Start-Up Manganese Imprinting Delays Breakthrough of Representative PFAS in Biological Activated Carbon through Persistent Bio-Carbon Interfacial Conditioning.

Per- and polyfluoroalkyl substances (PFAS) are difficult to control in drinking-water treatment because activated-carbon capacity declines under continuous loading and competition from natural organic matter (NOM). Here, we show that transient manganese (Mn) addition during biological activated carbon (BAC) start-up imprints a persistent bio-carbon interface that sustains NOM removal and delays PFAS breakthrough without continuous Mn input. Replicated BAC columns were operated for 400 days, with Mn supplied only during the first 60 days. Mn-imprinted BAC maintained >80% retention of 100 ng/L perfluorooctanoic acid (PFOA), whereas Mn-free BAC declined to ∼30%. After replacing PFOA with 100 ng/L perfluorooctanesulfonate (PFOS), Mn-imprinted BAC maintained 60-70% PFOS retention, compared with 30-40% in Mn-free BAC. Surface characterization and density functional theory indicated persistent Mn-O surface environments, plausibly including C-O-Mn motifs, which redistributed interfacial charge and stabilized anionic PFAS headgroups. In parallel, metagenomic, functional gene, and metabolomic analyses showed that Mn imprinting promoted a more active, extracellular polymeric substances (EPS)-rich, and functionally redundant biofilm with enhanced NOM-processing and Mn-oxidation potential. Microbial inhibition eliminated much of the retention benefit, while fluorine mass balance showed no measurable defluorination. Thus, start-up Mn imprinting improves BAC resilience by enhancing PFAS retention and delaying breakthrough.