Model development for the treatment of industrial wastewaters by the coagulation--flocculation process: an easy tool for linking experimental to theoretical data.

The present paper focuses on the treatment of indigo blue dye from an industrial wastewater using coagulation--flocculation process and explains removal mechanisms through the density functional theory. The conducted study analyzed the effect of different factors, including the dose and concentration of the coagulant AlCl₃, flocculant dose, and pH and their influence on coloration removal, chemical oxygen demand (COD) reduction, and sludge amount, and seeks the optimization of these factors using the design of experiment. The optimal removal efficiencies were found to be 96.42% for COD, 98.21% for absorbance, and 10.40 mL for sludge volume under optimal operational parameters, 11.25, 4.07 mL, 3.23 g/L, and 0.94 mL for pH, coagulant dose, concentration dose, and flocculant dose with a total cost of 0.0826 USD/m³, respectively. Analysis of the global reactivity descriptors for reagents indicated that AlCl₃ (ω = 6.156 eV) acts as an electrophile and the indigo blue dye (ω = 7.174 eV) as a nucleophile. The Parr's index analysis Pk + and Pk -- of indigo blue revealed that the vulnerable location for the nucleophilic attack is sited on the -C₈=O₁₀ and -C₁₁=O₁₉ bonding area. Finally, the developed model may emphasize the process engineering aspects of industrial wastewater treatment, and the linking with theoretical data could explain the involved removal mechanisms. [ABSTRACT FROM AUTHOR]