Recovery of ammonia and phosphate minerals from swine wastewater using gas-permeable membranes

Gas-permeable membrane technology is useful to recover ammonia (NH₃) from liquid manures. In this study, phosphorus (P) recovery via MgCl₂ precipitation was enhanced by combining it with NH₃ recovery through gas-permeable membranes. Anaerobically digested swine wastewater containing approximately 2300 mg NH₄⁺-N L^-1 and 450 mg P L^-1 was treated using submerged membranes plus low-rate aeration to recover the NH₃ from within the liquid and MgCl₂ to precipitate the P. The experiments included a first configuration where N and P were recovered sequentially and a second configuration with simultaneous recovery. The low-rate aeration reduced the natural carbonate, increased pH and accelerated NH₃ uptake by the gas-permeable membrane system, which in turn benefited P recovery. Phosphorus removal efficiency was >90% and P recovery efficiency was about 100%. With higher NH₃ capture, the recovered P contained higher P₂O₅ content (37-46%, >98% available), similar to the composition of the biomineral newberyite (MgHPO₄·3H₂O).