(314b) Using Fly Ash As pH Adjustment for Efficient Phosphorus Immobilization and Reutilization from Swine Manure in Hydrothermal Treatment

Concentrated animal feeding operations (CAFOs) are an important part of the U.S. economy, providing the country with a substantial low-cost source of consumable meat and dairy products such as beef, pork, poultry, milk, and eggs. However, CAFOs are becoming a greater public/government concern due to the amount of animal manure (waste) generated by such facilities, resulting in both air and water pollution. The United States Department of Agriculture (USDA) estimates that 335 million tons of dry manure waste is annually generated by CAFOs. This waste stream contains significant quantities of nutrients, accounting for nitrogen and potassium totals of approximately 6.17 and 1.85 million metric tons, respectively.

Application of manure to pasture and crop land is the most prevalent CAFO waste management practice. This practice can be beneficial as it improves soil quality by replenishing important nutrients for plant health. However, the amount of applied manure along with nutrient mobility leads to runoff into local watersheds, causing a host of local/regional public health and economic issues. Nutrient runoff (especially P) leads to growth of harmful algal blooms, which has led to the loss of water supply to U.S. cities (due to elevated microcystin levels), loss of aquatic life, and over $100 million in economic damage since 2008.

Due to its distributed nature, nutrient runoff is one of the most prevalent and challenging environmental issues in the U.S. To address this issue, Ohio University (OHIO) is developing a supercritical water (SCW)-based modular process to be operated at CAFO sites in order to recover the nutrients as a solid product. This nutrient-rich solid product may be used as a fertilizer supplement for field application, with significantly reduced potential for runoff into local watersheds. In addition, the process produces a methane-rich gas product, which may be utilized at the CAFO site or upgraded into pipeline-quality natural gas. SCW provides an advantageous media for recovery of nutrients from animal manure; its lower fluid density and hydrogen bonding strength promotes precipitation of solid P components, and provides a gasification medium for undigested carbonaceous species.

In this research, basic environment was evaluated at various temperatures to determine whether it has impacts on nutrient immobilization and phosphorus mobility of biochars. For a more controlled basic environment, 0.1 M NaOH was used to replace DI water; and for a more economical approach, fly ash was used for adjusting pH. After hydrothermal treatment, nutrient elements were found to be immobilized into the solid phase more efficiently with addition of basic materials, especially with addition of fly ash. In addition to being more efficient in immobilizing nutrient elements, fly ash also altered crystal phases formed at different temperature treatments which thus results in different profile of phosphorus mobility of the biochars. Results to be presented in this presentation include experimental results such as nutrient immobilization as a function of process conditions, post-trial analyses of biochar products (including XRD and SEM/EDS), and biochar phosphorous mobility.