Degradation of Indigo Carmine Using Advanced Oxidation Processes: Synergy Effects and Toxicological Study

Abstract

The physicochemical degradation of Indigo Carmine (IC) dye in aqueous solution was performed using single and combined Advanced Oxidation Processes (AOP’s). Photocatalysis (TiO 2 -UV), Ozonation (O 3 ) and Sonolysis (SN) were tested either in a standalone methodology or by combination of two simultaneous AOP’s. The dye conversion was followed by both measurements: 1) color removal determined by UV-VIS spectrometry and 2) organic and inorganic load determined by the chemical oxygen demand (COD). A complete and quick color disappearance of model water waste has been obtained by using combination of non-irradiated AOP’s, namely, O 3 /SN, which contrasts to the combination of irradiated photocatalysis with O 3 or sonolysis. Color removal with simultaneous TiO 2 -UV/SN reached 77% while TiO 2 -UV/ O 3 reached 96% at similar reaction time. On the other hand, the standalone O 3 yielded the highest color removal (94.4%) in 32 minutes whereas SN reached only 39.2% in 4 hours. The standalone light irradiated TiO 2 -UV reached 93.3% color re-moval in one hour of reaction time. These results indicated that non-irradiated (SN and O 3 ) enhance synergistic effects that provoke structural changes in dye molecule without reaching total degradation. This is evidenced from FTIR of residuals from reaction mixture in which it has been observed the presence of organic molecules such as aromatics, sulfonic and amines refractory compounds that are mechanisti-cally possible to be found during IC degradation. Also, toxicity tests (MicroTox ? Technique) were performed using commercially available bacteria culture before and after IC degradation for each AOP and their combination. Reduction of aqueous dye concentration decreased the level of toxicity of the treated water which is the main target of the AOP’s but the presence of the remaining recalcitrant compounds have also toxic effect.