Nitrofurantoin removal by the photo-Fenton process: degradation, mineralization, and biological inactivation

Abstract

Antibiotics may induce super-resistant bacteria if they are available in the environment. Therefore, the removal of aqueous nitrofurantoin (NFT), and more importantly, the removal of the remaining antimicrobial activity after treatment, by the photo-Fenton process, was herein studied. Degradation experiments were performed according to an experimental design (0.5% error; factors: concentrations of NFT, Fe³⁺, and H₂O₂). Degradation conditions were: 20 mg NFT L^-1, 10 mg Fe³⁺ L^-1, and 170 mg H₂O₂ L^-1. Fixed parameters were: 100 mL of the NFT solution, pH 2.5, 15-min stirring, and 25.0 ± 0.5°C. The initial rate constant (k₀) and the maximum oxidation capacity (MOC) of the system were 0.61 min^-1 and 100%, respectively (R² = 0.986). 97% of the NFT and 93% of the organic carbon initially present were removed. Five degradation products (DPs) were detected by HPLC-MS and their endpoints estimated by the ECOSAR (ECOlogical Structure-Activity Relationships) 2.0 software. NFT and its DPs presented no toxicity towards Lactuca sativa. The antimicrobial activity (Escherichia coli) of NFT and/or DPs was completely removed in 15 min. Structures were proposed for the detected DPs. In short, the tested advanced oxidation technology (AOP), besides being capable of removing and mineralizing aqueous NFT in a short time, 15 min, also rendered the treated water biologically inactive (no ecotoxicity, no antimicrobial activity).

Keywords: Nitrofurantoin; antimicrobial activity; black light bulb; ecotoxicity; photo-Fenton.