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Formation of Nitrosamines and Perfluoroalkyl Acids During Ozonation in Water Reuse Applications

Project: 11-08
Type: Scientific Investigation
Year Released: 2015

Program: Tailored Collaboration
Total Investment: $390,487 (Cash $ 149,987, In-Kind cash and service: $ 240,500)

Principal Investigator: Eric Dickenson, Southern Nevada Water Authority

Background

The ability of ozone treatment to mitigate human and environmental impacts associated with pathogens and trace organic contaminants is making it a promising and trending treatment alternative in water reuse applications, particularly potable reuse. However, the formation of potentially carcinogenic nitrosamines and perfluoroalkyl acids could be a barrier to the widespread use of ozone. Therefore, an evaluation of their occurrence, factors affecting formation, and potential mitigation strategies is warranted.

Goals and Objectives

The project targeted the following objectives:

  • Assess the formation of nitrosamines (e.g., NDMA) upon ozonation of treated wastewaters;
  • Assess the formation of perfluoroalkyl acids (PFAAs; e.g., PFOA and PFOS) upon ozonation of treated wastewaters;
  • Evaluate the factors responsible for the formation of these ozone byproducts;
  • Recommend potential mitigation strategies.

Research Approach

The research approach for this study included the following major tasks:

  • Perform a literature review on nitrosamine and perfluoroalkyl acid occurrence, relevant precursors and formation pathways, factors that affect formation, and proven and potential mitigation strategies;
  • Evaluate their occurrence, formation, and reduction in full- and pilot-scale treatment systems;
  • Perform bench-scale studies to determine critical factors affecting their formation;
  • Evaluate and identify useful mitigation strategies.

Findings and Conclusions

Based on full- and pilot-scale system performance data and systematic bench-scale studies, N-nitrosodimethylamine (NDMA) and some PFAAs, including perfluoropentanoic acid, perfluorohexanoic acid (PFHxA), perfluorooctanoic acid, and perfluorobutane sulfonic acid, were formed after ozonation of secondary treated wastewaters. NDMA was the dominant nitrosamine, and PFHxA was the most frequently formed PFAA. Depending on future regulatory determinations, these contaminants could be of concern for potable reuse treatment systems that employ ozone. The findings suggest that the ozone-reactive NDMA precursors are distinctly different than chloramine-reactive NDMA precursors (i.e., dimethylamine-containing compounds), that NDMA formation is due to reactions of precursors with molecular ozone as opposed to hydroxyl radical exposure, and that pH in the 6 to 8 range had little impact on either NDMA or PFAA formation with ozonation. Control strategies, such as full nitrification during secondary biological treatment, optimized ozone dosing, or certain post-treatment technologies can be implemented to potentially mitigate the formation of these contaminants. Full nitrification, UV photolysis, and biological activated carbon proved to be effective for NDMA mitigation, while granular activated carbon, anion exchange, and nanofiltration were effective for PFAA mitigation. In some instances, secondary biological treatment resulted in increases in PFAA concentrations.

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