Potential N-nitrosodimethylamine (NDMA) formation from amine-based water treatment polymers in the reactions with chlorine-based oxidants and nitrosifying agents

Abstract

The NDMA formation potential (NDMA FP) of four commonly used amine-based cationic water treatment polymers was assessed in reactions with chlorine-based oxidants (free chlorine, monochloramine and chlorine dioxide) and nitrosifying agents (nitrite and nitrate). Relatively high dosages of polymers were directly exposed to oxidants for long reaction times in the FP tests to assess the potential to form NDMA and obtain mechanistic insight. Results show that the NDMA FP of the polymers generally follows the trend of aminomethylated polyacrylamide (Mannich polymer)>>poly(epichlorohydrin-dimethylamine) (polyamine) > poly(diallyldimethylammonium chloride) (polyDADMAC) > cationic polyacrylamide copolymer (cationic PAM). The high NDMA FP of Mannich polymer was largely due to the high amount of dimethylamine (DMA) residue in the polymer solution. For the other three polymers, the DMA concentration was increased after oxidation, indicating polymer degradation, and the trend of DMA increase agreed with that of NDMA FP. Among the oxidants, NDMA formation followed the order of monochloramine > free chlorine > chlorine dioxide, despite that the DMA release from the polymers caused by the oxidant followed the opposite order. At equal dosages, nitrite and nitrate generated NDMA from the polymers at levels comparable to those by free chlorine and chlorine dioxide; even so, the nitrosifying agents are unlikely to contribute significantly to NDMA formation due to expected lower concentrations in drinking water treatment systems. Jar tests followed by monochloramination of real water samples using conditions in line with those at potable water treatment plants generally showed relatively small contributions from polyamines and polyDADMACs to the overall NDMA formation.

Nitrosamines and water

“…Releasing DMA from polymer breakdown accounts for a major mechanism of NDMA formation upon chloramination. The same was confirmed in another paper by Park et al [79]. Chlorine-based oxidants (NH 2 Cl, Cl 2 , and ClO 2 ) were shown to release DMA from four examined amine-based polymers used in water treatment technology.…”

“…Chlorine-based oxidants (NH 2 Cl, Cl 2 , and ClO 2 ) were shown to release DMA from four examined amine-based polymers used in water treatment technology. The paper of Park et al [79] confirms that oxidants are able to release DMA moiety from some organic compounds.…”

N-nitrosodimethylamine (NDMA) formation potential of amine-based water treatment polymers: Effects of in situ chloramination, breakpoint chlorination, and pre-oxidation

“…4A). Earlier work has shown that polymers, unlike simple DMA, undergo degradation to release DMA and other amine fragments during oxidation and the level of NDMA formation is strongly correlated to the degree of polymer degradation and release of DMA [25][26][27]. The current (Figs.…”

“…Previous work by Park et al [25,26] has demonstrated that polyamine is much more susceptible than polyDADMAC to oxidative degradation by free chlorine and chloramines. The tertiary amine chain ends and a higher DMA moiety fraction of polyamine were shown to be directly related to the higher NDMA-FP of polyamine than polyDADMAC.…”

“…Among the potential NDMA precursors, amine-based water treatment polymers that are commonly used as coagulant or flocculant aids have received considerable attention because of their intentional usage in water and wastewater treatment systems. Several coagulant/flocculant polymers have been reported to form NDMA in water that contained free chlorine, chloramines, or ozone [14,15,[21][22][23][24][25][26][27][28]. The dimethylamine (DMA)-based moieties in the water treatment polymers were responsible for their NDMA formation potential (NDMA-FP).…”