Vacuum-Assisted Multistage Membrane Distillation With Bubble Column Dehumidifier for Efficient Water Production

An experimental investigation of a novel integrated system of a multistage sweeping gas (air) membrane distillation module and a bubble column dehumidifier (BCD) is presented for an energy-efficient high production water desalination system. The sweeping air stream is created using a vacuum pump installed between the membrane distillation unit and the BCD to apply a degree of vacuum behind the membrane in the air channel of the membrane cell to reduce the vapor mass transfer resistance through the membrane pores. Performance metrics of the system include the measurement of permeate flux and the calculations of energy consumption at various operating conditions in a comprehensive manner. The system performance is mainly controlled by feed temperature and flowrate and the sweeping air flowrate. The dehumidifier water level and its temperature have moderate impacts in the tested ranges. A permeate flux of 18 kg/m² . h was measured with a relatively high gained output ratio of 0.62, low specific energy consumption of 1120 kWh/m³ when the feed temperature is 80 °C, and the dehumidifier column height of 4.5 cm. The study results revealed an enhanced system’s performance compared to other sweeping gas membrane distillation systems in the literature, which is very promising.