Micellar- and polymer-enhanced ultrafiltration for heavy metal and sulfate removal from aqueous solutions

Lin, Weiyun (2020) Micellar- and polymer-enhanced ultrafiltration for heavy metal and sulfate removal from aqueous solutions. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Micellar-enhanced ultrafiltration (MEUF) and polymer-enhanced ultrafiltration (PEUF) show potential as promising techniques to remove dissolved ions from wastewater, but they remain inadequately understood. In this thesis, the MEUF removal of copper, nickel, and cobalt ions from aqueous solutions was investigated. The effect of surfactant-to-metal (S/M) ratio and pH on MEUF performance (i.e., metal rejection rate and permeate flux) were examined to obtain the preferred operational conditions. A resampling-based artificial neural network (ANN) modeling was proposed as a promising tool to predict the MEUF performance and to reveal the importance of process parameters. The model-predicted values showed good agreement with experimental data (R² > 0.99). S/M ratio and pH had relatively greater contributions to the system performance, whereas sampling time contributed less. A high MEUF efficiency (Rejection > 99%) was achieved. To optimize the system performance and to observe the interactions among operational parameters, the statistical-based response surface methodology (RSM) was used to overcome the drawbacks of the commonly used one-factor-at-a-time method. The thesis is the first study to use an RSM method based on a Box-Behnken design to examine nickel ion removal in a MEUF system while combine with an ANN model. The generated RSM models described the relationship between each performance indicator (nickel rejection rate or permeate flux) and process variables (transmembrane pressure, feed nickel concentration, feed surfactant concentration, and membrane molecular weight cut-off (MWCO) of the membrane). Both RSM and ANN methods adequately described the performance indicators within the examined ranges of the process variables. Next, the thesis targets on sulfate ions, a dissolved anion of increasing concern but not tackled in the MEUF/PEUF field. The thesis is the first study to use MEUF and PEUF to remove sulfate ions as the target component from aqueous solutions. It is also the first to examine the adsorption mechanism of sulfate to surfactant/polymer in such systems. Both MEUF and PEUF were found technically viable to remove sulfate from aqueous streams, with the highest rejection rate (Rejection > 99%) found in dilute sulfate solutions. Further, adsorption equilibrium and kinetics studies show that Freundlich isotherm and pseudo-second-order kinetics can describe the adsorption process. This thesis adds knowledge to the existing MEUF/PEUF techniques by improving system operation, conducting system optimization, and exploring new components (i.e., sulfate ions) that can be removed. It also provides treatment information and potentially facilitates reservoir souring control and mining wastewater treatment.

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