Recent development of sludge biochar-based catalysts in advanced oxidation processes for removing wastewater contaminants: A review

Sewage sludge (SS) is a by-product of sewage treatment plant and a typical solid waste, which has dual properties of pollution and recycling. Using SS as raw material to prepare biochar-based catalytic materials for catalysis in water environment is a new way of sludge reduction and resource utilization. Sludge is a mixture of biomass organic matter, various inorganic oxides, metal ions and microorganisms; hence, carbon-based catalyst or carrier material prepared by sludge has readily available raw materials, excellent pore structure, dispersed active sites, easy regulation of surface chemical functional groups, and high specific surface area. It has been widely used in advanced oxidation processes (AOPs) and catalysis fields, such as catalytic H2O2 heterogeneous Fenton reaction, catalytic degradation based on persulfate (PS) and peroxymonosulfate (PMS), composite photocatalytic reaction, heterogeneous catalytic wet air oxidation and electrochemical catalytic oxidation. In this paper, the modification method for sludge biochar-based catalyst material is described. The key active sites and catalytic mechanism of sludge biochar-based catalysts in different oxidation systems are further revealed by examining the structure–activity relationship between the physical and chemical properties of the material and catalysis and their characteristics in the field of catalysis in water environment. Lastly, the main problems in this field and the future development direction were put forward to provide important reference for the further realization of the high-value-added resource utilization of sludge biochar.