Online fluorescence spectroscopy for the real-time evaluation of the microbial quality of drinking water

J.P.R Sorensen,A Vivanco,M.J Ascott,D.C Gooddy,D.J Lapworth,D.S Read,C.M Rushworth,J Bucknall,K Herbert,I Karapanos,L.P Gumm,R.G Taylor

doi:10.1016/j.watres.2018.03.001

Abstract

We assessed the utility of online fluorescence spectroscopy for the real-time evaluation of the microbial quality of untreated drinking water. Online fluorimeters were installed on the raw water intake at four groundwater-derived UK public water supplies alongside existing turbidity sensors that are used to forewarn of the presence of microbial contamination in the water industry. The fluorimeters targeted fluorescent dissolved organic matter (DOM) peaks at excitation/emission wavelengths of 280/365 nm (tryptophan-like fluorescence, TLF) and 280/450 nm (humic-like fluorescence, HLF). Discrete samples were collected for Escherichia coli, total bacterial cell counts by flow cytometry, and laboratory-based fluorescence and absorbance. Both TLF and HLF were strongly correlated with E. coli (ρ = 0.71–0.77) and total bacterial cell concentrations (ρ = 0.73–0.76), whereas the correlations between turbidity and E. coli (ρ = 0.48) and total bacterial cell counts (ρ = 0.40) were much weaker. No clear TLF peak was observed at the sites and all apparent TLF was considered to be optical bleed-through from the neighbouring HLF peak. Therefore, a HLF fluorimeter alone would be sufficient to evaluate the microbial water quality at these sources. Fluorescent DOM was also influenced by site operations such as pump start-up and the precipitation of cations on the sensor windows. Online fluorescent DOM sensors are a better indicator of the microbial quality of untreated drinking water than turbidity and they have wide-ranging potential applications within the water industry.

Highlights

Enteric pathogens in drinking water pose a significant threat to public health globally (Baldursson and Karanis, 2011; Machdar et al, 2013; Reynolds et al, 2008)
Of particular interest is tryptophan-like fluorescence (TLF) at an excitation-emission peak of around 280/350 nm as it has been demonstrated to be positively correlated with BOD, COD and TOC (Cohen et al, 2014; Reynolds and Ahmad, 1997; Reynolds, 2002)
The aim of this study was to understand the utility of online fluorescence spectroscopy for the real-time evaluation of the microbial quality of raw drinking water at public supplies

Summary

Introduction

Enteric pathogens in drinking water pose a significant threat to public health globally (Baldursson and Karanis, 2011; Machdar et al, 2013; Reynolds et al, 2008). J.P.R. Sorensen et al / Water Research 137 (2018) 301e309 wastewater generally displays more intense DOM fluorescence than natural waters, especially at particular excitation/emission wavelength pairs (Baker, 2001; Baker and Inverarity, 2004; Carstea et al, 2016; Goldman et al, 2012; Lapworth et al, 2008; Reynolds and Ahmad, 1997; Roehrdanz et al, 2016). It has been shown that contaminated drinking water sources containing thermotolerant (faecal) coliforms (TTCs) have significantly higher TLF than those that are uncontaminated (Sorensen et al, 2015, 2016). There is a strong positive correlation between TLF intensity and TTC concentration in both field studies of drinking water (Baker et al, 2015; Sorensen et al, 2015, 2016) and controlled laboratory conditions (Fox et al, 2017)

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