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Salt-Gradient Solar Pond and Membrane Distillation System for Water Desalination Powered by Renewable Energy
AuthorRuskowitz, Jeffrey A.
AdvisorChildress, Amy E.
Civil and Environmental Engineering
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A salt gradient solar pond (SGSP) coupled with a direct contact membrane distillation (DCMD) system was investigated to desalinate water for reclamation of Walker Lake, a terminal saline lake in Northern Nevada. Two transparent floating elements and a continuous plastic cover were tested to determine their ability to suppress evaporation rates and increase overall solar pond heat content. An aquatic chemistry analysis was performed on Walker Lake water to determine possible scalants when concentrating lake water to fill the SGSP and during DCMD concentration. Membrane cleaning was evaluated to remove membrane scalant and to recover flux.It was found that petri dishes were the best evaporation suppression element due to their transmissivity, low refraction of radiation, and ease of installation. Suppression of evaporative losses from the solar pond surface also resulted in increased temperatures throughout the solar pond and increased overall solar pond heat content. The investigation of transparent covers/elements is unique from previous studies in ponds where increasing temperature and heat content are not desired.Hydromagnesite and calcite were predicted to form during concentration of Walker Lake water to fill the SGSP. Hydromagnesite and halite were found to be the main scalants on the membrane surface. Halite most likely formed due to concentration polarization at the membrane surface; small quantities of calcite were also likely present although not detected. Cleaning cycles were conducted and were able to recover approximately 94% of the original flux using citric acid or EDTA cleaning solutions. The citric acid cleaning solution performed slightly better than the EDTA cleaning solution in terms of flux recovery and removal of scalant (as observed by SEM). SEM, EDS, and XRD analyses were performed in order to determine the magnitude of scale deposit and the type of scalant present.The proposed coupled SGSP/DCMD system was found to be feasible for terminal lake reclamation when utilizing floating elements to suppress evaporation and cleaning cycles to remove membrane scale and restore flux across the membrane. Positive freshwater production rates from the coupled SGSP/DCMD system, which have not been achieved in previous coupled systems, were achieved in this investigation.