Temporal andSpatial Variation in Hydroxyl RadicalScavenging Capacity in Drinking Water and Correlation to Water QualityParameters

Advanced oxidation processes (AOPs) are being used more frequently in drinking water treatment plants for purposes such as removing taste and odor-causing compounds or to control recalcitrant organic contaminants. Water’s hydroxyl radical scavenging capacity (<i>S</i>_c) is an important parameter for AOP design and operation, but due to complexity in its measurement, <i>S</i>_c data are limited and knowledge of its temporal and spatial variation is sparse. Furthermore, the feasibility of estimating <i>S</i>_c through monitoring common water quality parameters is unclear. The variability in <i>S</i>_c of water from five surface water plants and one groundwater plant was measured for 1 year along with total organic carbon, total inorganic carbon, ultraviolet absorbance at 254 nm, and fluorescence emission-excitation matrices. The results showed about a 10–25% variation in the <i>S</i>_c, and <i>S</i>_c was not well-correlated with any of the water quality parameters measured. The reduction in <i>S</i>_c across ultrafiltration treatment was similar to that across conventional treatment (15–30%). Due to the scavenging capacity of the added oxidant, the modeled variation in UV/H₂O₂ or UV/chlorine performance due to <i>S</i>_c variation was small (∼5–10% change in the pollutant removal rate).