Occurrence and removal of dissolved organic nitrogen in US water treatment plants

Dissolved organic nitrogen (DON) in watersheds may react with disinfectants to form carcinogenic, nitrogenous, disinfection by-products. However, despite the potential significance of DON-mediated reactions, a systematic study has not been conducted for DON occurrence or removal during water treatment. Two seasonal sampling campaigns of raw and finished waters from 28 water treatment plants in the United States were conducted to quantify the occurrence and removal of DON. A new dialysis-based pretreatment method that removes dissolved inorganic nitrogen, followed by a high-temperature combustion analytical method, was used to measure DON. Results demonstrated that average observed DON concentrations were 0.19 mg/L nitrogen for raw waters and 0.15 mg/L nitrogen for finished waters, making the high-temperature oxidation technique described in this article suitable for widespread use in the drinking water industry. Results also demonstrated that water treatment plants remove approximately 20% of DON and that adding polymer and ozonation aid in its removal.