Membrane distillation (MD) is a technology with the hydrophobic membrane which itself acts as a barrier to hold the liquid/vapor interfaces at the entrance of the pores, and the driving force is a vapor pressure difference across the membrane. It has the advantages of theoretically 100% salt rejection, lower operating temperature than conventional distillation processes, less requirements of membrane mechanical strength, and lower operating pressure compared to conventional pressure-driven membrane processes such as RO [16]. The first patents on MD were granted in the late 1960s, but it wasn't technologically feasible until ultrafiltration membranes in recent years enabled sufficiently high trans-membrane fluxes [17]. Since then, MD has regained extensive interests on membrane development, configuration design and application exploring