Developments in the desalination technologies have been driven not only to meet the increasing demands for freshwater, but also to reduce the energy demand and cost of the process and to make desalination more sustainable. Challenges facing the desalination industry include the salinity limits of commercial processes such as reverse osmosis (RO) and brine management issues. The membrane distillation process is positioned as an emerging zero liquid discharge (ZLD) technology, yet its large-scale implementation is hindered by the low water fluxes, poor long-term stability, and high production costs of membrane materials along with the low thermal energy efficiency of the process.

The aim of this thesis was to develop and assess membrane materials with high permeability, long-term stability and scalability prospects to reduce the energy and costs associated with desalination. To fulfil this aim, the integration of experimental evaluation of novel membrane materials with numerical modelling was conducted to improve understanding of factors hindering the widespread implementation of desalination technologies, including vacuum membrane distillation (VMD) and pervaporation (PV), and to gain insights for guiding future material design strategies.

Ceramic membrane materials, which exhibit favorable thermal and mechanical properties for VMD applications yet are sparsely represented in the literature, were evaluated for their feasibility for large-scale deployment. Selected alumina-based membranes with different characteristic properties were evaluated and benchmarked against a commercial polymeric membrane. A silane-based grafting method was developed and implemented for the hydrophobization of the selected ceramic membranes. Among the studied membranes were asymmetric α-alumina membranes that differ in thickness, along with symmetric anodic alumina membranes that exhibited superhydrophobic characteristics. For the short-term VMD evaluation, the developed anodic alumina membranes exhibited superior permeation properties, with fluxes as high as 316 kg/(m²·h) along with NaCl rejection above 99.9%. The water flux of symmetric membranes was successfully modelled, along with model extension to describe the performance of the asymmetric membranes. These evaluations also revealed the effect of the support used in reducing the effective transport area used for flux calculations of symmetric membranes.

The long-term stability of the silane-grafted membranes was assessed through500 hours of VMD operation using a feed with different NaCl concentrations at 80°C. Independent of the feed NaCl concentration, the asymmetric alumina membranes exhibited superior stability maintaining a water flux of 50 kg/(m²·h) and NaCl rejection as high as 99.9% over 500 hours of VMD operation. These membranes also exhibited superior wetting resistance in the presence of iron oxide particulate scalants. Thinner asymmetric α-alumina membranes and the symmetric membranes displayed higher water fluxes yet were prone to scaling and eventual wetting during their long-term operation.

Towards enabling the wider implementation of the VMD process, novel multi-stage VMD plant layouts with integrated energy recovery were simulated using the tubular form of the asymmetric α-alumina membranes that exhibited superior long-term stability. A techno-economic analysis of the plant layouts indicated that specific thermal energy consumptions as low as 180 kWh/m³ were feasible, along with a water recovery ratio as high as 85%. For simulations based on a prospective cost for the membranes, the levelized cost of water production was within a reasonable range of 3-8 $/m³. Furthermore, it was found that choice preference between the multi-stage VMD plant layouts is influenced by the type of waste heat source available (latent versus sensible heat sources). Furthermore, the potential of PV alongside nanofiltration as candidate processes for recovering water from a thermoresponsive draw solution in a hybrid desalination process was demonstrated. The experimental evaluation together with the simulation studies indicate the high potential of the α-alumina membranes developed in this thesis.