Electrochemical and Microbial Decolourization of Congo Red Dye-contaminated Wastewater: Experimental and Computational Studies

Abstract The decolourization of congo red (CR) dye-contaminated wastewater was carried out by indirect electrochemical oxidation (IEO) and microbial degradation processes. The effect of various electrochemical parameters such as anode materials, current densities, supporting electrolytes, electrolyte concentrations and pH on the degradation of CR dye were investigated. Microbial degradation was accomplished using indigenous isolates, including Bacillus megaterium, Lactobacillus delbrueckii, Bacillus sphaericus, Pseudomonas sp., Bacillus lentus, Erwinia sp., Bacillus pumilus, Aspergillus flavus and Aspergillus niger, under varied conditions of mineral salt and time. The results of the IEO experiment show the copper anode to be more effective than the graphite anode in degrading CR dye. At the same time, the degradation rate of the dye increased with current density, electrolytes concentration and pH. The microbial degradation of CR dye increased with time, and dye to mineral salt ratio – 2:1 enhanced the degradation rate. Density functional theory (DFT) computation was deployed to investigate the degradation mechanism of CR dye which revealed the sulfonate moeity, azo chromophore and amide group to be the most susceptible sites for attack by oxidizing species.