Kinetics, mechanisms, and influencing factors on the treatment of haloacetonitriles (HANs) in water by two household heating devices

Abstract

Haloacetonitriles (HANs) are a group of nitrogenous disinfection by-products (DBPs) commonly found in treated water with potential carcinogenic, cytotoxic, and genotoxic risks. In order to control HANs and understand their real intake levels by people via drinking water, this study evaluated a list of structural, operational, and environmental factors affecting the treatment of HANs by two domestic heating devices, i.e., an electric boiler and a microwave oven. Results show that the concentrations of HANs decreased exponentially over time with increasing temperature, water turbulence, and bubbles, and the phenomena were most likely due to a combined effect of volatilization and hydrolysis. Among HANs, the lability increased with increasing halogenation degrees (i.e., tri- > di- > mono- HANs) yet decreasing halogen molecular weights (i.e., Cl- > Br- > I- HANs); such trends were well captured by quantitative structure activity relationship models (R2 = 0.99). Operational factors played critical roles in controlling HANs too, including the rate of heating, water volume, water temperature at time of pouring, cooling method, and capping condition, suggesting that people could benefit from proper handling methods and procedures. In addition, HANs added to tap water exhibited higher removals than those added to ultrapure water, probably because of the presence of free chlorine in tap water.