On the thermodynamic properties of hydrolysed urine: Experimental data, predictive and correlative models for the design of concentrative urine treatment technologies

Abstract

Source-separated urine contains the potential for water, nutrient and energy recovery. During the recovery of such resources, urine treatment technologies undergo temporal changes in the thermodynamic properties of urine. To inform the design of thermal, membrane and electrochemical urine treatment processes, this study experimentally measured and modelled the thermophysical properties of synthetic hydrolysed urine (vapour pressure, osmotic pressure, density, and electrical conductivity) across temperature and concentration profiles using two approaches: predictive thermodynamic equations based on an ionic speciation model and correlative modelling. The vapour pressure and osmotic pressure were accurately predicted to 14 wt% for the predictive model, within an error of 0.30% and 0.46%, respectively, while the correlative model based on the experimental data from this study demonstrated an error of <1% for both parameters across the whole range of salt concentrations and temperatures (4.5 to 32.2 wt%; 333 to 373 K). The predictive and correlative models for density and electrical conductivity showed adequate agreement with the experimental data, where error did not exceed 2.12% and 1.2%, respectively, across the entire range of concentrations and temperatures.The value of the models for the development of sustainable urine treatment technologies was demonstrated by their application to determine the optimum heating surface area of a urine evaporator and the energy requirements of a reverse osmosis process.