Near real-time N-nitrosodimethylamine monitoring in potable water reuse via online high-performance liquid chromatography-photochemical reaction-chemiluminescence

Abstract

Direct potable reuse requires stringent water quality assurance to protect public health. This study developed an online analytical technique—high-performance liquid chromatography followed by photochemical reaction and chemiluminescence detection (HPLC-PR-CL)—for determination of the concentration of N-nitrosodimethylamine (NDMA) and three other N-nitrosamines. Its feasibility for near real-time analysis was evaluated by analyzing an ultrafiltration (UF)-treated wastewater before and after a pilot-scale reverse osmosis (RO) treatment system. The online instrument with a method detection limit of 0.3–2.7 ng L⁻¹ requires a direct injection (i.e., no sample pre-concentration) of only 20–200 μL sample volume for the determination of N-nitrosamine concentrations every 20 min. NDMA concentrations in UF-treated wastewater were successfully monitored in a range of 50–200 ng L⁻¹ over the course of 24 h. Likewise, NDMA concentrations in RO permeate ranged from 26–81 ng L⁻¹ over the course of 48 h. The online monitor was capable of recording variations in N-nitrosamine concentration in RO permeate that occurred following changes in feedwater concentration and temperature. This study demonstrates the potential for online water quality assurance via direct measurement of trace levels of organic contaminants, which is highly relevant to the implementation of potable reuse.