Evaluating biochar for adsorption of ammonium nitrogen in wastewater:insights into modifications and mechanisms.

Ammonium nitrogen (NH) is a highly recalcitrant pollutant, leading to severe degradation of aquatic ecosystems and posing serious risks to human health. The application of biochar for NH removal from wastewater has gained widespread attention. However, its inherent limitations in adsorption capacity present a significant constraint on its broader practical implementation. To address this limitation, various modification techniques have been developed to endow biochar with a range of physicochemical properties. In this review, a systematic investigation was conducted to assess the efficacy of various modification methods on the adsorptive capacity of biochar for NH in aqueous solutions. Additionally, this review summarizes the adsorption mechanisms which are divided into five categories: hydrogen bonding, pore filling, electrostatic interaction, ion exchange and surface complexation. This review offers valuable insights into the strategies for achieving enhanced adsorption of NH by modified biochar, along with a comprehensive summary of the associated removal mechanisms.