Fouling experiments of thin film composite and cellulose acetate reverse osmosis membranes by aluminum oxide colloids are reported. Membrane fouling was investigated at various solution chemistries under fixed hydrodynamic conditions. Results show that the fouling rate increases with an increase in the ionic strength of the solution. Fouling was significant at high ionic strengths, including in the presence of background dissolved organic matter, resulting in a gradual decrease in product water flux. Under the chemical conditions tested, colloidal fouling was found to be reversible, thus indicating that pore blockage is not an important factor in colloidal fouling of reverse osmosis membranes. The role of chemical-colloidal interactions in colloidal fouling of reverse osmosis membranes is elucidated. Fouling is controlled by particle-membrane and particle-retained particle interactions, which, in turn, are determined by solution chemistry, chemical properties of colloids and membranes, and the magnitude of permeation drag.

Xiaohua Zhu;Menachem Elimelech

Journal of Environmental Engineering, ASCE

1995

The fouling and subsequent cleaning of RO membranes fouled by a mixture of organic foulants simulating wastewater effluent has been systematically investigated. The organic foulants investigated included alginate, bovine serum albumin (BSA), Suwannee River natural organic matter, and octanoic acid, representing, respectively, polysaccharides, proteins, humic substances, and fatty acids, which are ubiquitous in effluent organic matter. After establishing the fouling behavior and mechanisms with a mixture of organic foulants in the presence and absence of calcium ions, our study focused on the cleaning mechanisms of RO membranes fouled by the mixture of organic foulants. The chemical cleaning agents used included an alkaline solution (NaOH), a metal chelating agent (EDTA), an anionic surfactant (SDS), and a concentrated salt solution (NaCl). Specifically, we examined the impact of cleaning agent type, cleaning solution pH, cleaning time, and fouling layer composition on membrane cleaning efficiency. Foulant-foulant adhesion forces measured under conditions simulating chemical cleaning of a membrane fouled by a mixture of the investigated organic foulants provided insights into the chemical cleaning mechanisms. It was shown that while alkaline solution (NaOH) alone is not effective in disrupting the complexes formed by the organic foulants with calcium, a higher solution pH can lead to effective cleaning if sufficient hydrodynamic shear (provided by crossflow) prevails. Surfactant (SDS), a strong chelating agent (EDTA), and salt solution (NaCl) were effective in cleaning RO membranes fouled by a mixture of foulants, especially if applied at high pH and for longer cleaning times. The observed cleaning efficiencies with the various cleaning agents were consistent with the related measurements of foulant-foulant intermolecular forces. Furthermore, we have shown that an optimal cleaning agent concentration can be derived from a plot presenting the percent reduction in the foulant-foulant adhesion force versus cleaning agent concentration.

Wui Seng Ang;Alberto Tiraferri;Kai Loon Chen;Menachem Elimelech

Journal of Membrane Science

2011-7-1

In this study, we analyze the effects of membrane properties, namely water permeability, solute permeability, and structural parameter, on the overall performance of an FO membrane module to extract water from simulated seawater (0.6M NaCl). By considering the thermodynamic limit of operation, we demonstrate that the maximum achievable water recovery is practically independent of membrane properties, and higher maximum water recovery is achievable with counter-current compared to co-current mode. Analysis of the module-scale model indicates that reducing the support layer structural parameter offers substantial reductions in the membrane area required to achieve a specified water recovery. For example, a 25% reduction of the structural parameter of a state-of-the-art thin-film composite (TFC) membrane (from 400 to 300μm) yields a sizable 20% reduction in membrane area. In contrast, quintupling the water permeability coefficient (from 2.0 to 10.0Lm^-2h^-1bar^-1) of a modern TFC membrane generates only a modest 10% saving in membrane area. In addition, because of the permeability-selectivity trade-off that governs current polymeric membranes, doubling the water permeability coefficient would cause crippling ~7-fold increases in forward and reverse solute permeation. This quantitative study models the potential performance of a module-scale FO desalination process and firmly highlights the need to prioritize the reduction of support layer mass transport resistances over water permeability increases in membrane development.

Akshay Deshmukh;Ngai Yin Yip;Shihong Lin;Menachem Elimelech

Journal of Membrane Science

2015-10-1

In developing countries, safe piped drinking water is generally unavailable, and bottled water is unaffordable for most people. Purchasing drinking water from community-scale decentralized water treatment and refill kiosks (referred to as isi ulang depots in Indonesia) is becoming a common alternative. This study investigates the association between diarrhea risk and community-scale water treatment and refill kiosk. We monitored daily diarrhea status and water source for 1,000 children 1-4 years of age in Jakarta, Indonesia, for up to 5 months. Among children in an urban slum, rate of diarrhea/1,000 child-days varied significantly by primary water source: 8.13 for tap water, 3.60 for bottled water, and 3.97 for water kiosks. In multivariable Poisson regression analysis, diarrhea risk remained significantly lower among water kiosk users (adjusted rate ratio [RR] = 0.49, 95% confidence interval [CI] = 0.29-0.83) and bottled water users (adjusted RR = 0.45, 95% CI = 0.21-0.97), compared with tap water users. In a peri-urban area, where few people purchased from water kiosk (N = 28, 6% of total population), diarrhea rates were lower overall: 2.44 for well water, 1.90 for bottled water, and 2.54 for water kiosks. There were no significant differences in diarrhea risk for water kiosk users or bottled water users compared with well water users. Purchasing water from low-cost water kiosks is associated with a reduction in diarrhea risk similar to that found for bottled water.

Laura C. Sima;Mayur M. Desai;Kathleen M. McCarty;Menachem Elimelech

American Journal of Tropical Medicine and Hygiene

2012-12

The effect of particle size on the kinetics of deposition of polystyrene latex particles on spherical glass beads in porous media was investigated theoretically and experimentally. The latex particles cover a wide size range (46-753 nm) and have comparable surface properties. Experimental collision efficiencies were calculated from measured particle deposition rates. The results are presented as stability curves, i.e., the logarithm of the collision efficiency as a function of the logarithm of concentration of electrolyte (KC1). Experimental curves were compared to those calculated theoretically. It was found, in a marked contrast to theory, that the slopes of the stability curves are insensitive to particle size. Possible explanations for this discrepancy are discussed and evaluated.

Menachem Elimelech;Charles R. O'Melia

Langmuir

1990

Fundamental understanding of membrane fouling in osmosis-driven membrane processes is important for further deployment of this emerging technology in desalination and wastewater reuse. In this study, we investigated the role of pressure in organic fouling and reversibility in forward osmosis (FO) and reverse osmosis (RO) using alginate as a model organic foulant. Varying contributions of pressure (i.e., osmotic versus hydraulic) to the overall driving force were realized in forward osmosis (FO), pressure-assisted FO (PFO), and reverse osmosis (RO) experiments, while the same total driving force for water permeation was applied. Confocal laser scanning microscopy was used to examine alginate fouling layer structure in the hydrated state, which informed two key parameters: fouling layer thickness and foulant volume. We observed that the resulting fouling layer became increasingly more compact in the order of FO, PFO, and RO experiments. Fouling layer reversibility followed the same trend, with the highest and lowest reversibility observed for the FO and RO fouling experiments, respectively. Possible mechanisms for fouling layer compaction in RO were discussed, including permeate drag force and foulant compressibility, as opposed to FO where only permeate drag force applies. Our findings suggest that pressure mechanistically alters the membrane fouling layer structure and fouling reversibility, leading to higher fouling reversibility in FO, where the driving force is osmotic pressure, than RO, where the driving force is hydraulic pressure.

Ming Xie;Jongho Lee;Long D. Nghiem;Menachem Elimelech

Journal of Membrane Science

2015-11-1

Improving solute selectivity is critical to enhancing the efficiency and sustainability of membrane separation processes. Doing so, however, requires understanding the molecular-level processes that culminate in solute transport through semipermeable membranes. Existing experimental techniques lack the spatiotemporal resolution necessary for probing such molecular-level events, and conventional simulation techniques cannot probe timescales relevant to the transport of unwanted solutes through ultra-selective membranes. Here, we use path-sampling molecular simulations to circumvent both these limitations. We not only accurately and efficiently compute arbitrarily long solute passage times but also identify induced charged anisotropy as a hidden variable affecting ion transport through nanopores. Our approach provides a scalable paradigm for computational studies of selectivity in applications such as desalination, chemical separation, and biological membrane transport.

Hessam Malmir;Razi Epsztein;Menachem Elimelech;Amir Haji-Akbari

Matter

2020-3-4

Graphene oxide (GO) is a promising material for the development of antimicrobial surfaces due to its contact-based antimicrobial activity. However, the relationship between GO physicochemical properties and its antimicrobial activity has yet to be elucidated. In this study, we investigated the size-dependency of GO antimicrobial activity using the Gram-negative bacteria Escherichia coli. GO suspensions of average sheet area ranging from 0.01 to 0.65 μm² were produced and their antimicrobial activity evaluated in cell suspensions or as a model GO surface coating. The antimicrobial activity of GO surface coatings increased 4-fold when GO sheet area decreased from 0.65 to 0.01 μm². The higher antimicrobial effect of smaller GO sheets is attributed to oxidative mechanisms associated with the higher defect density of smaller sheets. In contrast, in suspension assays, GO interacted with bacteria in a cell entrapment mechanism; in this case, the antimicrobial effect of GO increased with increasing sheet area, with apparent complete inactivation observed for the 0.65 μm² sheets after a 3 h exposure. However, cell inactivation by GO entrapment was reversible and all initially viable cells could be recovered when separated from GO sheets by sonication. These findings provide useful guidelines for future development of graphene-based antimicrobial surface coatings, where smaller sheet sizes can increase the antimicrobial activity of the material. Our study further emphasizes the importance of an accurate assessment of the antimicrobial effect of nanomaterials when used for antimicrobial surface design.

François Perreault;Andreia Fonseca De Faria;Siamak Nejati;Menachem Elimelech

ACS Nano

2015-7-28

Kai Loon Chen;Menachem Elimelech

2008

Bench-scale experiments were performed to assess the effectiveness of reverse osmosis (RO) and nanofiltration (NF) membranes in removing arsenic (As) from synthetic freshwater and source water. The authors examined the effects of operational conditions (applied pressure and feedwater temperature) and solution chemical composition (As oxidation state, pH, and presence of co-occurring inorganic solutes). Both As(V) and As(III) were effectively removed from synthetic freshwater by RO and tight NF membranes over a wide range of operational conditions. The relatively large molecular weight (>125 g/mol) of the As species governed their separation behavior. Applied pressure had little effect on As removal, but an increase in feedwater temperature decreased As removal by a small percentage. Removals of As(III) and As(V) were comparable, with no significant preferential rejection of As(V) over As(III). Variations in solution pH from 4 to 8 also did not affect the removal of As species by the membranes tested, despite changes in the speciation and charge of As(V). Co-occurring inorganic solutes had only a slight effect on As removal. Removal of As from source water was comparable to that obtained with synthetic freshwater, despite the presence of turbidity, natural organic matter, and a variety of co-occurring solutes.

John J. Waypa;Menachem Elimelech;Janet G. Hering

Journal - American Water Works Association

1997-10