Baoyou Shi

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.

Activated carbons (ACs) with various pore structures were prepared via steam activation, the most commercially viable method, and their adsorption isotherms and kinetics were evaluated for PFOA, PFOS, and GenX in ultrapure water and water containing dissolved organic matter (DOM). Results showed that moderate overactivation developed more mesopores, improving PFAS adsorption in both ultrapure and DOM-rich waters, likely due to the accommodation of PFAS aggregates requiring larger pore volume. Pearson correlation analysis confirmed that mesopore volume significantly correlated with adsorption capacity and kinetics. The overactivated mesoporous AC exhibited superior adsorption of PFAS compared to lightly activated microporous AC, showing nearly doubled adsorption capacities and faster kinetics for PFOA and PFOS, despite similar surface areas and total pore volumes, and its performance was less affected by background DOM molecular weight. Pore size distribution indicated that mesopores were the primary adsorption sites, and density functional theory calculations proved that the adsorption energy for PFAS aggregates in mesopores was much lower than in other pores. Secondary activation of commercial Calgon F400 also enhanced trace PFOA/PFOS removal (∼200 ng/L) in real water. This study clarifies the critical role of mesopores in PFAS adsorption and provides a feasible strategy for designing high-performance AC adsorbents.

The destruction of per- and polyfluoroalkyl substances (PFAS) poses a formidable global environmental challenge owing to their extreme persistence and resistance to degradation. Here, we report that commercial granular activated carbon (GAC) significantly accelerates the degradation kinetics of perfluorocarboxylic acids (PFCAs) in dimethyl sulfoxide (DMSO), enhancing the degradation rate by 70% and the defluorination efficiency by 153% compared to GAC-free controls. In contrast, other adsorbents such as molecular sieves with varied pore structures showed no catalytic activity. Comparative experiments using modified carbon materials and resins functionalized with different groups identified oxygen-containing surface functional groups, specifically carboxyl moieties, as the key catalytic sites. Density functional theory (DFT) calculations showed that hydrogen-bonding interactions between surface carboxyl groups and pentadecafluorooctanoic acid (PFOA) lower the activation Gibbs free energy for decarboxylation by approximately 5.3-fold relative to the uncatalyzed pathway. This work reveals a new catalytic role of commercial GAC and suggests a practical pathway for simultaneous PFAS destruction and adsorbent regeneration under substantially milder conditions than conventional thermal treatment.

Stringent control of Mn is critical for drinking water safety. However, conventional rapid sand filters exhibit slow biological maturation for Mn(II) removal, limiting their performance in engineered Mn(II) removal. This study examined the effectiveness of partially replacing sand with natural manganese ore (NMO) to enhance Mn(II) removal and elucidated the underlying mechanisms. The results showed that replacing only 1/8 of sand with NMO enabled consistently effective Mn(II) removal (residual x-mediated chemical processes rapidly diminished, after which MnO_x-enhanced biological processes promptly took over. Compared with sand columns, 1/8 NMO columns biologically matured nearly 100 days earlier, and biomass on the rough, porous MnO_x surface was 1-2 orders of magnitude higher than that on sand. Although NMO partly altered microbial communities, the relative abundance of Mn(II)-oxidizing bacteria did not increase; the larger absolute biofilm biomass primarily drove sustained efficient Mn(II) removal. These findings highlighted the important but previously overlooked role of MnO_x in promoting biofilm accumulation and accelerating the maturation of biological Mn(II) removal systems and provided a practical and cost-effective upgrade for conventional sand filtration.