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UCLA Electronic Theses and Dissertations UCLA UCLA Electronic Theses and Dissertations Title A Fundamental Perspective on Polyelectrolyte Coagulants and Flocculants in Water Treatment Permalink https://escholarship.org/uc/item/5f30h7k4 Author Bhattacharya, Arkadeep Publication Date 2021 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA Los Angeles A Fundamental Perspective on Polyelectrolyte Coagulants and Flocculants in Water Treatment A thesis submitted in partial satisfaction of the requirements for the degree Master of Science in Chemical Engineering by Arkadeep Bhattacharya 2021 ABSTRACT OF THE THESIS A Fundamental Perspective on Polyelectrolyte Coagulants and Flocculants in Water Treatment by Arkadeep Bhattacharya Master of Science in Chemical Engineering University of California Los Angeles, 2021 Professor Samanvaya Srivastava, Chair Coagulation and flocculation are important phenomena which find widespread applications in water treatment. Polyelectrolytes are charged macromolecules which have found relevance in this domain due to their proven efficiency and effectiveness. The objective of the thesis would be to review and emphasize the fundamental mechanisms on which both natural and synthetic polyelectrolyte coagulants and flocculants operate. Advances in understanding phase characteristics and structure of aggregated polyelectrolyte complexes post interaction with charged impurities are discussed. These would help elucidate the correlation between salient polyelectrolyte properties such as molecular weight, persistence length, charge density, and aggregated complex properties such as turbidity and size. This review aims to provide relevant insights that enable better coagulants and flocculants for water treatment systems through examples to ultimately correlate several concepts and develop a collective understanding. ii The thesis of Arkadeep Bhattacharya is approved. Panagiotis Christofides Carlos Morales Guio Samanvaya Srivastava, Committee Chair University of California, Los Angeles 2021 iii Contents LIST OF FIGURES ................................................................................................................................ v ACKNOWLEDGEMENT .................................................................................................................... vii 1. INTRODUCTION .......................................................................................................................... 1 2. COAGULATION AND FLOCCULATION IN WATER TREATMENT ..................................... 4 2.1 History .......................................................................................................................................... 4 2.2 Theory of Coagulation and Flocculation ...................................................................................... 5 2.3 Mechanisms for Coagulation and Flocculation........................................................................... 10 2.4 Factors Affecting Coagulation and Flocculation ........................................................................ 13 2.4.1 Coagulant Dosage ................................................................................................................ 13 2.4.2 Solution pH .......................................................................................................................... 16 2.4.3 Temperature ......................................................................................................................... 17 3. POLYELECTROLYTE COAGULANTS AND FLOCCULANTS ................................................. 19 3.1 Polyelectrolyte-Colloid Interactions: A Fundamental Perspective ....................................... 21 3.2 Structure of Polyelectrolyte-Colloid Mixtures ...................................................................... 21 3.3 Phase Behavior of Polyelectrolyte-Colloidal Complexes ..................................................... 25 3.4 BIOPOLYMER FLOCCULANTS ....................................................................................... 30 3.4.1 Chitosan Based Flocculants .......................................................................................... 31 3.4.2 Starch-Based Flocculants .............................................................................................. 32 4. POLYELECTROLYTE USAGE AND PERFORMANCE IN TREATMENT ............................... 35 5. CONCLUSION AND FUTURE PERSPECTIVES.......................................................................... 37 REFERENCES ..................................................................................................................................... 39 iv LIST OF FIGURES Figure 2.1 Schematic diagram depicting the electric double layer...........................................9 Figure 2.2 A representation of change in interaction energy (W) with distance between and varying surface charge density (휎)……………………………………………………………10 Figure 2.3 An illustration of different mechanism of coagulation and flocculation…………13 Figure 2.4 Depiction of multiple stabilization zones for coagulant dosage vs colloid concentration regimes ……………………………………………..........................................14 Figure 2.5 Quantification of the backwash effectiveness and membrane fouling by tracking the ultrafiltration resistance trajectory in real-time…………………………………….........……15 Figure 3.1 Classification of some polymeric flocculants used in wastewater treatment……...20 Figure 3.2 (a) A schematic representing the tail, loop, and train configuration of polymer adsorption on surfaces. (b) Illustration of U-shaped, solenoid and rosette structures of PE- colloid complex from left to right (c) Representation of variation of critical surface charge density of particles scales with curvature…………………………………………………...22 Figure 3.3 (a) Structures obtained from simulations where polymer persistence length increases from top to bottom and concentration increases horizontally. (b) Panels show a single PE chain with one particle (in the left column) and 4 particles (in the right column). The flexibility of polymer increases from top to bottom. (c) Cryo-TEM image of the rod-like complex formed with high silica nanoparticle and low chitosan concentrations (d) PE- Nanoparticle complex structures at different chain lengths and persistence lengths…………………….………………………………………………………………….24 Figure 3.4 (a) A general phase diagram for turbidity in PE-NP complexes with respect to the concentration of PE and NPs. (b) Polymer bridged (PB), monomer dominated aggregates (M), aggregates (A) and percolated aggregates (P) identified in simulations of PE-NP complexes for different PE and NP concentrations and NP charge ………………………………………….28 v Figure 3.5 Different structures protein-PE made of PSS and lysozyme, depicting their demonstrating the dependence on PE and protein concentrations, ionic strength and PE persistence length. ……………………………………………………………………………30 Figure 3.6 (a) Depicts the variation in the molecular structure of a starch-based flocculant which can respond to pH (PRAS). (b) Schematic representation of the cyclic flocculation/ regeneration process along with the observed turbidity in the solution as a function of solution pH…………………………………………………………………………………………….34 vi ACKNOWLEDGEMENT I would like to thank my parents for their unwavering support and belief in me, without which I would not have completed this degree. I am thankful to my advisor, Professor Samanvaya Srivastava, for being incredibly patient and persistent in correcting my mistakes. I am grateful to my group members, colleagues, and professors for their constant support and company. Lastly, I would like to thank my colleagues Divya Jayaram Iyer and Advait Holkar for their guidance. vii 1. INTRODUCTION Freshwater is an ever-dwindling resource, with 3.6 of of 7.7 billion poeple already deprived of reliable supply1. Human water usage has compounded 40 times in the last 300 years2 and six times in the last 100 years3. Moreover, the demand has increased by 1% annually, dependent on many factors, including population boom, development, and changing consumption patterns4. An impending crisis is inevitable as it is predicted5 that by 2050 global water demand will increase by 55%. As a result, a concerted effort has been initiated globally to reuse water and facilitate sustainable and industrially scalable water treatment processes to meet stricter regulatory norms, “down from 1.0 NTU in 1989 to 0.3 NTU in 2016 for processed water”6. Hence, research in water treatment and materials has been a subject of interest for scientists and researchers worldwide7–12. Materials in wastewater can be classified into several size categories ranging from coarse dispersions (10 mm), fine particulates (10-3 mm), colloidal (10-4 mm), to solution impurities (<10-6 mm) such as ions and molecules6. Particles from and below the colloidal size range are stable in solution due to the combined effect of steric repulsions, van der Waals forces, and electrostatic interactions13. Typically, pre-treatment is necessary for removal of such stable colloidal impurities before being subjected to energy-intensive methods such as ultrafiltration and reverse osmosis in a water treatment facility. Coagulation and flocculation are methods have evolved since ages into highly effective , methods to reduce natural organic matter (NOM)14–16, improve color and odor17, and reduce pathogens18 along with other charged and uncharged impurities. Coagulation and flocculation
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