Towards a Molecular-Scale Theory for the Removal of Natural Organic Matter by Coagulation with Trivalent Metals

Coagulation is one of the most common treatment processes for the removal of contaminants from water, representing ‘the first line of defence’ for drinking water safety. However, the macroscopic and descriptive theories of trivalent metal-based coagulation have limited the optimization of its performance in the removal of natural organic matter species, which are major precursors of hazardous disinfection by-products. In this study, we have extended the coagulation theory to the functional group level, highlighting the fundamental importance of η-H 2 O and η-OH groups on aluminium precipitates, and finding that the selectivity for natural organic matter during coagulation is determined by their functional groups. Drawing upon the fundamental characteristics of coagulants and organic substances, this study has elucidated their behaviour during the coagulation process and offers valuable theoretical insights to guide future applications of coagulation in practical settings.