Removal of toxic heavy metals from aquatic systems using low-cost and sustainable biochar: A review

Heavy metal pollution, mainly from industrial activity, has become a major environmental problem, raising awareness about environmental protection and human health. These metals threaten human health and the environment by accumulating in plants, animals, and humans, leading to neurological impairments, reproductive issues, and cancer. Biochar is a stable, carbon-rich, porous substance produced through the pyrolysis or carbonization of various biomasses, including agricultural, animal, and organic wastes. Growing interest in the beneficial applications of biochar has opened multidisciplinary areas in science and engineering. As a low-cost adsorbent, it shows great potential for treating heavy metals in wastewater. The type of feedstock biomass, pyrolysis conditions, and modification approaches significantly influence its adsorption capacity. This review explores advancements in the production, modification, and application of biochar for heavy metal removal from wastewater. It critically examines current challenges and research gaps in using biochar for heavy metal remediation, along with the adsorption mechanisms and factors affecting the process. The removal of heavy metals varies with the type of biochar, using mechanisms such as complexation, chemical and physical adsorption, precipitation, ion exchange, and electrostatic interactions. Additionally, it discusses the large-scale use, reusability, and regeneration of biochar, highlighting its significance.