Advanced Modification Techniques and Emerging Applications of Biochar from Sewage Sludge and Other Biomass Sources

Sewage sludge (SS) and biomass disposal has become a global environmental concern. Pyrolysis conversion into biochar provides a promising sustainable strategy, yet unmodified biochar often shows limited adsorption performance due to insufficient porosity and surface functional groups. This review provides a systematic and critical evaluation of advanced modification techniques and emerging applications of biochar derived from SS and other biomass sources. Modification methods are categorized into physical and chemical approaches, where metal modification is incorporated into chemical modification as a typical subcategory. Key preparation parameters including activator type, modification temperature, time, impregnation ratio, and concentration collectively determine the pore structure, surface chemistry, and adsorption capacity of modified biochar. Among these factors, activator type and modification temperature present the most significant impacts, while other parameters impose secondary but non-negligible effects. Modified biochar exhibits greatly enhanced performance in wastewater treatment, atmospheric pollutant removal, and soil remediation by improving pore structure, surface functional groups, and active sites. Major challenges remain in cost control, long-term stability, regeneration, and large-scale application. Future research should focus on process optimization, techno-economic evaluation, and field validation to promote the practical application of sludge‑derived biochar in environmental remediation and circular economy.