Hybrid forward osmosis - Freeze concentration process for process water purification and recovery

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Zero liquid discharge (ZLD) in chemical and mining industry operations has not been fully achieved yet and fresh water intakes are still high. At the Institute for Water Innovation of the University of Toronto, we recently developed a patented hybrid Forward Osmosis (FO)-Freeze Concentration (FC) process to recover water from contaminated industrial effluents. The water recovered in FO-FC can be reused in industrial operations, minimizing the fresh water intakes. In FO water permeates spontaneously through a membrane into a concentrated draw solution. The resulting dilute draw solution is then frozen (FC) to produce fresh water as ice, leaving behind the regenerated concentrated draw solution to be recycled into the process. The energy advantage of freezing water is up to seven times less than water evaporation. Particularly in Canada, the energy for freezing is free several months per year, due to the country's climate, suggesting an even more energy free green technology. An added advantage of this concept is the freedom to use any highly soluble and non-toxic electrolyte as the draw solute, which can generate very high osmotic pressure gradients capable of pulling 3 to 5 times more water more water from the contaminated streams compared to conventional FO technology. Advancing FO-FC will bring Canada one step closer to ZLD in an energy efficient and economical way, within a reasonable period of time. Although the FO-FC process was proven at the lab scale, we now propose to demonstrate the above process concept at a micro pilot scale by developing a continuous ice producing reactor that will be integrated with an existing forward osmosis membrane system. The resulting facility will be used to demonstrate the concept under continuous operation and bring this innovation one step closer to the market. Operating variables such as flow rate, retention time, type of electrolyte, freezing rate and temperature, type of membrane will be investigated to optimize the continuous operation.