A halo tolerant dye decolorizing bacterium Bacillus firmus (TSL9) was isolated from activated textile sludge and identified by 16S rRNA sequencing method. Due to the effect of casein enzymic hydrolysate, and yeast extract, a maximum of 97.23% remazol golden yellow decolorization was manifested by the strain in Luria Bertani medium. Bacterial dye decolorization was insignificant in the aqueous medium, when carbon and nitrogen sources were absent. Plackett-Burman experiments were carried out to screen the significance of factors like beef extract, size of the inoculum and pH on decolorization. Important factors were optimized at various levels by response surface methodology with central composite design. We concluded through model validation that the optimal values of the ingredients required to perform 78.33% decolorization are as follows: beef extract 0.48% (w/v), the size of the inoculum 7.71% (v/v) and pH 6.96. The obtained result specifies that the native bacterium had positive signs to perform effective dye decolorization under derived optimal conditions.