Microwave photo-oxidation with diverse oxidants for Congo red degradation: effect of oxidants, degradation pathway and economic analysis

Abstract

The present study investigated the efficacy of microwave photo-oxidation (MWPO) process with two oxidants i.e. persulphate (PS) and hydrogen peroxide (H2O2) for degradation of Congo red (CR). The result indicated a CR degradation efficiency of 98% and 96.8% with PS and H2O2, respectively, in 30 min of reaction with corresponding PS dosage of 50 mg/L and H2O2 dosage of 180 mg/L. The COD removal efficiency with the two oxidants were 97.7% and 94.9%, respectively. Higher dosages of oxidant and CR reduced the efficiency of the process in both the cases due to self-quenching. Effect of pH and initial CR concentration on CR removal efficiency also has been studied. Degradation of CR followed pseudo-first-order kinetics with a removal rate constant of 0.12/min and 0.09/min, respectively, with PS and H2O2. The main mechanism of CR degradation was cleavage of the benzene�benzene bond, cleavage of benzene�N bond and hydroxylation. Economic analysis of the MWPO process indicated an energy consumption of 18.3 kWh/g of CR removal and 18.4 kWh/g of COD removal. The process was effective in the rapid degradation and mineralization of high concentration of CR within 30 min. � 2019 Informa UK Limited, trading as Taylor & Francis Group.