Ammonium capture Kinetic, Capacity, and Prospect of Rice Husk Biochar produced by different pyrolysis conditions

This study explores the potential application of rice husk biochars, categorized by their pH (acidic, pH 5.98; neutral, pH 7.02; and alkali, pH 11.21) and particle sizes (micron-scale and sub-centimeter) in aquatic ecosystems for efficient removal of ammonium (NH₄⁺). To assess the NH₄⁺ adsorption capacity of the rice husk biochars, both NH₄⁺ adsorption kinetics and isotherms were employed. Additionally, we propose future prospects for utilizing rice husk biochar as an efficient adsorbent based on a review of previous studies. Our findings suggest that the NH₄⁺adsorption capacity of rice husk biochars is primarily influenced by their surface characteristics, specifically surface area of rice husk biochars and loss of acidic functional groups. In this study, the neutral rice husk biochars, which had the highest surface area at 9.86 m² g^-1, exhibited the highest NH₄⁺adsorption performance at 1.12 mg g^-1 (micron-scale) and 0.94 mg g^-1 (sub-centimeter) compared to acidic and alkali rice husk biochars. Additionally, particle size control proves to be a promising strategy for enhancing adsorption efficiency of rice husk biochars, with the micron-scale rice husk biochars being 1.19-fold higher than sub-centimeter ones. However, before implementing biochar-based pollutant removal strategies in aquatic ecosystems, several considerations (e.g., the potential harmfulness of inner components in biochar, side effects of biochar on aquatic life, and tracking the fate of biochar in aquatic ecosystems) must be addressed. By addressing these concerns, we can expect to expand the practical application of biochar for remediation in aquatic environments, contributing to the effective management of pollutants.