Hydrophobicity and molecular size distribution of unknown halogenated disinfection byproducts in drinking water

摘要

The analysis of total organic halogen (TOX) in drinking water indicates that a substantial amount of the TOX cannot be accounted for by known specific disinfection byproducts (DBPs). The primary aim of the research was to characterize the hydrophobicity and molecular size distribution of the unknown halogenated DBPs using XAD resins and ultrafiltration membranes. The impact of membrane rejection on the size analysis of unknown TOX was also investigated using chlorinated fulvic acid. Six finished waters from different locations and treatment processes were collected and fractionated into various hydrophobicity and molecular size groups. The results indicate that most unknown TOX is in the size range between 0.5 kDa and 10 kDa, but it can have a wide spectrum of hydrophobicites. Ultrafiltration membranes were shown to reject a significant fraction of DBPs with molecular weight (MW) lower than the membrane cutoffs. Flushing with deionized water was effective in removing these low MW compounds from the ultrafiltration cell. A significant reduction in the size distribution of unknown TOX resulted when low MW DBPs are flushed out of the cell (comparing with classic parallel ultrafiltration). Coagulation of fulvic acid can significantly reduce the size distribution of UTOX formed by chlorine.