Flow Cytometry: A tool for assessing drinking water quality and evaluating chlorine disinfection performance.

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.EngD in Wate