(432e) Modeling and Simulation of Electrodialysis Processes for Nutrient Recovery from Wastewater

Electrification of the fertilizer production industry can enable serious decarbonization efforts globally, especially those based on renewable electricity. Currently, ammonia is manufactured based on the heavily centralized Haber-Bosch process, which accounts for 2% of global energy consumption and 1.2% of carbon emissions. Moreover, phosphorous mines create heavy metal hazardous waste streams and are ultimately non-renewable. As an alternative, recovery of fertilizer nutrients from wastewater streams, either in wastewater treatment plants (WWTPs) or concentrated animal feeding operations (CAFOs), has been proposed to achieve more decentralized and sustainable fertilizer production. These wastewater streams contain large amounts of ammonia (N) and phosphorus (P) that can be recycled for direct use on farms. Currently, these components are not recovered in the vast majority of WWTPs and CAFOs. Usually the N/P components are either neutralized or directly released into the environment. The challenges with recovering these products is that the starting streams are very dilute, highly variable, and geographically distributed. Therefore, a viable recovery process must be flexible, modular, and able to exploit distributed renewable energy sources.

Currently, there are many methods for nutrient recovery including crystallization, air stripping, and biological treatment. However, these methods require additional chemicals, operate at high pH, require careful biological controls, and are not well-suited to modular implementations using renewable electricity. In contrast, electrochemical separations may provide a very promising route for distributed nutrient recovery . Over the last few decades, electrochemical separations have been used extensively for desalination purposes to meet drinking water needs where resources are constrained. Specifically, electrodialytic (ED) ion-exchange membrane-based processes allow for lower energy consumption and direct energy usage in the form of renewable electricity versus thermal or pressure driven systems. Electrodialysis systems also have fast dynamics which can easily deal with fluctuations in power caused by using renewable energy intermittency. Given the vast number of commercial installations for desalination, there is scant literature published on electrochemical separations for nutrient recovery of fertilizer from WWTP or CAFO streams.

This talk will present a novel modeling framework and process simulation tool for ED-based nutrient recovery processes. The tool can predict pilot and commercial scale performance to quickly iterate system designs based on number of stages required, membrane area, as well as energy requirements. This simulation tool also considers the key dynamics caused by renewable energy and feedstock variability, and is therefore well suited for studying process control strategies. This is a significant contribution because, at present, commercial chemical process simulators do not support electrochemical unit operations such as ED, and there is no easily accessible or standardized simulation code for such processes in the literature. Using this tool, we can pave a way for future process control strategies and design modular processes that can be dispatched where needed.