Use of redox mediators for the enhanced degradation of selected nitrophenols

In the present study, sequential anaerobic–aerobic treatment was utilized for the enhanced degradation of selected nitrophenols. Five identical reactors were evaluated for the degradation efficiency of 2-nitrophenol and 2,4-dinitrophenol, with one serving as a control. The reactors operated in an anaerobic phase were followed by sequential aerobic treatment, assessing nitrophenol concentrations of 5, 10, 20, and 40 mg/l. The performance was further analyzed with the introduction of redox mediators, specifically lawsone and anthraquinone sulphonic acid (AQSA), while the kinetics of degradation was examined at a concentration of 40 mg/l. Results indicated more than 98% degradation at lower concentrations, although a decrease in removal percentage was noted for 40 mg/l. COD inhibition occurred, but the inclusion of redox mediators led to over 95% degradation of nitrophenols and more than 85% COD removal. Additionally, the degradation rate increased with greater concentrations of redox mediators from 10 to 20 mg/l, with faster degradation observed using AQSA compared to lawsone. These findings suggest that the employment of redox mediators significantly enhances the degradation process in sequential anaerobic–aerobic treatment systems for nitrophenolic wastewater management.