A continuous-flow anoxic/aerobic (A/A) biological treatment system designed to treat swine wastewater was investigated. Laboratory studies were conducted to determine the heterotrophic bacteria kinetic parameter values in swine wastewater. Maximum specific growth rate estimates at 20 degrees C were low, 0.075 and 0.055 h-1 for aerobic and anoxic conditions, respectively, indicating that swine wastewater is relatively difficult to degrade. Estimates of the half saturation constant for aerobic and anoxic conditions, 167 and 163 mg/litre COD, and biomass yield, 0.51 and 0.47 mg COD/mg COD, were within ranges reported for heterotrophic bacteria in municipal wastewater. A bench-scale A/A system was operated at anoxic and aerobic hydraulic retention times of 35 and 36 h and a recirculation ratio of 1.0. At steady state, ammonia was reduced from an influent value of 1420 mg/litre to an effluent value of 209 mg/litre NH4-N, total COD was reduced from 10 480 to 3290 mg/litre COD, and total sulfide was reduced from 25 to <0.1 mg/litre S-2. The nitrate concentration increased from <0.1 mg/litre in the influent to 620 mg/litre NO3-N in the final effluent, resulting in an overall inorganic nitrogen (ammonia and nitrate) removal of 42%. These results indicate that the A/A system was effective in reducing the concentration of organic compounds, inorganic nitrogen and sulfide in swine wastewater.