Fenton, Photo-Fenton, H2O2 Photolysis, and TiO2 Photocatalysis for Dipyrone Oxidation: Drug Removal, Mineralization, Biodegradability, and Degradation Mechanism

Dipyrone (DIPY), an analgesic drug, is very quickly hydrolyzed to 4-methylaminoantipyrine (4-MAA) in an acidic solution. Batch study was conducted to compare the performance of different oxidation processes such as Fenton (FP), photo-Fenton (PFP), UV/H2O2 photolysis (UVP), and UV/TiO2 photocatalysis (UVPC) for removal of 4-MAA from aqueous solution. The degradation efficiency was evaluated in terms of total organic carbon (TOC) reduction and enhancement of biodegradability. Maximum 4-MAA removals of 94.1, 96.4, 74.4, and 71.2% were achieved in FP, PFP, UCP, and UVPC, respectively, against mineralization of 49.3, 58.2, 47, and 24.6%. The proposed mechanisms suggest that the cleavage of three methyl moieties followed by pyrazolinone ring breakage led to formation of various intermediates with low errors (-0.88 to 0.11 g/mol). The intermediates primarily were hydroxylated and carboxylic derivatives. BOD5 to COD (BOD, biochemical oxygen demand; COD, chemical oxygen demand) ratio of >= 0.4 resulted from DIPY decomposition in all processes with highest improvement in PFP (BOD5/COD approximate to 1.5). The collapse of iron(III)-chelates under UV irradiation gave higher biodegradability.