A continuous microwave/nZVI treatment system for malachite green removal: system setup and parameter optimization

A continuous microwave/nZVI treatment system was built for the removal of malachite green (MG). Using the system, MG was efficiently degraded in a short hydraulic retention time. Operational parameters, including flow rate of influent, aeration method, microwave power (MP), and pH of MG solution, were optimized. The results indicate that the removal efficiency of MG increased significantly following the decrease in influent flow rate (Q(i)). At Q(i)=4mL/min, the highest removal efficiency of MG reaches 98.5%, while the highest load of MG degradation per gram of nZVI was 74.3mg/g at Q(i)=16mL/min. Increasing the MP could slightly increase MG and TOC removal efficiency. And analysis of system shock resistance indicated the use of this system stabilized effluent quality. It was further concluded that MG removal efficiency could benefit from pre-acidification processes to reach the pH range from 5.0 to 7.0 and pre-aeration prior to using the system. The dominant gas product and the residual detected following degradation of MG in the nZVI system were CO2 and iron oxides, respectively.