Optimization of the parameters impacting the Direct Red 89 degradation with thermally activated persulfate using a full factorial design

Abstract

A two-level full factorial design with interactions was effectively used to screen for parameters impacting the degradation of Direct Red 89 (DR89) by thermally activated persulfate. Four variables were identified as critical: reaction temperature, persulfate concentration, initial pH of medium, and initial DR89 concentration. The goodness of fit of the reduced model was tested by generating plots of descriptive statistic, residuals versus predicted responses, normal probability versus residuals, and observed versus predicted values, as well as examining the analysis of variance table. The observed and the predicted response values of the reduced model exhibited a good correlation, with R2, [Formula: see text] , Q2, and p of 0.990, 0.983, 0.968, and 0.000, respectively. To determine optimal operating parameters, the desirability function was utilized, and it was determined to be 0.988 with a predicted response of 99.89% for an initial DR89 concentration of 51.96 mg/L, a persulfate concentration of 12 mmol/L, a reaction temperature of 60 °C, and a pH of 3.