Novel Natural Vacuum Membrane Distillation for water desalination: A combinational approach

Abstract

Many methods have been proposed to produce fresh water utilizing solar and low-grade energy. The natural vacuum method is widely used despite its limitations in water production. The entry of non-condensable gases into the condenser reduces the amount of water production in the natural vacuum system. In addition, it requires a large evaporator surface to produce fresh water at a high rate. This research resolves these limitations for the first time by integrating the natural vacuum and membrane distillation methods, increasing the evaporation area in a small space, and creating a re-vacuum. Based on the results, the amount of water production for feed water with a salinity of 0.5 M, a flow rate of 60 L/h, and temperatures of 45, 65, and 85 °C reach 5.5, 18.5, and 45.9 m3/day for each square meter of the membrane by combining the methods above without creating a re-vacuum for 24-hour tests. Re-vacuum occurs in this novel system by pumping the saline water upward against the outlet valve and the existing membrane. When a re-vacuum occurs every 6 h, the amount of water production for feed water temperatures of 45, 65, and 85 °C increases approximately by 70 % for all feed water temperatures. However, energy consumption does not rise significantly due to employing a pump instead of a vacuum pump.