Sewage sludge derived FeCl3-activated biochars as efficient adsorbents for the treatment of toxic As(III) and Cr(VI) wastewater

Effective utilization and resourcelization of sewage sludge into value-added by-products and insights into its environmental impacts during the fabrication process are urgent tasks to be tackled. Here, we adopt FeCl 3 to activate and functionalize sewage sludge to form FeCl 3 -activated biochars, which exhibited high adsorption capabilities for the treatment of toxic As(III) and Cr(VI) containing wastewaters. Kinetic studies suggested that the adsorption of As(III) and Cr(VI) species onto the biochar surface was attributed to physisorption and chemosorption, respectively. Equilibrium was reached after 3 h for the adsorption of Cr(VI), and slightly slower for that of As(III). Additionally, the structural stability of the adsorbent was maintained even in wastewater with high acidity (pH = 1), as corroborated by microscopic observations. Structural characterization of the adsorbents after adsorption showed that the excellent adsorption performance originated from adsorptive functionalities of the surface functional groups and the active Fe 3 O 4 particles forming Fe-O-As(III)/Fe-O-Cr(VI) complexes with the As(III)/Cr(VI) adsorbates. Evaluation via the green degree method demonstrated that transforming sewage sludge into biochar exerts very low impacts on the environment. Hence, this work offers a green alternative to convert the hazardous sewage sludge into value-added biochar materials, which can be further exploited as supporting frameworks for multifunctional catalysts or expanded to be investigated in reducing carbon footprints and energy conversion areas.