Practical Minimum Energy Use of Seawater Reverse Osmosis Facilities

Abstract

The global challenges of climate change and water scarcity demand increased energy efficiency of desalination technologies, especially the dominant seawater reverse osmosis (SWRO). While many studies have assessed individual improvements to SWRO like energy recovery devices, their combined potential for maximizing system energy efficiency has not been systematically explored. Therefore, this study combines a comprehensive data collection from 64 facilities, with detailed modeling of conventional, state-of-the-art, and practical minimum energy use configurations. For each of these three efficiency levels, we synthesized performances benchmarks for pump efficiency, membrane permeability, membrane spacer mass transfer coefficient, and pre- and post treatment. We use these parameters to benchmark potential efficiency gains of 39 of the facilities, examine performance across different recovery ratio and feed salinity, and prioritize the most promising innovations. The methodology encompasses detailed process- and component-level modeling, and includes the derivation of a maximum membrane mass trans- fer coefficient from the Chilton-Colburn J-factor analogy. We found that the combined state-of-the-art methods, including semi-batch reverse osmosis, could save 69% of the energy excess beyond the thermodynamic minimum, while the practical minimum, including batch RO, could save 82% of excess energy. The compiled data also show that modern facilities achieve a lower specific energy consumption (SEC) when using isobaric–energy recovery devices (ERD) compared to older devices like Pelton turbines. Factors affecting SEC and energy savings (i.e., capacity, equipment efficiency, and year of installation) are also analyzed for 39 of the SWRO facilities. Further substantial savings can be obtained by improving membrane spacers and shifting to more batch efficient configurations