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Abstract
Over recent decades, researchers have highlighted increasing dissolved organic carbon concentrations in fresh water sources. These long-term increases, along with seasonal variations and high organic matter (OM) surges during extreme weather events, are presenting challenges during drinking water treatment operation, and particularly process control and optimisation, with respect to ensuring that drinking water quality guidelines are met. It is difficult to monitor OM concentrations and character during treatment processes due to its complexity. Fluorescence spectroscopy has been shown to be a promising technique in this regard; furthermore, it has the potential to be an online monitoring tool.
In this study, fluorescence excitation emission matrices (EEMs) were acquired for samples collected from all treatment stages of five drinking water treatment plants (WTPs) situated in diverse locations from subtropical to temperate climatic regions. The WTPs incorporated various water sources, treatment processes and OM removal efficiencies. Despite these differences, four common fluorescence components were identified using parallel factor analysis (PARAFAC) and used for characterisation of OM and assessment of OM treatability. Fluorescence component ratios showed site-specific statistically significant correlations with OM removal, which were in contrast to correlations between specific UV absorbance at 254 nm and OM removal that were not statistically significant. Similar fluorescence PARAFAC components were identified during bench scale experiments investigating OM removal using powdered activated carbon, coagulation and sedimentation water treatment processes that were conducted on two source waters with contrasting OM treatability. These components and their ratios were shown to be useful for monitoring of OM removal and treatment process optimisation. Based on the identified fluorescence PARAFAC components, four optical locations were selected in order to move towards single wavelength online OM monitoring. An on-line fluorescence monitoring protocol was developed and successfully applied using three commercially available fluorescence probes at two drinking water treatment plants with contrasting source water quality and different treatment techniques. Overall, it was demonstrated that it is possible to monitor OM during drinking water treatment real-time in situ at strategic locations using standardised monitoring protocol that can be applied universally.