Low energy reverse osmosis process
AssigneeAquatech International Corporation
InventorRavi Chidambaran
Life of this patent
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Abstract
We provide a system and method for reverse osmosis treatment of water, including seawater and brackish water. Methods and systems of embodiments of the invention may include, for example, ultrafiltration followed by biofoulant removal, both of which precede reverse osmosis. In preferred embodiments the system is run at a low flux. For example, a flux of 6-8 GFD may be used with seawater. Additional embodiments may provide the above process in conjunction with a reverse-osmosis membrane cleaning system. The membrane cleaning system is a “clean in place” system that includes use of the natural pressure differential in the reverse osmosis system to remove biofoulants and their precursors.
Claims17
A method for desalination by reverse osmosis and reverse osmosis membrane cleaning, comprising:
- providing a feed stream of water to be desalinated;
- filtering the feed stream through an ultrafiltration membrane, thereby removing turbidity including bacteria and viruses from said feed stream;
- filtering the feed stream through positively charged media, thereby removing biofoulants, bacteria and viruses from said feed stream, wherein the step of filtering the feed stream through an ultrafiltration membrane is conducted prior to the step of filtering the feed stream through the positively-charged media;
- and
- removing salt from the feed stream by reverse osmosis, wherein the reverse osmosis is conducted at an operating flux, wherein the operating flux results in an energy consumption, and wherein conducting the reverse osmosis at a flux lower than the operating flux does not reduce the energy consumption by more than 10%;
- and
- cleaning at least one reverse osmosis membrane used in removing salt from the feed stream by reverse osmosis, comprising, for a reverse osmosis membrane having a feed side and a permeate side:
- maintaining a concentration differential by adding reverse osmosis concentrate to the feed side of the reverse osmosis membrane, thereby allowing the reverse osmosis concentrate to remain in the feed side and causing a flow of a permeate water from the permeate side to the feed side due to the concentration differential.
A method for desalination of a feed stream by reverse osmosis, comprising:
- preconditioning a feed stream of water for desalination by treatment in at least one member of the group consisting of a clarifier, a filter, and a dissolved air flotation unit to a turbidity of less than 8 NTU;
- treating the feed stream by passage through ultrafiltration membranes;
- backwashing the ultrafiltration membranes with ultrafiltration permeate water;
- treating the feed stream by passage through positively-charged media for biofoulant removal, wherein the step of treating the feed stream by passage through ultrafiltration membranes occurs before the step of treating the feed stream by passage through the positively-charged media;
- feeding the feed stream to a reverse osmosis membrane unit having an operating flux, wherein the operating flux results in an energy consumption, and wherein conducting the reverse osmosis at a flux lower than the operating flux does not reduce the energy consumption by more than 5%;
- and, producing a desalinated reverse osmosis permeate stream and a reverse osmosis reject stream;
- recovering pressure from the reverse osmosis reject stream;
- cleaning at least one reverse osmosis membrane used in removing salt from the feed stream by reverse osmosis, comprising, for a reverse osmosis membrane having a feed side and a permeate side:
- further cleaning comprising reverse osmosis concentrate on the feed side and reverse osmosis permeate on the permeate side, and regulating flow to the feed side of the reverse osmosis membrane, thereby allowing the reverse osmosis concentrate to remain in the feed side and causing a flow of reverse osmosis permeate from the permeate side to the feed side due to a concentration differential maintained by adding reverse osmosis concentrate to the feed side.
Dependencies are inferred from the claim text.