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

Abstract 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 (H 2 O 2 ) 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 COD 0 under optimal experimental conditions (1 mmol L −1 Fe(II) 0 , H 2 O 2 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%.