# Biochar from Swine Manure: An Alternative for Nutrient Recovery and Slow-Release Fertilization

## TL;DR

This study shows that biochar made from swine manure using MgCl2 at high temperatures can effectively recover nutrients and act as a slow-release fertilizer.

## Contribution

The study identifies MgCl2-activated biochar at 800°C as the optimal method for nutrient recovery and slow-release fertilization from swine manure.

## Key findings

- MgCl2-activated biochar at 800°C (3:1) achieved the highest phosphate and ammonium adsorption.
- Phosphate adsorption followed the Langmuir isotherm, while ammonium followed the Freundlich isotherm.
- Desorption tests confirmed limited phosphate solubility and partial ammonium release, supporting slow-release properties.

## Abstract

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.