Mechanistic insights into removal of pollutants in adsorption and advanced oxidation processes by livestock manure derived biochar: A review

The conversion of livestock manure into harmless biochar for pollutants removal from wastewater is in accordance with the principle of sustainable development. However, a comprehensive understanding of the reaction mechanisms involved in the mechanism of adsorption/degradation removal of aqueous pollutants is still lacking, which limits the current application of pristine livestock manure derived biochar (MDBC) and its composites (MDBCs) in wastewater treatment. To enhance understanding in this aspect, this review summarized the latest research on the utilization of MDBCs as adsorbents and as catalysts in persulfate (PS), photocatalysis, self-catalytic system and Fenton-like advanced oxidation processes (AOPs) for pollutants removal from water environment. Additionally, a comprehensive summary of adsorption mechanisms of MDBCs were provided. For heavy metals, the main adsorption mechanisms involved co-precipitation and surface complexation, while for organic contaminants, the main adsorption mechanisms were π-π interactions and hydrogen bonding. According to random forest method, the carbon content and surface area are identified as key characteristics of MDBCs that influence the adsorption of heavy metals and organic contaminants, respectively. An emphatic summarizes of activation mechanisms of MDBCs in AOPs systems were presented, including radical oxidation and non-radical oxidation pathways. Especially, the connections between different physicochemical characteristics of MDBCs and nonradical contribution based on persulfate were investigated. This analysis will offer valuable insights for the rational design of MDBCs to enhance nonradical pathways selectively. Finally, the challenges and future perspectives related to MDBCs are proposed to facilitate research into this sustainable livestock manure derived biochar.