RESPONSE SURFACE MODELLING FOR REACTIVE DYE REMOVAL USING BIO-SOLIDS: APPLICATION OF BOX-BEHNKEN EXPERIMENTAL DESIGN

The removal of reactive dyes is rather difficult by chemical coagulation/flocculation because of strong resistance to biodegradation in aerobic environments. The removal of color from textile wastewater using low-cost adsorbents instead of expensive adsorbents is considered to be an important application of adsorption. In this study, powder-activated sludge was studied for the removal of color from aqueous solutions in a batch system using response surface methodology. Effects of initial pH, initial reactive dye concentration (Everzol Yellow 3RS H/C), contact time, and amount of bio-solid dosage (dried activated sludge) was optimized by using a four-factor, three-level Box-Behnken design for response surface modeling. Experiments were carried out in a lab-scale batch study. Four independent variables (initial pH: 2-8, initial concentration of dye ions (Co): 25-200 mg/L, contact time (tc): 10-180 min, and bio-solid amount (m): 1-15 g/L) were labeled as A, B, C, and D at three levels (-1, 0, 1), and a second-order polynomial regression equation was used to predict responses. The variables were tested by using analysis of variance (ANOVA). The optimal conditions were found to be pH = 2, Co = 200 mg/L, tc = 95 min, and m = 0.8 g/100 ml for which EY3RS removal was 92.75%. The results show that dye concentrations, bio-solid amount, and contact time are the most important factors in color removal. All factors showed combined effects on dye removal.