Abstract
Abstract. The presence of N-nitrosodimethylamine (NDMA) in drinking water supplies has raised concern over its removal by common drinking water treatment processes. However, only limited studies have been examined to evaluate the potential removal of NDMA by numerous water treatment technologies within a realistic range (i.e., sub μg/L) of NDMA levels in natural water due to analytical availability. In this study, a simple detection method based on scintillation spectroscopy has been used to quantify the concentration of 14C-labeled NDMA at various ratios of sample to scintillation liquid. Without sample pretreatment, the method detection limits are 0.91, 0.98, 1.23, and 1.45 ng/L of NDMA at scintillation intensity ratios of 10:10, 5:15, 15:5, and 2.5:17.5 (sample: scintillation liquid), respectively. The scintillation intensity in all cases is linear (R2>0.99) and is in the range of 0 to 100 ng/L of NDMA. In addition, because scintillation intensity is independent of solution pH, conductivity, and background electrolyte ion types, a separate calibration curve is unnecessary for NDMA samples at different solution conditions. Bench-scale experiments were performed to simulate individual treatment processes, which include coagulation and adsorption by powdered activated carbon (PAC), as used in a drinking water treatment plant, and biosorption, a technique used in biological treatment of waste water. The results show that coagulation and biosorption may not be appropriate mechanisms to remove NDMA (i.e., hydrophilic based on its low octanol-water partitioning coefficient, Log Kow=0.57). However, relatively high removal of NDMA (approximately 50%) was obtained by PAC at high PAC dosages and longer contact times.
Highlights
N-nitrosodimethylamine (NDMA) is a toxic and carcinogenic yellow liquid that has been identified as a contaminant in drinking water, ground water, and a variety of other matrices (NRC, 1981; Leoppky and Micheljda, 1994; Mitch and Sedlak, 2004)
NDMA is listed as a priority pollutant in the United States (CFR, 2001), a federal maximum contaminant level has not been established for drinking water
Ultrapure (natural organic matter (NOM) free) water prepared from water purification system (DirectQ 3 system, Millipore, Korea) and raw drinking water (RDW) collected from a local water treatment plant (WTP), were selected for this study
Summary
N-nitrosodimethylamine (NDMA) is a toxic and carcinogenic yellow liquid that has been identified as a contaminant in drinking water, ground water, and a variety of other matrices (NRC, 1981; Leoppky and Micheljda, 1994; Mitch and Sedlak, 2004). Several previous studies investigated NDMA removal using drinking water treatment technologies (Kaplan and Kaplan, 1985; Gumnison et al, 2000; Holgneand Bader, 1983; Siddiqui and Atasi, 2001), only high initial concentrations (>1000 ng/L) were tested. Analytical determination of NDMA content from surface water and wastewater commonly involves the use of gas chromatography-mass spectrometry (GC-MS or MS/MS) with chemical ionization, or traditional electron impact with continuous liquid-liquid extraction, solid phase extraction, or solid phase microextraction for ppt level NDMA analysis (Yoo et al, 2000; Mitch et al, 2003; Eaton and Briggs, 2000) These analytical techniques have issues regarding pretreatment requirements, compound recoveries, and detection limits. We have demonstrated role of scintillation counting for process studies with emerging contaminant available from pharmacological studies
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