Revealing a Size-Resolved Fluorescence-Based Metric for Tracking Oxidative Treatment of Total N-Nitrosamine Precursors in Waters from Wastewater Treatment Plants

Abstract

N-Nitrosamines make up a nonhalogenated group of disinfection byproducts that form during chloramination, particularly in drinking waters impacted by wastewater treatment plant (WWTP) effluents. Here, we reveal a size-resolved fluorescence-based precursor surrogate for tracking total N-nitrosamine formation potential (TONOFP) through oxidative treatment. Samples were collected at seven WWTPs, at the finished effluent and prior to final disinfection (i.e., secondary effluent). Asymmetric flow field-flow fractionation (AF4) with inline fluorescence detection at excitation and emission wavelengths of 280 and 340 nm, respectively (i.e., I 280/340), showed protein-rich natural organic matter peaks between 10–445 and 445–1500 kDa. TONOFP was measured by chemiluminescence on samples dosed with 250 mg L–1 Cl2 monochloramine at pH 7 for 7 days. Metrics from AF4 I 280/340 (i.e., area under the curve and peak height) and I 257/277 from whole water excitation–emission matrices were leveraged in multivariate models to develop correlations with TONOFP. The TONOFP of the finished effluent divided by that of the secondary effluent (i.e., the TONOFP Ratio) was strongly correlated (R 2 = 0.996; p = 0.000) to a model of AUC for the 10–445 kDa peak, maximal peak height, and I 257/277. This TONOFP precursor surrogate requires 2 mL of sample and is transformational with respect to assessing the impact of oxidative treatments on N-nitrosamine precursor concentrations.

N-Nitrosodimethylamine Formation during UV/Hydrogen Peroxide and UV/Chlorine Advanced Oxidation Process Treatment Following Reverse Osmosis for Potable Reuse

“…NDMA is particularly challenging for facilities purifying municipal wastewater effluents for potable reuse. The full advanced treatment (FAT) train frequently employed at these facilities consists of microfiltration (MF) and reverse osmosis (RO) membranes as physical barriers to contaminants, followed by an UV-based advanced oxidation process (AOP) as a photochemical barrier. , NDMA concentrations in sewage or primary effluents can be ≥30 ng/L. , NDMA precursors are associated with wastewater effluents, − and the chloramines applied to control biofouling on MF and RO membranes react with these precursors to form NDMA upstream of RO treatment. − Because NDMA is only partially rejected by RO membranes, ,− the AOP employs up to 1000 mJ/cm 2 UV fluence to reduce the NDMA concentrations in RO permeates to <10 ng/L. ,, …”

Comparative Evaluation of Chemical and Photolytic Denitrosation Methods for Chemiluminescence Detection of Total N-Nitrosamines in Wastewater Samples

“…Our setup utilized a large-volume purge vessel with a bottom injection port, whereas Breider and von Gunten used a commercially available small-volume purge vessel with a top injection port. Indeed, replacing the large-volume vessel with the small-volume unit led to apparent peak broadening (i.e., CV = 7.8% for five injections; Figure a), which was likely caused by the dilution effect on the acidic triiodide solution resulting from continuous sample injections . For our setup, five 100-μL injections of the NDMA standard would dilute the acidic triiodide solution (i.e., ∼4 mL with constant N 2 purging) inside the small-volume purge vessel by ∼11% and presumably lowered the conversion efficiency of NDMA to NO • .…”

“…Indeed, replacing the large-volume vessel with the small-volume unit led to apparent peak broadening (i.e., CV = 7.8% for five injections; Figure 2 a), which was likely caused by the dilution effect on the acidic triiodide solution resulting from continuous sample injections. 35 For our setup, five 100-μL injections of the NDMA standard would dilute the acidic triiodide solution (i.e., ∼4 mL with constant N 2 purging) inside the small-volume purge vessel by ∼11% and presumably lowered the conversion efficiency of NDMA to NO • . Contrary to prior speculation by Hausladen et al, 26 spiking sodium nitrite or NDMA into the freshly prepared acidic triiodide solution did not produce characteristic UV–visible absorption bands of nitrosyl iodide in the gas phase above the solution ( Figure S1 ).…”