Batch Reverse Osmosis (RO): Desalination with minimum wastage of energy and water

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Conventional sources of good quality water from rivers and underground aquifers are no longer sufficient to meet the growing demand for fresh water across the world. People are turning instead to sources of poorer quality, such as brackish groundwater, that have to be desalinated to make them potable. Desalination is typically carried out using reverse osmosis (RO) membranes that allow water to pass while excluding salt. However, existing RO desalination plants waste a significant fraction of the source water as rejected brine. They also waste significant amounts of energy due to inefficiency of the conventional technology. A third drawback of existing technology is the short life of the RO membranes, as they readily clog with sparingly soluble salts and colloids. Batch RO is a new approach to desalination that, compared to conventional processes, reduces the wastage of water and energy and is less prone to fouling. Unlike conventional RO that works by a steady continuous process, batch RO works by means of a cyclic, unsteady process which is not yet fully studied or understood. Pilot results have shown that batch RO is practically feasible and likely to achieve energy efficiency 2-3 times better than conventional RO technology. Specific areas of improvement needed to achieve the target performance have been identified.To achieve the aims and objectives listed above, research will be undertaken in three work packages. The first work package will take a micro view of the batch RO process by using submicron particles to track motion of fluid near the RO membranes, thus providing understanding of the behaviour of similarly-sized particles such as colloidal silica, that tend to cause fouling. Alongside powerful direct numerical simulations, these experiments will result in a predictive tool for local transport phenomena. The important outputs from the simulations - such as clean water flux through the membrane, required driving pressure and consumed energy - will be averaged for use in a coarser scale model to be developed in the second work package. This model will predict the whole system performance, enabling us to choose the best among several options for the configuration of the batch RO system, each of which has certain pros and cons. Finally, in the third work package, we will build and test the preferred design and compare it against a conventional RO system. We will test the system for energy efficiency, recovered fraction of freshwater, and tendency to foul with contaminants (especially calcium sulfate and silica) which commonly occur in groundwater. Autopsies of the RO membranes will be performed to check our predictions and gain a full understanding of fouling and its distribution within the RO module. Because the tests will be representative of real applications of the batch RO system, the results will inform and support subsequent commercialisation of the technology in collaboration with industrial partners.