Dissolved Ozone Flotation for COD and TOC Removal From Secondary Municipal Wastewater Effluent: Effects of Ozone‐Generator Setting, Mixing Speed, and Treatment Time

Advanced polishing can improve the quality of secondary municipal wastewater effluent and enhance its potential for beneficial reuse. In order to remove total organic carbon (TOC) and chemical oxygen demand (COD) from secondary effluent obtained from the Al‐Rustamiah Wastewater Treatment Plant in Baghdad, Iraq, this study assessed dissolved ozone flotation (DOF) as a tertiary treatment method. Three mixing speeds (70, 150, and 250 rpm), four ozone‐generator control settings (0.21, 0.25, 0.31, and 0.48), and treatment durations of 30, 60, 90, and 120 min were used in the experiments. While higher mixing speeds decreased treatment performance, COD and TOC removal generally rose with increasing ozone‐generator setting and treatment time. At 70 rpm, an ozone‐generator setting of 0.48, and a treatment duration of 120 min, the maximum removal efficiencies were 99% for COD and 98% for TOC. COD and TOC removal dropped to 87% at 150 rpm and 80% at 250 rpm with the same generator setting and treatment duration. These results suggest that the DOF system under investigation may be used as a tertiary polishing method to lower residual organic matter in secondary municipal wastewater. However, the results should be considered as observed treatment performance under the examined conditions because the ozone‐generator parameters were not calibrated in terms of transferred ozone mass or dissolved ozone concentration, and the experimental runs were not independently duplicated. To further evaluate process performance and its feasibility for reuse applications, more research involving calibrated ozone dosing, experimental replication, and additional water‐quality criteria is needed.