A Novel Draw Solution for Forward Osmosis for Low Energy Desalination

The forward osmosis process using ammonia (NH3) and carbon dioxide (CO2) attracts increasing attention because of its potential for desalination with only waste heat. On the other hand, new draw solution is needed because the NH3/CO2 system requires a large quantity of absolute energy and the reverse flux of ammonia across a FO membrane is serious problem. The purpose of this study is to overcome the above two problems.

 The detail of the required energy of the NH3/CO2 system is thermodynamically calculated with OLI system's simulator. And it was revealed that more than three fourth of whole energy is used for the latent heat and vaporization heat of water at distillation process. It shows that new draw solution system must minimize the amount of water vaporization.

 The possibility of new draw solution was explored. The required energy was calculated with the simulator and the reverse flux of the draw solute was evaluated in a crossflow mode with originally developed FO membranes. As a result, it was revealed that the required energy is almost half and the reverse flux is less than one tenth with the formulations of some organic cations with carbon dioxide, compared to the NH3/CO2 system, most notably the reverse flux can be diminished moreover with suitable membrane properties. The presentation will detail the findings of some of the candidate draw solution.