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<p>Phosphorus (P) recovery is critical for mitigating environmental pollution and promoting sustainable development, particularly in light of the progressive depletion of phosphate rock resources. Sewage sludge ash (SSA) represents a reliable secondary source of P. In this study, an integrated ultrasound-assisted bioleaching strategy using lemon juice (sonoleaching) was developed to enhance P extraction from SSA, followed by struvite crystallization for P recovery. Response Surface Methodology (RSM) was employed to optimize the key leaching parameters, including SSA concentration, lemon juice concentration, ultrasonic power, and leaching time, as well as three crystallization parameters: Mg/P molar ratio, N/P molar ratio, and pH. A reduced cubic model developed using Central Composite Design showed strong agreement with the experimental data, with R<sup>2</sup> and adjusted R<sup>2</sup> values of 0.95 and 0.92. Under the optimized extraction conditions of 1.34% w/v SSA, 55% v/v lemon juice, an ultrasonic power of 137&#xa0;W, and a leaching time of 70&#xa0;min, the P extraction efficiency reached 98.4%. The leachate was then purified using a cation-exchange resin, AG 50W-X8, applied at 0.08&#xa0;g&#xa0;ml<sup>−1</sup>, which effectively removed co-extracted metals while retaining dissolved P. The recovered struvite contained 11.55% P, 5.3% N, and 10.3% Mg. These values corresponded to a P: N: Mg molar ratio of 0.86:1.3:1.1 and a struvite purity of 77.4%. XRD and SEM-EDX analyses confirmed the formation of orthorhombic struvite crystals with a well-defined morphology. Overall, the combined bio-acid and ultrasound-assisted process provides an efficient, low-chemical route for producing a slow-release phosphorus fertilizer with reduced metal impurities.</p> Graphical abstract <p></p>

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Phosphorus recovery from sewage sludge ash via ultrasound-assisted leaching with lemon juice for struvite production

  • 期刊论文

  • 发表日期：

    2026年4月29日

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  • T. Nazari,
  • M. B. Motlagh,
  • S. O. Rastegar,
  • M. H. Sedri

摘要

Phosphorus (P) recovery is critical for mitigating environmental pollution and promoting sustainable development, particularly in light of the progressive depletion of phosphate rock resources. Sewage sludge ash (SSA) represents a reliable secondary source of P. In this study, an integrated ultrasound-assisted bioleaching strategy using lemon juice (sonoleaching) was developed to enhance P extraction from SSA, followed by struvite crystallization for P recovery. Response Surface Methodology (RSM) was employed to optimize the key leaching parameters, including SSA concentration, lemon juice concentration, ultrasonic power, and leaching time, as well as three crystallization parameters: Mg/P molar ratio, N/P molar ratio, and pH. A reduced cubic model developed using Central Composite Design showed strong agreement with the experimental data, with R2 and adjusted R2 values of 0.95 and 0.92. Under the optimized extraction conditions of 1.34% w/v SSA, 55% v/v lemon juice, an ultrasonic power of 137 W, and a leaching time of 70 min, the P extraction efficiency reached 98.4%. The leachate was then purified using a cation-exchange resin, AG 50W-X8, applied at 0.08 g ml−1, which effectively removed co-extracted metals while retaining dissolved P. The recovered struvite contained 11.55% P, 5.3% N, and 10.3% Mg. These values corresponded to a P: N: Mg molar ratio of 0.86:1.3:1.1 and a struvite purity of 77.4%. XRD and SEM-EDX analyses confirmed the formation of orthorhombic struvite crystals with a well-defined morphology. Overall, the combined bio-acid and ultrasound-assisted process provides an efficient, low-chemical route for producing a slow-release phosphorus fertilizer with reduced metal impurities.

Graphical abstract