Effects of molecular ozone and hydroxyl radical on formation of N-nitrosamines and perfluoroalkyl acids during ozonation of treated wastewaters

Abstract

N-Nitrosamines-toxic disinfection byproducts commonly associated with chloramination-have recently been shown to increase after ozonation of some surface waters and treated wastewaters. In addition to five nitrosamines, two perfluoroalkyl acids (PFAAs) are included in the most recent U.S. EPA Contaminant Candidate List due to potential public health risks. In this manuscript, the potential roles of molecular ozone (O 3 ) and hydroxyl radical (˙OH) were investigated in the formation of N-nitrosamines and PFAAs in treated wastewaters. The results herein are based on controlled bench-scale experiments designed to isolate the effects of O 3 with the use of t-butanol as a˙OH scavenger. Nitrous oxide gas saturated samples were exposed to gamma radiation to isolate the effects of˙OH, and para-chlorobenzoic acid was used to assess˙OH exposure. This study found that the presence of molecular ozone versus the hydroxyl radical promoted N-nitrosodimethylamine (NDMA) formation. Six other N-nitrosamines showed very little or no formation upon the ozonation of six treated wastewaters up to an O 3 : TOC ratio of 1.0. For PFAAs, perfluorohexanoic acid (PFHxA) formed the highest and most consistently upon ozonation (up to an O 3 : TOC ratio of 2.0) of the same six treated wastewaters. Presence of molecular ozone (more so than hydroxyl radical), appears to promote the formation of PFHxA and perfluorobutane sulfonic acid (PFBS). The effect of pH in the range of 6-8 upon the formation of NDMA and PFAAs was found to be minimal. These findings provide new understanding of the formation of oxidation byproducts during ozonation of reclaimed wastewaters. Depending on future regulatory determinations, NDMA and a few PFAAs could be of concern for potable reuse treatment systems that employ ozone.Environ. Sci.: Water Res. Technol. This journal is

Persistent contaminants of emerging concern in ozone‐biofiltration systems: Analysis from multiple studies

“…Similar to NDMA discussed above, the concentrations of these compounds increased following ozonation but further decreased to the same level as influent concentrations or even less after BAF treatment. While the data are insufficient to discuss in the present study, it is important to note that PFAS were also shown to increase after ozonation, especially the smaller-molecular-weight compounds (Pisarenko, Marti, Gerrity, Peller, & Dickenson, 2015). Further information about the transformation of perfluoroalkyl acid precursors in ozone-BAF systems is thus warranted.…”

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“…As a control strategy, the relationship between ∆UVA254 and ∆TrOC as proposed by several authors (Bahr et al, 2007;Chys et al, submitted;Dickenson et al, 2009;Gerrity et al, 2012;Pisarenko et al, 2015;Wittmer et al, 2015) was evaluated for both ozonation as a stand-alone treatment and for its combination with TF, SSF or BAC. In particular, the correlations experimentally constructed by Chys et al(submitted) (see Appendix) for 9 model TrOCs with an ozone reactivity ranging from fast (kO3 > 5×10 4 M -1 s -1 ) to slow (kO3 < 10 M -1 s -1 ) are investigated: diclofenac, trimethoprim, levofloxacin (kO3 > 5×10 4 M -1 s -1 ), amitriptyline, ciprofloxacin, venlafaxine (5×10 4 M -1 s -1 > kO3 > 10 M -1 s -1 ), amantadine, flumequine and metronidazole (kO3 < 10 M -1 s -1 ).…”

Investigation on the compositions of unsymmetrical dimethylhydrazine treatment with different oxidants using solid-phase micro-extraction-gas chromatography–mass spectrometer

“…The NDMA formation mechanism during wastewater ozonation has attracted much attention [10,26–28]. Transformation of UDMH to NDMA is mainly induced by ozone or HO · rather than the dissolved oxygen proposed previously.…”

“…[28] found that wastewater with higher HO · scavenging may also lead to higher NDMA formation during ozonation. Radiolysis experiments [28] were performed to isolate the contribution of hydroxy radicals. During radiolysis experiments, there was no NDMA formation observed in any of the wastewater samples.…”