The Economics of Future Membrane Desalination Processes and Applications

Seawater desalination, the desalination of waters flowing back from hydraulic fracturing processes and brackish water desalination constitute important desalination applications. These have a combined market size in excess of $25 billion per annum and a combined water production rate equivalent to the domestic consumption of over 300 million people. Each application offers its own distinct challenge. Reductions in energy consumption are key to driving down seawater desalination costs. The optimisation of water treatment in tandem with the formulation of fracturing fluids is key to reducing water management costs and environmental impacts in hydraulic fracturing. The development of desalination technologies that allow for high water recovery and high product purity is key to meeting industrial and municipal needs from brackish water sources. This thesis develops and investigates three emerging technologies: forward osmosis, electrodialysis at high salinity and hybrid electrodialysis-reverse osmosis with a view to addressing the three above challenges. Forward osmosis has often been viewed as a technology with the potential to reduce energy consumption in seawater desalination. An analysis is therefore undertaken into the theoretical limits upon its energy requirements paying particular attention to the energy penalty involved in drawing water from the feed stream into a more concentrated solution. Although unaddressed in literature this energy penalty is an important and distinguishing factor between FO and other desalination technologies. In the case of seawater, it is shown to put FO at a disadvantage that makes it difficult to compete with reverse osmosis. Consequently, it is argued that forward osmosis research should be reoriented away from seawater desalination to focus on alternate applications where salinities are above those which reverse osmosis can handle or where draw solution regeneration is not required. For these alternate applications a new framework is provided that explains the influence of the membrane orientation upon water flux through the membrane, an insight that is of particular use in considering the trade-off between water flux and fouling. The conventional view of electrodialysis is that it is most cost effective for the desalination of low salinity waters, and less so for moderate and high salinities, such