Chemical and Biomolecular Engineering - Research Publications
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ItemConvective transport of boron through a brackish water reverse osmosis membrane(Elsevier, 2013-10-15)In this work, cross-flow filtration experiments using a brackish water reverse osmosis polyamide membrane have been performed to gather boron rejection data as function of feed concentration, pressure, pH and salinity. Increasing transmembrane pressure increases the permeation of boron indicating that convective flow is important. This result is in contrast to the normal assumption that solution diffusion dominates in such systems. The extended Nernst-Planck equation with a Donnan-steric partition coefficient is used to analyse the transport mechanisms of both neutral boric acid and negatively charged borate ions through the RO membrane. The contribution of surface charge is experimentally determined by streaming potential measurements and the electrokinetic surface charge density is then calculated as a function of ionic strength and pH. It is found that a 0.380 nm pore radius and an effective membrane porosity of 0.05 shows good agreement with experimental data. Charge screening becomes more dominant with increasing ionic strength and this contribution is readily incorporated into the model. The study extends our understanding of the transport mechanism of boric acid and borate ions which can assist in predicting the performance of polyamide reverse osmosis membranes. It also raises questions as to the true mechanism of transport through such a membrane.
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ItemFormation of a thick aromatic polyamide membrane by interfacial polymerisation(Elsevier, 2013-02-05)Thin film composite membranes (TFCs) consist of a thin film of polymer that is responsible for high salt rejection. This layer is made via interfacial polymerisation of two monomers 1,3 phenylene diamine and trimesoyl chloride, with the membrane reported to reach a self limiting thickness of less than 200 nm. This paper reports for the first time the formation of thick free-standing aromatic polyamide membranes of greater than 50 μm in thickness via the well-known interfacial polymerisation technique. The membrane thickness as a function of polymerisation time and monomer concentration was investigated. The polyamide layer formed through interfacial polymerisation is not necessarily homogeneous, but can indeed feature areas of porosity. A mechanism for such a porous structure is proposed and discussed. The ability to form thick free-standing polyamide membranes allows bulk polymer properties to be evaluated for the first time. In particular, in this work we are able to measure the zeta potential of the membrane surface that usually faces the membrane support. We show that this surface is still negatively charged for all pH values above 4.0.
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ItemWater vapor sorption and free volume in the aromatic polyamide layer of reverse osmosis membranes(Elsevier, 2013-01-01)Thin film composite membranes consist of an ultra thin active layer of polymer that governs the membrane's salt rejection and water permeation properties. However, the fragility of the ultrathin layer makes it challenging to select a technique capable of differentiating between the properties of this layer from the supporting layer. In this study, we isolated enough active layer material to characterise the water vapour sorption and free volume cavity size as functions of water activity. The sorption data were modelled using the Guggenheim–Anderson–De Boer (G.A.B.) isotherm and from this the number of sorption sites for water was calculated to be 189×1019 per gram for the active layer from a commercial Dow Filmtec SW30 membrane and 188×1019 per gram for an aromatic polyamide material prepared in house. The activation energy for diffusion of water through the active layer of SW30 was also evaluated and found to be 6.95 kcal/mol, lower than the heat of liquefaction of water. This suggests that water does not permeate as individual molecules in the vapour state, but rather as clusters of water molecules. The free volume cavity size in the active layer as a function of moisture uptake was also investigated and the results were explained using a pore filling and pore swelling mechanism. This study sheds light on the mechanisms of water entry into the active layer, water transport through the active layer, and the corresponding response of the polymer chains, thereby giving critical insight for the development of more novel systems.
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ItemThe within-day behaviour of 6 minute rainfall intensity in Australia(COPERNICUS GESELLSCHAFT MBH, 2011)Abstract. The statistical behaviour and distribution of high-resolution (6 min) rainfall intensity within the wet part of rainy days (total rainfall depth >10 mm) is investigated for 42 stations across Australia. This paper compares nine theoretical distribution functions (TDFs) in representing these data. Two goodness-of-fit statistics are reported: the Root Mean Square Error (RMSE) between the fitted and observed within-day distribution; and the coefficient of efficiency for the fit to the highest rainfall intensities (average intensity of the 5 highest intensity intervals) across all days at a site. The three-parameter Generalised Pareto distribution was clearly the best performer. Good results were also obtained from Exponential, Gamma, and two-parameter Generalized Pareto distributions, each of which are two parameter functions, which may be advantageous when predicting parameter values. Results of different fitting methods are compared for different estimation techniques. The behaviour of the statistical properties of the within-day intensity distributions was also investigated and trends with latitude, Köppen climate zone (strongly related to latitude) and daily rainfall amount were identified. The latitudinal trends are likely related to a changing mix of rainfall generation mechanisms across the Australian continent.
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ItemDegradation of progestagens by oxidation with potassium permanganate in wastewater effluents.(Springer Science and Business Media LLC, 2013)BACKGROUND: This study investigated the oxidation of selected progestagenic steroid hormones by potassium permanganate at pH 6.0 and 8.0 in ultrapure water and wastewater effluents, using bench-scale assays. Second order rate constants for the reaction of potassium permanganate with progestagens (levonorgestrel, medroxyprogesterone, norethindrone and progesterone) was determined as a function of pH, presence of natural organic matter and temperature. This work also illustrates the advantages of using a novel analytical method, the laser diode thermal desorption (LDTD-APCI) interface coupled to tandem mass spectrometry apparatus, allowing for the quick determination of oxidation rate constants and increasing sample throughput. RESULTS: The second-order rate constants for progestagens with permanganate determined in bench-scale experiments ranged from 23 to 368 M(-1) sec(-1) in both wastewater and ultrapure waters with pH values of 6.0 and 8.0. Two pairs of progestagens exhibited similar reaction rate constants, i.e. progesterone and medroxyprogesterone (23 to 80 M(-1) sec(-1) in ultrapure water and 26 to 149 M(-1) sec(-1) in wastewaters, at pH 6.0 and 8.0) and levonorgestrel and norethindrone (179 to 224 M(-1) sec(-1) in ultrapure water and 180 to 368 M(-1) sec(-1) in wastewaters, at pH 6.0 and 8.0). The presence of dissolved natural organic matter and the pH conditions improved the oxidation rate constants for progestagens with potassium permanganate only at alkaline pH. Reaction rates measured in Milli-Q water could therefore be used to provide conservative estimates for the oxidation rates of the four selected progestagens in wastewaters when exposed to potassium permanganate. The progestagen removal efficiencies was lower for progesterone and medroxyprogesterone (48 to 87 %) than for levonorgestrel and norethindrone (78 to 97%) in Milli-Q and wastewaters at pH 6.0-8.2 using potassium permanganate dosages of 1 to 5 mg L(-1) after contact times of 10 to 60 min. CONCLUSION: This work presents the first results on the permanganate-promoted oxidation of progestagens, as a function of pH, temperature as well as NOM. Progestagen concentrations used to determine rate constants were analyzed using an ultrafast laser diode thermal desorption interface coupled to tandem mass spectrometry for the analysis of water sample for progestagens.
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ItemA comparative study of the coagulation behaviour of marine microalgae(SPRINGER, 2012-12)
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ItemAdsorption technology for CO2 separation and capture: a perspective(SPRINGER, 2014-02)
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ItemDrying-induced changes in the structure of alkali-activated pastes(SPRINGER, 2013-05)