Forward Osmosis (FO) is not new and it has limited ability to yield total energy savings - likely 10 to 30 % of that needed conventional SWRO desalination. Similar to reverse osmosis, FO is limited by the energy needed to break the the chemical bonds of salts and water or other soulite in which the salts are dissolved. State of the art SWRO technologies and membranes available today allow to desalinate water at not more than 70 to 80 % of this minimum theroetical energy and therefore, whatever technology we use cannot yield much more than 70 to 80-% savings theoretically. Since we can never recover 100 % of this difference (in seawater desalination we can only recover 40 to 50 %), the maximum theoretical savings are proportionally smaller. When we consider the much higher fouling potential of state of the art FO membranes as compared to SWRO membranes , their higher trans-membrane pressure and energy needed to pump the water between the FO system components which are more complex than RO system components, the overall maximum savings go down very fast. FO requires lower energy to drive water movement through a membrane, but is does not produce fresh water directly - it just drives it from one solution with high osmotic pressure (i.e. seawater) to another solution with high osmotic pressure (solute -.i.e., ammonium bicarbonate). Getting the water out of the solute still needs energy; more energy is also needed to pump the water between the separation and recovery components, etc.- so in total, the savings are practically limited.
Published by Nikolay Voutchkov, Water Globe Consulting, LLC - President
Forward Osmosis (FO) is not new and it has limited ability to yield total energy savings - likely 10 to 30 % of that needed conventional SWRO desalination. Similar to reverse osmosis, FO is limited by the energy needed to break the the chemical bonds of salts and water or other soulite in which the salts are dissolved. State of the art SWRO technologies and membranes available today allow to desalinate water at not more than 70 to 80 % of this minimum theroetical energy and therefore, whatever technology we use cannot yield much more than 70 to 80-% savings theoretically. Since we can never recover 100 % of this difference (in seawater desalination we can only recover 40 to 50 %), the maximum theoretical savings are proportionally smaller. When we consider the much higher fouling potential of state of the art FO membranes as compared to SWRO membranes , their higher trans-membrane pressure and energy needed to pump the water between the FO system components which are more complex than RO system components, the overall maximum savings go down very fast. FO requires lower energy to drive water movement through a membrane, but is does not produce fresh water directly - it just drives it from one solution with high osmotic pressure (i.e. seawater) to another solution with high osmotic pressure (solute -.i.e., ammonium bicarbonate). Getting the water out of the solute still needs energy; more energy is also needed to pump the water between the separation and recovery components, etc.- so in total, the savings are practically limited.