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<p>Hydrothermal carbonization (HTC) converts sugarcane residues into functional hydrochar, but its performance for ammonium (NH<sub>4</sub><sup>+</sup>) recovery from real wastewaters remains unexplored. It was hypothesized that divalent Mg<sup>2+</sup> would cause disproportionately greater inhibition of NH<sub>4</sub><sup>+</sup> adsorption than monovalent K<sup>+</sup> due to charge density effects. Hydrochars produced at 200–240&#xa0;°C were characterized, with sugarcane leaf hydrochar at 220&#xa0;°C (SLH/220) exhibiting optimal uptake. Adsorption capacity reached 20&#xa0;mg&#xa0;g<sup>−1</sup> in synthetic solutions, but decreased by approximately 50% to 10.25&#xa0;mg&#xa0;g<sup>−1</sup> in liquid fraction of digestate. Despite its 11-fold lower concentration, Mg<sup>2+</sup> caused stronger inhibition (32%) than K<sup>+</sup> (24%), demonstrating that charge density, not concentration, governs cation competition. Adsorption followed the Langmuir isotherm (R<sup>2</sup> = 0.96) and pseudo-second-order kinetics (R<sup>2</sup> = 0.97), indicating monolayer chemisorption. Per ton of feedstock, the integrated HTC-adsorption-AD pathway yielded 41 m<sup>3</sup> CH<sub>4</sub> and recovered 5.1&#xa0;kg N as slow-release fertilizer, supporting decentralized circular economy systems. These findings establish that wastewater cation composition is the primary determinant of hydrochar performance, with direct implications for biorefinery design.</p> Graphical abstract <p></p>

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Ammonium adsorption from anaerobic digestate on sugarcane hydrochar: performance, competitive ion mechanisms, and biorefinery integration

  • 期刊论文

  • 发表日期：

    2026年8月1日

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  • Edy Kurniawan,
  • Rattana Jariyaboon,
  • Alissara Reungsang,
  • Prawit Kongjan

摘要

Hydrothermal carbonization (HTC) converts sugarcane residues into functional hydrochar, but its performance for ammonium (NH4+) recovery from real wastewaters remains unexplored. It was hypothesized that divalent Mg2+ would cause disproportionately greater inhibition of NH4+ adsorption than monovalent K+ due to charge density effects. Hydrochars produced at 200–240 °C were characterized, with sugarcane leaf hydrochar at 220 °C (SLH/220) exhibiting optimal uptake. Adsorption capacity reached 20 mg g−1 in synthetic solutions, but decreased by approximately 50% to 10.25 mg g−1 in liquid fraction of digestate. Despite its 11-fold lower concentration, Mg2+ caused stronger inhibition (32%) than K+ (24%), demonstrating that charge density, not concentration, governs cation competition. Adsorption followed the Langmuir isotherm (R2 = 0.96) and pseudo-second-order kinetics (R2 = 0.97), indicating monolayer chemisorption. Per ton of feedstock, the integrated HTC-adsorption-AD pathway yielded 41 m3 CH4 and recovered 5.1 kg N as slow-release fertilizer, supporting decentralized circular economy systems. These findings establish that wastewater cation composition is the primary determinant of hydrochar performance, with direct implications for biorefinery design.

Graphical abstract