Minimisation of regulated and unregulated disinfection by-products in drinking water

This research, involving a collaboration between Imperial College London and Anglian Water, and had the overall aim to understand the occurrence and fate of a wide range of disinfection by-products (DBPs) during drinking water distribution and to establish operational strategies to simultaneously control them in water supply systems. Therefore, the research is essentially centred on two main issues: i) improving our understanding of the impact of water quality and operational parameters on regulated and unregulated DBPs in water distribution networks, and ii) the validation of a prediction tool to proactively design and adapt operational practices to minimise DBPs. The research explored these issues through a series of experiments focused on the analysis of 29 DBPs upon chlorination and chloramination, under various water ages and water quality conditions, by sampling from four locations in four full-scale distribution systems in four sampling rounds and simultaneously running Simulated Distribution System (SDS) tests. This resulted in one of the most comprehensive databases of the occurrence and behaviour in distribution systems of regulated trihalomethanes (THMs), the likely-to-be-soon-regulated-in-the-UK haloacetic acids (HAAs), as well as unregulated haloacetonitriles (HANs) and haloacetamides (HAcAms) of potential health significance, and their individual species. For the first time, SDS tests were shown to be able to successfully predict the levels and speciation of HANs and HAcAms in chlorinated and chloraminated systems, by direct comparison with actual distribution water samples. The configuration of SDS tests addressed the spatial and temporal variation of the selected DBPs, indicating that even though THM concentrations significantly increase with water age (on average by ~54% between water ages of6-106 h) and present high seasonal dependence. together with HAAs. The latter, HANs, and HAcAms concentrations had fluctuations that resulted in less pronounced overall increases, with the two N-DBPs relatively unaffected by water temperature. To explore the impact of disinfectant alteration in distribution, free chlorine and chloramination were applied in the same real water samples in SDS tests. This showed that the implementation of chloramination minimises the formation not only of THMs and HAAs, but also HANs and HAcAms, though it shifts speciation towards more brominated HAAs, HANs and HAcAms species. Through this research, SDS tests can be recommended to water utilities to both estimate the concentrations of DBPs (those included in this study) in their supply systems and assess the effect of potential DBP minimisation strategies. The interesting behavioural patterns of HAcAms in distribution systems raised questions concerning their formation mechanisms and determining factors. Therefore, a laboratory study was conducted whereby chlorination and chloramination were applied to six model amide compounds to investigate their relative contributions as N-DBPs precursors, under a range of water quality conditions (pH, bromide dose, water age). The findings of this study suggest that the N-oxidation of amide structures, more evident in aromatic moieties, is a potential mechanism for HAcAms formation, which occurs completely separately from HAN hydrolysis. This suggests that if precursor removal is to be used as a treatment strategy for minimising HAcAms and HANs, the success in minimising these groups of N-DBPs may differ based on the relative success in removing their independent precursors.Open Acces