Adsorption of organic and inorganic pollutants onto biochars: Challenges, operating conditions, and mechanisms

The presence of toxic substances in the environment has increased due to population growth, urbanization, industrialization, as well as changes in people's lifestyles. Among many technologies, adsorption has proven to be an effective and inexpensive technique for water and wastewater treatment. Biochar has been identified as a promising and low-cost material, which can be produced from various carbonaceous materials with different origins, compositions, and processing methods. Consequently, the interaction between biochars and adsorbate species is not simple and may involve different adsorption mechanisms, such as van der Waals forces, electrostatic interactions, surface complexation, ion-exchange, hydrophobic interactions, π-interactions, co-precipitation, partition, and pore-filling. In addition, many operating conditions can affect the performance of adsorption processes. However, the development of biochars as competitive adsorbent materials depends on standardization, continuous-supply, application, and regulation. Thus, this paper discusses the challenges, the operating conditions, and the adsorption mechanisms to remove organic and inorganic micropollutants using biochar. • Biochar challenges include standardization, continuous supply, and real application. • Operating conditions and adsorbent-adsorbate interactions were intensively discussed. • Chemical interactions have been dominant for adsorption of inorganic/ionic species. • Physical interactions have been dominant for adsorption of organic micropollutants.