Browsing by Author "Cheswick, Ryan Ashley"

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    Comparing flow cytometry with culture-based methods for microbial monitoring and as a diagnostic tool for assessing drinking water treatment processes
    (Elsevier, 2019-06-18) Cheswick, Ryan Ashley; Cartmell, Elise; Lee, Susan; Upton, Andrew; Weir, Paul; Moore, Graeme; Nocker, Andreas; Jefferson, Bruce; Jarvis, Peter
    Flow cytometry (FCM) and the ability to measure both total and intact cell populations through DNA staining methodologies has rapidly gained attention and consideration across the water sector in the past decade. In this study, water quality monitoring was undertaken over three years across 213 drinking water treatment works (WTW) in the Scottish Water region (Total n = 39,340). Samples subject to routine regulatory microbial analysis using culture-based methods were also analysed using FCM. In addition to final treated water, the bacterial content in raw water was measured over a one-year period. Three WTW were studied in further detail using on-site inter-stage sampling and analysis with FCM. It was demonstrated that there was no clear link between FCM data and the coliform samples taken for regulatory monitoring. The disinfectant Ct value (Ct = mg·min/L) was the driving factor in determining final water cell viability and the proportion of intact cells (intact/total cells) and the frequency of coliform detections in the water leaving the WTW. However, the free chlorine residual, without consideration of treatment time, was shown to have little impact on coliform detections or cell counts. Amongst the three treatment trains monitored in detail, the membrane filtration WTW showed the greatest log removal and robustness in terms of final water intact cell counts. Flow cytometry was shown to provide insights into the bacteriological quality of water that adds significant value over and above that provided by traditional bacterial monitoring.
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    Flow Cytometry: A tool for assessing drinking water quality and evaluating chlorine disinfection performance.
    (Cranfield University, 2019-02) Cheswick, Ryan Ashley; Jarvis, Peter; Jefferson, Bruce
    Chlorine disinfection is a process that has been in use for over a century for drinking water treatment; however rare detections of faecal indicator organisms in final treated water still occur. Assessing the performance of the disinfection process in-situ is challenging. Most often this is achieved by monitoring abiotic parameters such as chlorine, turbidity and pH, whereas microbiological sampling takes place daily. Typically, chlorine disinfection occurs within chlorine contact tanks which should be designed to achieve plug flow and minimise short circuiting. In reality, the design of contact tanks vary considerably, and water utilities have inherited many legacy assets that do not conform to modern day design standards. Furthermore, microbiological culture-based data is hard to evaluate when there are sporadic detections of culturable organisms. There is therefore a need to quantify deviation from optimal plug flow design of chlorine contact tanks and a requirement for an alternative microbiological approach to achieve this. This thesis explores the application of use of flow cytometry (FC), a novel culture independent technique for measuring bacterial cell viability, for disinfection applications. Firstly, an assessment of FC and its value as a monitoring tool for the water industry was carried out. This utilised the largest drinking water FC dataset in the world and concluded that there was no link between coliform detections and FC data, yet coliform detections were shown to be driven by the contact time (Ct) in disinfection, not just the sole parameter of chlorine residual. Secondly, the key process variables of chlorine disinfection were investigated and pilot scale studies demonstrated that hydraulic efficiency during chlorination impacted upon disinfection efficacy and FC provided insights of bacterial inactivation rates where traditional culture-based methods could not. The findings from this work culminated in an assessment of Ct across Scottish Water and the cost of investment required to bring high risk (large production volume) water treatment works (WTW) up to current standards was estimated. Finally, the implications of this thesis and the learning around chlorine disinfection and the application of FC for the water industry were discussed.