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<p>Green composites based on poly(<i>β</i>-hydroxybutyrate) (PHB), starch, and clay (PHBSMMt) were developed as hybrid materials for the controlled release of nutrients such as NPK (nitrogen, phosphorus, and potassium) (PHBSMMtNPK) and KNO₃ (PHBSMMtKNO<sub>3</sub>). This study investigates their biodegradation patterns (measured via CO<sub>2</sub> production), nutrient release profiles in water, and corresponding kinetic models. Fertilizer incorporation enhanced biodegradation, with NPK composites generating more CO<sub>2</sub> than KNO₃ composites over 97&#xa0;days. CO<sub>2</sub> production from the PHBSGMMtNPK and PHBSGMMtKNO₃ composites reached 72.50&#xa0;mg and 58.36&#xa0;mg, respectively, whereas the PHBSGMMt composite (without nutrient addition) released only 19.08&#xa0;mg. Biodegradation kinetics were described using the two simultaneous reactions (PHBSMMt and PHBSMMtKNO<sub>3</sub>) and combined first-zero-order models (PHBSMMtNPK), revealing a two-phase degradation mechanism: a labile fraction rapidly degraded by soil microbes and a stable fraction, resistant to microbial attack. The PHBSGMMt sample exhibited a <i>C</i><sub>o</sub> of 3.90&#xa0;mg C/kg and a shorter half-life of 4.67&#xa0;days. In contrast, the PHBSGMMtKNO₃ composite showed the highest labile carbon fraction (17.52&#xa0;mg C/kg) with a comparable half-life of 4.78&#xa0;days. For the PHBSGMMtNPK composite, the labile fraction comprised 7.13&#xa0;mg C/kg with a half-life of 1.84&#xa0;days, while the stable fraction contained 76.02&#xa0;mg C/kg and degraded more slowly (half-life = 31.19&#xa0;days). These findings suggest that fertilizer incorporation enhances the availability of biodegradable carbon, thereby accelerating its decomposition. Nutrient release in water demonstrated complete potassium and nitrogen release within 24&#xa0;h from NPK and KNO<sub>3</sub>, while phosphorus release from NPK reached 80%. The Peppas–Sahlin model best described the nutrient release kinetics, highlighting two mechanisms: diffusion and polymer chain relaxation. Results indicated that starch degraded first as the labile fraction, followed by PHB as the stable fraction. These green composites demonstrated potential as enhanced-efficiency fertilizers, achieving complete biodegradation by the end of the study.</p> Graphical abstract <p></p>

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Impact of NPK and KNO3 fertilizers on biodegradation, kinetics, and nutrient release in enhanced-efficiency fertilizer green composites

  • 期刊论文

  • 发表日期：

    2025年6月6日

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  • Josiane de Lima Souza,
  • Camila Gruber Chiaregato,
  • Aline Gambaro Balieiro,
  • Roselena Faez

摘要

Green composites based on poly(β-hydroxybutyrate) (PHB), starch, and clay (PHBSMMt) were developed as hybrid materials for the controlled release of nutrients such as NPK (nitrogen, phosphorus, and potassium) (PHBSMMtNPK) and KNO₃ (PHBSMMtKNO3). This study investigates their biodegradation patterns (measured via CO2 production), nutrient release profiles in water, and corresponding kinetic models. Fertilizer incorporation enhanced biodegradation, with NPK composites generating more CO2 than KNO₃ composites over 97 days. CO2 production from the PHBSGMMtNPK and PHBSGMMtKNO₃ composites reached 72.50 mg and 58.36 mg, respectively, whereas the PHBSGMMt composite (without nutrient addition) released only 19.08 mg. Biodegradation kinetics were described using the two simultaneous reactions (PHBSMMt and PHBSMMtKNO3) and combined first-zero-order models (PHBSMMtNPK), revealing a two-phase degradation mechanism: a labile fraction rapidly degraded by soil microbes and a stable fraction, resistant to microbial attack. The PHBSGMMt sample exhibited a Co of 3.90 mg C/kg and a shorter half-life of 4.67 days. In contrast, the PHBSGMMtKNO₃ composite showed the highest labile carbon fraction (17.52 mg C/kg) with a comparable half-life of 4.78 days. For the PHBSGMMtNPK composite, the labile fraction comprised 7.13 mg C/kg with a half-life of 1.84 days, while the stable fraction contained 76.02 mg C/kg and degraded more slowly (half-life = 31.19 days). These findings suggest that fertilizer incorporation enhances the availability of biodegradable carbon, thereby accelerating its decomposition. Nutrient release in water demonstrated complete potassium and nitrogen release within 24 h from NPK and KNO3, while phosphorus release from NPK reached 80%. The Peppas–Sahlin model best described the nutrient release kinetics, highlighting two mechanisms: diffusion and polymer chain relaxation. Results indicated that starch degraded first as the labile fraction, followed by PHB as the stable fraction. These green composites demonstrated potential as enhanced-efficiency fertilizers, achieving complete biodegradation by the end of the study.

Graphical abstract