Ansley Zora

Nutrient recovery from cities’ wastewater to meet American agricultural fertilizer demand: Feasibility study and comparative analysis

This thesis aims to determine if cities in the United States have the capacity to meet domestic fertilizer demands through nutrient recovery from its municipal wastewater. This is achieved through the analysis of an existing nutrient recovery facility in the United States and the surrounding agricultural demand for fertilizer.

Nutrients are a critical resource that must be accounted for as the population of the planet, and therefore demand for fertilizers for agriculture, continues to grow. Deposits of mineable nutrients such as phosphorus and potassium are at risk of being depleted, and the production of nitrogen fertilizer consumes great amounts of greenhouse-gas emitting energy. Additionally, as internationally traded commodities, the prices are influenced by conflicts and market fluctuations. Municipal wastewater is full of these nutrients, and the production of fertilizer through nutrient recovery has the potential to nourish agriculture while safeguarding finite resources, allowing a country to have “nutrient security” while respecting Earth’s planetary boundaries for nutrients.

A variety of existing nutrient recovery practices are reviewed and a large wastewater treatment plant, the Stickney Water Reclamation Plant outside of Chicago, Illinois, is selected for study. A Material Flow Analysis is performed to demonstrate the flow of nitrogen and phosphorus entering the system and leaving as finished fertilizer through Ostara’s “Crystal Green” process. These quantities are then analyzed and compared with nutrient supply and fertilizer demand across the United States.

The results show that while there are nutrient recovery technologies operating at a commercial scale, they do not produce enough fertilizer to meet demand. While the case study did produce enough fertilizer to feasibly meet demand within the surrounding urban county, it fell short once the analysis expanded to the adjacent agriculturally dominant county. Additionally, because of the distances between large cities and agricultural areas in the United States, it is unlikely that any cities’ recovery could produce enough excess fertilizer to be transported across the country to these less populous areas. This means that the negative effects of commercial fertilizer production and use cannot be expected to be mitigated through nutrient recovery from wastewater, as commercial fertilizers will continue to be required to meet the demands of agriculture. However, nutrient recovery from wastewater is still a growing field, and further areas of research are discussed to provide insight on the hopes and challenges of creating a circular nutrient economy in the United States.