Biochar, a carbon-rich material produced through the pyrolysis of biomass, has been shown to have the potential to remove contaminants from water and wastewater. However, due to the weak adsorption capacity and narrow adsorption range of pure biochar, it is modified, either chemically or physically, in order to optimize its applications in water and wastewater treatment. This study summarizes the recent advancements in the application of modified biochar for water and wastewater treatment. Modification of biochar increases its surface area and porous structure, which makes it an effective adsorbent to immobilize a range of contaminants, such as heavy metals, dyes, and organic contaminants. It can also be used as a catalyst in the biodegradation of organic pollutants as it can provide a substrate for microbial growth and metabolism, enhancing pollutant degradation. This study also summarizes various biochar modifications such as gas, acid, alkali, metal, organic compounds, and oxidizing agents. Among the metal-modified biochar, Iron-modified biochar has shown the highest tetracycline (TC) removal efficiency (90.7%) and nitrate adsorption capacity (32.33 mg g-1). N-doped biochars were found to be the most effective biochars for removing heavy metals such as Cd2+ or Cu2+ and aromatic compounds as they can increase the adsorption of raw biochar by up to 70%. Increasing the number of functional groups on the surface of the biochar by using organic compounds like acrylonitrile and chitosan showed a two to three-fold increase in the adsorption capacity of pollutants such as Cd2+ and Hg2+. According to this review, modified biochar technology is a cost-effective and environmentally friendly wastewater treatment method.
