Concentrated animal feeding operations have been reported to cause nutrient pollution throughout the United States. In the Delmarva Peninsula, an annual production of 600 million broilers generates over a million tons of litter each year, leading to high nutrient flux into the Chesapeake Bay watershed. To address this issue, we have developed the Phosphorus Extraction and Recovery System (PEARS), which uses CO2 gas and strong acid to mobilize phosphorus and nitrogen in poultry litter and NaOH and air to generate nutrient-laden minerals. The two main topics investigated in this study were (1) the thermodynamic and kinetic dependence of nutrient extraction on slurry conditions, and (2) the preferential formation of struvite (NH4MgPO4.6H2O) and potassium struvite (KMgPO4.6H2O). An operational pH set point of approximately 5.0 achieved greater than 80% extraction of phosphorus and nitrogen in less than 5 minutes. The kinetics of the nutrient extraction did not exhibit any significant dependence on the slurry solid loading under well mixed conditions. In the precipitation stage, over 80% of phosphorus was recovered at pH 8-10. Selective precipitation was dependent on the pH, base, and use of chelating agents. Magnesium-based phosphates were obtained with the use of chelating agents, such as ethylenediaminetetraacetic acid (EDTA), to inhibit calcium-based precipitates. Operation below pH 9.25 resulted in greater production of struvite, whereas higher pH caused generation of potassium struvite. Production of these two minerals allows for mixed fertilizer products with custom N:P:K ratios. Ultimately, we expect that nutrient recovery from poultry litter will play a critical role in addressing nutrient challenges in the Chesapeake Bay watershed.

Recovering high-quality phosphorus- and nitrogen-laden fertilizers from poultry litter

253rd National Meeting (2017)

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