Formation pathway of disinfection by-products of lignin monomers in raw water during disinfection

In this study, the dissolved organic matter (DOM) profiles of water samples from a water source in northeastern China were analyzed by high-resolution mass spectrometry (HRMS), and its changes after chlorination were investigated. The results showed that lignin substances accounted for a significant proportion in DOM and chlorinated products and were the main precursors of disinfection by-products (DBPs). During disinfection, macromolecular DOM was transformed into small molecules, and lignin substances have the most obvious and complex changes in reaction. Two lignin monomers 4-propylphenol (4PP) and 4-propylguaiacol (4PG) were used as model compounds to study their reaction kinetics and degradation pathways during disinfection. The degradation of both lignin monomers conformed to pseudo -first-order reaction kinetics, and the reaction rate constant of 4PG was higher than that of 4PP. The effects of chlorine dosage, pH and temperature on the degradation reaction kinetics of two lignin monomers were investigated. The degradation rates of 4PP and 4PG increased with increasing chlorine dosage, pH and temperature. The two monomers showed similar properties in the chlorination degradation process, and generated multiple intermediates, which were mainly transformed into small molecules by chlorine electrophilic substitution and nucleophilic substitution, and further generated DBPs.