Steven J. Duranceau

Study of the effect of nanoparticles and surface morphology on reverse osmosis and nanofiltration membrane productivity.

To evaluate the significance of reverse osmosis (RO) and nanofiltration (NF) surface morphology on membrane performance, productivity experiments were conducted using flat-sheet membranes and three different nanoparticles, which included SiO2, TiO2 and CeO2. In this study, the productivity rate was markedly influenced by membrane surface morphology. Atomic force microscopy (AFM) analysis of membrane surfaces revealed that the higher productivity decline rates associated with polyamide RO membranes as compared to that of a cellulose acetate NF membrane was due to the inherent ridge-and-valley morphology of the active layer. The unique polyamide active layer morphology was directly related to the surface roughness, and was found to contribute to particle accumulation in the valleys causing a higher flux decline than in smoother membranes. Extended RO productivity experiments using laboratory grade water and diluted pretreated seawater were conducted to compare the effect that different nanoparticles had on membrane active layers. Membrane flux decline was not affected by particle type when the feed water was laboratory grade water. On the other hand, membrane productivity was affected by particle type when pretreated diluted seawater served as feed water. It was found that CeO2 addition resulted in the least observable flux decline, followed by SiO2 and TiO2. A productivity simulation was conducted by fitting the monitored flux data into a cake growth rate model, where the model was modified using a finite difference method to incorporate surface thickness variation into the analysis. The ratio of cake growth term (k1) and particle back diffusion term (k2) was compared in between different RO and NF membranes. Results indicated that k2 was less significant for surfaces that exhibited a higher roughness. It was concluded that the valley areas of thin-film membrane surfaces have the ability to capture particles, limiting particle back diffusion.

The Reaction of α-Methylstyrene Analogs and Related Compounds With Sodium Perborate in Acetic Acid

Abstract A series of α-substituted styrene analogs have been reacted with sodium perborate in acetic acid to produce l-acetoxy-2-aryl-2-propanol analogs in good yield. The reaction constitutes a mild and convenient method for the oxidation of styrene type double bonds.

A survey of desalinated permeate post-treatment practices

Abstract As part of the Water Research Foundation (Denver, CO) project “Post-Treatment Stabilization of Desalinated Water,” a questionnaire was developed and distributed to water utilities employing desalination processes to survey post-treatment practices, compile process and water quality data, highlight operating cost and post-treatment operation experiences, and identify distribution system secondary impacts. A total of eighty-three surveys were distributed to water utilities in the United States (USA), Caribbean and Europe, and responses collected over a period of six months duration from the time of initial mailing. Twenty-five questionnaires were returned yielding a thirty percent response rate. Twenty-one of the twenty-five responses were received from the USA, three from Europe and one response was received from the Caribbean. The average-daily permeate flow of the facilities surveyed ranged from 0.39 m3/min (0.15 million gallons per day (MGD)) to 184 m3/min (70 MGD). Results indicated a variety ...

Comparison of nonhomogeneous and homogeneous mass transfer in reverse osmosis membrane processes

AbstractReverse osmosis (RO) membranes are pressure driven, diffusion controlled processes. Current diffusion controlled solute mass transfer models assume a homogeneous membrane surface. This study evaluated mass transfer processes assuming mass transport is not a homogeneous process, which is dependent on the thickness variation of the membrane’s active layer. Three-dimensional ridge and valley active layer morphologies were created numerically using Gaussian random vectors. A nonhomogeneous solution diffusion model (NHDM) was then developed to account for surface variation through the active layer. NHDM was further modified by incorporating concentration polarization (CP) effects. A comparison of the NHDM and the NHDMCP with the commonly accepted homogeneous solution diffusion model (HSDM) using pilot-scale brackish water RO operating data indicated that the NHDM is more accurate, when the solute concentration in the feed stream is low, while NHDMCP appears to predict better with a high solute feed con...

Impact of bottled water storage duration and location on bacteriological quality

An investigation studying the effects of storage duration and location on the persistence of heterotrophic microorganisms in oligotrophic bottled water environments has been completed. One-gallon high-density polyethylene water containers stored for up to 16 weeks at temperatures ranging from 2°C to >49°C in a refrigerator, indoor cabinet, covered porch, and car trunk were evaluated for microbiological quality. Heterotrophic plate counts (HPCs) of up to 4 × 103 cfu/mL were detected in containers stored on a porch and car trunk; whereas, HPCs were found not to exceed 400 cfu/mL and 100 cfu/mL for bottles stored in indoor cabinets and refrigerators, respectively. Containers stored on an enclosed porch for up to seven years contained HPC of up to 4 × 104 cfu/mL. Logistic and Gompertz growth models predicted microbial growth rates for bottled water stored on a protected porch environment for long (R 2 0.99) and short-term (R 20.86) durations.

Seasonal Variation of Paraquat Photodegradation Rate on Polyethylene Mulch

Field studies were conducted to determine the effect of season of the year, sunlight exposure time, and mulch color on paraquat photodegradation rate on polyethylene mulch. Experiments were established in winter, spring, and summer, with white and black polyethylene mulch, and paraquat-applied films were exposed to sunlight for 1, 4, 8, 24, 30, 48, 72, or 96 h after herbicide application. There was significant effect of the season by mulch color by time of exposure interaction on paraquat concentration recovered from mulch eluants. Winter paraquat photodegradation was lower than during the other seasons. At 48 h of sunlight exposure, predicted photodegradation on white mulch was 67, 83, and 88%, during winter, spring, and summer, respectively, whereas these values were 66, 82, and 84% on black mulch. The difference in paraquat photodegradation in winter with respect to the other seasons may be attributed to reduced ultraviolet radiation in winter, when solar radiation has to penetrate a larger atmosphere mass. In practical terms, transplanting on paraquat-applied mulch requires a minimum of 96 h during the spring and summer seasons, when concentrations were 5% or less, whereas a longer waiting period might be necessary in the winter. Nomenclature: Paraquat; tomato, Lycopersicon esculentum Mill. Additional index words: Tomato, Lycopersicon esculentum, herbicide breakdown, ultraviolet radiation.

Membrane replacement in desalting facilities

As membrane facilities increase in number and age, the need for membrane replacement has continued to be required. Membrane replacement requires careful planning, and should involve computer modeling, membrane probing, membrane profiling and hydraulic evaluations to document modifications in plant performance. Although many existing plants have undergone membrane replacement, little information has been published in the literature on this component of membrane plant operation. The purpose of this paper is to present an overview of membrane replacement, and describe two case studies to document membrane replacement. One case study describes membrane replacement at a hollow fiber membrane facility (Sarasota, Florida), and a second case study describes membrane replacement at a spiral-wound membrane facility (Marco Island, Florida).

Screening the toxicity of phosphorous-removal adsorbents using a bioluminescence inhibition test.

When found in excess, phosphorus (P) has been linked to surface water eutrophication. As a result, adsorbents are now used in P remediation efforts. However, possible secondary toxicological impacts on the use of new materials for P removal from surface water have not been reported. This study evaluated the toxicity of adsorbent materials used in the removal of P from surface water including: fly ash, bottom ash, alum sludge, a proprietary mix of adsorbents, and a proprietary engineered material. Toxicity screening was conducted by performing solid‐liquid extractions (SLEs) followed by the bacterial bioluminescence inhibition test with a Microtox® M500. Of the materials tested, the samples extracted at lower pH levels demonstrated higher toxicity. The material exhibiting the most toxic response was the iron and aluminum oxide coated engineered material registering a 66–67% 15‐min EC50 level for pH 4 and 5 SLEs, respectively. However, for SLEs prepared at pH 7, toxic effects were not detected for this engineered material. Fly ash and bottom ash demonstrated between 82 and 84% 15‐min EC50 level, respectively, for pH 4 SLE conditions. Dried alum sludge and the proprietary mix of adsorbents were classified as having little to no toxicity.

An indium tin oxide electrode modified with gold nanorods for use in potential-controlled surface plasmon resonance studies

AbstractThe modification of electrodes with gold nanoparticles results in an increased electrode surface area, enhanced mass transport, and improved catalytic properties. We have extended this approach to indium tin oxide (ITO) electrodes to obtain optically transparent gold nanorod-modified electrodes which display enhanced electrochemical capabilities and have the additional advantage of showing a tunable surface plasmon resonance. The procedures for attaining high surface coverage (15 gold nanorods per square µm) of such electrodes were optimized, and the potential-dependent surface plasmon resonance was studied under controlled electrical potential. In an exemplary sensor application, we demonstrate the detection of mercury via potential-dependent formation of an Au-Hg amalgam. Immobilization of gold nanorods on optically transparent ITO electrodes provides tunable surface plasmon resonance detection coupled with electrochemical potential control. These novel sensors are applied to the detection and quantification of mercury with a combined SPR-electrochemical technique

Modeling the improvement of ultrafiltration membrane mass transfer when using biofiltration pretreatment in surface water applications

In surface water treatment, ultrafiltration (UF) membranes are widely used because of their ability to supply safe drinking water. Although UF membranes produce high-quality water, their efficiency is limited by fouling. Improving UF filtrate productivity is economically desirable and has been attempted by incorporating sustainable biofiltration processes as pretreatment to UF with varying success. The availability of models that can be applied to describe the effectiveness of biofiltration on membrane mass transfer are lacking. In this work, UF water productivity was empirically modeled as a function of biofilter feed water quality using either a quadratic or Gaussian relationship. UF membrane mass transfer variability was found to be governed by the dimensionless mass ratio between the alkalinity (ALK) and dissolved organic carbon (DOC). UF membrane productivity was optimized when the biofilter feed water ALK to DOC ratio fell between 10 and 14.