Particle and DBP removal efficiency and toxicity evaluation of polypropylene cotton filters in household drinking water purification systems

Abstract

Polypropylene cotton filters (PCFs) are traditionally considered an essential pretreatment unit for coarse-particle removal in household water purification systems. However, the actual roles of PCFs in controlling drinking water quality risks, especially in discolored water, have not been well understood, and the particulate matter collected on PCFs has not been well-studied. In this study, the detailed characterization of a used PCF found that many types of iron particles, which usually are dominant in drinking water distribution systems, including magnetite, hematite, maghemite, goethite, and lepidocrocite, were mainly captured by the outer-most layer (20% of the total thickness) of PCF. MTT tests using human hepatocytes showed that the iron particles captured by the PCF exhibited obvious cytotoxicity, and the particle toxicity decreased from the outer layer to the inner layer, indicating that PCFs can efficiently reduce iron-particle-associated toxicity risk. In addition, the PCF had a significant ability for the enrichment of trace organic pollutants (e.g. perfluorooctanoic acid), which would further reduce the water quality risks. Furthermore, some common opportunistic microbial pathogen species, including Acinetobacter, Mycobacteria, and Pseudomonas, could be intercepted effectively by the PCF. Filtration experiments using a new PCF showed that PCF was effective not only in particle removal (96.1–99.8%) but also in disinfection by-product (DBP) removal (7.9–65.9%). Above all, as a household water treatment unit, PCFs not only protect the purification units but can also have many previously unrecognized functions in water quality risk control.