NATURAL ORGANIC MATTER FRACTIONATION ALONG THE TREATMENT OF WATER FOR HUMAN CONSUMPTION

Abstract

The main objective of this study was to characterize the organic matter present in raw water and along the treatment process, as well as itsseasonal variation.A natural organic matter fractionation approach has been applied to Lever water treatment plant located in Douro River, in Oporto (Portugal). The process used was based on the sorption of dissolved organic matter in different types of ion exchange resins, DAX-8, DAX-4 and IRA-958, allowing its separation into four fractions: very hydrophobic acids (VHA), slightly hydrophobic acids (SHA), charged hydrophilic (CHA) and hydrophilic neutral (NEU). The dissolved organic carbon (DOC) determi nation was used to quantify dissolved organic matter. Samples werecollected monthly, during approximately one year, from raw water captured at the surface and under the bed of the river, and after each step of the treatment: pre-filtration in sand/anthrac ite filters, ozonation, coagulation/flocculation, counter current dissolved air flotation and filtration (CoCoDAFF) and chlorination. The NEU fraction showed a seasonal variation, with maximum values in autumn for the sampling points corresponding toraw water captured at the surface and under the bed of the river . It was usually the predominating fraction and did not show a significant decreasethroughout the treatment. Nevertheless their low concentration, the same occurred for the CHA and VHA fractions.There was an overalldecrease in the SHA fraction throughout the water treatment (especiallyafterCoCoDAFF and ozonation)as well as in theDOC . The TSUVA 254 values obtainedfor raw watergenerally variedbetween 2.0 and 4.0LmgC -1 m -1 and between 0.75and 1.78 LmgC -1 m -1 for treated water. It wa s observed a decrease of TSUVA values along the treatment,especially after ozonation. These results may contribute to a further optimization in the process of treating water for human consumption.