New applications of fluorescence spectroscopy for monitoring drinking water disinfection and distribution

Licentiate thesis, 2017

The task of providing safe drinking water requires proper monitoring of water quality and treatment performance from source to tap. Accordingly, the demand for online monitoring is increasing both at treatment plants and within distribution networks. Some of the available techniques use correlations between the optical properties of dissolved organic matter (DOM), mainly absorbance, and other water quality parameters. Fluorescence spectroscopy is significantly more sensitive than absorbance and gives comprehensive information about the composition and concentration of organic matter, so has a strong potential for online monitoring applications. In this thesis, the application of fluorescence spectroscopy was investigated at two locations in the drinking water treatment system: the distribution network and the ultraviolet (UV) disinfection chambers. In the distribution network, the sensitivity of fluorescence to detect contamination caused by entrainment was compared to the sensitivity of other common water quality parameters including several trace elements and microbial indicator species abundances. Of these, fluorescence was the most sensitive tracer for distinguishing contamination from natural variation, followed by absorbance. The relationship between fluorescence and microbial regrowth was also examined, however, no correlation was observed. Following UV disinfection, the application of fluorescence as a proxy of the UV dose was examined. Fluorescence was sensitive enough to detect changes in the fluorescent fraction of organic matter due to UV irradiation at disinfection doses. A linear relationship was observed between UV dose and changes in humic-like fluorescence intestines at doses up to 350 mJ/cm2.