Release behavior of fertilizers and heavy metals from iron-loaded sludge biochar in the aqueous environment

Lijiao Yang; Jirong Zhao; Qingxia Huang; Jinchao Wang; Chengtao Xu; Yufeng Xu; Liheng Liu

doi:10.1016/j.envpol.2023.122163

Release behavior of fertilizers and heavy metals from iron-loaded sludge biochar in the aqueous environment

Environ Pollut. 2023 Oct 1:334:122163. doi: 10.1016/j.envpol.2023.122163. Epub 2023 Jul 8.

Authors

Lijiao Yang¹, Jirong Zhao², Qingxia Huang¹, Jinchao Wang¹, Chengtao Xu¹, Yufeng Xu³, Liheng Liu⁴

Affiliations

¹ College of Environmental Science and Engineering, Guilin University of Technology, Guilin, 541004, China.
² College of Environmental Science and Engineering, Guilin University of Technology, Guilin, 541004, China; School of Civil and Hydraulic Engineering, Xichang University, Xichang, 615000, China. Electronic address: 1256164162@qq.com.
³ College of Environmental Science and Engineering, Guilin University of Technology, Guilin, 541004, China; Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, Guilin University of Technology, Guilin, 541004, China; Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Area, Guilin University of Technology, Guilin, 541004, China.
⁴ College of Environmental Science and Engineering, Guilin University of Technology, Guilin, 541004, China; Guangxi Key Laboratory of Environmental Pollution Control Theory and Technology, Guilin University of Technology, Guilin, 541004, China; Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Area, Guilin University of Technology, Guilin, 541004, China. Electronic address: deanhenry_liu01@126.com.

PMID: 37429492
DOI: 10.1016/j.envpol.2023.122163

Abstract

In this study, the release behavior of fertilizers (NH₄⁺-N, PO₄^3- and K) and heavy metals (Mn, Zn, Ni, Cu, Pb and Cr) from iron-loaded sludge biochar (ISBC) was investigated to evaluated the feasibility and risks of ISBC as a slow release fertilizer. Their release capacity was significantly enhanced with decreasing initial pH, increasing solid-liquid ratio (R_S-L) and rising temperature (p < 0.05). When the initial pH, R_S-L and temperature were separately 5 (fertilizers)/1 (heavy metals), 1:5 and 298 K, the final concentrations of NH₄⁺-N, PO₄^3-, K, Mn, Zn and Ni were 6.60, 14.13, 149.4, 53.69, 72.56, and 1.01 mg L^-1, while the maximum concentrations of Cu, Pb and Cr were 0.94, 0.77, and 0.22 mg L^-1, respectively. Due to the tiny difference between the R² values, revised pseudo-first-order and pseudo-second-order kinetics models described their release behavior well, suggesting that physical and chemical interactions played an important role. Activation energies greater than 40 kJ mol^-1 indicated that the rate-controlling steps of the release of NH₄⁺-N, PO₄^3- and Ni were chemical reactions, while chemical reactions and diffusion together determined the release rates of K, Mn, Zn, Cu, Pb and Cr because their activation energies were in the range of 20-40 kJ mol^-1. The increasingly negative ΔG and positive ΔH and ΔS suggested that their release was a spontaneous (except Cr) and endothermic process with an increase of randomness between the solid-liquid interface. The release efficiency of NH₄⁺-N, PO₄^3- and K were in the ranges of 28.21%-53.97%, 2.09%-18.06% and 39.46%-66.14%, respectively. Meanwhile, the pollution index and evaluation index of heavy metals were in the ranges of 33.31-227.4 and 4.64-29.24, respectively. In summary, ISBC could be used as a slow-release fertilizer with low risk when the R_S-L was less than 1:40.

Keywords: Fertilizers and heavy metals; Iron-loaded sludge biochar; Kinetics; Risk evaluation; Thermodynamics.

MeSH terms

Fertilizers
Iron*
Lead
Metals, Heavy*
Sewage
Water

Substances

Iron
Fertilizers
Sewage
biochar
Lead
Metals, Heavy
Water