The potential of biochar and lignin-based adsorbents for wastewater treatment: Comparison, mechanism, and application—A review

•Adsorption technique has been considered as one of the best method for heavy metal removal.•Biochar and lignin present great potential for wastewater treatments.•Modification of bichar and lignin can enhance the adsorption capacity of heavy metals.•Biochar and lignin can be recylced and reused efficiently in application. In recent years, low-cost and high-performance properties of adsorbents have become a strong demand in adsorbents preparation. Biochar and lignin present great potential for wastewater treatment due to their unique physicochemical properties, and were found to be promising candidate materials in pollutant removal by adsorption in the practical application process. Researchers have adopted various methods to modify biochar and lignin to enhance their adsorption efficiency. In this study, the source, preparation methods, and structural features of biochar and lignin are thoroughly reviewed. The latest progress of biochar-based adsorbents (BBAs) and lignin-based adsorbents (LBAs) in wastewater treatment were reported and comparatively analyzed. The adsorption mechanisms between BBAs/LBAs and various pollutants were analyzed. Besides, the potential and challenge of BBAs and LBAs in pollution remediation and industrial application were comprehensively discussed. To accelerate the development of LBAs and BBAs in wastewater treatment, further explorations are necessary for the preparation of the novel LBAs/BBAs, exploring the adsorption mechanism and industrial application.