Dissolved Organic Nitrogen Measurement in Reclaimed Water
Dissolved organic nitrogen (DON) is an emerging concern for wastewater reclamation and reuse communities since DON may react with disinfectants to form carcinogenic nitrogenous disinfection byproducts (DBP) (e.g., haloacetonitriles, N-nitrosodimethylamine (NDMA)) and to affect the speciation of currently regulated DBP (trihalomethanes and haloacetic acids). Also, DON is present in proteins that foul membrane treatment systems (e.g., membrane bioreactors). The purpose of the present research is to compare existing DON measurement methods and to document DON concentrations of reclaimed wastewater. DON quantification involves subtracting dissolved inorganic nitrogen (DIN) concentrations from the total dissolved nitrogen (TDN) concentration. The traditional method for measuring DON in raw and treated wastewaters, Total Kjeldahl Nitrogen (TKN, the sum of DON and ammonia nitrogen) method has several significant limitations: a large sample volume (500 mL) is required for a low-level analysis; the analysis is time consuming; the method detection limit is relatively high (0.1 to 0.2 mgN/L); and the analysis suffers from incomplete oxidation of some nitrogenous compounds. Other wet chemical oxidation (WCO; e.g., persulfate oxidation) and high temperature combustion (HTC) methods has been used in the fields of ecology and marine biology to measure TDN due to their better accuracy. Several techniques measure DIN species, but colorimetric and ion chromatographic methods are most commonly used: DON = TDN – NO3 − – NO2 − – NH4 +.