Electrochemical Formation of N-Nitrosodimethylamine in Nitrite-Impacted Waters

Electrochemical water treatment is increasingly popular for a variety of applications, including resource recovery and advanced oxidation processes. In complex environmental matrices, electro-oxidative processes are known to form hazardous byproducts. This study identifies a new pathway for N-nitrosodimethylamine (NDMA) formation via nitrite electro-oxidation in spiked synthetic and natural electrolytes. In a novel flow-through electrochemical cell, NDMA formation was observed from 1 mg/L N nitrite and 100 μg/L dimethylamine, yielding 169-553 ng/L NDMA in a 1 mM Na2SO4 electrolyte and 189-715 ng/L NDMA in a drinking water treatment plant matrix across various cell potentials (2-12 V and 2-10 V, respectively), exceeding the resident tap water regional screening level for NDMA (0.11 ng/L) by over 1000-fold. Uniquely, formation exclusively occurred in cathode-to-anode flow. Voltammetric data and mechanistic insights are consistent with a cathodic process increasing downstream pH, consequently facilitating amine deprotonation and enabling its nitrosation via N2O4 generated from nitrite oxidation. Generally, nitrite or chloride oxidation activity monitoring (via chlorine residual measurement) was not predictive of nitrosamine yield, and direct measurement of nitrosamines using sensitive analytical techniques (limit of quantification: 55 ng/L) was necessary. This work highlights the understudied formation potential for toxic nitrogenous byproducts in emerging electrochemical treatment technologies, particularly in nitrate recovery contexts.