Development of an Air Sparged Continuous Flow Reactor for Struvite Precipitation from Two Different Liquid Swine Manure Storage Systems

Forced precipitation of struvite (MgNH4PO4*6H2O) has been demonstrated to be an effective method to reduce dissolved reactive phosphorus (DRP) from swine manure. The development of a robust and flexible continuous flow struvite precipitation reactor is essential to the application of this method to modern livestock operations. Swine manure generally requires pH adjustment, magnesium amendment and a sufficient reaction time to create optimum conditions for struvite precipitation. A bench-scale (14-L) continuous flow reactor was developed to force struvite precipitation and reduce DRP. The bench scale system was developed to quantify system performance prior to building a much larger pilot-scale unit. The benchscale reactor used air sparging to provide pH adjustment and mixing. Influent manure slurry was continuously amended with magnesium chloride (MgCl2 . 6H2O) to promote maximum DRP removal. During continuous flow operation, a 10-minute hydraulic retention time was provided for struvite precipitation. This paper discusses the design and development of the continuous flow air sparged tank reactor (ASTR) and reports on the reactor's DRP reduction capabilities on manure collected from two commercially utilized swine manure storage systems; 1) a concrete storage tank with a permeable cover, and 2) a shallow under floor pit manure collection system. Continuous flow ASTR treatment provided a 95% reduction of DRP from the covered storage tank manure and a 78% reduction of DRP from the under floor pit manure.