Patent ID: 7144511

Claim:
A method for desalinating seawater, comprising: pumping filtered seawater having a total dissolved solids content of not less than 35,000 mg/l feed through a first stage desalination operation consisting of one or more nanofiltration membranes to produce a first permeate and a first retentate, where the first permeate exiting the first stage desalination operation has a total dissolved solids content of no more than twelve percent compared with a total dissolved solids content of seawater immediately prior to entering said first stage desalination operation; and pumping said first permeate having a salinity approximately the same as that which exited the first stage desalination operation through a second stage desalination operation consisting of one or more nanofiltration membranes to produce a second permeate and a second retentate, where the second permeate exiting the second stage desalination operation has a total dissolved solids content of no more than 500 mg/l.