A set of anaerobic-anoxic-aerobic (A(2)/O) bioreactor system was designed and used to treat domestic wastewater mixed with landfill leachate in Datansha Sewage Treatment Plant in Guangzhou, south China. The optimal mixing proportion of combined treatment of domestic wastewater with landfill leachate and the optimal operating conditions for the removal efficiencies of nitrogen by using Taguchi orthogonal array test was conducted to evaluate the influence of parameters. The results showed that: the optimal volume ratio of landfill leachate and domestic wastewater in the A(2)/O process was 1:500. The average removal efficiencies of NH4+-N, TN and COD was achieved to be 96.5%, 61.0% and 81.7%, respectively in the case of the hydraulic retention time (HRT) of 11 h, dissolved oxygen (DO) of 3 mg L-1, the mixed-liquid return ratio (r) of 200% and sludge return ratio (R) of 80% in the case of the confirmatory experiment. The pilot scale (3.8 m(3)) investigation results were applied in the large-scale (220,000 m(3)/d) combined treatment of sewage wastewater with landfill leachate in Guangzhou Datansha Domestic Sewage Wastewater Treatment Plant. The removal efficiencies of COD. NH4+-N, T-N and T-P were 82.65%, 92.69%, 57.10% and 76.55%, respectively. (C) 2010 Elsevier B.V. All rights reserved.