Influence of Seasonal Variation of Water Temperature and Dissolved Organic Matter on Ozone and OH Radical Reaction Kinetics During Ozonation of a Lake Water
This study used key description parameters of the ozonation process in lake water samples over a 1-year period to better understand the influence of seasonal variations in water quality such as water temperature and dissolved organic matter on ozone decomposition and OH radical formation and reaction kinetics. The parameters were the initial ozone demand (IOD), ozone decay rate constant after the IOD (ksec), ratio of OH radical exposure to the ozone exposure (RCt), and ratio of ozone consumption to the OH radial exposure multiplied by the second-order rate constant for the reaction of the OH radical with an OH radical probe compound (Ω). The seasonal variations in water quality had the most significant influence on RCt (39–64%), followed by ksec (35–38%), Ω (27–34%), and IOD (11–25%) for the raw lake water and sand-filtered water in which the numbers inside parentheses indicate the percent standard deviation of the measured values for 1 year. For the oligotrophic-type lake water, the seasonal variation in water temperature (6–26 °C) had the most significant influence on the ksec, RCt, and Ω. The Ω was newly found to be inversely related with water temperature, possibly due to the temperature-dependent OH radical yield from ozone decomposition. This implies that the OH radical oxidation capacity during ozonation can be significantly influenced by the temperature due to the varying ozone decomposition rate and the intrinsic OH radical yield. This study also demonstrated the Ω is a useful, alternative parameter to the RCt for describing or predicting OH radical exposure from ozone consumption especially when the ozone decay is rapid or varies over time such as the initial ozonation phase of natural water or wastewater where a considerable OH radical exposure takes place.