Optimization of operating parameters for sludge process reduction under alternating aerobic/oxygen-limited conditions by response surface methodology

► Alternating aerobic/oxygen-limited condition was the first time applied to the excess sludge reduction. ► The initial MLSS, HRT and Temperature were used as the three key parameters in oxygen-limited tank. ► We model the reciprocal relationships of the key parameters using RSM. ► The optimum condition was under the initial MLSS of 10,195 ± 50 mg/L, HRT of 9.8 h with T of 20.4 °C. ► HRT was a relative important parameter and more concentration on HRT should be concerned in continuous-flow experiment.