Abstract
Pharmaceutical residues in secondary municipal wastewater effluents pose severe ecological risks due to their persistence and bioaccumulation potential. Conventional ozonation often suffers from low gas-liquid mass transfer efficiency and high operational costs. In this study, a continuous-flow microbubble ozonation process was developed and optimized to enhance the degradation of representative pharmaceutical compounds, including carbamazepine, diclofenac, sulfamethoxazole, and ibuprofen. A three-variable Box-Behnken design coupled with response surface methodology was employed to evaluate the interactive effects of ozone dose (1.0–5.0 mg/L), hydraulic retention time (5–15 min), and gas flow rate (0.2–0.8 L/min) on removal efficiency and specific ozone consumption. Under optimal operating conditions—an ozone dose of 3.2 mg/L, hydraulic retention time of 10.4 min, and gas flow rate of 0.45 L/min—complete depletion of diclofenac and carbamazepine (>98%) was achieved, while sulfamethoxazole and ibuprofen removals reached 94.5% and 88.2%, respectively. The volumetric mass transfer coefficient (KLa) for microbubble ozonation was calculated to be 3.8 times higher than that of conventional macrobubble diffusion, leading to a 42% reduction in ozone consumption per mass of target contaminant removed. Ecotoxicity assays utilizing Daphnia magna demonstrated a significant decrease in acute toxicity following treatment. These findings highlight continuous-flow microbubble ozonation as an energy-efficient tertiary treatment technology for mitigating pharmaceutical contamination in municipal wastewater systems.
