Design of a Process for Supercritical Water Desalination with Zero Liquid Discharge

Conventional desalination methods have a major drawback; the production of a liquid waste stream which must be disposed. The treatment of this waste stream has always presented technical, economic, and environmental challenges. The supercritical water desalination (SCWD) process meets these challenges as it allows for the treatment of salt-water streams with zero liquid discharge (ZLD). An experimental apparatus has been designed, built, and operated to show the proof of principle of the SCWD process using NaCl–H2O as a model solution. Next, a SCWD process with a two-stage separation step was designed. Enthalpy calculations for a 3.5 wt % NaCl feed and experimental results show that the SCWD process operated at 460 °C and 300 bar will produce drinking water (750 ppm total dissolved solids) and salt crystals (2–5 μm) with an estimated stand-alone thermal energy consumption of 450 MJth/m3 product water.