Comparative effectiveness of biochar derived from tropical feedstocks on the adsorption for ammonium, nitrate and phosphate

Biochar has been extensively studied as a soil amendment to reduce nutrients losses. However, the comparative effectiveness of biochar adsorption capacity for ammonium (NH4-N), nitrate (NO3-N), and phosphate (PO4-P) remains unknown. In the present study, the effects of feedstock (banana stem and coconut shell) and temperature (300, 500, and 700 degrees C) on biochar adsorption ability for NH4-N, NO3-N, and PO4-P were investigated and fitted by three adsorption models, viz Freundlich, Langmuir, and linear. Freundlich (R2 = 0.95-0.99) and Langmuir (R2 = 0.91-0.95) models were found suitable for adsorption of NH4-N. The maximum adsorption capacity (Qm) for coconut shell biochar increased with pyrolysis temperature (Qm = 12.8-15.5 mg g-1) and decreased for banana stem biochar (Qm = 12.9-9.7 mg g-1). In the case of NO3-N adsorption, Freundlich (R2 = 0.82-0.99) and linear model (R2 = 1.00) were found suitable while Langmuir model showed much less contribution, similarly adsorption of PO4-P, was not supported by these three models. The minimum concentrations required for adsorption of phosphate were recorded as 36, 8, and 3 mg L-1 using pyrolyzed biochar at the temperatures of 300, 500, and 700 degrees C, respectively. These results indicate that the feedstock and pyrolysis temperature, as well as aquatic nutrient concentration, were important factors for the adsorption of inorganic nitrogen and phosphorus.