Boron-doped diamond (BDD) film electrodes were used to electrochemically destroy N-nitrosodimethylamine (NDMA) in reverse osmosis (RO) concentrates. Batch experiments were conducted to investigate the effects of dissolved organic carbon (DOC), chloride (Cl-), bicarbonate (HCO3 -), and hardness on rates of NDMA destruction via both oxidation and reduction. Experimental results showed that NDMA oxidation rates were not affected by DOC, Cl-, or HCO3- at concentrations present in RO concentrates. However, hydroxyl radical scavenging at 100 mM concentrations of HCO3- and Cl- shifted the reaction mechanism of NDMA oxidation from hydroxyl radical mediated to direct electron transfer oxidation. In the 100 mM Cl- electrolyte experimental evidence suggests that the in situ production of ClO3̇ also contributes to NDMA oxidation. Density functional theory calculations support a reaction mechanism between ClO3̇ and NDMA, with an activation barrier of 7.2 kJ/mol. Flow-through experiments with RO concentrate yielded surface area normalized first-order rate constants for NDMA (40.6 ± 3.7 L/m 2 h) and DOC (as C) (38.3 ± 2.2 L/m2 h) removal that were mass transfer limited at a 2 mA/cm2 current density. This research shows that electrochemical oxidation using BDD electrodes has an advantage over other advanced oxidation processes, as organics were readily oxidized in the presence of high HCO3- concentrations.
ASJC Scopus subject areas
- Environmental Chemistry