Biopolymer Flocculant Systems and Their Chemically Modified Forms for Aqueous Phosphate and Kaolinite Removal
Agbovi, Henry K
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The fate and build-up of phosphate (Pi) nutrients in aquatic environments is an urgent environmental problem affecting global water security. At elevated levels, Pi causes eutrophication, leading to oxygen depletion. This thesis is aimed at the development, optimization and application of a sustainable biopolymer-based coagulation-flocculation (CF) system that has improved Pi and turbidity (Ti) removal performance over conventional CF systems. In Chapters 3 and 4, the removal efficacy of Pi from wastewater was investigated using variable combinations of coagulant and biopolymer-flocculant (chitosan and alginate) systems. The CF process was affected by several independent variables (CF factors). The optimization studies provided an empirical relationship between the Pi removal efficiency and these factors. The results demonstrated that the biopolymer-flocculants are more efficient in a ternary system in removing Pi from wastewater and the process is controlled by charge neutralization and polymer-bridging mechanisms. Chapters 5 and 6 are aimed at designing a high molecular weight amphoteric bioflocculant (CMC-CTA) for the co-removal efficacy of Pi and Ti in a binary system with FeCl3. The effects of pH, settling time, coagulant and flocculant dosages were investigated through optimization studies, and the results showed that Fe(III)-CMC-CTA binary system was effective at acidic to neutral pH. Kinetics and equilibrium adsorption studies showed that the process was well described by kinetic pseudo-first-order and equilibrium Langmuir isotherm for uptake of Pi and Ti and the process was spontaneous and endothermic. Chapter 7 focused on the design of high molecular weight cationic chitosan-based flocculant (CTA-Chi-g-PAM). The functional properties of the flocculants were examined for the removal of Pi, and Ti, where the effects of several CF factors were tested in a single-component system. The experimental data were fitted by several kinetic (time-dependent) and adsorption (concentration dependent) models. Thermodynamic parameters revealed that the CF process was favored by entropy-driven electrostatic interactions and polymer bridging. Individual kaolinite-colloidal particles showed a higher aggregation rate due to Coulombic electrostatic and van der Waals attractive forces in the presence of CTA-Chi-g-PAM to form flocs. The studies reported herein provide a greater understanding of the structure-property relationship for biopolymer-based CF phenomena, and the findings will add to the design of bioflocculants with superior and tunable physicochemical properties.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorWilson, Lee D
CommitteeGrosvernor, Andrew P; Pickering, Ingrid; Peng, Jian; Müller, Jens
Copyright DateAugust 2020