Phosphorus transformation in pig slurry due to diet and continuous aeration treatments

The experiment was conducted to study the transformation of phosphorus (P) in slurry from pigs fed two different diets, a regular corn soybean meal diet with or without supplementation of 40% soybean hulls (SBH). The slurry was collected and treated either without aeration or continuous aeration at an airflow rate of 0.5 1/m ³/s for 21 days. Two slurries and two treatments constituted a 2 × 2 factorial design. The slurry was sampled and measured on days 1, 2, 3, 4, 7, 14, and 21. Results indicated that the pH of aerated slurries was increased (P < 0.01) by 0.9 unit within 24 hours, but the pH of non-aerated slurries was unchanged. Aeration decreased total inorganic P, insoluble inorganic P, and soluble P, but increased organic P by approximately 163 mg/1. The average organic P in the slurry from both diets with aeration was about 34% higher than that in the same slurry without aeration. Aeration decreased insoluble inorganic P by about 10.6% and soluble P by about 4.2%. The mass balance of P fractions showed transformation of insoluble inorganic P into organic forms during the aeration stage. The insoluble inorganic P takes about 68% of the total P in the slurry, so it is essential to perform solid-liquid separation prior to aeration to enhance the efficiency of soluble P removal because insoluble inorganic P is mainly contained in the slurry solids.