Phosphorus recovery from solid swine slurry: enhanced approach via chemical extraction and selective precipitation

Swine solid slurry (SSS) exerts pressure on land and poses environmental risks due to nutrient overload. This study developed a phosphorus extraction and recovery process to address these issues. SSS exhibited low phosphorus bioavailability and high metal contamination. Treatment with 0.1 M H₂SO₄ at an H⁺/P ratio of 4.0 achieved 99.8% phosphorus extraction. The purified solution (2nd ) yielded a precipitate with higher phosphorus and calcium levels than the raw leachate, demonstrating effective iron separation. Adjusting the 2nd solution to pH 7.5 resulted in 86.2% phosphorus recovery. Fourier-transform infrared spectroscopy, optical emission spectrometry, and X-ray diffraction analyses confirmed that the recovered material was rich in macronutrients and had reduced toxic metal levels compared to raw SSS. These findings highlight the potential for converting SSS into a valuable phosphorus resource, promoting sustainable nutrient recycling and improved waste management. Future work should improve the physical quality of the recovered phosphorus. The current sludge form has high moisture content, limiting reuse and transport. A fluidized-bed reactor could produce low-moisture granules with better handling and practicality.