Forward Osmosis and Freeze Crystallization as Low Energy Water Recovery Processes for a Water-Sustainable Industry
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A water-sustainable future chemical industry that is using water in its operations (such as the metals and mining industry) relies on the development of low energy water recovery technologies. Among them are Forward Osmosis (FO) and Freeze Crystallization (FC), two innovative processes that promise to minimize fresh water intakes in the chemical industry at a significantly lower energy input compared to conventional processes, such as Reverse Osmosis (RO), evaporation, or crystallization. FO is a membrane process that requires a concentrated draw solution (CDS) to osmotically recover water. The separation of the draw solutes from the draw solution and the regeneration of the CDS is the main source of energy consumption in the FO process. On the other hand, FC involves processes in which water is removed directly from aqueous solutions, as ice, by freezing or freeze-thaw cycling. Research advancements in the two aforementioned processes are reported. The economical effectiveness of an FO process using Trimethylamine-CO2-H2O as the CDS was evaluated through an optimization study designed and carried out in Minitab and Aspen Plus. Optimum operating conditions for the separation of the draw solutes from the product water were identified, and the most important parameters that affect its performance were determined. Further, the economic sustainability of this FO process was assessed. Regarding the FC process, the natural freezing of a 0.5 m MgSO4 aqueous solution was studied. Freezing temperatures ranged from −2 °C to −26 °C, while melting of the recovered solid, i.e., ice with entrapped solute contamination, was done at room temperature (25 °C) and at 3 °C. The optimum conditions for maximizing water recovery while reducing impurity contamination were determined.
KeywordsWater recovery Forward osmosis Natural freezing Freeze crystallization Water sustainability
The authors would like to acknowledge the University of Toronto, NSERC, Ontario Centres of Excellence and Southern Ontario Water Consortium (SOWC) for the financial support in this project, and Forward Water Technologies Inc. for their technical advice in the Forward Osmosis part. An initial shorter version of this paper has been presented in the 10th World Congress of European Water Resources Association (EWRA2017) “Panta Rei”, Athens, Greece, 5-9 July 2017 (http://ewra2017.ewra.net/).
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