Bench-scale column evaluation of factors associated with changes in N-nitrosodimethylamine (NDMA) precursor concentrations during drinking water biofiltration
(Zhang, Z., B. Ma, R.M. Hozalski, C.G. Russell, A.N. Evans, K.O. Led, M. Van Dyke, S. Peldszus, P.M. Huck, A. Szczuka, and W.A. Mitch. Water Research, 2019, 167, 1-11.)
NDMA is a highly potent carcinogen with a maximum acceptable concentration (MAC) of 40 ng/L set out in the Canadian Drinking Water Guidelines and a MAC of 9 ng/L in Ontario (Ontario Reg. 196/03). NDMA can be formed from NDMA precursors upon chloramination, and it has been reported that NDMA precursors can increase, decrease or remain constant during biofiltration. To look further into this phenomenon the NSERC Chair collaborated with a team of researchers and consultants on a bench-scale study, which was part of a Water Research Foundation project (WRF 4669). The project has been completed and we recently published a paper on these bench-scale studies in ‘Water Research’. Here a synopsis:
Bench-scale tests compared biofiltration columns exposed to different conditions, to understand factors associated with changes in NDMA precursor concentrations in the biofilter effluents. Side-by-side comparisons of biofiltration media from different facilities fed with water from each of these facilities showed that differences in source water quality was the most important factor determining whether NDMA precursor concentrations increased, decreased or remained constant across biofilters. Any original differences in the microbial communities on the biofiltration media were not important for NDMA precursor formation across biofilters.
Spiking of various nitrogen containing compounds such as ammonia, chloramine, hydroxylamine, wastewater and cationic polymer in the bench-scale biofilter influents did NOT promote NDMA precursor formation across biofilters. Biotransformation of uncharacterized (unknown) components in the source waters determined whether NDMA precursor concentrations increased or decreased across biofilters. These uncharacterized source water components varied temporally and across locations.
Ozone pre-treatment significantly reduced NDMA precursor concentrations at one facility, suggesting that pre-oxidation upstream of biofiltration could be an effective technique to mitigate the increase in NDMA precursor concentrations across biofilters. But further testing with ozone is needed at additional biofiltration facilities.
Please contact Lorena Baku (lorena.baku@uwaterloo.ca ) if you would like a pdf copy of this paper.
