Scaling up an Electrochemical Nitrogen Recovery Process from Lab Benchtop to Pilot Wastewater Plant
Authors: Williams Kindle Shea , Yribarren Sarah , Kogler Anna , Coombs Orisa , Sharma Neha , Liu Matthew Junjie , Tarpeh William Abraham 
Published: September 2023

Municipal wastewater and agricultural runoff contain large amounts of reactive nitrogen, which can pollute the environment upon release, leading to harmful algal blooms and poor drinking water quality. At the same time, these reactive nitrogen species are valuable and can be recycled to generate fertilizers and commodity chemicals; it has been estimated that doing so would offset the need for ~30% of global Haber-Bosch ammonia production. For this reason, both removal and recovery of active nitrogen from wastewaters are important goals. An electrochemical separations technique known as Electrochemical Stripping (ECS) has been developed to achieve selective ammonia recovery from wastewater.1 This technique leverages pH swings induced by water-splitting, coupled with appropriate cation- and gas-selective membranes, to remove and recover ammonia nitrogen from wastewaters. ECS has been demonstrated at the benchtop scale with relatively high efficiency (>90% total ammonia nitrogen [TAN] recovery) in various wastewaters, and the effects of certain process variables such as temperature, influent TAN concentration, and gas-permeable membrane material have previously been reported.2

Our goal with this work is to initiate ECS process scale-up by at least 3 orders of magnitude in order to match the scale of municipal wastewater treatment. In order to do this, we set out to build a more complete fundamental process model to inform our design decisions during scale-up. Here we will present results of exploratory tests varying multiple process parameters, including current density, relative electrolyte volumes, reactor residence time, catholyte solution chemistry, and reactor geometry. We then translate these results into a process model comprising thermodynamic relationships as well as kinetic equations, describing both the rates of species generation/consumption as well as transport between reactor compartments. This model, which yields molecular-level insights, is then used in an iterative fashion to first predict performance at small scales under new sets of conditions, and then ultimately inform the design of a ~1000 L/day ECS reactor at a pilot-scale wastewater treatment facility.

In addition, we will discuss findings from stakeholder engagement conducted in parallel to lab-scale tests, indicating utility limitations, priorities, needs for certain effluent specs, desired product specs, cost bounds, and details around hydrogen coproduct handling. These discussions additionally feed into design decisions and are crucial for eventual technology deployment.

References:

(1) Tarpeh, W. A.; Barazesh, J. M.; Cath, T. Y.; Nelson, K. L. Electrochemical Stripping to Recover Nitrogen from Source-Separated Urine. Environ. Sci. Technol.
2018, 52 (3), 1453–1460. https://doi.org/10.1021/acs.est.7b05488.

(2) Liu, M. J.; Neo, B. S.; Tarpeh, W. A. Building an Operational Framework for Selective Nitrogen Recovery via Electrochemical Stripping. Water Res.
2020, 169, 115226. https://doi.org/10.1016/j.watres.2019.115226.