Characteristics of dissolved organic matter in a water purification plant and distribution pipes

Dissolved organic matter (DOM) needs to be characterized todetermine the ability of a water treatment unit to reduce organic matter andits relationship to the levels of chlorine required for disinfection. Weinvestigated water quality parameters, including DOM, in a waterpurification plant and distribution pipes located in central Japan. Thedissolved organic carbon (DOC) concentration decreased from 0.73 mg/Lin raw water to 0.50 mg/L in purified water by conventional treatmentprocesses. The DOC of purified water decreased slightly in the pipesdownstream of the plant. The three-dimensional excitation-emission matrixfluorescence spectra showed some specific peaks for humic-like substancesand protein-like substances in all water samples, and the compositions ofDOM in purified water were close to those in raw water. However, therewas a peak of protein-like substances in purified and returned water, whichwas not observed for raw water. The fluorescence intensities of humic-likesubstances in purified water decreased downstream of the plant, while thefluorescence intensities of protein-like substances increased in the pipes. The measured molecular weight distributions of DOM in water presentedsome specific peaks, and DOM with a smaller molecular weight was noteasily removed by water treatment processes. There were positiverelationships between decreases in the intensities of some peaks andresidual chlorine decay