Biochar as a highly efficient adsorption carrier for sewage sludge-derived nutrients and biostimulants: component fixation and mechanism

Highlights

•	SB was better able to fix N (TKN, NO3−−N, proteins, amino acids) than WCB.
•	More humic acid fluorescent substances from neutral SS-NB adsorbed on biochar.
•	WCB and SB had excellent immobilization capacity for phytohormones and allelochemicals.
•	WCB had higher adsorption efficiencies for N-, P-, and S-containing molecules.
•	Hydrogen bonding and pore size-exclusion effect enhanced the adsorption of WCB.

Abstract

Production of liquid fertilizers containing nitrogenous nutrients and biostimulants from sewage sludge (SS-NB) has been attracting increasing attention due to its excellent fertilization effect and resource recycling attributes. To better understand the functional effects of nutrients and biostimulants in SS-NB on soil, the adsorption capacity and mechanism of straw biochar (SB) and wood chip biochar (WCB) for alkaline and neutral SS-NB components were investigated. The adsorption of total organic carbon (TOC) from alkaline and neutral SS-NB by WCB was 61.14% and 89.73%, respectively, higher than that by SB, which was 56.25% and 83.36%. Moreover, TOC from neutral SS-NB was more readily adsorbed, especially for fulvic and humic acids. SB had a strong adsorption capacity for calcium ions and nitrogen (TKN, nitrate N, protein, amino acid) and released large amounts of P. In addition, WCB and SB showed a strong affinity for macromolecules (proteins) and reducing substances (lignin and lipids) and excellent fixation ability for phytohormones and allelochemicals. However, WCB adsorbed more types of molecular substances than SB while maintaining a high immobilization rate. Analysis of the adsorption mechanism showed that surface amino groups of the biochar were involved in adsorption, while WCB had additionally high adsorption efficiencies through pore adsorption, hydrogen bonding adsorption and pore size-exclusion effects. The study revealed that biochar can be used as an efficient adsorption carrier for SS-NB to improve soil fertility management.

Funding

National Key Research and Development Program of China(2023YFC3207602); Jiangsu Special Funding of Science and Technology Innovation for Carbon Emission Peaking and Carbon Neutrality(BE2022303); Postgraduate Research & Practice Innovation Program of Jiangsu Province(KYCX22-2382); Jiangsu Students' Key Project (Innovation) for Innovation and Entrepreneurship Training Program(202310295011Z)