Coupled 3-D Hydrodynamics and Mass Transfer Analysis of Mineral Scaling-Induced Flux Decline in a Laboratory Plate-and-Frame Reverse Osmosis Membrane Module
A 3-D (3-dimensional) numerical modeling approach to analyze the coupling of mineral scale, concentration polarization and permeate flux was developed and demonstrated for a gypsum membrane scaling test in a plate-and-frame RO membrane module geometry. The impact of concentration polarization on mineral gypsum scaling, and in turn the impact of mineral scale on the concentration polarization field, were explored via 3-D finite-element numerical solutions of the coupled fluid hydrodynamics and solute mass transfer equations, along with detailed experimental data on the extent and location of mineral scale. Numerical simulations of the concentration field for a scale-free membrane revealed that the regions of highest supersaturation with respect to calcium sulfate corresponded to regions of highest gypsum scale density, as observed through real-time imaging of the membrane surface in the gypsum scaling test. 3-D simulations of the concentration field in the presence of mineral scale revealed that the concentration polarization modulus and permeate flux were largely unaffected in contiguous scale-free regions of the membrane. However, near and just downstream of individual crystal formations, the local concentration polarization modulus decreased (by similar to 5%) and the permeate flux increased (by similar to 2%) relative to the same positions in the absence of scale. The model-calculated and experimental permeate flux decline agreed closely with an average absolute error of 1.8%. The present study suggests that flux decline due to mineral scaling can be reasonably described by the surface blockage mechanism.
Lyster E, Au J, Rallo R, Giralt, F, Cohen Y (2009). Coupled 3-D Hydrodynamics and Mass Transfer Analysis of Mineral Scaling-Induced Flux Decline in a Laboratory Plate-and-Frame Reverse Osmosis Membrane Module. Journal of Membrane Science, 339,39:48.
Organic solute permeation, sorption, and rejection by reverse osmosis membranes, from aqueous solutions, were Studied experimentally and via artificial neural networks (ANN)-based quantitative structure-property relations (QSPR), for a set of fifty organic compounds for polyamide and cellulose acetate membranes. Membrane solute sorption and passage for dead-end filtration model experiments were quantified based on radioactivity measurements for radiolabeled compounds in the feed, permeate and the membrane, while solute rejection was determined from a mass balance on the permeated solution Volume. Artificial neural networks-based quantitative structure-property relations models were developed for the organic passage (P), sorbed (M) and rejected (R) fractions using the most relevant set of molecular descriptors selected from a pool of 45 molecular descriptors by means of a correlation-based feature selection method and self-organizing maps (SOM). The analysis included pre-screening with principal components analysis and SOM of the chemical domain for the study chemicals as defined by chemical descriptors to identify the applicability domain and chemical similarities. The QSPR models predicted the P and M mass fractions within the range of the standard deviations of measurements for the experimental data set of fifty compounds. Mass balance closure (requiring that M, P and R sum to unity) was satisfactory for the experimental data set of fifty compounds and for an external set of 144 test chemicals, which were not included in the model development. Somewhat higher prediction errors were encountered for a few chemicals that were not well represented within the present chemical domain. The quality of the QSPR/NN models developed suggests that there is merit in extending both the present compound database and the present approach to develop a comprehensive toot for assessing organic solute behavior in RO water treatment processes.
Libotean D., Giralt J., Rallo R., Cohen Y., Giralt F., Ridgway H.F., Rodriguez G., Phipps D. (2008). Organic Compounds Passage through RO Membranes. Journal of Membrane Science, (313)1-2:23-43