AWWA WQTC58816

Experiments were conducted at the bench scale to determine the effects of pH, total organic carbon (TOC), alkalinity, temperature, and H₂O₂ dose on the removal rate of atrazine (ATZ) using ultraviolet light (UV) emitted from a medium-pressure mercury lamp. Simulated natural water was used to control these parameters independently. Initial experiments showed very little effect of alkalinity alone, and the effect of TOC was ascribable solely to light screening since TOC had no effect on the UV dose-based rate constants (which account for light screening by the water matrix). On the other hand, increasing temperature and H₂O₂ dose positively affected the removal rates while increasing the pH had a small but negative effect both with and without H₂O₂ that was most discernable at higher temperatures. These three parameters (H₂O₂, T, and pH) were therefore selected for further study to design a dose-response model of ATZ removal. Other experiments examined whether nitrate (NO₃ ^-) has a photosensitizing effect on ATZ degradation (via ^.OH production during NO₃ ^- photolysis). Nitrate concentrations up to 7 mg-N/L enhanced the ATZ removal rates (s^-1) in deionized water but decreased the rates slightly in synthetic natural water. This latter effect is due to a combination of light screening and ^.OH scavenging by natural organic matter. Nonetheless, the rates remain higher than expected on the basis of light screening alone indicating that a large fraction of ATZ reacts with ^.OH even in the presence of ^.OH scavengers. Includes 19 references, tables, figures.