In this study, the effects of air pressure, dissolved oxygen (DO) concentration and carbon-nitrogen (C/N) ratio on the treatment efficiency of a pilot-scale bioreactor consisted of pressurized aeration and dissolved air flotation (PA-DAF) were evaluated for domestic wastewater treatment. Results show that SS removal increased with an increased air pressure in the range of 0.10-0.50 MPa, and COD removal peaked at 86% for 0.40 MPa. At DO concentrations ranging from 0.5 to 5.5 mg/L, NH4+-N removal increased to up to 99% as DO concentration was increased, while a peak for TN removal was observed due to nitrification and denitrification. NH4+-N removal decreased while the C/N ratio was increased from 3 to 12, and a peak TN in removal was also observed. The optimal NH4+-N and TN removal efficiency achieved were 99% and 78% when the DO concentration was 2.5 mg/L and 3.5 mg/L, respectively. The NH4+-N removal efficiency was close to 100% at a C/N ratio of 3, and the maximal TN removal efficiency was 80% at a C/N ratio of 5. These results demonstrated the effectiveness of the bioreactor for domestic wastewater treatment. (C) 2014 Elsevier B.V. All rights reserved.