Mapping the Phosphorus Recovery Benefits from Centralized Infrastructure in the Food-Energy-Water Nexus
Advisor: Professor Ro Cusick
Abstract
Phosphorus (P) is a critical nutrient in maintaining security and resiliency in the food and agricultural system. Inefficiencies in the current usage of P fertilizers has led to excessive mining of phosphate rock and loss of excess P to surface water bodies, contributing to eutrophication. The reduction, recovery, and reuse of P throughout the agricultural system can assist in generating a more effective circular P economy. In the United States (US), corn ethanol biorefineries are major intermediate agricultural processors that can recover renewable P (rP) for reuse as a fertilizer, resulting in reductions of P in distillers grain feed, an animal feed co-product, and associated animal wastes. On a global scale, the generation of human-grade soy-based proteins, such as soy protein concentrate (SPC), from soybean meal typically fed to animals and recovery of rP during SPC processing could reduce P requirements and improve circularity of human diets.
The first part of this research models and maps the P benefits of recovery from corn ethanol biorefineries across the US and compares them to recovery benefits at water resource recovery facilities (WRRFs). Existing models for biorefinery and WRRF P recovery were used to generate inventories of rP potential across facilities in the US. Inventories showed that biorefineries could generate over twice the amount of rP fertilizer as WRRFs, while mapping of biorefineries related to croplands demonstrated that they were better co-located with P fertilizer needs than WRRFs. A transportation optimization model was developed for distillers grain feed to determine geospatial P reduction benefits from a reduced P feed, showing largely intra-state distribution and localized P benefits at animal operations. The P reduction benefits from animal wastes were also found to be nearly twice the potential reductions from human wastes at WRRFs. These national analyses showed that P benefits from biorefineries were largely concentrated in the Midwest US, where most biorefineries are located. Watersheds of six Upper Midwestern states were then assessed for localized P benefits of recovery as it relates to state Nutrient Loss Reduction Strategies, finding that sixty-six watersheds could realize localized benefits of recovery where 79% had higher P reduction potential from animal wastes at local concentrated animal feeding operations than WRRFs. The second part of this research focused on improving global P utilization in food production through the reduction of virtual P in human diets by generating SPC based protein from soybean meal commonly fed to animals. Complete replacement of animal proteins with SPC could generate a potential 90% reduction in the total global P utilization and average footprint associated with animal-based protein consumption. Additionally, P recovery during SPC processing could generate enough rP to account for 17% of total utilization for global soybean production. Overall, this research showed large P reduction and recovery opportunities through modification of animal and human food products at centralized infrastructure in the US and globally.