Mechanism study on organic pollutant accumulation by iron-based particles in drinking water conditions

Discoloration events in drinking water distribution systems (DWDSs) caused by iron oxide particles have occurred worldwide, but the mechanism of organic pollutant accumulation by iron-based particles in DWDSs has not yet been fully recognized. Here, iron particle-dominated loose deposits were collected from a real DWDS through pipe flushing. Also, FeOOH-based particles, as an important component of deposits, were grown with various coexisting substances to further simulate the influence of structure on accumulation effects. Here, we found that the presence of cations, including Al3+ and Mn2+; phosphate anion; and organic pollutants, such as the disinfection byproducts (DBPs) and persistent organic pollutants (POPs) with trichloroacetic acid (TCA) and perfluorosulfonic acid (PFOA) as representatives, could influence the accumulation effects of FeOOH particles in DWDSs due to the structural transformation. The FeOOH particles grown with coexisting organic matter (FeOOH-TCA and FeOOH-PFOA) had a higher specific area and more -OH groups than other samples. With abundant contact sites due to their hairy urchinlike structures and rich surface oxygen-containing functional groups, the FeOOH-based particles had higher accumulation abilities for antibiotics, with FeOOH-TCA presenting the highest ability. The formation of Fe-O-C confirmed that the eOH groups in organics could bind with iron ions and guide hydrolysis to induce obvious structural transformation into a material with a higher specific area and more contact sites. Moreover, molecular dynamics (MD) simulations suggested that hydrogen bonding played an important role in this accumulation process. The results not only revealed the importance of focusing on the complex iron-based particles in DWDSs, but also showed previously unknown risks of DBPs and POPs, as such compounds may promote the accumulation effect of deposits.