Development of phosphorus recovery technologies for sustainable utilization of livestock manure

Phosphorus (P) recovery from livestock manure is a potential approach to address the depletion of P rock reserves. However, P in manure primarily exists in insoluble solid form, which poses a major challenge to the recovery process since only soluble P can be effectively separated and recovered. Traditional chemical acidification methods, while effective in solubilizing P, are limited by high chemical consumption, elevated costs, and the generation of secondary pollutants, underscoring the need for more sustainable alternatives. To overcome these limitations, this study investigated biological acidification and electrolytic acidification, focusing on optimizing key reaction conditions and analyzing the underlying mechanisms of P release and acidification. It also investigated the integration of these P release methods with struvite crystallization in terms of recovery performance and product characteristics. Biological acidification was performed by co-fermenting pig manure (PM) with food waste (FW) under anaerobic conditions. The results showed FW promoted lactic acid production and rapid acidification. As FW increased from 0 to 80%, the concentrations of lactic acid rose from 0.12 ± 0.04 g/L to 11.95 ± 1.37 g/L, with pH decreasing from 7.55 to 4.43. The ratio with FW/PM=1:2 was the optimal condition, which led to the highest dissolved phosphate (PO43--P) concentration of 350.39 ± 8.59 mg/L in 72 h, with a total P release of 74.2 ± 1.8%. Multiple regression analyses established key relationships to predict pH changes in the reactor. Electrolytic acidification was conducted using an electrochemically mediated phosphorus release (EMR) reactor at different voltages. The results showed over 70% of particulate P was converted to soluble reactive P during the EMR process, involving the dissolution of inorganic P and the conversion of organic P. Increasing the voltage appropriately enhanced ion migration and acidification rates. At 9 V, the release of 92.1 ± 1.3% was obtained in 36 h. Subsequent P recovery from P-rich supernatants was conducted using struvite crystallization. The fermentation supernatant achieved the highest struvite purity of 91.9 ± 2.2% at pH of 8.0 and an Mg/P ratio of 1.5, with a P recovery of 97.9%. In contrast, the EMR supernatant yielded a struvite purity of 51.7 ± 0.3% under optimal conditions of pH of 9.0 and an Mg/P ratio of 1.75, with a P recovery of 96.3%. Morphological analysis revealed well-defined crystalline struvite from the fermentation supernatant, whereas the product from the EMR supernatant contained irregular aggregates and more impurities, such as brushite and hydroxyapatite. This research demonstrates the feasibility of sustainable P recovery by integrating acidification and struvite crystallization, offering practical solutions for nutrient recycling. It provides valuable insights for optimizing recovery systems, supporting the circular economy, and mitigating environmental risks associated with manure management.

Funder

China Scholarship Council

Publisher

University of Galway

Rights

Attribution-NonCommercial-NoDerivatives 4.0 International

cbn

Collections

University of Galway Theses (PhD Theses)