Continuous Solar-Adaptive Electrochemical Stripping for Circular Nitrogen Recovery from Urine
- 1Department of Mechanical Engineering
- 2Stanford University
- 3Department of Chemical Engineering
Abstract
Solar electrochemical stripping (ECS) is a low-carbon circular economy approach to recover ammonia from wastewater that faces challenges in scale up and intermittent energy supply management. We present a novel autonomous solar-adaptive multistage ECS system that removed > 94% of nitrogen from a continuous flow of influent urine and recovered >75% of nitrogen as ammonium sulfate fertilizer in over 80 hours of off-grid operation. To control urine flow rate, we identified a load ratio that maximizes nitrogen extraction across fluctuating solar power inputs. The first demonstrated multistage electrode stack configuration of ECS increased the system’s volumetric urine treatment capacity by 2.7x and revealed that hydraulic coupling of stages in series can increase nitrogen removal by 16.5% compared to parallel operation for the same urine flow rate and energy efficiency. Using these findings, ECS was operated as a three-stage configuration in real sunlight on two sunny days and one partially cloudy day, allowing current density to range from 4.7 mA/cm2 to 10.4 mA/cm2 proportionally to incident sunlight. Urine flow varied accordingly from 0.82 L/day to 1.92 L/day. Even as input power fluctuated, the system achieved consistent nitrogen extraction that varied less than 7% at steady state. This solar-adaptive (i.e., flexible) operation scheme would require 55% less battery storage than an equivalent constant operation scheme. Ultimately, this work elucidates a pathway to valorize alternative sources of ammonia nitrogen at the water-energy nexus, leverages demand-side response to support electrical grid stability, and reduces the need for renewable energy battery storage.
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BibTeX
@misc{coombs2026continuous,
title = {{Continuous Solar-Adaptive Electrochemical Stripping for Circular Nitrogen Recovery from Urine}},
author = {Orisa Coombs and O. Godson Osele and William A. Tarpeh},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009533/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009533/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Continuous Solar-Adaptive Electrochemical Stripping for Circular Nitrogen Recovery from Urine
AU - Orisa Coombs
AU - O. Godson Osele
AU - William A. Tarpeh
PY - 2026
DA - 2026/09/28
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009533/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009533/v1
AB - Solar electrochemical stripping (ECS) is a low-carbon circular economy approach to recover ammonia from wastewater that faces challenges in scale up and intermittent energy supply management. We present a novel autonomous solar-adaptive multistage ECS system that removed > 94% of nitrogen from a continuous flow of influent urine and recovered >75% of nitrogen as ammonium sulfate fertilizer in over 80 hours of off-grid operation. To control urine flow rate, we identified a load ratio that maximizes nitrogen extraction across fluctuating solar power inputs. The first demonstrated multistage electrode stack configuration of ECS increased the system’s volumetric urine treatment capacity by 2.7x and revealed that hydraulic coupling of stages in series can increase nitrogen removal by 16.5% compared to parallel operation for the same urine flow rate and energy efficiency. Using these findings, ECS was operated as a three-stage configuration in real sunlight on two sunny days and one partially cloudy day, allowing current density to range from 4.7 mA/cm2 to 10.4 mA/cm2 proportionally to incident sunlight. Urine flow varied accordingly from 0.82 L/day to 1.92 L/day. Even as input power fluctuated, the system achieved consistent nitrogen extraction that varied less than 7% at steady state. This solar-adaptive (i.e., flexible) operation scheme would require 55% less battery storage than an equivalent constant operation scheme. Ultimately, this work elucidates a pathway to valorize alternative sources of ammonia nitrogen at the water-energy nexus, leverages demand-side response to support electrical grid stability, and reduces the need for renewable energy battery storage.
ER -