CO₂-driven ion exchange for ammonium recovery from source-separated urine

Area of Science:

• Environmental Engineering
• Circular Economy Technologies
• Wastewater Treatment

Background:

• Nitrogen recovery from urine and CO2 utilization are critical for a circular economy and climate change mitigation.
• Existing solutions address these issues separately, lacking integrated approaches.
• There is a need for technologies that simultaneously recover nitrogen and utilize CO2.

Purpose of the Study:

• To demonstrate and evaluate a CO2-driven ion exchange for nitrogen recovery (CIXNR) from urine.
• To investigate the underlying ion exchange chemistry and optimize the process.
• To assess the feasibility of the CIXNR technology in resource-limited settings.

Main Methods:

• Utilized a proton-form weak acid cation exchanger (WAC-H) for nitrogen recovery from hydrolyzed urine.
• Studied the effect of aqueous pH and CO2 pressure on ion exchange chemistry and regeneration.
• Conducted multi-cycle tests with synthetic hydrolyzed urine and field outreach in Malawi.

Main Results:

• Optimized WAC-H capacity by regulating aqueous pH, leveraging urine's natural buffering capacity.
• Achieved over 75% nitrogen recovery in multi-cycle tests using CO2 regeneration.
• Demonstrated faster regeneration kinetics at higher CO2 pressures due to lower pH and increased proton gradient.

Conclusions:

• The CIXNR process offers an integrated solution for nitrogen recovery and CO2 utilization from urine.
• Process optimization through pH regulation enhances nitrogen recovery efficiency.
• Field evaluation in Malawi highlights the need for adapting the technology for rural, low-resource settings, promoting technology adoption in developing countries.