as the Earth's population continues to grow and develop our limited freshwater
0:05resources become increasingly scarce
0:10we're fortunate that the Earth's oceans offer an alternative and can provide a
0:14sustainable supply of potable water
0:17sea water can be economically and reliably converted to potable water
0:20through a process known as sea water reverse osmosis
0:25the process starts by extracting water from the ocean using wells located on
0:30the shoreline or by using an intake structure located in the open ocean
0:36osmosis is a naturally occurring process for a solvent such as water passes
0:41through a semi permeable barrier
0:45the semi permeable barrier or membrane allows some things to pass through it
0:49but not others
0:53in nature the direction of flow through the membrane is from a less concentrated
0:57solution such as fresh water to a more concentrated solution such as sea water
1:02until equilibrium is reached
1:05reverse osmosis is when the opposite occurs by pressurizing the concentrated
1:09solution
1:10the seawater we are able to force water molecules to pass from the salty sea
1:15water solution through the membrane to the fresh water to protect the reverse
1:19osmosis membranes from becoming clogged by solid particles that can be suspended
1:23in the sea water the sea water is filtered before passing through the
1:27membranes
1:28this is accomplished by using multimedia filters which are tanks or vessels
1:33containing a series of layered granular materials
1:37these materials can be anthracite garnet sand pebbles and or gravel which are
1:43assembled in layers
1:45the filters remove sand twigs seaweed and other particles from the sea water
1:51in some cases other types of membranes known as ultra filtration and micro
1:56filtration membranes are used instead of multimedia filters to pretreat the
2:00seawater
2:02next to the filtered sea water travels to the cartridge filters which act as a
2:07second stage filtration
2:09cartridge filter is used for sea water reverse osmosis are typically made from
2:13a yarn like synthetic material that is wound into cartridges
2:18these remove even smaller solid particles from the sea water such as
2:22fine sand and clay before the seawater proceeds to the reverse osmosis
2:26membranes
2:29high-pressure pumps increase the pressure of the sea water up to 1,000
2:33psi
2:34the pressure needs to be sufficiently high to overcome the naturally occurring
2:37osmotic pressure and force water from the salt water side through the reverse
2:42osmosis membranes to the freshwater side
2:45the salt particles in the seawater are rejected from passing through the
2:48membrane to the freshwater side and remain behind on the concentrated salt
2:53water side
2:59the reverse osmosis membrane can be thought of as a number of sealed
3:02envelopes connected at their open ends to a tube
3:06there are spacers between each envelope which allow water to flow across the
3:10membranes
3:11the membrane envelopes and spacers are then wound around the tube like a roll
3:16of paper towels
3:18the reverse osmosis membranes are then closed in a fiberglass shell
3:23the membranes are connected and to end usually six to seven membranes together
3:27and housed in vessels that are built to withstand pressures up to twelve hundred
3:31psi
3:33as the pressure icy water enters the pressure vessel and flows across the
3:37membrane surface the water molecules are forced into and through the membrane
3:41envelopes leaving the salt molecules behind
3:44the d salted water passes through the membrane and emerges at low pressure
3:48where it is collected in a tube and directed to one end of the pressure
3:52vessel the concentrated salt stream that is rejected from flowing through the
3:56membrane continues to pass across the membrane surface where it is collected
4:00separately
4:01the concentrated salt stream retains about fifty five percent of the total
4:05energy of the sea water stream that was originally fed to the membranes
4:10to reduce the energy that is required to operate the reverse osmosis plan
4:14the pressurized concentrated stream is piped into an energy recovery device
4:22here up to ninety percent of the energy of the concentrated salt stream is
4:26transferred to an equal volume of the incoming seawater in an isobaric energy
4:30recovery device
4:33the energy recovery device significantly reduces the plants operating costs by
4:37recovering the concentrated salt stream energy and using it to pressurize sixty
4:42percent of the sea water that is fed to the membranes
4:45the concentrated salt stream will have about a sixty percent higher salinity
4:48than the incoming seawater
4:51the concentrated salt stream is sent back to the ocean through a brine
4:54disposal well or a device known as a brine outfall
4:59the brine outfall is situated in an area of significant ocean flow so that the
5:03salt