Recovered Calcium-Based Phosphorus Products from Synthetic Swine Wastewater: Fate and Behavior in Soils

The increasing demand for phosphorus (P) sources and concerns about surface water quality raise the need to explore safe and efficient secondary P fertilizer sources. This study evaluated the effectiveness of a Ca-based recovered nutrient product (RNP) from synthetic swine wastewater using an innovative anaerobic membrane bioreactor (AnMBR) technology. This study aimed to characterize and compare the dissolution, transformations, and potential bioavailability of P in RNP with conventional P fertilizers (monoammonium phosphate; MAP, triple superphosphate; TSP) in selected soils over time by using short-term laboratory incubation studies in Petri dishes. Soil samples sectioned from the point of application were assessed for pH, total P, resin-extractable P, and selected samples by using X-ray absorption near-edge structure spectroscopy. The RNP treatment showed that over 90%, 70%, and 80% of added P remained in the center section in calcareous, neutral, and acid soils, respectively, where the potential plant-available P was greater than the control in all soils and similar to the MAP treatment only in acid soil after 5 weeks of incubation. The hydroxyapatite-like species dominated P speciation in both RNP and RNP-added soils, leading to less solubility. These results underscore the potential of Ca-based RNP as a P source for tested soils, and process modifications could yield a series of viable secondary P sources for agriculture.