On the potential of forward osmosis to energetically outperform reverse osmosis desalination

We provide a comparison of the theoretical and actual energy requirements of forward osmosis and reverse osmosis seawater desalination

Ronan K. McGovern; John H. Lienhard V

2014

Scholarcy highlights

  • Energy consumption accounts for approximately 20-35% of the total cost of water in reverse osmosis desalination of seawater, and a greater fraction when the price of electricity is high
  • This level of interest in forward osmosis for seawater desalination is surprising given that FO processes have higher theoretical and actual energy requirements than reverse osmosis, though this is seldom acknowledged or analysed
  • We perform an energetic comparison of reverse osmosis, the most energy efficient commercial desalination technology, and forward osmosis, an indirect means of desalination, consisting of two steps; the dilution of a concentrated draw solution, and, its subsequent regeneration
  • Since forward osmosis involves the initial transfer of water from the feed to a draw solution of higher osmotic pressure, the theoretical energy required for regeneration is different
  • The draw dilution step in forward osmosis desalination systems places the draw regeneration process at a significant energetic disadvantage compared to direct desalination of the feed stream with reverse osmosis
  • Desalination facility design and operation for maximum efficiency, Tech. rep., Water Research Foundation

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