Enhancing floc growth by oxidative and reductive modification of organic matter structure
File(s)
Accepted version
Author(s)
Zhu, Baofeng
Liu, Mengjie
Zhang, Kai
Graham, Nigel
Yu, Wenzheng
Type
Journal Article
Abstract
Coagulation is a critical process in drinking water treatment for removing contaminants, but its efficiency is challenged by complex natural organic matter (NOM) and emerging micropollutants. Conventional strategies (e.g., enhanced coagulation and novel coagulants) overlook the role of NOM characteristics in floc formation. Existing studies lack systematic evaluation of how chemical preconditioning (oxidation/reduction) modifies NOM functional groups and influences floc dynamics, particularly regarding molecular-scale mechanisms and water matrix effects. This study comparatively evaluates hypochlorite (NaClO), hydrogen peroxide (H₂O₂), and sodium borohydride (NaBH₄) pretreatments for NOM modification and their impacts on floc growth during coagulation. It was found that while NaClO (0.2–4 mg/L) reduced molecular weight and increased hydrophilicity, it consistently enhanced floc size (up to 44 %) by hydroxylating aromatic NOM. H₂O₂ exhibited a biphasic effect, and floc size improved at low doses (1 mg/L) but declined at high doses (>4 mg/L) due to excessive carboxyl group formation, inducing electrostatic repulsion. NaBH₄ (50–100 mg/L) promoted floc growth by reducing carbonyl to hydroxyl groups, though high doses (>100 mg/L) reduced efficacy due to borate interference. This work establishes molecular-level mechanisms for NOM-coagulant interactions, highlights the essential role of hydroxyl groups on floc formation, and provides a scientific basis for optimizing pretreatment-coagulation sequences tailored to specific water quality.
Date Issued
2026-03-01
Date Acceptance
2025-12-22
Citation
Water Research, 2026, 291
ISSN
0043-1354
Publisher
Elsevier
Journal / Book Title
Water Research
Volume
291
Copyright Statement
Copyright © 2025 Elsevier. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
License URL
Publication Status
Published
Article Number
125257
Date Publish Online
2025-12-22