Brackish Water Desalination: Energy and Cost Considerations

Energy recovery devices are employed in nearly all seawater reverse osmosis (SWRO) desalination plants to recover pressure from the membrane reject stream and return it to the process. Because of the high pressures and low membrane permeate recovery rates common in these systems, the membrane reject stream contains a considerable amount of energy. The use of energy recovery devices in seawater RO is readily justified on the basis of operating cost savings. However, the application of energy recovery is much less common in brackish water RO systems, primarily because of the relatively low feed pressure and low flow rate of the membrane reject stream. The fear is that energy recovery devices can also potentially limit the flexibility of a brackish RO process because of efficiency losses or flow-rate constraints encountered during off-peak operation.