Abstract

In this paper we comprehensively characterized particles in drinkingwater originating from a lake water source. We focused on particles smaller than a few hundred nm. Several analytical techniques were applied to obtain information on number concentration, size distribution, morphology and chemicalcomposition of the particles. Morphological information was obtained by atomic force microscopy (AFM) analysis. Two types of particles, spherical aggregates up to a few tens of nm and elongated fibers were identified. Similar structures were also observed in transmission electron microscope (TEM) images.

A size distribution of the particles was obtained by applying image analysis (IA) tools on the TEM images. IA results showed an exponential increase of the particlenumber concentration down to 40 nm, which is the lower detection limit of our setup. The total number of particles down to 10 nm and the average particle diameter were determined with the laser-induced breakdown detection (LIBD) method. The results were in good agreement with the TEM-IA data and showed a total number concentration of roughly 108 particles/mL in the purified water. The carbon of the particles was investigated with scanning transmission X-ray microscopy (STXM), which revealed that most particles were organic matter; the C-1s spectra were typical for dissolved organic matter.

The methods were applied to characterize the particles from two different drinkingwaters treated with different methods (conventional vs. ultrafiltration (cut-off 100 kDa)). The results showed that the particlenumber density following ultrafiltration was lower by a factor of 5–10, compared to conventional treatment. However, the average particle diameter in the finished water of both treatment trains was roughly the same.