Mineralization of Calcon by UV/oxidant systems and assessment of biotoxicity of the treated solutions by E. coli colony forming unit assay

Mineralization of Calcon, an azo dye, was carried out using UV254 in the presence of H2O2 (HP) and (NH4)2S2O8 (APS) as oxidants. Degradation is found to be pH dependent and with UV/HP system, it proceeds efficiently at pH 1 and 12.6 even though mineralization is efficient at pH 1. The mineralization efficiency is in the order: UV/APS > UV/HP in acidic to neutral medium and UV/HP > UV/APS in basic medium. Nevertheless, lowest mineralization is recorded at pH 7 and 9 for UV/HP and UV/APS systems respectively. Most importantly decay in degradation was not observed at higher concentrations of oxidants. Presence of anions exerts inhibition effect on the degradation process, which is in the order: Cl− > SO42− > NO3− and SO42− > Cl− > NO3− for HP and APS as oxidants respectively. Toxicity of the treated solutions was determined on the basis of E. coli growth and the detoxification efficiency of the systems was found to be in the order UV/APS > UV/HP. The solution after mineralization was completely detoxified by adjusting its pH to 7. Based on the results, it is recommended that APS is the most suitable oxidant for both mineralization and detoxification processes of Calcon.

Mineralization of Calcon at different pH. Inset: detoxification efficiency of UV/oxidant systems. Abbreviations: APS – ammonium persulphate; HP – hydrogen peroxide.Figure optionsDownload as PowerPoint slideHighlights
► High mineralization of Calcon is obtained at pH 1 using UV254 light.
► UV/(NH4)2S2O8 system is more efficient for both mineralization and detoxification processes.
► Inorganic salts have inhibition effect on the degradation process.
► Complete detoxification after mineralization is achieved at pH 7.
► Toxicity determination based on E. coli growth can be applied in wastewater treatment process.