Ti-containing NPs in raw water and their removal with conventional treatments in four water treatment plants in Taiwan

The ingestion of Ti-containing nanoparticles from drinking water has emerged as a concern in recent years. This study therefore aimed to characterize Ti-containing nanoparticles in water samples collected from four water treatment plants in Taiwan and to explore the challenges associated with measuring them at low levels using single particle-inductively coupled plasma mass spectrometry. Additionally, the study sought to identify the most effective processes for the removal of Ti-containing nanoparticles. For each water treatment plant, two water samples were collected from raw water, sedimentation effluent, filtration effluent, and finished water, respectively. Results revealed that Ti-containing nanoparticles in raw water, with levels at 8.69 μg/L and 296.8 × 10³ particles/L, were removed by approximately 35% and 98%, respectively, in terms of mass concentration and particle number concentration, primarily through flocculation and sedimentation processes. The largest most frequent nanoparticle size in raw water (112.0 ± 2.8 nm) was effectively reduced to 62.0 ± 0.7 nm in finished water, while nanoparticles in the size range of 50–70 nm showed limited changes. Anthracite was identified as a necessary component in the filter beds to further improve removal efficiency at the filtration unit. Moreover, the most frequent sizes of Ti-containing nanoparticles were found to be influenced by salinity. Insights into the challenges associated with measuring low-level Ti-containing nanoparticles in aqueous samples provide valuable information for future research and management of water treatment processes, thereby safeguarding human health.