Solar-pond assisted reverse osmosis-electrodialysis system for seawater desalination and hydroponic fertilizer solution production

A thermodynamic analysis is performed on a solar-pond assisted reverse osmosis-electrodialysis system to produce freshwater and a hydroponic fertilizer solution for sustainable desalination and waste recovery. The reverse osmosis unit desalinates seawater to produce freshwater and a waste concentrated salt solution rich in many useful ions and minerals. The reverse osmosis unit’s waste stream is sent to an electrodialysis unit that utilizes monovalent membranes to reject magnesium, calcium and sulfate ions. These ions are beneficial for plant growth and the product can be used as a hydroponic fertilizer solution for agricultural purposes. A solar pond is integrated into the system to reduce the power requirements. The solar pond utilizes energy from the sun to store thermal energy in a large body of concentrated salt water with temperatures up to 90°C in the lower convecting zone. This thermal energy is utilized in an organic Rankine cycle with the working fluid R113 to create a self-sustaining desalination and waste treatment system running on solar energy. The system produces about 4.52 kg/s of freshwater and 4.75 kg/s of hydroponic solution. The overall energy and exergy efficiencies of the integrated system are found to be 20.36% and 2.55%, respectively.