Introduction, Forward osmosis (FO) is an osmotic process that uses a semi-permeable membrane to effect separation of water from dissolved solutes. The driving force for this separation is an osmotic pressure gradient between a solution of high concentration, often referred to as a “draw” and a solution of lower concentration, referred to as the “feed”.
The osmotic pressure gradient is used to induce a net flow of water through the membrane into the draw, thus effectively concentrating the feed. The draw solution can consist of a single or multiple simple salts or can be a substance specifically tailored for forward osmosis applications. The feed solution can be a dilute product stream, a waste stream or seawater.
Most of the applications of FO, thus fall into three broad categories: product concentration, waste concentration or production of clean water as a bi-product of the concentration process. The most efficient FO applications combine all three. At it’s best, FO can concentrate waste, turning waste into a product all while producing clean water.
The Forward Osmosis process has applications in many different industries, including but not limited to: Water Reuse and Desalination; Food and Beverage; Mining; Oil and Gas; and the Power Industry.
Now, imagine a system where two compartments, holding aqueous solutions with different solute concentrations, are separated by a semi-permeable membrane, which only allows water to pass through. For the system in question, the difference in solute concentrations is spontaneously minimized by diffusion of water through the semi-permeable membrane. The direction of water diffusion is from the low concentration side to the high concentration side. This is the process of forward osmosis (FO) and the semi-permeable membrane is classified as a forward osmosis membrane (FO membrane).