Going Forward with Desalination; Solar-powered, Continuous, Salt Water Forward Osmosis

The effectiveness of an organic draw solution on forward osmosis desalination of seawater was shown in a previous study. An aqueous solution of a safely ingestible organic compound was used as the osmotic draw solution to avoid any possible human health hazard. The independent variable was the choice of organic draw solution. Forward osmosis was used to pull water through a semi-permeable membrane from seawater into a concentrated organic draw solution, until the total solute concentrations (in the draw solution and in the seawater) were equal and osmosis stopped. Brine was left in the seawater source. Filtration was then used to remove the organic draw solute from the permeate to recover water. The process required no added pressure or electric power, but the filtration step removed draw solute so that new draw solutions were required for additional cycles. In the current study, solar power is used to collect water from the draw solution reservoir, which simultaneously increases the concentration of the solute and allows forward osmosis to continue with the same draw solute. Water removal from the draw proceeds in a stepwise continuous fashion during daylight and desalination continues during the night until osmotic pressure is equalized. The system is designed to proceed with very little maintenance. The result is an economical, solar-powered, continuous, desalination process.