Biopolymer Flocculant Systems and Their Chemically Modified Forms for Aqueous Phosphate and Kaolinite Removal

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

Flocculation Optimization of Orthophosphate with FeCl₃ and Alginate Using the Box–Behnken Response Surface Methodology

A coagulation–flocculation process was employed to remove orthophosphate (P_i) in aqueous media using a ferric chloride (FeCl₃) and alginate flocculant system. Jar tests were conducted, and the response surface methodology (RSM) was used to optimize the P_i removal variables. The Box–Behnken design was used to evaluate the effects and interactions of four independent variables: pH, FeCl₃ dose, alginate dose, and settling time. The RSM analysis showed that the experimental data followed a quadratic polynomial model with optimum conditions at pH 4.6, [FeCl₃] = 12.5 mg·L^–1, [alginate] = 7.0 mg·L^–1, and a 37 min settling time. Optimum conditions led to a P_i removal of 99.6% according to the RSM optimization, in good agreement with experimental removal (99.7 ± 0.7%), at an initial concentration of 10.0 mg P_i/L. The isotherm adsorption data at the optimized conditions were analyzed by the pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models and several isotherms models (Langmuir, Freundlich, and Sips). The PFO kinetic model and Langmuir isotherm model yielded the best fit to the isotherm results. The maximum adsorption capacity of the flocculant system was 83.6 mg·g^–1. The flocculation process followed electrostatic charge neutralization and an ion-binding adsorption mechanisms

Biopolymer Flocculants and Oat Hull Biomass To Aid the Removal of Orthophosphate in Wastewater Treatment

This study reports on the removal of orthophosphate (P_i) by coagulation–flocculation with variable combinations of alum, biopolymers, and biomass. The combinatorial effects of these coagulant aids were evaluated for single, binary, and ternary systems. The role of pH, component dosages, and P_i concentration on the coagulation–flocculation efficacy was evaluated. There was an optimal dosage of alum (30 mg/L) while alginate and chitosan were 15 mg/L. P_i removal was 86% for alum and 98% for ternary systems containing chitosan and alginate where [P_i] = 10–11 mg P_i/L. P_i removal for the alum–alginate–chitosan ternary system was more efficient than that for the binary systems, especially at pH 6–7, where reduced efficiency occurred at pH > 7.5. P_i removal was independent of concentration except at lower levels, [P_i] < 10 mg/L. The alum–refined oat hull binary system was 99% effective for P_i removal, especially when [P_i] = 25 mg/L, with greater removal over the use of oat hulls alone