Biochar potential for pollutant removal during wastewater treatment: A comprehensive review of separation mechanisms, technological integration, and process analysis

The increasing urbanization and industrialisation worldwide are deteriorating ground and surface water quality. Biochar is derived from the pyrolysis of agro-residues, forestry residues, sewage sludge, fruit peels, poultry manure, and algal biomass. It has emerged as an efficient adsorbent for wastewater treatment. Modified biochar, treated with chemicals like ZnCl₂, KOH, and ZnO/ZnS, demonstrates enhanced performance over pristine biochar. Biochar derived from waste biomass stands out as a sustainable and efficient option. This review explores biochar production techniques, pre-treatment methods, and key characteristics that affect its effectiveness, with a focus on studies published over the past decade. Pollutant removal primarily depends on impurity types, with significant contaminants including nitrate, fluoride, phosphorus, ammonia, and heavy metals like Cd, As, Pb, and Cu. Key mechanisms include ion exchange, surface complexation, and physical adsorption, enabled by biochar multi-functional groups, high adsorption capacity, and large surface area. Pyrolytic process conditions, such as temperature and residence time, shape the quality of biochar. Engineered biochar, modified with doped ions, steam/CO₂ activation, or magnetic properties, achieves up to 95% pollutant removal efficiency, combining effectiveness, cost-efficiency, and environmental sustainability. This article offers a thorough summary of the most recent developments in the production of biochar, its uses in wastewater, and the adsorption processes for the removal of pollutants and heavy metals over the previous ten years. Additionally, techno-economic and regeneration studies highlight biochar feasibility. Future research perspectives and challenges emphasise the role of biochar in sustainable waste management practices, offering optimised solutions for environmental remediation.