Enhanced degradation of metronidazole by sunlight via photo-Fenton process under gradual addition of hydrogen peroxide

• New solar reactor conception for mineralization of Metronidazole solution.
• Slowly and gradually adding a small known quantity of hydrogen peroxide.
• Metronidazole solution was treated by a solar photo-Fenton reaction, using the solar energy as UV light source.
• HO radicals were the main oxidative intermediate species in the process.
• Solar energy is an important natural resource and using it in advanced oxidation processes is probably one of the best ways to make the degradation of MTZ.

The present paper has investigated the application of solar energy as renewable, abundant, free and clean energy driven advanced oxidation process (photo-Fenton), for the mineralization of metronidazole (MTZ) as the most important drug of the group of 5-nitroimidazole. The hydrogen peroxide (H2O2) was added slowly and gradually over time in order to limit side reactions. The kinetics of organic matter decay was monitored by the chemical oxygen demand (COD) and the absorbance measurements. The experimental results showed that the solar photo-Fenton system leads successfully to 96% of COD removal for 960 mg L−1 COD0 under optimal experimental conditions (1 mmol L−1 Fe(II)0, H2O2 dosing rate of 2 mmol min−1, pH 3 and at 60 °C) after 12 min. The MTZ concentration decay and the COD removal obeyed a pseudo-first-order kinetics. Compared with Fenton process, the exposition of the reactor to sunlight enhanced the mineralization process by 16%.

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