Magnesium activation affects the properties and phosphate sorption capacity of poultry litter biochar

Biochars with a high affinity for phosphorus (P) are promising soil amendments for reducing P in agricultural runoff. Poultry litter (PL) is an abundant biochar feedstock, however, PL-derived biochars are typically high in soluble P and therefore require chemical modification to become effective P sorbents. This study investigated the effect of magnesium (Mg) activation extractable P (EP) and P sorption capacities of PL-derived biochars. Biochar was produced at 500-900°C from PL activated with 0-1 M Mg. Three differentially aged PL feedstocks were evaluated (1-, 3-5-, or 7–9-year-old). Increased Mg activation level and pyrolysis temperature both resulted in EP reductions from the biochars. Specifically, biochars produced at temperatures ≥700°C from PL activated with ≥0.25 M Mg had negligible EP. X-ray diffractograms indicated that increased Mg loading favored the formation of stable Mg3(PO4)2 phases while increasing temperature favored the formation of both Mg3(PO4)2 and Ca5(PO4)3OH. Maximum P sorption capacities (Pmax) of the biochars were estimated by fitting Langmuir isotherms to batch sorption data and ranged from 0.66-10.35 mg g-1. Average Pmax values were not affected by PL age or pyrolysis temperature; however, biochars produced from 1 M Mg-activated PL did have significantly higher average Pmax values (p<0.05), likely due to a greater abundance of MgO. Overall, results demonstrated that Mg activation is an effective strategy for producing PL-derived biochars with the potential ability to reduce P loading into environmentally sensitive ecosystems.

Impact/Purpose

Poultry production and use of poultry litter as fertilizer on the Delmarva Peninsula have led to excessive phosphorus (P) in soil leachate and runoff that is impacting the water quality of the Chesapeake Bay. One strategy for managing poultry litter (PL) wastes is to pyrolyze it (i.e., heat in the absence of oxygen) and turn it into biochar. It’s hypothesized that doing so would render the PL P less soluble and could in fact sorb available soil P thereby reducing the potential for P movement into streams, rivers, lakes and Chesapeake Bay. This study found that to produce a PL-based biochar that sorbs P requires that the PL be activated with magnesium salts prior to pyrolysis. The resulting “activated” biochar does sorb and immobilize soil P. The results of this study demonstrated that Mg activation is an effective strategy for producing PL-derived biochars with the potential ability to reduce P loading into environmentally sensitive ecosystems.

Citation

Padilla, J., D. Watts, J. Novak, V. Cerven, J. Ippolito, A. Szogi, AND M. Johnson. Magnesium activation affects the properties and phosphate sorption capacity of poultry litter biochar. Springer Nature, LONDON, UK, 5:64, (2023). [DOI: 10.1007/s42773-023-00263-5]

DOI: Magnesium activation affects the properties and phosphate sorption capacity of poultry litter biochar