A wide range of technologies has been developed for the removal of dyes from wastewaters to decrease their environmental impact. Wastewater containing dyes is generally treated using more than one process such as adsorption/biosorption. In this study, effects of initial pH (2-8), initial azo dye concentration (Co:25-200 mg/l), contact time (tc:2.5-1440 min) and amount of waste sludge (m: 1-15 g/l) were studied by natural and modified dried waste aerobic sludge (WS) in a lab-scale batch study and also optimized by employing response surface methodology (RSM)-Box-Behnken Model for Maxilon Red GRL(MRGRL) and Everzol Red (ER) removal from wastewaters. The optimum experimental conditions were found to be pH=5, Co=112.5 mg/l, tc=180 min. and m=15g/l for dyes and MRGRL and ER removal was determined as about 97% and 95.85%, respectively. The results clearly showed that amount of WS and contact time are the most important parameters for color removal.