Distribution of dissolved organic matter fractions along several stages of a drinking water treatment plant

Abstract The present study was conducted to track dissolved organic carbon (DOC) through the different stages of a drinking water treatment plant that includes a conventional treatment CT (coagulation/flocculation, sedimentation and sand filtration) and two parallel advanced treatments consisting of ozonation plus activated carbon filtration (AT1) and ultrafiltration (UF) and reverse osmosis (RO) (AT2), respectively. Fractionation of DOC was performed by high-performance size exclusion chromatography (HPSEC), whereby DOC fractions are separated according to their molecular weight. Results demonstrated that the dominant fraction in the raw feed water was constituted by humic substances (HS) (28–54%), followed by the fractions building blocks (BB) and low molecular weight neutrals (LMWN) (20–25%). The fraction with highest molecular weight constituted by biopolymers (BP) was found in the range 4–8%. These fractions exhibited different treatability along the treatment units. High molecular weight compounds (fractions BP and HS) were more effectively removed by CT than low molecular weight compounds (fractions BB and LMWN), which were better removed by AT1 and AT2 than CT. Differences in DOC fractions removal were also observed between AT1 and AT2. The passage through AT1 led to a decrease of BP and HS during ozonation, in opposition to BB and LMWN, which were removed to a greater extent during GAC filtration. In AT2, BP was removed by UF and RO, while HS, BB and LMWN were marginally removed by UF but largely by RO. Backwash stream water from UF membranes was also analysed to provide insight into the fouling reversibility of DOC fractions.