Browsing by Author "Cheswick, Ryan"
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Item Open Access Chlorine disinfection of drinking water assessed by flow cytometry: new insights(Elsevier, 2020-07-10) Cheswick, Ryan; Moore, Graeme; Nocker, Andreas; Hassard, Francis; Jefferson, Bruce; Jarvis, PeterThe efficacy of chlorine disinfection was assessed for the first time over a range of disinfection conditions using flow cytometry (FCM) to provide new insights into disinfection processes. Inactivation was assessed for pure culture bacteria (Escherichia coli) and micro-organisms in real treated water from operational water treatment works (WTWs). A dose dependent increase in inactivation rate (k) was observed for both test matrices, with values of 0.03 to 0.26 and 0.32 to 3.14 L/mg min for the WTW bacteria and E. coli, respectively. After 2 min, E. coli was reduced by 2 log for all chlorine doses (0.12 to 1.00 mg/L). In the case of the WTW filtrate bacteria, after 2 min log reductions were between 0.54 and 1.14 with increasing chlorine concentration, reaching between 1.32 and 2.33 after 30 min. A decrease in disinfection efficacy was observed as temperature decreased from 19 to 5 °C for both microbial populations. With respect to chlorination at different pH (pH 6, 7, 8), membrane damage was more pronounced at higher pH. This was not consistent with the higher disinfection efficacy seen at lower pH. when culture based methods are used to assess bacterial reductions. This provides evidence that more understanding into the fundamental mechanisms of chlorine disinfection are required and that methodological alterations may be required (e.g. pH standardisation) to fully utilise FCM over the entire range of chlorination conditions observed in operational environmentsItem Open Access Effect of turbidity on water disinfection by chlorination with the emphasis on humic acids and chalk(Taylor and Francis, 2019-03-21) Léziar, Tangui; Dutheil de la Rochere, Pierre-Marie; Cheswick, Ryan; Jarvis, Peter; Nocker, AndreasChlorine is globally the most widely used chemical for water disinfection. Whereas disinfection efficiency is well known to depend on water pH and temperature, the effect of turbidity is less well studied. Although turbidity is measured online in most drinking water works and most countries where regulations exist have set limits of <1 NTU for water leaving the works, the composition of turbidity is typically unknown. Given the heterogeneous nature of substances contributing to turbidity, the aim of this work was to study the effect of selected compounds on chlorination efficacy. The effect of humic acids and chalk on the inactivation of the indicator bacteria Escherichia coli and Enterococcus faecalis was assessed at neutral pH at different turbidity levels using both plate counting and flow cytometry in combination with membrane integrity staining. For humic acids, a turbidity of 1 NTU (corresponding to 2 mg L−1) was identified as a critical threshold, which when exceeded was found to have a negative impact on chlorine disinfection. Chalk, on the other hand, had no measurable impact up to 5 NTU. The observation applied to both bacterial species with identical conclusions from the two diagnostic methods. Results corroborate that different turbidity causing substances affect chlorination efficiency to very different extents with chlorine demand by organic material probably being the most important determinant. In the case of turbidities >1 NTU, turbidity measurement benefits from the consideration of the organic content as mere NTU values do not allow predicting an impact on chlorination efficiency.Item Open Access Exploring the use of flow cytometry for understanding the efficacy of disinfection in chlorine contact tanks(Elsevier, 2022-04-06) Cheswick, Ryan; Nocker, Andreas; Moore, Graeme; Jefferson, Bruce; Jarvis, PeterA pilot scale chlorine contact tank (CCT) with flexible baffling was installed at an operational water treatment plant (WTP), taking a direct feed from the outlet of the rapid gravity filters (RGF). For the first time, disinfection efficacy was established by direct microbial monitoring in a continuous reactor using flow cytometry (FCM). Disinfection variables of dose, time, and hydraulic efficiency (short circuiting and dispersion) were explored following characterisation of the reactor's residence time distributions (RTD) by tracer testing. FCM enabled distinction to be made between changes in disinfection reactor design where standard culture-based methods could not. The product of chlorine concentration (C) and residence time (t) correlated well with inactivation of microbes, organisms, with the highest cell reductions (N/N0) reaching <0.025 at Ctx of 20 mg.min/L and above. The influence of reactor geometry on disinfection was best shown from the Ct10. This identified that the initial level of microbial inactivation was higher in unbaffled reactors for low Ct10 values, although the highest levels of inactivation of 0.015 could only be achieved in the baffled reactors, because these conditions enabled the highest Ct10 values to be achieved. Increased levels of disinfection were closely associated with increased formation of the trihalomethane disinfection by-products. The results highlight the importance of well-designed and operated CCT. The improved resolution afforded by FCM provides a tool that can dynamically quantify disinfection processes, enabling options for much better process control.