Formation of nitrosamines during chloramination: Importance of chloramine speciation

The formation of nitrogenous disinfection by-products (N-DBPs) is becoming of increasing concern to drinking water and wastewater treatment utilities. Formation of N-DBPs in water supplies occurs via reactions of chlorine or chloramines and dissolved organic nitrogen precursors. In the past, much research has been conducted on the formation of carbonaceous DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAS) in pristine water supplies. However, as a result of population growth-related impacts to drinking water supplies and recent trends in drinking water disinfection, the concentrations of dissolved inorganic and organic nitrogen in drinking water supplies are increasing.; Oxidation of dissolved organic nitrogen compounds can form several families of toxic byproducts. The main objective of this research was to identify key aspects of formation pathways for nitrosamines, one N-DBP family of current interest, during chloramination. Previously, nitrosamine formation during chloramination has been linked to a reaction between monochloramine and organic nitrogen precursors. However, this research has shown three factors to be more important for nitrosamine formation than monochloramine: (i) the chlorination state of the organic nitrogen precursor, (ii) the partial formation of dichloramine and (iii) the presence of molecular oxygen. A new nitrosamine formation pathway involving dichloramine and dissolved oxygen was developed that suggests that relatively minor concentrations of dichloramine (i.e., < 5% of chloramine residual) via monochloramine disproportionation can explain nearly all nitrosamine formation. With the improved understanding of nitrosamine formation pathways, strategies were developed that could significantly reduce nitrosamine formation during chloramination.; Another objective of this research was to determine the persistence and fate of nitrosamines and their precursors in wastewater-impacted surface waters. Using a boron analysis technique developed in this study to account for dilution, the decay of nitrate and nitrosamine precursors in a wastewater-impacted river was assessed. Both groups of nitrogen compounds were shown to decay with half-lives of several days, which indicates that dissolved nitrogen compounds can persist in wastewater-impacted surface waters to potentially impact downstream drinking water supplies.