Acclimation of sludge-derived biofilms for effective removal of emerging contaminants: Impacts of inoculum source and carbon supplementation

Contaminants of emerging concern (CECs) have gathered significant public attention due to their widespread occurrence, high persistence, and increasing exposure potential. In this study, we used polyethylene biocarriers for acclimating biofilms from singular or combined activated sludges collected from three wastewater treatment plants (R, P, and L) over 5 month-long cycles. The acclimated biofilms achieved an average removal rate at 0.333, 0.313, and 0.185 week^-1 for N, N-diethyl-meta-toluamide (DEET), sulfamethoxazole (SMX), and carbamazepine (CBZ), respectively, when external carbon was supplemented, which were significantly higher (p < 0.05) than biofilms that did not receive external carbons. Metabolite screening revealed SMX transformation through ipso-hydroxylation and acetyl conjugation, while CBZ degradation could be initiated by epoxidation. Significant but slower degradation rates (0.024∼0.031 week^-1) were observed for aminotriazole (AMT), lidocaine (LDC), and trimethoprim (TMP), whereas atrazine (ATZ) exhibited minimal removal, highlighting its high recalcitrance. Biofilms acclimated from individual R and P sludges, with external carbon supplementation, attained the greatest removal efficiencies for 7 CECs. Multivariate statistical correlations (p < 0.05) identified potential degraders, including Sphingomonas and Zoogolea for AMT, Labrys and Koazkia for CBZ, and Asprobacter, unclassified Cyclobacteriaceae (ELB16-189) and Bryobacteraceae (Fen-178) for LDC. Abundance distribution of potential degraders among biofilms revealed that Sludge R favored the enrichment of key degraders for AMT, CBZ and LDC, while Sludge P was more conducive to acclimating CBZ degraders. This study advances our understanding of strategies in biofilm acclimation to improve CEC removal and provides insights into degradation pathways and associated microbial communities for future research.