Transport models for predicting the performance of membrane processes in water treatment applications.

摘要

Membrane process in water treatment experience permeate flux decline mainly due to fouling associated with natural organic matter (NOM). Two membrane transport models (designated Models I and II) were conceptualized and developed to predict the performance of membrane processes and examine the membrane transport mechanisms associated with concentration polarization, gel layer formation, and internal pore fouling attributed to organic foulants. Model I was applicable to nanofiltration and reverse osmosis where surface fouling dominated, and Model II was universal in its applicability to all membrane processes as it incorporated both surface fouling and internal pore fouling.; The membrane performance tests were conduced by varying operation conditions. The predictive capability of Model I was verified using tannic acid and dextran as model compounds for simulating NOM of moderate and high molecular weights, respectively, while that of Model II was validated using a real groundwater containing NOM. The model predictive capabilities were excellent as evidenced from comparison of experimental results and model simulations. The model simulations were useful in evaluating the relative contributions of various mass transfer resistances to the overall resistance. Sensitivity analyses for the models demonstrated that precise determination of input parameters was of critical importance for obtaining accurate predictions and simulations. The membrane filtration studies further demonstrated that interactions between the organic solute and membrane polymers could play an important role in gel layer formation and membrane fouling.; Several membrane surface characteristics, including surface charge, affinity for foulants, hydrophobicity, and surface micro-morphology were studied for different types of membranes and under various experimental conditions. These studies were performed for model compounds such as tannic acid and dextran. Three new and/or improved techniques were employed to provide a more realistic evaluation of membrane surface characteristics, including dynamic adsorption tests, zeta potential measurements, and atomic force microscopy. These techniques were employed for evaluating their fouling potential based on the physical chemistry of the membrane surfaces and the membrane-solution interactions, and for selecting appropriate membranes for various water treatment applications.