Disinfection By-Products

Identification of treatment conditions which minimise DBP formation - version 2

Reference: 20/TX/05/3
ISBN: 978-1-84057-892-8
Published Date: 15/07/2020

Disinfection by-products (DBPs) are formed from the reaction between an oxidative disinfectant (such as chlorine or ozone), and organic and inorganic precursor compounds, usually natural organic matter or bromide ions. This research sought to determine the relative importance of different DBPs and the factors that influence their formation, with the objective of developing a practical guide to assist water companies in managing DBPs. This was achieved through a literature review of toxicity data to establish a ranked list of priority DBPs. Extensive laboratory investigations were undertaken to determine the influence of different treatment processes on precursor removal across five different chemical groups of DBPs (21 individual compounds) for different types of water source. Samples were also taken across drinking water treatment works to validate the laboratory results. The toxicity data was used to assess potential risk (the hazard index) and the relative importance of DBPs shown to change for different water sources and treatment processes. A limited number of DBPs were dominant in the overall assessment of hazard index. These were principally the haloacetic acids, specifically those that incorporated bromide into their structure. However, when present, the nitrogenous DBPs were also important. Guidance was developed on the operation of different treatment processes for minimisation of the priority DBPs.

APPENDIX A COMPREHENSIVE LIST OF DBP INCORPORATING THEIR LIKELIHOOD OF OCCURRENCE IN DRINKING WATER AND HUMAN TOXICITY TO PROVIDE A RANK LIST BY OVERALL SIGNIFICANCE

Reference: 20/TX/05/3
ISBN: 978-1-84057-892-8
Published Date: 15/07/2020

Disinfection by-products (DBPs) are formed from the reaction between an oxidative disinfectant (such as chlorine or ozone), and organic and inorganic precursor compounds, usually natural organic matter or bromide ions. This research sought to determine the relative importance of different DBPs and the factors that influence their formation, with the objective of developing a practical guide to assist water companies in managing DBPs. This was achieved through a literature review of toxicity data to establish a ranked list of priority DBPs. Extensive laboratory investigations were undertaken to determine the influence of different treatment processes on precursor removal across five different chemical groups of DBPs (21 individual compounds) for different types of water source. Samples were also taken across drinking water treatment works to validate the laboratory results. The toxicity data was used to assess potential risk (the hazard index) and the relative importance of DBPs shown to change for different water sources and treatment processes. A limited number of DBPs were dominant in the overall assessment of hazard index. These were principally the haloacetic acids, specifically those that incorporated bromide into their structure. However, when present, the nitrogenous DBPs were also important. Guidance was developed on the operation of different treatment processes for minimisation of the priority DBPs.

Workshop Presentation

Reference: 14/TX/05/2
ISBN: 1 84057 704 5
Published Date: 27/01/2014

The disinfection by-product (DBP) rule requires water companies to keep DBPs in drinking water as low as possible without compromising the effectiveness of disinfection. In the UK, emphasis has been on the regulated DBPs, mainly the trihalomethanes (THMs), but other DBPs must not be present at concentrations that constitute a potential danger to human health. 

The large number of known DBPs makes measurement impractical, if not impossible. Accordingly, a pragmatic risk-based approach to identify potential DBPs has been developed, based on knowledge of factors which lead to their formation and mitigation. DBPs have been categorised according to their chemical structures and the potential risks for these categories, based on toxicity, likely occurrence and concentration.

This approach has been encapsulated in a spreadsheet-based risk assessment tool that enables the potential formation of DBPs at treatment works to be quickly assessed, and the works to be ranked according to the risk.