An evaluation of NOM precursors and bromide ion in the formation of haloacetic acids (HAAs) in water treatment

• Main Author: Huang, Jin
• Other Authors: Graham, Nigel
• Published: Imperial College London 2010
• Subjects: 628
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514536

Haloacetic acids (HAAs) are a group of disinfection by-products (DBPs) found in drinking water which are regulated in the USA but not yet in the EU. Epidemiology tests have shown that they may have carcinogenic and mutagenic effects on human beings. HAAs are produced during the disinfection process from the use of chlorination and they may persist during water distribution and finally reach the customers’ tap at concentrations of concern. The formation of HAAs arises from the reaction between precursor material – principally natural organic matter (NOM) – and chlorine, and the species and amount of HAAs produced depends on the nature of the NOM and the reaction conditions, such as the temperature, chlorine dose, pH, and the presence of bromide. NOM is a heterogeneous mixture of numerous organic molecules originating from aquagenic and pedogenic sources, and its content changes significantly with water source, and temporarily for a given water source. Due to the complex properties of NOM, no conclusive connections have been established between the properties of precursor materials and HAA formation (compound yield or individual species distribution). The thesis provides details of a new-developed fractionation method that has been used to characterise NOM obtained from natural waters. This method can effectively reveal the effect of seasonal variation and traditional treatment on NOM properties. The reactivity of each organic fraction in terms of HAA formation, seasonal variation and treatment efficiency has also been studied and is discussed in the thesis. Algae represent an important component of NOM, and as such algae species can also be responsible for the formation of HAAs. The thesis describes an extensive study of two prominent algae species in terms of their role in producing trihalomethane (THM) and HAA compounds, and their productivity in comparison with other organic precursors. Finally, the presence of bromide ion in source water leads to formation of brominated HAA species during chlorination which are believed to be of greater toxicological significance than non-brominated species. This thesis summarises an experimental investigation of the fundamental role of bromide in HAA formation and the relationship with initial NOM concentration and chlorine dose.