Treatment of dye (Remazol Blue) and heavy metals using yeast cells with the purpose of managing polluted textile wastewaters

The bioaccumulation of chromium(VI), nickel(II), copper(II), and reactive dye by the yeast Rhodotorula mucilaginosa has been investigated in media containing molasses as a carbon and energy source. Optimal pH values for the yeast cells to remove the pollutants were pH 4 for copper(II) and dye, pH 6 for chromium(VI) and dye, and pH 5 for nickel(II) and dye in media containing 50 mg l−1 heavy metal and 50 mg l−1 Remazol Blue. The maximum dye bioaccumulation was observed within 4-6 days and uptake yields varied from 93% to 97%. The highest copper(II) removal yields measured were 30.6% for 45.4 mg l−1 and 32.4% for 95.9 mg l−1 initial copper(II) concentrations. The nickel(II) removal yield was 45.5% for 22.3 mg l−1, 38.0% for 34.7 mg l−1, and 30.3% for 62.2 mg l−1. Higher chromium(VI) removal yields were obtained, such as 94.5% for 49.2 mg l−1 and 87.7% for 129.2 mg l−1 initial chromium(VI) concentration. The maximum dye and heavy metal bioaccumulation yield was investigated in media with a constant dye (approximately 50 mg l−1) and increasing heavy metal concentration. In the medium with 48.9-98.8 mg l−1 copper(II) and constant dye concentration, the maximum copper(II) bioaccumulation was 27.7% and 27.9% whereas the maximum dye bioaccumulation was 96.1% and 95.3%. The maximum chromium(VI) bioaccumulation in the medium with dye was 95.2% and 80.3% at 48.2 and 102.2 mg l−1 chromium(VI) concentrations. In these media dye bioaccumulation was 76.1% and 35.1%, respectively. The highest nickel(II) removal was 6.1%, 20.3% and 16.0% in the medium with 23.8 mg l−1 nickel(II) + 37.8 mg l−1 dye, 38.1 mg l−1 nickel(II) + 33.4 mg l−1 dye and 59.0 mg l−1 nickel(II) + 39.2 mg l−1 dye, respectively. The maximum dye bioaccumulation yield in the media with nickel(II) was 94.1%, 78.0% and 58.7%, respectively.