The evaluation of drinking water treatment performed with HPSEC

Abstract

Characterization of natural organic matter (NOM) removal in the drinking-water treatment train can give valuable information, while optimizing the treatment process. In this study, high-performance size-exclusion chromatography (HPSEC) was applied to evaluate the relative changes of molecular size distribution (MSD) of NOM in different treatment steps. The full-scale treatment train consisting of coagulation, flocculation, sedimentation, sand filtration, and ozonation was studied in Pitkäkoski water treatment plant, Helsinki, Finland. Furthermore, in a pilot-scale process, the effect of the subsequent two-step granular activated carbon (GAC) filtration on MSD was evaluated. Chemical treatment followed by sand filtration decreased NOM efficiently. The fraction of the largest molecules disappeared completely, and the next two fractions were reduced by 92% and 85%, respectively. No significant changes in the smallest molecular fractions were observed. Ozonation shifted MSD slightly towards smaller molecules, depending on the applied ozone dose. However, the increase of assimilable organic carbon (AOC) could not be related to the certain fraction of NOM. On the contrary, MSD did not change considerably during two-step GAC-filtration, except in the fresh GAC columns, where the adsorption of large molecules was slower than with smaller ones. Conversely, the smallest molecules seemed to escape from the exhausted GAC filter. Finally, significant correlations were established between HPSEC results, KMnO 4 number, UV absorbance (254 nm), chlorine demand, and TOC results.