CHLORAMINES: COMMUNICATION, NITRIFICATION, AND KNOWLEDGE GAPS · Source: Krasner et al. (2013) Formation, Precursors, Control and Occurrence of Nitrosamines in Drinking Water: A review.
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— Chemistry and biology— Number of useful approaches to preventing/recovering — Manageable
• Nitrosamines— Waters vary in ability to form nitrosamines— Pre-oxidation beneficial— Treatment chemicals a possible culprit
• Communications— Utilities a “trusted” source— Start early and be prepared— Tailor messages for different audiences— Be open, respectful, helpful, knowledgeable
—63% experienced some nitrification—25% experienced severe nitrification—90% of systems with signs of had 2 mg/l or less
of total chlorine residual
• 2004 WRF Report with 56 responding utilities—48% experienced nitrification—25% experienced to or more times per summer—48% had established “nitrification plans”
• UCMR2 Data – 27% of public water systems show some detection of NDMA—Max 630 nanograms/liter—Detection limit is 2 nanograms/liter—Median 4 nanograms/liter
• While low levels, concerns are real due to increased toxicity compared to THMs/HAAs –give numbers
• Solutions are real too – although some still under development
Drinking Water Processes to Control NDMA Formation
Treatment Importance
Polymer Optimization High
Precursor Pre-oxidation High
Alternative Polymer High
Activated Carbon High
Riverbank Filtration Moderate
Modify Chloramination Protocol Moderate
Biofiltration Low/Moderate
UV Treatment Low
Anion Exchange Low
Coagulation/Softening LowSource: Krasner et al. (2013) Formation, Precursors, Control and Occurrence of Nitrosamines in Drinking Water: A review. Water Research
Polymer OptimizationReduction in polyDADMAC dosage can reduce, but not eliminate NDMA formation
Precursor Pre-oxidation • Involves risk tradeoffs
because increasing pre-oxidant exposure promotes the formation of DBPs associated with each pre-oxidant
• Ozone most effective, followed by chlorine
• UV treatment only partially effective at advanced oxidation process fluence
• Chlorine dioxide relatively ineffective
Alternative PolymerNearly all cationic polymers currently in use will contribute to nitrosamine formation because they are amine-based. Epi-DMA polymers are more potent precursors than polyDADMAC. Polyacrylamide has much less precursors than PolyDADMAC
Activated carbon• Activated carbon is more
efficient at removing NDMA precursors than TOC in limited studies
• The ability to remove precursors for other nitrosamines is limited to one study in China
Riverbank FiltrationLimited evidence shows that riverbank filtration can remove NDMA precursors
Modify Chloramination Protocol• Minimizes dichloramine, the
active inorganic chloramine for promoting nitrosamine formation
• Involves a hydraulic mixing phenomenon. Needs more pilot or full-scale testing to characterize importance
BiofiltrationBiofiltration may remove NDMA precursors, but can also increase NDMA formation by transforming some precursors into more potent forms
UV Treatment • Full-scale applications
ongoing for hazardous waste treatment and wastewater recycling applications.
• Destroys nitrosamines, but only modest destruction in nitrosamine precursors (see pre-oxidation)
• Nitrosamine formation would continue from remaining precursors within chloraminated distribution systems
Anion Exchange• Anion exchange resins can
increase nitrosamines• The ability of anion exchange
resins to remove nitrosamine precursors is unclear
Coagulation/SofteningNeither process significantly removes NDMA precursors