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

Abstract

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°C) on biochar adsorption ability for NH 4-N, NO 3-N, and PO 4-P were investigated and fitted by three adsorption models, viz Freundlich, Langmuir, and linear. Freundlich (R 2 = 0.95–0.99) and Langmuir (R 2 = 0.91–0.95) models were found suitable for adsorption of NH 4-N. The maximum adsorption capacity (Q m) for coconut shell biochar increased with pyrolysis temperature (Q m = 12.8–15.5 mg g-1) and decreased for banana stem biochar (Q m = 12.9–9.7 mg g-1). In the case of NO 3-N adsorption, Freundlich (R 2 = 0.82–0.99) and linear model (R 2 = 1.00) were found suitable while Langmuir model showed much less contribution, similarly adsorption of PO 4-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°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.

Keywords

• nutrients
• soil amendment
• adsorption model
• biochars
• tropical feedstock