Central composite Design (RSM-CCD) design was used to optimize the
effect of process variables on the removal of Congo red dye. The NZVI-CNS prepared by simple liquid-phase
reduction method, namely, borohydride reduction method. The results of RSM-CCD method showed the significant
effect of pH (A), Dose (B), initial concentration (C), time (D), and temperature (E) on Congo red dye removal from
aqueous solution. The results of ANOVA and regression of second order model showed that the linear effects of
Dose (B) and Temperature (E) were more significant. All the critical variables having greatest effect on the removal
of