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Biofouling of reverse osmosis (RO) membranes is a major impediment in both wastewater reuse and desalination of sea/brackish waters. A benefit to the industry would be a simple screening approach to evaluate biofouling resistant RO membranes for their propensity to biofoulants. To observe the relationship between initial membrane productivity and control of biofilm formation governed by surface modification to the aromatic polyamide thin-film composite RO membranes, three different RO membranes developed by the FilmTec Corporation including FilmTec's commercial membrane BW30 (RO#1) and two experimental membranes (RO #2 and #3) were used. RO #2 and RO #3 were modified with a proprietary aliphatic group and with an extra proprietary aromatic group, respectively. Membrane swatches were fixed on coupons in rotating disk reactor systems without filtration and exposed to water with indigenous organisms supplemented with 1.5 mg/L organic carbon under continuous flow. After biofouling had developed, the membranes were sacrificed and subjected to several analyses. Staining and epifluorescence microscopy revealed more cells on RO #2 and #3 compared to RO #1. Based on image analysis of 5-μm thick stained biofoulant cryo-sections, the accumulation of hydrated biofoulants on RO #1 and #3 were from 0.87 to 1.26 μm/day, which was lower than that on RO#2 (2.19 μm/day). Biofoulants increased the hydrophobicity of RO #2 to the greatest amount, up to 32°, as determined by contact angle. In addition, a wide range of changes of the chemical elements of the RO surfaces was observed with X-ray photoelectron spectroscopy analysis. RO #2 with the highest initial membrane productivity showed the poorest biofouling resistance. A combination of these novel approaches showed good agreement and suggested that membrane productivity, heterogeneity of anti-biofouling agents on membrane surface, stability of surface chemical elements and the role of virgin RO surface hydrophobicity should be jointly considered during the development of anti-biofouling polyamide thin-film RO surfaces.

Biofouling is a major reason for flux decline in the performance of membrane-based water and wastewater treatment plants. Initial biochemical characterization of biofilm formation potential and biofouling on two commercially available membrane surfaces from FilmTec Corporation were investigated without filtration in laboratory rotating disc reactor systems. These surfaces were polyamide aromatic thin-film reverse osmosis (RO) (BW30) and semi-aromatic nanofiltration (NF270) membranes. Membrane swatches were fixed on removable coupons and exposed to water with indigenous microorganisms supplemented with 1.5 mg l(-1) organic carbon under continuous flow. After biofilms formed, the membrane swatches were removed for analyses. Staining and epifluorescence microscopy revealed more cells on the RO than on the NF surface. Based on image analyses of 5-μm thick cryo-sections, the accumulation of hydrated biofoulants on the RO and NF surfaces exceeded 0.74 and 0.64 μm day(-1), respectively. As determined by contact angle the biofoulants increased the hydrophobicity up to 30° for RO and 4° for NF surfaces. The initial difference between virgin RO and NO hydrophobicities was ∼5°, which increased up to 25° after biofoulant formation. The initial roughness of RO and NF virgin surfaces (75.3 nm and 8.2 nm, respectively) increased to 48 nm and 39 nm after fouling. A wide range of changes of the chemical element mass percentages on membrane surfaces was observed with X-ray photoelectron spectroscopy. The initial chemical signature on the NF surface was better restored after cleaning than the RO membrane. All the data suggest that the semi-aromatic NF surface was more biofilm resistant than the aromatic RO surface. The morphology of the biofilm and the location of active and dead cell zones could be related to the membrane surface properties and general biofouling accumulation was associated with changes in the surface chemistry of the membranes, suggesting the validity of the combination of these novel approaches for initial assessment of membrane performance.

Transition‐state theory was employed to study the dynamics of light gases dissolved in rigid microstructures of glassy polycarbonate and rubbery polyisobutylene modeled in atomistic detail. The gaseous molecules migrated through the polymer structures in a sequence of ‘‘hops’’ between local minima of the potential energy. The solute dynamics was characterized by three time domains: at short times

The application of the technique of resonance-enhanced multiphoton iontzation (REMPI) spectroscopy to the detection of triplet states via a first photon resonance is examined. It is shown to work well for the a 3 A 2 state of CS 2 . This technique promises to permit the detection of spin-forbidden transitions at high resolution and with great sensitivity.

Hydrophilic polymers such as perfluorinated ionomers with sulfonic acid functional groups have high water permeabilities and good selectivities for water over most gases and organic liquids. Understanding the water transport mechanism in these water plasticized membranes is necessary in order to effectively utilize them for dehydration applications. Water diffusion in these polymers is non-Fickian. Water permeabilities and solubility coefficients are a function of water vapor pressure. A careful analysis is required to arrive at the concentration dependent diffusion coefficients. An approach for calculating thermodynamic diffusion coefficients based on steady state permeabilities and equilibrium sorption measurements is presented in this paper. At very low water vapor pressures, strong ion-water interactions give rise to high solubility coefficients and low diffusion coefficients. At water activities of 0.1 to 0.6, the solubility coefficient decreases and the diffusion coefficient increases with water activity. At very high water activities (≥0.6), the diffusion coefficient appears to attain a limiting value while the solubility coefficient sharply increases. An anomalous thickness effect was also observed. Thickness normalized permeabilities increased with increasing membrane thickness. Several mechanisms were considered.