Photodestruction of Direct Yellow 11 in aqueous TiO2 suspension: effect of operational parameters on detoxification, Langmuir-Hinshelwood kinetic expression and biodegradability

This study concerns the decolorization, dearomatization, mineralization and detoxification of the azo dye "Direct Yellow 11" using heterogeneous UV-TiO2 process. Eco-toxicological evaluation was conducted using three-days of seed germination and root growth of dicotyledonous plant (Lepidium sativum L). Dependence of initial decolorization and mineralization rate on catalyst mass was investigated; meanwhile, hydroxyl radical portionin photocatalytic degradation of dyehas been evaluated in different catalyst concentrations. There was an unexpected increment in the toxicity of solution within the first 60 min of illumination. Although maximum decolorization and mineralization rates were obtained in alkaline pH, the highest detoxification rate was achieved in natural pH. In the pH values of 5, 6.8 and 9, adsorption constants in dark and photocatalytic degradation were determined; consequently, only at pH of 5 rate data was fitted correctly to the Langmuir-Hinshelwood kinetic model. Detoxification rate was increased slightly with the hoist of temperature and activation energy for photocatalytic decolorization and mineralization processes have been determined. Energy consumption was investigated in different dye concentrations and effective concentration (EC50) of target dye was determined as 38.30 +/- 0.79 (mg/L). Biodegradability of treated effluent of dye has also been investigated using ratio of biological oxygen demand to chemical oxygen demand (BOD5/COD).