Phosphate sorption by iron-activated biochars derived from quick-washed poultry litter and swine manure

Authors: Padilla, Joshua; SZOGI, ARIEL - Retired ARS Employee; Watts, Donald

Submitted to: Cleaner Engineering and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2026
Publication Date: 4/21/2026
Citation: Padilla, J.T., Szogi, A., Watts, D.W. 2026. Phosphate sorption by iron-activated biochars derived from quick-washed poultry litter and swine manure. Cleaner Engineering and Technology. 32. https://doi.org/10.1016/j.clet.2026.101208.
DOI: https://doi.org/10.1016/j.clet.2026.101208

Interpretive Summary: Animal manure is an abundant resource commonly used as a low-cost fertilizer in agricultural production. However, the overapplication of manure to soils can cause water quality problems due to high concentrations of nutrients in agricultural runoff. Therefore, alternatives to land-application are needed to manage large amounts of animal manure and minimize its environmental impact. In this study, we developed a three-step process to convert poultry litter and swine manure into phosphorus (P) adsorbents: 1) Manures were treated to reduce their P content, 2) heated in the absence of oxygen to produce biochar, a charcoal-like substance, and 3) chemically activated using magnesium (Mg) or iron (Fe) salts to increase the biochar’s ability to bind P. We determined that the Fe-activated biochars were superior for binding P compared to nonactivated or Mg-activated biochars across a wide range of experimental conditions. Under environmentally relevant conditions, we determined that the maximum amount of P that the biochars could bind ranged from 2.0-2.6 mg P per gram of biochar. The results demonstrated that our three-step process was successful for converting poultry litter and swine manure into P adsorbents. These adsorbents could be used to minimize agricultural P-losses and reduce the negative environmental effects of the overapplication of animal manures.

Technical Abstract: Continuous land application of animal manure is environmentally unsustainable. Therefore, alternative beneficial uses of animal wastes are needed to manage large amounts of manure in an environmentally safe manner. We used a three-step process to convert poultry litter and swine manure into biochar-based phosphorus (P) sorbents: 1) manures were treated using the “quick-wash” procedure to reduce their P content, 2) converted to biochar via pyrolysis, and 3) then chemically activated to improve their affinity for soluble P. Batch sorption results indicated that post-pyrolysis iron-activated biochars derived from quick-washed poultry litter (FewPL) or swine manure (FewSM) had the highest affinity for soluble P compared to nonactivated or magnesium-activated biochars. Phosphorus sorption by FewPL and FewSM was strongly pH dependent, with higher P sorption under more acidic conditions. Specifically, FewPL and FewSM removed >99% of added P from aqueous solutions at pH <7.3 and <3.7, respectively. Both biochars were repeatedly equilibrated with 2.5 mg P L-1 at pH 6.2 to obtain estimates of their maximum P sorption capacities under environmentally relevant P concentrations. Based on Langmuir model descriptions of sorption data, the maximum P sorption capacities of FewPL and FewSM were 2.0 and 2.6 mg g-1, respectively. These results demonstrate that our three-step process is viable for converting poultry litter and swine manure into biochar-based P sorbents, representing a possible alternative beneficial use of animal manures.