Study of the cytotoxicity of reactive dyeing effluent treated by Fenton oxidation

Fenton oxidative wastewater treatment of CI Reactive Black 5 and CI Reactive Blue 19 effluent was performed after a simulated laboratory-scale dyeing process, and the cytotoxicity of the treated effluent was evaluated using human skin cell lines. Among the components for Fenton oxidation, the human skin cell results showed that iron(II)sulfate at 150 mm did not show any significant cytotoxic effect, while other components, such as Glauber's salt solution (20 g l^-1; 14%), CI Reactive Black 5 (30 mg l^-1; 24%), caustic soda (5 g l^-1; 30%), CI Reactive Blue 19 (30 mg l^-1; 32%), hydrogen peroxide (0.01 m) and soda ash (5 g l^-1) showed cytotoxic potential; the reagent sodium sulfite (30 mm; 48%) exhibited the strongest cytotoxicity level. Fast decolorisation (>95%) was achieved within 10 min for CI Reactive Black 5, while for CI Reactive Blue 19 it took longer (1.5 h) to achieve the same decolorisation. Studies showed that decolorisation for both dyes followed second-order kinetics. In spite of the remarkable efficacy of the Fenton oxidation process in removing colour within a short period of time, the resulting treated wastewater (within a reaction time of 1.5 h) also showed cytotoxicity towards the human HaCaT skin keratinocyte cell line. This observation can be explained by the strong oxidant and intermediate species produced during the advanced oxidation process, and a treatment step using sodium sulfite and a prolonged residence time can help to reduce the cytotoxicity.