Quantity and quality of dissolved organic matter (DOM) in source water are critical factors affecting both the drinking water quality and operation of the water treatment process. As major water sources for many cities, deep reservoirs usually suffer seasonal thermal stratification, which has a significant influence on the fate and transport of many contaminants including iron, manganese, ammonia and DOM. This study focuses on the variation of properties and the fouling potential of DOM in a deep-source water reservoir during the thermal stratification period. Excitation-emission matrix (EEM) fluorescence spectra and ultraviolet absorption spectra were used to characterize the DOM. The results indicate that the quantity and quality of DOM vary with the water depth due to thermal stratification. The DOC of epilimnion is lower than that of the metalimnion and hypolimnion due to photochemical degradation. Moreover, organic matter released by phytoplankton, such as algae, play an important role in the DOM composition. Therefore, the DOM of the epilimnion exhibits a lower aromaticity, lower fluorescence intensities of Component 1 (i.e., fulvic-like substance) and Component 2 (i.e., humic-like substance), and higher fluorescence intensity of Component 3 (i.e., tryptophan-like substance). The DOM of the metalimnion is dominated by runoff input and therefore the concentration, aromaticity, and fluorescence intensities of Components 1 and 2 are higher. In terms of membrane fouling, total fouling caused by the DOM of the epilimnion is the largest, but its reversibility is better. The DOM of the metalimnion and hypolimnion results in lower total fouling but poor reversibility. The analysis of the fate of different fluorescence components during ultrafiltration suggests that the UF shows a relative high rejection rate for Component 3, which could be readily removed by backwash, whereas Component 1 and Component 2 retained by the membrane are difficult to be removed by backwash.
Keywords: UV absorbance; dissolved organic matter (DOM); excitation-emission matrix (EEM) fluorescence spectra; membrane fouling; stratified reservoir.