Forward Osmosis: Energy Efficient Water Recovery from Industrial Effluents

To date, in Ontario hazardous industrial effluents are shipped to Ohio in the US at a significant cost. The amount of such streams generated every year is approximately 2 million m³. Recovering water from hazardous effluent streams with a low-cost process would enable clean water recycling in industrial operations and reduction of the volume of hazardous effluents requiring disposal or further treatment.  Forward Osmosis (FO) is an innovative membrane process, able to recover water from industrial effluent solutions containing up to 240,000 ppm total dissolved solids (TDS) at low cost. An engineered concentrated draw solution (CDS) selectively draws water molecules from an effluent solution, across the pores of a semi-permeable membrane through a spontaneous osmotic phenomenon. Water flows without any external energy input, due to the osmotic pressure gradient generated between the two solutions. Eventually, the CDS becomes diluted and must be treated to separate the draw solutes from the water recovered. This step requires energy input. However, if the CDS consisted of a thermolytic salt, such as trimethylamine (TMA) bicarbonate, which decomposes to gaseous TMA and CO₂ upon moderate heating, the energy input would be small. In the present work, the effectiveness of an aqueous carbonated trimethylamine solution as the CDS in FO is evaluated. Its ability to draw water from industrial effluents as well as the separation efficiency of the draw solutes from the water recovered are also reported. Finally, the overall energy requirements in a continuous integrated FO process are estimated, using results from a micro pilot unit and the OLI-Flowsheet software.