Bubble Column Dehumidification for Sweeping Air Membrane Distillation

The performance of a novel integrated desalination system of sweeping gas membrane distillation (SGMD) module and a bubble column dehumidifier (BCD) was experimentally investigated to enhance freshwater productivity and reduce energy consumption of the system. The SGMD module acts as a humidifier by separating water vapor into the sweeping air channel to deliver humid air to the bubble column dehumidifier. The sweeping air stream was created using a vacuum pump between the SGMD module and the BCD. To evaluate the system performance, different operating conditions were tested for closed and open sweeping air cycles and with different cooling methods. Results showed a marginal enhancement of 7 to 10% in productivity and 10 to 20% in the system’s gained output ratio when the closed-air cycle was used compared to the open-air cycle. Feed temperature and flow rate and sweeping air flow rate mainly control the system’s performance, while the water column height in dehumidifier and its temperature have moderate impacts. In addition, both air cooling and no cooling modes of operation showed promising results regarding energy efficiency, especially with elevated dehumidifier water column heights between 6 and 9 cm.