Disinfection by-products (DBPs) are produced during disinfection through reactions between organic/inorganic materials and chemical disinfectants (e.g. chlorine and chloramines). Switching from chlorination to chloramination may reduce formation of regulated DBPs but can increase formation of nitrogenous DBPs (N-DBPs). Some N-NDBPs have received attention, because they have relatively higher genotoxicity and cytotoxicity than regulated DBPs so may be of greater toxicological significance. Nitrogenous organic compounds are important precursors of N-DBPs. Amino acids are the most studied materials of these precursors, which are widespread in surface waters and difficult to remove using charge based water treatment processes such as coagulation. Previous work carried out in 2006 to 2008 on waters collected from the Scottish Water region identified the occurrence of DBPs at significant levels. Since the work carried out in 2008, a number of factors have changed. These are: 1. The focus is now on minimising DBPs as a whole rather than specific DBPs. 2. The use of chloramination in the distribution system has increased. 3. There has been a shift in focus from removing colour to removing dissolved organic carbon (DOC) as well as understanding the organic make-up of water sources to improve DOC removal at Scottish Water. Previously surveyed sites and new sites were recently (2016-2019) investigated to assess the impact of the improvements in terms of regulated and unregulated DBP occurrence with a focus on HAAs acids and nitrogenous DBPs. As well as the concentration of DBPs being determined, a hazard index was assigned to the measured DBPs in each sample based on WHO guideline values and results from animal tests carried out by the US National Toxicological Program.

Disinfection by-products in Scottish waters impact of treatment improvements a decade later

ACS Fall 2021

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