Prototyping and Modeling a Photovoltaic/Thermal Electrochemical Stripping System for Distributed Urine Nitrogen Recovery

Distributed solar-enabled nitrogen capture from urine helps manage the nitrogen cycle and increases fertilizer, sanitation, and electricity access. We provide proof-of-concept for a Photovoltaic/Thermal Electrochemical Stripping (ECS) system, known as Solar-ECS, that recovers ammonium sulfate fertilizer from real urine independently from an electricity grid. Controlling photovoltaic currents and extracting waste heat to cool the solar panel while heating ECS enabled 59.3% ± 3.6% more power production and improved ammonia recovery efficiency by 22.4% ± 7.4%. The added heat accelerated ammonia volatilization (the rate-limiting step of ECS), while controlled currents reduced energy use by 2.24 ± 0.25 kJ/g N per excess mA/cm2. A new process model for ECS operation at different currents and temperatures was proposed and applied to estimate possible fertilizer revenues of up to $2.13/kg N based on US markets. By advancing recovery of high-purity commodity chemicals from underutilized wastewaters, this work supports United Nations Sustainable Development Goals for zero hunger, clean water and sanitation, clean energy, and responsible production.