Experimental design as a tool for studying trihalomethanes formation parameters during water chlorination

• Humic acid chlorination
• Multivariate assessment of THMs formation
• Higher-order effects

Chlorination systems are widely used to ensure municipal drinking water's safety, providing defense against disease-causing organisms. However, previous studies indicated that, depending on the conditions of this treatment, a group of byproducts known as trihalomethanes (THMs), such as chloroform, may be formed and represent a considerable health risk. In this study, the effect of five variables (substrate and ClO− concentration, presence of KBr, temperature, and pH) on THMs' formation during chlorination of aqueous solutions of humic acid is discussed using a factorial design. Results showed that in the absence of KBr, only traces of brominated THMs are produced, probably due to contamination of ClO− by active bromine species. In the presence of KBr, the formation of chloroform is negligible, whereas within the group of brominated THMs, bromoform is produced in higher concentrations. Most relevant results are related to the existence of numerous higher-order effects, which shows the complexity of the involved reactions and also that THMs formation is not simply a function of substrate and ClO− molar ratio but also depends on the number of reactive sites available for chlorination in the substrate.