Colour removal of binary mixture of food colouring dye by classical fenton oxidation: Effect of salts, citric acid and kinetics study

Abstract

Food colouring dyes, such as Food Red 9 (FR9) and Food Green 3 (FG3), which are widely used in the food industry, due to their intense colour when discharged untreated, hinder photosynthesis, degrade soil quality, hamper plant growth, and pose risks to aquatic animals. To address these issues, the colour removal of mixture of two food colouring dyes, viz FR9 and FG3 was studied by classical Fenton oxidation. Using a face-centered central composite design (FCCD), the optimum parameters were [FR9] = [FG3] = 0.17 mM; [] = 0.3 mM; ] = 4.0 mM (pH 3.0, 200 rpm, 25 ). Under these conditions, colour removal efficiencies of 47.78 % (422 nm) and 93.45 % (624 nm) were achieved after 120 min. The removal followed a two-step pattern: rapid (5–50 min) and slower (50–120 min). pH significantly influenced efficiency: maximum removal at pH 3 (92.58 %), decreasing at pH 5.8 (89.12 %), pH 7.0 (80.75 %), pH 9.0 (69.39 %), and pH 11.0 (39.65 %). The effect of inorganic salts found in wastewater has been studied, and shows slight inhibition, and shows significant inhibition and shows a slight increase in the colour removal. Citric acid (CA) addition accelerated the process, achieving equivalent removal in 40 min and increasing efficiency by 3.9-fold (422 nm) and 3.1-fold (624 nm). Among kinetic models tested, the Behnajady-Modirshahla-Ghanbary (BMG) kinetic model best fit the data ( = 0.99). Fenton oxidation effectively removes synthetic food dyes under optimized conditions. CA enhances performance and mitigates oxidation.