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Fluorescence Sensors for Early Detection of Nitrification in Drinking Water Distribution Systems – Interference Corrections (Abstract)
Citation:
Do, T., A. Pifer, W. Zhang, Z. Chowdhury, D. Wahman, AND J. Fairey. Fluorescence Sensors for Early Detection of Nitrification in Drinking Water Distribution Systems – Interference Corrections (Abstract). Presented at 2017 AWWA WQTC, Portland, OR, November 12 - 16, 2017.
Impact/Purpose:
To improve nitrification detection in chloraminated DWDSs, we seek to develop a real-time fluorescence-based sensor system to detect the early onset of nitrification events. The guiding hypothesis is that soluble microbial products (SMPs) specific to nitrifying bacteria produce unique fluorescence signals that can be detected in early nitrification stages, before changes in pH or inorganic nitrogen.
Description:
Nitrification event detection in chloraminated drinking water distribution systems (DWDSs) remains an ongoing challenge for many drinking water utilities, including Dallas Water Utilities (DWU) and the City of Houston (CoH). Each year, these utilities experience nitrification events that necessitate extensive flushing, resulting in finished water loss of billions of gallons. Biological techniques used to quantify the nitrifying bacteria activity are impractical for real-time monitoring because they require significant laboratory efforts and/or lengthy incubation times. At present, DWU and CoH regularly rely on physicochemical parameters, including total chlorine, monochloramine, free ammonia, nitrite, and nitrate concentrations as nitrification indicators, but these metrics lack specificity to nitrifying bacteria. To improve nitrification detection in chloraminated DWDSs, we seek to develop a real-time fluorescence-based sensor system to detect the early onset of nitrification events. The guiding hypothesis is that soluble microbial products (SMPs) specific to nitrifying bacteria produce unique fluorescence signals that can be detected in early nitrification stages, before changes in pH or inorganic nitrogen. Preliminary data indicates that fluorescence-based metrics have the sensitivity to detect these SMPs, but finished drinking water is a complex matrix, and water treatment chemicals, natural organic matter, and pipe corrosion products have the potential to interfere with fluorescence measurements. In this poster presentation, we will focus on assessing and correcting potential interferences such as those from monochloramine, pH, iron, nitrite, nitrate, and humic substances using titration-based methods. Sample waters for these studies include reconstituted dissolved organic matters (DOM) from the Ohio River and effluents from ongoing biofilm annular reactor (BAR) experiments at various nitrification stages. Benchtop fluorescence excitation−emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) were used to assess interference impacts. Experiments using a tryptophan sensor (Excitation/Emission of 285/350 nm) and tryptophan-spiked BAR effluent samples indicates that interference corrections are needed to account for shifts in pH, but changes in nitrite and nitrate are minimal over the typical concentration ranges in nitrification. However, the interference amount may depend on the background water’s composition, which is the subject of ongoing work to be completed in October 2017. This work will inform interference correction algorithm development to be integrated into fluorescence sensor packages for full-scale testing and validation in the DWU and CoH systems. Findings from this research could be leveraged to identify nitrification events in their early stages, facilitating proactive interventions and decreasing nitrification episode severity and frequency and water loss due to flushing.