Comparative life-cycle assessment of molten salt and impregnation methods for producing activated carbon from sewage sludge

The implementation of life-cycle assessment (LCA) was to quantify the potential environmental impact of activated carbon production from sewage sludge by the molten salt and impregnation methods. Based on the experiments of the molten salt and impregnation methods, a flowchart was developed and the environmental impact was determined. The results showed that the environmental impacts dominated by roasting, followed by grinding or impregnating and finally by washing and drying. The uses of electricity and ZnCl₂ in the production of activated carbon were the main factors causing environmental impact. The energy consumptions of the molten salt and impregnation methods were 56.16 and 73.44 MJ/kg activated carbon, respectively. The global warming potential of the molten salt and impregnation methods was found to be 14.68 and 17.15 kg CO₂ eq/kg activated carbon, respectively. The impregnation method had higher energy consumption and CO₂ emissions than those for the molten salt method. The LCA showed that the molten salt method offered environmental advantages in most impact categories in comparison with the impregnation method.