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| Home > Documents in process > Structural Characterization of Polymer-BasedFlocculation of Humic Acid as a Tool forOptimizing Water Treatment |
| Home > Documents in process > Structural Characterization of Polymer-BasedFlocculation of Humic Acid as a Tool forOptimizing Water Treatment |
| Dissertation / PhD Thesis | PUBDB-2025-04016 |
2025
Abstract: The complexation/flocculation induced by cationic polyelectrolytes (cPE) is regarded as aneffective method in conventional water treatment process for addressing negatively chargedhumic acid (HA), which exists ubiquitously in aquatic environments as a degradation productof plants and negatively affects the quality of drinking water.The interaction between oppositely charged HA and cPE can be regarded as the formation ofinterpolyelectrolyte complexes (IPEC), where HA serves as the polyanion with high rigidityand polydispersity. IPEC of cationic polydiallyldimethylammonium chloride (PDADMAC)and HA was first studied with a focus on the Ca2+ effects. This was accomplished bydetermining the phase behavior and characterizing the structures in solution through the use oflight scattering and small-angle neutron scattering (SANS). This allowed for the probing of theformation of aggregates with a radius of 120–150 nm and a compaction in the size range of10−50 nm within these aggregates with the addition of Ca2+. The presence of Ca2+ was foundto exert a considerable influence on both the macroscopic phase behavior and the mesoscopiccomplex structure.Chitosan, a natural polymer derived from waste materials, has been identified as a promisingcandidate for altering synthetic cationic polyelectrolyte (cPEs) to develop an environmentallyfriendly flocculant. A library of different modified cationic (quaternized) chitosans (QCSs) withpermanent charges was synthesized by the substitution of glycidyl trimethylammoniumchloride (GTMAC). A comparison of the HA removal efficiency of QCS and the commercialsynthetic PDADMAC revealed that with QCS the precipitation of HA was enhanced andoccurred at a lower charge mixing ratio due to the intrinsic hydrophobic domain of QCS. Bytailoring the degree of quaternization of QCS, a shift in the phase diagram was observed, whichcorrelated with the aggregate structure.Moreover, the kinetic process was obtained specifically for the initial stage, during which theHA complexes are immediately formed upon mixing. This process may ultimately determinethe final flocculation performance and the removal efficiency of HA in water treatment. Time-resolved small-angle X-ray scattering (TR-SAXS) combined with stopped-flow was employedto probe the early-stage complex formation over a timescale of milliseconds. This approachfacilitated the elucidation of the rate and efficacy with which HA can interact with diversecationic polyelectrolytes, including quaternized chitosan with varying degrees of chargedgroups and PDADMAC, which is 100% charged. By systematically varying the type of cationicpolyelectrolyte, the charge ratio between cPEs and humic acid, and additionally by adjustingthe pH value, comprehensive insight into the initial formation process and factors controllingthe final structures was obtained. This insight from colloid science is promising to optimize thewater treatment process in industrial settings.
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