Evaluation of Electro-Fenton processes for treatment of Metronidazole from pharmaceutical wastewater: modeling, simulation and experimental

Abstract: Metronidazole (MNZ) with antibacterial and anti-inflammatory properties is a kind of nitroimidazole antibiotic, which is commonly used in clinical applications and widely used for the treatment of infectious diseases caused by anaerobic bacteria and protozoans, such as Giardia lamblia and Trichomonas vaginalis [1]. Aside from being widely used as antibiotics for humans, MNZ is also abused as an additive in poultry and fish feed to eliminate parasites [2]. As a result, MNZ was accumulated in animals, fish farm water, and effluents from meat industries. Therefore, the current study aimed to evaluate the efficiency of Electro-Fenton (EF) process for removing MNZ from pharmaceutical wastewater. Response surface methodology (RSM) under central composite design (CCD) category of Design Expert 7 software was used to achieve efficient removal of MNZ. The main objective of CCD method is to optimize the response surface and quantifies the relationship between the controllable input parameters and the obtained response surfaces. The effect of various variables including; pH solution (2-8), current density (5-15 mA.cm-2), initial MNZ concentration (20-100 mg.L-1) were investigated to achieve the best efficient and economical MNZ contamination removal condition. The maximum removal rate was achieved at the current density of 6.8 mA.cm-2, initial MNZ concentration of 83 mg.L-1, pH 3.0 within the reaction time of 4 min. The kinetics of the process follows the pseudo first-order model with rate constants of 0.291 min−1 (R2=0.9810). Using ordinary radical scavengers demonstrated that hydroxyl radical (•OH) was the main oxidant species contributed in degradation of MNZ under the EF process. The obtained results revealed that in optimized condition, the removal efficiency of aniline was 100% and the consumed energy was 0.206 kWh.m-3. Statistical tests (ANOVA and regression) showed that the designed model was in satisfactory agreement with the obtained experimental results.