Repurposing Reverse Osmosis Concentrate as a Low-Cost Thermal Energy Storage Medium

The reject of the reverse osmosis water treatment process (aka brine, concentrate, ROC) is a mixture of salts that are dissolved in high salinity water. The ROC is classified as an industrial waste by the U.S. Environmental Protection Agency and can face regulatory limitations on disposal. State-of-the-art of ROC disposal includes deep-well injection, surface discharge to rivers, discharge to the ocean, and evaporation ponds. In this study, the feasibility of using Reverse Osmosis Concentrate as a low-cost Thermal Energy Storage (TES) medium is explored by a techno-economic analysis. The normalized cost of TES (cost per unit volume of stored thermal energy) is estimated through a series of cost analyses and is compared to the cost targets of the U.S. Department of Energy for low-cost thermal energy storage. It was shown that the normalized cost of TES using ROC salt content is in the range of $6.11 to $8.73 depending on ROC processing methods.