Degradation of NSAIDs by optimized photo-Fenton process using UV-LEDs at near-neutral pH

This paper addresses the degradation of waterborne drugs. Depending on the drug, endocrine disruption, antibiotics-resistant bacteria, (eco)toxicity etc. are common reported problems. As the existing tretment stations are not capable of completely removing those pollutants, new and highly efficient technologies should be developed for this purpose. The Fenton's reaction is a good candidate for that. However, acidic pH, sludge generation, and the need for the continuous addition of ferrous ion are problems to be overcome, e.g., by the photo-Fenton reaction. Here, the degradation of NSAIDS (salicylic acid, ketoprofen, diclofenac, paracetamol), and caffeine by the photo-Fenton process mediated by ferrioxalate with UV-LEDs was assessed. The initial concentration of each drug was 10 mg L-1 and the medium pH was set to 6.5. The optimized (response surface methodology) experimental conditions were: LEDs power: 1.768 W, CFe3+: 15.0 mg L-1, and C H2O2: 47.6 mg L-1. After 25 min, the concentrations of all studied drugs were below their respective detection limits, 30 and 40% of carbon (mineralization) and COD removals were achieved. All drugs followed a pseudo-first order degradation. Fast removals (approximately 80% in the first 10 min) and virtually identical rate constants (approximately 10(-1) min(-1)) were also achieved. The medium oxidation number of carbon ranged from 2.7 to 1.9. Phytotoxicity tests (Lactuca sativa) indicated that the proposed treatment did not generate ecotoxicity, despite the significant formation of degradation products.