Comparative studies of mineralization and detoxification of Mordant Black 17 in aqueous solution by UV light induced Mⁿ⁺/H₂O₂ and Mⁿ⁺/S₂O₈²⁻ systems

The present study reports a process for simultaneous mineralization and detoxification of Mordant Black 17 with high electrical energy efficiency. Hydrogen peroxide and ammonium persulphate (APS) were used for the generation of hydroxyl and sulphate radicals using UV light (λ = 254 nm) and Fe²⁺ and Ag⁺ ions as catalysts. The detoxification and energy efficiency of various processes were measured by monitoring growth inhibition of Escherichia coli and Electrical Energy per Order (EE/O) applicable for low concentration contaminants respectively. Systems catalyzed by Fe²⁺ are more energy efficient and possess higher mineralization and detoxification efficiency than that of Ag⁺. The concentration of the catalysts and oxidants were found to strongly influence the EE/O of the systems. The most cost efficient processes for simultaneous mineralization and detoxification are Fe²⁺/APS/UV at pH 3.00 and Fe²⁺/H₂O₂/UV at pH 3.00 and 5.78. The upper limit concentration of Fe²⁺ is fixed at 0.01 mM for complete detoxification. The treated solutions start detoxifying at this concentration, above which they remain more toxic than the original dye solution irrespective of the extent of mineralization. On the contrary, no such limit could be established for Ag⁺ systems for complete detoxification even after 91% mineralization.