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 (lambda = 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.