CHAPTER 38: Risk-Based Approach to the Formation of DBPs of Concern in UK Drinking Water

Water companies in the UK are required to operate their disinfection processes to keep the concentration of disinfection by-products (DBPs) in drinking water as low as possible. At present, this is can be achieved largely by maintaining trihalomethane (THM) and haloacetic acid (HAA) levels below regulated or guideline values. However, several hundred DBPs have been identified and the increasing emphasis on a risk-based approach to water quality is likely to make consideration of these a priority. Routine monitoring and analysis for the wide range of known DBPs would be impractical, if not impossible. However, knowledge of the factors that lead to their formation and mitigation would allow other DBPs to be considered in a risk-based approach. This paper outlines raw water characteristics and water treatment processes that promote the formation of different categories of DBPs. Indicative concentrations and toxicological properties for the different categories of DBPs are combined to yield a prioritisation factor that indicates the potential for the formation of DBPs under different water treatment scenarios. This risk-based approach has been encapsulated in a spreadsheet-based tool developed for assessing the potential formation of DBPs at water treatment works.