Formation and control of emerging C- and N-DBPs in drinking water

A survey of 16 US drinking water treatment plants was conducted regarding the occurrence, formation, and control of emerging disinfection by-products (DBPs), with a focus on drinking waters that were impacted by treated wastewater and/or algae. The formation and control trends of certain emerging carbonaceous (haloacetaldehyde) and nitrogenous (haloacetonitrile, halonitromethane, cyanogen halide, nitrosamine) DBPs were different from those of the regulated trihalomethanes (THMs). This was due to differences in the sources of precursors (e.g., humic substances versus proteinaceous materials) plus differences in the effect of disinfection processes on these DBPs. For example, ozone increased the formation potential (FP) of chloropicrin (median = 226%), whereas biofiltration typically decreased the FP of the ozonated water (median = 48%), which-together with coagulation or softening-resulted (in general) in a net decrease (median = 33%) in FP through the ozone plants. Alternatively, coagulation with the polymer polyDADMAC (a source of N-nitrosodimethylamine [NDMA] precursor) increased the FP of NDMA (43-82%), whereas ozonation often destroyed NDMAFP (median to maximum = 10-87%). This article discusses how utilities can minimize and balance the formation of THMs and haloacetic acids with that of certain emerging DBPs.