Sludge-based biochar preparation: pyrolysis and co-pyrolysis methods, improvements, and environmental applications

The pyrolysis of sewage sludge to produce biochar is a promising method for sewage sludge end-treatment. Key parameters influencing biochar properties include pyrolysis temperature, heat transfer rate, residence time, additives, and raw material types. Sludge-based biochar (SBC) features a porous structure, aromatic compound composition, high absorbency, stable chemical properties, large specific surface area, and numerous surface functional groups, making it suitable for environmental applications such as soil remediation and water quality improvement. However, SBC alone can pose a risk due to excessive heavy metal content. Co-pyrolysis of biomass with sewage sludge has been shown to mitigate this risk by fixing heavy metals and reducing their accumulation in biochar. Research indicates that co-pyrolysis produces biochar with superior properties, including a larger specific surface area, better pore structure, more surface functional groups, and greater pollutant adsorption capacity compared to SBC alone. Thus, sludge-biomass biochar has significant potential to overcome the limitations of single sludge-based biochar, facilitating large-scale production and application for environmental management.