Agricultural waste has traditionally been considered as a source of pollutants to environmental systems. Poultry litter has been a topic of recent interest due to high nutrient loads in runoff from agricultural areas. We will present results of a hybrid technology that allows for continuous-flow treatment of poultry litter and high recovery of phosphorus (P). In Stage I of this process, the poultry litter is mixed with water and sparged with CO2 to effect P release from the waste solids. Next, a base is added to force precipitation of struvite (MgNH4PO4●6H2O) or potassium struvite (MgKPO4●6H2O). In Stage II, the filtrate from Stage I is passed through a fixed-bed column that contains a specialty polymeric ligand exchanger (PLE) impregnated with hydrated ferric oxide (HFO). This polishing step generates an effluent that has a non-detect P concentration (&lt; 5 ppb). The effluent is recirculated to Stage I (after pH manipulation) and upon exhaustion, the PLE column is regenerated to strip-off P as a highly-concentrated regenerant solution from which P is extracted as struvite (MgNH4PO4●6H2O). The regenerant solution can be reused multiple times. Thus, the overall process extracts P from the solid waste, generates a high-purity P-based fertilizer, and reuses process water and the regenerant stream multiple times. This presentation will cover the following aspects: (1) chemical equilibrium modeling of poultry litter slurries; (2) effect of dissolved organic matter on P release (from litter), P uptake (by PLE), and purity of P-based fertilizer; (3) optimizing stage I composition to control the N:P:K ratio in recovered solids; (4) characterization of HFO deposited in the PLE (HFO loading, degree of crystallinity, and average size of HFO nanoparticles); (5) calculation of selectivity coefficients and separation factors for phosphorus with competing anions (SO42-, Cl-, HCO3-, etc.) for HFO-impregnated PLE; and, (6) characterization of the phosphorus-laden fertilizer, including the presence of trace elements or antibiotic contaminants.

Two-stage process for phosphorus extraction and recovery from agricultural waste

253rd National Meeting (2017)

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