TY - JOUR

T1 - Increasing phosphorus plant availability from P-rich ashes and biochars by acidification with sulfuric acid

AU - Kopp, Clara

AU - Sica, Pietro

AU - Lu, Changyong

AU - Tobler, Dominique

AU - Stoumann Jensen, Lars

AU - Müller-Stöver, Dorette

N1 - Publisher Copyright: © 2023 The Authors

PY - 2023

Y1 - 2023

N2 - Biochars and ashes derived from thermal treatment of P-rich wastes could be used as bio-based fertilizers to improve P recycling. However, thermal treatments often result in low plant P availability. Acidification of these materials before soil application could potentially increase plant P availability. Based on the water-extractable P levels obtained in titration experiments, sulfuric acid concentrations between 2.5 M and 10 M were applied to digestate solids char and ash (DS-C, DS-A), poultry litter ash (PL-A), insect frass char (IF-C), sewage sludge char and ash (SS-C, SS-A) and meat and bone char (MB-C). Acidified and untreated materials were applied in a pot experiment with maize in 33P labeled soil to determine fertilizer P uptake. The acidification resulted in a significant increase in P solubility. The amount of acid required depended on the materials’ buffer capacity and P speciation. Based on XRD analysis, we assume that mainly Ca-associated P was solubilized. In the pot experiment, acidified materials outperformed untreated materials and the unfertilized control in terms of biomass and P uptake. The P recovery from the acidified materials ranked in the order DS-C > SS-A > PL-A > IF-C > DS-A > SS-C > MB-C. The acidification did not significantly decrease soil pH, nor was there an effect on plant heavy metal availability. In conclusion, acidification increased plant growth and P uptake without affecting plant heavy metal uptake and soil pH. Therefore, acidification to increase the P fertilizer value of ashes and chars is a promising approach to facilitate P recycling.

AB - Biochars and ashes derived from thermal treatment of P-rich wastes could be used as bio-based fertilizers to improve P recycling. However, thermal treatments often result in low plant P availability. Acidification of these materials before soil application could potentially increase plant P availability. Based on the water-extractable P levels obtained in titration experiments, sulfuric acid concentrations between 2.5 M and 10 M were applied to digestate solids char and ash (DS-C, DS-A), poultry litter ash (PL-A), insect frass char (IF-C), sewage sludge char and ash (SS-C, SS-A) and meat and bone char (MB-C). Acidified and untreated materials were applied in a pot experiment with maize in 33P labeled soil to determine fertilizer P uptake. The acidification resulted in a significant increase in P solubility. The amount of acid required depended on the materials’ buffer capacity and P speciation. Based on XRD analysis, we assume that mainly Ca-associated P was solubilized. In the pot experiment, acidified materials outperformed untreated materials and the unfertilized control in terms of biomass and P uptake. The P recovery from the acidified materials ranked in the order DS-C > SS-A > PL-A > IF-C > DS-A > SS-C > MB-C. The acidification did not significantly decrease soil pH, nor was there an effect on plant heavy metal availability. In conclusion, acidification increased plant growth and P uptake without affecting plant heavy metal uptake and soil pH. Therefore, acidification to increase the P fertilizer value of ashes and chars is a promising approach to facilitate P recycling.

KW - Agronomic efficiency

KW - Animal manure

KW - Bio-based fertilizer

KW - Digestate

KW - Phosphorus recycling

KW - Sewage sludge

U2 - 10.1016/j.jece.2023.111489

DO - 10.1016/j.jece.2023.111489

M3 - Journal article

AN - SCOPUS:85178487642

VL - 11

JO - Journal of Environmental Chemical Engineering

JF - Journal of Environmental Chemical Engineering

SN - 2213-3437

IS - 6

M1 - 111489

ER -