Browsing by Author "Goslan, Emma"

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    The Behaviour of Haloacetic Acids in Distribution Zones in Scotland
    (Cranfield University, 2014-09) Agori, Georgia; Goslan, Emma
    HAAs are the second most prevalent class of DBPs after THMs in chlorinated drinking water and are of concern due to their potential human health risk. Their concentrations in drinking water are regulated by the US Environmental Protection Agency (US EPA) and other regulatory agencies and are currently under consideration by the European Union to be regulated at 80μg/L. However their monitoring in the distribution system is complicated because several parameters influence their formation and speciation. In addition the kinetics of HAAs and their formation and stability remain largely unidentified. The HAAs are not as chemically or biologically stable as THMs in aquatic systems and their stability may impact their measurement. The levels of HAAs within a distribution system may vary seasonally and spatially. Many studies have shown that their concentration in a distribution system can rise as well as fall. The levels of HAAs in the distribution system could be increased in the presence of residual chlorine or due to the decomposition from other DBPs and be decreased by biodegradation or hydrolysis and abiotic degradation. However biodegradation is likely the major loss process occurring in drinking water distribution systems. This study provides an interesting picture of HAAs levels in distribution water in Scotland. A statistical analysis has been carried out using measurements of HAAs concentrations and other water quality parameters from 298 Scottish water distribution zones in to investigate the relative occurrence and speciation of HAAs, and determine their behaviour in water distribution systems, monitoring differences between zones. This study also allowed evaluation of the impact of seasons on HAAs concentrations and speciation in Scotland’s distribution zones. The results obtained show that the median concentrations of HAA5 is 11.5μg/L. The average HAA5 in distribution systems were about 50% lower than total trihalomethanes (THMs). In 0.7% of the zones under study, the average HAA5 concentration exceeds 60μg/L. These zones are supplied by small WTWs (<3,300 people) and are using chlorination. HAAs concentrations varied according to their water source and the disinfection strategy used. Low HAA5 levels (the median was <5.3 μg/L) were observed in the groundwater systems and higher levels were observed in the surface water systems (the median was 12.4 μg/L). The chloraminated waters have lower HAA5 and THMs levels compared to chlorinated waters, but the difference is not that pronounced. Generally chlorinated HAAs dominated in the waters of the distribution under study. The dominant species were trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA). DCAA and TCAA were present at almost in equal levels in chlorinated waters but DCAA was the dominant group detected when using chloramination. Furthermore seasonal variations of the concentrations of different HAAs species were observed. The concentrations of HAA5 were higher in summer and autumn and lower in winter and spring but the difference was not statistically significant. THMs has a similar seasonal pattern but with a more pronounced variation than HAAs. The median data show almost no seasonal variation for dichlorinated HAAs. However the seasonal variation of TCAA is more pronounced and higher concentrations were detected during summer and autumn.When the data sets from all distribution zones were combined there was a strong correlation between total THMs and HAA5, total THMs and TCAA and HAA5 and total organic carbon (TOC). The spatial variability of HAAs and THMs concentrations in two distribution zones using different disinfection strategies (chloramination and chlorination) was also studied. There has previously been no full scale study in the UK with the attempt to link the behaviour to distribution factors such as microbial water quality or distribution mains material. In both systems THMs generally presented stable and increasing concentration profiles along the system, whereas HAAs increased and decreased, a phenomenon probably related to biodegradation. There is also evidence that abiotic reduction of HAAs is possible in the iron pipes for the chlorinated distribution system. Using flow cytometry we observed generally higher levels of total and intact cells in the chloraminated distribution zone. Thus large numbers of dead cells can contribute to HAAs formation.
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    Chlorate occurrence in drinking water
    (Cranfield University, 2023-08) Briones Carles, Pablo; Goslan, Emma; Jarvis, Peter
    The use of chlorine for disinfection of potable water has been the major public health advancement in the last century. Sodium hypochlorite is currently used worldwide for potable water disinfection. Arising from sodium hypochlorite solutions, chlorate forms as the sodium hypochlorite ages. Chlorate has been recently regulated in the EU directive and is catalogued as a compound of concern for the Drinking Water Inspectorate. The WHO recommended in 2015 a guideline level of 0.7mg/L, and chlorate is currently set at level of 0.25 mg/L in potable water supplies. As chlorate was previously a guidance, and not extensively monitored, this presents a regulatory challenge for most water companies to adopt. From a large historical data set, from 2014 to 2020, it was extrapolated that chlorate monthly running average values were expectedly higher during the warmer season, likely explained by the increased chlorine demand during warmer months, but far from the current regulation limit for well-resourced sites. A questionnaire was completed in cooperation with operators and process scientist on site. The interviews were completed across various WTW in Scotland. The aim was to demonstrate the varying disinfection practices and extract conclusions on the hypothetical chlorate levels arising during the dosing and storage of sodium hypochlorite. The selection of sites provided a good overview on the particularities of the disinfection stage, from small WTW, where the sodium hypochlorite gets diluted on site, to large WTW with bulk storage of 15% sodium hypochlorite. Sites with a varied risk of chlorate occurrence were also included such as on-site electro-chlorination and chlorine gas disinfection. It was concluded that there are correct measures in place during the operation and maintenance of the disinfection stage, but chlorate levels during storage are not centrally reported. The questionnaire has shown some sites where the solutions of sodium hypochlorite were potentially exposed to warm temperatures and extended periods of storage. It is likely that high room temperature is the underpinning cause leading to sudden chlorate increase in combination with high chlorine demands during the warmer months. This emphasised the need for longitudinal studies on the degradation of hypochlorite solutions during storage. It has been identified that a robust supply chain providing fresh hypochlorite deliveries could be a major implementation aiming to tackle high chlorate levels, particularly for remote and isolated potable water treatment works. The need for an accurate determination of chlorine demand on site remains of crucial relevance aiming to adjust disinfectant capability across varying treatment processes. The importance of regular procurement of hypochlorite solutions and the need for contingency was emphasised by the operators in order to avoid high seasonal chlorate levels. As a part of the experimental plan, the aim was to analyse the long-term stability of sodium hypochlorite during storage with a focus on the impact of disinfectant concentration on chlorate formation. The decay rates for sodium hypochlorite solutions and chlorate formation have been determined at varying initial concentrations using incubation experiments in the laboratory. It was determined the application of consecutive refilling during sodium hypochlorite storage with remaining old solutions of hypochlorite. Via bench scale kinetic experiments, it was determined whether the use of a 10% free chlorine concentration of sodium hypochlorite is less prone to promote further chlorate formation compared to the currently used 15% hypochlorite solutions. It has been found the relative chlorate to free chlorine content remains high even after the adoption of lower concentration hypochlorite solutions. This has implications for sites currently using dilution of hypochlorite and high chlorine demands. Lower initial concentrations of sodium hypochlorite also presented more stability and remaining disinfectant capacity during the bench scale studies. It is concluded that extensive monitoring and control will be required in order to achieve tighter chlorate standards. The relative chlorate to free chlorine ratio (mg Chlorate/ mg of free chlorine) has been highlighted as a concern resulting from high values in diluted solutions of hypochlorite and on-site electro chlorination systems. Further mitigation strategies have been summarised discussing the risk factors for future chlorate occurrences, implementations aiming to tackle chlorate occurrence pre-emptively, and limit exceedances of the EU directive, now adopted in Scotland. Overall, the thesis provided a better understanding on the drivers prompting chlorate levels derived from sodium hypochlorite disinfection, a list of comprehensive evidence-based interventions at water treatment facilities and highlighted best management practices.
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    Formation potential of disinfection by products of 4 water sources after Nanofiltration (NF) and Advanced Oxidation Processes (AOPs) at optimal and sub-optimal conditions
    (2017-09-02) Losty, Erin; Goslan, Emma
    The importance of understanding the impact of different precursor removal treatments on disinfection byproducts (DBP) formation concentrations. This can be elucidated by exploiting the physico-chemical characteristics of NOM in raw water source groups to minimise the formation of DBPs.. Pre-curser technology treatments include coagulation, Ion exchange, Adsorption, membranes biotreatment, ozone and AOPs. Establishing correlations experimentally between different raw water sources, water treatment used and DBP formation, by measuring raw water characteristics at the point before treatment and DBP-FP in the corresponding final water just after treatment using the analytical methods as above and the previously established methods for HAA and THM analysis. Analytical methods for the determination of DBPs from 16 categories are used to determine an extensive range of DBPs, giving a better understanding of the composition of the DBP mixture as a whole. The analytical methods can then be used to determine and compare water treatment technologies under optimal and suboptimal conditions and hence provide operational advice on minimising DBP formation by comparing treatment methods.
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    Investigating the importance of emerging disinfection by-products formation through traditional flowsheets and advanced treatment technologies.
    (2019-05) Losty, Erin; Goslan, Emma; Jefferson, Bruce
    Chlorine was first used to disinfect drinking water in the US as early as 1908 with other disinfectants, ozone, chlorine dioxide to follow. However, it wasn’t until the 1970’s that Rook discovered a possible link to higher levels of chloroform in drinking water treated with chlorine and inadvertently linked the possibility of precursor material to products of the disinfection process. While the introduction of chlorine to disinfect water has been significant in eliminating pathogens for safe drinking water, it becomes important to safeguard the public against disinfection by-product (DBP) exposure. This thesis intends to give an understanding into the relationship between the control pathway and total DBP formation, giving an insight to the occurrence and the formation for DBPs in drinking water. Emphasis is placed on the natural organic matter characteristics and precursors involved in the formation of DBPs through the treatment process with the use of 3 surface waters. Analysis of 27 traditional and emerging DBPs seek to give a better understanding of the composition of the DBP mixture as a whole, their formation and subsequent minimisation. Comparing two advanced treatment methods, Advanced Oxidative Processes and Nanofiltration with optimal and sub optimal conditions and provide operational advice on minimising DBP formation. AOPs reduced the DBPs and HI more efficiently than nanofiltration but only when high H₂O₂ levels are used. At lower H₂O₂ doses, DBPs increased where as nanofiltration reduced the DBP precursors considerably under optimal and sub-optimal conditions, becoming important in waters with high seasonal variability. Minimising DBPs, specifically THM concentrations has been a priority of water treatment to date, but to reduce the hazard index associated to DBPs would be more beneficial. WHO in vivo generated guideline values exists for only 19 of the 27 DBPs measured, this could potentially limit the ability to understand the impact of the broadest range of emerging DBPs. Over 600 have been discovered and more research is needed to define this mixture and stipulate DBP interactions impacting the hazard index. The key emerging DBPs impacting the HI, using the guideline values, are the brominated and nitrogenated species, BDCAA, BCAA, DCAN and BCAN. Recommendations to monitoring and regulation would be to add these to the current regulatory list by extending HAA5 to HAA9 or as a minimum to include the Br-HAAs. Bromine removal and its subsequent formation of Br-DBPs when not removed effectively, can impact the HI dramatically and, therefore, emphasis for removal is needed. Traditionally upland waters have been the focus due to its high formation of THMs, but it has the lowest HI throughout. Lowland lake, with the highest bromine levels generated the highest HI, consideration is needed to better minimise DBP formation.