Mineralization of mefenamic acid from hospital wastewater using electro-Fenton degradation: Optimization and identification of removal mechanism issues

Mefenamic acid (MFA) is a nonsteroidal anti-inflammatory drug widely used for the short-term treatment of mild to moderate pain as well as treatment of primary dysmenorrhea and for decreasing the pain and blood loss during menstrual periods. Since MFA has been detected in raw and sewage water worldwide, the current work deals with the optimizing of removal of MFA from hospital wastewater using the electro-Fenton (E-Fenton) process. A cylindrical Pyrex reactor containing 250 ml of wastewater was employed for treatment investigation. The effects of main variables on the removal process were investigated and the optimum experimental condition was obtained with adequate desirability under the response surface methodology. The obtained results revealed that the removal efficiency of 95.3% was achieved under the optimal experimental condition, including MFA initial concentration of 7.0 mg L-1, the H2O2 dosage of 700 mu l/L, the current density of 6.6 mA cm(-2), and the reaction time of 12 min. The removal mechanism studies showed that (OH)-O-center dot as the dominant radical species plays the main role in E-Fenton process. The MFA removal followed the pseudo-first-order kinetic model. Under the optimum condition of the E-Fenton process, the removal efficiency of MFA from synthetic wastewater was in satisfactory agreement with the real hospital wastewater treatment.