Unveiling the mechanism and driving factors of pharmaceutical and personal care product (PPCP) removal in wastewater treatment plants.

Wastewater treatment plants (WWTPs) are primary point sources of pharmaceuticals and personal care products (PPCPs) entering the environment; however, few studies have systematically elucidated the PPCP removal mechanism in WWTPs. In this study, we conducted two composite sampling campaigns, collecting water and sludge samples from each treatment stage of four secondary or tertiary WWTPs with various processes. Our goal was to identify the mechanisms and driving factors behind the removal of 30 common PPCPs. The average removal efficiency of all PPCPs was 62.57 %, with significant variations (-308.03 %-91.03 %) among individual PPCPs. The contribution of sludge adsorption, biodegradation and chemical degradation to the removal of 30 PPCPs was quantified. The average biodegradation efficiency of sulfonamides was 44.90 %, but reconversion of chelate products to the sulfonamides after chemical treatment (UV) was the main reason for their low removal efficiency (about 30 %). Base dissociation constant (pKb) and logKow were used to evaluate the contribution of charge interactions and hydrophobic partitioning to the adsorption capacity of PPCPs for the first time. For PPCPs that could ionize into cations, higher pKb increased adsorption capacity, whereas for other PPCPs logKd (distribution coefficient) and logKow showed a significant positive correlation. The biodegradation of sulfonamides was positively correlated with their solubility. The presence of hydroxyl and carboxyl groups promoted microbial degradation of non-antibiotic compounds. This study reveals the universal mechanisms and driving factors behind PPCP removal in WWTPs, providing insights to guide the targeted optimization of treatment processes for PPCP removal.