Improving the performance of the air gap membrane distillation process by using a supplementary vacuum pump

• The performance of AGMD significantly improved by using a supplementary vacuum pump.
• The permeate flux, performance ratio, gained output ratio and thermal efficiency increased by 24.96, 15.25, 14.29 and 11.99%, respectively, from AGMD to V-AGMD.
• Compared with AGMD, the energy consumption of V-AGMD didn’t increase.

In this study, the process of air gap membrane distillation (AGMD) supplemented by a vacuum pump was developed to eliminate the disadvantage of the air gap and to improve the process performance. The vacuum-air gap membrane distillation (V-AGMD) process was evaluated by comparing with the AGMD process while varying operating conditions such as the feed inlet temperature, feed flow rate, cooling water temperature and feed salt concentration. The optimal operating conditions were obtained by orthogonal experiments of the AGMD and V-AGMD processes. It was found that the vacuum pump could promote the permeate flux (PF), thermal efficiency (η), gained output ratio (GOR) and performance ratio (PR). Under the optimal conditions, a feed flow rate of 4 l/min and feed inlet temperature of 50 °C, PF and GOR could be increased by 24.96% and 14.29%, respectively, from AGMD to V-AGMD. While the feed inlet temperature at 80 °C, cooling water temperature at 20 °C and feed salt concentration at 253 ppm, PR and η increased about 15.25% and 11.99% at 2 l/min and 4 l/min, respectively. The results of this work proved that improving the performance of the AGMD process is possible by using a supplementary vacuum pump.