N-nitrosodimethylamine (NDMA) is a potential carcinogen that is produced as a disinfection by-product of chloramination or chlorination process in water and wastewater treatment systems. The ability of the dioxygenase-expressing bacteria, Rhodococcus sp. strain L4, to degrade NDMA after induction with cumene was examined in the presence and absence of its potential precursors. Dimethylamine (DMA), aniline (AN) and humic acid (HA) were selected as the precursors. The induced bacteria were able to degrade NDMA from initial concentrations ranging between 1 and 10 mg L-1 to an undetectable level (< 0.24 µg L-1) while there was no degradation of NDMA by the corresponding non-induced strain. The specific first-order degradation rate of NDMA ranged from 0.337 to 0.426 μg g-protein-1 h-1. Successful removal of all precursors was achieved by the induced bacteria. The presence of DMA had no negative effect on NDMA degradation. In contrast, a lag period was observed for the degradation of NDMA when AN or HA was present (except for the presence of 0.1 mg L-1 AN). In the presence of all precursors, NDMA degradation was negatively affected by the increased concentration (from 1 to 10 mg L-1) of all precursors.
Keywords: Amine compounds; Biodegradation; Cometabolism; Dioxygenases; Induced bacteria.