Abstract
Wastewater treatment by reverse osmosis is an energy-intensive process. Processes utilizing direct osmosis, a novel variation of reverse osmosis, have the potential to provide low cost methods of purifying wastewater. Standard reverse osmosis is technically limited by membrane fouling when treating complex wastewater streams because the separation driving force is hydraulic pressure which pushes all components in a solution against the membrane. By contrast, direct osmosis uses osmotic pressure as the driving force which pulls rather than pushes water through a membrane and does not act on larger molecules (foulants). Direct osmosis therefore has minimal membrane cleaning requirements. This performance advantage gives significant cost advantages to direct osmosis as a treatment technique for complex wastewater. Because membranes designed specifically for direct osmosis applications are not commercially available, previous studies on direct osmosis have employed commercial reverse osmosis membranes. Most of these studies applied direct osmosis for applications such as concentration of fruit juices and tomato paste.In this presentation, we present our work in applying direct osmosis to wastewater treatment. A laboratory-scale flat sheet membrane filtration cell was used to investigate the osmotic behavior of different commercial reverse osmosis membranes. The osmotic water flux through these membranes was measured using pure water as the feed stream as functions of different NaCl solutions and flow rates. Based on these results, experiments using a synthetic wastewater were then conducted under optimized operating conditions. Results show that the technology is ideal for concentrating wastewater with complex compositions.
