Use of redox mediators for the enhanced degradation of selected nitrophenols

Abstract

In the present study, sequential anaerobic-aerobic treatment was used for the enhanced degradation of selected nitrophenols. Five identical reactors were used to assess the degradation of 2-nitrophenol and 2,4-dinitrophenol. Reactor 1 was used as control, and another four reactors were operated in anaerobic phase followed by sequential aerobic treatment. The performance of reactors was studied for nitrophenol concentrations of 5, 10, 20 and 40 mg/l and in next phase effect of redox mediators [lawsone and anthraquinone sulphonic acid (AQSA)], along with kinetics of degradation studied for 40 mg/l of nitrophenols. More than 98% degradation of nitrophenols was achieved at lower concentrations but for 40 mg/l removal percentage was reduced, and also COD inhibition was observed. However, with the addition of redox mediators, both nitrophenols and COD removal percentage were greater than 95% and 85%, respectively. Kinetics of degradation revealed that the rate of degradation was found to increase with the increase in concentration of redox mediators from 10 to 20 mg/l, and it was found that degradation was faster with the use of AQSA in comparison with lawsone solution. It indicates that use of redox mediators is favourable for the enhanced degradation of nitrophenols. Sequential anaerobic-aerobic treatment is possible potential treatment method for treating nitrophenolic wastewaters.