grafted onto a membrane surface in order to inhibit bacterial growth. This modified membrane was compared to a negatively charged polymer and the native membrane surface with respect to potential to reduce bacterial growth and biofouling of a microfiltration membrane. Monomer units were grafted on 0.1 μM pore size polyethersulfone (PES) microfiltration membrane with [2-(acryloyloxy)ethyl] trimethyl ammonium chloride (AETMA) (positively charged, hydrophilic) and acrylic acid (AA) (negatively charged, hydrophilic) by initiating the co-polymerization reaction using ultraviolet radiation. Variation of reaction times from 5 to 15 min yielded grafted amounts ranging from 50 to 350 μg/cm2. After acrylic acid modification, the membranes were more negatively charged, while the charge reversed to positive (∼+30 mV) after modification with AETMA. The hydrophilicity of the membranes increased upon modification for each monomer with the contact angle decreasing from 68° to 54°. For all modified membranes, the initial membrane permeability decreased with increasing degree of grafting, however the flux in presence of Escherichia coli was 30–200% higher for the AETMA-modified membranes when compared to the unmodified membrane flux. AA-modified membranes had relatively low flux when compared to the AETMA-modified membranes and did not exhibit significant flux decline during the E. coli filtration. The flux recovery after chemical cleaning was greater than 80% for AETMA-modified membranes, suggesting that most of the fouling is reversible, whereas recovery of unmodified membrane flux was <10% even after chemical cleaning. AETMA-modified membranes were found to have a measurable antibacterial effect, whereas the AA-modified and unmodified membranes do not.

Formed-in-place Polyelectrolyte Complex Membranes for Atrazine Recovery from Aqueous Media

A permeable system composed of a polyelectrolyte complex (PEC) membrane formed by alternated deposition of chitosan (CHI) and carboxymethylcellulose (CMC) onto a porous solid substrate was investigated. The films, with thicknesses not superior to 20 nm, were obtained by a self-assembly technique, i.e., by direct dipping of chemically cleaned porous glass membranes, into concentrated polymeric precursor solutions. The resulting depositions have irregular structures and reduce the initial membrane permeability, especially for higher flux velocities. Concerning filtration tests for herbicide removal in aqueous medium, the chitosan deposition attained better results. A tentative model of binding involving hydrogen bonding and/or charge-transfer to nonspecific sites available dynamically as a function of the conformational estate of the deposited polymers is proposed for polysaccharide-herbicide interactions.

Effect of iron oxides scaling on the MD process performance

Membrane distillation (MD) was used for treatment of the effluents generated during regeneration of an ion exchange system in the water treatment plant. The separation of these effluents was performed on the MD pilot plant equipped with the capillary modules made from polypropylene membranes. The precipitation of iron compounds was observed during the operation of MD installation. To assess the fouling phenomena one of the MD modules was subjected to autopsy after several weeks of process duration. A severe fouling of the membrane surface caused by the iron oxides was found. The morphology and composition of the precipitated layer were studied using the scanning electron microscopy (SEM) coupled with energy dispersion spectrometry (EDS). The Fourier transform infrared with diffuse reflectance spectroscopy (FTIR-DRS) was also employed for this analysis. The performance of fouled membranes was evaluated in a laboratory module assembled with the capillary membranes subjected to autopsy. It was found that the formed deposit did not significantly affected the permeate flux in the MD process. A possibility of the membrane regeneration by rinsing with HCl solutions was investigated. An increase of the permeate flux from 770 to 830 dm 3/m 2d was observed due to a partial dissolution of deposit from the membrane surface by hydrochloric acid. However, the dissolution all of the deposit (also including that precipitated into the pores) caused a partial wettability of the membranes, therefore the permeate flux was decreased from 830 to 650 dm 3/m 2d. The initial membrane permeability was restored for a short time, when the membranes were subjected to drying.

The effects of natural organic matter (NOM) fractions on fouling characteristics and flux recovery of ultrafiltration membranes

Natural organic matter (NOM) which is a complex mix of particulate and soluble materials in surface water has been identified and reported by previous studies as responsible for membrane fouling. However the component of NOM which primarily causes the fouling problem is still not well understood, especially relating to the specific fraction that is mainly responsible for flux decline. Therefore, the main objective of this study is to gain a better understanding on the ultrafiltration membrane fouling characteristics due to fractionated NOMs. The 68 kDa MWCO polysulfone (PSF) and 50 kDa MWCO cellulose acetate (CA) membranes formed by a simple phase inversion technique were employed, and the experiments were carried out in a submerged membrane configuration. The Ulu Pontian River water was fractionated into several components which were hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI) fractions using DAX-8 and XAD-4 ion exchange resins. The experimental results showed that the HPI component of NOM exhibited the worst flux decline despite lesser DOC and UV 254 rejections compared to other fractions (HPO and TPI). On the other hand, the HPO fraction showed the highest DOC and UV 254 removals despite possessing lower organics concentration than HPI fraction. Therefore the degree of flux decline is not necessarily proportional with the DOC and UV 254 removals and in fact the degree of DOC and UV 254 rejections are relatively independent of the amount of organics in the source water. Thus, it is worth to note that rejection and fouling are not greatly dependent on the SUVA and DOC concentrations but mostly on the rejection mechanism resulted from the membrane-feed interactions. The hydraulic resistance in series assessment elucidated that the concentration polarization, adsorptive fouling and cake layer deposition were the dominant fouling mechanisms for HPO, HPI and TPI fractions, respectively. Furthermore the effect of cleaning solutions on flux recovery was found significant in nearly restoring the initial membrane permeability. Surprisingly, the HPI fraction was found to exhibit better flux recovery than HPO fraction despite its higher adsorption resistance ( R a ). Therefore, in future applications, the type of fouling resistance and the dominant fouling mechanism are useful tools which can be employed as quantitative measurements for flux recovery and cleaning techniques effectiveness.

Factors Affecting the Permeability ofPseudomonas aeruginosaCell Walls toward Lipophilic Compounds: Effects of Ultrasound and Cell Age

The objective of this research was to elucidate the factors effecting the permeability of cell membranes of gram-negative bacteria toward hydrophobic compounds. Ultrasound treatment, cell age, and the phase state of phospholipid membranes were considered. Spin-labeling EPR method was used to quantify the penetration and distribution of a lipophilic spin probe, 16-doxylstearic acid (16-DS), inPseudomonas aeruginosacell membranes. This bacterium was chosen because of its reported resistance to the action of hydrophobic antibiotics caused by the low permeability of the outer cell membrane for hydrophobic compounds. EPR spectra were collected from cell pellets and cell lysates. The overall spin probe uptake was measured in 10% SDS–cell lysates. Lysis with 0.6% SDS revealed the fraction of the probe located in membrane sites readily accessible to the surfactant. The results indicated a structural heterogeneity ofP. aeruginosamembranes, with the presence of structurally “stronger” and “weaker” sites characterized by different susceptibility to the SDS treatment. The intracellular concentration of 16-DS was higher in insonated cells and increased linearly with the sonication power. EPR spectra indicated that ultrasound enhanced the penetration of the probe into the structurally stronger sites of the inner and outer cell membranes. The effect of ultrasound on the cell membranes was transient in that the initial membrane permeability was restored upon termination of the ultrasound treatment. These results suggest that the resistance of gram-negative bacteria to the action of hydrophobic antibiotics was caused by a low permeability of the outer cell membranes. This resistance may be reduced by the simultaneous application of antibiotic and ultrasound. This hypothesis was confirmed in our experiments withP. aeruginosaexposed to erythromycin.

A helical baffle for cross-flow microfiltration

The use of a helical-shape baffle in a mineral (Carbosep) membrane provided an increase of more than 50% in permeate flux compared with that obtained without a baffle at the same hydraulic dissipated power. Two types of solutions were used: bakers yeast (5% dry weight) and dodecane- water emulsion (0.1%, w/w). The effect of the number of helices with respect to baffle length shows that the permeate volume increases with increasing number of helices but to a lesser degree when the number of helices is more than 4 per 25-mm baffle length. Also, when the baffle's maximum diameter was reduced by about 40% a small variation in permeate flux values was observed. More interesting results were obtained with experiments at very low transmembrane pressures (0.1–0.2 bar) when the permeate flux remained almost constant even from the begining of the experiment, indicating that progressive fouling was practically absent. Flow visualization was made with a video camera (VHS) and showed that the flow was rotational around the baffle axis and that the rotational velocity increased the mixing and migration of the rejected particles from the membrane surface. The manufacturing and installation of this type of baffle was found to be easy, and the cleaning time required for membrane regeneration was found to be shorter than after unbaffed steady flow experiments; so it was possible to recover the initial membrane permeability.