Effects of Effluent Organic Matter (EfOM) in Secondary Effluent on the Removal of Emerging Contaminants by Ozonation

Removal of emerging contaminants such as pharmaceutical compounds in wastewater treatment is essential to ensure the ecological health of the receiving water bodies. Ozonation is a promising technology to achieve this purpose but important wastewater characteristics affecting the optimal removal efficiency has not been fully elucidated. The secondary effluent contains effluent organic matter (EfOM), which can react directly with ozone as well as react as the initiator, promoter and inhibitor in the hydroxyl radical (·OH) chain reactions resulting from ozone decomposition. These different reaction modes of EfOM collectively determine the ozone and ·OH exposures and the degradation of pharmaceutical compounds. The objectives of this study were (1) to determine the rate constants of EfOM in terms of direct ozone reaction, initiation, promotion and inhibition reactions using a new experimental procedures that integrate the transient steady-state ·OH model, the Rct concept and the pseudo first-order ozone decomposition model, (2) to investigate the influences of pH value and temperature on these rate constants, and (3) to determine and model the effects of EfOM on the removal of selected model pharmaceutical compounds. The rate constants of EfOM in secondary effluents collected from Neihu and Dihua wastewater treatment plants were determined in this study. It was found that the rate constants of direct reaction and initiation (both resulting from the reaction with ozone) generally increase with the increasing pH value while the rate constants of promotion and inhibition (both resulting from the reaction with ·OH) do not vary significantly. All rate constants increase with the increasing temperature. The removal of ibuprofen, acetylsulfamethoxazole and metoprolol in diluted Neihu secondary effluent using ozonation can be fairly-well modeled by using the determined rate constants of EfOM.