Use of response surface methodology for the bioaccumulation of Violet 90 metal-complex dye by Candida tropicalis

Abstract

In this study, the combined effects of initial dye (40-700 mg/L) and initial reducing sugar concentration (1-15 g/L) on the bioaccumulation of Violet 90 metal-complex dye by growing cells of Candida tropicalis yeast were investigated in growth media containing sugar beet molasses as a carbon and energy source. The bioaccumulation experiments were performed at pH 3 at 30 $^{\circ}$C and at 140 rpm agitation rate in a batch system. The highest uptake was obtained as 61.46% at 14.9 g/L reducing sugar concentration and at 38 mg/L dye concentration while the maximum uptake capacity was achieved as 56.28 mg/g at 3.2 g/L reducing sugar concentration and at 711.1 mg/L dye concentration. Higher uptakes were obtained at lower dye concentrations; higher uptake capacities were observed at higher initial dye concentrations. The combined effects of the initial dye (100-500 mg/L) and initial reducing sugar concentration (5-15 g/L) on dye uptake capacity and growth rate of Candida tropicalis yeast were also investigated by response surface methodology (RSM). Optimum design variables from RSM were calculated by numerical optimization with the Design Expert program. The optimum values of the variables to maximize uptake capacity were estimated as 5.1 g/L reducing sugar concentration and 499 mg/L dye concentration. The maximum uptake capacity was achieved as 41.3 mg/g at these optimized conditions.