Evaluation of Select Sensors for Real-Time Monitoring of Escherichia coli in Water Distribution Systems

Abstract

This study evaluated real-time sensing of Escherichia coli as a microbial contaminant in water distribution systems. Most sensors responded to increased E. coli concentrations, showing that select sensors can detect microbial water quality changes and be utilized as part of a contaminant warning system.Monitoring water distribution systems (DSs) for a microbial intrusion has been a challenge for water utilities. Many contaminants that can cause degradation in the water quality in DSs are not monitored, and contamination events are difficult to detect due to the low frequency of required samplings (6). As a consequence, DSs are relatively unprotected and vulnerable to intentional, natural, or accidental contamination from microbial agents (5). Therefore, there is a need for real-time monitoring to recognize water quality disturbances. To date there are a limited number of studies that have evaluated the use of commercial sensors for real-time monitoring of DSs, and even fewer that demonstrate how sensors respond to microbial contaminants. The objective of this study was to evaluate the potential of multiple water quality sensors for real-time monitoring of E. coli as a surrogate for microbial contamination.At the University of Arizona Real Time Monitoring Laboratory, water is delivered by the City of Tucson Water public utility. Deionized (DI) water as a control or prefiltered tap water (1-m pore size) was used during experiments, and a baseline output from the sensors was established. Sensors were arranged in parallel and challenged with two or more replicates of E. coli (ATCC 15597) at a final concentration of 10 3 , 10 4 , 10 5 , or 10 6 CFU/ml. The experiments used late-log-phase E. coli suspended in either tryptic soy broth (TSB) or phosphate-buffered saline (Sigma catalog no. P3813), termed "washed" (centrifuged three times at 4,000 rpm for 25 min). Water samples were obtained throughout the injection to confirm cultural analysis (by dilution, plating, and incubating at 37°C for 24 h on tryptic soy agar [BD catalog no. 236920]) or total cell analysis (by acridine orange direct count [AODC] [4]). A separate set of experiments neutralized the chlorine residual to allow for determination of the E. coli concentrations.Sensors evaluated included the Hach GuardianBlue event detection system, the BioSentry technology, the S::CAN Spectrolyser technology, and the GE 5310 online total organic carbon (TOC) unit. The BioSentry was the only sensor with the potential to detect microbial contaminants (categorizing particulates as rods, spores, protozoa, and unknown) and therefore was also evaluated to determine if it could differentiate turbidity-causing particulates from E. coli. E. coli at 10 4 and 10 5 CFU/ml with the addition of 0.3 nephelometric turbidity units (NTU) (Ricca Chemical catalog no. 8830-32) was evaluated for any increase in BioSentry response above the actual E. coli concentration due to the turbidity added to DI water. Most parameters analyzed in this study exhibited an increase in response to an inc...

Evaluation of Real-Time Water Quality Sensors for the Detection of Intentional Bacterial Spore Contamination of Potable Water

“…These data suggest that BioSentry had difficulty distinguishing the mixture of cells and spores, and therefore classified more of them into the unknown category. Our results agree with Miles et al [5] who investigated the effects of turbidity to determine whether the BioSentry could Other comparisons can be made between different sensor outputs for Total Organic Carbon (TOC) following the addition of spores to DI and filtered tap water. Multiple TOC and DOC measurements are provided by the real-time data acquired from the HACH and the S::CAN sensors.…”

“…However, despite the development of a number of laboratory based sensors for the detection of Bacillus spores, it is uncommon for these devices to operate in an on-line or real-time mode within water samples. the use of commercial water quality sensors for real-time monitoring in distribution systems [4,5,10,[12][13][14]. These studies that evaluated commercial sensors in a distribution system show that the magnitude of the response depended on the sensor's ability to detect the contaminant, and the concentration of the contaminate itself.…”

“…However, only a few published studies demonstrate how sensors respond to microbial contaminants in real-time, which highlights the challenge for the detection of microbial intrusion events. The great majority of commercial sensors measure chemical parameters within drinking water; but in contrast, there are only a few available sensors that allow for the detection of microorganisms in real time [5,15]. This study was successful in evaluating water quality sensors when B. thuringiensis was introduced into water within a distribution system.…”

Real-Time Online Monitoring for Assessing Removal of Bacteria by Reverse Osmosis

“…Many commercial devices are capable of detecting bacteriological cells within a short analysis time (every 5 min to several hours) . Among them, flow cytometric bacterial cell counters combined with general nucleic acid staining make up an emerging technology capable of rapidly counting total bacterial cells. , In recent years, several near real-time or real-time bacteriological sensing technologies (e.g., BioSentry sensor) have been evaluated for relatively clean waters, including drinking water . Nevertheless, to date, real-time monitoring techniques have not been fully established with respect to potable reuse because of limitations with availability and adaptability in analyzing treated wastewater.…”

Potential and limitations of modern equipment for real time control of urban wastewater systems

“…While increasingly quick methods are under development for fast-throughput Urban Water Journal 303 analysis in the lab (e.g. Fayad et al 2010, Miles et al 2011, the availability of such data for RTC still seems far away. For now the practical use of water quality sensors in automatic control remains limited to WWTPs (Olsson et al 2005) where they are not only applied for effluent quality control but also for reduction in resource use such as energy and chemicals.…”