Dual role of polypropylene composite filter as particle barrier and microbial incubator under point-of-use drinking...

Although polypropylene-based filters are traditionally regarded as essential pretreatment units in domestic drinking water systems, their actual effectiveness in reducing water quality risks remains poorly understood. This study evaluated the performance of fresh and aged household activated carbon-polypropylene composite filters (CPFs) in improving water quality and reducing microbial contamination under simulated usage conditions. All the tested filters, including fresh (P1) and aged (P2, P3) CPFs effectively removed free chlorine, but P1 caused insufficient microbial inactivation, with effluent bacterial counts (6 ×10 ³ CFU/mL) far exceeding tap water (∼10 CFU/mL). Aged filters showed lower microbial loads (2 ×10²∼7 ×10² CFU/mL) due to prolonged interaction with residual chlorine, yet both fresh and aged CPFs posed microbial risks. CPFs retained iron particles, stabilizing turbidity below 0.2 NTU and reducing total iron by 50%. Aged CPFs exhibited higher disinfection byproduct (DBP) levels (effluent: 51∼55 μg/L; internal: 99∼121 μg/L) than P1 (effluent: 16 μg/L; internal: 75 μg/L). Fresh CPFs initially removed 75% of DBPs, but efficiency dropped to 30% by day 9 due to fouling. Microbial analysis revealed CPFs enriched filter-adapted taxa, including 9.21% potential pathogens in P1, and supported viable but non-culturable microbes. Correlation analysis shows significant positive correlations between different DBPs and specific microbial species, indicating a close relationship between these microorganisms and the corresponding DBP levels. These findings highlight CPFs' dual role under chlorine-depleted, nutrient-rich conditions, emphasizing the need for advanced post-filtration treatment.