A and B shows the main effects of the process parameters for the CAC and BFS AC, respectively. the sign of the main effect indicates the directions of the effect. It can be seen from fig2.that in case of CAC, the effect of pH was characterized by a greater degree of departure and also had a negative effect on the response, whereas for BFS AC, the concentration of Cr (VI) has a positive effect on the response with greater departure. Contour plots for the significant interactions of CAC and BFS AC were shown in Fig3