Dye separation using a semi-batch foaming process: Process optimization using Taguchi methodology and Grey relational analysis

Abstract

Foam fractionation is one of the novel techniques used nowadays for the wastewater treatment. The present paper discusses the removal of methylene blue dye by using a surfactant, sodium dodecyl sulfate, as a collector, by semi-batch foam fractionation technique. The influence of operating variables like aeration rate (150 – 250 mL.min^-1), liquid height (600 – 900 mL), dye concentration (5 – 25 ppm), pH (3 – 10), surfactant dose (250 – 2000 ppm) on percentage removal, enrichment ratio and surface excess were investigated. The results revealed fairly high percentage removals at various operating conditions due to strong electrostatic interaction between dye and surfactant. Further, in order to augment separation, optimization was performed by employing Taguchi-based experimental design followed by Grey relational analysis (GRA) technique. The optimal conditions were found to be: 150 mL.min^-1 air flow rate, 600 mL liquid loading and 5 ppm dye concentration for percentage removal of 95.7% and an enrichment ratio of 7.49. The analysis of variance (ANOVA) suggested dye concentration to be the most influencing operating variable. Lastly, the equilibrium relationship between bulk and surface phase was established which qualitatively indicates as to how much the actual process departs from equilibrium.