Aerated Fluidized Bed Treatment for Phosphate Recovery from Dairy and Swine Wastewater

An aerated fluidized bed reactor (aerated-FBR) was used for recovery of orthophosphate (PO₄-P) from dairy wastewater (D-WW) and swine wastewater (S-WW) by struvite (MgNH₄PO₄·6H₂O) precipitation. Model wastewater solutions (S-model, D-model) free of organic material were also treated. The maximum PO₄-P recovery for treated livestock wastes was 94% for S-WW and 63% for D-WW. The PO₄-P recovery did not improve for S-model compared to S-WW, but increased to 81% for D-model relative to D-WW, suggesting that the high organic content of D-WW may hinder the recovery process. X-ray diffraction (XRD) analysis of recovered solids revealed that treated S-WW produced mostly struvite (95-98%) while D-WW yielded a mixture of struvite (28-33%), calcite (CaCO₃; 17-55%), and monohydrocalcite (CaCO₃·H₂O; 13-42%). The Fourier transform infrared (FTIR) spectra of the solids confirm the presence of vibrational bands associated with these minerals. Simultaneous thermal analysis (STA) indicated that all solids, except for D-WW, show thermogravimetric (TG) trends consistent with the struvite and calcium carbonate content. The D-WW solids had additional TG steps, possibly due to high organic and colloidal content, and slightly improved ammonium stability. The aerated-FBR treatment is an effective method to reduce PO₄-P from livestock wastewater through precipitation of pure struvite and struvite/calcium carbonate mixtures.