Impact of adaptation time on lincomycin removal in riverbank filtration: A long-term sand column study

Riverbank filtration (RBF) is an effective pretreatment technology for drinking water, removing organic micropollutants (OMPs) mainly through biodegradation. Despite documented improvements in OMP removal with extended adaptation time, the mechanisms remain poorly understood. This study assessed the removal of 128 OMPs over 82 d in a simulated RBF system, identified those with improved removal, and analyzed their properties. Additionally, microbial community shifts after 400 d of lincomycin exposure were studied to understand the underlying mechanisms. We found that the removal efficiencies of 24 OMPs, including lincomycin and fluconazole, improved by 3-77 % over 82 d while being positively correlated with the presence of tertiary amides and secondary sulfonamides. Lincomycin removal efficiency rose from 20 % to 95 % over 68 days and stayed high. We identified eight potential degradation products of lincomycin, occurring primarily via hydroxylation, N-demethylation, and amide hydrolysis. Additionally, lincomycin notably increased the abundances of specific antibiotic-resistant bacteria (e.g., Thiobacillus, 8.3-fold) and ammonia-oxidizing archaea (e.g., Nitrososphaera, 46.8-fold). The β-lactam resistance gene in Thiobacillus and the amoA gene in Nitrososphaera may enhance lincomycin's removal by promoting its hydrolysis and hydroxylation. Overall, this study provides insights into OMP biodegradation mechanisms and the impact of ng/L levels of lincomycin on microbial communities.