Synthesis mechanisms and real-world wastewater applications of modified biochar adsorbents for heavy metal removal

Aquatic contamination with heavy metals has a significant impact on the ecology and human health. Native biochar from waste biomass produced using thermochemical conversion provides a low-cost, carbon-negative adsorption platform; however, in complex effluents, the inherent material properties can have restricted capacity and selectivity. This study examines recent developments in engineered biochar, combining an extensive bibliometric analysis of 5,845 publications from the Scopus database (2000–2026) with a critical narrative review of the latest advances in surface modification methods and techniques (physical, chemical, nanocomposite, and bioinspired). Maximum adsorption capacity is quantitatively compared among the significant modification families, and the synergistic molecular mechanisms, primarily surface complexation, ion exchange, electrostatic attraction, and precipitation, are explained for these exponential performance increases. Importantly, this review examines the critical change from scaled-up laboratory batch testing to actual continuous operation, highlighting operational considerations such as the impact of competition with dissolved organic matter, mesopore fouling, and the lifetime of the fixed beds. In addition, we discuss the concept of crop-based modification to tailor the biochar properties for the circular economy and address the current potential of AI/ML to facilitate relationships between properties and performance. In conclusion, the study offers a strategic blueprint to address current challenges in wastewater treatment and presents the engineered biochar as a pivotal technology for sustainable wastewater treatment on a larger scale.