(24c) Electrochemical Processing to Capture Phosphorus from Concentrated Animal Feeding Operations Waste: Experimental and Process Simulation Investigations

Recovery of phosphates and nitrates to prevent watershed eutrophication presents a new challenge in animal waste management. In 2011, the United States applied 4.32 million short tons of inorganic P₂O₅ fertilizer with continued growth in application rate expected [1]. Beneficiated phosphate rock is the primary source of phosphorus found in fertilizer products, with an estimated 68 Gt remaining worldwide and 74% of these reserves located in Morocco [2,3]. Although peak phosphorus supply is not a major present concern, phosphorus supply chain sustainability requires further consideration to ensure food and clean water security.

The development of phosphorus recycling technologies has recently become of interest, sparking a proliferation of scientific and technical research. Reducing phosphorus loss by increasing its recycling will increase phosphorus supply chain sustainability, food security, and watershed health. Recovery of nitrogen and phosphorus via struvite (MgNH₄PO₄·6H₂O) precipitation is a recycling technique which can reduce watershed eutrophication and potentially increase fertilizer supply chain sustainability. Nucleation and growth of struvite crystals is controlled by solution pH which is dependent upon soluble magnesium, ammonia, and phosphorus specie concentrations.

Ohio University (OHIO) has been investigating a modular electrochemical-based technique to indirectly induce struvite precipitation within the liquid fraction of animal waste. Struvite precipitation was performed via chronoamperometry and struvite precipitates were characterized by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Key parameters controlling electrochemical struvite precipitation include: solution pH, temperature, turbulence, and the presence of competing ions (Ca²⁺). Solution temperature greater than 20°C had negligible effects on struvite precipitation kinetics. The presence of Ca²⁺ was found to suppress phosphorus removal. The impact of operating voltage on phosphorus removal efficiency and current efficiency with time has also investigated. Further, process simulations have been developed to aid estimating operating costs for a commercial scale system integrated into a concentrated animal feeding operation (CAFO). This presentation will review recent laboratory and process simulation results.

[1] "https://www.ers.usda.gov/data-products/fertilizer-use-and-price/," USDA, 2 May 2018. [Online]. [Accessed 2018].

[2] M. Heckenmüller, D. Narita, G. Klepper, Global availability of phosphorus and its implications for global food supply: an economic overview, Kiel Institute for the World Economy, Germany, (2014).

[3] S. M. Jasinski, Phosphate rock, U.S. Geological Survey, Mineral Commodity Summaries, (2017).

[4] A. B. Ribeiro, E. P. Mateus, N. Couto, Electrokinetics across disciplines and continents, Springer International Publishing Switzerland, New York (2016).