Fenton-Enhanced zero-valent iron powder oxidation: Investigating transformation products of antimicrobials and its removal

The occurrence of pharmaceuticals and pesticides in water is of concern due to their hazardous effect on the environment. Such micropollutants deteriorate environmental quality and can induce antimicrobial resistance in pathogenic bacteria. Thus, removal of these emerging contaminants is a necessity and thus requires a clear understanding of the effective treatment and mechanistic approach utilized in degradation and removal. Frequently, treatment systems are optimized for the removal of contaminants while the formation of transformation products and their removal are not targeted. We utilized our established iron powder catalyzed Fe (0) Fenton Oxidation treatment to study the degradation of emerging contaminants — sulfamethoxazole, gabapentin, diuron, and triazine class pesticides. We used state-of-the-art mass spectrometry to establish the common oxidative mechanistic approach after identifying the transformation products formed during the Fe (0) Fenton Oxidation processes. Fenton transformed product was produced after 60 min reaction time when treatment was initiated after adding the optimized H2O2 and iron powder Fe (0)) in a micropollutant solution adjusted to pH 5. About 5-to-7 transformed products of each micropollutant were identified and predicted to have low toxicity risk to aquatic organisms. The oxidative degradation pathway of micropollutants illustrates the shared oxidative mechanism where the aliphatic chain of the heteroatom: Sulphur (R—S—R as thiosulphate), functional groups (R—C=O, R—COOR, R—NH2, R— NH=O—N) and alkyl chain present in the target compound was suggested as the prime region of hydroxyl radicle (•OH) attack. The tandem mass spectrometry estimated the evolution of sulfamethoxazole-transformed product formation and removal during the treatment. The informed optimization of Fe (0) Fenton treatment, confirmed through MS2 was established at 40 min reaction time at which both the sulfamethoxazole and its transformed product were reduced to trace levels (ngL-1).