The production of swine manure (SM) biochar was optimized to improve the nutrient recovery. SM was activated with KOH, HCl, or MgCl2 at different ratios (1:1 and 3:1, v/w) and carbonized at 400, 600, and 800 °C. Results showed that MgCl2-activated biochar at 800 °C (3:1) showed enhanced production (84.9%) and the highest phosphate adsorption (2.93 mg g–1) and ammonium adsorption (1.27 mg g–1). Adsorption followed Langmuir isotherm for phosphate (qm = 67.56 mg g–1) and Freundlich for ammonium (qm = 17.48 mg g–1). Adsorption kinetics indicated that phosphate uptake was best described by the Elovich model (R2 = 0.99), while ammonium followed pseudo-second order kinetics (R2 = 0.90), suggesting distinct but predominantly chemisorption-controlled mechanisms. Desorption tests showed a limited solubility of phosphate in water and partial ammonium release, supporting the use of biochar as a slow-release fertilizer. Overall, MgCl2-activated biochar at 800 °C proved to be the most effective condition, combining high adsorption capacity with nutrient release potential, highlighting its value for sustainable nutrient recovery in agriculture.
Nascimento et al. (Wed,) studied this question.