Membrane distillation assisted by heat pump for improved desalination energy efficiency

Thermal desalination technologies are required for minimal and zero liquid discharge (MLD/ZLD). However, conventional and emerging thermal desalination technologies, such as mechanical vapor compression (MVC) and membrane distillation (MD), are usually highly expensive to implement or/and energy intensive to operate. In this study, we develop a novel desalination technology by using a vapor-compression pump to assist membrane distillation (MD). Comparing the energy efficiencies of the novel heat-pump assisted MD (HPMD), MVC, and conventional MD under similar operating conditions, demonstrates that HPMD is an energy-efficient thermal desalination technology. Furthermore, through process modeling, we provide guidelines for HPMD system design and show that the HPMD can theoretically obtain low energy consumption (~10 kWh of electrical energy per cubic meter of produced fresh water or gain output ratio, GOR, of ~60) and high water vapor flux (i.e., >60 L m−2 h−1). We conclude by highlighting promising applications of HPMD for MLD/ZLD, enabled by its high energy efficiency, low capital cost, and modularity.