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Membrane technology, which basically is used for water treatment, can now be used to protect the environment. public health, resource recovery, and pollution control, among others.

Colloidal materials were extracted from rain water in the Brays Bayou region of Houston, TX. Samples were tested for dissolved organic carbon, Si, Al, Fe, Cr, Cu, Mn, Zn, Ca, Mg, and Ba. Colloids accounted for 17 percent of the carbon, 32 percent of the silica, 79 percent of the Al, 85 percent of the Fe, 52 percent of the Cr, 43 percent of the Mn, and 29 percent of the Zn over the period of the storm. However, levels were not constant. During the dry period, colloids were mainly composed of silica, and the height of the storm flow. Carbon dominated the colloidal fraction and the beginning and end of the storm. Different morphologies were also observed for the colloidal material, such as crystallized phases, and amorphous phases.

It is not enough to rely on simple power law as a means of measuring particle size distributions in air, water and soil. When utilized against the context of fractal dimension, the method comes up with an approximation of the geometrical features of particles and characteristics of aggregates in terms of their density and porosity. There is an alternative method of sealing identified as multifractal, which addresses the inadequacy of using the simple power law. Data on soil grain size distributions were studies to illustrate how much more appropriate it would be to use multifractal behavior.

Results of dialysis investigations of surface and groundwaters to determine atrazine retention indicated that initial concentration do not affect atrazine retention. Natural organic matter (NOM) appeared to aid atrazine retention in membranes with molecular mass cut-offs less than 500 Da by transitory hydrogen bonding and subsequent physical entrapment. Atrazine retention, however, is observed to decrease at higher ionic strengths.

Selective particle transport and accumulation on membranes occur in membrane filtration, as evidenced by a comparison of particle size distributions in the membrane feed suspensions and deposited cakes. This affirms that a previously hypothesized minimum in particle back-transport from the membrane is a function of particle size. Brownian diffusion appears to account for the back-transport of smaller particles, while an orthokinetic mechanism controls larger macrocolloids. Cake-specific resistances measured in the dead-end mode were higher than those of corresponding feed suspensions, and those measured under a crossflow were higher than those in the dead-end mode.

The re-deposition of colloids mobilized in the aquifer and gas binding due to hydrogen peroxide decomposition, rather than to iron precipitation, likely caused the reduced permeability of the aquifer near delivery systems. This was found following an investigation of the effects of iron oxidation state and concentration, the presence of colloidal materials and the impact of nutrient solutions and hydrogen peroxide in the feedwater on the permeability of the aquifer material in the bioremediation experience at Eglin Air Force Base in Florida. Bioremediation at the site was stopped because of the failure of delivery systems owing to iron precipitation.

A study of the effects of laminar cross-flow membrane filtration on particle transport and deposition is presented. Theoretical predictions incorporating such factors as Coulombic and hydrodynamic forces were compared with particle residence time distributions determined experimentally. The study found that such factors as particle size, permeation rate and cross-flow velocity determined the extent of transport and deposition. The research from this study may be useful for wastewater treatment.

Column experiments were conducted to investigate the transport of aqueous C60 (aqu-nC60), fullerol, silver nanoparticles (NPs) coated with polyvinylpyrrolidone (Ag-PVP) and stabilized by citrate (Ag-CIT) in biofilm-laden porous media. Gram-negative Pseudomonas aeruginosa (PA) and Gram-positive Bacillus cereus (BC) biofilm-laden glass beads were selected to represent the bacterial interfaces NPs might encounter in the natural aquatic environment. The biomass distribution, extracellular polymeric substances (EPS) components, electrokinetic property, and hydrophobicity of these interfaces were characterized, and the hydrophobicity was found to correlate with the quantity of proteins in EPS. The retention of NPs on glass beads coated with bovine serum albumin (BSA) and alginate were also studied. Except for Ag-PVP, the affinity of NPs for porous medium, indicated by attachment efficiency a, increased in the presence of biofilms, BSA and alginate. For hydrophobic aqu-nC60, the larger the proteins/polysaccharides ratio, the larger the α, suggesting the hydrophobic interaction determines the attachment of aqu-nC60 to the collector surface. Uncharged PVP stabilized Ag-PVP by steric repulsion, and the attachment to glass beads was not enhanced by biofilm. The presence of divalent ion Ca2+ significantly hydrophobized biofilm, BSA, and alginate-coated glass beads and further retarded the mobility of aqu-nC60, fullerol, and Ag-CIT; while Ag-PVP was again sterically stabilized. [ABSTRACT FROM AUTHOR]

Theoretical and experimental approaches were employed to study the effect of aggregation on the affinity between nanoparticles (NPs) and a flat surface that is quantified by the attachment efficiency. Computer simulations were used to generate virtual aggregates formed via either diffusion limited cluster aggregation or reaction limited cluster aggregation. The colloidal interactions between the simulated aggregates and a flat surface were evaluated based on the surface element integration approach. It was found that the strength of colloidal interaction for the aggregated NPs was on the same order of magnitude as those for the primary particles and was significantly weaker than that for an equivalent sphere defined by the gyration radius of the aggregate. The results from the deposition experiments using quartz crystal microbalance suggested that the attachment efficiencies (unfavorable deposition) for aggregated NPs were higher at the initial stage but later became similar to that of the primary NPs when equilibrium deposition was reached. The high initial affinity was postulated to be attributable to secondary minimum deposition. These results suggest that it is the size of the primary particles, not that of the aggregates, that determines the strength of the colloidal interaction between the aggregate and an environmental surface. [ABSTRACT FROM AUTHOR]

A theoretical investigation was conducted upon the stericinteractionbetween a spherical particle and a flat plate. The effects of curvatureon both the segment density distribution of polymer and on the stericinteraction energy between a particle and a plate were examined. Itwas found that the conventional approach using Derjaguin approximationmay overestimate the interaction energy, especially for very smallparticles. Based on the results obtained from applying the Flory–Krigbaumtheory with the accurate geometry change during the interaction, simpleapproximate expressions of exponential form were proposed for boththe osmotic (mixing) and elastic contributions to the steric interactionenergy for a sphere-plate interaction. The proposed model was validatedagainst a set of experimental results from a reported study employingatomic force microscopy. Also investigated was the steric interactionbetween a spherical particle coated with polymer and an uncoated flatsurface. It was found that the steric interaction energy from theosmotic contribution is significantly higher than that from the elasticcontribution and that steric interaction is considerably weaker whenthe polymer exists on only one of the interacting surfaces. [ABSTRACT FROM AUTHOR]

We introduce a novel methodology based on hyperspectral imagery with enhanced Darkfield microscopy for detection, characterization, and analysis of engineered nanoparticles in both ultrapure water and in complex waters, such as simulated-wetland ecosystem water and wastewater. Hyperspectral imagery analysis of 12 different nanoparticle sample types, scattering the obliquely incident visible and near-infrared light (VNIR: 400-1000 nm) in an enhanced Darkfield background, showed that the sample information in terms of the spatial distribution as well as spectral characteristics unique to each nanoparticle types, at a sensitivity of single nanoparticle (size ≥10 nm) can be obtained. Hyperspectral imagery and Raman spectral analyses of the silver nanoparticles (AgNPs) revealed that the apparent hydrodynamic size of the particle increased while the primary size remained unchanged in the presence of coatings, which is further confirmed by dynamic light scattering measurements. Similar in size, AgNPs with different coatings exhibited similar spectral color (or peak position) but a red-shift in the peak positions by same amount relative to Bare AgNPs was observed. In conclusion, hyperspectral imagery with enhanced Darkfield microscopy can be a promising tool for detection and characterization of engineered nanoparticles in environmental systems, facilitating studies on fate and transformation of these particles in various types of water samples. [ABSTRACT FROM AUTHOR]

The scaling of electrical double layer interaction energyfroma plate–plate system to a sphere–plate system was reexamined,and it was found that accurate scaling without resorting to the Derjaguinapproximation theoretically predicts the destabilization of nanoparticlesin water depleted of added electrolyte and, consequentially, a maximumstability at a moderate ionic strength. This theoretical feature re-emphasizesthe dual-role nature of added electrolyte that was supported by experimentalresults of direct surface force measurement but not by those of colloidalstability of nanoparticle deposition/aggregation. Inconsistences betweenthe theoretical prediction and the experimental observation and betweenexperimental observations in different systems were discussed. Possiblereasons leading to the inconsistences were explored, including theeffect of curvature, the contribution from counterions, the mode ofinteraction, and the applicability of an equilibrium model to describethe colloidal interaction of a nanoparticle suspension. [ABSTRACT FROM AUTHOR]