title: Sustainable nutrients recovery and recycling by optimizing the chemical addition sequence for struvite precipitation from raw swine slurries.
abstract: Livestock farming contributes heavily to nitrogen (N) and phosphorus (P) flows into the environment, a major cause of eutrophication of coastal and freshwater systems. Furthermore, the growing demand for N-P fertilizers is increasing the emission of anthropogenic reactive N into the atmosphere and the depletion of the current P reserves. Therefore, it is essential to minimize the anthropogenic impact on the environment and recycle the wasted N-P for agricultural reuse. This study focused on enhancing struvite (MgNH4PO4*6H2O) precipitation from raw swine slurries in batch and laboratory-scale reactors. Different chemical addition sequences were evaluated, and the best removal efficiency (E%) was obtained when the chemicals were mixed before the precipitation process. Struvite was detected at a pH as low as 6 (E%N-P∼50%), and high E%N-P was found at pH 7-9.5 (80-95%). Furthermore, air stripping was used in place of NaOH to adjust pH, returning the same efficiency as if only alkali had been used. XRD and FE-SEM analysis of the precipitate showed that the recovered struvite was of high purity with orthorhombic crystalline structure and only trace amounts of impurities from matrix organics, co-precipitation products (CaO and amorphous calcium-phosphates), and residuals of added chemicals (MgO).
authors.affiliation: Tampere University of Technology, Department of Chemistry and Bioengineering, P.O. 541, FIN-33101, Tampere, Finland. Electronic address: raffaele.taddeo@tut.fi.
authors.forename: Raffaele
authors.initials: R
authors.lastname: Taddeo
authors.affiliation: Tampere University of Technology, Department of Material Science, P.O. 589, FI-33101, Tampere, Finland.
authors.forename: Kari
authors.initials: K
authors.lastname: Kolppo
authors.affiliation: Tampere University of Technology, Department of Chemistry and Bioengineering, P.O. 541, FIN-33101, Tampere, Finland.
authors.forename: Raghida
authors.initials: R
authors.lastname: Lepistö
mesh_terms: D000641:Ammonia / Q000737:chemistry; D000818:Animals; D011232:Chemical Precipitation; D005308:Fertilizers; D006863:Hydrogen-Ion Concentration; D017616:Magnesium Compounds / Q000737:chemistry; D008372:Manure; D008855:Microscopy, Electron, Scanning; D059027:Recycling; D000069877:Struvite / Q000737:chemistry*; D013552:Swine; D014865:Waste Disposal, Fluid / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D005308:Fertilizers; D017616:Magnesium Compounds; D008372:Manure; D000641:Ammonia; D000069877:Struvite
keywords: Air stripping; Chemical addition; Crystallization; Manure management; Nutrients recycling; Struvite