The investigation presented here focussed on the steel industrial wastewater (SIWW) FeCl3 rich as an original coagulant to remove the synthetic textile wastewater. Response surface methodology was used to study the cumulative effect of the various parameters namely, coagulant dosage, initial pH of dye solution, dye concentration and to optimize the process conditions for the decolourization and COD reduction of disperse blue 79 solution. For obtaining the mutual interaction between the variables and optimizing these variables, a 23 full factorial central composite rotatable design using response surface methodology was employed. The efficiencies of decolourization and COD reduction for disperse blue 79 solution were accomplished at optimum conditions as 99% and 94%, respectively. (C) 2008 Elsevier B.V. All rights reserved.