Engineered Sludge-Derived Biochar for Lincomycin Removal from Water

The conversion of biowaste into biochar for use in water and wastewater treatment has gained significant attention in recent years. Activated sludge biomass as a by-product of biological wastewater treatment processes contains a high proportion of organic matter that can be converted into biochar. Biochar, as a carbon-rich, fine-grained, and porous substance, offers a dual solution for solid waste management and pollution control through the removal of contaminants from water when derived from sludge biowaste. This study investigates the feasibility of producing biochar with enhanced textural and adsorptive properties from activated sludge biomass through a one-step chemical activation process using zinc chloride (ZnCl₂) and microwave pyrolysis. The biochar produced was tested as a potential adsorbent material for the removal of a pharmaceutically active compound (PAC), lincomycin (LIN), from water. It was found that the structural and chemical properties of ZnCl₂-modified biochar (ZnBC) were significantly enhanced in comparison to raw biomass. The porous layered structure of ZnBC revealed an enhancement in the active surface area, which increased from 5 to 214 m² g⁻¹, and the average pore volume, which rose from 0.014 to 0.127 cm³ g⁻¹. Microwave pyrolysis resulted in a stable carbon-rich graphitized crystalline structure for effective removal of LIN. The results of the adsorption isotherm and kinetic models revealed that the adsorption process was controlled by both chemisorption and multilayer heterogeneous adsorption of LIN onto the external and internal surfaces of the ZnBC with a maximum adsorption capacity of 15.9 mg g⁻¹. Moreover, the presence of co-existing ions (NaCl) had little effects on LIN adsorption. Thermodynamically, LIN adsorption on ZnBC was more favorable at higher temperatures indicating an endothermic adsorption process. In conclusion, these results have significant implications for presenting biochar derived from sludge waste as a promising adsorbent for the removal of PACs from water in a sustainable manner.