Comparative analysis on the electrochemical reduction of colour, COD and turbidity from municipal solid waste leachate using aluminium, iron and hybrid electrodes

The treatment of municipal solid waste leachate using electrocoagulation–flocculation with metal electrodes: aluminium (Al) and iron (Fe) were investigated in this work. The feasibility of using this method for leachate treatment was determined in terms of turbidity, chemical oxygen demand (COD), and colour removal. The influence of pH, current dosage, electrolysis time, setting time, temperature and NaCl concentration on the process were examined. The effects of using the hybrid of Al and Fe in different arrangements (Al–Al, Fe–Fe, Fe–Al and Al–Fe) were also considered for the ECF process. The applicability of the perikinetic flocculation theory proposed by Von Smoluchowski was confirmed for the study through the regression coefficient (R²) values. The time evolution of aggregating particles or species was predicted. The properties of the sludge (flocs) were determined via the Fourier transform infrared (FTIR) analysis. The optimum pH using Al–Al, Fe–Fe, Al–Fe, and Fe–Al were 2, 4, 10 and 2, respectively. Al–Al electrode presented a higher turbidity removal (93.12%) and COD removal (75.28%) on the leachate than the other electrodes arrangements. Fe–Fe electrodes were the best for colour reduction (73.25%). The kinetic data obeyed the Brownian perikinetic flocculation theory. The mechanisms that accounted for the particle distribution evolution were both sweep flocculation and charge neutralisation. The FTIR results indicate that the particles were adsorbed from the leachate and no significant changes in the composition of the sludge were observed using the different electrode arrangements. The electrocoagulation–flocculation was very effective for pollutants reduction from municipal leachate.