Optimization of Microwave Hydrothermal Carbonization Conditions of Hydrochar for Ammonium Adsorption

This study aimed to optimize microwave hydrothermal carbonization (MHTC) conditions of rice husk hydrochar for maximum ammonium adsorption capacity. Processing parameters including hydrothermal temperature (150 - 200°C), residence time (20 - 60 min), and water to biomass ratio (5 - 15 mL g
⁻¹
) were optimized based on the Box-Behnken design. The ANOVA results indicated that only hydrothermal carbonization temperature showed a significant effect on the ammonium adsorption capacity of rice husk hydrochar. The optimum MHTC conditions were the water to biomass ratio of 10 mL g
⁻¹
under 200°C for 60 min. Hydrochar produced under the optimum condition had the ammonium adsorption capacity of
$\mathbf{0.89}\pm \mathbf{0.4\ mg}$
NH
4
⁺
-N g
⁻¹
. Findings from this study suggested that hydrochar derived from rice husk through MHTC has the potential to be an alternative adsorbent for preventing ammonium run off from the agricultural area.