Synthesis of activated carbon from sewage sludge using phosphoric acid as activating agent

This study addresses the management of sewage sludge (SS), a growing waste worldwide. In the case of the Canary Islands, Spain, 47.3% of the SS is disposed in landfills without further reuse. In this research, SS was used as a precursor to produce activated carbons (ACs), to remove pollutants from wastewater. The ACs were synthesized through chemical activation with phosphoric acid. The carbonization temperature and acid impregnation ratio were optimized, being 650 °C and 2 g H₃PO₄·g^-1 precursor, respectively. The methylene blue (MB) number of the optimized AC (AC-650-2) was 140, and that of a commercial AC used for comparison was 160. Additionally, magnetic activated carbons (MACs) were produced to facilitate material recovery and the regeneration of the adsorbent using an advanced oxidation technique (Fenton). AC-650-2 and MAC-3 adsorbed a maximum of 76.34 mg MB·g^-1 and 56.76 mg MB·g^-1, respectively, at 25 °C. The regeneration of the materials was investigated using conventional chemical methods and the Fenton reaction: NaOH washing (for AC-650-2 and MAC) and Fenton (for MAC) enabled recoveries higher than 50% after four cycles. The cost of producing AC-650-2 was estimated at 5.41 €·kg^-1.