Molecular-Level\nExplanation of AOM Removal by a Composite\nCoagulant Based on the Subdivision of Organic Components

Algal organic matter (AOM), comprising intracellular\norganic matter\n(IOM) and extracellular organic matter (EOM), poses a significant\nchallenge to drinking water safety. Coagulation serves as an effective\nmethod for removing algae, and investigating the binding sites of\ncoagulant hydrolyzates is crucial for comprehending the coagulation\nmechanism. In this study, a novel polyferric titanium sulfate (PFTS)\ncomposite coagulant was prepared and used to remove AOM. Characterization\ntechniques, including Fourier infrared (FTIR), X-ray photoelectron\nspectroscopy (XPS), hydrolysis polymerization curves, and chemical\nspecies analysis were utilized to identify the hydrolyzates of PFTS.\nThe results revealed the formation of Fe–Ti copolymers through\nthe interaction between Fe hydroxyl and Ti hydroxyl, facilitated by\na Fe–O–Ti bond. Under optimal coagulation conditions\n(50 mg/L dosage at neutral pH), PFTS demonstrated superior performance\nin treating EOM and IOM compared to PFS and PTS, achieving significant\nDOC removal efficiencies of 46.69% and 56.8%, respectively. Furthermore,\nthe removal characteristics of organics were investigated at the molecular\nlevel using Fourier transformation cyclotron resonance mass spectrometry\n(FT-ICR MS). It was found that organic compounds with unsaturated\n(H/C < 1.0) and oxidized (O/C > 0.5) substances containing carboxyl\ngroups in AOM could be preferentially removed by PFTS for the carboxyl\ngroup demonstrate a higher affinity to Fe and Ti hydroxyl formed in\nPFTS coagulation. XPS and water contact angle analysis were conducted\nto gain deeper insights into the interaction between the hydrolyzates\nof PFTS and AOM. The findings demonstrated that Fe–Ti hydrolyzates\ncould bind with EOM and IOM by forming coordination bonds and H–O···O\nand H–O···N hydrogen bonds with its −COOH,\n−NH<sub>2</sub>, and −OH groups through bonding reactions.\nThis study highlights the potential of composite coagulants as alternatives\nto conventional coagulants for the purification of algae-laden water.