Exploring the in-situ recovery of low-grade heat from urine via thermoelectrochemical cell

Recovering low-grade heat from source-separated urine in eco-toilets reduces on conventional energy sources, lowers greenhouse gas emissions, and enhances energy efficiency, contributing to environmental protection and economic benefits. However, challenges such as the small volume, unstable source, and intermittent discharge of urine, result in rapid heat dissipation. Traditional wastewater heat recovery methods struggle to utilize this heat, hindering the exploration of multifunctional eco-toilets. In this study, thermoelectrochemical cell (TEC) was employed for in-situ low-grade heat recovery with simulated urine as heat source and air as the cold source, applying temperature gradient to drive thermoelectric conversion process. The impacts of flow rate and temperature gradient on the TEC performance were studied, and the process stability and environmental adaptability of TEC under dynamic environmental conditions (such as seasonal variations and toilet frequency) were evaluated. The results indicated that the TEC system achieved its maximum operational performance under optimal conditions of a flow rate of 40 mL/min and a temperature difference of 27 degrees C, reaching a maximum Carnot efficiency of 0.0153%. The system demonstrated strong adaptability in high-temperature environments and quickly responded to heat input in simulations of varying toilet usage frequencies, maintaining stable operation under diverse conditions. These results highlight the potential of TEC for in-situ low-grade heat recovery from urine, with promising applications in dynamic real-world environments.