Production of drinking water from saline water by direct contact membrane distillation (DCMD)

Nine types of commercially available membranes were used for a DCMD system to investigate the effect of membrane difference on permeation flux and conductivity. Some characteristics such as liquid entry pressure (LEP), contact angle (CA), gas permeability were checked to understand the membranes more comprehensively. Three different depth membrane modules were set up to study the heat and mass transfer process in a DCMD system. The effect of different operation parameters were studied including flow mode, flow rate, temperature, and NaCl concentration. The permeation conductivity values were under 8 μS/cm for all the experimental conditions. With real seawater, the permeate flux dropped from 23.76 L/m2 h to 14.36 L/m2 h over one month at the following conditions: hot side inlet temperature of 60 °C, cold side inlet temperature of 20 °C, and hot and cold side flow rate of 0.6 L/min for PTFE pore size 0.22 μm membranes. After cleaning, the membrane successfully reused in the DCMD system. A mathematical model was built to simulate the mass and heat transfer process, and the experimental results agree with the theoretical calculations.