ABSTRACT This study analyzes widely used dose‐response (DR) models from potable reuse quantitative microbial risk assessments (QMRAs) to identify the low‐dose ranges where the log 10 ‐transformed probability of infection and pathogen dose exhibit a linear relationship. Target pathogens include norovirus, adenovirus, enterovirus, Cryptosporidium , and Giardia . This study (i) defines the low‐dose linear range for each DR model, (ii) extracts slope and intercept parameters via regression, and (iii) shows that municipal drinking water risk thresholds fall within these ranges. This promotes low‐dose risk estimation transparency, reproducibility, and accessibility for utility decision making, regardless of the underlying complexity of the DR model. Also, this study shows that within the low‐dose ranges relevant to potable reuse, commonly used DR models exhibit linear relationships with a slope of ~1. Therefore, each 10‐fold reduction in pathogen concentration, equivalent to one log reduction value (LRV), reduces risk by a corresponding order of magnitude. Finally, the outputs from the various DR models are separated by relatively constant risk differentials, thereby reducing the need for complex DR‐based sensitivity analyses when conducting potable reuse QMRAs.
ABSTRACT This study identified per‐ and polyfluoroalkyl substances (PFAS) surrogates to benchmark granular activated carbons (GACs) and ion‐exchange resins (IXRs) for drinking water treatment. Three GACs and two IXRs were evaluated using isotherm, kinetic, and rapid small‐scale column tests with 16 PFAS (C3–C8) across five classes. IXRs outperformed GACs in adsorption affinity (Freundlich constant, K F = 50.0 vs. 11.8), maximum adsorption capacity (qmax = 116.3 vs. 30.0 μg/g), and kinetics (pseudo‐first‐order kinetic constant, k1 = 0.0019 vs. 0.0008 min −1 ) due to combined hydrophobic and electrostatic interactions. IXRs exhibited substantially greater PFAS adsorption, with saturation occurring beyond ~130,000 BVs, compared with < 40,000 BVs for GACs. PFBA exhibited the earliest breakthrough; PFOA also broke through early among regulated PFAS. Average BV50 followed FASAs>FTSAs>PFSAs>>PFECAs>PFCAs for GACs and PFSAs>FASAs>PFECAs≈FTSAs>PFCAs for IXRs. Elevated DOC reduced GAC BV50 by 17% but had < 8% impact on IXRs. Inorganic anions reduced IXR BV50 by up to 52%.
ABSTRACT Opportunistic pathogens (OPs), such as Pseudomonas aeruginosa , can form biofilms and proliferate in drinking water distribution systems (DWDS) and building premise plumbing even in the presence of a disinfectant residual and are responsible for the largest number of deaths attributable to waterborne disease in the United States. There is a need for strategies to prevent biofilm formation and therefore the sustained occurrence of OPs throughout DWDS. This study demonstrates how UV LED disinfection (282 nm, 50 mJ/cm 2 ) before entering a distribution system or at a building's point‐of‐entry can delay the start of detectable biofilm formation for up to 6 days and significantly reduce the concentration of biofilm‐bound cells for up to and beyond 8 days compared to untreated controls. Biofilm growth after UV LED disinfection was evaluated on different materials (PTFE, CPVC, and Cu) and under different carbon nutrient conditions (19 mg/L TOC, 100 μg/L C, 250 μg/L C). PTFE supported the highest biofilm growth, followed by CPVC, while Cu supported the least. UV pre‐treatment reduced downstream biofilm formation by 0.33–2.42 log CFU/coupon (53.0%–99.6%) on CPVC surfaces over 5–8 days, with more realistic drinking water carbon conditions (100 or 250 μg/L C) increasing efficacy compared to heightened carbon conditions (19 mg/L TOC). These results inform how UV LEDs could be implemented within drinking water infrastructure to aid in biofilm and OP control.
ABSTRACT Activated carbon is expected to be widely applied to meet perfluorooctanoic acid (PFOA) and perfluorooctanoic sulfonic acid (PFOS) maximum contaminant levels (MCL) of 4 ng/L in drinking water. Theoretical dose ratio relationships suggest powdered activated carbon (PAC) should become more favorable than granular activated carbon (GAC) as removal requirements decrease. Accordingly, PAC and GAC were evaluated at bench‐scale under realistic conditions across six different public water systems using surface water as their source water. Observed trends generally followed an increase in PAC favorability as removal requirements decreased, but not as exaggerated as theory suggested. A linear relationship developed between common PAC and GAC products identified an inflection point at ~43% PFOA and PFOS removal and was used to develop adsorbent cost relationships based on varying their relative unit costs. Non‐cost factors were also presented that may influence adsorbent selection more than their relative doses.
