Effect of Anaerobic Digestion on Manure Characteristics for Phosphorus Precipitation from Swine Waste

Swine production facilities today are larger in size and are concentrated in smaller geographical areas than they were two decades ago. Additionally, there is an increasing trend to base manure land application rates on crop phosphorus requirements rather than crop nitrogen requirements alone. These factors have resulted in a need to find a feasible method for removing phosphorus from swine waste prior to land application. Economically concentrating and transporting excess phosphorus to phosphorus deficient cropping areas would benefit the current production scheme. Forced precipitation of phosphorus as struvite (MgNH4PO46H2O) is an option for phosphorus concentration and removal. Economic feasibility of phosphorus precipitation improves when reactive phosphorus represents a high percentage of the total phosphorus in slurry, and when a limited amount of chemical amendment is required for the precipitation reaction. In this study, anaerobic digestion of swine slurry increased reactive phosphorus (PO4) and magnesium ion (Mg2+) in solution by 26% and 254%, respectively. Additionally, during phosphorus precipitation experiments, PO4 removal and reduction efficiencies were greatest in the tests performed with anaerobically digested swine slurry.