Long-Term Robustness and Failure Mechanisms of Electrochemical Stripping for Wastewater Ammonia Recovery

Anna Kogler; Neha Sharma; Diana Tiburcio; Meili Gong; Dean M Miller; Kindle S Williams; Xi Chen; William A Tarpeh

doi:10.1021/acsenvironau.3c00058

Long-Term Robustness and Failure Mechanisms of Electrochemical Stripping for Wastewater Ammonia Recovery

ACS Environ Au. 2024 Jan 12;4(2):89-105. doi: 10.1021/acsenvironau.3c00058. eCollection 2024 Mar 20.

Authors

Anna Kogler¹, Neha Sharma^{2

3}, Diana Tiburcio⁴, Meili Gong³, Dean M Miller³, Kindle S Williams³, Xi Chen³, William A Tarpeh³

Affiliations

¹ Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, United States.
² Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94205, United States.
³ Department of Chemical Engineering, Stanford University, 443 Via Ortega, Room 387, Stanford, California 94305, United States.
⁴ Department of Mechanical Engineering, Temple University, Philadelphia, Pennsylvania 19122, United States.

Abstract

Nitrogen in wastewater has negative environmental, human health, and economic impacts but can be recovered to reduce the costs and environmental impacts of wastewater treatment and chemical production. To recover ammonia/ammonium (total ammonia nitrogen, TAN) from urine, we operated electrochemical stripping (ECS) for over a month, achieving 83.4 ± 1.5% TAN removal and 73.0 ± 2.9% TAN recovery. With two reactors, we recovered sixteen 500-mL batches (8 L total) of ammonium sulfate (20.9 g/L TAN) approaching commercial fertilizer concentrations (28.4 g/L TAN) and often having >95% purity. While evaluating the operation and maintenance needs, we identified pH, full-cell voltage, product volume, and water flux into the product as informative process monitoring parameters that can be inexpensively and rapidly measured. Characterization of fouled cation exchange and omniphobic membranes informs cleaning and reactor modifications to reduce fouling with organics and calcium/magnesium salts. To evaluate the impact of urine collection and storage on ECS, we conducted experiments with urine at different levels of dilution with flush water, extents of divalent cation precipitation, and degrees of hydrolysis. ECS effectively treated urine under all conditions, but minimizing flush water and ensuring storage until complete hydrolysis would enable energy-efficient TAN recovery. Our experimental results and cost analysis motivate a multifaceted approach to improving ECS's technical and economic viability by extending component lifetimes, decreasing component costs, and reducing energy consumption through material, reactor, and process engineering. In summary, we demonstrated urine treatment as a foothold for electrochemical nutrient recovery from wastewater while supporting the applicability of ECS to seven other wastewaters with widely varying characteristics. Our findings will facilitate the scale-up and deployment of electrochemical nutrient recovery technologies, enabling a circular nitrogen economy that fosters sanitation provision, efficient chemical production, and water resource protection.