Building an operational framework for selective nitrogen recovery via electrochemical stripping

Recovering nitrogen from wastewater can simultaneously fulfill the roles of traditional removal technologies such as nitrification-denitrification and fertilizer production processes such as Haber-Bosch. We have recently demonstrated a proof-of-concept for selective recovery of the fertilizer ammonium sulfate via electrochemical stripping, a combination of electrodialysis and membrane stripping. In this study, we furthered electrochemical stripping from concept to informed practice by investigating the effects of influent concentration (30, 300, and 3000 mg N/L), catholyte temperature (15, 23, and 35 °C), and gas permeable membrane choice on electrochemical nitrogen removal and recovery. We also proposed and validated a nitrogen mass transport model for the experimental results, providing mechanistic rationale behind observed effects of varying operating parameters. While changing operating parameters did affect performance, electrochemical stripping exhibited robust performance over a range of realistic ambient temperatures, three gas permeable membranes, and three orders of magnitude of influent concentrations. Practically, these results demonstrate that electrochemical stripping is viable across a range of waste streams and resilient to fluctuations in temperature and nitrogen concentration; they also establish operational trade-offs between residence time and energy consumption. As a result of this work, electrochemical stripping continues to mature from concept to practice and provides lessons for developing other resource recovery technologies.